2017 Volume 58 Issue 10 Pages 1404-1410
Microstructure and mechanical properties of Ti-Al-Nb-based alloys were investigated as they are important in the development of new generation high temperature Ti alloys due to good oxidation resistance. The alloy compositions Ti-15Al-2Nb (to obtain α2 precipitates) and Ti-15Al-2Nb-0.5Si (at%) (to obtain solid-solution hardening by Si) were selected. Heat treatment at 1000℃ after forging and rolling at 900℃ transformed the β phase to α phase and α' martensite during cooling. By heat treatment at 900℃, a single α phase was obtained in both alloys. The α2 phase was formed by aging treatment at 600 and 700℃ of Ti-15Al-2Nb and at 600, 700, and 800℃ of Ti-15Al-2Nb-0.5Si. Compressive strength was investigated for samples heat treated at 900℃ with a single α phase and those aged at 600, 700, 800℃ with α2 precipitates. The solid solution hardening effect of Si was found at all test temperatures. Precipitation hardening effect by α2 precipitates was also observed in both alloys and the effect improved with Si addition. Peaks of precipitation hardening were obtained at 300℃ in both alloys; the precipitation hardening effect decreased with increase of test temperature above 300℃. It is suggested that a shearing mechanism occurs up to 300℃, which changes to a bypass mechanism above 450℃.
