STEADY-STATE CREEP-BEHAVIOR OF SILICON-CARBIDE PARTICULATE REINFORCED ALUMINUM COMPOSITES

The roles of volume fraction and size of reinforcement on the steady state creep behaviour of pure aluminium matrix silicon carbide particulate composites have been studied in the temperature range 623-723 K. The observed apparent stress exponents are higher than 15 and apparent activation energy is 249 kJ mol-1. By considering the existence of a threshold stress, the data for 1.7 mum particulate reinforced composites with different volume fraction can be rationalized according to the substructure invariant model. The effective stress strain rate behaviour of composites with 10 vol.% of coarser particulates (14.5 and 45.9 mum), however, agree with the stress dependent substructure model. The present analysis is validated by constructing a new type of "dislocation creep mechanism map". The observed threshold stress varies with the volume fraction of reinforcement and is independent of particulate sizes and test temperatures. It is suggested that a model based on an lied stress independent load transfer is required to explain the origin of such a threshold stress.