Increasing Ta Content Research Articles

Microstructure and mechanical behavior of TaxHf1−xC–SiC fabricated by reactive hot‐pressing: Effect of Ta:Hf ratio

AbstractTaxHf1–xC are promising candidates for many applications under harsh environments due to their unique properties. Up until now, low‐temperature densification is still a big challenge for these ceramics. Moreover, the effect of Ta:Hf ratio on microstructure development and mechanical behavior of the ceramics is not clear. In this work, highly dense TaxHf1−xC–SiC ceramics (x = 0.2, 0.4, 0.6, 0.8) were fabricated at 1700°C by a novel reactive hot‐pressing processing with 8 wt% Si as sintering aid, which present excellent mechanical properties. Fracture toughness of the ceramics is higher than 6.3 MPa·m1/2, with the highest toughness achieved in Ta0.6Hf0.4C–SiC (8.5 MPa·m1/2). With the increase of Ta content, hardness of the ceramics tends to increase, while the bending strength tends to decrease. The highest bending strength is achieved in Ta0.2Hf0.8C–SiC (637 MPa), and the highest hardness is achieved in Ta0.8Hf0.2C–SiC (17.6 GPa). This work lays the foundation for the composition design of TaxHf1−xC‐based ceramics and composites.

Enhancing microstructural stability and creep properties by Ta addition in Ni-based single crystal superalloys

To investigate influences of Ta content on microstructural stability during thermal exposure at 900 °C (up to 3000 h) and creep properties at 980 °C/163 MPa in Ni-based SX superalloy, alloys with 7Ta, 8Ta and 9Ta (wt.%) were studied utilizing DSC, SEM, TEM, HR-XRD and APT. The results shows that Ta addition enhanced the partitioning behavior of alloying elements. Besides, lattice misfit was controlled by both alloy composition and temperature. Ta addition increased absolute misfit both room temperature and 980 °C. The difference was that the γ/γ′ lattice misfit changed from positive to negative at room temperature. The γ′ coarsening indicated that Ta addition reduced the effective diffusion coefficient and exacerbated W segregation at γ/γ′ interface, which was beneficial to improve the microstructural stability. Merging of several adjacent γ′ precipitates in preferred direction was observed to be delayed with increasing Ta content, which occurred at 500 h for 7Ta alloy, 800 h for 8Ta alloy and 1000 h for 9Ta alloy, respectively. Ta addition affected the diffusion kinetics and greatly prolonged the steady creep duration, and then resulted in longer creep rupture life. It was discussed based on the γ matrix channels, γ′ raft thickness, the perfection degree of γ′ rafts, residual γ′ precipitates, interfacial dislocation networks and solid solution strengthening.

Influence of tantalum addition on the microstructure and wear resistance properties of NiCuBSi/65WC composite coatings

Nickel-based tungsten carbide composite coatings are extensively utilized on various wear-resistant workpiece surfaces due to their exceptional properties, including high hardness and wear resistance. However, as the WC content increases, uneven structure and susceptibility to cracking of the coating during the forming process are enhanced, thereby impacting its service performance. To address these issues, NiCuBSi/65WC composite coatings with varying tantalum (Ta) contents were fabricated on 42CrMo steel substrates by laser cladding. The influence mechanism of Ta content on the microstructure and wear resistance of the coatings was investigated. The results demonstrate that the addition of tantalum promotes the formation of reinforcement phases such as TaC and W2C in the coating. Moreover, with increased Ta content, the edge of WC particle reaction layers in the coating gradually transforms from sawtooth to shorter rod-shaped morphology. Additionally, as the Ta content increases, the dissolution degree of WC particles rises, thereby facilitating the formation of TaC and W2C compound carbide. This leads to an enhancement in both the quantity and uniform distribution of carbide reinforced phases within the coating, resulting in an increase in average coating hardness from 482.4 HV0.2 to 580.1 HV0.2. When the Ta content reaches 7 wt% in particular, no cracks are observed on the coating surface, and a uniform distribution of carbides is achieved. The relative wear resistance of NiCuBSi/65WC coating with 7 wt% Ta is approximately 2.36 times higher than that without Ta.

