Creep behavior in an Al-Fe-V-Si alloy and SiC whisker-reinforced Al-Fe-V-Si composite

Abstract

High temperature strengthening mechanisms in discontinuous metal matrix composites were examined by performing a close comparison between the creep behavior of 15vol. pct SiCw/8009Al and that of its matrix alloy, 8009Al. Both the alloy and composite exhibit a single-slope behavior with anomalously high values of apparent stress exponent and high apparent activation energy. The presence of SiC whiskers does not remarkably influence these two kinds of dependence of creep rates but reduces the creep rates by about two orders of magnitude. Transmission electron microscopy examination of the deformation microstructure reveals the occurrence of attractive dislocation/particle interaction. The creep data were analyzed by the threshold stress approach and by the dislocation-climb theories based on attractive interaction between dislocations and dispersoids. All data can be rationalized by a power-law with a stress exponent of 5 and a creep activation energy close to that for the self-diffusion in aluminum. The threshold stress decreases linearly with increasing temperature. General climb together with the attractive but not strong interactions between the dislocations and dispersoids is suggested to be the operative deformation mechanism. The contribution of SiC whiskers to the creep strength of 8009 Al composite can be evaluated quantitatively when the shear-lag model is applied. However, the effects of whisker length and whisker orientation distributions must be considered. Two probability density functions are used for modelling the distribution of whisker length and whisker orientation.