Effect of Gradient Heat Treatment on Microstructure and Properties of Cu-Al-Mn Shape Memory Alloy.

Jili Liu,Bowen Shi,Shuyang Zheng,Jingling Lan,Xu Li,Luohui Zhou

doi:10.3390/ma12162505

Jili Liu, Bowen Shi + Show 4 more

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https://doi.org/10.3390/ma12162505

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Abstract

The columnar-grained Cu–Al–Mn shape memory alloys (SMAs), which have good shape memory properties and are prepared by a unidirectional solidification technique, were subjected to a gradient heat treatment under temperatures ranging from 100 to 450 °C. After this treatment, the microstructure, hardness, transformation temperature and shape memory properties of these samples could exhibit gradient changing trends, all of which were investigated by optical microscope, scanning electron microscopy (SEM), a Vickers microhardness tester, and a compression machine. The microstructure observation result shows that the acicular bainite-precipitated phase produces from scratch and then grows continuously with the increasing of the heat treatment temperature, finally presenting a graded distribution from one end section to another of the sample. The hardness tests give the samples results also increasing with temperature. Specifically, the change relationship between hardness and the treatment temperature mathematically satisfies dynamic function. In addition, it can be concluded from mechanical tests the compressive elastic–superelastic strain and strength of the samples show gradient variation features. Overall, our experimental investigation indicates that a gradient heat treatment is an effective way to conduct microstructure control or design for the Cu–Al–Mn SMAs, and their graded properties are mainly caused by the different fractions of the bainite phase producing in different local areas after the gradient heat treatment.

Highlights

Shape memory alloys (SMAs) possess intrinsic characteristics, superelasticity and shape memory effect due to a reversible diffusionless martensitic transformation induced by external stimuli such as thermal and mechanical loadings [1,2]
The influence mechanism and control of these factors on the distribution of gradient stress are worthy of further research. These results indicate that the shape memory properties and bearing capacity of the Cu–Al–Mn
Through a simple gradient heat treatment, the graded distribution of heat treatment temperature could be realized in the Cu–Al–Mn shape memory alloy, resulting in a graded distribution of the bainite phase to realize the gradient hardness and shape memory properties for this alloy

Summary

Introduction

Shape memory alloys (SMAs) possess intrinsic characteristics, superelasticity and shape memory effect due to a reversible diffusionless martensitic transformation induced by external stimuli such as thermal and mechanical loadings [1,2]. (iii) A microstructure gradient is based on the fact that some microstructures (such as grain orientation, grain size, precipitated phase, and material defects) significantly affect the properties of alloys Some special methods, such as thermo–mechanical treatments [18,19], graded pore sintering [20], laser surface annealing [21], gradient heat treatments [22] and surface mechanical grinding [23,24], are used to make the microstructure of the alloy gradient change in a certain direction to realize the macro graded properties. The relationship between the graded structure and properties was investigated, and this can provide important references for the gradient treatment and practical application of Cu–Al–Mn alloys

Experimental Materials and Methods

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Compressive

Conclusions