Grain Scale Straining Processes during High Temperature Compression of a PM Disk Alloy

Abstract

Microstructural-scale straining processes that occur during high temperature compression of powder-consolidated nickel-based superalloy René 88DT at 1050˚C (1925˚F) have been studied. A high temperature strain mapping technique has been utilized to quantify grain-level strain accumulation. Orientation imaging has also been employed to study grain-level straining and dislocation storage. Two distinct straining mechanisms were observed. At low strain rates grain boundary sliding dominates while intragranular plastic deformation is observed during high rate compression. Stored strain and microstructural evolution are dependent on strain rate during compression. At low strain rates superplastic deformation occurs with low levels of stored strain and some grain growth. At high strain rates dynamic recrystallization occurs along with higher levels of stored strain within selected grains, particularly those at the high end of the grain size distribution. Dynamic recrystallization results in grain refinement and flow stress softening, which all occur when misorientation within individual grains exceeds a level of approximately 5°.

Formation mechanism of abnormally large grains in a polycrystalline nickel-based superalloy during heat treatment processing

“…Agnoli et al [26,30] reported the stored energy heterogeneity using level-set simulation and experiment and argued that strain-induced selective grain growth was responsible for the formation of ALGs, which involves the excessive growth of a few lower stored energy grains at the expense of grains with higher stored energy. This heterogeneous stored energy distribution in grain scale was also observed in forged nickel base superalloys [31][32][33].…”