Addition Of Ta Research Articles

Development of Corrosion Resistant and Electrically Conductive Coatings on Metallic Bipolar Plates for Applications in PEMFC

Proton exchange membrane fuel cell (PEMFC) is considered as one of the most promising alternative energy devices due to its high efficiency, low pollutants emission and possible application in automobiles. However, the application of PEMFC is still hindered by the high cost of some of its components such as bipolar plates (BPP) which are a key component in PEMFC to facilitate electron transfer, gas flow, heat and water removal. To reduce the cost, increase conductivity and durability, metallic bipolar plates, typically made of stainless steel, are normally used but they could suffer from severe corrosion in the acidic environment of PEMFC; the formation of corrosion products on the metal surface could reduce the through-plane electrical conductivity and increase the interfacial contact resistance (ICR) between the bipolar plates and gas diffusion layer, eventually causing high power loss in the fuel cell stack. Therefore, developing corrosion resistant and electrically conductive bipolar plates is of vital importance for the practical applications of PEMFC.Transition nitride coated stainless steel, such as titanium nitride (TiN) coated 316L SS, is considered as a possible solution to improve the performance metallic bipolar plates. In this work, TiN coated 316L SSs with heat treatment at different temperatures were prepared. The corrosion behaviours of the prepared samples were investigated in the simulated working environments of fuel cell. The heat treated samples exhibit the improved corrosion resistance compared with the pristine TiN coated samples and with an increase of the heat treatment temperature, the corrosion resistance tends to increase due to the formation of oxide and oxynitride on the sample surface. The ICR test results indicate that high temperature (450 ℃) heat treatment has detrimental effect on the electrical conductivity of samples due to the formation of a thick oxide dominated layer, while the samples heat treated at 300 ℃ only form the graded layers with suitable oxide amount which endows the coated specimens with a very low ICR value both before and after the corrosion tests.Moreover, TiN coatings with different amounts of Ta addition were also prepared. After the corrosion tests in the H2SO4 solution with pH=3 at 70 ℃, the results reveal that Ti150Ta30N samples exhibit the highest corrosion resistance compared with the pristine TiN coated samples and the samples with different amount of Ta addition. The steady state current density of Ti150Ta30N samples after long term potentiostatic polarization at 0.6 V (vs Ag/AgCl) is 0.02 μA/cm2 which is much lower than that of TiN coated samples. The Ti150Ta30N samples also presents a good electrical conductivity with low ICR values before and after the corrosion tests. These studies suggest that a suitable amount of oxygen or Ta incorporation into TiN is a feasible strategy to improve the corrosion resistance while maintaining considerable electrical conductivity of TiN samples.

High-temperature oxidation behaviour of SPS-prepared Mo and Mo–5Ta alloys

ABSTRACT The high-temperature oxidation behaviour of SPS-prepared Mo and Mo–5Ta alloys are investigated under the temperature range 300–700°C for 0–120 min in static air condition. The oxidation weight gains of Mo and Mo–5Ta conform to parabolic law at different oxidation times of 500°C and all remain at low levels. At low temperature (≤ 500°C), the oxidation resistance improves with Ta addition. However, at 600°C and 700°C, the oxidation of Mo–5Ta increases and the weight gain is obvious. Compared with pure Mo, a continuous and dense oxide scale can be formed quickly on the surface of Mo–5Ta alloys during the oxidation process at 500°C, which improves the oxidation resistance of the alloys. The volatile MoO3 and generated Ta2O5 above 500°C cause more voids to form in the matrix, resulting in the deterioration of the oxidation resistance of the alloys.

Effect of solutes on the performance of Zn-coating and Zn-inducing transgranular cracking in steel based on DFT calculations