Microstructure evolution and performance of TiMoCrWxTay refractory high-entropy alloy coatings prepared using laser cladding

Refractory high entropy alloy (RHEA) coatings containing W and Ta elements at the same time usually have excellent performance at high temperature, which are promising candidate materials for high temperature protective coating materials. In this work, the effects of W and Ta on the microstructure and performance evolution of TiMoCrWxTay RHEA coatings have been investigated. Experimentally, TiMoCrWxTay coatings are mainly composed of BCC phase, Laves phase and Ti-rich phase, with W and Ta atoms preferably dissolved in BCC phase. The W atoms promote the formation of dendrites and the growth of rod-like and equiaxed crystals and the Ta atoms promote the formation of cellular crystals and produce the effect of fine crystal strengthening. W and Ta atoms have significant influence on the tribological properties of TiMoCrWxTay coatings. The tribological properties of TiMoCrWxTay coatings at 800 °C are better than those at room temperature. TiMoCrWxTay RHEA coatings follow near-linear oxidation kinetics during the oxidation of 50 h at 800 °C.The oxidation resistance of the coatings first increases and then decreases with the increase of Ta content. Ta2O5, TiO2 and other oxides may have a shielding effect on the oxidation of W. In particular, The W0.3Ta0.5 shows the best tribological properties and oxidation resistance, and the mass gain of W0.3Ta0.5 is only 13.4 mg/cm2 after the oxidation test for 50 h. It indicates that TiMoCrWxTay coatings can obtain good high temperature performance by optimizing the content of W and Ta in RHEA coatings. This work can provide guidance for the research and application of TiMoCrWxTay RHEA coatings.

Pd–Ta alloy films hydrogen sensors based on partially coated π -phase-shifted FBG

A fiber-optic hydrogen sensor based on Pd–Ta alloy films partially coated π-phase-shifted fiber-Bragg grating (FBG) is proposed and experimentally demonstrated. Three types of Pd–Ta alloy films with different Ta content were prepared via co-sputtering technology. Material characterization shows the transformation of Pd–Ta alloy to amorphous phase with the increase of Ta content, and the phase transition between α-PdTaHx and β-PdTaHx is inhibited at 2 % hydrogen concentration. Hydrogen sensing experiments show that in-situ temperature compensation is possible with Pd/Ta films partially coated on π-phase-shifted FBG. Moreover, the sensor's hysteresis phenomenon was eliminated with an increase in Ta content due to the first-order phase transition. Pd–Ta alloy films hydrogen sensor with a Ta content of 27 % is capable of in-situ temperature compensation, fast response, good stability, and reliability.

The microstructure and properties of Mo0.5NbTiZrTax high entropy alloys enhanced by Ta addition

In this study, the Mo0.5NbTiZrTax (x = 0.3, 0.5, 0.7) HEAs obtained by arc melting were controlled by the change of Ta content. The microstructure, the wear properties, and the corrosion resistance of the alloys were studied systematically. The results revealed that the alloys have the BCC (major) phase + BCC (minor) phase structure. At the same time, the increase in Ta content promotes the refinement of grains and the formation of sub-grains with gradually random orientation at grain boundaries but suppresses the randomization of crystal orientation. This also enriched the defect structure inside the alloys, further induced the formation of Zr-rich second phase particles, high-density stacking fault structures, and disordered Zr-rich BCC phases. The increase in Ta content significantly improved the wear properties of the alloys, which is mainly ascribed to the presence of the tough BCC phase and the combined effects of solid solution strengthening, second phase strengthening, fine grain strengthening, lattice distortion effect, and stacking fault strengthening. The electrochemical measurements confirm that the overall corrosion resistance of the alloys shows a trend of first increasing and then decreasing with the increase of Ta content due to the formation of micro batteries between the second phase rich in Zr as the anode and dendrites.

