GH4169 superalloy and Si₃N₄ ceramics were vacuum-brazed with AgCuTi+Cu foam composite filler. The effect of brazing temperature on the microstructure and mechanical properties of the GH4169/Si₃N₄ joint was studied. The results show that the interface microstructure of the GH4169/Si₃N₄ joint is the GH4169 superalloy/TiCu+Ti₂Ni+TiCu₂+Ag(s, s)+TiCu₄+Cu(s, s)+TiN+Ti₅Si₃/Si₃N₄ ceramics. With the increase in brazing temperature, the element diffusion between the base metal and the brazing filler intensifies, and the interfacial reaction layer thickens, which is conducive to the improvement of shear strength. At 850 °C, the maximum shear strength of the joint is 196.85 MPa. After further increases in the brazing temperature, Cu foam dissolves completely, and the Ti-Cu intermetallic compounds increase, which is harmful to the shear strength due to the increases in the brittle phase. However, when the brazing temperature reaches 910 °C, the shear strength of the brazing joint slightly increases under the combined effect of the Ti-Cu intermetallic compounds and the thickness of the reaction layer.

The phase composition, microstructure, mechanical, corrosion, and wear behaviors of the Ti15Zr35Ta10Nb10Sn30 (Sn30) and Ti15Zr30Ta10Nb10Sn35 (Sn35) biomedical high-entropy alloys (BHEAs) were studied. We found that the Ti–Zr–Ta–Nb–Sn BHEAs showed hyper-eutectic and eutectic structures with body-centered cubic (BCC) and face-centered cubic (FCC) solid-solution phases. The Sn30 BHEA exhibited a high Vickers hardness of approximately 501.2 HV, a compressive strength approaching 684.5 MPa, and plastic strain of over 46.6%. Furthermore, the Vickers hardness and compressive strength of Sn35 BHEA are 488.7 HV and 999.2 MPa, respectively, with a large plastic strain of over 49.9%. Moreover, the Sn30 and Sn 35 BHEA friction coefficients are 0.152 and 0.264, respectively. Sn30 BHEA has the smallest and shallowest furrow-groove width, and its wear rate is 0.86 (km/mm³); at the same time, we observed the delamination phenomenon. Sn35 BHEA has a wear rate value of 0.78 (km/mm³), and it displays wear debris and the largest–deepest furrow groove. Sn30 BHEA has the highest impedance value, and its corrosion current density I_corr is 1.261 × 10⁻⁷ (A/cm²), which is lower than that of Sn35 BHEA (1.265 × 10⁻⁶ (A/cm²)) by 88%, and the passivation current density I_pass of Sn30 BHEA and Sn35 BHEA is 4.44 × 10⁻⁴ (A/cm²) and 3.71 × 10⁻³ (A/cm²), respectively. Therefore, Sn30 BHEA preferentially produces passive film and has a small corrosion tendency, and its corrosion resistance is considerably better than that of the Sn35 BHEA alloy.

Based on the excellent comprehensive mechanical properties of high–entropy alloy (HEA), the NiAl-based HEA was designed to achieve excellent high-temperature strength, toughness, and wear resistance. In this work, vacuum arc melting technology was used to prepare (NiA1)₇₈(CoCrFe)_16.5Cu_5.5 HEA, and its microstructure, phase composition, and mechanical properties were systematically studied. The results showed that (NiA1)₇₈(CoCrFe)_16.5Cu_5.5 HEA was composed of FCC and BCC/B2, with a spinodal decomposition structure in the matrix, and nano-precipitation in the interdendritic, exhibiting a good high-temperature performance. At 600 °C, the compressive fracture strength is 842.5 MPa and the fracture strain is 24.5%. When the temperature reaches 800 °C, even if the strain reaches 50%, the alloy will not fracture, and the stress–strain curve shows typical work hardening and softening characteristics. The wear coefficient of the alloy first increases and then decreases with the increase in temperature in the range of room temperature to 400 °C. However, the specific wear rate shows the opposite trend. At 100 °C, the wear rate reaches the lowest of 7.05 × 10⁻⁵ mm³/Nm, and the wear mechanism is mainly abrasive wear.

