Effects of ball milling time and sintering temperature on microstructure and room-temperature mechanical properties of Nb-16Si-22Ti-2Al-2Hf-2Cr alloy synthesized by powder metallurgy

Nb-16Si-22Ti-2Al-2Hf-2Cr bulk alloys have been prepared by powder metallurgy. The effects of milling time (5, 10, 20 h) of powder mixtures and hot-pressing temperatures (1500, 1600°C) on the microstructure and room-temperature mechanical properties of the bulk alloys were investigated. It is revealed that the hot-pressed alloys are mainly composed of 3 phases including Nb solid solution (Nb_SS), Ti solid solution (Ti_SS) and Nb₅Si₃ silicides. With prolonging the milling time, the volume fractions of Nb₅Si₃ and Ti_SS phases increase, but that of Nb_SS phases decreases. The improvement in room-temperature hardness of bulk alloys is achieved with milling time and hot-pressing temperature increasing, and the bulk alloy milled for 20 h and hot-pressed at 1600°C has the highest hardness of 11500 MPa. Moreover, the fracture toughness of the alloys hot-pressed at 1500°C and 1600°C both decreased with milling time prolonging. The bulk alloy milled for 5 h and hot-pressed at 1500°C has the highest fracture toughness of 10.14 MPa·m^1/2.