Abstract
Effects of microstructural and compositional factors on creep and room temperature tensile properties of α+α2 titanium alloys were examined by using five Ti-Al-Sn-Zr-Nb-Si alloys designed by thermodynamic calculation to have the volume fraction of α2 precipitate (Vα2) of 0.1 or 0.2.
Increase in the creep strength due to additions of Nb and Si was confirmed in β treated alloys. In the relationship between the creep strength and the amount of primary α phase (Vαp), the peak was observed for the alloys GT-88, 89, and 90, while the creep strength of the GT-91 decreased rapidly with increasing Vαp, and that of the GT-79 was not changed so much with the change in Vαp. The observed dependence of Vαp on the creep strength seemed to result from variations of the Vα2 and the grain size due to the heat treatment. In a room temperature tensile test, remarkable improvements in elongation were obtained by the α+β solution treatment in alloys having Vα2 of about 0.1. From the present results, the Vα2 of about 0.1 at 823 K combined with the α+β solution treatment is proposed as the best design condition for α+α2 type high temperature titanium alloys.