The effect of solutes, Co, Cu, Cr, Mn, Mo, Nb, Ni, Ta, Ti, V and Zr, in steel on the penetration properties of Zn and stability of surface or matrix were explored theoretically using density functional theory method, and the role of solutes in the Zn-coated surface and Zn-induced transgranular fracture performance was considered. The effect of solution on α-Fe are more obvious than that on γ-Fe, they significantly change surface energy value and the order of stability of low-index surface in α-Fe. The segregation energies of solutes were calculated and concluded that most of selected elements possibly segregate to the surface from the matrix. The study about Zn adsorption properties found that Zn atoms is energetically favorable to absorb at the (001) surface layer in α-Fe, and the segregation of Zr, V, Nb and Ta are helpful to the process of Zn-coating and increase the stability of Zn-coated surface. In addition, the solutes in the matrix increase the difficulty of transgranular fracture. Although the surrounding of solutes is the preference site for cracking occurring and propagation, alloying is found to lead to a general increase in the cleavage energy of α-Fe during Zn penetration, suggesting a reduction in the tendency for transgranular fracture. Therefore, it is feasible that the addition of Zr, V, Nb and Ta as alloy element in steel to improve the properties of Zn-coating and inhibit the occurrence of Zn-inducing transgranular cracking. Our results are helpful to understand and design AHSSs inhibiting LME susceptibility.

Combinatorial discovery of irradiation damage tolerant nano-structured W-based alloys

One of the challenges in fusion reactors is the discovery of plasma facing materials capable of withstanding extreme conditions, such as radiation damage and high heat flux. Development of fusion materials can be a daunting task since vast combinations of microstructures and compositions need to be explored, each of which requires trial-and-error based irradiation experiments and materials characterizations. Here, we utilize combinatorial experiments that allow rapid and systematic characterizations of composition-microstructure dependent irradiation damage behaviors of nanostructured tungsten alloys. The combinatorial materials library of W-Re-Ta alloys was synthesized, followed by the high-throughput experiments for probing irradiation damages to the mechanical, thermal, and structural properties of the alloys. This highly efficient technique allows rapid identification of composition ranges with excellent damage tolerance. We find that the distribution of implanted He clusters can be significantly altered by the addition of Ta and Re, which play a critical role in determining property changes upon irradiation.

Preliminary exploration of a WTaVTiCr high-entropy alloy as a plasma-facing material

With great power comes great challenges. For nuclear fusion, the holy grail of energy, taming the flame of a miniature star in a solid container remains one of the most fundamental challenges. A tungsten armour for the solid container marks a temporary triumph—a solution adopted by the world’s largest fusion experiment, ITER—but may be insufficient for future challenges. High-entropy alloys (HEAs), which are characteristic of a massive compositional space, may bring new solutions. Here, we explore their potential as plasma-facing materials (PFMs) with a prototype W57Ta21V11Ti8Cr3 HEA that was designed by exploiting the natural-mixing tendency among low-activation refractory elements. Revealed by x-ray diffraction analysis and energy-dispersive x-ray spectroscopy, it predominantly consists of a single bcc-phase but with V, Ti, and Cr segregation to grain boundaries and at precipitates. Its yield strength improves ∼60% at room temperature and oxidation rate reduces ∼6 times at 1273 K, compared with conventionally used W. The Ti–V–Cr rich segregations and the formed CrTaO4 compound contribute to the improved oxidation resistance. However, the Ti–V–Cr rich segregations, along with the decreasing valence-electron concentration of the matrix by the addition of Ta, V and Ti elements, considerably increase the deuterium retention of the W57Ta21V11Ti8Cr3 HEA to ∼675 multiples of recrystallized W. Moreover, its thermal conductivity decreases, being ∼40% of W at 973 K. However, the maximum tolerable steady-state heat load is still ∼84% of W because of its exceedingly high yield strength at elevated temperatures. Overall, despite being preliminary, we expect HEAs to play an important role in the development of advanced PFMs, for their disadvantages are likely to be compensated by their advantages or be overcome by composition optimization.

Microstructure and properties of Ta-reinforced cobalt based composite coatings processed by direct laser deposition

Circulating water pump is an important component in coastal nuclear power plant, and is prone to suffering erosion and corrosion from the sea water. In the present study, Ta-reinforced cobalt-based composite coatings were prepared on the surface of a martensitic stainless steel by direct laser deposition technology. The effect of Ta on the phase composition, microstructure, micro-hardness, residual stress, corrosion resistance and erosion performance of the cobalt-based composite coatings was systematically investigated. The results indicated that the addition of Ta can lead to the formation of dispersed TaC ceramic particles in the coatings. In the meantime, TaC particles with flaky shape greatly changed the morphology of reticular eutectic carbides and residual stress distribution in the coatings. The potentiodynamic polarization testing and electrochemical impedance spectroscopy (EIS) measurements showed that the addition of Ta had no prominent influence on the corrosion resistance of cobalt-based coatings. Generally speaking, the coating with 30 wt% Ta addition exhibited the best comprehensive performance considering micro-hardness measurement, residual stress value, potentiodynamic polarization testing, and slurry erosion testing under two erosion angles. In situ synthesized TaC phases could effectively alleviate the impact of solid particles in the erosion process, and improve the erosion resistance of the cobalt-based composite coating.

