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Experimental investigations of the Co–Ni–Ti system: Liquidus surface projection and isothermal section at 1373 K
Accepted Manuscript Experimental investigations of the Co–Ni–Ti system: Liquidus surface projection and isothermal section at 1373�K Chenyang Zhou, Cuiping Guo, Jingbo Li, Changrong Li, Zhenmin Du PII:
S0925-8388(18)31576-7
DOI:
10.1016/j.jallcom.2018.04.253
Reference:
JALCOM 45891
To appear in:
Journal of Alloys and Compounds
Received Date: 2 January 2018 Revised Date:
16 April 2018
Accepted Date: 21 April 2018
Please cite this article as: C. Zhou, C. Guo, J. Li, C. Li, Z. Du, Experimental investigations of the Co– Ni–Ti system: Liquidus surface projection and isothermal section at 1373�K, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.04.253. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Experimental investigations of the Co–Ni–Ti system: liquidus surface projection and isothermal section at 1373 K Chenyang Zhoua, Cuiping Guoa, Jingbo Lib, Changrong Lia, Zhenmin Dua* Department of Materials Science and Engineering, University of Science and
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a
Technology Beijing, Beijing 100083, P.R. China b
School of Materials Science and Engineering, Beijing Institute of Technology,
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Beijing 100081, P.R. China
Abstract: The liquidus surface projection and isothermal section at 1373 K of the Co–Ni–Ti system have been established by using the methods of scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX),
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powder X-ray diffraction (PXRD), and differential thermal analysis (DTA). 9 primary solidification regions and 6 ternary invariant reactions were deduced in the liquidus surface projection. 7 three-phase regions and 16 two-phase regions
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were derived in the isothermal section at 1373 K. Besides, the PXRD results
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indicated that the ternary compound τ with Co3V-structure existed in both liquidus surface projection and isothermal section at 1373 K. The ternary compound τ formed the extended primary field in the centre of the liquidus surface projection and its homogeneity ranges of Co in the isothermal section were measured to be from 34 to 51 at.%. The present experimental results could be used as guidance to practical applications and input to future thermodynamic assessments.
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Keywords: Phase diagram; Liquidus surface projection; Isothermal section;
*Corresponding author at: Tel./Fax: +86 10 62333772
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E-mail address: [email protected] (Z. Du).
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Co–Ni–Ti system
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1. Introduction In recent years, the Co–Ni–Ti system has attracted increasing attention of different researchers owing to its technological importance:
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superalloys [1, 2], shape memory alloys [3], high-entropy alloys [4-6], permanent magnets [7, 8]. The addition of titanium can improve the
formation of the γ' phase and increase the strength at high temperature of
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the Co- and Ni-based superalloys. The addition of cobalt can enhance the
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corrosion resistance in the Ni–Ti shape memory alloys. The cobalt, nickel, and titanium are also the principal elements in high-entropy alloys. For strengthening the Co- and Ni-based superalloys [9], homogenization annealing should be carried out around 1373 K and above, so the
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solidification paths of the as-cast alloys and phase equilibria relations at 1373 K are very meaningful.
It is well known that phase diagram is a basic guidance for selection of
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the alloy compositions, the route of heat treatment, etc., which can reduce
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the development time of new materials. In order to facilitate future thermodynamic modeling and material research and development, the experimental determination of phase diagram is essential. In the current work, the liquidus surface projection and isothermal section at 1373 K are constructed by a combination of SEM/EDX, PXRD, and DTA techniques.
2. Literature review -1-
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2.1 Binary systems The Co–Ni system was relatively simple without any intermediate phase and the available experiment information was summarized by
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Nishizawa and Ishida [10] and then revised by Predel [11]. Guillermet [12] performed a thermodynamic assessment of the Co–Ni system, which was accepted in the present work.
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The Co–Ti phase diagram was assessed by Murray [13], in which four
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terminal solution phases αCo, εCo, βTi and αTi, and five intermetallic compounds Co3Ti, γCo2Ti, βCo2Ti, CoTi and CoTi2 were included. Subsequently, Davydov et al. [14] re-determined the temperature of the congruent melting for the CoTi phase and re-assessed the Co–Ti system.
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Therefore, the Co–Ti phase diagram updated by Davydov et al. [14] was adopted in the current work.
Murray [15] reviewed the phase equilibria and thermochemical
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properties of the Ni–Ti system. The Ni–Ti phase diagram was made up of
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three disordered solution phases γNi, βTi and αTi, and three intermediate compounds Ni3Ti, NiTi and NiTi2. Several thermodynamic assessments of the Ni–Ti system were available [16–24], in which the work of Keyzer et al. [22] showed good agreement with experimental data and was widely used in the multicomponent system, and thus was accepted in the present work. The phase diagrams for three binary systems Co–Ni [12], Co–Ti [14], -2-
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and Ni–Ti [22] adopted in this study are shown in Fig. 1a-c.
2.2 Ternary system
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The vertical section at the CoTi–NiTi joint was determined using hardness, XRD, density and thermal analysis by Kornilov et al. [25],
which was the first experimental information on the Co–Ni–Ti system.
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Using diffusion couples and electron probe microanalysis (EPMA), the
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isothermal sections at 1073, 1173, and 1273 K were investigated by Gryzunov et al. [26–28]. They confirmed a complete solid solution between the phases Co3Ti and Ni3Ti. Furthermore, they also reported the three-phase regions between the phases NiTi, Co2Ti, and Co3Ti, but not
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separated the two phases βCo2Ti and γCo2Ti.
Loo and Bastin [29] measured the isothermal section at 1173 K using diffusion couples and equilibrated alloys by means of the optical analysis,
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EPMA and XRD methods and reported a very narrow phase boundary
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between the phases Ni3Ti and τ. Du et al. [30] used same method as [29] to investigate the isothermal section at 1123 K, but the ternary compound τ was not found. Based on the above experimental data [25–30], the Co–Ni–Ti system was reviewed concretely by Gupta [31]. Recently, Riani et al. [32] critically reviewed and re-determined the Co–Ni–Ti system at 1173 K using equilibrated alloys by means of SEM/EDS, XRD techniques, which was in good consistency with the -3-
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work of Loo and Bastin [29]. Besides, they confirmed that the ternary compound τ had a large solubilities and was stable down to 773 K. The crystallographic data of the binary and ternary systems [29, 33–43]
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are listed in Table 1.
3. Experimental methods
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3.1 Samples preparation
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Cobalt (99.99 wt.%), Nickel (99.99 wt.%) and Titanium (99.99 wt.%) were used as starting materials in the present work. The proper amounts of the elements about 5g were prepared on a water-cooled copper hearth in the arc-furnace (MTI MSM20-7) in an argon atmosphere (99.998%
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purity) with a non-consumable tungsten electrode and a tantalum piece as oxygen getter. To improve the homogeneity, every sample was turned around and melted at least five times. Then, the arc-melted buttons were
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cut into several pieces for different purposes.
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Some samples were homogenized at 1373 K for 500 h (Alloys B1 and B2 for 30 h) in evacuated quartz capsules (6 × 10-2 Pa). In the process of annealing, a chamber furnace (MTI KSL-1400) with a temperature accuracy of ± 1 K was used. After heat treatment, the annealed samples were quenched in water.
3.2 SEM/EDX analysis -4-
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Before microstructural characterization, all samples were polished and partial samples were etched in a chemical solution (H2O: HCl: H2O2 = 3: 2: 1) at room temperature for 5–10 s. The phases and element
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distributions of the as-cast samples were studied using SEM (Carl Zeiss EVO 18) in combination with EDX (Bruker Quantax EDS), and that of the annealed samples were performed by SEM (Carl Zeiss LEO 1450)
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equipped with EDX (Thermo Scientific UltraDry EDS). The same
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acceleration voltage of 20 kV was applied. In order to increase the precision of the composition measurements, 3–5 points or areas were analysed for each phase.
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3.3 PXRD analysis
PXRD analysis was carried out using X-ray diffractometer (Rigaku Ultima IV) with Cu-Kα radiation at 40 kV and 40 mA and a Ni-crystal
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monochromator. Diffraction patterns were generally acquired in a scan
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step 0.02° of over a 2θ range 20–90°. Before analysis, powder samples were annealed in evacuated quartz capsules (6 × 10-2 Pa) at 873 K during 2 h. Phase identification and crystal structure refinement were conducted with Jade 5.0 [44] and FullProf [45].
3.4 DTA analysis The reaction temperatures of all as-cast samples and partial annealed -5-
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samples were determined by DTA (TA Instruments, SDT-Q600) using Al2O3 crucibles and Pt/Pt-13%Rh string thermocouples. The DTA measurements were performed with heating and cooling rates of 10 K
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min-1 under argon atmosphere (99.998% purity). The certified standards of pure metal Al, Ag and Cu were used for the calibration, and an
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accuracy of ±1 K for the measured temperatures was obtained.
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4. Results and discussion 4.1 Liquidus surface projection
For the construction of the liquidus surface projection of the Co–Ni–Ti system, 35 alloys are prepared. The microstructure analyses and phase
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compositions of the as-cast Co–Ni–Ti alloys are presented in Table 2. In addition, their solidification paths and corresponding reaction temperatures are also given in Table 3.
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In case of the BSE micrograph and PXRD patterns of the alloy A2, a
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fully eutectic microstructure αTi + (Co,Ni)Ti2 is identified (Fig. 2a-b). A divorced eutectic microstructure is also observed in the alloy A6, but the PXRD results only support the existence of the two phases (Co,Ni)Ti2 and (Co,Ni)Ti, which is probably due to < 5 at.% content of the black phase (Fig. 2c-d). Therefore, the DTA analysis is used to help identifying the final state of the black phase. On the basis of the DTA results (Table 3), we can conclude that the eutectoid reaction βTi → αTi + (Co,Ni)Ti2 -6-
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does not happen and the black phase is βTi in the alloy A6. The alloys A12 and A14 are located in the primary solidification region (Co,Ni)Ti (Fig. 3a–b). Unlike the alloy A12, the PXRD patterns confirm
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the existence of the additional phase Co3Ti in the alloy A14 (Fig. 3c). Therefore, the eutectic microstructure of the alloy A14 is regarded as βCo2Ti + Co3Ti in the present work.
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It should be noted that βCo2Ti with MgCu2-structure is difficult to be
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distinguished from γCo2Ti with MgNi2-structure using the PXRD technique. Thus, the primary phases of the alloy A21 and A27 are judged by the morphology and composition analyses. The morphologies of the alloys A21 and A27 are different, and the EDX results also support that
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the alloy A21 is situated in the primary solidification βCo2Ti (31 at.% Ti), while the alloy A27 is located in the primary solidification γCo2Ti (28 at.% Ti) (Fig. 4a and c and Table 2). Furthermore, the PXRD analyses of
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the alloys A21 and A27 definitely confirm the existence of γCo2Ti and
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Co3Ti and so their eutectic microstructures of the alloys A21 and A27 are considered to be γCo2Ti + Co3Ti (Fig. 4b and d). As shown in the BSE micrographs of the alloys A17–A19, their
primary phase morphologies look the same (Fig. 5a-c). But as stated in section 2.2, the new ternary compound τ is likely to exist in the liquidus surface projection. In order to confirm the stability of the phase τ and distinguish the phases Ni3Ti and τ, a series of the powder samples are -7-
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used for XRD measurements. According to the PXRD results, the phase τ with Co3V-structure has been identified in the alloys A19 and A22 (Fig. 5d).
