Experimental investigation of the Fe-Sn-Ti ternary isothermal section at 873 K

Accepted Manuscript Experimental investigation of the Fe-Sn-Ti ternary isothermal section at 873 K Ming Yin, Philip Nash, James A. Kaduk, Julius Clemens Schuster PII:

S0925-8388(16)32928-0

DOI:

10.1016/j.jallcom.2016.09.174

Reference:

JALCOM 39008

To appear in:

Journal of Alloys and Compounds

Received Date: 11 April 2016 Revised Date:

5 September 2016

Accepted Date: 16 September 2016

Please cite this article as: M. Yin, P. Nash, J.A. Kaduk, J.C. Schuster, Experimental investigation of the Fe-Sn-Ti ternary isothermal section at 873 K, Journal of Alloys and Compounds (2016), doi: 10.1016/ j.jallcom.2016.09.174. 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 investigation of the Fe-Sn-Ti ternary isothermal section at 873 K Ming Yin a *, Philip Nash a, James A. Kaduk b, Julius Clemens Schuster c a Thermal Processing Technology Center, Illinois Institute of Technology (IIT), 10 West 32nd Street, Chicago, IL 60616, USA

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b Chemistry Department, Illinois Institute of Technology (IIT), Chicago, IL 60616, USA c Institut für Physikalische Chemie, Universität Wien, Vienna, Austria

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Abstract

The isothermal section of the Fe-Sn-Ti ternary system at 873 K was investigated over the whole

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composition range using X-ray diffraction and scanning electron microscopy with an energy dispersive spectrometer. Three ternary compounds Fe2SnTi, Fe5Sn9Ti6 and FeSnTi2 were observed. _

The crystal structure of FeSnTi2 is solved (Pearson symbol hP18, space group P62m) and Fe5Sn9Ti6 _

is a cubic structured ternary compound (Pearson symbol cF116, space group Fm 3 m). The

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compound FeSnTi was found to have a hexagonal structure (Pearson symbol hP6, space group P63mc) in the as-cast sample and the 1273 K annealed sample rather than the reported cubic half-

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Heusler structure.

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.

Keywords: Fe-Sn-Ti; Phase diagram *Corresponding author: Ming Yin

Phone: 1+(312) 567 3203 fax: 1+(312) 567 8875 e-mail: [email protected]

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1. Introduction

Heusler intermetallic compounds, which have a generic chemical formula of X2YZ (prototype _

Cu2MnAl, Pearson symbol cF16, space group Fm3m), are a class of very promising materials [1] with wide potential applications. Fe2TiZ (Z = Al, Ga, Si, Sn) compounds attract a lot of attention

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because of their distinct properties. For example, Fe2TiAl is known for its great thermoelectric properties [2]. Fe2TiSn is a typical example as a nonmagnetic semimetal with a pseudo-gap at the Fermi level [3]. A lot of work has been devoted to investigate its physical properties. Szytula et al.

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[4] carried out X-ray diffraction, neutron diffraction and magnetic measurements on Fe2TiSn and obvious chemical disorder was observed. Using X-ray photoemission measurement and ab initio

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electronic structure calculations, Ślebarski et al. [5] revealed the occurrence of weak ferromagnetism below 240 K and the heavy fermion behavior in Fe2TiSn might be induced by atomic disorder. Lue et al. [6] found that the electrical resistivity and Seebeck coefficient were very sensitive to off-stoichiometric compositions. Xu et al. [7] used full-potential linearized augmented

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plane wave and local orbital method to investigate the optical properties and to show the origin of the different optical transitions.

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In a recent review of the phase equilibria of selected alloy systems containing Heusler compounds it

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was noted that Fe2TiZ (Z = Al, Ga, Si, Sn) all have been reported as Heusler compounds, while Fe2TiIn has not been reported [8]. However Fe-Ti-Sn was the only system with a reported Heusler phase for which no experimentally determined phase diagram is available in the ASM (American Society of Materials) Alloy Phase Diagram Database or the Springer Materials. A thorough understanding of the phase equilibria relationships of the Fe-Sn-Ti ternary system will contribute to the development of the Fe2TiSn Heusler compound as well as the other alloys in the system, especially for the fabrication process, alloy design and optimization of target properties. Kozakai et al. [9] studied the partial phase equilibria in the Fe-Ti rich part of the Fe-Sn-Ti system at 1123 K and 1173 K through arc melting and annealing 17 alloys and these were examined by means of

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scanning electron microscope (SEM) and X-ray diffraction (XRD). Ternary compounds Fe2SnTi and FeSnTi2 were reported but characterization of the crystal structure of the latter newly found compound was not provided. Yang [10] established the isothermal section at 773 K (Sn < 65 at. %) and 473 K for the Sn-rich (Sn > 40 at. %) area by means of X-ray powder diffraction of 150 alloy

