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Metals 2017, 7(4), 145; doi:10.3390/met7040145

Role of Severe Plastic Deformation in Suppressing Formation of R Phase and Ni4Ti3 Precipitate of NiTi Shape Memory Alloy

1
College of Mechanical and Electrical Engineering, Harbin Engineering University, Harbin 150001, China
2
College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China
*
Author to whom correspondence should be addressed.
Received: 22 March 2017 / Revised: 14 April 2017 / Accepted: 17 April 2017 / Published: 19 April 2017
(This article belongs to the Special Issue Shape Memory Alloys 2017)
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Abstract

Microstructural evolution of NiTi shape memory alloy (SMA) with a nominal composition of Ni50.9Ti49.1 (at %) is investigated on the basis of heat treatment and severe plastic deformation (SPD). As for as-rolled NiTi SMA samples subjected to aging, plenty of R phases appear in the austenite matrix. In terms of as-rolled NiTi SMA samples undergoing solution treatment and aging, Ni4Ti3 precipitates arise in the austenite matrix. In the case of as-rolled NiTi SMA samples subjected to SPD and aging, martensitic twins are observed in the matrix of NiTi SMA. With respect to as-rolled NiTi SMA samples subjected to solution treatment, SPD, and aging, neither R phases nor Ni4Ti3 precipitates are observed in the matrix of NiTi SMA. The dislocation networks play an important role in the formation of the R phase. SPD leads to amorphization of NiTi SMA, and in the case of annealing, amorphous NiTi SMA samples are subjected to crystallization. This contributes to suppressing the occurrence of R phase and Ni4Ti3 precipitate in NiTi SMA. View Full-Text
Keywords: shape memory alloy; NiTi alloy; severe plastic deformation; microstructure shape memory alloy; NiTi alloy; severe plastic deformation; microstructure
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Hu, L.; Jiang, S.; Zhang, Y. Role of Severe Plastic Deformation in Suppressing Formation of R Phase and Ni4Ti3 Precipitate of NiTi Shape Memory Alloy. Metals 2017, 7, 145.

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