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High Temperature may exert a great impact on the service life and reliability of friction materials during friction sliding. Tribological behavior of a new developed copper metal matrix composite (Cu-MMC) against a steel disc was investigated using a home-built pin-on-disc tribometer in the ambient temperature range of 25–800 °C. Detailed analyses of worn surfaces and subsurfaces were performed using scanning electron microscope, optical microscope, X-ray diffractometer and 3D optical profiler. The worn surface of Cu-MMC exhibited different features at various ambient temperatures, resulting in a significant difference in tribological properties. The friction coefficient increased slightly from 0.563 to 0.640 as the ambient temperature varied from 25 °C to 400 °C, then a further increase in the ambient temperature led to a sharp decrease in the friction coefficient to 0.323 at 800 °C. A prompt increase in the mass loss of Cu-MMC was evident with increasing the ambient temperature from 25 °C to 400 °C, and then a slight increase occurred in mass loss of Cu-MMC upon increasing the ambient temperature up to 600 °C after which a significant declining trend of Cu-MMC was observed. The worn surfaces with a rugged and fluctuant morphology contributed to the high and unstable friction coefficient, as well as the high mass loss of Cu-MMC. The dominant wear mechanisms of Cu-MMC were severe oxidation, abrasive wear and adhesive wear at 400 °C and 600 °C, then delamination wear and oxidation at 800 °C.

Compared with conventional casting process, laser direct metal deposition (LDMD) can effectively reduce component segregation in non-equiatomic high entropy alloys (HEAs). However, the non-equilibrium thermal history imparted by this method has a significant effect on the microstructure and mechanical properties of the HEA. The present work prepared non-equiatomic (FeNiCo)-(AlCrSiTi) HEAs using the LDMD process, after which some samples were subjected to a subsequent vacuum remelting (VRM) treatment. The variations in phase composition, microstructure and hardness between the HEAs processed using the LDMD or VRM methods were investigated. Differences in phase composition increased with increases in the proportion of the Al, Cr, Si and Ti components. Compared with the HEA samples processed using the VRM method, the LDMD specimens possessed much finer and simpler microstructures mainly comprising solid solution phases. At relatively high concentrations of the Al, Cr, Si and Ti components (32 at% and 40 at% in total), the HEAs processed under LDMD conditions had similar grain morphologies, intermetallic phases and microhardness values, while the VRM specimens presented completely different microstructures and properties.

Owing to the cocktail effect in high-entropy alloys, a good combination of strength and toughness of a welded joint could be theoretically achieved, by modifying the elemental composition of the filler metals with a high-entropy design. However, few studies have concentrated on this issue so far. In the present study, multi-component mixed powders of (CrMnFe)x(CoNi)y, with five types of the content ratios of the body-centered cube (BCC) and face-centered cube (FCC) forming elements, were used as filler metals to achieve dissimilar welding between 304 stainless steel and Q235 carbon steel by laser deposition welding. By comparative analysis of the microstructures and mechanical properties of the dissimilar joints, the effects of an elemental composition factor of μ (μ = x/y) on the hardness, tensile and bending properties of the dissimilar joints were explored. It was found that the elemental composition of mixed powders had an impact on the mechanical properties of dissimilar joints. Too high or too low content of BCC/FCC forming elements in filler metals cannot promote the appropriate mechanical properties. As an increase in the content of BCC forming elements, the hardness in weld zones was significantly increased, especially for the mixed powders with a high value of μ (≥7/3). The powders of (CrMnFe)5(CoNi)5 resulted in the best comprehensive mechanical properties of the dissimilar joint.

This paper provides a reference to determine the seal performance of metallic O-rings for a reactor pressure vessel (RPV). A nonlinear elastic-plastic model of an O-ring was constructed by the finite element method to analyze its intrinsic properties. It is also validated by experiments on scaled samples. The effects of the compression ratio, the geometrical parameters of the O-ring, and the structure parameters of the groove on the flange are discussed in detail. The results showed that the numerical analysis of the O-ring agrees well with the experimental data, the compression ratio has an important role in the distribution and magnitude of contact stress, and a suitable gap between the sidewall and groove can improve the sealing capability of the O-ring. After the optimization of the sealing structure, some key parameters of the O-ring (i.e., compression ratio, cross-section diameter, wall thickness, sidewall gap) have been recommended for application in megakilowatt class nuclear power plants. Furthermore, air tightness and thermal cycling tests were performed to verify the rationality of the finite element method and to reliably evaluate the sealing performance of a RPV.