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compositions produced by arc melting and three step annealing (1173 K for 15 days, 50 K below phase transformation temperature for 10 days, 773 K for 15 days) with the aid of differential thermal analysis (DTA), SEM with an energy dispersive spectrometer (EDS) and optical

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microscopy. Besides FeSn3Ti5, which can be viewed as the extreme composition of the solid solution where Fe atoms have been inserted into the binary compound Sn3Ti5 at the interstitial

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positions [11], three ternary compounds, a half-Heusler structured compound FeSnTi, FeSnTi2 and a Heusler compound Fe2SnTi were reported. However, the author did not provide the XRD pattern of FeSnTi and the crystal structure of FeSnTi2 was not solved. Romaka et al. [12] studied the phase equilibria at 773 K in the whole concentration range using X-ray diffraction and metallographic analysis of arc melted and annealed (773 K for 30 days) alloys and two ternary compounds were

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reported, Fe2SnTi and Fe0.6Sn2Ti0.4 besides FeSn3Ti5. The enthalpy of formation from the electronic structure calculations confirmed the instability of FeSnTi of a half-Heusler structure since the

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enthalpy of formation of FeSnTi of a half-Heusler structure is less negative than the hull energy, i.e. the convex surface of the minimum energy in the system as a function of composition. The two

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complete isotherms at the same temperature (773 K) are compared in Fig. 1. Seven obvious differences are indicated with circles. Because of the discrepancies in the published phase diagrams for this system, it is necessary to do some further investigation to resolve the disputes.

In this work, the complete isothermal section of the Fe-Sn-Ti ternary system at 873 K was determined experimentally using powder metallurgy samples and equilibrated alloys from arc melting.

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2. Materials and methods

All elemental materials were purchased from Alfa Aesar®, the properties of which are listed in Table 1. Fe powders were heat treated at 873 K for an hour in flowing hydrogen to remove oxides on the surface. The reduced powders were ground and sieved (< 44 µm) immediately prior to sample

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preparation.

Fifty-six alloys of 5 g each were prepared using an arc melting furnace (MRF Inc., model No.: ABJ-

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900), the compositions of which are shown as the empty triangles in Fig. 2 together with the assessed binary phase diagrams [13, 14, 15]. The alloy compositions corresponding to possible

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ternary compounds are presented using solid round symbols, which were also prepared. The steel chamber was evacuated to 1×10-2 Pa using an Edwards® Diffstak Vapor Diffusion pump and filled with ultra high purity argon (99.999%) to 50 kPa three times successively. Elements were mixed in the required ratio, placed in the water cooled copper hearth and then arc melted at a partial pressure of 50 kPa Ar. The buttons were turned over and remelted at least three times to ensure homogeneity.

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The surface of the samples was ground to remove possible surface oxidation.

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Four alloys with a very low melting point, i.e. Sn-rich samples, were prepared using powder metallurgy, the compositions of which are presented as solid triangles in Fig. 2. Elemental powders

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of the desired ratio FexSnyTiz were mixed using a spoon and compressed together with a load of around 15 MPa. The compressed pellets had dimensions of φ 4 × 1.5 mm × mm with a weight of 100 mg.

To reach the equilibrium state, samples were sealed in quartz tubes which were evacuated using a mechanical pump and filled with high purity argon (99.998 vol. %) alternatively 6-7 times and then put into a furnace at 873 ± 5 K for 30 days. The quartz tubes were then quenched in ice water. If the annealed samples were not considered to have achieved equilibrium, as can be assessed from the

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microstructure, they were sealed again and annealed at 1173 K for 14 days followed by heat treatment at 873 K for 30 days. After characterization, all the samples were further annealed at 873 K for 30 days and examined again to ensure the prior results corresponded to the equilibrium state.

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All samples were characterized using XRD (Thermo ARL, X’TRA). The brittle samples, which were the majority of the alloys, were crushed to powders and sieved to achieve a size less than 44 µm for XRD analysis while the ductile alloys were ground, polished and cleansed in an ultrasonic

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bath before examination. CrystalMaker® and CrystalDiffract® were used to simulate crystal structures and generate XRD patterns which were used for matching with experimental data. An

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SEM (JEOL, JSM-5900LV) with an EDS (Oxford Instruments, 80 mm2 X-ManN Silicon Drift Detector) was used to observe the microstructure and determine the composition of each phase (atomic percentage) after standard metallographic preparation. Phase transformation temperatures were measured using a Setaram® Setsys 1700 DSC using a heating rate of 10 K/min in flowing

3. Results and Discussion

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argon at atmospheric pressure. NIST SRM 720 sapphire was used as the reference material.

