Microstructural investigation on marforming and conventional cold deformation in Ni-Ti-Fe-based shape memory alloys

A hot-rolled Ni-Ti-Fe alloy was subjected to 50% cold rolling by laboratory rolling mill and was subsequently annealed at 800 C for 1.5 h. This sample was then deformed through another 10% reduction in thickness by two different routes (i) conventional cold rolling and (ii) marforming (rolling in liquid nitrogen) followed by annealing under identical conditions. The grain refinement during normal cold rolling was attributed to relatively large presence of dislocations in the ND // left angle 110 right angle grains in the starting microstructure. The regions of higher dislocation densities became gradually textured to ND // left angle 111 right angle orientation, with cold rolling. Marforming (deformation in liquid nitrogen following phase transformation) on the other hand led to more significant grain refinement and also change in the bulk texture. The objective of this study was to compare the grain refinement and microstructural modification produced through marforming with that obtained in conventional cold deformation.