Designing eutectic medium-entropy alloys CoFeNiTax with outstanding mechanical properties

The eutectic medium-entropy alloys CoFeNiTax (x = 0.4, 0.5, 0.6) were designed successfully based on binary eutectic systems and thermodynamics calculations in this study. With the increase of Ta content, the solidified microstructures evolved from hypoeutectic to full eutectic and finally to hypereutectic. The primary phases in the hypoeutectic and hypereutectic were FCC solid solution and C14-Laves phase, respectively. The solidified microstructures were coarsened and spheroidized by the heat treatment, and a high-density of needle-like Laves phase precipitated in the FCC phase of the CoFeNiTa0.4. The crystallographic orientation relationship between the precipitated phase and matrix phase was [2‾ 42‾ 3]Laves//[011]FCC, and the crystal plane (1 1‾ 1)FCC was almost parallel to (0 1‾ 12)Laves, just with a mismatch angle of about 6°. The compressive strength and fracture strain of the heat-treated alloys were within 2232∼2465 MPa and 22.5–32.8 %, respectively, being superior to most high-entropy alloys. The excellent combination of strength and toughness was attributed to the synergistic effects of various strengthening-toughening mechanisms, including the second-phase strengthening, the solid solution strengthening, the interface strengthening and toughening, and the twinning toughening.

Enhanced effective spin Hall efficiency contributed by the extrinsic spin Hall effect in Pt1- x Ta x /CoFeB structures

High effective spin Hall efficiency and low magnetic damping constant are essential to achieve efficient spin-charge conversion for energy-efficient spintronic devices. We report the measurements of effective spin Hall efficiency and magnetic damping constant of Pt1- x Ta x /CoFeB structures using spin-torque ferromagnetic resonance (ST-FMR) techniques. With the increase of Ta content, the spin Hall efficiency increases and peaks x = 0.15 with the value of θSHeff=0.35 , before decreases for further Ta content. This non-monotonic variation is attributed to the interaction between the contribution of the extrinsic skew scattering mechanism and the spin-orbit coupling (SOC). The weakening of the SOC in the Pt1-x Ta x layer leads to a decrease in the effective magnetic damping constant with increasing Ta concentration. High-temperature ST-FMR measurements confirm the influence of the Ta concentration on the spin Hall effect and magnetic damping mechanism. Additionally, the decrease in spin mixing conductance and the increase in spin diffusion length leads to a decrease in the interfacial spin transparency.

Effect of nanoheterogeneities on the fracture toughness and tensile ductility of CuTa metallic glass thin films

Nanoheterogenenous metallic glasses (MG) can offer improved ductility through a nanoscale modulation in their mechanical properties. However, the relationship between the modulation parameters and the mechanical behavior is not well understood. Physical vapor deposition can directly control the compositional and morphological parameters of nanoheterogeneous MGs and enables the systematic investigation of this problem. This work explores the microstructure and mechanical properties of a range of CuTa-based nanolayered amorphous/amorphous (A/A) and amorphous/semi-crystalline (A/SC) nanoheterogeneous MGs and MG composites. The first step was the identification of three microstructural regimes in CuTa, namely, a fully amorphous form (23–65 at.% Ta), a Ta-rich amorphous-crystalline composite (65–75 at.% Ta), and a Cu-rich amorphous-crystalline composite (16–23 at.% Ta). The hardness of the films increased from 6 GPa to 17 GPa with increasing Ta content. Next, a range of CuxTa1−x/CuyTa1−y nanolayers composed of A/A and A/SC nanolayers were investigated. The hardness of all nanolayers follows the rule of mixture. A/A structures do not provide a significant increase in fracture toughness and only a minor increase in tensile ductility despite the high amplitude modulation of hardness between layers. A/SC nanolayers’ hardness and toughness was higher than A/A nanolayers as well as monolithic amorphous films, but still remained below the monolithic Cu25Ta75 SC film. The results show that the design of nanoheterogeneities in MGs requires careful optimization to achieve a useful improvement in mechanical properties.

