International Journal of Refractory Metals & Hard Materials最新文献

Solid-solutioning in multicomponent ultra-high temperature ceramics (MC-UHTCs) has been shown to improve their thermo-mechanical properties unattainable by conventional UHTCs. Herein, MC-UHTCs are synthesized by varying the components from binary up to quaternary in (Ta,Nb,Hf,Ti)C system using spark plasma sintering (SPS). The present work identifies real-time quantitative failure events such as cracking, crack propagation and fracture using a high-speed camera during 4-point flexural testing in MC-UHTCs. Quaternary UHTCs showed the highest flexural strength of 726 MPa, representing an improvement of ∼166 % over binary and ∼ 24 % over ternary UHTCs. This has been attributed to processing-induced solid solutions and sub-micron feature defects, such as dislocations, intergrain twisting, and plasticity, revealed from the high-resolution microscopy. Crack-propagation rate significantly depreciated over 37 times in quaternary UHTC. An improvement in crack shielding is observed in quaternary UHTC, showcasing the highest fracture toughness at 4.7 MPa·m^0.5, surpassing binary and ternary UHTCs by ∼270 % and ∼ 166 %, respectively. The lower mechanical properties in binary UHTCs are also attributed to high porosity. Post-fracture microstructural analysis supports this finding due to the presence of river patterns contrived by crack-arrest at grain boundary or crack re-initiation in different orientations. The study reveals the exceptional damage tolerance of quaternary UHTCs over other compositions, making them a potential structural material for hypersonic applications.

This study investigates the influence of minor deformation on the corrosion resistance of pure tantalum in strongly acidic and alkaline solutions. The electrochemical behavior of samples with varying degrees of deformation was characterized through open circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. The results indicate that in acidic solutions, the corrosion current density and EIS results suggest that low degree deformation reduces the corrosion resistance of tantalum viewed from a kinetic perspective. Conversely, in alkaline solutions, the corrosion potential shifts towards more positive values, but the corrosion current density remains relatively stable, and the electrochemical impedance increases, indicating enhanced corrosion resistance in minor deformed tantalum samples. Analysis reveals that in acidic solutions, the corrosion resistance is primarily affected by the density of geometrically necessary dislocations and the degree of strain, whereas in alkaline solutions, the crystal orientation and grain boundaries are the predominant factors influencing the corrosion resistance.

Tungsten heavy alloys (WHAs) have been widely investigated due to their high density and strength, thus making them suitable candidates for defense applications, especially those involving high strain rates, such as Kinetic Energy Penetrators (KEP) for armour-piercing fin-stabilized discarding sabot (APFSDS) ammunition. Besides their mechanical properties, the extent of the thermomechanical coupling, i.e., the Taylor-Quinney coefficient (TQC), is relevant for producing accurate numerical models of high strain rate configurations. However, the TQC of WHAs has not been investigated yet.

Four different WHA prototypes were evaluated. Changing the content of tungsten from 70 to 92.5 wt% had little effect on the TQC which had an average value of 0.24. Those low TQC values are accompanied by a significant strain-rate sensitivity with minimal strain hardening. Throughout the tests, dynamic shear localization was not observed.

In this paper, the influences of Al element originating from AlN additives on the mechanical properties and oxidation behavior of WC-Co-Ni-Fe hardmetals were studied systematically. During the sintering process, Al element diffused into the WC hard grains and led to the formation of (Ni,Co,Fe)₃Al particles in the metal binder phase of hardmetals. A small amount of Al element enhanced the hardness of WC-Co-Ni-Fe hardmetal via the solution strengthening and dispersion strengthening. However, the addition of Al element decreased the fracture toughness of hardmetals. The hardness and fracture toughness of multicomponent hardmetals with the addition of 0.5 wt% AlN were 90.4HRA and 10.6 MPa m^1/2, respectively. Additionally, the introduction of Al also significantly improved the oxidation resistance of hardmetals due to the existence of Al in WO₃ and (Ni,Co,Fe)WO₄. With the addition of 2.0 wt% AlN, the weight gain of WC-Co-Ni-Fe-Al multicomponent hardmetal after 5 h of oxidation at 700 °C was 66.82 % of that of the Al-free hardmetal.

Modifying the architecture from a monolithic to a multilayered structure allows adjusting the mechanical properties and cutting performance of industrially relevant hard coatings. The present work focuses on the microstructural, micro-mechanical and cutting performance evaluation of a multilayered TiC_0.67N_0.33/TiC coating grown by chemical vapor deposition. Energy dispersive X-ray spectroscopy and atom probe tomography confirmed the presence of individual TiC and TiC_0.67N_0.33 layers of ∼120 nm thickness with well-defined interfaces. The overall C/(C + N) ratio of the coating amounts to 0.82. Individual peaks for the TiC_0.67N_0.33 and the TiC layer can be observed in the X-ray diffractogram of the TiCN/TiC coating. Scanning electron microscopy showed that the grains grow through the interfaces between the TiCN and TiC layers. Finally, the micro-mechanical properties and cutting performance of the TiCN/TiC multilayer were compared with a monolithic TiCN coating. The fact that the TiCN/TiC coating outperformed the monolithic reference TiCN in regard of hardness and cutting performance emphasizes the high potential of multilayered coatings for use in demanding applications.