A novel Ni-Cr-Si-B filler metal (JNi-5) was designed and further fabricated into the amorphous brazing filler metal for joining the GH4169 alloy. The effect of brazing temperature on the microstructure and mechanical properties of GH4169 joints was investigated. The typical microstructure of the joint at 1030 °C is composed of four specific zones: the base metal (BM), heat-affected zone (HAZ), isothermal solidification zone (ISZ), and athermal solidification zone (ASZ). The typical microstructure of the joint is GH4169/(Nb, Mo)-rich boride+(Cr, Nb, Mo)-rich boride/γ(Ni)/Ni-rich boride+γ(Ni)/γ(Ni)/(Cr, Nb, Mo)-rich boride+(Nb, Mo)-rich boride/GH4169. As the temperature increased, the HAZ continued to widen and the ASZ depleted at 1090 °C and 1120 °C. Additionally, the borides within the HAZ coarsened at temperatures of 1090 °C and 1120 °C. At 1030 °C, the fracture path is in the ASZ, and the existence of the brittle phase in the ASZ provides the potential origin for crack growth. The fracture mode is a quasi-cleavage fracture. At 1060 °C, 1090 °C, and 1120 °C, the fracture behavior mainly happened in the HAZ, and the existence of borides in the HAZ provides the potential origin for crack growth. Namely, the shear strength of joints was principally dominated by the brittle precipitations in the HAZ. The fracture mode of these joints is the hybrid ductile. At 1060 °C, the shear strength of the obtained joint is the highest value (693.78 MPa) due to the volume fraction increase in the Ni-based solid solution. Finally, the optimized brazing parameter of 1060 °C/10 min was determined, and the corresponding highest shear strength of 693.78 MPa was obtained owing to the increased content of the Ni-based solid solution in the joint.

The Inconel 718 alloy clad coating was successfully prepared via pulsed laser deposition. The effect of pulse frequency on the evolution of microstructure, hardness and tribological properties of the as-deposited samples were analyzed via scanning electron microscopy (SEM), microhardness tester and ball-on-plate tribometer. The results showed that with the decrease in pulse frequency, the cooling rate of molten pool increases gradually, which effectively refines the γ-(Ni, Cr, and Fe) dendrites and restrains Nb segregation. Hence, the morphology of the brittle Laves phase changed from long chained to granular and its volume fraction decreased from 6.59% to 2.41%. The hardness of the coating increased from 261 HV_0.1 to 297 HV_0.1 and the tribological property also improved simultaneously. The friction coefficient decreased from 0.2387 to 0.2066, and the wear rate decreased from 27.30 × 10⁻⁴ mg·N⁻¹·m⁻¹ to 19.15 × 10⁻⁴ mg·N⁻¹·m⁻¹. It can also be observed that the wear area of the counterpart, Si₃N₄ ball, increased from 2.016 mm² to 2.662 mm². The increase in the hardness and tribological property were attributed to the grain refining strengthening.

The enhancement of the mechanical properties of TiAl alloys through the introduction of a second-phase reinforcement is highly essential. In this paper, using graphite powder as a carbon source, the Ti₂AlC phase is introduced to improve the compression and friction properties of the TiAl alloy. Concurrently, the effects of graphite powder additions on the microstructure and room-temperature mechanical properties of Ti-45Al-8Nb-xC (mass%) alloys are investigated. The results show that as the volume fraction of Ti₂AlC and the interdendritic γ phase increases, the length–diameter ratio of the Ti₂AlC phase decreases with increases in the graphite powder addition. The addition of graphite powder results in a refining effect on the grain size and lamellar spacing of the Ti-45Al-8Nb-xC (mass%) alloys. As the graphite powder content increases from 0 to 0.9 mass%, the microhardness increases from 557 HV to 647 HV. The room-temperature compressive strength and strain of the Ti-45Al-8Nb-xC (mass%) alloys first increase and then decrease with the addition of graphite powder. Specifically, when the content of graphite powder is 0.6 mass%, the alloy exhibits a maximum compressive strength and strain of 1652 MPa and 22.2%, respectively. Compared with the alloy without the graphite powder addition, the compressive strength and strain are improved by 37.7% and 62.1%, respectively. The wear resistance of the alloys is improved through the addition of graphite powder and the wear rate decreases from 5.062 to 2.125 × 10⁻⁴ mm³·N⁻¹·m⁻¹ as the content of graphite powder increases from 0 to 0.9 mass%.