The interactive role of inclusions and SiC reinforcement on the high-cycle fatigue resistance of particle reinforced metal matrix composites

The effect of intermetallic inclusions on the fatigue crack initiation and growth in 2080 Al alloy and 2080/SiC _p composites was investigated. Using surface replication, it was determined that, in the highcycle fatigue region, life is dominated by the initiation process. It was also determined that the majority of initiation sites were associated with intermetallic inclusions. While 2080/SiC/20 _p showed a definitive relationship between inclusion size and fatigue life, i.e., a higher inclusion size resulted in lower fatigue life, there was no correlation in 2080/SiC/30 _p . This was attributed to more of the load being shared by the higher volume fraction of SiC particles and smaller average inclusion sizes in the latter composite. A conceptual model is proposed that accounts for these observations and qualitatively shows the effect of reinforcement on stress enhancement in near-surface inclusions. This article is based on a presentation made in the Symposium “Mechanisms and Mechanics of Composites Fracture” held October 11–15, 1998, at the TMS Fall Meeting in Rosemont, Illinois, under the auspices of the TMS-SMD/ASM-MSCTS Composite Materials Committee.