The effect of crystallization of the grain-boundary phase on ambient temperature fatigue short-crack growth behaviour in Y-α′-β′-Sialon

The cyclic fatigue short-crack growth behaviour of Y-α′-β′-Sialons with both crystallized and amorphous grain-boundary phases, were investigated to determine whether crystallization of grain boundaries affected crack-growth behaviour under cyclic and monotonic loads. Micromechanisms for fatigue-crack growth in Y-α′-β′-Sialon were examined by scanning electron microscopy and high-resolution electron microscopy. These results show that the wear debris on the fatigue fracture surfaces gave evidence of a frictional wear crack-growth mechanism. Comparison of fatigue short-crack growth rates for Sialon of crystallized grain-boundary phases with that for the amorphous grain-boundary phases indicated that crystallization of grain-boundary phases does not appear to affect cyclic fatigue growth behaviour, similar to long-crack growth behaviour. The similarity of fatigue short-crack growth behaviour in both the crystallized and amorphous grain boundaries sialons is rationalized in terms of the thin residual amorphous grain-boundary regions.