Stray Grain Formation and Solidification Cracking Susceptibility of Single Crystal Ni-Base Superalloy CMSX-4

Abstract

The stray grain formation behavior and susceptibility to solidification cracking in autogenous welds on single crystal alloy CMSX-4 have been investigated. Welds were prepared using the electron beam (EB) and gas tungsten arc welding (GTAW) processes. The stray grain area fraction and cracking susceptibility were determined and correlated to the processing parameters and process type. The stray grain content initially increased and then decreased with increasing travel speed. This effect is attributed to the complex effect of travel speed on the temperature gradient and growth rate and resulting amount of constitutional supercooling in the weld. The stray grain content decreased with decreasing weld power. In general, the amount of stray grains and resultant cracking susceptibility were observed to decrease by the use of low heat inputs. The stray grain content and cracking susceptibility of welds prepared with the GTA process was always higher than welds made with the EB process. This difference is attributed to differences in power density and concomitant temperature gradient, where the EB process produced a higher temperature gradient that reduced the amount of stray grains and resultant susceptibility to cracking. For the conditions evaluated in this work, EB welds produced at heat inputs below ~ 13 J/mm produced welds that were crack-free with stray grain contents <5%.