Amelioration of weld-crack resistance of the M951 superalloy by engineering grain boundaries

Abstract

Fusion weld is a portable and economical joining and repairing method of metals. However, weld cracks often occur during the fusion weld of Ni-base superalloys, which hinder the applications of fusion weld on this kind of materials. In this work, the effects of microstructures of grain boundaries (GBs) of the prototype M951 superalloy on its weldability were investigated. The precipitated phases, the elemental segregations on GBs, and the morphologies of GBs can be largely altered by regulating the cooling rates of pre-weld heat treatments. With decreasing the cooling rate, chain-like M23X6 phase precipitates along the GBs, accompanying segregations of B, and GBs becomes more serrated in morphology. During fusion weld, the engineered GBs in the M951 superalloy with a low cooling rate favor the formation of the continuous liquid films on GBs, which together with the serrated GB morphology significantly prevents the formation of weld cracks. Our findings imply that the weld-crack resistance of the superalloys can be ameliorated by engineering GBs.