W-rich Phase Research Articles

Surface modification of W–Ta–V–Cr multi-component alloy after low-energy He plasma irradiation

This study explores a hypothetical scenario where low-activation refractory multi-component alloys (RMCAs) are considered for use as divertor target materials in fusion reactors. To investigate the surface modifications under divertor service conditions, a multi-phase W–Ta–V–Cr RMCA is irradiated with low-energy helium (He) plasma at varying temperatures to approximately 5.0 × 1025 He·m−2. The W-rich and Cr-rich phases in the multi-phase RMCA mimic the mono-phase W–Ta–V–Cr RMCA and segregation at grain boundaries, respectively. Following irradiation, fuzz layer formation is observed for all phases at temperatures lower than pure W requires. Additionally, nano He bubbles are identified in the fuzz tendrils at 920 °C. The modified layers exhibit reduced V and Cr content with increasing temperature, transitioning into W-Ta binary alloys at 920 °C. Notably, the fuzz layer on the W-rich phase is thinner than that on pure W at 920 °C. While a thinner fuzz layer suggests the alloy’s potential as a divertor target material, challenges include a lower fuzz formation temperature and potential high V and Cr sputtering yield, raising concerns for plasma contamination during fusion reactor operation. This dual perspective highlights both the promise and challenges of utilizing RMCAs as divertor target materials in severe fusion reactor environments.

Hot compressive deformation of W-modified FeCr2V-based medium entropy alloys: Microstructure and strengthening mechanism studies

The microstructure and mechanical properties of FeCr2VWx (x = 0, 0.1, 0.3, 0.5) medium-entropy alloys (MEAs) manufactured using arc melting under an argon atmosphere were investigated. The investigated FeCr2VWx (x = 0, 0.1, 0.3) MEAs exhibited a dual-phase microstructure consisting of body-centred-cubic (BCC) phases. With the further addition of W, additional W-rich phase formed in the microstructure of the FeCr2VW0.5 sample. Compression tests at the ambient and elevated temperatures revealed that the compressive performance of the MEAs improved with the introduction of W. Among them, FeCr2VW0.3 demonstrated an exceptional combination of enhanced strength and ductility, showing the yield strength of 1452 MPa at ambient temperature and 627 MPa at 1223 K as well as compression reduction over 30% at both temperatures. These compressive properties are comparable to those of existing low activation refractory high-entropy alloys. The excellent high-temperature performance was attributed to the enhanced strengthening effects of precipitation and solid-solution resulting from W addition. Moreover, it was found that during the hot deformation process FeCr2VWx MEAs with higher W contents (above 0.3) resulted in more work hardening than that of the lower W contents, and required more dynamic recrystallization to achieve the dynamic equilibrium. These results provide valuable insights for the future development and microstructural engineering of new MEAs.

Microstructure and compressive deformation behavior of W-Ni3Al-Co model alloys by two-step sintering

The regulation of microstructure can improve the mechanical properties of tungsten alloys. To regulate the microstructure, the W-Ni3Al-Co alloys with different Ni3Al/Co ratios were prepared using a two-step sintering method, and the microstructure and compressive deformation behavior were investigated. The results showed that the particle sizes of the W-rich phase in the network structure were refined with the increase of the Ni3Al/Co ratio, and a large fraction of twin boundaries were detected in the adhesive phase. The compressive deformation behavior of a W-7Ni3Al-3Co alloy with excellent compressive properties was investigated by the EBSD technique. The results demonstrated that twins in the FCC binder phase hindered the stress concentration in the binder phase and at the interface of the W/binder phases through twin-dislocation interactions. The W network structure underwent the uniform global deformation that restricted grain boundary sliding during deformation and prevented crack extension and consolidation. Twins in the binder phase and the W network structure were both important factors in improving the compressive properties of W-Ni3Al-Co alloys.

