Effect of Particulate Phase on Kinetics of Fatigue Crack Growth in Cast Al-SiC Particulate Composites

摘要

Fatigue crack growth studies were conducted in cast Al-SiC particulate composites using 2124 type Al-alloy with the addition of SIC particulates up to 20 % by weight with an average particulate size of 20 μm. Microstructural studies were conducted, and tensile properties were determined. With increasing weight fraction of the particulate phase, the yield strength increased significantly whereas the tensile strength showed decreasing tendency. Fatigue crack growth rate (FCGR) studies were conducted employing CT specimens, and the crack growth rate, da/dN, was evaluated as a function of ΔK. In addition, the measurement of crack closure was also done using compliance technique.The results indicate that the da/dN is minimum for the Al-20 SiC composite and maximum for the base alloy in the lower regime of ΔK. With increasing ΔK, the base alloy showed a better performance.The beneficial effect of particulate phase on the FCGR is considered to be due to diversion of propagating crack and crack branching caused by the SiC particulates. At increased ΔK, however, the cracking of the particulate phase in the 20 % SiC composite resulted in increased crack growth rate. The crack closure was found to play a beneficial role in case of the base alloy due to plasticity induced closure, whereas its effect was not so predominant in the composites.