Blended elemental P/M synthesis and property evaluation of an orthorhombicTi-22Al-27Nb alloy

The orthorhombic (O) phase based on the compound Ti2AlNb (Ti-25Al-25Nb (mol %)) has a higher strength-to-density ratio and better room temperature duct ility than conventional titanium aluminides such as TiAl and Ti3Al. In the present study, orthorhombic Ti-22Al-27Nb alloy was produced by the blended elemental (BE) powder metallurgy (P/M) method, and the microstructures and mechanical properties such as tensile and high cycle fatigue were evaluated . Homogeneous BE P/M Ti-22Al-27Nb was successfully produced by using extra lo w chlorine Ti powder and AI-Nb master alloy powder with a particle size sma ller than 45 mu m. The microstructure in the as-HIP'ed condition consisted of O, alpha(2) and beta phases. The O and beta phases were distributed in t he interior of the grains whereas the alpha(2) phase was mainly formed alon g the grain boundaries. The post-HIP heat treatment at 1173 K for 36 ks mad e the distribution of these three phases more homogeneous. Although the ten sile specimen was broken before the peak tensile strength was attained in t he temperature range up to 923 K, both 0.2% proof stress and fracture stren gth were higher than those for the Ti-6Al-2Sn-4Zr-2Mo alloy. The Young's mo dulus and high cycle fatigue strength at 10(7) cycles in the as-HIP'ed cond ition were 129 GPa and 480 MPa, respectively. High cycle fatigue strength w as increased to 540 MPa by the post-HIP heat treatment.