Micromechanisms of Creep–Fatigue Crack Growth in a Silicide‐Matrix Composite with SiC Particles

Abstract

An experimental study has been conducted to examine the cyclic fatigue crack growth characteristics in 1200oC air of a MoSi2‐50 mol% Wsi2 alloy the unreinforced condition and with 30 vol% SiC particles. For comparison purposes, crack growth experiments under sustained loads were also carried out in the silicide‐matrix composite. Particular attention is devoted to developing an understanding of the micromechanisms of subcritical crack‐tip damage. The results indicate that enhanced viscous flow of glass films along interfaces and grain boundaries imparts pronounced levels of subcritical crack growth in the composite material; the composite exhibits a higher fatigue fracture threshold and a more extended range of stable fracture than the unreinforced alloy. The effects of glass phase in influencing fatigue crack growth in the silicide‐based material are compared to the influence of in situ‐formed and preexisting glass films on high‐temperature cyclic fatigue crack growth in ceramics and ceramic composites. The paper concludes with a comparison of present results with the high‐temperature damage tolerance of a variety of intermetallic alloys and ceramic materials.