International Journal of Refractory Metals & Hard Materials最新文献

The high pressure-high velocity oxy liquid fuel (HP-HVOLF) is a current industry-adopted thermal spraying technique for developing high melting point powder coating over surfaces. In the current manuscript, the rare earth (La₂O₃/CeO₂/Er₂O₃–0.3 wt%. each) doped and without rare earth doped carbide (WC-10Co-4Cr) coatings have been deployed on stainless steel (SS410) via HP-HVOLF process. The comparison among the properties of the substrate, without rare earth coating and rare earth oxides doped coatings have been characterized by conducting mechanical, microstructural, and slurry jet erosion analysis. The results show that the hardness, modulus of elasticity, and flexural strength of the cermet coating are considerably higher for rare earth-doped coatings than those without rare earth-doped coatings and substrates (SS410). The EDX (energy dispersive X-ray spectroscopy) has recognized the occurrence of different elements on the surface together with rare earth. Moreover, its compounds such as Co₃W₃C and W₂C were inveterate using X-ray diffraction (XRD) measurements. The porosity level of the rare earth doped, and un-doped coatings are obtained to be less than 1 % and≥1 to ≤2 % respectively. Moreover, the rare earth-doped cermet coated surface shows hydrophobic behavior with a maximum water contact angle (WCA) of ≈129.4°. Furthermore, the slurry jet behavior of rare earth doped coating shows high wear resistance as compared to without RE doped coatings, indicating its potential for robust performance under erosive conditions.

Metal oxycarbide solid solution possesses an extensive potential applications due to its remarkable physical features. In this paper, TaC_xO_1-x solid solution is successively and controllably synthesized by carbothermal reduction of Ta₂O₅. Based on the thermodynamic calculation, the possible reactions under different conditions in the carbothermal reduction process were analyzed, which provides theoretical guidance for controllable regulation and optimization of carbon thermal reduction process. The effects of carbon content, sintering temperature, and holding time on the synthesis of TaC_xO_1-x solid solution were investigated and the ideal process parameters for the synthesis of single-phase solid solution were identified. A single-phase solid solution with a carbon‑oxygen ratio close to 1:1 can be created as a soluble anode if the synthesis temperature is 1500 °C, the holding period is 6 h, and the molar ratio of C/Ta is 3.42. Moreover, the process feasibility of preparing metal tantalum by electrolysis of tantalum-based soluble anode is discussed, which provides a new method for metal tantalum preparation.

In this work, coarse-grained WC–6Co hardmetals featuring dual-scale and plate-like structures were successfully fabricated via conventional powder metallurgy process using W, ultrafine WC, Co and carbon black as raw materials. The investigation focuses on the effects of two critical factors, sintering temperature and ultrafine WC powder content, on the microstructures, densities, and mechanical properties. The results demonstrate that increasing the sintering temperature accelerates the growth of WC grains via 2D nucleation growth mechanism, thus enhancing the plate-like structure of WC grains. The addition of ultrafine WC powder reduces the mean WC grain size and eliminates the preferential orientation of WC grains because of its separating effect on coarse WC grains. Moreover, the dual-scale and plate-like structures can be achieved with sufficient ultrafine WC content (≥ 20 wt%) and adequate sintering temperature (≥ 1500 °C). Notably, the coarse-grained WC–6Co alloy sintered at 1550 °C with the addition of 20 wt% ultrafine WC powder exhibits good comprehensive mechanical properties: hardness of 1493 ± 7 HV30, transverse rupture strength of 2698 ± 58 MPa and fracture toughness of 16.93 ± 0.65 MPa·m^1/2.

One of the key strategies to enhance the performance of composites is the implementation of a lamellar structure, which has demonstrated remarkable success. In this study, an ultrathin lamellar WCu composite was fabricated using a combination of freeze-casting and infiltration techniques. Compared to the homogeneous WCu composite, the aligned structure in this composite provides continuous conductive channels for electrons, reducing interface scattering. Additionally, the ultrathin lamellae offer exceptional load-bearing capacity. These synergistic effects result in both superior strength and enhanced electrical conductivity. This innovative design strategy for WCu composites presents promising potential for advancing the development of next-generation composite materials.

In this study, Ti-xNb (x = 0–40 wt%) alloys produced by the powder metallurgy were borided with the aim of clarifying the effect of Nb on the structural and mechanical properties of the boride layer. After smearing the paste prepared from nano boron powder on the surfaces of the alloys, boriding was conducted at three different temperatures (900, 1000 and 1100 °C) for 8 h in a vacuum atmosphere. Unlike those formed at 900 °C, boriding temperatures of 1000 and 1100 °C provided thicker and homogenous boride layers. However, the boriding temperature of 1100 °C induced cracking within the boride layer of the Ti40Nb alloy. For these reasons, the optimum boriding temperature was determined as 1000 °C. Increase in the Nb content not only increased the fraction of β-Ti phase in the microstructure of the sintered alloy at the expense of α-Ti, but also induced NbB₂ in the structure of the boride layer along with TiB₂. While Nb-poor α-Ti grains favoured the growth of TiB₂, TiB₂·NbB₂ mixture preferentially developed over the Nb-rich β-Ti grains. As the result of this, the hardness of the boride layer tended to decrease with increasing Nb content of the substrate. For example, the average hardness of the boride layers formed on Nb-free Ti and Ti40Nb alloy were measured as ∼2674 HV_0.025 and ∼ 2460 HV_0.025, respectively. But regardless from the hardness, the boride layers provided a good protection for the underlying substrates against dry sliding contact and triggered abrasive wear on the contact surface of the counterface (WC-Co ball). The presence of NbB₂ in the boride layer led to a reduction in abrasive wear of the counterface. This finding revealed that in any wear-related application, where borided Ti alloys were intended to be used, it is better to choose high Nb-containing Ti alloys instead of α-Ti to minimize the wear of the tribo-couple via reducing the abrasion at the counter body.

