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 1200° C 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.