GROWTH BEHAVIOR OF FATIGUE CRACK IN SPRAY-FORMED SiCp/Al-7Si COMPOSITE

In order to investigate the fatigue crack growth behaviors of SiCp/Al-7Si composite and the unreinforced alloy prepared by spray deposition, compact tension (CT) specimens were prepared and tension-tension fatigue tests were carried out under constant-amplitude load and load shedding technique (ΔK-decreasing) control to obtain the fatigue threshold. The experimental data demonstrate that the addition of SiC particles results in superior fatigue crack propagation properties for a given ΔK, i.e. lower crack growth rate and higher intrinsic threshold stress intensity factor. The SiC particles play a significant role in dictating the rate of fatigue crack growth. OM and SEM observations show that crack deflections around SiC particles and particle cracking are the principle mechanisms of interaction between SiC particles and crack tip. Moreover, detailed quantitative analysis indicates that the extent of particle cracking induces a high level of fatigue crack closure, which effectively reduces the driving force of crack growth and so slows down fatigue crack growth. However, when the closure-corrected effective stress intensity factor range (ΔKeff) acts as the crack driving force, the composite shows a higher crack growth behavior than the unreinforced alloy.