High-temperature precipitation behavior of W-containing 444-type ferritic stainless steel in a simulated cyclic annealing process

An important aspect of energy conservation and emission reduction in automotive industry is to improve the combustion efficiency of gasoline. The full combustion of gasoline will inevitably cause an increase in exhaust temperature. The coarsening and dissolution behavior of precipitates in steel will lead to a decrease in its high-temperature mechanical properties when the engine is used for a long time in such an alternating heating and cooling environment. In order to obtain ferritic stainless steel with good high-temperature resistance, this paper is based on 444 ferritic stainless steel and attempts to partially replace Mo element with W element to obtain Laves phase containing W, Mo, and Nb with more stable high-temperature performance. A simulated cyclic high-temperature annealing process up to 1050 °C was designed to investigate the precipitation behavior in this modified ferritic stainless steel. The results show that using W to replace Mo in 444 ferritic stainless steel can refine the grains of ferritic stainless steel. It can not only provide better solid solution strengthening at elevated temperature, but also stabilize the Laves phase and provide precipitation strengthening. The reason is that the W elements can change the composition of the Laves phase in ferritic stainless steels and precipitate Fe2(Nb, W) with high thermal stability to provide stable precipitation strengthening during long-term alternating annealing. The W-rich Laves phase is prone to precipitation at grain boundaries, effectively pinning grain boundaries and preventing microcracks from propagating along grain boundaries during service, thereby improving the service life of the steel.

Radiation-induced amorphization behavior of thermally-aged M23C6 in F82H-BA12 steel

ABSTRACT To improve the understanding of the microstructural stability of F82H under fusion reactor environments, the synergistic effects of irradiation and thermal aging on the instability of M23C6 particle was investigated utilizing ion accelerator irradiation. Results show that the W-rich Laves phase growing along the grain boundaries was observed in the specimen after thermal aging at 773 K up to 10,000 hr. A bilayer contrast of the M23C6 particles consisting of an amorphous-rim and inner crystalline core was observed in the specimen irradiated by 10.5 MeV-Fe3+ at 623 K, but not in the specimen irradiated at 673 K, demonstrating that the critical temperature of the radiation-induced amorphization (RIA) in thermally aged M23C6 particles falls in the range of 623–673 K. These results show that thermal aging seems to play an insignificant role in the RIA behavior of M23C6 particles. Regarding the radial distribution function analysis, a relatively poor crystallinity was observed in the unirradiated thermally aged M23C6 particles, while the crystallinity was improved in the specimen irradiated at 673 K, which is ascribed to enhanced diffusion at elevated temperatures. Results indicate that the temperature-dependent point defect generation and recovery is the key factor related to the occurrence of RIA in M23C6 particles.

Microstructure and wear resistance of AlCoCrFeNi-WC/TiC composite coating by laser cladding

AlCoCrFeNi has excellent mechanical properties, however, its hardness and wear resistance are insufficient for engineering applications. In order to improve the wear resistance of AlCoCrFeNi coating, WC and in-situ TiC particles were used in this work. Subsequently, the microstructure, hardness, and wear resistance were studied in detail. The results showed that the in-situ TiC particles were uniformly distributed in the whole coating, ameliorating the uneven distribution of WC particles. A sound interface was formed between the particles and the coating matrix, proving the composite coating with excellent performance in wear resistance. The phase constituents of the coating matrix were the BCC and B2 phases. And BCC phase occurred lattice distortion due to the dissolution of W atoms, resulting in the solid solution strengthening of coating matrix. Furthermore, with the increase of WC content, a needle W-rich BCC phase appeared in the coating matrix. Finally, the hardness of AlCoCrFeNi-WC/TiC coatings increased from 516.4 HV 0.3 to 808.7 HV 0.3 , and the wear resistance was increased by 14 times. The improvement in hardness can be attributed to the WC particles, in-situ TiC particles, and solid solution strengthening. We prepared the AlCoCrFeNi-WC/TiC coating by laser cladding. The hardness and wear resistance are improved significantly by the WC particles, in-situ TiC particles, and solid solution strengthening. • The AlCoCrFeNi-WC/TiC coatings are reinforced by the WC particles, in-situ TiC particles, and solid-solution strengthening. • The in-situ TiC particles were uniformly distributed in the whole coatings, which ameliorates the uneven distribution of the WC particles. • The W element enhances the lattice distortion of the BCC phase, and the coating matrix is strengthened by the solid-solution strengthening. • The average hardness is increased by 292.3 HV 0.3 , and the wear resistance is increased by 14 times.

