Creep of the orthorhombic phase based on the intermetallic Ti2AlNb

The orthorhombic phase based on Ti2AlNb intermetallic is an important constituent of several alloys currently under investigation as both monolithic products and as matrix material for intermetallic–matrix composites. The creep behaviour of Ti2AlNb intermetallic phase has been studied over a strain rate range of 10−7–10−9/s and a temperature range 973–1023 K. A well defined steady state with a normal transient is observed after stress jump tests. The stress exponent decreases gradually from 7 to 5 with increasing temperature, suggesting that the activation energy for creep may have a mild stress dependence. The activation energies are similar to those for diffusion in Ti3Al binary intermetallic. The dislocation structure consists of ‘a’, ‘a*’ and pure ‘c’ dislocations which are arranged in a three-dimensional network. Based on these observations, it is hypothesised that a network model of creep, as proposed for example by McLean, may be appropriate to describe the creep of this intermetallic. The rate-controlling mechanism is believed to be the climb of super-dislocations. The effect of Nb content on the creep of this intermetallic has also been studied. It is found that Nb content does not affect the creep behaviour of the O phase.