TiB metal matrix composite obtained by PPS approach

    Ultrafast densification and microstructure evolution of in situ Ti/TiB metal matrix composite obtained by PPS approach Andrzej Miklaszewski PII: DOI: Reference:

S0263-4368(16)30431-0 doi:10.1016/j.ijrmhm.2016.10.007 RMHM 4343

To appear in:

International Journal of Refractory Metals and Hard Materials

Received date: Revised date: Accepted date:

26 July 2016 25 August 2016 7 October 2016

Please cite this article as: Miklaszewski Andrzej, Ultrafast densification and microstructure evolution of in situ Ti/TiB metal matrix composite obtained by PPS approach, International Journal of Refractory Metals and Hard Materials (2016), doi:10.1016/j.ijrmhm.2016.10.007

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ACCEPTED MANUSCRIPT Ultrafast densification and microstructure evolution of in situ Ti/TiB metal matrix composite obtained by PPS approach.

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ANDRZEJ MIKLASZEWSKI

Poznan University of Technology, Institute of Materials Science and Engineering, M. Sklodowska-Curie 5 Sq., 60-965 Poznan, Poland [email protected] tel/fax +48616653776

Keywords: Plasma Pulse Sintering, XRD, metal matrix composites,

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Abstract

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The newly methods of material production based on electrical pulse utilised for metal matrix composites preparation, interest and attracts due to possibilities of

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sintering of a wide range of materials to high densities in a short time period at relatively low temperatures. Advantages of this approach allow avoiding the grain

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growth and lead to more precise control of final material properties also by the

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starting precursor choice. Morphology, grain size and purity of precursor, connected with it physical properties and chemical composition that is next

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submitted to the process parameters could reveal subtle dependence in microstructure and densification mechanism in obtained composite sinters. Ultrafast electric pulse consolidation allows to obtained the in situ Ti/TiB metal matrix composites due to reaction mechanism kinetics, focusing however on heating rate and energy availability. Specific heating conditions for Pulse Plasma Sintering process used to consolidate the precursor material with a high-current pulse approach correlate with final obtained properties. 1. Introduction Titanium-based composites were developed to meet specific requirements in highly demanding engineering applications [1,2]. They're characteristic combine

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ACCEPTED MANUSCRIPT good corrosion and wear resistance and exhibit high mechanical properties also in elevated temperatures with high bonding strength [3,4]. Among possible titanium reinforcement phases like TiC, SiC, TiB2, B4C, Al2O3, TiN or Si3N4 the TiB

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seems to shows the best estimation [5]. TiB precipitation has been found to be an attractive reinforcement for several reasons such as its favourable orientation relationship with the Ti matrix; that promotes a good interfacial bonding and a clean interface with the low solubility of boron in titanium, and it is comparable

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densities. In addition to the excellent crystallographic compatibility of hexagonal TiB with the Ti matrix due to the atomically sharp interfaces, the residual stresses

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due to thermal expansion for this composites are negligible, as the coefficient of thermal expansion of TiB is also close to that of titanium. Considering mentioned

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facts processing of this pair also remains less challenging than for other ceramicreinforcements.

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Different processing techniques such as self-propagating reaction synthesis [6,

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7], solid fabrication [8], mechanical alloying [9] or blended powder metallurgy [10-12] engaged in making these composites. Most of them involve several steps,

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time exhaustive and expensive operations with investment materials. There is a lack of information about the fully optimised process that could give a near-shape part product without intermediate operation of machining, polishing or heat treatment in a short period. In the case of conventional reactive sintering of powder blends in most cases, TiB2 remain as a boron source. This approach, however, may lead to a rather slow reaction kinetics of TiB2 and some of its residual remains in the final sample microstructure [11]. From the above reasons, pure elements were proposed in this work with a sintering technique involving the action of an ultrafast electric pulse discharge. The PPS (Plasma Pulse Sintering) method applied in this research

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ACCEPTED MANUSCRIPT utilises pulsed high electric current discharges to heat the powder subjected to pressing. Broadly describe phenomena, taking place during the high-current pulses discharge [13-15], which heat the powder and activate the sintering

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process that also run much more intensively with possible sintering temperature decrease, than in the other innovative methods like SPS (Spark Plasma Sintering) allowing to obtained densities close to the theoretical value. Typically PPS method characterises with an ultrafast pulse electric discharge alternatively to fast

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SPS [13], where an impulse could take place by hundreds of milliseconds, which is now the most commonly used method of powder consolidation involving the

