喷射沉积SiC_P／Al-7Si复合材料的疲劳裂纹扩展

采用紧凑拉伸试样进行恒载和降K控制的拉--拉疲劳实验, 研究了喷射沉积SiC_p/Al-7Si复合材料及其基体的疲劳裂纹扩展行为. 通过金相显微镜和扫描电镜观察了复合材料及其基体的组织和疲劳裂纹扩展形貌, 研究了SiC颗粒对复合材料疲劳裂纹扩展机制的影响. 结果表明: 复合材料在任何相同的ΔK水平下其抗疲劳裂纹扩展能力优于基体材料, 并表现出较高的疲劳门槛值. 其原因是复合材料中裂纹裂尖遇到增强颗粒时, 裂纹发生偏转, 特别是SiC颗粒自身微裂纹萌生有效降低了裂纹尖端的应力强度因子, 复合材料的裂纹闭合效应也随之增大. 去除裂纹闭合效应的影响, 当有效应力因子ΔK_eff作为裂纹扩展的驱动力时, 复合材料的裂纹扩展速率却高于基体.

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

In order to investigate the fatigue crack growth behaviors of SiC_p/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 (ΔK_eff) acts as the crack driving force, the composite shows a higher crack growth behavior than the unreinforced alloy.