Effects of high-temperature homogenizing and aging treatments on the microstructure of Nb-Ti-Si based ultrahigh temperature alloy

The master alloy ingot of Nb-Ti-Si based ultrahigh temperature alloy was prepared by vacuum nonconsumable arc melting. The coupons were homogenized at 1300, 1400, 1500 and 1600°C for 50 hours respectively, and then aged at 1100°C for 50 hours. The heat-treated microstructures were still composed of Nbss and (Nb, x)₅Si₃ (x represents Ti, Hf and Cr elements). But after the heat treatments both at 1600°C, 50 h and 1600°C, 50 h+1100°C, 50 h, HfO₂ was found in the mucrostructure. With the increase of heat treatment temperatures, polygonal and plate-like big (Nb, x)₅Si₃ is desolved gradually or broken into small ones, and the amount of retained typical lamellar or rod eutectic colonies reduced gradually. 1500°C, 50 h+1100°C, 50 h is an optimum heat treatment process for Nb-Ti-Si based ultrahigh temperature alloy.