A Short Review on the Microstructure, Transformation Behavior and Functional Properties of NiTi Shape Memory Alloys Fabricated by Selective Laser Melting.

Xiebin Wang,Sergey Kustov,Jan Van Humbeeck

doi:10.3390/ma11091683

Xiebin Wang, Sergey Kustov + Show 1 more

Open Access

https://doi.org/10.3390/ma11091683

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Abstract

Due to unique functional and mechanical properties, NiTi shape memory alloys are one of the most promising metallic functional materials. However, the poor workability limits the extensive utilization of NiTi alloys as components of complex shapes. The emerging additive manufacturing techniques provide high degrees of freedom to fabricate complex structures. A freeform fabrication of complex structures by additive manufacturing combined with the unique functional properties (e.g., shape memory effect and superelasticity) provide great potential for material and structure design, and thus should lead to numerous applications. In this review, the unique microstructure that is generated by selective laser melting (SLM) is discussed first. Afterwards, the previously reported transformation behavior and mechanical properties of NiTi alloys produced under various SLM conditions are summarized.

Highlights

Near equiatomic NiTi shape memory alloys (SMAs) could appear in a B2 structured austenite (A), a B19’ structured martensite (M) or a rhombohedral R-phase, depending on the thermal or mechanical conditions [1]
NiTi alloy powders are exposed to the laser beams with high energy density during selective laser melting (SLM)
(1273 K, 2 h), we could conclude that the variation of martensite transformation temperatures (MTTs) of NiTi samples that were produced under different SLM conditions is mainly due to the modification of effective Ni/Ti ratio

Summary

Introduction

Near equiatomic NiTi shape memory alloys (SMAs) could appear in a B2 structured austenite (A), a B19’ structured martensite (M) or a rhombohedral R-phase, depending on the thermal or mechanical conditions [1]. The work on additively fabricating the NiTi parts by SLM starts from producing dense and porous-free parts by optimizing the SLM process. An even higher energy density of 595 J/mm was used by Ma et al [42], by reducing the hatch spacing This indicates that many other factors have to be considered in order to optimize the SLM process, for instance, particle size, laser type, and spot size, as well as different combinations of SLM process parameters [50]. It is essential to understand the interrelation between SLM process and the resulted microstructure, and the phase transformation behavior and functional properties of the produced NiTi parts. Afterwards, the previous works on explaining the phase transformation behavior, as well as improving the tensile properties of SLM fabricated NiTi parts, are summarized

Microstructure

Phase Transformation Behavior

Tensile Properties

Findings

Conclusions