First principles calculations and synthesis of multi-phase (HfTiWZr)B2 high entropy diboride ceramics: Microstructural, mechanical and thermal characterization

First principles calculations were conducted on (HfTiWZr)B2 high entropy diboride (HEB) composition, which indicated a low formation energy and promising mechanical properties. The (HfTiWZr)B2 HEBs were synthesized from the constituent borides and elemental boron powders via high energy ball milling and spark plasma sintering. X-ray diffraction analyses revealed two main phases for the sintered samples: AlB2 structured HEB phase and W-rich secondary phase. To investigate the performance of multi-phase microstructures containing a significant percentage of the HEB phase was focused in this study. The highest microhardness, nanohardness, and lowest wear volume loss were obtained for the 10 h milled and 2050 °C sintered sample as 24.34 ± 1.99 GPa, 32.8 ± 1.9 GPa and 1.41 ± 0.07 × 10−4 mm3, respectively. Thermal conductivity measurements revealed that these multi-phase HEBs have low values varied between 15 and 23 W/mK. Thermal gravimetry measurements showed their mass gains below 2% at 1200 °C.

Microstructure and Oxidation Behavior of a CrMoNbTaW Refractory High Entropy Alloy

This work reports on the microstructure and oxidation behavior of a refractory CrMoNbTaW high entropy alloy (HEA) produced by vacuum arc melting. Microstructure and mechanical properties of both the as-synthesized alloy and that annealed in air for 6 h in the temperature range 600–900 °C were evaluated in detail. The phase identification and microstructure analyses were performed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) while microhardness was measured using Vickers hardness tests. The as-fabricated alloy consists of a multiphase microstructure consisting of three phases: a W-rich phase, a Mo-rich phase, and a solid solution phase of BCC structure. As-synthesized HEA for this composition demonstrates excellent microhardness values, of 787 ± 83.6 HV, which was retained after annealing. The oxidation resistance in air was evaluated from 600 to 1400 °C for both 12 and 24 h of exposure time. The alloy exhibits a parabolic mass gain until 1100 °C, for which it begins to exhibit a decreasing mass gain at 1200 °C and, subsequently, a mass loss at 1300 and 1400 °C. The surface oxidation products were investigated, for which no protective oxides were identified. The surface oxide scale consisted of Cr, Nb, Ta, and trace amounts of W. The Mo content at the surface decreased as temperature increased, with no Mo content identified after 1100 °C.

The effect of fine W particles in matrix phase on mechanical properties of tungsten heavy alloys

Tungsten heavy alloys 90W-7Ni-3Co (WNC) and 89.6W-6.2Ni-1.8Fe-2.4Co (WNFC), produced using liquid phase sintering followed by thermo-mechanical processing, were investigated for microstructure and mechanical properties. 90W-7Ni-3Co alloy processed following a cyclic heat treatment showed fine tungsten particles in the matrix. The alloy, when heat treated at a temperature 850°C (the lower temperature of cyclic treatment), formed a W-rich intermetallic phase in the matrix that subsequently dissolved during high temperature (1150°C) solution treatment leaving behind fine W particles. On the other hand, the matrix phase of the alloy, 89.6W-6.2Ni-1.8Fe-2.4Co showed a clean structure devoid of any such precipitates. Both the alloys were subjected to a thermomechanical treatment that included two stage swaging with intermediate heat treatments. 90W-7Ni-3Co alloy exhibited superior strength, but lower elongation to failure and impact toughness as compared to 89.6W-6.2Ni-1.8Fe-2.4Co alloy. Microstructure-property correlation was undertaken in order to elucidate the effect of enhanced W dissolution and fine W precipitates (in the matrix) on mechanical behaviour of the alloys investigated.

Effect of increasing Ti content on the phase, interface, dynamic mechanical properties and ballistic performance of W–Ti–Zr alloys

