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 high-cycle 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.