Low-cycle Fatigue Properties of TiAl Intermetallic Compounds

Abstract

Axial strain-controlled fatigue tests were carried out for an annealled Ti-34.7Al-1.74 V (wt%) intermetallic compound at RT and 800°C. It showed cyclic strain hardening behaviors at both temperatures. The fatigue strength at 800°C was higher than that at RT.
The fracture surface tested at RT was a mixture of three modes: (1) crystallographic fracture with linear steps, (2) intergranular fracture with smooth facets of grain boundaries and (3) transgranular cleavage fracture with river patterns. The fatigue cracks were found to be initiated by several mechanisms including slip-off steps or cracking under stress concentrations due to coarse slip or double slip lines.
The fracture mode at 800°C also consisted of the same three types, but the initiation was found to be controlled by grain boundary cracking, with striped patterns on the facets, under stress concentrations due to large twin-deformations across a grain.