Cellular η phase precipitation and its effect on the tensile properties in an Fe–Ni–Cr alloy

The precipitation mechanism of cellular η phase at grain boundaries and its effect on the high temperature tensile properties in an Fe–Ni–Cr alloy were investigated by using TEM, SEM, EBSD and tensile testing. It was revealed that η phase nucleates at high energy grain boundaries and has a coherent orientation relationship with the austenite matrix: {0 0 1}η//{1 1 1}γ, <2 1 0>η//<1 1 0>γ. The cellular austenite in the vicinity of the η phase has the same orientation as the grain from which the η phase growth starts. The formation of cellular austenite is suggested to proceed by grain boundary migrating with precipitated η phase into the neighboring grain which is incoherent with the η phase. The precipitation of cellular η phase at grain boundary improves the high temperature ductility of the alloy dramatically.