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In case of the BSE micrographs and PXRD patterns of the alloys A30 and A31, both are located in the primary solidification fcc-(Co,Ni) (Fig.
6a-d). The eutectic microstructure of the alloy A30 is fcc-(Co,Ni) + Ni3Ti
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and the black phase surrounding fcc-(Co,Ni) of the alloy A31 is identified
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as Co3Ti. It should be pointed out that the third phase of the alloy A31 is not measured using the PXRD method due to < 5 at.% content. But according to the available experimental results, the eutectic microstructure of the alloy A31 is to be fcc-(Co,Ni) + τ. Subsequently, the
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DTA curves are performed to identify the reaction temperatures (Fig. 7a–b). Liquidus temperatures are clear to be obtained. Two visible peaks with onset at 1538 K on heating and 1532 K on cooling and one weak
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peak (Due to less content of the eutectic microstructure fcc-(Co,Ni) + τ)
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with onset at 1533 K correspond to the three-phase eutectic reaction (liq. ↔ fcc-(Co,Ni) + τ). The rest peaks with onset at 1522 K on heating and 1518 K on cooling should correspond to the ternary peritectic reaction P1 (liq. + fcc-(Co,Ni) + τ ↔ Co3Ti). Also of note is that the two smaller peaks in the alloys 30 and 31 occur mainly due to the slight weight change in the process of the solid-liquid transformation. Table 4 sums up the temperatures and the estimated liquid -8-
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compositions for the ternary invariant reactions in the Co–Ni–Ti system. The predicted liquidus surface projection and complete reaction scheme
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are shown in Figs. 8–9.
4.2 Isothermal section at 1373 K
For the investigation of the isothermal section at 1373 K of the
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Co–Ni–Ti system, 34 alloys are prepared. The constituent phases and
summarized in Table 5.
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their compositions of the Co–Ni–Ti alloys annealed at 1373 K are
Same eutectic microstructures are identified in the alloys B1 and B2 and should be marked as the liquid phase in the present work (Fig.
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10a-b).
Two typical three-phase microstructures (Co,Ni)Ti + βCo2Ti + τ and βCo2Ti + τ + Co3Ti occur in the alloys B9 and B25 (Fig. 11a and c),
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agreeing with their PXRD patterns (Fig. 11b and d). Furthermore, two
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typical two-phase microstructures βCo2Ti + Co3Ti and γCo2Ti + Co3Ti are also observed in the alloy B15 and B16 (Fig. 12a and c), which is in consistence with their PXRD patterns (Fig. 12b and d). The Ni solubilities of Co3Ti (27 at.%) and βCo2Ti (13 at.%) are larger than that of γCo2Ti (5 at.%) in the isothermal section at 1373 K, which is in consistency with the experimental results at 1173 K [29, 32]. However, the γCo2Ti has a larger Ni solubilities (18 at.%) than Co3Ti (6 at.%) and -9-
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βCo2Ti (5 at.%) at 1123 K [30], which maybe need to be re-determined. The alloys annealed at 1373 K B26-B34 have very good strength and toughness and the powder samples are impossible to be obtained.
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Therefore, the analyses of the composition and morphology are adopted for these alloys in this work. In case of the BSE micrographs of alloys B30–B32, the micrograph of the alloy B31 looks like a combination
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between B30 and B32 (Fig. 13a-c). And the EDX analyses of the alloy
fcc-(Co,Ni) (Table 5).
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B31 also show the existence of three-phase microstructures τ + Co3Ti +
As shown in the BSE micrographs of the alloys B11 and B12, only two-phase microstructures can be observed (Fig. 14a and c). It should be
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noted the phases Ni3Ti and τ with hexagonal structure have a similar morphology. The PXRD analyses are used for distinguishing the black phase Ni3Ti in the alloy B11 and τ in the alloy B12 (Fig. 14b and d).
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In Fig. 15, the PXRD patterns of alloys B23 and B24 support the
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presence of the new ternary compound τ with Co3V-structure. A single phase τ is clearly identified in alloy B23, and the lattice parameters are modified to be a = 5.11150 Å and c = 12.49365 Å by the crystal structure refinement, as shown in Fig. 16. Loo and Bastin [29] and Riani et al. [32] found a very narrow two-phase region between Ni3Ti and τ (from 25 to 28 at.% Co) in the isothermal section at 1173 K, which may explain why we do not succeed in finding the two-phase or three-phase equilibrium - 10 -
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related to Ni3Ti and τ simultaneously. On the basis of the present SEM/EDX and PXRD results, we can presume that the two-phase region Ni3Ti + τ is located between 30 and 34 at.% Co at a constant composition
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of 25 at.% Ti. Based on the above experimental results, the isothermal section of the Co–Ni–Ti system at 1373 K is constructed and presented in Fig. 17.
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There are 4 three-phase regions detected, liquid + (Co,Ni)Ti2 + (Co,Ni)Ti,
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(Co,Ni)Ti + βCo2Ti + τ, βCo2Ti + τ + Co3Ti, τ + Co3Ti + fcc-(Co,Ni). 3 three-phase regions (Co,Ni)Ti + Ni3Ti + τ, βCo2Ti + γCo2Ti + Co3Ti, Ni3Ti + τ + fcc-(Co, Ni) can be further inferred. The phases CoTi and NiTi can form a continuous solution (Co, Ni)Ti. The Ni solubilities of the
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phases βCo2Ti, γCo2Ti and Co3Ti are determined to be 13, 5 and 27 at.%, and the Co solubilities of the phase Ni3Ti are measured to be 30 at.%. The
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at.% Co.
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homogeneity ranges of the phase τ were determined to be from 34 to 51
5. Conclusion
The liquidus surface projection and the isothermal section at 1373 K of
the Co–Ni–Ti system have been determined by using SEM/EDX, PXRD and DTA techniques. The whole liquidus surface projection of the Co–Ni–Ti system was proposed, which consisted of 9 primary solidification regions βTi, - 11 -
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(Co,Ni)Ti2, (Co,Ni)Ti, Ni3Ti, τ, βCo2Ti, γCo2Ti, Co3Ti, fcc-(Co,Ni) and 6 ternary invariant reactions U1: liq. + Ni3Ti ↔ fcc-(Co,Ni) + τ, P1: liq. + fcc-(Co,Ni) + τ ↔ Co3Ti, P2: liq. + βCo2Ti + γCo2Ti ↔ Co3Ti, P3: liq. +
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Ni3Ti + τ ↔ (Co,Ni)Ti, U2: liq. + (Co,Ni)Ti ↔ τ + βCo2Ti, E1:liq. + (Co,Ni)Ti ↔ τ + βCo2Ti.
The isothermal section at 1373 K of the Co–Ni–Ti system was
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constructed, which included 7 three-phase regions liquid + (Co,Ni)Ti2 +
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(Co,Ni)Ti, (Co,Ni)Ti + Ni3Ti + τ, (Co,Ni)Ti + βCo2Ti + τ, βCo2Ti + τ + Co3Ti, βCo2Ti + γCo2Ti + Co3Ti, Ni3Ti + τ + fcc-(Co,Ni), τ + Co3Ti + fcc-(Co,Ni).
Both in the liquidus surface and isothermal section at 1373 K, a ternary
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compound τ with Co3V-structure was clearly identified according to the present PXRD results.
It should be pointed out that Co3Ti with Cu3Au-structure was still
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stable after annealed at 1373 K for 500 h and the addition of Ni seemed to
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enhance the high temperature stability of Co3Ti. This was a new phenomenon and further study would be carried out in our future work.
Acknowledgement
This work was supported by the National Key R&D Program of China (Grant No. 2016YFB0701401) and National Natural Science Foundation of China (NSFC) (Grant No. 51771021). - 12 -
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Soc. Japan 28 (1970) 1451–1456. [39] P. Duwez, J.L. Taylor, The structure of intermediate phases in alloys of titanium with iron, cobalt, and nickel, Trans. AIME, 188
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(1950) 1173–1176. [40] H.J. Wallbaum, H. Witte, The crystal structure of TiCo2, Z. Metallkd. 31 (1939) 185–187.
SC
[41] A.E. Dwight. CsCl-type equiatomic phases in binary alloys of
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transition elements, Trans. AIME 215 (1959) 283–286. [42] A.V. Skripov, A.L. Buzlukov, A.V. Soloninin, V.I. Voronin, I.F. Berger, T.J. Udovic, et al., Hydrogen motion and site occupation in Ti2CoHx(Dx): NMR and neutron scattering studies, Phys. B, 392
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(2007) 353–360.
[43] G.A. Yurko, J.W. Barton, J.G. Parr, The crystal structure of Ti2Ni, Acta Cryst. 12 (1959) 909–911.
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[44] Jade 5.0, XRD Pattern Processing Materials Data Inc. (1999).
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[45] J. Rodríguez-Carvajal, Recent advances in magnetic structure determination by neutron powder diffraction, Phys. B 192 (1993) 55–69.
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Figure captions
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Fig. 1a. Co–Ni phase diagram by Guillermet [12].
SC
Fig. 1b. Co–Ti phase diagram by Davydov et al. [14].
M AN U
Fig. 1c. Ni–Ti phase diagram by Keyzer et al. [22].
Fig. 2a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
TE D
Ni–79Ti–9Co (alloy A2).
Fig. 2b. Powder X-ray diffraction (PXRD) patterns of as-cast alloy
EP
Ni–79Ti–9Co (alloy A2).
AC C
Fig. 2c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–62Ti–19Co (alloy A6).
Fig. 2d. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–62Ti–19Co (alloy A6).
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Fig. 3a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–41Ti–55Co (alloy A12).
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Fig. 3b. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–37Ti–52Co (alloy A14).
SC
Fig. 3c. Powder X-ray diffraction (PXRD) patterns of as-cast alloys
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Ni–41Ti–55Co (alloy A12) and Ni–37Ti–52Co (alloy A14).
Fig. 3d. Result of DTA-analysis of as-cast alloy Ni–37Ti–52Co (alloy
TE D
A14).
Fig. 4a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
EP
Ni–31Ti–67Co (alloy A21).
AC C
Fig. 4b. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–31Ti–67Co (alloy A21).
Fig. 4c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–25Ti–75Co (alloy A27).
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Fig. 4d. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–25Ti–75Co (alloy A27).
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Fig. 5a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–34Ti–30Co (alloy A17).
SC
Fig. 5b. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
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Ni–34Ti–39Co (alloy A18).
Fig. 5c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
TE D
Ni–33Ti–48Co (alloy A19).
Fig. 5d. Powder X-ray diffraction (PXRD) patterns of as-cast alloys Ni–33Ti–20Co (alloy A16), Ni–34Ti–30Co (alloy A17), Ni–34Ti–39Co
AC C
EP
(alloy A18), Ni–33Ti–48Co (alloy A19), and Ni–31Ti–49Co (alloy A22).
Fig. 6a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–19Ti–32Co (alloy A30).
Fig. 6b. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–19Ti–32Co (alloy A30).
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Fig. 6c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–18Ti–40Co (alloy A31).
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Fig. 6d. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–18Ti–40Co (alloy A31).
SC
Fig. 7a. Result of DTA-analysis of as-cast alloy Ni–19Ti–32Co (alloy
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A30). I: Heating; II: Cooling.
Fig. 7b. Result of DTA-analysis of as-cast alloy Ni–18Ti–40Co (alloy
TE D
A31). I: Heating; II: Cooling.
Fig. 8. Liquidus surface projection of the Co–Ni–Ti system.
AC C
EP
Fig. 9. Invariant reaction scheme in the Co–Ni–Ti system.
