The creep fracture of a single-crystal superalloy

The creep fracture of the single-crystal superalloy SRR99 at 750°C was studied for crystals oriented close to the [001] and [011] directions. The results indicate that the fracture processes operating within both orientations are highly dependent on the deformation mechanisms which operate during creep deformation. In [001] orientations, homogeneous deformation leads to the formation of macroscopically "square" mode I cracks with sides parallel to 〈011〉 directions. These cracks propagate through the γ′ precipitates from microporosity. Final rupture in this orientation occurs by the interlinkage of these mode I cracks by fracture along four {111} planes when the resolved shear stress on the remaining material is equal to the critical resolves shear stress of the alloy. Conversely, failure in [011] orientations occurs in a fast and catastrophic manner, with a single crack growing along heterogeneous shear bands which lie along {111} type planes. © 1993.