Effect of ternary additions on mechanical properties of TiAl

Abstract

The effect of ternary additions such as V, Cu, Nb, Zr and Mn as well as the deviation from the stoichiometric composition to the Al-rich composition on mechanical properties of TiAl was studied at room temperature (RT) in air, and RT, 873 and 1073 K in vacuum. V, Zr and Mn additions increased the bend yield stress at RT, 873 and 1073 K while Cu additions increased the yield stress at 873 and 1073 K only. The fracture stress was increased by the addition of V, Nb, Zr and Mn at RT and 873 K. The RT fracture strain was improved by additions of Nb and Mn. At 873 K by microalloying with any of the ternary elements generally tended to increase the fracture strain. The work hardening rate was increased at 873 K and decreased at 1073 K by the ternary additions investigated. The fracture strains obtained in air were about a half of those in vacuum at RT, except high V addition which seems to suppress the environmental brittleness. The fracture strain increased with increasing strain rate within 10 −5–10 −3 s −1. The bend yield and fracture stresses and the fracture strain increased with the inverse of square root of grain size, d −1/2. Fractography revealed that the transgranular cleavage was a main fracture type in air and in vacuum at RT. At 873 K, the area of the intergranular fracture was larger than that at RT. The effects of microalloying elements on the mechanical properties have been discussed in terms of changes in lattice parameters, grain size, test atmosphere, strain rate, gaseous impurity elements and test temperature.