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The crystal structures of the possible phases in the Fe-Sn-Ti ternary system at 873 K are listed in

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Table 2. The reported lattice parameters and the corresponding references are included.

Representative analyzed results of all the alloys are listed in Table 3. The overall compositions were obtained through area scan at a magnification of 90. The compositions of each phase are the averaged value of five point measurements.

All the measured overall compositions of the alloys are close to the nominal ones within 2 at. %. Deviations from nominal could be due to formation of some oxides from the raw materials, loss of element during arc melting, or the measurement error from the EDS instrument. All the measured

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overall compositions were verified to be in a three-phase triangle or on the two-phase tie-line of measured phase compositions. When there were two or more alloys prepared in the same threephase triangle and the compositions of the same phase were not exactly the same, two criteria were considered to select the most accurate one to construct the phase diagram. One was the size of the

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phase, i.e. the equivalent diameter estimated from backscattered electron micrographs. Larger size was preferred since it indicates enough time for phase growth and therefore, enough time for phases to reach equilibrium. Also, the EDS measurement is less likely to penetrate through or collect X-

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rays from neighboring phases. Some phases underwent solid state reactions and correspondingly, their sizes were too small to be determined unambiguously and therefore, the compositions were not

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provided in Table 3 to avoid misunderstanding. The other criterion was that the phase composition which was the furthest from the tie-line connecting the other two phases was preferred. Due to phase size, it was unavoidable sometimes to collect X-rays from other phases and the measured compositions would then be a value in the three-phase triangle rather than at the vertex. Choosing

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the more extreme value helps to reduce the error.

3.1. Terminal solution phases

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Four terminal solution phases were observed as shown in Table 2. The maximum solubility of Sn in α-Fe is around 5 at. % and that of Ti is about 2 at. %. Very limited solubility (< 1 at. %) of the two

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elements, Fe and Ti, is observed in the liquid phase which transforms to β-Sn after quenching. 10 at. % of Sn is observed in α-Ti while 3 at. % Sn is observed in β-Ti with Fe ranging from 10 to 14 at. %. Except for the solubility of Fe and Ti in the liquid phase measured by Romaka [12], all studies at relatively low temperature (773 and 873 K) are in good agreement.

3.2. Binary compounds All the binary compounds listed in Table 2 were observed. Additionally, Fe3Sn2 with an undetectable solubility of Ti was sometimes observed since the investigated isothermal temperature

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(873 K) is very close to its lower formation temperature 880 K [13]. FeSn2 was formed on quenching in several cases. Considering that the binary Fe-Sn phase diagram is well established, Fe3Sn2 and FeSn2 are not considered to be stable at this temperature in this work. Very limited solubility of the third element is found for FeSn, FeTi, Sn3Ti2, SnTi2 and SnTi3. The solubility of Sn

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in Fe2Ti is as much as around 15 at. % and its phase field, i.e., the composition which corresponds to the specific phase, Fe2Ti here, extends parallel to the Sn-Ti side indicating the substitution between Sn atoms and Ti atoms on the crystal lattice. This is in agreement with the high

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temperature work (1123 and 1173 K) by Kozakai [9]. A maximum solubility of 18 at. % Fe is found in Sn5Ti6 in this work, mainly as substitution for Ti. The large solubility of Fe is accepted by many For Sn3Ti5, the insertion of Fe

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researchers except Romaka et al. [12] who observed only 5 at. %.

atoms into the interstitial space could be as much as 11 at. % at 1073 K and forms the FeSn3Ti5 compound [10] which will be viewed as Sn3Ti5 in the following text for convenience. Therefore, the extension of the Sn3Ti5 single phase field should point to the Fe-corner as was determined in this work while those determined by Yang [10] and Romaka et al. [12] do not. In this work, the

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investigated temperature is lower and therefore a maximum solubility of around 9 at. % Fe is

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observed.

3.3. Ternary compounds

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The Heusler compound Fe2SnTi was observed in agreement with all the other published work. However, the solubility range in this work is larger with the content of Fe varying from 47 at. % to 56 at. % and at almost constant content of Sn. This discrepancy may be because the investigated temperature in this work is higher than the previous work by Yang [10] and Romaka [12]. Kozakai et al. [9] observed that the content of Fe in the Fe2SnTi single phase field at 1123 K could change from 47 at. % to 64 at. % while the variation of the content of Sn was very limited, around 5 at. %, which is consistent with this work.

