Low temperature and high strain rate superplasticity of nickel base alloys

This paper will describe features of micro-, submicro-, and nano- crystalline structure formation under severe plastic deformation and the influence of structure on superplastic (SP) behavior of high alloyed nickel base alloys with a range of hardened precipitates ( gamma '; gamma '' + delta , gamma ' + Y sub 2 O sub 3 ). It has been shown that severe plastic deformation over a wide range of homologous temperatures (0.9-0.2 T sub m ) can refine the microstructure to a size of several tens of nanometers. In comparison with the microcrystalline (MC) state, the submicrocrystalline (SMC) structure in dispersion hardened alloys reduces the optimal temperature of SP deformation from 0.9-0.8 T sub m to 0.7-0.6 T sub m . The PDS alloy combines precipitation and dispersion hardening ( gamma ' + Y sub 2 O sub 3 ), and, in the SMC state, it can display both low temperature and high strain rate superplasticity. Features of microstructure transformations and failure of samples during SP deformation are considered.