Stress-induced detwinning and martensite transformation in an austenite Ni-Mn-Ga alloy with martensite cluster under uniaxial loading.

Long Hou,Yanchao Dai,Ying Niu,Bo Yang,Lansong Ba,Zongbin Li,Claude Esling,Yves Fautrelle,Xi Li

doi:10.1107/s2052252519003208

Abstract

Stress-induced martensitic detwinning and martensitic transformation during step-wise compression in an austenite Ni-Mn-Ga matrix with a martensite cluster under uniaxial loading have been investigated by electron backscatter diffraction, focusing on the crystallographic features of microstructure evolution. The results indicate that detwinning occurs on twins with a high Schmid factor for both intra-plate and inter-plate twins in the hierarchical structure, resulting in a nonmodulated (NM) martensite composed only of favourable variants with [001]NM orientation away from the compression axis. Moreover, the stress-induced martensitic transformation occurs at higher stress levels, undergoing a three-stage transformation from austenite to a twin variant pair and finally to a single variant with increasing compressive stress, and theoretical calculation shows that the corresponding crystallographic configuration is accommodated to the compression stress. The present research not only provides a comprehensive understanding of martensitic variant detwinning and martensitic transformation under compression stress, but also offers important guidelines for the mechanical training process of martensite.

Highlights

Deformation-induced martensitic detwinning and martensitic transformation are fundamental issues in shape-memory alloys (SMAs) and they play important roles in many unique properties, such as giant magnetic field-induced strain (Sozinov et al, 2002), super-elasticity (Tanaka et al, 2010) and magnetocaloric and elastocaloric effects (Liu et al, 2012; Bonnot et al, 2008)
In this paper, using electron backscatter diffraction (EBSD), the detwinning process of nonmodulated (NM) martensite and an austenite–martensite transformation during step-wise uniaxial compression are analysed in detail
In order to gain an insight into the crystallographic evolution of martensitic clusters in an austenitic matrix under increasing loading, typical EBSD Kikuchi patterns collected from each compression stage were indexed and analysed

Summary

Introduction

Deformation-induced martensitic detwinning and martensitic transformation are fundamental issues in shape-memory alloys (SMAs) and they play important roles in many unique properties, such as giant magnetic field-induced strain (Sozinov et al, 2002), super-elasticity (Tanaka et al, 2010) and magnetocaloric and elastocaloric effects (Liu et al, 2012; Bonnot et al, 2008). The detwinning process and transformation mechanism during a step-wise compression process for martensitic embryos within bulk austenite Ni–Mn–Ga alloys, which is more. In order to obtain the crystallographic features during the evolution of multiple martensitic variant detwinning and of martensitic transformation under mechanical loading, the morphology of a nucleated martensitic cluster was examined, and the crystal orientation relationship (OR) between lowsymmetry wedge-like martensite and high-symmetry parent austenite was determined. We confine ourselves only to following the crystallographic evolution of a martensite cluster within an austenite Ni–Mn–Ga alloy under uniaxial loading. In this paper, using electron backscatter diffraction (EBSD), the detwinning process of nonmodulated (NM) martensite and an austenite–martensite transformation during step-wise uniaxial compression are analysed in detail. The present research provides a comprehensive understanding of martensitic variant detwinning and martensitic transformation under compression stress, and offers important guidelines for the mechanical training process of martensite

Experimental

Results and discussion

Conclusions

Funding information