Temperature dependence of tensile deformation mechanisms in a powder metallurgy Ni–Co–Cr based superalloy with Ta addition

To further develop Ni-based powder metallurgy (PM) superalloys for aero-engines, it is critical to understand their deformation mechanisms at various service temperatures. For turbine disks, the tensile strength and absorbed impact energy are critical parameters. The varying stress during tensile deformation makes it essentially different from creep. In this study, a high-performance PM superalloy with various Ta contents was evaluated by tensile tests at different temperatures from room temperature to 815 °C. The relationship between the temperature and plastic deformation mechanisms was explored at multiple scales using scanning electron microscopy and transmission electron microscopy, and the temperature dependence of the deformation mechanism map was established. The results demonstrated that the main deformation mechanism gradually changed from antiphase boundary shearing to superlattice stacking fault shearing as the temperature increases. The extended stacking faults (ESFs) were the source of the microtwins, which extended within the individual grains and thickened with increasing temperature. In addition, a novel mechanism of ESF formation was observed, i.e., Shockley shearing separated by one layer of atoms. Furthermore, the effects of Ta on the tensile strength and plasticity in PM superalloys were discussed.

Microstructure evolutions of Ti-Al-Nb alloys with different Ta addition, produced by mechanical alloying and spark plasma sintering

• The microstructure evaluation of Ti-Al-Nb-Ta alloys produced by mechanical alloying and SPS was investigated. • The analysis showed the Ti ss and Nb ss as a matrix with binary, and ternary intermetallic compounds. • By increasing Ta content, the hardness and toughness of the samples increased simultaneously. In this study, the microstructure and mechanical properties of Ti-Al-Nb alloy with different percentages of tantalum produced by mechanical alloying and spark plasma sintering (SPS) were investigated. The microstructure study by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis showed the Ti ss and Nb ss as matrix with binary (Nb,Ti), (Ta,Ti), and (Ta,Al), and NbTi 2 Al ternary intermetallic compounds. It was found that with increasing tantalum percentage up to the 7 at%, the hardness and toughness of the samples increased simultaneously.

Long-term structural stability and excellent mechanical properties of CoCrNi system medium entropy alloys

CoCrNi medium entropy alloys (MEAs) are promising candidates for high- temperature application, but their structural stability and mechanical properties during long-term service are still an open question. This work comprehensively investigated the microstructure and mechanical properties at both room and high temperatures of CoCrNi MEAs after being aged for 500 h at 850 °C. It has been shown that the long-term aged CoCrNi MEA has held a single γ phase, a nanoparticulate and discontinuous block γ′ phase, and η-Ni3(Ti,Ta) phase in acicular Widmanstätten, cellular and rod-like shapes with the addition of Al, Ti, and Ta. Long-term aged CoCrNi MEAs hold same levels (or sometimes slightly weaker levels) of room- and high-temperature strengths as those MEAs under the standard heat treatment. Specifically, CoCrNi MEA with 2%Al, 2%Ti, and 1%Ta presents an ultimate strength of 1012 MPa at room temperature and a yield strength of 695 MPa at 700 °C. Surprisingly, all of the relevant long-term aged MEAs exhibit superior plasticity to that under standard heat treatment. The anomalous mechanical properties are firstly attributed to the γ' phase precipitation. Next, η phase plays an important role in strengthening, improving or at least harmless plasticizing effect since the η phase has the preferential orientation relationship of [011]γ//[2110]η, {111}γ//{0001}η with the γ matrix. It has been confirmed that the strengthening mechanisms are ascribed to the dislocation accumulation and proliferation, formation of stacking faults and nanotwinning in γ, γ' and η phase induced by the precipitation of γ′ and η phase.

