Fg. Gaudette et al., Effects of sulfur on the fatigue and fracture resistance of interfaces between gamma-Ni(Cr) and alpha-Al2O3, MET MAT T A, 31(8), 2000, pp. 1977-1983
Dramatic effects of S on the adhesion and fatigue resistance of interfaces
between gamma-Ni(Cr) and alpha-Al2O3, have been explicitly demonstrated and
quantified. This has been achieved by using two bonding conditions: one in
volving solid-state diffusion (SSDB) and another through a liquid phase (LP
B) that forms at temperatures above a eutectic that releases a S-rich Liqui
d. Upon SSDB, there is no significant S excess at the interface, whereas LP
B forms a thin interphase with a high local concentration of S. The SSDB ma
terials have interfaces with such high toughness (above 300 J m(-2)) and fa
tigue resistance that mode I cracks divert into the Al2O3, rather than prop
agate at the interface. Conversely the LPB materials delaminate at the inte
rface, solely as a result of the residual stresses from thermal expansion m
isfit, with an interface toughness in the range 2 to 7 J m(-2).