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Shape memory effect in nanocrystalline NiTi alloy processed by high-pressure torsion
Shahmir, H.,Nili-Ahmadabadi, M.,Huang, Y.,Myun Jung, J.,Seop Kim, H.,Langdon, T.G. Elsevier Sequoia 2015 Materials science & engineering. properties, micro Vol.626 No.-
A NiTi alloy was processed by high-pressure torsion for 10 turns followed by post-deformation annealing at 673K for various times. An anneal for 60min gave a nanocrystalline microstructure with a superior shape memory effect and an improvement of more than 40% over the initial state.
Nanostructural Evolution and Deformation Mechanisms of Severely Deformed Pure Fe
N. Forouzanmehr,H. R. Jafarian,M. Samadi‑khoshkhoo,M. Bönisch,M. Nili‑Ahmadabadi 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.6
Microstructural evolution and mechanical behavior of commercially pure Fe during severe deformation by cold caliber rollingfollowed by wire drawing were investigated using transmission electron microscopy and electron backscatter diffraction. Following by a drastic increment of strength in the early stage of deformation, shear banding as a softening mechanism leadsto decreasing of work hardening rate and finally a steady state situation at medium strains, creating a bimodal microstructure. Increasing strain beyond 3 is associated with increasing the rate of work hardening and refinement of the material. Severelydeformed Fe after cold caliber rolling to equivalent strain of 4.5 evolves from lamellar ultrafine-grained structure. Additionaldeformation by drawing results in more homogeneous structure and activates new mechanisms. A dynamic recovery appearsat severe strains through mechanically assisted triple junction motion. It is found that suppression of triple junction motionenhances the refinement of microstructure and the strength, such that the highly deformed Fe after equivalent strain of 7 hasa nano/ultrafine-grained structure combined with a high tensile strength of 1115 MPa.