High temperature creep of precipitation-strengthened Ni3Al-based alloy

High temperature creep of a precipitation-strengthened Ni3Al-based alloy wi th chemical composition Ni-20.2Al-8.2Cr-2.44Fe (at %) was investigated. The creep characteristics, including the stress exponent and activation energy for creep, are reported for the temperature range 1050-1150 K and applied approximately constant stresses ranging from 150 to 350 MPa. The steady-sta te creep rate is found to depend on the applied stress and temperature. The power law stress exponent for steady state creep is determined to be 4.1 /- 0.1 and the apparent activation energy for creep is calculated to be 316 +/- 9 kJ mol(-1). Analysis of the creep data in terms of an effective stre ss normalised with respect to the temperature dependence of the elastic mod ulus gives a true activation energy for creep of 301 +/- 9 kJ mol(-1) and a stress exponent of 3. This activation energy for creep corresponds to the activation energy for lattice diffusion of Ni in Ni3Al. The kinetics of the steady-state creep deformation within the studied temperature range is pro posed to be governed by the diffusion controlled climb of dislocation loops along the alpha-Cr precipitates. During the tertiary creep stage an intens ive formation of large slip bands is observed. The alloy fails by growth an d coalescence of voids within the columnar grains and cavities at the grain boundaries. (C) 1999 Elsevier Science Ltd. All rights reserved.