FATIGUE CRACK-GROWTH MECHANISMS IN AL-SIC PARTICULATE METAL MATRIX COMPOSITES

The fatigue crack growth rate under tension-to-tension loading was evaluated and the predominant fracture mechanism determined in two commercially available metal matrix composites produced by powder metallurgical technology. The investigated materials (Al7091-30vol.%SiCp and Al2014-40vol.%SiCp) differed both in the metal matrix and in the volume fraction, size and distribution of the SiC reinforcement. It was found that the crack growth rate in the entire ΔK region of the Al7091-30vol.%SiCp composite was much lower, having Paris law parameters n = 7.8 and C = 1.67 × 10-11 m MPa-n m -n 2 while the corresponding values for the Al2014-40vol.%-SiCp composite were found to be n = 23.2 and C = 5.60 × 10-17 m MPA-n m -n 2. The fractographic investigation revealed a good interfacial bond in the Al7091-SiC composite, while in Al2014-SiCp, which has a strong tendency to particle clustering, poor bonding was observed within the clusters. In the Al7091-SiCp composite the crack propagates through the matrix with branching around individual SiC particles forming fine striation patterns, while in the Al2014-SiCp composite coarse striations formed around clusters of particles. © 1990.