Effect of SiC Particles on Fatigue Crack Growth Behavior of SiC Particulate-reinforced Al-Si Alloy Composites Produced by Spray Forming

Abstract

Fatigue crack growth (FCG) and closure mechanisms in spray-formed Al-7Si alloy matrix composites reinforced by SiC particles with two different sizes have been studied. The experimental data indicated that the as-sprayed composite containing the small SiC particles (4.5μm) exhibited a superior resistance to fatigue crack growth as compared to the composite with 20μm SiC particles and the unreinforced alloy, with the threshold stress intensity factor range ΔKth of 3.878 MPa•m1/2 for the former being slightly higher than that for the 20μm SiC reinforcement composite (3.630 MPa•m1/2) and the unreinforced alloy (3.605 MPa•m1/2). The SEM crack path observation showed that the extent of micocracking inside in the 4.5μm SiC particles induced higher level of fatigue crack closure, which effectively reduced the crack growth driving force and thus slowed down fatigue crack growth. Crack deflection caused by the SiC particles resulted in a decrease in FCG rate for the 20μm SiC composite due to the high levels of roughness-induced crack closure at the low ΔK, however with the value of ΔK increasing, the propensity for the fracture of large SiC particles and the frequent separation between the SiC particles and the matrix increased, and then contributed to a higher FCG rate in the fast fracture state.