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action of an electric pulse. Applied third generation electric pulse consolidation method should give better results simultaneously with time and costs limitation

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for analysed MMC composition. Importantly, time processing restrictions minimise grain grow and by the direct current assisted mode applied in this work,

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the Joule heat may distribute in a sample more uniformly. In particular, proposed

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internal heating approach at the first place allows to decreases the energy input. Additionally, it may lower the temperatures and shorter the sintering times,

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giving the possibility to obtained nearly theoretical densities without the grain grow effect. The main objective of this work was to process in very short time regime, Ti–TiB composites through PPS technique with an applied current assisted mode and next characterises their properties. 2. Materials and methods 2.1 Samples preparation Starting precursor material with 0, 2, 5 and 10 wt.% of boron to titanium was prepared by 5-minute ball-milling (BM) in Spex mixer mill from substrates metallic elements of the Ti and B (Alfa Aesar) with 99% purity level. The

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ACCEPTED MANUSCRIPT powders (Ti, B: < 200μm) were firstly mixed in the glove box (LabMaster 130) with high purity argon atmosphere and than poured into the hardened tool steel vial for preparation. Obtained compositions of precursor material design to be

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sintered was placed into a non-conductive ceramic die in-between two graphite punches with initial applied force of 1kN in vacuum conditions of 4 Pa. The apparatus used for powders consolidation - PPS module that was schematically shown on Figure 1, has been designed and constructed by Elbit

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company according to an expectation profiled by an Institute of Materials Science and Engineering at Poznan University of Technology. The current pulses in the

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module are generated by discharging of a 250 µF capacitor, charged to a voltage of maximum 8 kV. The pulse duration during sintering process is automatically

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controlled due to a temperature measurement by a pyrometer direct on the upper punch. Voltage, pulse frequency, force, temperature, and real-time vacuum

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measurement with 0,1s duration are control during the sintering procedure.

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Control temperature measurement variance is kept at ±25°C. Constant process parameters gathered in Table 1 were used for a titanium matrix composite

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preparation due to the save/load operational instrument mode function. Stabile for die material, geometry and size with assumed punches distance and material amount, parameter setup were loaded and control for specified temperature variance. 2.2 Material characterization Obtained after PPS approach samples were ground at the transverse section and polished to 1-micron finish for measurements. For microstructural observation, the etching step in Kroll’s reagent was performed to reveal the grain boundary and phase contrast. The phase constitution of obtained composites was

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ACCEPTED MANUSCRIPT analysed by XRD with Cu Kα1 radiation (Panalytical Empyrean - Netherlands). Microhardness measurements were carried out on samples in order to determine average hardness by Innovatest Nexus Vickers tester with an applied load of 3kg

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and loading time 10 s. The density of the composites was measured by immersing the samples in deionized water and using Archimedes’ principle. Measured density values were compared with the theoretical density calculated from the rule of mixtures. Finally, the percentage value of relative density was determined.

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Reinforcement volumetric phase amount was estimated from a microscopic planar analysis using Stream Essential Olympus Software and calculation from

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XRD data using Maud software and Rietveld refinement where a standard fit residual indicator of the calculated pattern data was added: Rwp – weighted pattern residual indicator

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Rb – Bragg intensity value of residual indicator

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Rexp – expected residual indicator

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χ –goodness of fit

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For microstructural analysis, Scanning electron and Optical microscopy were used.

3. Results and discussion Obtained for the setup PPS parameters composite compacts consists as an XRD analyse showed from hexagonal titanium matrix and in situ TiB reinforcement phase (Figure 2.). What was also confirmed from XRD data, TiB2 phase appearance was noted for increasing boron amount. Getting involve earlier obtained results from a traditional powder metallurgy approach [16], the restrictions for a diffusion coefficient factor seems to appear in a microstructural range. Lately, the results confirmed that higher sintering temperatures influence

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ACCEPTED MANUSCRIPT obtained microstructure by available energy, which effect on the morphological change of precipitates in the samples, diminution of porosity and increase of coherency of strengthening phase with the matrix mostly by grain boundary

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diffusion mechanism. Realised research with a PPS module utilisation, focuses however on highest possible composites densities with the lowest grain grow sample reply through delivered heat contribution. Composites based on a titanium and boron powder blends precursor mixtures (which morphology and size were

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depictured in Figure 3), shows on Figure 4 the microstructure that is characterised with a homogeneously distributed reinforcement phase appearance that size ratio,

