Formation mechanism of heterogeneous microstructures and shape memory effect in NiTi shape memory alloy fabricated via laser powder bed fusion

H.Z. Lu; L.H. Liu; X. Luo; H.W. Ma; W.S. Cai; R. Lupoi; S. Yin; C. Yang

Materials & Design (Aug 2023)

Formation mechanism of heterogeneous microstructures and shape memory effect in NiTi shape memory alloy fabricated via laser powder bed fusion

H.Z. Lu,
L.H. Liu,
X. Luo,
H.W. Ma,
W.S. Cai,
R. Lupoi,
S. Yin,
C. Yang

Affiliations

H.Z. Lu: National Engineering Research Center of Near-net-shape Forming for Metallic Materials, Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic Materials, South China University of Technology, Guangzhou, China; School of Mechatronic Engineering, Guangdong Polytechnic Normal University, Guangzhou, China; Trinity College Dublin, the University of Dublin, Department of Mechanical, Manufacturing and Biomedical Engineering, Parsons Building, Dublin 2, Ireland
L.H. Liu: National Engineering Research Center of Near-net-shape Forming for Metallic Materials, Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic Materials, South China University of Technology, Guangzhou, China
X. Luo: National Engineering Research Center of Near-net-shape Forming for Metallic Materials, Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic Materials, South China University of Technology, Guangzhou, China
H.W. Ma: National Engineering Research Center of Near-net-shape Forming for Metallic Materials, Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic Materials, South China University of Technology, Guangzhou, China
W.S. Cai: National Engineering Research Center of Near-net-shape Forming for Metallic Materials, Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic Materials, South China University of Technology, Guangzhou, China
R. Lupoi: Trinity College Dublin, the University of Dublin, Department of Mechanical, Manufacturing and Biomedical Engineering, Parsons Building, Dublin 2, Ireland
S. Yin: Trinity College Dublin, the University of Dublin, Department of Mechanical, Manufacturing and Biomedical Engineering, Parsons Building, Dublin 2, Ireland; Corresponding authors.
C. Yang: National Engineering Research Center of Near-net-shape Forming for Metallic Materials, Guangdong Provincial Key Laboratory for Processing and Forming of Advanced Metallic Materials, South China University of Technology, Guangzhou, China; Corresponding authors.

Journal volume & issue: Vol. 232
p. 112107

Abstract

Read online

Additive manufacturing involves the process of track-by-track melt pools accompanied by the localized rapid melting/solidification, which can determine unique nonequilibrium microstructures. In this study, we report formation of heterogeneous nonequilibrium microstructures in near-equiatomic NiTi fabricated via laser powder bed fusion (LPBF) additive manufacturing, and further discuss their underlying formation mechanisms and influences on shape memory effect of the LPBF NiTi. Specifically, the heterogeneous microstructures include the core (HCP α-Ti)-shell (Ti2Ni) structural nano-sized precipitation phases in columnar grains, which were resulted from high undercooling and cooling rate during LPBF solidification, the intermediate R phase in cellular and columnar grains, which was stemmed from residual thermal stress during LPBF, the nano-sized cellular substructure in columnar grains with boundaries decorated with Ti2Ni precipitates, which was originated from enriched Ti atoms at the solidification front during directional and orderly solidification of melt pools, together with the abundant dislocations. Interestingly, the two-way shape memory strain of 0.8% in LPBF NiTi was obtained by cycle loading–unloading-heating–cooling training process. These findings achieved in this work enrich the knowledge on formation mechanism of heterogeneous microstructures in LPBF NiTi SMAs, and further pave the way for engineering applications of two-way shape memory effect of LPBF NiTi shape memory alloys.

Published in Materials & Design

ISSN: 0264-1275 (Print); 1873-4197 (Online)
Publisher: Elsevier
Country of publisher: United Kingdom
LCC subjects: Technology: Electrical engineering. Electronics. Nuclear engineering: Materials of engineering and construction. Mechanics of materials
Website: https://www.journals.elsevier.com/materials-and-design

About the journal

Abstract

Keywords