Structure, mechanical and thermal properties of Ti1−x−y−zAlxTayBzN coatings

Multiple alloying is a preferred and practical approach to tailor the properties of TiAlN coatings. Here, we studied the structure, mechanical and thermal properties of Ti1−x−y−zAlxTayBzN coatings by cathodic arc evaporation. Increasing Ta content causes a structural transition from mixed cubic and wurtzite Ti0.35Al0.54Ta0.03B0.08N, Ti0.35Al0.54Ta0.05B0.06N, and Ti0.34Al0.52Ta0.09B0.05N to cubic Ti0.33Al0.51Ta0.13B0.03N and Ti0.33Al0.50Ta0.15B0.02N. This structural change causes an increased hardness, where the maximum hardness of 38.0 ± 0.8 GPa is obtained by Ti0.33Al0.51Ta0.13B0.03N. The cubic Ti0.33Al0.51Ta0.13B0.03N and Ti0.33Al0.50Ta0.15B0.02N coatings reveal higher hardness during the whole annealing range, which reach the peak hardness of 39.3 ± 0.9 and 36.7 ± 1.0 GPa at 1000 °C, respectively. In addition, the oxidation resistance of Ti1-x-y-zAlxTayBzN coatings is closely related to the Ta content. After oxidation of 10 h at 1000 °C, the oxide scale of Ti0.35Al0.54Ta0.05B0.06N, Ti0.34Al0.52Ta0.09B0.05N, Ti0.33Al0.51Ta0.13B0.03N, and Ti0.33Al0.50Ta0.15B0.02N are ∼2.31, ∼1.44, ∼1.23, and ∼ 1.08 μm, respectively, while Ti0.35Al0.54Ta0.03B0.08N has been entirely oxidized.

Delayed surface degradation in W-Ta alloys at 400 °C under high-fluence 40 eV He plasma exposure

The surface modifications in W-xTa alloys (x = 0, 6, 11 wt.%), as potential material candidates for tokamak components facing the fusion plasma, have been assessed at a temperature of ∼400 °C, by exposing the material surface to 40 eV He for increasing He fluences up to 1027 m−2 and flux of ∼1023 m−2 s−1. Surface wave-like structures appear in all samples at a fluence of ∼1026 m−2, whereas at the higher fluence of ∼1027 m−2 the material's surface is characterised by the presence of blisters and ablations. This suggests a new critical fluence for blistering in pure He plasma to be between 1026 and 1027 m−2. There is also a near-surface layer with a thickness of ∼200 nm that contains He bubbles of 2.20–2.70 nm in average size. Increasing Ta content leads to a small reduction in bubble size, and to clear reductions in the presence of blisters and ablations. Ta alloying can improve the hardness and yield strength and reduce the He diffusivity in the material. This therefore delays bubble formation and surface blistering and ablations that are affected by these mechanical properties. This was exemplified at the highest fluence by a large mitigation of surface material ablation.

Passive behaviour of non-equiatomic NiCoCrTa multi-principal element alloys in dilute sulfuric acid

The passive behaviour of non-equiatomic multi-principal element alloys, Ni(58-x)Co20Cr22Tax (x = 0, 0.64, 1.64, 3.39 at.%), was investigated in 0.1 M H2SO4 at 25 °C by electrochemical methods and surface analysis. After 24 h immersion, the alloys were all found to be in a spontaneously passivated state, and the value of the open circuit potential shifted to the positive direction with the increase of Ta content. The grain size of the alloys reduced with increasing the Ta content. The relationship between the passive current density and the grain size was in agreement with a linear model. The capacitance measurements indicated that the passive film formed on the alloys was of n-type semiconductor characteristic and the donor density was decreased with the increase of Ta. The thickness of the passive film improved primarily due to the obstacle to the dissolution of the outer layer as the accumulation of Ta2O5 in the outer layer. The improved corrosion resistance of the alloys with increasing Ta content can be ascribed to the formation of a complex film containing more Ta2O5, which enhanced the stability, thickness, and compactness of the passive film. The developed alloys show good passivity in dilute sulfuric acid.