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In agreement with the result by Yang [10] and Kozakai et al. [9], the ternary compound FeSnTi2 (Fe25Sn28Ti47) was observed and formed through a peritectic reaction (L+Sn3Ti5

FeSnTi2, 1427 K)

as shown in the as-cast microstructure of the Fe25Sn28Ti47 alloy in Fig. 3. This alloy (Fe25Sn28Ti47) is selected to represent the compound is because it is close to the center of the single phase field.

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The powder pattern was indexed on a primitive trigonal/hexagonal unit cell using DICVOL14 [21]. There were no systematic absences, so potential space groups were used in order of their frequency in the PDF Metals & Alloys subfile. Software FOX [22] and Jana2006 [23] were used to solve the _

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crystal structure. Charge flipping in several different space groups suggested that P62m was the most likely space group. The refined lattice sites and occupancy using software GSAS [24] are

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listed in Table 4 and the crystal model is shown in Fig. 4. The data are given to four significant figures in order to produce the correct intensities in the XRD pattern. The Rietveld plot is presented in Fig 5.

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A new ternary compound Fe5Sn9Ti6 (composition Fe22Sn46Ti32, prototype Mn23Th6, Pearson symbol cF116, space group Fm3m) was observed which is formed through a ternary peritectic reaction

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(Liquid+Fe2SnTi+Sn5Ti6→Fe5Sn9Ti6, < 1273 K) since it is not observed in the as-cast structure nor in the annealed sample at 1273 K after 3 days as shown in Fig. 6. The same phase was observed

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after annealing at 773 K for 5 days. The analogues of this compound were also observed in the FeGa-Ti [25] and Fe-Al-Ti [26] systems. The structure was solved by direct methods using EXPO2014 [27]. The proposed site positions based on GSAS analysis are listed in Table 5 and the Rietveld plot is presented in Fig 7.

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The half-Heusler phase “FeSnTi” (prototype MgAgAs, Pearson symbol cF12, space group F43m) was not observed, in agreement with the work by Romaka et al. [12] and contradictory to the work by Yang [10]. The primary phase FeSnTi (Fe30Sn35Ti35, prototype GaGeLi, Pearson symbol hP6,

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space group P63mc) was found together with Fe2SnTi and Sn in the as-cast structure. FeSnTi (Fe31Sn35Ti34, prototype GaGeLi) and Fe2SnTi (Fe47Sn26Ti27) were also observed after annealing at 1273 K for 3 days. Additional annealing for 7 days at the same temperature was performed and the relative intensity of the diffraction peaks did not change. However, after annealing at 873 K for 30

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days, Fe2SnTi (Fe47Sn26Ti27) and Sn5Ti6 (Fe18Sn43Ti39) were observed in equilibrium as shown in Fig. 8 and Fig. 9. Kuentzler et al. [19] obtained the FeSnTi half-Heusler compound by arc melting and annealing at 1123 K for 1 week while Tobola et al. [28] prepared it after annealing at 1073 K

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for 1 week. However, the lattice parameter determined by Kuentzler et al. (a = 0.6330 nm) is quite unreliable and that by Tobola et al. (a = 0.6056 nm) possibly corresponds to the Heusler compound

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Fe2SnTi (a = 0.6066 nm) since the difference between similar compounds Ni2TiSn (a = 0.6091 nm) [29] and NiTiSn (a = 0.5946 nm) [30] is much larger. The calculated enthalpies of formation of the half-Heusler structure (Ti (4a) 0 0 0; Sn (4b) 1/2, 1/2, 1/2; Fe (4c) 1/4, 1/4, 1/4) from the Aflow [31] (-9.7 kJ/mole of atoms when a = 0.6029 nm) and that by Romaka et al. (-37.9 kJ/mole of atoms when a = 0.5816 nm) [12] are still less negative than the hull energy derived from the enthalpy of

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formation of the three phases comprising the three-phase field (Sn3Ti2, Sn5Ti6, Fe2SnTi) where the half-Heusler composition is located. Therefore, the conclusion is that the half-Heusler structured

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FeSnTi compound does not exist at the above mentioned temperatures. The hexagonal equiatomic compound FeSnTi is only stable at high temperature (Tm = 1323 K), forms congruently from the

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melt, and decomposes into Fe2SnTi and Sn5Ti6 at a lower temperature ( 1217 K from DSC). Occupation of the Fe, Sn, and Ti atoms in the crystal structure is the same as that of CuSnTi [32] with the same crystal structure and similar atoms.