Fig. 10b. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–58Ti–32Co (alloy B2).
Fig. 11a. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–36Ti–50Co (alloy B9).
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Fig. 11b. Powder X-ray diffraction (PXRD) patterns of annealed alloy Ni–36Ti–50Co (alloy B9).
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Fig. 11c. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–26Ti–52Co (alloy B25).
SC
Fig. 11d. Powder X-ray diffraction (PXRD) patterns of annealed alloy
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Ni–26Ti–52Co (alloy B25).
Fig. 12a. Back-scattered electron (BSE) SEM micrograph of annealed
TE D
alloy Ni–28Ti–61Co (alloy B15).
Fig. 12b. Powder X-ray diffraction (PXRD) patterns of annealed alloy
EP
Ni–28Ti–61Co (alloy B15).
AC C
Fig. 12c. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–27Ti–65Co (alloy B16).
Fig. 12d. Powder X-ray diffraction (PXRD) patterns of annealed alloy Ni–27Ti–65Co (alloy B16).
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Fig. 13a. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–16Ti–50Co (alloy B30).
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Fig. 13b. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–16Ti–59Co (alloy B31).
SC
Fig. 13c. Back-scattered electron (BSE) SEM micrograph of annealed
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alloy Ni–16Ti–64Co (alloy B32).
Fig. 14a. Back-scattered electron (BSE) SEM micrograph of annealed
TE D
alloy Ni–32Ti–31Co (alloy B11).
Fig. 14b. Powder X-ray diffraction (PXRD) patterns of annealed alloy
EP
Ni–32Ti–31Co (alloy B11).
AC C
Fig. 14c. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–32Ti–41Co (alloy B12).
Fig. 14d. Powder X-ray diffraction (PXRD) patterns of annealed alloy Ni–32Ti–41Co (alloy B12).
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Fig. 15. Powder X-ray diffraction (PXRD) patterns of as-cast alloys Ni–25Ti–0Co (alloy B18), Ni–25Ti–10Co (alloy B19), Ni–25Ti–20Co (alloy B20), Ni–25Ti–25Co (alloy B21), Ni–25Ti–30Co (alloy B22),
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Ni–25Ti–35Co (alloy B23), and Ni–25Ti–40Co (alloy B24).
Fig. 16. Experimental powder X-ray diffraction (PXRD) patterns of
SC
annealed alloy Ni–25Ti–35Co (alloy B23) with the theoretical patterns of
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τ (Co3V-structure).
AC C
EP
TE D
Fig. 17. Isothermal section at 1373 K of the Co–Ni–Ti system.
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Table 1. The crystallographic data of all phases in the Co–Ni–Ti system. Strukturbericht Pearson
Prototype
References
–
–
–
–
A1
cF4
Fm3m
Cu
[33]
εCo
A3
hP2
P63 /mmc
Mg
[34]
γNi
A1
cF4
Fm3m
Cu
[35]
βTi
A2
cI2
Im3m
W
[36]
αTi
A3
hP2
P63 /mmc
Mg
[37]
Co3Ti
L12
cP4
Pm3m
Cu3Au
[38]
γ-Co2Ti
C36
hP24
P63 /mmc
MgNi2
[39]
β-Co2Ti
C15
cF24
Fd3m
MgCu2
[40]
CoTi
B2
cP2
Pm3m
CsCl
[41]
CoTi2
E93
cF96
Fd3m
NiTi2
[42]
Ni3Ti
D024
hP16
P63 /mmc
Ni3Ti
[33]
NiTi
B2
cP2
Pm3m
CsCl
[41]
NiTi2
E93
cF96
Fd3m
NiTi2
[43]
τ
–
hP24
P6m2
Co3V
[29]
symbol
liquid
–
αCo
AC C
EP
TE D
M AN U
designation
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Space group
SC
Phase
1
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Alloy
Analysed composition (at.%)
As-cast phases
Primary phase
No.
Co
Ni
Ti
A1
4.20
18.71
77.09
αTi + (Co,Ni)Ti2
–
A2
9.31
11.38
79.31
αTi + (Co,Ni)Ti2
–
A3
14.93
7.31
77.76
αTi + (Co,Ni)Ti2
–
A4
17.45
3.70
78.85
αTi + (Co,Ni)Ti2
A5
9.70
29.89
60.41
A6
19.05
19.09
A7
26.74
A8
RI PT
Table 2. The microstructure analyses and phase compositions of the as-cast Co–Ni–Ti alloys.
Phase composition Co
Ni
Ti
–
–
–
–
–
–
(Co,Ni)Ti + βTi + (Co,Ni)Ti2
61.86
13.08
10.73
A9
Eutectic phases
Eutectic composition Co
Ni
Ti
αTi + (Co,Ni)Ti2
–
–
–
–
αTi + (Co,Ni)Ti2
–
–
–
–
–
αTi + (Co,Ni)Ti2
–
–
–
–
–
–
αTi + (Co,Ni)Ti2
–
–
–
(Co,Ni)Ti
12.23
35.00
52.77
βTi + (Co,Ni)Ti2
–
–
–
(Co,Ni)Ti + βTi + (Co,Ni)Ti2
(Co,Ni)Ti
28.40
18.53
53.07
βTi + (Co,Ni)Ti2
–
–
–
60.18
(Co,Ni)Ti + βTi + (Co,Ni)Ti2
(Co,Ni)Ti
37.36
9.32
53.32
βTi + (Co,Ni)Ti2
–
–
–
48.47
40.80
(Co,Ni)Ti + Ni3Ti
(Co,Ni)Ti
11.93
43.35
44.72
(Co,Ni)Ti + Ni3Ti
7.15
55.74
37.11
20.58
38.86
40.56
(Co,Ni)Ti + Ni3Ti
(Co,Ni)Ti
23.70
31.90
44.40
(Co,Ni)Ti + Ni3Ti
16.49
46.35
37.16
A10
28.58
27.24
44.18
(Co,Ni)Ti + Ni3Ti
(Co,Ni)Ti
29.48
26.21
44.31
(Co,Ni)Ti + Ni3Ti
26.38
35.44
38.18
A11
39.22
20.31
40.47
(Co,Ni)Ti + τ
(Co,Ni)Ti
39.85
15.63
44.52
(Co,Ni)Ti + τ
37.52
24.63
37.85
A12
54.83
4.45
40.72
(Co,Ni)Ti + β-Co2Ti
(Co,Ni)Ti
50.22
6.82
42.96
–
–
–
–
A13
50.63
13.65
35.72
(Co,Ni)Ti + β-Co2Ti + Co3Ti
(Co,Ni)Ti
48.21
10.18
41.61
β-Co2Ti + Co3Ti
51.98
15.64
32.38
A14
52.32
10.32
37.36
(Co,Ni)Ti + β-Co2Ti + Co3Ti
(Co,Ni)Ti
48.84
8.86
42.30
β-Co2Ti + Co3Ti
54.07
13.93
32.00
A15
9.79
57.22
32.99
Ni3Ti + (Co,Ni)Ti
Ni3Ti
8.71
63.45
27.84
Ni3Ti + (Co,Ni)Ti
10.27
51.54
38.19
A16
19.71
47.24
33.05
Ni3Ti + (Co,Ni)Ti
Ni3Ti
20.36
52.26
27.38
Ni3Ti + (Co,Ni)Ti
18.87
43.04
38.09
AC C
EP
TE D
M AN U
SC
–
2
30.01
35.90
34.09
Ni3Ti + (Co,Ni)Ti
Ni3Ti
30.02
41.52
28.46
Ni3Ti + (Co,Ni)Ti
29.72
32.53
37.75
A18
37.67
28.73
33.60
Ni3Ti + (Co,Ni)Ti
Ni3Ti
39.15
33.06
27.79
Ni3Ti + (Co,Ni)Ti
37.06
25.68
37.26
A19
47.73
19.76
32.51
τ + (Co,Ni)Ti
τ
48.04
23.71
28.25
τ + (Co,Ni)Ti
46.93
17.42
35.65
A20
58.30
9.54
32.16
β-Co2Ti + Co3Ti
β-Co2Ti
60.14
7.49
32.37
β-Co2Ti + Co3Ti
56.54
11.95
31.51
A21
67.27
1.82
30.91
β-Co2Ti + γ-Co2Ti + Co3Ti
β-Co2Ti
66.24
2.37
31.39
γ-Co2Ti + Co3Ti
73.38
3.03
23.59
A22
49.07
20.35
30.58
τ + (Co,Ni)Ti
τ
A23
60.04
10.78
29.18
β-Co2Ti + Co3Ti
–
A24
50.55
23.47
25.98
Co3Ti + β-Co2Ti
A25
69.00
5.50
25.50
A26
73.45
1.50
A27
74.55
A28
23.86
30.08
τ + (Co,Ni)Ti
50.00
14.98
35.02
–
–
–
β-Co2Ti + Co3Ti
–
–
–
Co3Ti
47.98
27.04
24.98
Co3Ti + β-Co2Ti
56.64
11.81
31.55
Co3Ti + β-Co2Ti
Co3Ti
69.24
5.91
24.85
–
–
–
–
25.05
γ-Co2Ti + Co3Ti
γ-Co2Ti
70.25
1.41
28.34
γ-Co2Ti + Co3Ti
74.94
2.10
22.96
0.00
25.45
γ-Co2Ti + Co3Ti
γ-Co2Ti
71.55
0.00
28.45
γ-Co2Ti + Co3Ti
77.07
0.00
22.93
9.87
73.85
16.28
fcc-(Co,Ni) + Ni3Ti
fcc-(Co,Ni)
11.21
73.12
15.67
fcc-(Co,Ni) + Ni3Ti
9.05
70.37
20.58
A29
21.38
62.12
16.50
fcc-(Co,Ni) + Ni3Ti
fcc-(Co,Ni)
22.07
62.74
15.19
fcc-(Co,Ni) + Ni3Ti
17.94
60.53
21.53
A30
32.34
48.98
18.68
fcc-(Co,Ni) + Ni3Ti
fcc-(Co,Ni)
32.47
52.74
14.79
fcc-(Co,Ni) + Ni3Ti
29.25
50.43
20.32
A31
39.86
42.22
17.92
fcc-(Co,Ni) + τ + Co3Ti
fcc-(Co,Ni)
42.95
41.87
15.18
fcc-(Co,Ni) + τ
37.62
41.67
20.71
A32
50.21
33.01
16.78
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
49.59
36.28
14.13
–
–
–
–
A33
60.47
23.47
16.06
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
62.48
23.52
14.00
–
–
–
–
A34
69.15
14.21
16.64
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
71.22
15.11
13.67
–
–
–
–
A35
78.54
4.76
16.70
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
81.22
5.02
13.76
–
–
–
–
AC C
EP
M AN U
46.06
TE D
RI PT
A17
SC
ACCEPTED MANUSCRIPT
3
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Table 3. Reaction temperatures of the as-cast Co–Ni–Ti alloys measured by DTA.
