Parameters for Ductility Improvement in TiAl

Abstract

ABSTRACTThe effect of the Ti/Al ratio and third elements (Cr, Hf and Nb) on the mechanical properties of TiAl has been studied. Solution hardening in these elements is so large that, e.g., the strength doubles by the addition of 3 at.% Cr. Ductility to fracture strain has been improved up to 2.7 % and 2.7 % by the Cr addition and the use of high purity base metals, respectively. Parameters relating to the improvement of ductility have been discussed. Namely, the improvement of ductility was caused by the decreases of the grain size, axial ratio and impurity. A hypothesis has been proposed that the ductility improvement was related with the excess shrinkage of volume of a unit cell due to the addition of the third element which implies the strengthening of chemical bonds and vice versa. The effect of twins and a lamellar structure with the plate-like Ti3Al and the matrix on the ductility have been discussed.