The effects of different brazing processes on the interfacial microstructure and shear strength of TiZrHfNbMo high-entropy alloy (HEAS) and Si₃N₄ ceramic brazed joints were studied. There is no obvious defect in a brazed TiZrHfNbMo HEAS/AgCuTi/Si₃N₄ ceramic joint, and the two materials have good metallurgical bonding. The typical interface microstructure is Si₃N₄/Ti₅Si₃/Ag solid solution +Cu (s,s)+ CuTi/Cu₂Ti/Cu₄Ti + TiCu(Hf,Zr)NbMo/TiZrHfNbMo HEAs. With the increase of brazing temperature, the dispersed CuTi phase agglomerates in the brazed joint, and acts as the nucleate of the Cu-based solid solution. The thickness of the reaction layer increases with the increase of phases in the reaction layer on both sides of the joint. When the brazing temperature is 800 °C, 820 °C, 840 °C and 860 °C, the shear strength of the brazed joint is 30 MPa, 72 MPa, 86 MPa and 21 MPa, respectively. The formation of CuTi and Ti₅Si₃ intermetallic compounds increases the thickness of the reaction layer, and improves the strength of the joint. However, excessive CuTi and Ti₅Si₃ intermetallic compounds lead to a significant decrease in joint strength. The grain coarsening of the joint can also affect the strength of the joint.

To further improve the mechanical properties of Al-Si alloys. The phase, microstructure and mechanical properties of Al₂O₃/Al-20Si composites under different pressures were studied. The results show that the phase of Al₂O₃/Al-20Si composites are composed of α-Al phase, β-Si phase and Al₂O₃. Under the condition of hot-pressing sintering (0.02 GPa), a large number of Si phases with irregular shape and sharp angle are distributed on the α-Al matrix. Under high pressure solidification, the growth of primary Si phase is inhibited and the eutectic Si is spheroidized obviously. The microhardness of Al₂O₃/Al-20Si composite increases from 102.5 HV_0.05 at 0.02 GPa to 156.4 HV_0.05 at 4 GPa, which increases by 52.6%. The compressive strength increased from 381.5 MPa at 0.02 GPa to 469.1 MPa at 4 GPa, increasing by 23%. With the increase of solidification pressure, the fracture mechanism changes from cleavage fracture to quasi cleavage fracture.

In this work, the Ti-48Al-2Cr alloy, solidified under different pressures and temperatures, was investigated in detail. The effect of high pressure on the microstructure and nanohardness of the Ti-48Al-2Cr alloy was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and a nanoindenter XP testing machine. The results showed that the B2 phase disappeared after high-pressure solidification. Compared with ambient pressure solidification, high pressure led to the increase of (α₂ + γ) lamellar structure and the decrease of γ phase. The nanohardness of the lamellar structure was discussed based on the microstructure observation. When solidified at 5 GPa/1873 K, the hardness rose to 5.54 GPa, an increase of 60.5% compared with that solidified at ambient pressure. However, the increased holding temperature of 1973 K made the dislocation density in the lamellar structures greatly decrease, and reduced the structure’s hardness to 4.48 GPa.

In the present paper, new heat treatment was performed on 10 vol.% TiC/Ti-6Al-3Sn-9Zr-1.5Mo composite fabricated by an in situ casting technique. The aim is to obtain fully lamellar structure in matrix, control the lamellar structure quantitatively and understand the variation of the tensile properties of as-cast and heat-treated composites. For as-cast composite, matrix exhibited fully lamellar structure with some extent of basket-weave characteristics, and reinforcement was mainly in fine rod and strip shape. After β heat treatment, matrix microstructure was refined visibly. As the new cooling method was employed, wider α lath in matrix was obtained. The composite with very fine lamellar structure showed better yield strength (YS) in comparison with that with coarse lamellar microstructure below 650 °C. At 700 °C, fine grain strengthening cannot exert effective influence on tensile strength. It is proved that the enhanced YS is mainly ascribed to the refinement of α lath at ambient temperature. The heat-treated composites with wider α lath displayed excellent ductility at ambient temperature. Above 600 °C, the effect of α phase size on tensile elongation was negligible in the heat-treated composites, since matrix was softened.