A4 A5
A6
A7
A8
liq. → (Co,Ni)Ti2 + βTi
1242
1242
βTi → (Co,Ni)Ti2 + αTi
1016
–
liq. → (Co,Ni)Ti2 + βTi
1264
βTi → (Co,Ni)Ti2 + αTi
1007
liq. → (Co,Ni)Ti2 + βTi
1280
βTi → (Co,Ni)Ti2 + αTi
994
liq. → (Co,Ni)Ti2 + βTi
1291
1289
βTi → (Co,Ni)Ti2 + αTi
979
–
liq. → (Co,Ni)Ti
1574
1578
liq. + (Co,Ni)Ti → (Co,Ni)Ti2
1297
–
liq. → (Co,Ni)Ti2 + βTi
1236
1244
liq. → (Co,Ni)Ti
1665
1671
liq. + (Co,Ni)Ti → (Co,Ni)Ti2
1302
1291
liq. → (Co,Ni)Ti2 + βTi
–
1275
liq. → (Co,Ni)Ti
1701
1709
liq. + (Co,Ni)Ti → (Co,Ni)Ti2
1318
1295
liq. → (Co,Ni)Ti2 + βTi
–
1267
liq. → (Co,Ni)Ti
1431
1436
liq. → (Co,Ni)Ti + Ni3Ti
1424
1430
liq. → (Co,Ni)Ti
1452
1470
liq. → (Co,Ni)Ti + Ni3Ti
1447
1451
A10
liq. → (Co,Ni)Ti
1521
1520
liq. → (Co,Ni)Ti + Ni3Ti
1457
1460
A11
liq. → (Co,Ni)Ti
1490
–
liq. → (Co,Ni)Ti + τ
1459
1458
A12
liq. → (Co,Ni)Ti
1644
1659
liq. + (Co,Ni)Ti → β-Co2Ti
1495
1491
A13
liq. → (Co,Ni)Ti
1497
1496
liq. + (Co,Ni)Ti → β-Co2Ti
–
1457
liq. → β-Co2Ti + Co3Ti
1449
–
RI PT
Cooling
AC C
A9
Heating
SC
A3
Temperature (K)
M AN U
A2
path
TE D
A1
Solidification
EP
Alloy No.
4
1262 –
1276
–
ACCEPTED MANUSCRIPT 1521
1522
liq. + (Co,Ni)Ti → β-Co2Ti
1472
1468
liq. → β-Co2Ti + Co3Ti
1462
1464
liq. → Ni3Ti
1572
1557
liq. → Ni3Ti + (Co,Ni)Ti
1430
1429
liq. → Ni3Ti
1548
1538
liq. → Ni3Ti + (Co,Ni)Ti
1448
liq. → Ni3Ti
1542
liq. → Ni3Ti + (Co,Ni)Ti
1465
liq. → Ni3Ti
1524
liq. → Ni3Ti + (Co,Ni)Ti
1460
1478
liq. → τ
1508
1505
liq. → τ + (Co,Ni)Ti
1455
1450
liq. → β-Co2Ti
1476
1469
liq. → β-Co2Ti + Co3Ti
1462
1453
liq. → β-Co2Ti
1498
1495
liq. + β-Co2Ti → γ-Co2Ti
1476
–
liq. → γ-Co2Ti + Co3Ti
1433
1430
liq. → τ
1512
1506
liq. → τ + (Co,Ni)Ti
1455
1485
A23
liq. → β-Co2Ti + Co3Ti
1468
1464
A24
liq. → Co3Ti
1480
1482
liq. → Co3Ti + β-Co2Ti
1448
1447
liq. → Co3Ti
1482
1478
liq. → Co3Ti + β-Co2Ti
1471
1468
liq. → γ-Co2Ti
1468
1469
liq. → γ-Co2Ti + Co3Ti
1439
1439
liq. → γ-Co2Ti
1473
1472
liq. → γ-Co2Ti + Co3Ti
1432
1433
liq. → fcc-(Co,Ni)
1595
1594
liq. → fcc-(Co,Ni) + Ni3Ti
1563
1558
liq. → fcc-(Co,Ni)
1594
1594
liq. → fcc-(Co,Ni) + Ni3Ti
1552
1548
liq. → fcc-(Co,Ni)
1585
1583
A19 A20
A21
A22
AC C
A25
SC
A18
M AN U
A17
TE D
A16
EP
A15
A26
A27 A28 A29
A30
RI PT
liq. → (Co,Ni)Ti
A14
5
1482
1533
1461
1516
ACCEPTED MANUSCRIPT
A33
A34
liq. → fcc-(Co,Ni)
1586
1585
liq. → fcc-(Co,Ni) + τ
1533
–
liq. + fcc-(Co,Ni) + τ → Co3Ti
1522
1518
liq. → fcc-(Co,Ni)
1606
1611
liq. + fcc-(Co,Ni) → Co3Ti
1508
1505
liq. → fcc-(Co,Ni)
1631
liq. + fcc-(Co,Ni) → Co3Ti
1487
liq. → fcc-(Co,Ni)
1592
liq. + fcc-(Co,Ni) → Co3Ti
1468
liq. → fcc-(Co,Ni)
1581
1577
liq. + fcc-(Co,Ni) → Co3Ti
1447
1448
AC C
EP
TE D
M AN U
A35
1532
RI PT
A32
1538
SC
A31
liq. → fcc-(Co,Ni) + Ni3Ti
6
1638
1483
1595
1467
ACCEPTED MANUSCRIPT
Table 4 Ternary invariant reactions in the Co–Ni–Ti system. Invariant reaction
Reaction
Reaction
Estimated
type
Temperature
composition of
(K)
liquid phase (at.%)
U1
~1535
liq. + fcc-(Co,Ni) + τ ↔ Co3Ti
P 1a
1520
liq. + β-Co2Ti + γ-Co2Ti ↔ Co3Ti
P2
~1470
liq. + Ni3Ti + τ ↔ (Co,Ni)Ti
P3
~1465
liq. + (Co,Ni)Ti ↔ τ + β-Co2Ti
U2
~1460
liq. ↔ τ + β-Co2Ti + Co3Ti
E1
~1450
42
21
48
31
21
70
4
26
39
25
36
50
15
35
51
17
32
EP
TE D
have been inferred in this work.
M AN U
Note that the invariant reactions P1 have been determined directly and the others
AC C
a
7
Ti
37
SC
liq. + Ni3Ti ↔ fcc-(Co,Ni) + τ
Ni
RI PT
Co
ACCEPTED MANUSCRIPT
Alloy Analysed composition No.
Identified phase
RI PT
Table 5. The constituent phases and their compositions of the Co–Ni–Ti alloys annealed at 1373 K. Phase composition (at.%)
(at.%)
Phase 1
Phase 2
Ti
Phase 1/2/3
Co
Ni
Ti
Co
Ni
Ti
Co
Ni
Ti
B1
22.71
20.83
56.46
liquid/(Co,Ni)Ti2/(Co,Ni)Ti
12.43
17.12
70.45
15.33
16.59
68.08
25.58
21.35
53.07
B2
32.23
10.00
57.77
liquid/(Co,Ni)Ti2/(Co,Ni)Ti
18.35
8.56
73.09
20.95
10.34
68.71
36.14
10.06
53.80
B3
11.11
48.44
40.45
(Co,Ni)Ti/Ni3Ti
12.55
42.33
45.12
6.73
67.12
26.15
–
–
–
B4
21.13
38.74
40.13
(Co,Ni)Ti/Ni3Ti
24.16
31.14
44.70
13.71
59.08
27.21
–
–
–
B5
30.60
28.92
40.48
(Co,Ni)Ti/Ni3Ti
33.50
22.21
44.29
23.09
49.31
27.60
–
–
–
B6
40.61
18.99
40.40
(Co,Ni)Ti/τ
41.93
15.30
42.77
39.50
32.78
27.72
–
–
–
B7
49.51
9.58
40.91
(Co,Ni)Ti/β-Co2Ti
47.12
9.63
43.25
55.74
10.31
33.95
–
–
–
B8
46.06
17.19
36.75
(Co,Ni)Ti/τ
46.23
12.37
41.40
46.11
26.60
27.29
–
–
–
B9
49.56
14.90
35.54
(Co,Ni)Ti/β-Co2Ti/τ
47.12
11.83
41.05
55.15
12.78
32.07
49.00
24.47
26.53
B10
21.54
46.01
32.45
(Co,Ni)Ti/Ni3Ti
29.34
25.84
44.82
19.19
52.09
28.72
–
–
–
B11
31.04
37.02
31.94
(Co,Ni)Ti/Ni3Ti
35.43
20.54
44.03
28.51
43.20
28.29
–
–
–
B12
41.04
27.42
31.54
(Co,Ni)Ti/τ
42.57
15.20
42.23
40.21
31.03
28.76
–
–
–
B13
56.58
12.66
30.76
β-Co2Ti/Co3Ti
57.10
10.53
32.37
54.47
20.68
24.85
–
–
–
B14
58.17
14.63
27.20
β-Co2Ti/Co3Ti
59.37
8.61
32.02
57.83
17.56
24.61
–
–
–
B15
61.39
10.88
27.73
β-Co2Ti/Co3Ti
62.00
5.76
32.24
60.71
14.22
25.07
–
–
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64.87
8.40
26.73
γ-Co2Ti/Co3Ti
66.20
3.96
29.84
64.88
10.14
24.98
–
–
–
B17
71.39
1.96
26.65
γ-Co2Ti/Co3Ti
68.91
1.39
29.70
74.19
2.99
22.82
–
–
–
B18
0.00
74.57
25.43
Ni3Ti
0.00
74.31
25.69
–
–
–
–
–
–
B19
9.78
65.03
25.19
Ni3Ti
9.92
64.75
25.33
–
–
–
–
–
–
B20
19.77
55.57
24.66
Ni3Ti
19.83
54.83
25.34
–
–
–
–
–
–
B21
24.57
50.20
25.23
Ni3Ti
24.89
49.32
25.79
–
–
–
–
–
–
B22
29.81
45.40
24.79
Ni3Ti
29.01
45.35
25.64
–
–
–
–
–
–
B23
34.60
40.75
24.65
τ
35.11
39.77
25.12
–
–
–
–
–
–
B24
39.54
35.92
24.54
τ
38.14
36.32
25.54
–
–
–
–
–
–
B25
52.30
22.15
25.55
β-Co2Ti/τ/Co3Ti
55.24
13.10
31.66
50.47
23.82
25.71
52.99
22.74
24.27
B26
10.62
72.75
16.63
Ni3Ti/fcc-(Co,Ni)
6.31
71.45
22.24
13.21
72.97
13.82
–
–
–
B27
20.88
62.21
16.91
Ni3Ti/fcc-(Co,Ni)
13.19
63.84
22.97
24.89
62.38
12.73
–
–
–
B28
30.12
52.66
17.22
Ni3Ti/fcc-(Co,Ni)
19.59
56.92
23.49
37.64
49.70
12.66
–
–
–
B29
39.38
43.67
16.95
Ni3Ti/fcc-(Co,Ni)
29.40
46.80
23.80
48.54
39.63
11.83
–
–
–
B30
49.51
34.90
15.59
τ/fcc-(Co,Ni)
37.77
39.44
22.79
58.63
29.07
12.30
–
–
–
B31
59.34
24.80
15.86
τ/Co3Ti/fcc-(Co,Ni)
47.87
28.90
23.23
52.65
26.23
21.12
63.94
23.45
12.61
B32
64.25
19.38
16.37
Co3Ti/fcc-(Co,Ni)
58.11
21.30
20.59
69.80
17.18
13.02
–
–
–
B33
67.94
16.89
15.17
Co3Ti/fcc-(Co,Ni)
60.83
18.85
20.32
70.28
15.90
13.82
–
–
–
B34
78.71
5.16
16.13
Co3Ti/fcc-(Co,Ni)
73.07
6.58
20.35
81.16
5.58
13.26
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–
–
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ACCEPTED MANUSCRIPT •The liquidus surface projection of the Co–Ni–Ti system was investigated. •The isothermal section at 1373 K of the Co–Ni–Ti system was determined. • The new ternary phase τ with Co3V-structure was confirmed to be stable at 1373 K.