Investigation of room temperature strengthening mechanism on PM Ni-base superalloys with tantalum addition

In this paper, the mechanical properties of the high-performance powder metallurgy (PM) superalloys with Ta addition fabricated by the Central Iron and Steel Research Institute (CISRI) were evaluated at room temperature (RT). We focus on the reason why the solute element Ta affects RT properties of PM superalloys. To this end, the necessary advanced characterization methods were used to study the plastic deformation and fracture mechanisms. The results revealed that the leading cause for the enhancement in RT yield strength with Ta increasing is the antiphase boundary (APB) strengthening of the bimodal γ' precipitates, the extended stacking fault (ESF) shear and the interaction between ESF and dislocation. Importantly, the microtwin structure was found in the deformed substructure, which is an extraordinary phenomenon in RT plastic deformation for PM superalloys. • The microtwin configuration was found inL1 2 -γ' strengthening Ni-base PM superalloys after RT tensile defromation. • The microtwins are formed by the a/6 〈112〉Shockley partials shearing precipitates on adjacent {111} planes. • The deformation induced ESFs (or microtwins) is the major reason for the increase in yield strength.

Microstructure and Superconducting Properties of Hf–Ta Addition Bronze-Route Nb3Sn Wire

The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn superconducting wire is a promising candidate for cutting-edge high-field magnets such as the next generation particle accelerator and fusion reactor. Recently, Hf–Ta addition to Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires has attracted our great interest, because it results in significant grain refinement and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> enhancement, maintaining high <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c2</sub> . In this work, we studied how much effect the Hf–Ta addition has on the layer formation and superconducting characteristics, when it is applied to bronze-route Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires, through microstructural and microchemical analysis by using EBSD and EDS. For simplicity, single-core composite wires were fabricated and tested. The tested wires included conventional Ti-doped Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Hf–Ta-doped Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn wires. As a result, grain refinement in Hf–Ta addition was not significant in bronze process, compared with internal-tin process. Apparently, the thickness of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn layer was thick especially when Ti was doped into the Cu-Sn bronze matrix. Sn content seems to be also high in Ti-doping to Cu-Sn bronze matrix. In the bronze-route process, impact of Ti addition on the promotion of Sn diffusion seems to be relatively large, compared with Hf–Ta addition.

Investigation on influence of Ta on microstructure evolution of directionally solidified Ni-based superalloys

The microstructure evolution in directionally solidified Ni-based superalloys DZ411 with different Tantalum (Ta) compositions (2.72, 3.10, and 4.00 wt%) was investigated to develop Ta-containing hot corrosion superalloys. It is found that the addition of Ta promote the element segregation in the interdendritic region, thus, leading to the increase in volume fraction of MC carbides and eutectics, while the morphology of them are not obviously changed. In addition, both the volume fraction of regions increases with increasing Ta composition, which is attributed to the reason that Ta is the main forming element of γ' phase. Besides, the previous controversy on the dependence of both the primary and secondary dendrite arm spacing on Ta composition was solved. The increase of dendrite arm spacing with increasing Ta composition can be attributed to increasing solidification range of these superalloys through both JMatPro and Different Scanning Calorimetry (DSC) analysis. Furthermore, the atomic arrangement of γ and γ' phases in alloys was characterized by spherical aberration corrected transmission electron microscopy. Both the saturation of refractory elements in γ matrix and the lattice constant of γ matrix was found to increase with increasing Ta composition, leading to the increase of lattice mismatch of γ/γ' phase and more regular shape of γ' phase which has also been confirmed by JMatPro analysis.

Injectable and Self-Healing Hydrogel Based on Chitosan-Tannic Acid and Oxidized Hyaluronic Acid for Wound Healing.

Self-healing performance plays an important role in the in situ microinvasive injection of hydrogels, which can reduce sudden drug release and prolong the service life of hydrogels. In this paper, a multifunctional injectable and self-healing hydrogel for wound healing was developed. Chitosan (CS) was modified with TA to achieve potential adhesion, anti-inflammatory properties, and slower degradation rate. The hydrogel was formed by Schiff base reaction based on amino groups in CS and aldehyde groups in oxidized hyaluronic acid (OHA). The gel formation process was quick and convenient in mild conditions without extra initiators. Due to the dynamically reversible covalent bonds, the hydrogel could self-heal within 2 min after injection. It also had good biocompatibility and hemostatic performance. With the addition of TA, the hydrogel acquired anti-inflammatory properties and promoted cell growth, effectively accelerating the wound-healing process in vivo. The CS-TA/OHA hydrogel is expected to be used for skin repair.