The other ternary compound “Fe0.6Sn2Ti0.4” reported by [12] was not observed. In the 873 K annealed Fe20Sn67Ti13 alloy, Fe2SnTi and Sn were observed, Fig. 10. Haeussmann et al. [20] prepared the Fe0.6Sn2Ti0.4 compound using powder metallurgy and annealing at 823 K for 3 days. Unfortunately, the measured XRD pattern was not provided in the publication. The discrepancy

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between our results and theirs may be due to the formation of this compound below the current investigated temperature.

3.4. Three-phase region

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Sixteen three-phase regions were observed. The three phase equilibrium (Fe, Fe2Ti, Fe2SnTi) in the Fe70Sn15Ti15 and Fe80Sn10Ti10 alloys, (FeTi, Fe2Ti, Sn3Ti5) in the Fe11Sn33Ti56, Fe44Sn10Ti46 and Fe53Sn5Ti42 alloys, (Fe, FeSn, Fe2SnTi) in the

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Fe62Sn32Ti6 and Fe70Sn20Ti10 alloys, shown in Fig. 11, are in agreement with all previously discussed references [10, 12]. In the Fe45Sn45Ti10 alloy, the three phase equilibrium (Fe2SnTi, FeSn,

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liquid) is observed which is modified at low temperatures (773 K) by the formation of FeSn2 compound (Liquid + FeSn→FeSn2, 786 K). Actually, a minor amount of FeSn2 is observed which is formed during quenching and the liquid phase transforms to β-Sn.

Three phase equilibrium (Sn3Ti5, SnTi2, SnTi3) was verified in the Fe5Sn33Ti62 alloy and (FeTi,

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Sn3Ti5, SnTi3) in the Fe8Sn25Ti67, Fe8Sn34Ti58, Fe20Sn23Ti57 and Fe30Sn13Ti47 alloys. This is in agreement with the work by Romaka et al. [12] but different from that by Yang [10] who believed

and

(FeTi,

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the relationship between the four phases should be the two three-phase fields, (FeTi, Sn3Ti, Sn2Ti) Sn2Ti,

Sn3Ti5).

This

could

be

explained

by

a

transition

reaction

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Sn3Ti5+SnTi3→SnTi2+FeTi. However, there is still the issue that the isotherms of Romaka and Yang are nominally at the same temperature.

Two additional three-phase regions (β-Ti, FeTi, SnTi3) and (α-Ti, β-Ti, SnTi3) were observed when compared with the 773 K isotherms due to the allotropic transformation between α-Ti and β-Ti (868 K). XRD can easily distinguish the two phases and SEM with an EDS is also useful since α-Ti has a good solubility for Sn while β-Ti has a preference for Fe atoms.

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FeSnTi2 forms four three-phase regions, (Fe2Ti, Fe2SnTi, FeSnTi2), (Fe2Ti, Sn3Ti5, FeSnTi2), (Sn3Ti5, Sn5Ti6, FeSnTi2) and (Sn5Ti6, Fe2SnTi, FeSnTi2), as shown in Fig. 12. The results agree with those determined by Yang [10]. The (Sn5Ti6, Fe2SnTi, FeSnTi2) equilibrium is modified by the presence of FeSnTi (prototype GaGeLi) at high temperature (1273 K). The observed phase

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relationships between Sn5Ti6, Fe2SnTi, FeSnTi2 and Fe5Sn9Ti6 are also supported by the presence of the two-phase field (Sn5Ti6, Fe2SnTi) in the Fe33Sn33Ti33 and Fe24Sn37Ti39 alloys.

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The newly found ternary compound Fe5Sn9Ti6 is also involved in four three-phase regions, (liquid, Fe2SnTi, Fe5Sn9Ti6), (Sn5Ti6, Fe2SnTi, Fe5Sn9Ti6), (Sn3Ti2, Sn5Ti6, Fe5Sn9Ti6) and (liquid, Sn3Ti2,

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Fe5Sn9Ti6) in Fig. 13.

After compiling all the available experimental information, the isothermal section at 873 K was constructed, Fig. 14. It is obvious that the phase fields are generally extended parallel to the Fe-Ti side indicating the substitution between Fe and Ti on the crystal lattices due to their atomic

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similarity. What could also be inferred from the phase diagram is that when preparing single phase Fe2SnTi Heusler compound, special care should be paid to avoid excess Sn which will embrittle the

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4. Conclusions

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grain boundaries if the material is processed above the melting point of Sn.

The isothermal section of the Fe-Sn-Ti ternary system at 873 K was determined. Comparison with the results from prior work is discussed in detail. Three ternary compounds Fe2SnTi, Fe5Sn9Ti6 and FeSnTi2 were observed. The crystal structure of FeSnTi2 was solved (Pearson symbol hP18, space _

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group P62m) and so is the compound Fe5Sn9Ti6 (Pearson symbol cF116, space group Fm3m). The half-Heusler structured compound FeSnTi was not observed but an equiatomic phase (Pearson symbol hP6, space group P63mc) was observed at high temperature (1273 K). Sixteen three-phase regions were observed.