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• The high solubility of Ni in Co3Ti-L12 phase was observed.
S0925-8388(18)31576-7
DOI:
10.1016/j.jallcom.2018.04.253
Reference:
JALCOM 45891
To appear in:
Journal of Alloys and Compounds
Received Date: 2 January 2018 Revised Date:
16 April 2018
Accepted Date: 21 April 2018
Please cite this article as: C. Zhou, C. Guo, J. Li, C. Li, Z. Du, Experimental investigations of the Co– Ni–Ti system: Liquidus surface projection and isothermal section at 1373�K, Journal of Alloys and Compounds (2018), doi: 10.1016/j.jallcom.2018.04.253. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Experimental investigations of the Co–Ni–Ti system: liquidus surface projection and isothermal section at 1373 K Chenyang Zhoua, Cuiping Guoa, Jingbo Lib, Changrong Lia, Zhenmin Dua* Department of Materials Science and Engineering, University of Science and
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a
Technology Beijing, Beijing 100083, P.R. China b
School of Materials Science and Engineering, Beijing Institute of Technology,
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Beijing 100081, P.R. China
Abstract: The liquidus surface projection and isothermal section at 1373 K of the Co–Ni–Ti system have been established by using the methods of scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX),
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powder X-ray diffraction (PXRD), and differential thermal analysis (DTA). 9 primary solidification regions and 6 ternary invariant reactions were deduced in the liquidus surface projection. 7 three-phase regions and 16 two-phase regions
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were derived in the isothermal section at 1373 K. Besides, the PXRD results
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indicated that the ternary compound τ with Co3V-structure existed in both liquidus surface projection and isothermal section at 1373 K. The ternary compound τ formed the extended primary field in the centre of the liquidus surface projection and its homogeneity ranges of Co in the isothermal section were measured to be from 34 to 51 at.%. The present experimental results could be used as guidance to practical applications and input to future thermodynamic assessments.
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Keywords: Phase diagram; Liquidus surface projection; Isothermal section;
*Corresponding author at: Tel./Fax: +86 10 62333772
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E-mail address: [email protected] (Z. Du).
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Co–Ni–Ti system
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1. Introduction In recent years, the Co–Ni–Ti system has attracted increasing attention of different researchers owing to its technological importance:
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superalloys [1, 2], shape memory alloys [3], high-entropy alloys [4-6], permanent magnets [7, 8]. The addition of titanium can improve the
formation of the γ' phase and increase the strength at high temperature of
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the Co- and Ni-based superalloys. The addition of cobalt can enhance the
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corrosion resistance in the Ni–Ti shape memory alloys. The cobalt, nickel, and titanium are also the principal elements in high-entropy alloys. For strengthening the Co- and Ni-based superalloys [9], homogenization annealing should be carried out around 1373 K and above, so the
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solidification paths of the as-cast alloys and phase equilibria relations at 1373 K are very meaningful.
It is well known that phase diagram is a basic guidance for selection of
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the alloy compositions, the route of heat treatment, etc., which can reduce
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the development time of new materials. In order to facilitate future thermodynamic modeling and material research and development, the experimental determination of phase diagram is essential. In the current work, the liquidus surface projection and isothermal section at 1373 K are constructed by a combination of SEM/EDX, PXRD, and DTA techniques.
2. Literature review -1-
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2.1 Binary systems The Co–Ni system was relatively simple without any intermediate phase and the available experiment information was summarized by
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Nishizawa and Ishida [10] and then revised by Predel [11]. Guillermet [12] performed a thermodynamic assessment of the Co–Ni system, which was accepted in the present work.
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The Co–Ti phase diagram was assessed by Murray [13], in which four
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terminal solution phases αCo, εCo, βTi and αTi, and five intermetallic compounds Co3Ti, γCo2Ti, βCo2Ti, CoTi and CoTi2 were included. Subsequently, Davydov et al. [14] re-determined the temperature of the congruent melting for the CoTi phase and re-assessed the Co–Ti system.
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Therefore, the Co–Ti phase diagram updated by Davydov et al. [14] was adopted in the current work.
Murray [15] reviewed the phase equilibria and thermochemical
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properties of the Ni–Ti system. The Ni–Ti phase diagram was made up of
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three disordered solution phases γNi, βTi and αTi, and three intermediate compounds Ni3Ti, NiTi and NiTi2. Several thermodynamic assessments of the Ni–Ti system were available [16–24], in which the work of Keyzer et al. [22] showed good agreement with experimental data and was widely used in the multicomponent system, and thus was accepted in the present work. The phase diagrams for three binary systems Co–Ni [12], Co–Ti [14], -2-
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and Ni–Ti [22] adopted in this study are shown in Fig. 1a-c.
2.2 Ternary system
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The vertical section at the CoTi–NiTi joint was determined using hardness, XRD, density and thermal analysis by Kornilov et al. [25],
which was the first experimental information on the Co–Ni–Ti system.
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Using diffusion couples and electron probe microanalysis (EPMA), the
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isothermal sections at 1073, 1173, and 1273 K were investigated by Gryzunov et al. [26–28]. They confirmed a complete solid solution between the phases Co3Ti and Ni3Ti. Furthermore, they also reported the three-phase regions between the phases NiTi, Co2Ti, and Co3Ti, but not
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separated the two phases βCo2Ti and γCo2Ti.
Loo and Bastin [29] measured the isothermal section at 1173 K using diffusion couples and equilibrated alloys by means of the optical analysis,
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EPMA and XRD methods and reported a very narrow phase boundary
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between the phases Ni3Ti and τ. Du et al. [30] used same method as [29] to investigate the isothermal section at 1123 K, but the ternary compound τ was not found. Based on the above experimental data [25–30], the Co–Ni–Ti system was reviewed concretely by Gupta [31]. Recently, Riani et al. [32] critically reviewed and re-determined the Co–Ni–Ti system at 1173 K using equilibrated alloys by means of SEM/EDS, XRD techniques, which was in good consistency with the -3-
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work of Loo and Bastin [29]. Besides, they confirmed that the ternary compound τ had a large solubilities and was stable down to 773 K. The crystallographic data of the binary and ternary systems [29, 33–43]
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are listed in Table 1.
3. Experimental methods
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3.1 Samples preparation
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Cobalt (99.99 wt.%), Nickel (99.99 wt.%) and Titanium (99.99 wt.%) were used as starting materials in the present work. The proper amounts of the elements about 5g were prepared on a water-cooled copper hearth in the arc-furnace (MTI MSM20-7) in an argon atmosphere (99.998%
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purity) with a non-consumable tungsten electrode and a tantalum piece as oxygen getter. To improve the homogeneity, every sample was turned around and melted at least five times. Then, the arc-melted buttons were
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cut into several pieces for different purposes.
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Some samples were homogenized at 1373 K for 500 h (Alloys B1 and B2 for 30 h) in evacuated quartz capsules (6 × 10-2 Pa). In the process of annealing, a chamber furnace (MTI KSL-1400) with a temperature accuracy of ± 1 K was used. After heat treatment, the annealed samples were quenched in water.
3.2 SEM/EDX analysis -4-
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Before microstructural characterization, all samples were polished and partial samples were etched in a chemical solution (H2O: HCl: H2O2 = 3: 2: 1) at room temperature for 5–10 s. The phases and element
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distributions of the as-cast samples were studied using SEM (Carl Zeiss EVO 18) in combination with EDX (Bruker Quantax EDS), and that of the annealed samples were performed by SEM (Carl Zeiss LEO 1450)
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equipped with EDX (Thermo Scientific UltraDry EDS). The same
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acceleration voltage of 20 kV was applied. In order to increase the precision of the composition measurements, 3–5 points or areas were analysed for each phase.
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3.3 PXRD analysis
PXRD analysis was carried out using X-ray diffractometer (Rigaku Ultima IV) with Cu-Kα radiation at 40 kV and 40 mA and a Ni-crystal
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monochromator. Diffraction patterns were generally acquired in a scan
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step 0.02° of over a 2θ range 20–90°. Before analysis, powder samples were annealed in evacuated quartz capsules (6 × 10-2 Pa) at 873 K during 2 h. Phase identification and crystal structure refinement were conducted with Jade 5.0 [44] and FullProf [45].
3.4 DTA analysis The reaction temperatures of all as-cast samples and partial annealed -5-
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samples were determined by DTA (TA Instruments, SDT-Q600) using Al2O3 crucibles and Pt/Pt-13%Rh string thermocouples. The DTA measurements were performed with heating and cooling rates of 10 K
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min-1 under argon atmosphere (99.998% purity). The certified standards of pure metal Al, Ag and Cu were used for the calibration, and an
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accuracy of ±1 K for the measured temperatures was obtained.
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4. Results and discussion 4.1 Liquidus surface projection
For the construction of the liquidus surface projection of the Co–Ni–Ti system, 35 alloys are prepared. The microstructure analyses and phase
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compositions of the as-cast Co–Ni–Ti alloys are presented in Table 2. In addition, their solidification paths and corresponding reaction temperatures are also given in Table 3.
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In case of the BSE micrograph and PXRD patterns of the alloy A2, a
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fully eutectic microstructure αTi + (Co,Ni)Ti2 is identified (Fig. 2a-b). A divorced eutectic microstructure is also observed in the alloy A6, but the PXRD results only support the existence of the two phases (Co,Ni)Ti2 and (Co,Ni)Ti, which is probably due to < 5 at.% content of the black phase (Fig. 2c-d). Therefore, the DTA analysis is used to help identifying the final state of the black phase. On the basis of the DTA results (Table 3), we can conclude that the eutectoid reaction βTi → αTi + (Co,Ni)Ti2 -6-
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does not happen and the black phase is βTi in the alloy A6. The alloys A12 and A14 are located in the primary solidification region (Co,Ni)Ti (Fig. 3a–b). Unlike the alloy A12, the PXRD patterns confirm
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the existence of the additional phase Co3Ti in the alloy A14 (Fig. 3c). Therefore, the eutectic microstructure of the alloy A14 is regarded as βCo2Ti + Co3Ti in the present work.
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It should be noted that βCo2Ti with MgCu2-structure is difficult to be
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distinguished from γCo2Ti with MgNi2-structure using the PXRD technique. Thus, the primary phases of the alloy A21 and A27 are judged by the morphology and composition analyses. The morphologies of the alloys A21 and A27 are different, and the EDX results also support that
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the alloy A21 is situated in the primary solidification βCo2Ti (31 at.% Ti), while the alloy A27 is located in the primary solidification γCo2Ti (28 at.% Ti) (Fig. 4a and c and Table 2). Furthermore, the PXRD analyses of
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the alloys A21 and A27 definitely confirm the existence of γCo2Ti and
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Co3Ti and so their eutectic microstructures of the alloys A21 and A27 are considered to be γCo2Ti + Co3Ti (Fig. 4b and d). As shown in the BSE micrographs of the alloys A17–A19, their
primary phase morphologies look the same (Fig. 5a-c). But as stated in section 2.2, the new ternary compound τ is likely to exist in the liquidus surface projection. In order to confirm the stability of the phase τ and distinguish the phases Ni3Ti and τ, a series of the powder samples are -7-
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used for XRD measurements. According to the PXRD results, the phase τ with Co3V-structure has been identified in the alloys A19 and A22 (Fig. 5d).
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In case of the BSE micrographs and PXRD patterns of the alloys A30 and A31, both are located in the primary solidification fcc-(Co,Ni) (Fig.