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does not oversize the starting material reactants. Above view confirmed also proper reactants distribution with a 5-minute ball milling preparation step,

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however increasing boron amount influence morphology of precipitating phase that a higher volume manifests by a coarse grain and aggregation tendency. The

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appearance of the titanium diboride phase in the structure for discussed

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circumstances involves available mechanism kinetics of transformations, processing condition and starting precursor composition and morphology,

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suggesting partially local reaction for higher boron concentration. Nucleation of the TiB2 phase in the same could be expected for a microstructural range composites that boron starting amount to titanium is above 2 wt.% and where the grain boundary diffusion is suggested as the main mass transport mechanism. Summarised data allow concluding that for obtained in situ reinforced composites during PPS processing a higher microstructure sample uniformity appears for a lower boron amount added to micro precursor powder blends. Microstructure and XRD examination confirmed an increasing reinforcement phase volumetric ratio due to growing boron weight amount in starting precursor composition, that calculated and refined data was gathered in Table 2. Planar estimation results,

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ACCEPTED MANUSCRIPT taken from the histogram spectra shows summarised data; including porosity and not specified phases on the matrix background present in Table 3 as a total reinforcement phase amount. Additionally obtained from Maud software

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quantitative analysis data shows with a growing boron amount higher accordance to its planar reference.

Summarised in table 3 results of relative density measurements show very close relation to theoretical densities, even for a short overall time of processing

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that not exceed 6 minutes. The influence of boron addition and it the same reinforcement phase amount increase could be noticed simultaneously at the

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inverse relation of density and hardness. The matrix that undergoes strengthening by growing number of reinforcement nucleation centres restricts also its own

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movement for density increase during processing. This finding could be observed by a growing number and volume of pores that appearance near reinforcement

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phase strongly relates to its amount. Average hardness results show at the same

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time typical nearly linear relation to growing reinforcement phase amount. A disused example of different starting precursor compositions shows that an

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ultrafast electric pulse assisted synthesis could be successfully used for the in situ TiB reinforced titanium matrix composite preparation and in the same confirmed the possibilities of the method for the demanding materials processing use.

5. Conclusions In this work titanium powders mixed with different content of boron weight amount was used for the electric pulse assisted synthesis of in situ TiB reinforced titanium matrix composite. The studies lead to the following conclusions:

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plasma pulse sintering method allows to obtained nearly fully dense

titanium matrix composite compacts -

increasing boron amount in starting precursor composition influence

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reinforcement phase volume ratio,type and morphology

reinforcement phase amount influence density and average hardness

measurements

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Acknowledgements

(2014/13/N/ST8/00601).

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References

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This work was financially supported by The National Science Centre Poland

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composites reinforced by TiB and Nd2O3, Mater Lett 2003;57:4054–4057.

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[3] Radhakrishnabhat B.V., Subramanyam J., Bhanuprasad V.V., Preparation of Ti-TiB-TiC & TiTiB composites by in-situ reaction hot pressing, Mater Sci Eng A 2002;325: 126-130. [4] Atri R.R., Ravichandran K.S., Jha S.K., Elastic Properties of in-Situ Processed Ti-TiB Composition Measured by Impulse Excitation of Vibration, Mater Sci Eng A 1999;271:150-159. [5] Saito T., The automotive application of discontinuously reinforced TiB-Ti composites, JOM (2004) : 33-36.

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ACCEPTED MANUSCRIPT [6] Ranganath S., A Review on Particulate-Reinforced Titanium Matrix Composites, Journal of Materials Science Volume 32, Issue 1, 1 (1997):1-16 [7] Ma Z.Y., Tjong S.C., Gen L., In-situ Ti-TiB metal-matrix composite prepared

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by a reactive pressing process, Scripta Materialia, 42 (2000):367–373 [8] Tsang H.T., Chao C.G., Ma C.Y., Effects of volume fraction of reinforcement properties of in-situ TiB/Ti MMC, Scripta Materialia, 37(1997), No.9:13591365,

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[9] Godfrey T.M.T., Wisbey A., Goodwin P.S., Bagnall K., Ward-Close C.M., Microstructure and tensile properties of mechanically alloyed Ti–6A1–4V

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with boron additions, Materials Science and Engineering A282 (2000):240– 250

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[10] Gorsse S., Miracle D.B., Mechanical properties of Ti-6Al-4V/TiB composites with randomly oriented and aligned TiB reinforcements, Acta

