Grain Size Effect of the γ Phase Precipitation on Martensitic Transformation and Mechanical Properties of Ni-Mn-Sn-Fe Heusler Alloys.

Hong Yang,Yingchao Li,Junsong Zhang,Yinong Liu,Jinpei Guo,Yajiu Zhang,Wei Zhou,Zhigang Wu,Minting Zhong

doi:10.3390/ma14092339

Hong Yang, Yingchao Li + Show 7 more

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https://doi.org/10.3390/ma14092339

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Abstract

Isothermal annealing of a eutectic dual phase Ni–Mn–Sn–Fe alloy was carried out to encourage grain growth and investigate the effects of grain size of the γ phase on the martensitic transformation behaviour and mechanical properties of the alloy. It is found that with the increase of the annealing time, the grain size and volume fraction of the γ phase both increased with the annealing time predominantly by the inter-diffusion of Fe and Sn elements between the γ phase and the Heusler matrix. The isothermal anneals resulted in the decrease of the e/a ratio and suppression of the martensitic transformation of the matrix phase. The fine γ phase microstructure with an average grain size of 0.31 μm showed higher fracture strength and ductility values by 28% and 77% compared to the coarse-grained counterpart with an average grain size of 3.31 μm. The fine dual phase microstructure shows a quasi-linear superelasticity of 4.2% and very small stress hysteresis during cyclic loading, while the coarse dual phase counterpart presents degraded superelasticity of 2.6% and large stress hysteresis. These findings indicate that grain size refinement of the γ phase is an effective approach in improving the mechanical and transformation properties of dual phase Heusler alloys.

Highlights

Ni–Mn-based Heusler alloys offer multiple useful properties as functional materials, such as the magnetic-field-induced shape memory effect [1,2,3] and giant magnetocaloric effect [4,5,6,7]
Ni–Mn–Ga systems because the strength of the γ phase in Fe-doped system was the lowest, presenting the smallest resistance to martensitic transformation [23]. This suggests that the Fe-doped dual phase Ni–Mn–based alloys may be promising for practical use if an optimized combination of ductility and shape memory effect is achieved
Villa et al studied the γ phase distribution correlation with improvements in mechanical and functional properties. They found that the localization of the γ phase at the grain boundaries has the maximum benefits for ductility improvement and the least adverse effect on shape memory effect and pseudoelasticity in a Ni–Mn–Ga-Fe system [24]

Summary

Introduction

Ni–Mn-based Heusler alloys offer multiple useful properties as functional materials, such as the magnetic-field-induced shape memory effect [1,2,3] and giant magnetocaloric effect [4,5,6,7]. Ni–Mn–Ga systems because the strength of the γ phase in Fe-doped system was the lowest, presenting the smallest resistance to martensitic transformation [23] This suggests that the Fe-doped dual phase Ni–Mn–based alloys may be promising for practical use if an optimized combination of ductility and shape memory effect is achieved. Villa et al studied the γ phase distribution correlation with improvements in mechanical and functional properties They found that the localization of the γ phase at the grain boundaries has the maximum benefits for ductility improvement and the least adverse effect on shape memory effect and pseudoelasticity in a Ni–Mn–Ga-Fe system [24]. This provides an opportunity to clarify the effects of the grain size of the γ phase on the martensitic transformation behaviour and mechanical properties of these dual phase Heusler alloys

Materials and Methods

Microstructure and Composition Analysis

Phase Structure and Transformation Behaviour

Mechanical Properties and Superelasticity

Crack Propagation and Fractographic Examination