查看更多>>摘要：Hardness is defined as the resistance of a material to localized plastic deformation. Owing to their nondestructive nature, static indentation hardness tests are widely used in industry. Hardness testing is particularly useful for the mechanical characterization of materials that cannot be tested otherwise, e.g. powdered materials. In this study, challenges related to Vickers microindentation hardness testing of hard brittle cast tungsten carbide (CTC) powders were extensively investigated. Test load was optimized to obtain sufficiently large crack-free indentations allowing for precise measurement of the diagonal lengths. The influence of the operator and imaging technique on the measured hardness value was evaluated. Topography of residual imprints was investigated using atomic force microscopy (AFM) and a systematic and operator bias-free method to locate the indentation vertexes was developed. Results suggested that measurement variability introduced by AFM scanning and post-processing was as low as 3.1% and 1.3% with respect to the mean hardness value, respectively. Since the variability due to the measuring system can be isolated, the homogeneity of powders can be reliably evaluated from the hardness measurements thus obtained.
查看更多>>摘要：The fundamental reason for analysing the microstructure of a material is to achieve a higher degree of under -standing of the microstructural mechanisms governing its mechanical properties and to use this knowledge as a tool for further developments. In this study, Ti(C,N)-based cermets were sinter-HIP'ed at different temperatures, the mechanical properties of the samples were measured and the obtained microstructures were analysed by light optical and electron microscopy. A tailored python-based image processing tool was developed to combine and analyse the microstructures obtained by EBSD and BSE. The goal of the study was to determine the influence of the sintering temperature on the microstructural features of the cermets.
查看更多>>摘要：Nickel-coated molybdenum metal core-shell (Mo@Ni) nanopowder was prepared by a heterogeneous nucleation-thermal reduction method and then used as the metal binder phase in (W,Ti)C ceramic materials. (W,Ti)C/ Mo@Ni/Co cermet was prepared by dual-power spark plasma sintering. The effects of sintering rate and sintering temperature on the microstructure and mechanical properties of (W,Ti)C/Mo@Ni/Co cermets were investigated. Results showed that when the sintering rate was 400 C/min and the sintering temperature was 1325 degrees C, the (W, Ti)C/Mo@Ni/Co tool material had the best comprehensive mechanical properties, with a Vickers hardness of 17.44 +/- 0.23 GPa, a fracture toughness of 11.27 +/- 0.46 MPa.m(1/2), and a flexural strength of 1450.23 +/- 23 MPa. The core-shell structure of Mo@Ni made full use of the solid solution characteristics of the Mo-Ni binary alloy and produced a solid solution in situ without liquid phase diffusion, which accelerated the sintering rate. The use of Mo nanopowder took advantage of its small-size effects and high surface energy, which reduced the temperature at which the solid solution effect began and reduced the sintering temperature. The combination of these two aspects was used to prepare a (W,Ti)C cermet with good strength and toughness by low-temperature rapid sintering. Low-temperature and ultrafast sintering are helpful to reduce the energy consumption in the preparation of cermets.
查看更多>>摘要：The static and dynamic properties of several bulk liquid 4d transition metals at thermodynamic conditions near their respective melting points have been evaluated by using ab-initio molecular dynamics simulations. The calculated static structure factors show an asymmetric second peak followed by a more or less marked shoulder which points to a sizeable amount of icosahedral local order. Special attention is devoted to the analysis of the obtained longitudinal and transverse current spectral functions and the corresponding dispersion of collective excitations. For some metals, we have found the existence of two branches of transverse collective excitations in the second pseudo-Brillouin zone. Finally, results are also reported for several transport coefficients.
查看更多>>摘要：WC-Co composites comparable to titanium in thermal expansion coefficient can be used as wear-resistant coatings, extending the applications of titanium alloys. This study aims to investigate the effect of laser power on the quality of composite coatings on the Ti-6Al-4 V substrate, and to study the phase constituents comprehensively, microstructural evolution, microhardness, and wear behavior of composite coatings. The experimental results show that there is a good metallurgical bonding between the WC-Co composite coatings with high densification and the substrate. Furthermore, a considerably high microhardness up to 1536 HV0.5, and a wear rate of 1.5 g/h were achieved owing to the synergistic effect of excellent metallurgical bonding and fine microstructures of the composite coating under laser power of 2000 W. Based on the experimental results, the process-structure-properties relationship of laser cladded WC-Co composite was established. It is expected to be applied to improve the wear resistance of petroleum titanium alloys in deep and ultra-deep wells.
查看更多>>摘要：Aiming to explore a sustainable process for tungsten extraction from wolframite concentrate, the digestion behavior and mechanism of wolframite in HCl solution at atmospheric pressure were firstly investigated in this work. The results showed that the digestion efficiency of wolframite reached 99.3% at the optimum condition: particle size of D(95) = 20 mu m, stirring intensity of 250 r/min, reaction temperature of 90 degrees C, HCl stoichiometric ratio of 3.0, liquid to solid ratio of 3:1, and duration of 4 h. In the initial stage of digestion, tungsten was mainly dissolved into HCl solution, when the tungsten dissolution reached balance, solid H2WO4 layers were formed on the particle surface. The accumulation of Fe2+ and Mn2+ in HCl solution reduced the digestion efficiency of wolframite. The process of atomization-oxidative thermal decomposition is feasible for the recovery of Fe and Mn and recycling of HCl from the mother solution of digestion. Additionally, it was showed that the digested product had an excellent leachability of tungsten in NH3 center dot H2O solution with WO3 leaching efficiency above 99.5%, and the (NH4)(2)WO4 solution was qualified for ammonium paratungstate (APT) production. The wrapping of wolframite by quartz, as well as the solid H2WO4 layers covering on wolframite particles, is a crucial factor for the incomplete digestion. This work has the potential to develop a novel technique for tungsten extraction from wolframite concentrate bypassing the alkali leaching process.
