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Open AccessArticle

The Mechanism of Inhomogeneous Grain Refinement in a NiTiFe Shape Memory Alloy Subjected to Single-Pass Equal-Channel Angular Extrusion

College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001, China
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Metals 2017, 7(10), 400; https://doi.org/10.3390/met7100400
Received: 6 September 2017 / Revised: 20 September 2017 / Accepted: 26 September 2017 / Published: 29 September 2017
(This article belongs to the Special Issue Advances in Plastic Forming of Metals)
Based on electron backscattered diffraction analysis and transmission electron microscopy observation, the mechanism of inhomogeneous grain refinement in a NiTiFe shape memory alloy (SMA) subjected to single-pass equal-channel angular extrusion (ECAE) was investigated. The results show that refined grains are mainly nucleated near grain boundaries and a small fraction of them emerges in the grain interior. The size of refined grains increases as deformation temperature increases, which indicates that a higher deformation temperature is adverse to grain refinement in the ECAE of NiTiFe SMAs. It is the accumulation and rearrangement of geometrically necessary dislocations as plastic strain increases that leads to the transition of lower angle subgrain boundaries, and finally higher angle subgrain boundaries are induced and finer grains are formed. Due to the limitation of slip systems, the mechanism of grain refinement in a NiTiFe SMA subjected to ECAE is different from that in face-centered cubic and body-centered cubic crystals. Dislocation cells and shear bands are two transition microstructures of grain refinement in the ECAE of NiTiFe SMAs. The nucleation of fine grains mainly occurs along shear bands or grain boundaries, which leads to the inhomogeneity of grain refinement. View Full-Text
Keywords: shape memory alloy (SMA); NiTiFe alloy; grain refinement; equal-channel angular extrusion (ECAE); microstructure shape memory alloy (SMA); NiTiFe alloy; grain refinement; equal-channel angular extrusion (ECAE); microstructure
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MDPI and ACS Style

Zhang, Y.; Jiang, S. The Mechanism of Inhomogeneous Grain Refinement in a NiTiFe Shape Memory Alloy Subjected to Single-Pass Equal-Channel Angular Extrusion. Metals 2017, 7, 400.

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