In this study, WC-12Co and WC-12CoCrMo cemented carbides were prepared by the hot press sintering technique and subsequently post-treated by applying the hot isostatic pressing (HIP) technique. The effects of the binder phase and post-HIP treatment on the microstructures and mechanical and tribological properties of the two cemented carbides were investigated for ambient temperature use. The hardness and wear resistance of WC-12CoCrMo were increased by 87 % and two orders of magnitude compared to WC-12Co, respectively. The post-HIP did not affect the wear mechanism of cemented carbide. The binder phase was the fundamental factor in changing the wear mechanism. Post-HIP is a more viable option to enhance mechanical properties for complex carbide systems, as it promotes solid-state chemical reactions and results in an increased precipitation of secondary phases.

With the rapid development of the photovoltaic industry, tungsten alloys have been selected to replace the high‑carbon steel to fabricate the busbars for diamond wire saws due to their superior mechanical properties, and the La₂O₃ doped tungsten alloy has been widely used. However, the yield of eligible W alloy wires is not very high due to serious wire breakage problems during the production process, especially in the solid-liquid mixing route. To discover the possible reason, the commonly produced lanthanum tungstate (La₃₀W₁₇O₉₆) in the solid-liquid mixing route has been systematically studied in the work, and its possible influence on the mechanical properties is also explored. It is found that the La₃₀W₁₇O₉₆ leads to the formation of brittle second phases at grain boundaries (GBs), which weakens the intergranular bonding, resulting in a significant decrease in the compressive strength of tungsten alloys, manifested as intergranular fracture. Transmission electron microscopy (TEM) analysis reveals that these second phases are consisted of polycrystalline La₆W₂O₁₅, La₂W₃O₁₂ and amorphous states, and the La₃₀W₁₇O₉₆ can decompose into a more stable structure during sintering. This work highlights the destructive effect of La₃₀W₁₇O₉₆ on the intrinsic properties of tungsten alloys and provides a new perspective for solving the problem of tungsten wire breakage.

Additive manufacturing (AM) is a valuable tool for the fabrication and repair of refractory parts such as molybdenum alloys. Cracking is a common defect encountered during AM processing of refractory parts, that is generally associated with the segregation of light elements to grain boundaries which affect grain boundary cohesion and, ultimately, affect the final performance of the part. Similarly, because of the high melting points of refractory metals, lack-of-fusion defects are also common. The effect of build substrate and small alloying additions on suppression of defects during multilayer builds was investigated using directed energy deposition (DED) printing. Identical sample matrices were printed on three different build substrates: molybdenum (Mo), commercially pure titanium (Cp-Ti), and 316 stainless steel (316). Twenty-six usable samples were produced. Samples were cross sectioned, polished, and were characterized for total cross-section defect area. Additionally, samples from each substrate material were analyzed for grain boundary oxygen content. The strongest defect suppression, producing crack free material, was observed in samples printed on a Cp-Ti build substrate with a ten atomic percent addition of titanium in the molybdenum powder feed. The part quality was enhanced due to three factors: 1) the moderation of thermal diffusivity through a change in build plate material, 2) the suppression of light element segregation via increased solubility through titanium addition, and 3) a lack of brittle phase formation due to metallurgical compatibility of the build material with the build substrate. Analysis of defect area versus dimensionless number, π₁, shows that increasing π₁ reduced defects throughout the part.

Nitrogen-valent (NV) color centers exhibit unique quantum and physical properties, making them valuable in advanced scientific research and technical fields. Type IIa diamonds are ideal carriers for NV⁻color centers. Therefore, the development of methods for incorporating these centers into diamonds is a key research focus. To enhance the preparation techniques, this study introduces a donor impurity element doping method for the successful synthesis of type IIa diamonds containing only NV⁻color centers. Optical microscopy and scanning electron microscopy characterizations revealed that the introduction of H–S–O impurity elements hindered the synthesis of high-quality diamonds. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy analyses indicated that incorporating H–S–O into the diamond lattice led to the successful preparation of H–S–O multi-doped IIa diamonds. Photoluminescence results confirmed that these H–S–O multi-doped type IIa diamonds exhibited only NV⁻ color centers. Additionally, the effects of H–S–O and Al on diamond properties and growth characteristics were thoroughly analyzed through Raman spectroscopy and residual stress analysis. This study provides valuable insights into the origins of natural IIa diamonds and introduces a vital method for preparing NV⁻color centers in functional IIa diamonds.