High-temperature creep behavior of TiC particulate reinforced Ti-6Al-4V alloy composite

Tensile creep tests were carried out on a 15 vol% TiC particulate reinforced Ti-6Al-4V alloy composite at 823923 K. The creep rate data show three regions: a low-stress region with a stress exponent of 2.4-2.6, a medium-stress region with a stress exponent of 4.3-6.1, and a high-stress region with a stress exponent of 8.1-14.3. In the medium-stress region, the high values of the stress exponent (n = 6.1) and activation energy (Q = 310kJ/mol) at 823 K indicate the presence of threshold stress. By incorporating the threshold stress into analysis, all the creep data can be rationalized to a single stress exponent of 4.3, which is consistent with the lattice diffusion controlled dislocation climb process in alpha-Ti. In the low-stress region, after introducing the threshold stress into analysis, the creep data fit into a single stress exponent of 2, and the activation energy is reduced to be close to that for the lattice diffusion, indicating that the creep mechanism of the composite in the low-stress region is the grain boundary sliding accommodated by the lattice self-diffusion controlled dislocation climb. In the high-stress region, an abnormally high stress exponent of 8.1-14.3 at 823-873 K is attributed to the occurrence of power-law breakdown. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.