EFFECTS OF THE PARTICLE DISTRIBUTION ON FATIGUE CRACK-GROWTH IN PARTICULATE SIC/6061 ALUMINUM-ALLOY COMPOSITES

Fatigue crack growth rates have been examined in powder-metallurgy-processed 6061 aluminium alloy composites containing 15 and 30 wt.% SiC particles with different particle distributions. Over the range 10(-9) to 10(-6) m/cycle the fatigue crack growth rates in the composite materials were lower than those reported for the monolithic alloy. SEM observations of the broken specimens showed very few SiC particles on the fatigue surfaces produced at low values of DELTA-K. An increased area fraction of the fractured coarse particles was evident on the fatigue surfaces of the bimodal distribution composites tested at high DELTA-K. Quantitative examination of the crack path profile was used to highlight the interaction between the particles and the crack path. The fatigue crack avoids SiC particles at low-DELTA-K ranges, but at high DELTA-K ranges the crack appears to proceed by linking fractured SiC particles ahead of the main crack front.