Characterization of localized deformation near grain boundaries of superalloy René-104 at elevated temperature

Abstract

in situ surface deformation measurement techniques were applied to characterize strain localization sites in nickel-based superalloys when tested under constant load at 700°C. Deformation maps were coupled with electron backscatter diffraction (EBSD) measurement of grain location and orientation to correlate localization sites with underlying surface microstructure. Superalloy René-104 was heat treated and quenched to create two microstructures with similar grain sizes but different grain boundary character: the standard microstructure had microscopically planar grain boundaries, and the other microstructure had serrated grain boundaries. Analysis of full field strain maps calculated from in situ scanning electron microscopy (SEM) images indicated distinct differences in strain localization as a function of total strain for the two microstructures. The standard microstructure showed very little intra-granular strain accumulation, and annealing twin boundaries played an important role in strain localization sites, whereas the serrated microstructure experienced strain accumulation more evenly throughout the microstructure. Grain boundary sliding (GBS) was observed in both microstructures, but the development of serrated grain boundaries significantly decreased the contribution of this mechanism to the overall strain accommodation from 20% to 14% of the total plastic strain being accommodated by GBS.