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This research is supported by NSF Grant #DMR1307631.

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Heusler compounds, J. Alloys Compd. 660 (2016) 258-265.

[30] M. Yin, P. Nash, Standard enthalpies of formation of selected XYSn half-Heusler compounds, J. Chem. Thermodynamics. 91 (2015) 1-7.

[31] R. H. Taylor, F. Rose, C. Toher, O. Levy, K. Yang, M. B. Nardelli, S. Curtarolo, A RESTful API

192.

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for exchanging materials data in the AFLOWLIB.org consortium, Comp. Mater. Sci. 93 (2014) 178-

[32] N. O. Koblyuk, L. G. Akselrud, R. V. Skolozdra, Interactions between the components in the

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Ti-Cu-Sn system at 670 K, Pol. J. Chem. 73 (1999) 1465-1471.

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Fe Sn Ti

Powder Bulk Purity, (wt. %) Size, (µm) Purity, (wt. %) Morphology 99.9+ 10 99.97 irregular pieces 99.999 < 44 99 shot 99.9 < 149 99.9 sponge

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Table 2. Crystallographic characteristics of possible phases in the Fe-Sn-Ti ternary system at 873 K. Pearson Space symbol group

α-Fe

W

cI2

FeSnTi2

W Mg Sn CoSn ClCs MgZn2 Sn3Ti2 Sn5Ti6 Mn5Si3 Co1.75Ge CdMg3 CuHf5Sn3 Cu2MnAl FeSnTi2

cI2 hP2 tI4 hP6 cP2 hP12 oS40 hP22 hP16 hP6 hP8 hP18 cF16 hP18

_

Im3m P63/mmc I41/amd P6/mmm _

Pm3m P63/mmc Cmca P63/mmc P63/mcm P63/mmc P63/mmc P63/mcm _

Fm3m _

0.33065 0.29506 0.58318 0.5288 0.2976 0.47870 0.5967 0.922 0.8047 0.4653 0.5916 0.8152 0.6066

P62m _

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-

0.75284 -

Fe5Sn9Ti6 Mn23Th6 cF116 1.26839 Fm3m FeSnTi GaGeLi hP6 P63mc 0.4374 _ FeSnTi* AgAsMg cF12 0.6330 F43m Fe0.6Sn2Ti0.4* Mg2Ni hP18 P6222 0.54933 a * indicates the phase was not observed in this work.

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1.995 -

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β-Ti α-Ti Liquid FeSn FeTi Fe2Ti Sn3Ti2 Sn5Ti6 Sn3Ti5 SnTi2 SnTi3 FeSn3Ti5 Fe2SnTi

_

Im3m

a/nm a b 0.28665 -

Reference

c -

[16]

0.46835 0.31818 0.4442 0.78150 0.7013 0.569 0.5451 0.5700 0.4764 0.5544 -

[16] [16] [16] [16] [16] [16] [16] [16] [16] [16] [16] [11] [18]

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Prototype

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0.61262 This work 0.5810 1.38456

This work This work [19] [20]

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Table 3. Measured compositions of selected three-phase alloys, observed phases and their compositions.

