U. Ramamurty et al., MICROMECHANISMS OF CREEP-FATIGUE CRACK-GROWTH IN A SILICIDE-MATRIX COMPOSITE WITH SIC PARTICLES, Journal of the American Ceramic Society, 76(8), 1993, pp. 1953-1964
An experimental study has been conducted to examine the cyclic fatigue
crack growth characteristics in 1200-degrees-C air of a MoSi2-50 mol%
WSi2 alloy in the unreinforced condition and with 30 vol% SiC particl
es. For comparison purposes, crack growth experiments under sustained
loads were also carried out in the silicide-matrix composite. Particul
ar attention is devoted to developing an understanding of the micromec
hanisms of subcritical crack growth by recourse to optical and electro
n microscopy, including transmission electron microscopy of crack-tip
damage. The results indicate that enhanced viscous flow of glass films
along interfaces and grain boundaries imparts pronounced levels of su
bcritical crack growth in the composite material; the composite exhibi
ts a higher fatigue fracture threshold and a more extended range of st
able 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 fil
ms on high-temperature cyclic fatigue crack growth in ceramics and cer
amic composites. The paper concludes with a comparison of present resu
lts with the high-temperature damage tolerance or a variety of interme
tallic alloys and ceramic materials.