Effect of cold rolling on microstructure, texture, and tensile properties of a Ni-Fe-based superalloy

In this work, the effect of cold rolling on microstructure, texture, and tensile properties of a Ni-Fe-based superalloy for Generation Ⅳ nuclear reactor application was systematically investigated. The results show that different deformed microstructures were observed during cold rolling, including dislocation tangles, slip bands, and microtwins (MTs). The dominant cold rolling deformation mechanism of the alloy gradually changed from planar slipping to deformation twinning, which was a little different from Ni-/Co-based superalloys. A texture transition from Copper {112}< 111 > to Brass {110}< 112 > and Goss {110}< 001 > at 25 % rolling reduction was detected due to the changed deformation mechanism. The standard heat treatment alloy exhibited a yield strength of 213 MPa and good elongation of 54 %. By increasing the rolling reduction up to 55 %, the yield strength was significantly enhanced to 872 MPa, which was attributed to the combined strengthening from both MTs and dislocations. Fine-spaced MTs with coherent interfaces can impede dislocation motion effectively and play a critical role in the strengthening, contributing 75–235 MPa to the yield strength. MTs can also provide ample room for dislocation accumulation, which maintained a reasonable elongation of 12 %. Moreover, due to the texture evolution during cold rolling, the averaged Schmid factor (SF) values for {111}< 110 > slip system exhibited a decreasing trend with the increased rolling reduction, contributing to the progressive increase in yield strength. The present work demonstrates that the formation of MTs at high rolling reductions is an essential reason for the improvement of mechanical properties of the alloy, which also provides a new strategy for designing and optimizing high-performance solid-solution strengthened Ni-Fe-based superalloys.