查看更多>>摘要：? 2022Tungsten carbide (WC) is a well-established material used in glass molding field due to its low thermal expansion and high compressive strength at elevated temperatures. During glass molding process, the WC mold has to withstand thousands of thermo-mechanical coupled interactions in the aerobic environment. Understanding the degradation mechanism of WC substrate during precision glass molding is very important for the design and preparation of protective coatings and the optimization of glass molding process. In this study, surface failure analysis of WC substrate was carried out using barrel compression test and ball-to-disk friction test. The microstructures, element compositions, surface morphology of the WC substrates were measured by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and white light interferometer (WLI). Damaging phenomena such oxidation, interdiffusion, spallation, glass sticking, and surface roughening on the WC substrate were observed. The experimental results showed that the WC substrate degraded very rapidly at above 600 °Cand air environment. The fundamental degradable reason of WC substrate is the oxidation, which directly leads to the decrease of the material strength, the aggravation of the wear, occurring of the glass sticking, and the increase of surface roughness. Furthermore, the WC mold microhole array without protective coatings can be used to fabricate the glass microlens array in a suitable glass molding environment. This work provides engineering guidance for the fabrication of glass optics during glass molding process.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, diamond-reinforced Cu matrix composites were successfully prepared by introducing diamond into Cu melts based on Ti-diamond (D)-Si reaction. When Ti[sbnd]D mixture is added into Cu melts, TiC will be immediately synthesized on the surface of the diamonds and tend to connect with each other to form a network structure, which will lead to the formation of the Cu-Ti-D refractory block. When Si is added into Ti[sbnd]D, Ti[sbnd]Si reaction will precede Ti[sbnd]D reaction and form Ti5Si3. In this case, the formed TiC will be prevented from forming a continuous network. As a result, the diamond with the TiC shell will be effectively dispersed into Cu melts. It is found that the effect of Ti and Si on the microstructures of the prepared Cu-Ti-Si-D composites is not independent but related to each other, and the optimal mass ratio of Ti-Si-D is in the range of 2:(0.83–1.11):(1–1.25).
查看更多>>摘要：? 2022 Elsevier LtdIn this study, we designed and prepared (FeCoNi)88-x(AlTi)12Mox high-entropy alloys (HEAs) with good comprehensive properties by vacuum arc melting technology. The influence of Mo content on the microstructure, mechanical properties, and tribological properties of the HEAs were systematically studied. The results showed that all HEAs in this study are simple fcc solid solution structure, all HEAs are composed of γ + γ' phase, and they are in a coherent relationship. The tensile test results show that all the HEAs exhibit excellent strength-ductility combination, and the final tensile fracture mechanism is a ductile fracture. Mo1.0 HEA has the best comprehensive mechanical properties, with the yield strength, tensile strength, and elongation of 980 MPa, 1260 MPa, and 34.5%, respectively. The reciprocating friction and wear test results show that the HEAs have excellent friction and wear properties. Compared with the four HEAs, the order of friction and wear properties from good to poor is Mo1.0 HEA, Mo1.5 HEA, Mo0.5 HEA, and Al6Ti6 HEA. The wear mechanisms of all HEAs are abrasive wear and oxidation wear, as well as the Al6Ti6 and Mo1.0 HEAs also have delamination wear.
查看更多>>摘要：? 2022 Elsevier LtdThe method of adding the initial elements greatly affects the structure and mechanical properties of a tungsten alloy. In this study, the 90(W[sbnd]20Ta)–Ni–Fe alloy was prepared by the direct addition of elements and W[sbnd]Ta pre-alloying. The element diffusion and phase transformation behavior under different states are discussed. The matrix phase to segregate into lumpy Ni3Ta and Fe2Ta phases after sintering by directly adding tantalum, which deteriorated the structure of the alloy. The pre-alloyed group first formed body-centered cubic W[sbnd]Ta solid solution with fine particles through mechanical milling. During the sintering process, the tantalum element gradually precipitated to form the acicular Ni3Ta phase, which improved the uniformity of the microstructure. Through W[sbnd]Ta pre-alloying, the main failure mode transformed from an interfacial fracture to a trans-granular fracture, which increased the strength of the alloy by 130%.
查看更多>>摘要：? 2022 Elsevier LtdIn this study, the evolution of microstructure and crystallographic texture of two-phase tungsten heavy alloy (almost pure tungsten embedded in nickel?tungsten?iron matrix) during cold rolling was investigated systematically. Electron back scatter diffraction studies reflected that the matrix phase accommodates more strain in the early stages of deformation and that as deformation progresses, the matrix phase exhausts its work hardening ability, resulting in the onset of micro-shear band formation. The tungsten phase on the other hand showed the presence of large orientation gradients accompanied with significant flattening and elongation of grains. At higher rolling reductions (effective true strain of ?2.66), extensive shear bands spanning across several tungsten particles and the matrix were observed in the microstructure, which in turn had implications on the evolution of the crystallographic texture. It was observed that weak αb. c. c. (<110>∥RD) and γ fiber (<111>∥ND) emerge in tungsten at low to intermediate rolling reductions, and that αb. c. c. fiber strengthens much more than γ fiber at higher rolling reductions with prominent intensity at rotated cube position. For the matrix phase, a weak beta fiber (fiber connecting the brass {011}<211>, copper {112}<111>, and S {123}<634> orientations in the Euler space) was observed at low to intermediate rolling reductions, followed by strengthening of Goss and Brass orientations at higher rolling reductions.
NSTL
Elsevier