6a-d). The eutectic microstructure of the alloy A30 is fcc-(Co,Ni) + Ni3Ti
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and the black phase surrounding fcc-(Co,Ni) of the alloy A31 is identified
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as Co3Ti. It should be pointed out that the third phase of the alloy A31 is not measured using the PXRD method due to < 5 at.% content. But according to the available experimental results, the eutectic microstructure of the alloy A31 is to be fcc-(Co,Ni) + τ. Subsequently, the
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DTA curves are performed to identify the reaction temperatures (Fig. 7a–b). Liquidus temperatures are clear to be obtained. Two visible peaks with onset at 1538 K on heating and 1532 K on cooling and one weak
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peak (Due to less content of the eutectic microstructure fcc-(Co,Ni) + τ)
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with onset at 1533 K correspond to the three-phase eutectic reaction (liq. ↔ fcc-(Co,Ni) + τ). The rest peaks with onset at 1522 K on heating and 1518 K on cooling should correspond to the ternary peritectic reaction P1 (liq. + fcc-(Co,Ni) + τ ↔ Co3Ti). Also of note is that the two smaller peaks in the alloys 30 and 31 occur mainly due to the slight weight change in the process of the solid-liquid transformation. Table 4 sums up the temperatures and the estimated liquid -8-
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compositions for the ternary invariant reactions in the Co–Ni–Ti system. The predicted liquidus surface projection and complete reaction scheme
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are shown in Figs. 8–9.
4.2 Isothermal section at 1373 K
For the investigation of the isothermal section at 1373 K of the
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Co–Ni–Ti system, 34 alloys are prepared. The constituent phases and
summarized in Table 5.
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their compositions of the Co–Ni–Ti alloys annealed at 1373 K are
Same eutectic microstructures are identified in the alloys B1 and B2 and should be marked as the liquid phase in the present work (Fig.
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10a-b).
Two typical three-phase microstructures (Co,Ni)Ti + βCo2Ti + τ and βCo2Ti + τ + Co3Ti occur in the alloys B9 and B25 (Fig. 11a and c),
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agreeing with their PXRD patterns (Fig. 11b and d). Furthermore, two
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typical two-phase microstructures βCo2Ti + Co3Ti and γCo2Ti + Co3Ti are also observed in the alloy B15 and B16 (Fig. 12a and c), which is in consistence with their PXRD patterns (Fig. 12b and d). The Ni solubilities of Co3Ti (27 at.%) and βCo2Ti (13 at.%) are larger than that of γCo2Ti (5 at.%) in the isothermal section at 1373 K, which is in consistency with the experimental results at 1173 K [29, 32]. However, the γCo2Ti has a larger Ni solubilities (18 at.%) than Co3Ti (6 at.%) and -9-
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βCo2Ti (5 at.%) at 1123 K [30], which maybe need to be re-determined. The alloys annealed at 1373 K B26-B34 have very good strength and toughness and the powder samples are impossible to be obtained.
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Therefore, the analyses of the composition and morphology are adopted for these alloys in this work. In case of the BSE micrographs of alloys B30–B32, the micrograph of the alloy B31 looks like a combination
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between B30 and B32 (Fig. 13a-c). And the EDX analyses of the alloy
fcc-(Co,Ni) (Table 5).
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B31 also show the existence of three-phase microstructures τ + Co3Ti +
As shown in the BSE micrographs of the alloys B11 and B12, only two-phase microstructures can be observed (Fig. 14a and c). It should be
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noted the phases Ni3Ti and τ with hexagonal structure have a similar morphology. The PXRD analyses are used for distinguishing the black phase Ni3Ti in the alloy B11 and τ in the alloy B12 (Fig. 14b and d).
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In Fig. 15, the PXRD patterns of alloys B23 and B24 support the
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presence of the new ternary compound τ with Co3V-structure. A single phase τ is clearly identified in alloy B23, and the lattice parameters are modified to be a = 5.11150 Å and c = 12.49365 Å by the crystal structure refinement, as shown in Fig. 16. Loo and Bastin [29] and Riani et al. [32] found a very narrow two-phase region between Ni3Ti and τ (from 25 to 28 at.% Co) in the isothermal section at 1173 K, which may explain why we do not succeed in finding the two-phase or three-phase equilibrium - 10 -
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related to Ni3Ti and τ simultaneously. On the basis of the present SEM/EDX and PXRD results, we can presume that the two-phase region Ni3Ti + τ is located between 30 and 34 at.% Co at a constant composition
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of 25 at.% Ti. Based on the above experimental results, the isothermal section of the Co–Ni–Ti system at 1373 K is constructed and presented in Fig. 17.
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There are 4 three-phase regions detected, liquid + (Co,Ni)Ti2 + (Co,Ni)Ti,
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(Co,Ni)Ti + βCo2Ti + τ, βCo2Ti + τ + Co3Ti, τ + Co3Ti + fcc-(Co,Ni). 3 three-phase regions (Co,Ni)Ti + Ni3Ti + τ, βCo2Ti + γCo2Ti + Co3Ti, Ni3Ti + τ + fcc-(Co, Ni) can be further inferred. The phases CoTi and NiTi can form a continuous solution (Co, Ni)Ti. The Ni solubilities of the
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phases βCo2Ti, γCo2Ti and Co3Ti are determined to be 13, 5 and 27 at.%, and the Co solubilities of the phase Ni3Ti are measured to be 30 at.%. The
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at.% Co.
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homogeneity ranges of the phase τ were determined to be from 34 to 51
5. Conclusion
The liquidus surface projection and the isothermal section at 1373 K of
the Co–Ni–Ti system have been determined by using SEM/EDX, PXRD and DTA techniques. The whole liquidus surface projection of the Co–Ni–Ti system was proposed, which consisted of 9 primary solidification regions βTi, - 11 -
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(Co,Ni)Ti2, (Co,Ni)Ti, Ni3Ti, τ, βCo2Ti, γCo2Ti, Co3Ti, fcc-(Co,Ni) and 6 ternary invariant reactions U1: liq. + Ni3Ti ↔ fcc-(Co,Ni) + τ, P1: liq. + fcc-(Co,Ni) + τ ↔ Co3Ti, P2: liq. + βCo2Ti + γCo2Ti ↔ Co3Ti, P3: liq. +
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Ni3Ti + τ ↔ (Co,Ni)Ti, U2: liq. + (Co,Ni)Ti ↔ τ + βCo2Ti, E1:liq. + (Co,Ni)Ti ↔ τ + βCo2Ti.
The isothermal section at 1373 K of the Co–Ni–Ti system was
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constructed, which included 7 three-phase regions liquid + (Co,Ni)Ti2 +
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(Co,Ni)Ti, (Co,Ni)Ti + Ni3Ti + τ, (Co,Ni)Ti + βCo2Ti + τ, βCo2Ti + τ + Co3Ti, βCo2Ti + γCo2Ti + Co3Ti, Ni3Ti + τ + fcc-(Co,Ni), τ + Co3Ti + fcc-(Co,Ni).
Both in the liquidus surface and isothermal section at 1373 K, a ternary
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compound τ with Co3V-structure was clearly identified according to the present PXRD results.
It should be pointed out that Co3Ti with Cu3Au-structure was still
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stable after annealed at 1373 K for 500 h and the addition of Ni seemed to
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enhance the high temperature stability of Co3Ti. This was a new phenomenon and further study would be carried out in our future work.
Acknowledgement
This work was supported by the National Key R&D Program of China (Grant No. 2016YFB0701401) and National Natural Science Foundation of China (NSFC) (Grant No. 51771021). - 12 -
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SC
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transition elements, Trans. AIME 215 (1959) 283–286. [42] A.V. Skripov, A.L. Buzlukov, A.V. Soloninin, V.I. Voronin, I.F. Berger, T.J. Udovic, et al., Hydrogen motion and site occupation in Ti2CoHx(Dx): NMR and neutron scattering studies, Phys. B, 392
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Figure captions
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Fig. 1a. Co–Ni phase diagram by Guillermet [12].
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Fig. 1b. Co–Ti phase diagram by Davydov et al. [14].
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Fig. 1c. Ni–Ti phase diagram by Keyzer et al. [22].
Fig. 2a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
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Ni–79Ti–9Co (alloy A2).
Fig. 2b. Powder X-ray diffraction (PXRD) patterns of as-cast alloy
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Ni–79Ti–9Co (alloy A2).
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Fig. 2c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–62Ti–19Co (alloy A6).
Fig. 2d. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–62Ti–19Co (alloy A6).
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Fig. 3a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–41Ti–55Co (alloy A12).
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Fig. 3b. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–37Ti–52Co (alloy A14).
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Fig. 3c. Powder X-ray diffraction (PXRD) patterns of as-cast alloys
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Ni–41Ti–55Co (alloy A12) and Ni–37Ti–52Co (alloy A14).
Fig. 3d. Result of DTA-analysis of as-cast alloy Ni–37Ti–52Co (alloy
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A14).
Fig. 4a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
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Ni–31Ti–67Co (alloy A21).
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Fig. 4b. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–31Ti–67Co (alloy A21).
Fig. 4c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–25Ti–75Co (alloy A27).
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Fig. 4d. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–25Ti–75Co (alloy A27).
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Fig. 5a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–34Ti–30Co (alloy A17).
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Fig. 5b. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
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Ni–34Ti–39Co (alloy A18).
Fig. 5c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy
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Ni–33Ti–48Co (alloy A19).
Fig. 5d. Powder X-ray diffraction (PXRD) patterns of as-cast alloys Ni–33Ti–20Co (alloy A16), Ni–34Ti–30Co (alloy A17), Ni–34Ti–39Co
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(alloy A18), Ni–33Ti–48Co (alloy A19), and Ni–31Ti–49Co (alloy A22).
Fig. 6a. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–19Ti–32Co (alloy A30).
Fig. 6b. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–19Ti–32Co (alloy A30).
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Fig. 6c. Back-scattered electron (BSE) SEM micrograph of as-cast alloy Ni–18Ti–40Co (alloy A31).
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Fig. 6d. Powder X-ray diffraction (PXRD) patterns of as-cast alloy Ni–18Ti–40Co (alloy A31).
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Fig. 7a. Result of DTA-analysis of as-cast alloy Ni–19Ti–32Co (alloy
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A30). I: Heating; II: Cooling.
Fig. 7b. Result of DTA-analysis of as-cast alloy Ni–18Ti–40Co (alloy
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A31). I: Heating; II: Cooling.
Fig. 8. Liquidus surface projection of the Co–Ni–Ti system.
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Fig. 9. Invariant reaction scheme in the Co–Ni–Ti system.
Fig. 10b. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–58Ti–32Co (alloy B2).
Fig. 11a. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–36Ti–50Co (alloy B9).
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Fig. 11b. Powder X-ray diffraction (PXRD) patterns of annealed alloy Ni–36Ti–50Co (alloy B9).
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Fig. 11c. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–26Ti–52Co (alloy B25).
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Fig. 11d. Powder X-ray diffraction (PXRD) patterns of annealed alloy
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Ni–26Ti–52Co (alloy B25).
Fig. 12a. Back-scattered electron (BSE) SEM micrograph of annealed
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alloy Ni–28Ti–61Co (alloy B15).
Fig. 12b. Powder X-ray diffraction (PXRD) patterns of annealed alloy
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Ni–28Ti–61Co (alloy B15).
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Fig. 12c. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–27Ti–65Co (alloy B16).
Fig. 12d. Powder X-ray diffraction (PXRD) patterns of annealed alloy Ni–27Ti–65Co (alloy B16).