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Mater. 51, 9 (2003):2427-2444

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[11] Kobayashi M., Funami K., Suzuki S., Ouchi C., Manufacturing process and mechanical properties of fine TiB dispersed Ti–6Al–4V alloy composites

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obtained by reaction sintering, Mater. Sci. Eng. A 243 (1998):279-283 [12] Selvakumar M., Chandrasekar P., Mohanraj M. , Ravisankar B., Balaraju J.N, Role of powder metallurgical processing and TiB reinforcement on mechanical response of Ti–TiB composites, Materials Letters 144 (2015):58-61 [13] Yurlova M. S., Demenyuk V. D., Yu. Lebedeva, Dudina D. V., Grigoryev E. G., Olevsky E. A., Electric pulse consolidation: an alternative to spark plasma sintering, J Mater Sci (2014) 49:952–985 [14] Song Shi-Xue, Wang Zhi, Shi Guo-Pu, Heating mechanism of spark plasma sintering, Ceramics International 39 (2013):1393-1396

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ACCEPTED MANUSCRIPT [15] Suárez M., Fernández A., Menéndez J.L., Torrecillas R., Kessel H. U., Hennicke J., Kirchner R., Kessel T., Sintering Applications, Chapter 13 (2013) [16] Miklaszewski A. Effect of starting material character and its sintering

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temperature on microstructure and mechanical properties of super hard Ti/TiB metal matrix composites, Int. Journal of Refractory Metals and Hard Materials 53

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(2015) 56–60

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Figure captions

Figure 1. Schematic arrangement of PPS module

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Figure 2: XRD spectra of the compacts obtained from a starting precursor SPEX milled powder composition with a) 0, b) 2%, c) 5% and d) 10 wt.% of boron to titanium

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Figure 3. SEM morphology of the starting powders where a) and b) represents the elemental titanium and boron respectively with additional photographs of precursor SPEX milled powder with 2% c) and 10 wt.% of boron to titanium d)

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Figure 4: Microstructure examination of compacts obtained from starting precursor composition with a) 0, b) 2%, c) 5% and d) 10 wt. % of boron to titanium Table 1. Plasma Pulse Sintering process parameters adapted for in situ TiB reinforced titanium matrix composite sinters preparation Table 2. Phase amount calculated data based on Rietveld refinement with the profile function global variables Table 3. Measured properties of Titanium Matrix Composite compacts obtained by PPS method with TRPA (total reinforcement phase amount) data

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Figure 1

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Figure 2

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Figure 3

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Figure 4

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ACCEPTED MANUSCRIPT Table 1 Plasma Pulse Sintering process parameters adapted for in situ TiB reinforced titanium matrix composite sinters preparation Value

Pressure [Pa]

4

60

Load [MPa] Sintering temperature [°C]

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Heating time [s]

90

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Cooling time [s]

120

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Sintering time [s]

15

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Constant parameter

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ACCEPTED MANUSCRIPT Table 2. Phase amount calculated data based on Rietveld refinement with the profile function global variables Sample

Ti+2%B Unit 17.83 78.77 9.34 1.91

21.29 29.92 9.55 2.23

18.57 54.69 9.73 1.91

Phase amount Ti(α)

[%]

90.19±6.08

83.73±10.06

80.07±3.10

Phase amount TiB

[%]

9.81±0.44

15.33±0.51

18.29±0.55

Phase amount TiB2

[%]

0.95±0.21

1.62±0.16

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χ

[%] [%] [%] -

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Ti+10%B

value

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Parameter Rwp Rb Rexp

Ti+5%B

ACCEPTED MANUSCRIPT Table 3. Measured properties of Titanium Matrix Composite compacts obtained by PPS method with TRPA (total reinforcement phase amount) data

Starting precursor

TD

RD

TRPA (planar)

TRPA (XRD)

[g/cm3]

[%]

Ti

4.5070

99.36

Ti+2%B

4.4661

Ti+5%B Ti+10%B

[%]

[%]

232±15

0

0

98,49

393±32

4.2±0.8

≈10

4.4046

97,212

495±38

13.5±2.4

≈16

4.3023

95,84

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material

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HV3

21.56±4.5

≈20

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616±53

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Highlights

PPS method allows to obtained nearly fully dense titanium matrix composite compacts

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boron influence reinforcement phase amount it morphology and agglomeration tendency

reinforcement phase amount influence average hardness

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measurements

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