Creep of the orthorhombic phase based on the intermetallic Ti₂AlNb

Abstract

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.