Electronic and nanoscale structures of metal oxyhalide intergrowth photocatalysts

Multimetal oxyhalide intergrowths show promise for photocatalytic water splitting. However, the relationships between intergrowth stoichiometry and their electronic and nanoscale structures are yet to be identified. This study investigates Bi4TaO8Cl–Bi2GdO4Cl intergrowths and demonstrates that stoichiometry controls the tilting of [TaO6] octahedra, influencing the bandgap of the photocatalyst and its valence and conduction band positions. To determine how the [TaO6] octahedral tilting in the intergrowths manifests as a function of intergrowth stoichiometry, we investigated changes in crystal symmetry by analyzing features arising at the higher order Laue zone (HOLZ) of convergent-beam electron diffraction patterns. Higher Ta content intergrowths displayed a more intense outer HOLZ ring compared to lower Ta content intergrowths, indicating transformation from P21cn (orthorhombic) to P4/mmm (tetragonal). This finding suggests that more distortion occurs along the ⟨001⟩ directions of the crystal than the ⟨100⟩ and ⟨010⟩ directions. This variation directly impacts the electronic structure, affecting both conduction and valence band energy levels. By combining ultraviolet photoelectron spectroscopy, UV-visible diffuse reflectance spectroscopy, and electron energy loss spectroscopy, the absolute band positions of the intergrowths were determined. Agreement between the bandgaps obtained via ensemble and nanoscale measurements indicates nanoscale homogeneity of the electronic structure. Overall, the integrated approach establishes that the bandgap energy increases with increasing Ta content, which is correlated with the crystal symmetry and [TaO6] octahedral tilting. Broadly, the modular nature of intergrowths provides building block layers to tune octahedral tilting within perovskite layers for manipulation of optoelectronic properties.

The microstructure and mechanical properties of novel Fe-rich Fe–Cr–Ni–Ta eutectic multi-principal element alloys

Co–Cr–Fe–Ni–Ta eutectic multi-principal element alloys (MPEAs) demonstrate great potential to replace structural alloys in engineering applications. However, the cost of these alloys is high due to the usage of a number of precious metals. To decrease the cost, the present work developed a set of novel Fe55Cr15Ni30−xTax (x = 0, 5, 8, 10 and 15 at.%) eutectic MPEAs and the effect of Ta on microstructure and compressive mechanical properties were investigated for the first time. As the Ta content increases, the microstructure changes from a single-phase FCC solid solution (x = 0) to hypoeutectic microstructure (x = 6), then to eutectic microstructure (x = 8), and eventually to hypereutectic microstructure (x = 10 and 15). The yield strength and the hardness increase at the expense of ductility reduction with increasing Ta content. The strengthening mechanism of this alloy system is mainly second-phase strengthening caused by Laves phase and grain boundary strengthening produced by eutectic interface, supplemented by solid solution strengthening. The Fe55Cr15Ni22Ta8 and Fe55Cr15Ni20Ta10 alloys present the excellent comprehensive mechanical properties. The yield strength, fracture strength and fracture strain of the former are 838 MPa, 1994 MPa and 45.1%, respectively. The yield strength, fracture strength and fracture strain of the latter are 1029 MPa, 1956 MPa and 43.0%, respectively. The phase formation of Fe55Cr15Ni30−xTax alloys can be predicted by Md criterion. When Md ≥ 0.89, the alloys consist of FCC phase and Laves phase. Otherwise, the alloys consist of FCC single phase.