Evolution of creep rupture mechanism in advanced powder metallurgy superalloys with tantalum addition

To further understand the effect of Ta additive on the creep damage for polycrystalline Ni-base superalloys, creep rupture tests on powder metallurgy (PM) superalloys with various Ta were carried out under different conditions in this study. The results indicated that the multiple crack propagation and damage mechanisms could occur at the identical creep condition. These different fracture mode areas had distinct boundaries on the fracture surface, its size could be altered by Ta addition. However, the effects of Ta were radically changed by the creep conditions. The creep rupture mechanism transformed significantly with temperatures and applied stresses, and even subversive laws appeared in the creep life for high-Ta alloys. The substructure observation after creep rupture demonstrated that the annealing coherent twin boundaries gradually lose coherence with the matrix, which could become sites for cavities nucleation or crack propagation that followed. Furthermore, the creep-induced microtwins were critical for the creep damage and rupture. The electron back-scattered diffraction (EBSD), high-resolution transmission electron microscope (TEM) imaging, and quantitative elemental analysis assisted in comprehending these alterable creep rupture mechanisms.

Effect of Nb and Ta addition on mechanical properties of Zr-based bulk metallic glasses and composites

To modify the poor plasticity of bulk metallic glasses (BMGs) under room temperature, the present work reported that microalloying can improve the plasticity of BMGs, and the deformation mechanism at room temperature was elucidated. The selection of minor elements, Nb and Ta have a positive heat of mixing with the based compositions. The maximum plasticity of 32.9% is shown in the Nb1 sample. The self-organize to a critical state (SOC) occurred in all BMGs, the scaling exponent β value maintains the constant 0.24. The variation of the rotation angle of primary shear bands (SBs) is in agreement with plasticity. Meanwhile, the yield strength is linearly dependent on the local fracture toughness of BMGs. Summarily, the compressive plasticity of BMGs at room temperature can be improved by adding elements that can form positive mixing heat with the components of based compositions.

Improving the intermediate- and high-temperature strength of L12-Co3(Al,W) by Ni and Ta additions

The effects of Ni and Ta additions on the mechanical properties in the L12 compound Co3(Al,W), the strengthening phase of Co-based superalloys, have been investigated by compression tests between room temperature and 1000 °C, in order to elucidate the effects of stability of the L12 phase on the mechanical properties. The additions of Ni and Ta, both of which are L12-stabilizers that increase the L12 solvus temperature, increase the yield strength at intermediate and high temperatures. The strength increase is shown to be more significant as the amount of additions of these elements and thereby the stability of the L12 phase increases. Two factors account for the strength increase at intermediate temperatures: The reduction of the onset temperature of yield stress anomaly (YSA-onset) due to the increased complex stacking fault (CSF) energy and the increase in both the base strength and the intensity of the yield stress anomaly associated with an increased anti-phase boundary (APB) energy on (111) planes. The strength increase at high temperatures, on the other hand, arises from the increase in the peak temperature due to the increased L12 solvus temperatures. The increased strength of the L12 phase due to a higher phase stability thus partly accounts for the improved creep strength of Co-based superalloys upon alloying with Ni and Ta.

Effect of Ta Content on Microstructure and Properties of (Ti,W)C-Based Cermets

(Ti,W)C-based cermets are an ideal material for the preparation of high-performance cutting tools due to their excellent mechanical properties, high temperature oxidation resistance, and corrosion resistance. However, their lower toughness limits the application of cutting tools. In order to solve the problem of low toughness faced by the current materials used in tools, in this study, a (Ti,W)C solid solution was used as the hard phase to prepare cermets with high toughness via vacuum sintering. The effects of Ta content on the composition, morphology, and microstructure of the cermets were analyzed through XRD analysis and SEM and EDS characterization methods. The mechanical properties such as hardness, transverse fracture strength, and the fracture toughness of the cermets and corrosion resistance in an HNO3 solution were also investigated. The results show that the microstructure of (Ti,W)C solid solution-based cermets exhibit simpler core-rim (single-rim) and acyclic structures, which weaken the formation and propagation of cracks at the interface. The relative density and grain size of cermets increases and decreases, respectively, with the greater amount of Ta addition, while excessive Ta addition leads to a decrease in the relative density and agglomeration between grains. The cermet with 3 wt.% Ta addition possessed excellent mechanical properties with a Vickers hardness, transverse rupture strength, and fracture toughness of 13 GPa, 1907.4 MPa, and 15.5 MPa m1/2, respectively. The addition of Ta leads to the formation of a Ta-rich protective layer on the surface of the cermet under the corrosion of the acidic solution, and with the increase in the Ta content, the corrosion resistance of the cermet gradually improves.

