The above analysis of the manner in which the state of stress controls the crack propagation process, depending upon the nature of the crack can be verified by the examination of fracture surface showninFig.7 andFig.12.Forexample,thematerialwith the lowest rupture time has been identified to fracture by the propagation of wedge crack. Its intergranular boundary facets are scattered with the precipitates and cavities with shapes similar to those of the precipitates that have been pulled out from the surface. Indications of deformation around the precipitates as well as on the boundary surface are not evident. This is also true for the material with a clean grain boundaries, in which the trace of slip lines due to the deformation of grain material are well preserved. In contrast to this, the material which is suggested to have fractured by the propagation of void-formed cracks shows massive deformation on the grain boundaries, which must be by a stressalong the direction parallel to the boundary surfaces.