查看更多>>摘要：The hot deformation behavior of nanostructural oxide dispersion-strengthened (ODS) Mo alloy was investigated in the temperature range of 1200-1500 degrees C and strain rate range of 0.001-1 s(-1) with a constant strain of 0.50 by analyzing constitutive equations, hot processing maps, and microstructure evolution. The results show that the flow behavior is greatly affected by the deformation temperatures and strain rates, exhibiting typical hardening, softening, and steady stages. The constitutive equation is established, which can predict the flow stress precisely. The stress exponent n and the apparent activation energy Q are estimated to be 5.44 and 384.26 kJ.mol(-1), respectively, revealing that the deformation mechanism is dominated by the dislocation climb. Furthermore, the hot processing maps of ODS Mo alloy are developed based on the dynamic materials model, presenting two stability zones of 1350-1450 degrees C/0.001 s(-1) and 1450-1500 degrees C/0.1-1 s(-1). By observing microstructures, dynamic recovery and dynamic recrystallization occur in the stability zone 1500 degrees C/1 s-1, and the mechanism of the stability zone 1400 degrees C/0.001 s(-1) is dominated by dynamic recovery and grain growth.
查看更多>>摘要：W-Zr-C alloy with nanoscale ZrC particles dispersion was fabricated via powder metallurgy method using W, ZrH2 and nanoscale C powders as starting materials. The average size of in-situ formed particles is 55 nm. The smaller particles in the grain interior are dominantly ZrC particles. Zr decomposed from ZrH2 can also react with impurity oxygen to form ZrO2 particles and reduce the detrimental effects of oxygen on grain boundaries. The asswaged W-Zr-C alloy is ductile at 200 degrees C, and the ultimate tensile strength and total elongation (TE) at 300 degrees C are 643.5 MPa and 23.5%, respectively. After annealing at 1400 degrees C, the UTS at 300 degrees C of W-Zr-C alloy is still as high as 611.4 MPa and the TE is 33.2%. The recrystallization start temperature of the as-swaged W-Zr-C alloy is between 1400 and 1500 degrees C, which is 200 degrees C higher than that of pure W. The in-situ formation of nanoscale second-phase particles via the dissolution-precipitation mechanism provides a feasible strategy for improving the low-temperature toughness and high-temperature stability of tungsten alloys.
查看更多>>摘要：TiC reinforced titanium matrix composites are promising for advanced applications. In this study, the Ti-30MoxTiC composites with the TiC content of 0, 0.5, 2.5 and 5 wt% were prepared using a powder metallurgy method. The results showed that TiC in Ti-30Mo exhibited a stoichiometric ratio of Ti to C over 1:1, along with demonstrating a semi-coherent lattice relationship with the beta-Ti matrix lattice. Further, the excess C element diffused from the TiC particles to the matrix at the interface with large solid solubility, thus, promoting the sintering densification. Compared with Ti-30Mo, the composites with TiC addition revealed much higher relative density. Increasing the TiC content could increase the matrix microhardness and elastic modulus, however, the ultimate tensile strength and elongation were decreased. The mechanical properties were improved owing to the cooperative effect of densification, TiC particle reinforcement, solid solution of Mo and C elements and semi coherent interface. As a result, the Ti-30Mo-0.5TiC composite presented an excellent combination of properties: matrix microhardness of 294 HV0.3, ultimate tensile strength of 820 MPa, elongation of 6.5% and elastic modulus of 112 GPa.
查看更多>>摘要：To study the penetration ability of tantalum-tungsten alloy rod penetrator into armor plate and clarify its deformation and failure behavior in the process of penetration, the experimental and numerical study of tantalum-tungsten alloy rod penetrator penetrating armor plate was carried out in this paper. The results show that the penetration efficiency of tantalum-tungsten alloy rod penetrator and tungsten alloy rod penetrator into 30CrMnMoRE armor plate is equivalent in the range of impact velocity from 1100 m/s to 1700 m/s, whereas the penetration efficiency per unit specific kinetic energy of tantalum-tungsten alloy rod penetrator is higher than that of tungsten alloy rod penetrator when the impact velocity is greater than 1500 m/s. The ultimate penetration velocity of tantalum-tungsten alloy rod penetrator with length-to-diameter ratio of 6.25 and diameter of 8 mm to 30CrMnMoRE armor plate with the thickness of 60 mm is about 1695 m/s. At the moment of impacting the target plate, the velocity of the head of the tantalum-tungsten alloy rod penetrator decreases sharply, but the velocity at the rear of the penetrator remains basically unchanged. In the process of penetration, the head of the penetrator deforms and flows outward under the huge impact pressure, and finally, the length of the penetrator is shortened to zero, forming a barrel-like structure, but the barrel structure still has a certain penetration ability. This study can help to further understand the flow characteristics and penetration ability of tantalum-tungsten alloy rod penetrator in high-speed penetration.
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Elsevier