Effect of TiC on microstructures and mechanical behaviors of low-density Nb-Ti-Al alloys fabricated by laser solid forming

Ultra-high temperature Nb alloys are prospective for practical applications as aircraft materials. Sufficient efforts must be made to improve their manufacturing technologies and properties. The Nb-Ti-Al alloys with TiC addition were fabricated by laser solid forming (LSF) in this work. LSFed Nb-Ti-Al-TiC alloys which were composed of Nbss and (Nb,Ti)C had excellent formability and metallurgical quality. There were columnar and equiaxed Nbss grains in Nb-37Ti-10Al-3TiC and Nb-37Ti-10Al-5TiC while there were entire equiaxed Nbss grains in Nb-37Ti-10Al-8TiC. Expectant columnar-to-equiaxed transition was realized by the addition of TiC. Moreover, the grain sizes gradually decreased from the addition of 3TiC to 8TiC, and the average grain size of Nb-37Ti-10Al-8TiC decreased to 22.08 μm. The strip-like and particle-like (Nb,Ti)C precipitation coexisted in Nb-37Ti-10Al-3TiC and Nb-37Ti-10Al-5TiC, but only particle-like (Nb,Ti)C formed in Nb-37Ti-10Al-8TiC. The tensile strength, compression strength and fracture toughness of all Nb-Ti-Al-TiC alloys increased with the increase of TiC content. For Nb-37Ti-10Al-8TiC, the maximum tensile strength of 754.14 ± 3.84 MPa, compression strength of 3310.0 ± 55.28 MPa and fracture toughness of 34.96 MPa·m1/2 were obtained. The simultaneous increase of strength and fracture toughness was mainly attributed to fine grain strengthening by TiC addition. Compared with Nb alloy with the addition of Ta, W, Mo and Hf, the LSFed Nb-Ti-Al-TiC alloy had considerably high strength and was of low density. This confirmed the feasibility of preparing Nb alloy by LSF technology and adjusting the microstructure and property.

Effect of Ta, Nb and Zr additions on the microstructures and mechanical properties of 70 vol% TiC/Al cermets

In this work, 70 vol% TiC/Al cermets with the addition of 5 vol% Ta, Nb and Zr elements were successfully fabricated by combustion synthesis and hot-pressing method. Among them, Ta, Nb and Zr elements generated (Ti, X)C (X = Ta, Nb and Zr) solid solutions and Al3X (X = Ta, Nb and Zr) intermediate phases during the reaction process, and refine TiC particles significantly. Especially, Ta and Nb elements decreased the crystallographic mismatch of the Al/TiC interface. The addition of Ta improves the compression properties of TiC/Al cermets at room temperature and high temperature. The addition of Nb and Zr impairs the room temperature compressibility of the TiC/Al cermet, but improves the high temperature (300 °C) compressibility. The strengthening mechanisms of TiC/Al cermets after adding Ta, Nb and Zr were mainly solid solution strengthening, grain refinement strengthening and the reduction of lattice mismatch at the Al/TiC interface. The reduced mechanical properties of TiC/Al cermets at room temperature after the addition of Nb and Zr elements were due to the presence of intermediate phases.

The effect of Ta, W, and Re additions on the tensile-deformation behavior of model Ni-based single-crystal superalloys at intermediate temperature

The influence of refractory additions on tensile deformation behavior has been studied at an intermediate temperature (760°C) using scanning and transmission electron microscopy. Tensile experiments revealed that elemental additions of tantalum (Ta), tungsten (W), and rhenium (Re) could improve the yield strength (YS) of the model alloys with an order of YS(Ni–Al–W) > YS(Ni–Al–Ta) > YS(Ni–Al-Re) > YS(Ni–Al). During the plastic deformation of model alloys at the intermediate temperature, the deformation via Orowan bypassing and shear could be activated synergistically. The changes of anti-phase boundary (APB) energies on {001} and {111} planes are related to the cross-slip driving force, critical resolved shear stress and stage II work hardening rate in γ' precipitates. The effects of γ' size and refractory additions (Ta, W, and Re) on the yield strength of model alloys at intermediate temperature are also discussed, which can provide qualitative reference for alloy design.