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Fig. 13a. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–16Ti–50Co (alloy B30).
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Fig. 13b. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–16Ti–59Co (alloy B31).
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Fig. 13c. Back-scattered electron (BSE) SEM micrograph of annealed
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alloy Ni–16Ti–64Co (alloy B32).
Fig. 14a. Back-scattered electron (BSE) SEM micrograph of annealed
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alloy Ni–32Ti–31Co (alloy B11).
Fig. 14b. Powder X-ray diffraction (PXRD) patterns of annealed alloy
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Ni–32Ti–31Co (alloy B11).
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Fig. 14c. Back-scattered electron (BSE) SEM micrograph of annealed alloy Ni–32Ti–41Co (alloy B12).
Fig. 14d. Powder X-ray diffraction (PXRD) patterns of annealed alloy Ni–32Ti–41Co (alloy B12).
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Fig. 15. Powder X-ray diffraction (PXRD) patterns of as-cast alloys Ni–25Ti–0Co (alloy B18), Ni–25Ti–10Co (alloy B19), Ni–25Ti–20Co (alloy B20), Ni–25Ti–25Co (alloy B21), Ni–25Ti–30Co (alloy B22),
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Ni–25Ti–35Co (alloy B23), and Ni–25Ti–40Co (alloy B24).
Fig. 16. Experimental powder X-ray diffraction (PXRD) patterns of
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annealed alloy Ni–25Ti–35Co (alloy B23) with the theoretical patterns of
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τ (Co3V-structure).
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Fig. 17. Isothermal section at 1373 K of the Co–Ni–Ti system.
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Table 1. The crystallographic data of all phases in the Co–Ni–Ti system. Strukturbericht Pearson
Prototype
References
–
–
–
–
A1
cF4
Fm3m
Cu
[33]
εCo
A3
hP2
P63 /mmc
Mg
[34]
γNi
A1
cF4
Fm3m
Cu
[35]
βTi
A2
cI2
Im3m
W
[36]
αTi
A3
hP2
P63 /mmc
Mg
[37]
Co3Ti
L12
cP4
Pm3m
Cu3Au
[38]
γ-Co2Ti
C36
hP24
P63 /mmc
MgNi2
[39]
β-Co2Ti
C15
cF24
Fd3m
MgCu2
[40]
CoTi
B2
cP2
Pm3m
CsCl
[41]
CoTi2
E93
cF96
Fd3m
NiTi2
[42]
Ni3Ti
D024
hP16
P63 /mmc
Ni3Ti
[33]
NiTi
B2
cP2
Pm3m
CsCl
[41]
NiTi2
E93
cF96
Fd3m
NiTi2
[43]
τ
–
hP24
P6m2
Co3V
[29]
symbol
liquid
–
αCo
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designation
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Space group
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Phase
1
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Alloy
Analysed composition (at.%)
As-cast phases
Primary phase
No.
Co
Ni
Ti
A1
4.20
18.71
77.09
αTi + (Co,Ni)Ti2
–
A2
9.31
11.38
79.31
αTi + (Co,Ni)Ti2
–
A3
14.93
7.31
77.76
αTi + (Co,Ni)Ti2
–
A4
17.45
3.70
78.85
αTi + (Co,Ni)Ti2
A5
9.70
29.89
60.41
A6
19.05
19.09
A7
26.74
A8
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Table 2. The microstructure analyses and phase compositions of the as-cast Co–Ni–Ti alloys.
Phase composition Co
Ni
Ti
–
–
–
–
–
–
(Co,Ni)Ti + βTi + (Co,Ni)Ti2
61.86
13.08
10.73
A9
Eutectic phases
Eutectic composition Co
Ni
Ti
αTi + (Co,Ni)Ti2
–
–
–
–
αTi + (Co,Ni)Ti2
–
–
–
–
–
αTi + (Co,Ni)Ti2
–
–
–
–
–
–
αTi + (Co,Ni)Ti2
–
–
–
(Co,Ni)Ti
12.23
35.00
52.77
βTi + (Co,Ni)Ti2
–
–
–
(Co,Ni)Ti + βTi + (Co,Ni)Ti2
(Co,Ni)Ti
28.40
18.53
53.07
βTi + (Co,Ni)Ti2
–
–
–
60.18
(Co,Ni)Ti + βTi + (Co,Ni)Ti2
(Co,Ni)Ti
37.36
9.32
53.32
βTi + (Co,Ni)Ti2
–
–
–
48.47
40.80
(Co,Ni)Ti + Ni3Ti
(Co,Ni)Ti
11.93
43.35
44.72
(Co,Ni)Ti + Ni3Ti
7.15
55.74
37.11
20.58
38.86
40.56
(Co,Ni)Ti + Ni3Ti
(Co,Ni)Ti
23.70
31.90
44.40
(Co,Ni)Ti + Ni3Ti
16.49
46.35
37.16
A10
28.58
27.24
44.18
(Co,Ni)Ti + Ni3Ti
(Co,Ni)Ti
29.48
26.21
44.31
(Co,Ni)Ti + Ni3Ti
26.38
35.44
38.18
A11
39.22
20.31
40.47
(Co,Ni)Ti + τ
(Co,Ni)Ti
39.85
15.63
44.52
(Co,Ni)Ti + τ
37.52
24.63
37.85
A12
54.83
4.45
40.72
(Co,Ni)Ti + β-Co2Ti
(Co,Ni)Ti
50.22
6.82
42.96
–
–
–
–
A13
50.63
13.65
35.72
(Co,Ni)Ti + β-Co2Ti + Co3Ti
(Co,Ni)Ti
48.21
10.18
41.61
β-Co2Ti + Co3Ti
51.98
15.64
32.38
A14
52.32
10.32
37.36
(Co,Ni)Ti + β-Co2Ti + Co3Ti
(Co,Ni)Ti
48.84
8.86
42.30
β-Co2Ti + Co3Ti
54.07
13.93
32.00
A15
9.79
57.22
32.99
Ni3Ti + (Co,Ni)Ti
Ni3Ti
8.71
63.45
27.84
Ni3Ti + (Co,Ni)Ti
10.27
51.54
38.19
A16
19.71
47.24
33.05
Ni3Ti + (Co,Ni)Ti
Ni3Ti
20.36
52.26
27.38
Ni3Ti + (Co,Ni)Ti
18.87
43.04
38.09
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EP
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SC
–
2
30.01
35.90
34.09
Ni3Ti + (Co,Ni)Ti
Ni3Ti
30.02
41.52
28.46
Ni3Ti + (Co,Ni)Ti
29.72
32.53
37.75
A18
37.67
28.73
33.60
Ni3Ti + (Co,Ni)Ti
Ni3Ti
39.15
33.06
27.79
Ni3Ti + (Co,Ni)Ti
37.06
25.68
37.26
A19
47.73
19.76
32.51
τ + (Co,Ni)Ti
τ
48.04
23.71
28.25
τ + (Co,Ni)Ti
46.93
17.42
35.65
A20
58.30
9.54
32.16
β-Co2Ti + Co3Ti
β-Co2Ti
60.14
7.49
32.37
β-Co2Ti + Co3Ti
56.54
11.95
31.51
A21
67.27
1.82
30.91
β-Co2Ti + γ-Co2Ti + Co3Ti
β-Co2Ti
66.24
2.37
31.39
γ-Co2Ti + Co3Ti
73.38
3.03
23.59
A22
49.07
20.35
30.58
τ + (Co,Ni)Ti
τ
A23
60.04
10.78
29.18
β-Co2Ti + Co3Ti
–
A24
50.55
23.47
25.98
Co3Ti + β-Co2Ti
A25
69.00
5.50
25.50
A26
73.45
1.50
A27
74.55
A28
23.86
30.08
τ + (Co,Ni)Ti
50.00
14.98
35.02
–
–
–
β-Co2Ti + Co3Ti
–
–
–
Co3Ti
47.98
27.04
24.98
Co3Ti + β-Co2Ti
56.64
11.81
31.55
Co3Ti + β-Co2Ti
Co3Ti
69.24
5.91
24.85
–
–
–
–
25.05
γ-Co2Ti + Co3Ti
γ-Co2Ti
70.25
1.41
28.34
γ-Co2Ti + Co3Ti
74.94
2.10
22.96
0.00
25.45
γ-Co2Ti + Co3Ti
γ-Co2Ti
71.55
0.00
28.45
γ-Co2Ti + Co3Ti
77.07
0.00
22.93
9.87
73.85
16.28
fcc-(Co,Ni) + Ni3Ti
fcc-(Co,Ni)
11.21
73.12
15.67
fcc-(Co,Ni) + Ni3Ti
9.05
70.37
20.58
A29
21.38
62.12
16.50
fcc-(Co,Ni) + Ni3Ti
fcc-(Co,Ni)
22.07
62.74
15.19
fcc-(Co,Ni) + Ni3Ti
17.94
60.53
21.53
A30
32.34
48.98
18.68
fcc-(Co,Ni) + Ni3Ti
fcc-(Co,Ni)
32.47
52.74
14.79
fcc-(Co,Ni) + Ni3Ti
29.25
50.43
20.32
A31
39.86
42.22
17.92
fcc-(Co,Ni) + τ + Co3Ti
fcc-(Co,Ni)
42.95
41.87
15.18
fcc-(Co,Ni) + τ
37.62
41.67
20.71
A32
50.21
33.01
16.78
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
49.59
36.28
14.13
–
–
–
–
A33
60.47
23.47
16.06
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
62.48
23.52
14.00
–
–
–
–
A34
69.15
14.21
16.64
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
71.22
15.11
13.67
–
–
–
–
A35
78.54
4.76
16.70
fcc-(Co,Ni) + Co3Ti
fcc-(Co,Ni)
81.22
5.02
13.76
–
–
–
–
AC C
EP
M AN U
46.06
TE D
RI PT
A17
SC
ACCEPTED MANUSCRIPT
3
ACCEPTED MANUSCRIPT
Table 3. Reaction temperatures of the as-cast Co–Ni–Ti alloys measured by DTA.
A4 A5
A6
A7
A8
liq. → (Co,Ni)Ti2 + βTi
1242
1242
βTi → (Co,Ni)Ti2 + αTi
1016
–
liq. → (Co,Ni)Ti2 + βTi
1264
βTi → (Co,Ni)Ti2 + αTi
1007
liq. → (Co,Ni)Ti2 + βTi
1280
βTi → (Co,Ni)Ti2 + αTi
994
liq. → (Co,Ni)Ti2 + βTi
1291
1289
βTi → (Co,Ni)Ti2 + αTi
979
–
liq. → (Co,Ni)Ti
1574
1578
liq. + (Co,Ni)Ti → (Co,Ni)Ti2
1297
–
liq. → (Co,Ni)Ti2 + βTi
1236
1244
liq. → (Co,Ni)Ti
1665
1671
liq. + (Co,Ni)Ti → (Co,Ni)Ti2
1302
1291
liq. → (Co,Ni)Ti2 + βTi
–
1275
liq. → (Co,Ni)Ti
1701
1709
liq. + (Co,Ni)Ti → (Co,Ni)Ti2
1318
1295
liq. → (Co,Ni)Ti2 + βTi
–
1267
liq. → (Co,Ni)Ti
1431
1436
liq. → (Co,Ni)Ti + Ni3Ti
1424
1430
liq. → (Co,Ni)Ti
1452
1470
liq. → (Co,Ni)Ti + Ni3Ti
1447
1451
A10
liq. → (Co,Ni)Ti
1521
1520
liq. → (Co,Ni)Ti + Ni3Ti
1457
1460
A11
liq. → (Co,Ni)Ti
1490
–
liq. → (Co,Ni)Ti + τ
1459
1458
A12
liq. → (Co,Ni)Ti
1644
1659
liq. + (Co,Ni)Ti → β-Co2Ti
1495
1491
A13
liq. → (Co,Ni)Ti
1497
1496
liq. + (Co,Ni)Ti → β-Co2Ti
–
1457
liq. → β-Co2Ti + Co3Ti
1449
–
RI PT
Cooling
AC C
A9
Heating
SC
A3
Temperature (K)
M AN U
A2
path
TE D
A1
Solidification
EP
Alloy No.