Fe5.1Sn33.4Ti61.5

Fe8Sn25Ti67

Fe8.3Sn25.6Ti66.1

Fe8Sn38Ti54

Fe8.1Sn38.6Ti53.3

Fe10Sn56Ti34

Fe9.5Sn56.2Ti34.3

Fe16Sn46Ti38

Fe15.6Sn46.4Ti38.0

Fe20Sn10Ti70

Fe20.0Sn10.1Ti69.9

Fe25Sn41Ti34

Fe24.1Sn42.1Ti33.8

Fe26Sn26Ti48

Fe25.3Sn26.4Ti48.3

Fe26Sn33Ti41

Fe25.2Sn34.2Ti40.6

Fe33Sn42Ti25

Fe30.9Sn44.4Ti24.7

Fe44Sn10Ti46

Fe42.9Sn10.6Ti46.5

Fe45Sn20Ti35

Fe44.2Sn21.4Ti34.4

Fe45Sn45Ti10

Fe41.1Sn49.1Ti9.8

Fe70Sn15Ti15

Fe70.7Sn14.9Ti14.4

Fe70Sn20Ti10

Fe69.2Sn20.9Ti9.9

α-Ti Sn8.5Ti91.5 Sn3Ti5 Fe7.6Sn35.3Ti57.1 Sn3Ti5 Fe4.8Sn33.7Ti61.5 FeSnTi2 Fe23.0Sn28.8Ti48.2 Fe5Sn9Ti6 Fe21.6Sn46.2Ti32.2 Sn5Ti6 Fe17.8Sn43.1Ti39.9 SnTi3 Fe0.3Sn24.3Ti75.4 Sn5Ti6 Fe13.1Sn43.3Ti43.6 Fe2Ti Fe62.3Sn6.9Ti30.8 Fe2SnTi Fe46.7Sn27.9Ti25.4 Fe2SnTi Fe47.0Sn27.0Ti26.0 Fe2Ti Fe65.4Ti34.6 FeSnTi2 Fe27.1Sn28.9Ti44.0 Fe2SnTi Fe48.1Sn26.5Ti25.4 Fe2SnTi

β-Ti / SnTi2 Fe1.8Sn34.7Ti63.5 SnTi3 Fe0.5Sn25.6Ti73.9 Sn3Ti5 Fe8.2Sn36.0Ti55.8 Sn3Ti2 Sn60.6Ti39.4 Fe5Sn9Ti6 Fe21.6Sn46.0Ti32.4 FeTi Fe47.9Sn0.4Ti51.7 Fe2SnTi Fe47.0Sn26.8Ti26.2 Sn3Ti5 Fe7.9Sn36.6Ti55.5 FeSnTi2 Fe28.3Sn30.1Ti41.6 Fe5Sn9Ti6 Fe21.8Sn46.3Ti31.9 FeTi / Fe2Ti Fe65.3Sn5.4Ti29.3 FeSn Fe48.2Sn51.8 Fe2Ti

SnTi3 / SnTi3 Sn25.9Ti74.1 FeTi / Sn5Ti6 Fe5.5Sn43.6Ti50.9 Liquid Sn100 Sn3Ti2 Sn60.4Ti39.6 β-Ti Fe9.0Sn2.3Ti88.7 Fe5Sn9Ti6 Fe21.5Sn45.4 Ti33.1 FeSnTi2 Fe22.7Sn28.6Ti48.7 Sn5Ti6 Fe10.0Sn42.5Ti47.5 Liquid Sn100 Sn3Ti5 / Fe2SnTi Fe46.8Sn24.4Ti28.8 Liquid Sn100 Fe

Fe56.8Sn25.1Ti18.1 Fe2SnTi

Fe66.1Sn14.2Ti19.7 FeSn

Fe94.6Sn4.7Ti0.7 Fe

Fe56.5Sn24.7Ti18.8

Fe49.5Sn49.8Ti0.7

Fe94.8Sn4.4Ti0.8

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Fe5Sn33Ti62

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Fe5.1Sn5.5Ti89.4

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Phase 1

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Table 4. Site positions and occupancy of the FeSnTi2 compound (space group P62m, Pearson symbol hP18, lattice parameter a = 0.75284(2) nm, c = 0.61262(3) nm). Site fraction Site Occupancy Uiso, (Å2) Multiplicity X Y Z 0.0159 3 1 0.278 Fe + 0.722 Ti 0.2328(10) 0.0000 0.5000 6 2 0.278 Fe + 0.722 Ti 0.6294(7) 0.0000 0.2340(22) 0.0159 0.0159 2 3 Fe 0.3333 0.6667 0.0000 0.0067(6) 2 4 Sn 0.6667 0.3333 0.5000 0.0067(6) 3 5 Sn 0.3008(4) 0.0000 0.0000 2 6 Ti 0.0000 0.0000 0.2169(24) 0.0159 2 Rwp = 0.0792, Rp = 0.0620, χ = 1.359

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Table 5. Site positions and occupancy of the Fe5Sn9Ti6 compound (Pearson symbol cF116, space _

0.0100 0.0100 0.0100 0.0100 0.0100

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Z 0.0000 0.1065(2) 0.1555(2) 0.0000 0.0000

Uiso, (Å2) Multiplicity

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group Fm3m, lattice parameter a = 1.26839(3) nm). Site fraction Site Occupancy X Y 1 Fe 0.5000 0.2740(7) 2 0.458 Ti+0.542 Sn 0.3935(2) 0.1065(2) 3 Sn 0.6555(2) 0.3446(2) 4 Sn 0.5000 0.5000 5 Ti 0.2500 0.2500 2 Rwp = 0.2288, Rp = 0.1774, χ = 3.070

24 32 32 4 24

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Figure Captions

Fig. 1. The experimental isothermal sections at 773 K of Fe-Sn-Ti ternary system measured by (a) Romoka et al. [12] and (b) Yang [10]. Fig. 2. The compositions of the prepared alloys, together with the assessed binary phase diagrams

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from References [13, 14, 15]. Fig. 3. Backscattered electron micrograph of the as-cast Fe25Sn28Ti47 alloy. Fig. 4. Crystal structure of the FeSnTi2 compound.