Processing of W and W - Ta alloys via laser powder feed directed energy deposition

The microstructure, porosity and Vickers hardness of pure W, W - 15% Ta and W - 21% Ta fabricated by Laser Powder Feed Directed Energy Deposition (LPF-DED) in ambient air and inert build environments were studied in this work. Severe microcracking and porosity were observed in all samples when building in ambient air and Ta was selectively oxidized. Under inert atmospheres, pure W was manufactured with no bulk microcracking and 1.7% porosity. Increased Ta content led to decreased porosity and increased hardness with again no microcracking observed. The lack of cracking in the inert was attributed to the increase in build temperature and reduced oxidation.The decrease in porosity, increase in hardness with W - Ta was attributed to the decrease in liquidus temperature with increasing Ta. Micrographs also show grains refinement with increasing Ta content and a cell structure was reported for W - Ta alloys. This work provides relevent information about manufacturing of high temperature melting materials via LPF-DED.

In-vitro and in-vivo bio-corrosion and biocompatibility responses of bioactive TiTaNb films with various Ta contents on Ti6Al4V implants

Despite the widespread use of Ti6Al4V in orthopedics, the health concerns, innate bio-inert property and the pursuit of long-term implantation in the body limit its development. For these reasons, we intend to modify the chemical and physical properties of Ti6Al4V by the sputtered bioactive Ti–Ta–Nb films. All these elements exhibit great biocompatibility in human body and the Ti–Ta–Nb system can form more stable passive layer to prevent the corrosion. In this study, we evaluate the effectiveness of the surface modification for Ti–Ta–Nb system on Ti6Al4V and investigate the influence of bioactive element Ta content from 25, 33, to 50 at% by the bio-corrosion behavior, passivation, in-vitro biological analysis and in-vivo implantation. The results show the Ti–Ta–Nb system has higher corrosion resistance and better biological properties than Ti6Al4V. Furthermore, following the electrochemical tests and passive layer observation, with increasing Ta content in Ti–Ta–Nb system, the corrosion resistance increases. The in-vitro measurements demonstrate that the higher Ta content in this system would lead to favorable surface condition for cell viability, proliferation, differentiation and adhesion. As for the in-vivo response upon implantation, the Ta50 film demonstrates significantly greater osteointegration capability. In summary, the current results reveal that the Ti–Ta–Nb system could greatly promote the surface properties of Ti6Al4V, and Ta50 is demonstrated to be a more promising coating choice for orthopedic implants. The mechanisms of the influence on Ta via the corrosion resistance, passivation and biological performances have been extensively explored and discussed.

Microstructure, hardness and wear resistance of AlCoCrFeNiTax (x = 0, 0.1, 0.3) high-entropy alloys enhanced by laser remelting and Ta addition

Laser remelting (LR) treatment was used to regulate the microstructure of AlCoCrFeNiTax high-entropy alloys prepared by vacuum arc melting, and the microstructure and properties of the alloys before and after LR treatment were analyzed. The original AlCoCrFeNiTax alloys have typical dendritic morphology and the addition of Ta element promoted the formation of a Laves phase, gradually changing the alloys from two phase (BCC + B2) to three phase (BCC + B2 + Laves phase). After LR treatment, the grains were significantly refined, elemental segregation was alleviated, and a dense remelting layer with a thickness of 1200–1600 µm was formed on the surface of the alloy. In addition, the hardness and wear resistance of the alloys were improved with increasing Ta content and LR treatment, mainly caused by the combined effects of solution strengthening, second phase strengthening and fine grain strengthening. At the same time, the corrosion resistance of the alloys before and after LR treatment in 3.5 wt% NaCl solution is significantly improved by a stable Ta2O5 and TaO2 passivation films and the formation of a dense uniform remelting layer.