W2Zr intermetallic is an important reason for the brittleness of W–Zr binary system. When W–Zr alloys are used as the energetic fragment, the integrity of a projectile cannot be maintained under the explosion even propellant loading process, resulting in severe fracture of the projectile. Moreover, due to the strong atomic bonding in W2Zr intermetallic, the oxidation reactivity of the Zr atoms with oxygen in the air is significantly suppressed, limiting the effective energy release of W–Zr fragment under high-speed impacting process. In this study, based on the thermodynamic analysis, 30W-xTi-(70-x)Zr (wt.%) alloys were designed and prepared by powder metallurgy. It was found that the formation and stabilization temperature of W2Zr phase can be reduced by increasing the Ti content. The hard W-rich phase has changed from the coarse W2Zr particle to fine W2Zr precipitate and finally to the WTix solid solution with the increase of Ti content. Meanwhile, a semi-coherent interface between fine W2Zr precipitate and α matrix and even coherent interface between WTix and α matrix were formed, by which the intergranular fracture ratio between W-rich phases and α matrix was significantly decreased in the W–Ti–Zr alloys. Consequently, higher dynamic compressive strength and ductility of the W–Ti–Zr alloys were obtained by increasing the Ti content. The selected W–Ti–Zr alloys with high strength and proper failure strain exhibited good penetration and energy-releasing behaviors when they were used as reactive bullet launching at a velocity of about 1250 m/s. The relationship among the dynamic compressive strength, ductility and ballistic performance of the W–Ti–Zr reactive structural alloys was also discussed in detail.

Precipitation of supersaturated solute in H ion irradiated Fe-Au and Fe-Au-W alloys studied by positron annihilation spectroscopy

The effect of thermal aging of homogenized Fe-Au and Fe-Au-W alloys, irradiated at room temperature with hydrogen ions, was studied for an aging treatment at 300 °C for aging times up to 100 h. The aging behavior of the Fe-based alloys is compared to the results for pure Fe. The precipitation behavior of Au-rich and W-rich precipitates and its correlation to the H+ irradiation-induced defects is investigated by variable energy positron annihilation spectroscopy (VEPAS). The formation of open-volume defects after irradiation is monitored by an increase in the S parameter, while the recovery of the vacancy-like defects and the formation of precipitates are signalled by an increase in the W parameter. Au-rich precipitation continuously develops during long-term aging, as indicated by the increase in the W parameter. The change of the W parameter in the Fe-Au-W alloy is not only due to the effect of solute W on the Au precipitates, but also because of the interface of W-rich Laves phase with matrix.

Bimodal Microstructure Design of CrMnFeCoNi High-Entropy Alloy Using Powder Metallurgy

Single-phase equiatomic high-entropy alloy (HEA); CrMnFeCoNi, exhibits high strength and ductility at room temperature and low temperature due to the effect of twinning. In this study, a concept of a bimodal microstructure design for HEA using powder metallurgy was proposed. Microstructures of the sintered compact fabricated from HEA powder mechanically-milled using SUJ2 balls were analyzed by EBSD. A network structure of fine grains (Shell), which surrounded the coarse-grained structure (Core), was formed in the HEA compact. The hardness of the HEA with bimodal microstructure were higher than the compact fabricated from as-received HEA powder, and the network structure showed high hardness than Core phase. Furthermore, W-rich surface layer was formed on the HEA powder mechanically-milled using WC-Co balls owing to the transfer of WC-Co balls to the surface of HEA powder during mechanical milling. A network structure of the W-rich phase, which surrounded the HEA phase, was formed in the compact fabricated from the mechanically-milled HEA powder. In particular, the hardness of compact fabricated from HEA powder mechanically-milled using WC-Co balls was high due to the high concentration of tungsten and formation of Shell phase. These results indicate that developed method can control the microstructure of HEA; grain size and elementary diffusion distributions.

Microstructure, distortion characteristics and mechanical behaviour of NiB modified 90W-6Ni-4Co heavy alloys

In this work, the effect of NiB on densification, phase, microstructure, distortion and mechanical properties of conventionally sintered ternary 90W-6Ni-4Co heavy alloy has been investigated without altering (Ni+NiB)/Co ratio. No intermetallic phase was detected in the heavy alloys upon addition of NiB. Instead, the partial and complete exchange of Ni with NiB in 90W-6Ni-4Co has elicited relatively better densification (>99% theoretical), higher bulk hardness (HV3 ~ 389–396 VHN), higher hardness of matrix (~352 HV0.025) when the alloys were sintered at 1500 °C. In addition to W grains and matrix, the completely NiB-substituted heavy alloy (90W-6NiB-4Co) sintered at 1500 °C exhibits the occurrence of W-rich third phase which contains ~75 wt% of W. Although the samples prevented slumping at 1475 °C, elephant foot formation was found inevitable in the base composition (90W-6Ni-4Co) when sintering was carried out at 1500 °C. However, the decreased distortion parameter (from 24.8 to 8.5) with optimal NiB addition affirms the enhanced shape retention capability of 90W-3Ni-3NiB-4Co and 90W-6NiB-4Co heavy alloys. Room temperature compression test of WHAs sintered at 1475 °C was performed at a fixed strain rate of 0.1 s-1. No crack formation was observed in NiB containing samples up to 40% deformation. Moreover, the systematic addition of 3–6 wt% NiB resulted in lower coefficient of thermal expansion of NiB-containing heavy alloys in the temperature range of 400–600 °C.