4
1262 –
1276
–
ACCEPTED MANUSCRIPT 1521
1522
liq. + (Co,Ni)Ti → β-Co2Ti
1472
1468
liq. → β-Co2Ti + Co3Ti
1462
1464
liq. → Ni3Ti
1572
1557
liq. → Ni3Ti + (Co,Ni)Ti
1430
1429
liq. → Ni3Ti
1548
1538
liq. → Ni3Ti + (Co,Ni)Ti
1448
liq. → Ni3Ti
1542
liq. → Ni3Ti + (Co,Ni)Ti
1465
liq. → Ni3Ti
1524
liq. → Ni3Ti + (Co,Ni)Ti
1460
1478
liq. → τ
1508
1505
liq. → τ + (Co,Ni)Ti
1455
1450
liq. → β-Co2Ti
1476
1469
liq. → β-Co2Ti + Co3Ti
1462
1453
liq. → β-Co2Ti
1498
1495
liq. + β-Co2Ti → γ-Co2Ti
1476
–
liq. → γ-Co2Ti + Co3Ti
1433
1430
liq. → τ
1512
1506
liq. → τ + (Co,Ni)Ti
1455
1485
A23
liq. → β-Co2Ti + Co3Ti
1468
1464
A24
liq. → Co3Ti
1480
1482
liq. → Co3Ti + β-Co2Ti
1448
1447
liq. → Co3Ti
1482
1478
liq. → Co3Ti + β-Co2Ti
1471
1468
liq. → γ-Co2Ti
1468
1469
liq. → γ-Co2Ti + Co3Ti
1439
1439
liq. → γ-Co2Ti
1473
1472
liq. → γ-Co2Ti + Co3Ti
1432
1433
liq. → fcc-(Co,Ni)
1595
1594
liq. → fcc-(Co,Ni) + Ni3Ti
1563
1558
liq. → fcc-(Co,Ni)
1594
1594
liq. → fcc-(Co,Ni) + Ni3Ti
1552
1548
liq. → fcc-(Co,Ni)
1585
1583
A19 A20
A21
A22
AC C
A25
SC
A18
M AN U
A17
TE D
A16
EP
A15
A26
A27 A28 A29
A30
RI PT
liq. → (Co,Ni)Ti
A14
5
1482
1533
1461
1516
ACCEPTED MANUSCRIPT
A33
A34
liq. → fcc-(Co,Ni)
1586
1585
liq. → fcc-(Co,Ni) + τ
1533
–
liq. + fcc-(Co,Ni) + τ → Co3Ti
1522
1518
liq. → fcc-(Co,Ni)
1606
1611
liq. + fcc-(Co,Ni) → Co3Ti
1508
1505
liq. → fcc-(Co,Ni)
1631
liq. + fcc-(Co,Ni) → Co3Ti
1487
liq. → fcc-(Co,Ni)
1592
liq. + fcc-(Co,Ni) → Co3Ti
1468
liq. → fcc-(Co,Ni)
1581
1577
liq. + fcc-(Co,Ni) → Co3Ti
1447
1448
AC C
EP
TE D
M AN U
A35
1532
RI PT
A32
1538
SC
A31
liq. → fcc-(Co,Ni) + Ni3Ti
6
1638
1483
1595
1467
ACCEPTED MANUSCRIPT
Table 4 Ternary invariant reactions in the Co–Ni–Ti system. Invariant reaction
Reaction
Reaction
Estimated
type
Temperature
composition of
(K)
liquid phase (at.%)
U1
~1535
liq. + fcc-(Co,Ni) + τ ↔ Co3Ti
P 1a
1520
liq. + β-Co2Ti + γ-Co2Ti ↔ Co3Ti
P2
~1470
liq. + Ni3Ti + τ ↔ (Co,Ni)Ti
P3
~1465
liq. + (Co,Ni)Ti ↔ τ + β-Co2Ti
U2
~1460
liq. ↔ τ + β-Co2Ti + Co3Ti
E1
~1450
42
21
48
31
21
70
4
26
39
25
36
50
15
35
51
17
32
EP
TE D
have been inferred in this work.
M AN U
Note that the invariant reactions P1 have been determined directly and the others
AC C
a
7
Ti
37
SC
liq. + Ni3Ti ↔ fcc-(Co,Ni) + τ
Ni
RI PT
Co
ACCEPTED MANUSCRIPT
Alloy Analysed composition No.
Identified phase
RI PT
Table 5. The constituent phases and their compositions of the Co–Ni–Ti alloys annealed at 1373 K. Phase composition (at.%)
(at.%)
Phase 1
Phase 2
Ti
Phase 1/2/3
Co
Ni
Ti
Co
Ni
Ti
Co
Ni
Ti
B1
22.71
20.83
56.46
liquid/(Co,Ni)Ti2/(Co,Ni)Ti
12.43
17.12
70.45
15.33
16.59
68.08
25.58
21.35
53.07
B2
32.23
10.00
57.77
liquid/(Co,Ni)Ti2/(Co,Ni)Ti
18.35
8.56
73.09
20.95
10.34
68.71
36.14
10.06
53.80
B3
11.11
48.44
40.45
(Co,Ni)Ti/Ni3Ti
12.55
42.33
45.12
6.73
67.12
26.15
–
–
–
B4
21.13
38.74
40.13
(Co,Ni)Ti/Ni3Ti
24.16
31.14
44.70
13.71
59.08
27.21
–
–
–
B5
30.60
28.92
40.48
(Co,Ni)Ti/Ni3Ti
33.50
22.21
44.29
23.09
49.31
27.60
–
–
–
B6
40.61
18.99
40.40
(Co,Ni)Ti/τ
41.93
15.30
42.77
39.50
32.78
27.72
–
–
–
B7
49.51
9.58
40.91
(Co,Ni)Ti/β-Co2Ti
47.12
9.63
43.25
55.74
10.31
33.95
–
–
–
B8
46.06
17.19
36.75
(Co,Ni)Ti/τ
46.23
12.37
41.40
46.11
26.60
27.29
–
–
–
B9
49.56
14.90
35.54
(Co,Ni)Ti/β-Co2Ti/τ
47.12
11.83
41.05
55.15
12.78
32.07
49.00
24.47
26.53
B10
21.54
46.01
32.45
(Co,Ni)Ti/Ni3Ti
29.34
25.84
44.82
19.19
52.09
28.72
–
–
–
B11
31.04
37.02
31.94
(Co,Ni)Ti/Ni3Ti
35.43
20.54
44.03
28.51
43.20
28.29
–
–
–
B12
41.04
27.42
31.54
(Co,Ni)Ti/τ
42.57
15.20
42.23
40.21
31.03
28.76
–
–
–
B13
56.58
12.66
30.76
β-Co2Ti/Co3Ti
57.10
10.53
32.37
54.47
20.68
24.85
–
–
–
B14
58.17
14.63
27.20
β-Co2Ti/Co3Ti
59.37
8.61
32.02
57.83
17.56
24.61
–
–
–
B15
61.39
10.88
27.73
β-Co2Ti/Co3Ti
62.00
5.76
32.24
60.71
14.22
25.07
–
–
–
TE D
EP
AC C
SC
Ni
M AN U
Co
Phase 3
8
ACCEPTED MANUSCRIPT
64.87
8.40
26.73
γ-Co2Ti/Co3Ti
66.20
3.96
29.84
64.88
10.14
24.98
–
–
–
B17
71.39
1.96
26.65
γ-Co2Ti/Co3Ti
68.91
1.39
29.70
74.19
2.99
22.82
–
–
–
B18
0.00
74.57
25.43
Ni3Ti
0.00
74.31
25.69
–
–
–
–
–
–
B19
9.78
65.03
25.19
Ni3Ti
9.92
64.75
25.33
–
–
–
–
–
–
B20
19.77
55.57
24.66
Ni3Ti
19.83
54.83
25.34
–
–
–
–
–
–
B21
24.57
50.20
25.23
Ni3Ti
24.89
49.32
25.79
–
–
–
–
–
–
B22
29.81
45.40
24.79
Ni3Ti
29.01
45.35
25.64
–
–
–
–
–
–
B23
34.60
40.75
24.65
τ
35.11
39.77
25.12
–
–
–
–
–
–
B24
39.54
35.92
24.54
τ
38.14
36.32
25.54
–
–
–
–
–
–
B25
52.30
22.15
25.55
β-Co2Ti/τ/Co3Ti
55.24
13.10
31.66
50.47
23.82
25.71
52.99
22.74
24.27
B26
10.62
72.75
16.63
Ni3Ti/fcc-(Co,Ni)
6.31
71.45
22.24
13.21
72.97
13.82
–
–
–
B27
20.88
62.21
16.91
Ni3Ti/fcc-(Co,Ni)
13.19
63.84
22.97
24.89
62.38
12.73
–
–
–
B28
30.12
52.66
17.22
Ni3Ti/fcc-(Co,Ni)
19.59
56.92
23.49
37.64
49.70
12.66
–
–
–
B29
39.38
43.67
16.95
Ni3Ti/fcc-(Co,Ni)
29.40
46.80
23.80
48.54
39.63
11.83
–
–
–
B30
49.51
34.90
15.59
τ/fcc-(Co,Ni)
37.77
39.44
22.79
58.63
29.07
12.30
–
–
–
B31
59.34
24.80
15.86
τ/Co3Ti/fcc-(Co,Ni)
47.87
28.90
23.23
52.65
26.23
21.12
63.94
23.45
12.61
B32
64.25
19.38
16.37
Co3Ti/fcc-(Co,Ni)
58.11
21.30
20.59
69.80
17.18
13.02
–
–
–
B33
67.94
16.89
15.17
Co3Ti/fcc-(Co,Ni)
60.83
18.85
20.32
70.28
15.90
13.82
–
–
–
B34
78.71
5.16
16.13
Co3Ti/fcc-(Co,Ni)
73.07
6.58
20.35
81.16
5.58
13.26
–
–
–
AC C
EP
TE D
M AN U
SC
RI PT
B16
9
CE ED
PT
M AN US
CR
EP TE D
M AN US
C
CE ED
PT
M AN US
CR
EP TE D
M AN US
C
EP TE D
M AN US
C
EP TE D
M AN US
C
CE
ED
PT M AN US
C
TE D
M AN U
AC C EP TE D
M AN US
CR
IP T
CE
ED
PT M AN US
C
EP TE D
M AN US
C
EP TE D
M AN US
C
EP TE D
M AN US
C
EP TE D
M AN US
C
TE D
M AN U
TE D
M AN U
TE D
M AN U
ACCEPTED MANUSCRIPT •The liquidus surface projection of the Co–Ni–Ti system was investigated. •The isothermal section at 1373 K of the Co–Ni–Ti system was determined. • The new ternary phase τ with Co3V-structure was confirmed to be stable at 1373 K.
AC C
EP
TE D
M AN U
SC
RI PT
• The high solubility of Ni in Co3Ti-L12 phase was observed.