Effects of particle size on fatigue crack initiation and small crack growth in SiC particulate-reinforced aluminium alloy composites

摘要

Fatigue crack initiation and small crack growth were studied under axial loading using powder metallurgy 2024 aluminum-matrix composites reinforced with SiC particles of three different sizes of 5, 20 and 60 (mu)m. The 5 and 20 (mu)m SiC_p/Al composites exhibited nearly the same fatigue strength as the unreinforced alloy, while the 60 (mu)m SiC_p/Al composite showed a significantly lower fatigue strength due to its inferior crack initiation resistance that could be attributed to interface debonding between particles and the matrix. Small crack growth behaviour was different depending on stress level. At a low applied stress, the addition of SiC particles enhanced the growth resistance, particularly in the composites reinforced with coarser particles, while at a high applied stress, the 60 (mu)m SiC_p/Al composite showed a considerably low growth resistance, which could be attributed to interaction and coalescence of multiple cracks. In the 5 (mu)m SiC_p/Al composite small cracks grew avoiding particles and thus few particles appearing on the fracture surfaces were seen, particularly in small crack size region. In the 20 and 60 (mu)m SiC_p/Al composites, they grew along interfaces between particles and the matrix and the number of particles appearing on the fracture surfaces increased with increasing crack size or maximum stress intensity factor.