查看更多>>摘要：Nano-scaled WC powder is an important material for preparation of ultrafine or nano-grained WC-based cemented carbides via powder sintering method. In this paper, nano-scaled WC powder was prepared based on traditional carbothermic reduction method. First, the mixture of WO3 and carbon were reacted at 1000 degrees C to remove all the oxygen atom. Then, according to residual carbon content in the deoxidation products, the gasphase (by 90%H-2 + 10%CH4, at 900 degrees C) or solid-phase carburizing process (at 1100 degrees C) was selected to prepare WC powder, respectively. The results indicated that the use of nano carbon black in first stage could provide a large number of dispersed nuclei, and meanwhile, a low reaction temperature was beneficial to inhibit the growth of product particles. The thermodynamic calculation, reaction behavior and nuclei growth behavior in deoxidation and carbonization stages were studied in detail. As the C/WO3 ratio was 2.5 and 3.8, the WC powder with total carbon content of 6.23% and 6.19%, particle size of 80.29 nm and 95.24 nm, and BET value of 3.88 m(2)/g and 4.25 m(2)/g was obtained by this method, respectively.
Frisk, KarinSoria-Biurrun, TomasSanchez-Moreno, Jose M.
13页
查看更多>>摘要：The liquid phase formation temperatures of the quinary system W-C-Co-Fe-Ni with a ratio of Fe:Co:Ni = 40:20:40 were determined by means of DSC analysis. Besides, the experimental C-window of this system with a binder content of 14.3 +/- 2 wt% is accurately defined. Based on the experimental results, a thermodynamic modelling is carried out using the CALPHAD approach. Temperature-composition sections of the W-C-Co-Fe-Ni system with different binder contents are calculated to verify the rationality of the present modelling. There is a good correlation between the experimental and calculated results showing that the experimental data can be well reproduced by the present modelling.
查看更多>>摘要：Tungsten carbide cobalt hardmetals are commonly used as cutting tools subject to high operation temperature and pressures, where the mechanical performance of the tungsten carbide phase affects the wear and lifetime of the material. In this study, the mechanical behaviour of the isolated tungsten carbide (WC) phase was investigated using single crystal micropillar compression. Micropillars in two crystal orientations, 1-5 mu m in diameter, were fabricated using focused ion beam (FIB) machining and subsequently compressed between room temperature and 600 degrees C. The activated plastic deformation mechanisms were strongly anisotropic and weakly temperature dependent. The flow stresses of basal-oriented pillars were about three times higher than the prismatic pillars, and pillars of both orientations soften slightly with increasing temperature. The basal pillars tended to deform by either unstable cracking or unstable yield, whereas the prismatic pillars deformed by slip-mediated cracking. However, the active deformation mechanisms were also sensitive to pillar size and shape. Slip trace analysis of the deformed pillars showed that { 1010} prismatic planes were the dominant slip plane in WC. Basal slip was also activated as a secondary slip system at high temperatures.
查看更多>>摘要：Due to the importance of wear behavior in tungsten base alloys, this issue has rarely been considered. The present study deal with the effect of Y2O3, its amount and sintering on the microstructural and wear behavior of W-Ni-Cu-Y2O3 alloys. After 25 h of mechanical milling, alloys containing 0-0.6 wt% of yttrium oxide nano-particles were prepared by conventional (1400 degrees C, 30 min) and spark plasma sintering (1100 degrees C, 4 min). The composition, structure and morphology of the milled powders were investigated by SEM and XRD. Then, the microstructure, density, micro-hardness and wear behavior of the composite alloys were evaluated. The result of milling in the presence of yttria nanoparticles is a homogeneous distributed fine-grained powder whose crystallite size has been reduced from 34 to 24 nm. The addition of yttrium oxide nanoparticles caused microstructural modification including grain refinement, (Ni,Cu) binder phase distribution and reduced contiguity of the tungsten grains. Spark plasma specimens, although sintered at lower temperature, exhibited enhanced properties due to the finer grains (less than 4 mu m) compared to conventional sintering. The spark plasma sintered alloys with 0.6 wt% of Y2O3 and an average grain size of 2.56 mu m were found to have maximum relative density (96.9 g.cm(-3)), highest microhardness (504 HV) and minimum wear volume (9.5 x 10(-5) cm(3)) and rate (0.064 x 10(-7) cm(3) .N-1 .m(-1) ). Also, the coefficient of friction was lower and decreased with increasing of yttria for these specimens. Delamination, cracking, and brittle wear behavior in conventional sintered have turned into plastic deformation in spark plasma specimens.