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Fig. 5. Rietveld plot of the annealed Fe25Sn28Ti47 alloy (FeSnTi2).

Fig. 6. Backscattered electron micrograph of the Fe22Sn46Ti32 alloy, (a) as-cast; (b) annealed at 1273

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K for 3 days; (c) annealed at 873 K for 30 days.

Fig. 7. Rietveld plot of the annealed Fe22Sn46Ti32 alloy (Fe5Sn9Ti6).

Fig. 8. Backscattered electron micrograph of Fe33Sn33Ti33 alloys: (a) as-cast structure; (b) annealed at 1273 K for 3 days; (c) annealed at 873 K for 30 days.

Fig. 9. Measured XRD patterns of Fe33Sn33Ti33 alloys: (a) annealed at 1273 K for 3 days; (b)

and Fe2SnTi.

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annealed at 873 K for 30 days in comparison with the simulated XRD patterns of FeSnTi, Sn5Ti6

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Fig. 10. Backscattered electron micrograph of the Fe20Sn67Ti13 alloy annealed at 873 K for 30 days. Fig. 11. Backscattered electron micrographs of alloys annealed at 873 K for 30 days, (a)

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Fe70Sn15Ti15; (b) Fe44Sn10Ti46; (c) Fe70Sn20Ti10; (d) Fe45Sn45Ti10. Fig. 12. Backscattered electron micrographs of alloys annealed at 873 K for 30 days, (a) Fe45Sn20Ti35; (b) Fe26Sn26Ti48; (c) Fe20Sn30Ti50; (d) Fe26Sn33Ti41. Fig. 13. Backscattered electron micrographs of alloys annealed at 873 K for 30 days, (a) Fe26Sn42Ti32; (b) Fe25Sn41Ti34; (c) Fe16Sn46Ti38; (d) Fe10Sn56Ti34. Fig. 14. Experimentally determined isothermal section of the Fe-Sn-Ti ternary system at 873 K.

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Romoka et al. [12] and (b) Yang [10].

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Fig. 1. The experimental isothermal sections at 773 K of Fe-Sn-Ti ternary system measured by (a)

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Fig. 2. The compositions of the prepared alloys, together with the assessed binary phase diagrams

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from References [13, 14, 15].

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Fig. 3. Backscattered electron micrograph of the as-cast Fe25Sn28Ti47 alloy.

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Fig. 4. Crystal structure of the FeSnTi2 compound.

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Fig. 5. Rietveld plot of the annealed Fe25Sn28Ti47 alloy (FeSnTi2).

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Fig. 6. Backscattered electron micrograph of the Fe22Sn46Ti32 alloy, (a) as-cast; (b) annealed at 1273

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Fig.7. Rietveld plot of the annealed Fe22Sn46Ti32 alloy (Fe5Sn9Ti6).

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Fig. 8. Backscattered electron micrograph of Fe33Sn33Ti33 alloys: (a) as-cast structure; (b) annealed

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Fig. 9. Measured XRD patterns of Fe33Sn33Ti33 alloys: (a) annealed at 1273 K for 3 days; (b)

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Fig. 10. Backscattered electron micrograph of the Fe20Sn67Ti13 alloy annealed at 873 K for 30 days.

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Fig. 11. Backscattered electron micrographs of alloys annealed at 873 K for 30 days, (a)

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Fe70Sn15Ti15; (b) Fe44Sn10Ti46; (c) Fe70Sn20Ti10; (d) Fe45Sn45Ti10.

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Fig. 12. Backscattered electron micrographs of alloys annealed at 873 K for 30 days, (a)

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Fe45Sn20Ti35; (b) Fe26Sn26Ti48; (c) Fe20Sn30Ti50; (d) Fe26Sn33Ti41.

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Fig. 13. Backscattered electron micrographs of alloys annealed at 873 K for 30 days, (a)

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Fe26Sn42Ti32; (b) Fe25Sn41Ti34; (c) Fe16Sn46Ti38; (d) Fe10Sn56Ti34.

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Fig. 14. Experimentally determined isothermal section of the Fe-Sn-Ti ternary system at 873 K.

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Research highlights

Fe-Sn-Ti isotherm at 873 K was determined using equilibrated alloys;




16 three-phase regions were observed;




New compound Fe5Sn9Ti6 was found and the crystal structure was solved;




Crystal structures of FeSnTi and FeSnTi2 were solved.

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