The effect of Ta addition on mechanical properties of Zr-based bulk metallic glasses

Bulk metallic glasses (BMGs) exhibit poor room temperature plasticity, so improving their room temperature plasticity is important for amorphous alloys in engineering applications. In this paper, Zr60Cu(20-x)Al10Ni10Tax (x = 0, 1, 3, 5) bulk metallic glasses with 3 mm diameter rods were prepared by water-cooled copper mold suction casting, and investigated the effect of minor additions of Ta on the properties of Zr–Cu–Ni–Al alloys, especially on plasticity. The results show that the Zr-based alloys with a 3 mm diameter are amorphous. With the addition of Ta elements, the glass transition temperature hardly changed, the crystallization onset temperature increased from 747 K to 767 K, the width of the supercooled liquid phase zone increased from 49 K to 68 K, and the thermal stability of the alloy was improved. The room temperature uniaxial compression test found that with the increase of Ta content, the strength and plasticity of alloys showed a trend of first increasing and then decreasing, when the Ta content was 1 at.%, more interactive shear bands were observed on the side surface of the alloy after compression, while the fracture surface exhibited a complete vein pattern, and fracture strength and plasticity of samples reached to 1920 MPa and 13.8%, respectively. The results of nanoindentation tests indicated that when the Ta content was 1 at.%, the alloy exhibited the maximum indentation hardness and elastic modulus of 8.03 GPa and 101.48 GPa, respectively. It can be concluded that the right amount of Ta in Zr-based BMGs improves the mechanical properties, especially, the fracture strength, the plasticity, the indentation hardness, and the elastic modulus.

Investigation on the influence of Ta on the microstructure evolution of Ni-based superalloy DZ411 during directional solidification, heat treatment, and long-term aging

The microstructure evolution in directionally solidified Ni-based superalloys DZ411 with different Tantalum (Ta) contents (2.72, 3.10, and 4.00 wt%) was investigated. After directional solidification, three alloys with different Ta contents were subjected to standard heat treatment: solution treatment (1230 °C/2 h/AC)+ primary aging (1120 °C/2 h/AC)+ secondary aging (870 °C/24 h/AC). Then, following isothermal long-term aging treatments were performed at 950 °C for 50, 100, 200, 500 and 1000 h. The addition of Ta can lead to the increase of the volume fractions of MC carbides, eutectics, and γ′ phases during directional solidification. In addition, with the increase of Ta content, the mismatch of γ/γ′ increases, thus, the shape of γ′ becomes more regular. After solution heat treatment, the MC carbides are decomposed, and more M23C6 carbides are precipitated along the grain boundaries in alloys with increasing Ta contents. Besides, the eutectic cannot be completely eliminated. After secondary aging, more secondary γ′ phases are precipitated on the γ matrix channels in alloys with increasing Ta contents. Furthermore, the addition of Ta can delay the coalescence of the γ′ phase during long-term aging, which can be attributed to the reduction of the coarsening rate K according to the precipitation coarsening theory of Lifshitz and Slyozov and Wanger (LSW).

Effect of tantalum concentration on the microstructure and mechanical properties of novel W–Ta-Re alloy

Novel homogeneous and compact W–Ta-Re alloys with different concentrations of Ta were fabricated by spark plasma sintering. The effect of Ta concentration on the microstructure and mechanical properties of W-xTa-10 wt%Re (x = 0, 10, 20, and 30 wt%) alloys was studied. The single body centered cubic (BCC) phase W–Ta-Re matrix is formed by solid solution, and the grains are effectively refined with the addition of Ta. Attributing to the grain refinement and solution strengthening, the alloys exhibit excellent strength and good ductility. The average grain size reduces to 6.7 ± 2.5 μm after the addition of 30 wt% Ta, whereas it is 17.3 ± 5.5 μm for the W–Re matrix without the addition of Ta. In addition, its yield strength increased to 1248.8 ± 13.2 MPa, an enhancement by ∼183%. The ultimate compressive strength and strain rate for alloys are greater than ∼2940 MPa and ∼42%, respectively. With increasing Ta content, the matrix deteriorates because of hard oxides, causing transgranular cleavage fracture. The preferred orientation of grains along the compression direction is < 111> and <001> after deformation. The deformed structure showed several short curved and entangled dislocations, guaranteeing better mechanical properties. This research is of great significance for the strengthening and toughening of tungsten materials.