查看更多>>摘要：By the powder metallurgy, as well as subsequent forging and annealing processes, a series of W-3Re-HfC (WRH) composites were fabricated successively. Microstructure and performance of WRH composites were investigated comparatively. It is found that the sintered, forged and annealed WRH composites are consistently made up of WRe matrix, HfO2 and HfC second phase particles. The larger HfO2 particle is derived from the oxidation of HfH2 powder, playing an important role in purifying grain boundary and refining grain of matrix. The smaller HfC particle inside W-Re grains has a dispersion reinforcement effect. The forged WRH composites can obtain the highest relative density (99.9%), the micro-hardness (534.1 HV) and ultimate tensile strength (758 MPa), which is ascribed to the refinement of grains and dispersion strengthening. Although the performance of annealed WRH composites has a slight drop, an excellent interfacial matching between second phase particles and W-Re matrix can be produced, which facilitates to gain a better interfacial strength and homogenized microstructure.
查看更多>>摘要：As a highly controversial candidate superhard material, tungsten tetraboride (WB4) has attracted widespread attention due to its desirable mechanical properties. Here, single phase WB4 ceramics and WB4-based materials containing tantalum (Ta) have been successfully synthesized by a high-pressure reaction at 5.0 GPa and 1400 degrees C-3000 degrees C. We systematically investigated the effect of processing temperature on the phase stability of WB4 and doping with different amounts of Ta on mechanical properties and thermal stability. The results confirm that increasing treatment temperature is beneficial to the synthesis of the WB4 phase, and high pressure can effectively inhibit the decomposition of WB4. Additionally, the hardness value of the WB4-based ceramic is found to decrease with the increase of the doped tantalum content. However, the hardness of WB4 is less than W0.9Ta0.1B4 (10 at. % Ta), indicating that a small amount of Ta doping is positive for the mechanical properties of WB4. The results show that the W0.9Ta0.1B4 ceramic synthesized at a temperature of 2800 degrees C and 5.0 GPa has excellent overall properties. Its Vickers hardness is 42 GPa (0.49 N), and its oxidation resistance temperature is 542 degrees C, which is much higher than the hardness and thermal stability of tungsten carbide (WC). This work can provide practical guide for the design of new transition metal boride superhard materials, and point out the visual direction for exploring the next generation of superhard materials.
查看更多>>摘要：The cemented carbides have been gradually applied for marine equipment due to their high wear resistance, while the corrosive impact of seawater has a considerable effect on its wear performance. In this paper, the effect of Ni concentration on the resistance to corrosion, tribological properties, and microstructure of the cemented carbides based on tungsten carbide (WC) with metal binders sliding against silicon carbide (SiC) in seawater was investigated. The results showed that Ni element has a positive effect on the resistance to corrosion of cermet WC, and the resistance to corrosion is the best when the concentration of Ni element is 9% (WC-9Ni). In addition, the coefficient of friction (COF) of the WC-hNi/SiC tribopair first decreased and then increased with the increase of Ni concentration, and the quite low steady COF of WC-9Ni is observed. The wear mechanism of the WC-hNi balls is mainly abrasive wear, and the corrosion wear is mild. Furthermore, the wear rate of WC-9Ni is the lowest at different rotational speeds, which has great application potential in seawater hydraulic components.
NSTL
Elsevier