High-temperature mechanical and thermochemical properties of NbMoTaW refractory high-entropy alloy coatings produced via Nano Particle Deposition System (NPDS)

In this study, we investigated the oxidation resistivity and mechanical properties of NbMoTaW refractory high-entropy alloy (HEA)-based coatings at high temperatures. The coating layers were produced using mechanically alloyed HEA powders via Nano Particle Deposition System (NPDS). The as-milled powder is comprised of W-rich BCC1 and NbMoTa-rich BCC2 phases. After the deposition process, the W-rich BCC1 phase remained, while NbMoTa-rich BCC2 phases were transformed into complex NbMo-rich and Ta-rich oxides. Consequently, the NbMoTaW RHEA composite coating exhibited outstanding oxidation resistivity and high nanoindentation hardness at high temperatures compared to that of commercial coating materials, possibly owing to the combination of the W-rich solid solution phase and internal oxides.

Strain and temperature contributions to structural evolution in a Re-containing 10% Cr-3% Co-3% W steel during creep

ABSTRACT A Re-containing 10% Cr-3% Co-3% W steel with low N and high B contents subjected to normalising at 1050°C and tempering at 770°C was crept at 650°C under the applied stresses ranging from 200 to 100 MPa with a step of 20 MPa. During creep both the temperature and the strain affect the tempered martensite lath structure that causes the thermal and strain-induced recoveries, respectively, and degradation of structure. Both these recoveries lead to premature failure. The microstructure in the gauge and grip portions of the crept samples were investigated separately to estimate the contributions of temperature and strain during creep to the evolution of tempered martensite lath structure of the Re-containing 10% Cr-3% Co-3% W steel. The W depletion from the solid solution was accelerated by creep strain during short-term creep. The lath width and particle sizes were stable during long-term ageing at temperature of 650°C in the grip portions of the crept samples. The width of martensitic laths was 350 nm after 13,600 h of long-term ageing. The creep strain facilitates the recovery of the structure causing the subgrain formation with a mean size of subgrains of 1.1 μm and particle coarsening in the gauge and neck sections. The precipitation of W-rich Laves phase particles was observed in both grip and gauge portions. The constant coarsening rate of M23C6 carbides was significantly lower during long-term ageing than that during creep, whereas the constant coarsening rates of Laves phase particles were comparable in both grip and gauge sections of the crept samples.

Study on microstructure and mechanical properties of W-Ni3Al alloys prepared by ball milling and two-step sintering

In this paper, W-Ni3Al alloys with the different Ni3Al contents were prepared via ball milling and two-step sintering processes. The relationship of Ni3Al contents, microstructural evolution, and mechanical properties of W-Ni3Al alloys were also clarified. The results show that the milled powder has a lamellar structure and cold welding phenomenon. This structure encloses a small amount of ethanol, and this causes an Al2O3 phase to form when it undergoes an oxidizing reaction of Ni3Al with oxygen in ethanol during ball milling and drying. The W-rich phase is the network structure, and this structure is finer and denser with an increase in Ni3Al contents as a result of the grain refining effect of Al2O3 particles and the densification effect of liquid sintering. Under a load, the Al2O3 particles at the interface of W/binder phases increase the resistance of crack growth and compressive strain, which improves the mechanical properties and deformability of W-Ni3Al alloys. The Ni3Al binder provides a new strategy for improving the mechanical properties of tungsten alloys.

