M.A. Mohtadi-Bonab

Texture Development of ARB-Processed Steel-Based Nanocomposite

In this study, the evolution of deformation texture in steel-based nanocomposite fabricated via accumulative roll bonding (ARB) process was investigated. Textural evolution during the ARB process was evaluated using x-ray diffraction. It was found that with increasing number of ARB cycles, first, intensity of α-fiber, γ-fiber, and θ-fiber decreased and then increased, while ζ-fiber exhibited the opposite trend compared to these fibers. Also, there were texture transitions in ε-fiber and η-fiber. It was realized that with increasing the number of ARB cycles, volume fraction of low-angle grain boundary decreased and the fraction of high-angle grain boundary increased. In addition, shear texture was predominant after first cycle, while for other samples, rolling texture was dominant. When recrystallization occurred, the intensity of ζ-fiber increased, the intensity of α-fiber and γ-fiber decreased, and the intensity of {011}〈100〉 orientation in ε-fiber and η-fiber remarkably increased. Indeed, the transition from rolling texture to shear texture was a sign of occurrence of discontinuous recrystallization after the first ARB cycle. Moreover, in the one-cycle sample, nucleation of discontinuous recrystallization had occurred. Finally, with increasing the number of cycles, the intensity of rolling texture increased and the intensity of shear texture decreased.

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

Abstract 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 // <110> grains in the starting microstructure. The regions of higher dislocation densities became gradually textured to ND // <111> 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.