HIGH-TEMPERATURE CREEP OF SILICON-CARBIDE PARTICULATE REINFORCED ALUMINUM

The effect of stress on the creep properties of 30 vol.% silicon carbide particulate reinforced 6061 aluminum (SiCp-6061 Al), produced by powder metallurgy, has been studied in the temperature range of 618-678 K. The experimental data, which extend over seven orders of magnitude of strain rate, show that the creep curve exhibits a very short steady-state stage; that the stress exponent, n, is high (n > 7.4) and increases with decreasing the applied stress; and that the apparent activation energy for creep, Qa, is much higher than the activation energy for self-diffusion in aluminum. The above creep characteristics of SiCp-6061 Al are similar to those reported for dispersion strengthened (DS) alloys, where the high stress exponent for creep and its variation with stress are explained in terms of a threshold stress for creep that is introduced by the dispersoid particles. Analysis of the creep data of SiCp-6061 Al using the various threshold stress models proposed for DS alloys indicates that the threshold stresses introduced by the SiC particulates are too small to account for the observed creep behavior of the composite. By considering an alternate approach for the source of the threshold stress in SiCp-6061 Al, an explanation for the asymptotic behavior of the creep data of the composite is offered. The approach is based on the idea that the oxide particles present in the Al matrix, as a result of manufacturing the composite by powder metallurgy, serve as effective barriers to dislocation motion and give rise to the existence of a threshold stress for creep. © 1990.