Microstructure, mechanical properties, oxidation behaviors, and cutting performance of TiC0·5N0.5-X (X: W, Mo) cermet specimens prepared by spark plasma sintering

In this study we prepared a series of TiC0·5N0.5-W and TiC0·5N0.5-Mo cermet specimens with different W and Mo content by blending TiC0·5N0.5, W, and Mo powders with particle sizes of less than 1 μm and then spark plasma sintering the blended powders. We investigated the microstructures of the specimens using SEM-EDS and TEM-EDS, and examined their mechanical and oxidation properties at high temperatures. The microstructures of the specimens were unique: each Ti(C, N) particle in the TiC0·5N0.5-W cermet was surrounded by a W-rich phase, and each Ti(C, N) particle in the TiC0·5N0.5-Mo cermet was surrounded by an Mo-rich phase. The TiC0·5N0.5-(20–70) mass% W and TiC0·5N0.5-(20–40) mass% Mo cermet specimens exhibited a much higher microvickers hardness than the TiC0·5N0.5 and HTi10 (ISO K10) WC-Co cemented carbide specimens in a temperature range from room temperature to 1273 K. Further, the TiC0·5N0.5-(50–70)mass% W and TiC0·5N0.5-(20–40)mass% Mo cermet specimens exhibited much better oxidation resistance than the HTi10 specimens at 973 K. Lastly, the cutting tip specimens prepared using the TiC0·5N0.5-70mass% W and TiC0·5N0.5-60mass% Mo cermet specimens exhibited much higher wear resistance than commercially available HTi10 cutting tips when used to cut S32750 super-duplex stainless steel and Inconel 718 alloy round bars, two materials known for their high cutting resistance.

Metallurgical and Mechanical Properties of Laser Cladded AlFeCuCrCoNi-WC10 High Entropy Alloy Coating

In spite of excellent corrosion resistance, good ductility and low cost of AISI 316 austenitic stainless steel, the low hardness and poor mechanical characteristic of material restricts its applicability in several industrial services. To improve the mechanical properties AlFeCuCrCoNi-WC10 high-entropy alloy coatings were deposited via laser cladding on austenitic stainless steel AISI 316 substrate. The influence of WC on phase constituents, microstructure, microhardness and elemental distribution were investigated using X-ray diffractometry, optical microscopy microhardness tester and FESEM-EDS (Energy Dispersive Spectroscopy), respectively. The XRD peaks revealed that as clad AlFeCuCrCoNi-WC10 multiple principal element alloy coating composed of BCC, FCC and W-rich phase. The cladding zone microstructure is mainly consisting of fine-grained non-directional and equiaxed crystals away from the base material and columnar grains near the base material. The energy dispersive spectroscopy indicated segregation of W and Cr in the interdendritic region. However, other elements of the multiple principal element alloy are observed to be uniformly distributed throughout the cladding. The microhardness of the AlFeCuCrCoNi-WC10 (670 Hv0.5)high entropy alloy coating was 4.5 times greater than that of substrate AISI-316.

Nucleation of W-Rich Laves Phase Nanoparticles in Tempered Martensite Ferritic Steel During Long-Term Aging at Elevated Temperature.

The nucleation of W-rich Laves phase nanoparticles was studied during long-term aging at elevated temperature in tempered martensite ferritic steels (TMFS). The TMFS was fabricated by vacuum induction melting (VIM) process. The long-term aging tests are interrupted at various stages to simulate the different level of nucleation of intermetallic phases. In the present work, we employ scanning electron microscopy (SEM), Auger electron microscopy (AES), and transmission electron microscopy (TEM) to study the formation nucleation of Laves phase particles. We investigated the preference of Laves phase particles to nucleate next to M23C6 micrograin boundary carbides due to the segregation of W from the matrix to the micrograin boundaries.

Microstructures in a Nb-Cr-V-W-Ta high entropy alloy during annealing

A Nb-Cr-V-W-Ta high entropy alloy has been subjected to annealing treatment at 600, 700 and 800 °C in air for 6 hours. Five different phases have been identified based on their composition in the as received condition. The annealing treatment does not alter the phase analysis and compositions except for the W-rich phase where minor changes in the composition have been observed. This is considered as an experimental evidence of sluggish diffusivity associated with HEAs. Absence of phase transformation during the heating and the minimal changes in observed compositions of the phases is an indication of the resistance to diffusion offered by the elements of the high entropy alloy. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and color X-ray elemental mapping have been used to conduct this research.