From functional to intelligent: laser powder bed fusion additive manufactured NiTi shape memory alloys

Additive manufacturing technology is appropriate for fabricating NiTi products, but the control of microstructure, phase transformation, and mechanical property of NiTi alloys is scarce and imperative. The limitation and development tendency are also necessary for expanding application.

Prof. Yusheng Shi, Prof. Bo Song, and Ph.D. Shuaishuai Wei at Rapid Manufacturing Centre of Huazhong University of Science and Technology carried out this work (laser powder bed fusion additive manufacturing of NiTi shape memory alloys: A review), which was published in International Journal of Extreme Manufacturing.

The research summarizes the effect of process parameters on printability of LPBF-fabricated NiTi alloys. Furthermore, the mechanical properties and functional behaviors of NiTi SMAs depend on the microstructural characteristics, including morphology, phase, and texture, which manipulate the phase transformation behaviors during deformation process. controlling phases, crystallization and grain growth during the LPBF is crucial to regulating the microstructure of the NiTi part with different compositions.

The research indicates that the internal factor for variation of phase transformation behaviors and temperatures is chemical composition, and sums up the influence of process parameters and precipitate phases. The summaries of stress-strain response, critical stress to induce martensitic transformation, superelasticity response, and shape memory effect are showing to provide evidence for enhancing mechanical properties of LPBF-fabricated NiTi alloys.

“Shape memory alloy is an interesting material, because it can ‘remember’the original shape and recover to the original shape after external stimulus,” said Xiaobo Wang, a Ph.D. at Rapid Manufacturing Centre of Huazhong University of Science and Technology and the co-author on the study. “NiTi alloy, also known as Nitinol, is the most commonly-employed SMA in the industrial and biomedical fields due to its superior SME and SE performance,” said Shuaishuai Wei, a Ph.D. at Rapid Manufacturing Centre of Huazhong University of Science and Technology and the first author on the study.

However, due to the strong work-hardening and high tool wear, it is rather challenging to prepare NiTi SMA devices, especially those with complex geometries. In the past decades, additive manufacturing technology (AM) has been highly anticipated for investigators and engineers to prepare advanced complex components due to the virtually unlimited design freedom and near-net-shape production capability. LPBF is regarded as a significant part of AM to rapidly fabricate highly individualized metallic components on demand.

“The fusion of interesting material with superior performance and suitable process technique by scientists break out lots of possibilities,” said Jinliang Zhang, a Ph.D. at Rapid Manufacturing Centre of Huazhong University of Science and Technology. Thus, a systematic review of the recent research progresses of LPBF-fabricated NiTi alloys is necessary.

The process parameters and material components of NiTi alloys greatly influence the formation of defects, densification, element nickel evaporation, manufacturing fidelity, and impurity pick-up. These works focus on the effect of process parameters and material components on discrepancies in microstructure, phase TTs, and mechanical properties of the LPBF-manufactured NiTi alloys.

“The research of additive manufactured NiTi alloys is aim to realize intelligent applications,” said Bo Song, a professor at Rapid Manufacturing Centre of Huazhong University of Science and Technology and the corresponding author on the paper, “and structure design with different function and configuration is the foundation of application.” NiTi products can integrate extra functionalities geometrically dependent on the structure configurations, such as negative Poisson’s ratio structures, diamond-like lattice structures, cellular gyroid, and sheet gyroid structures. The design of lattice-based structural components for LPBF-manufactured NiTi alloys has unparalleled application in industrial engineering and biomaterial.

“We came up with some development tendencies: on the one hand, we need proceed the research of technology including the controllability of microstructures, the evaporation of Ni element and the novel NiTi component for LPBF; one the other hand, suitable structures and more possible application scenarios for NiTi alloys need further expand.” said Prof. Song. Although some limitations and shortcomings need further investigation, the unique characteristics of LPBF-fabricated NiTi alloys make them rapidly develop and achieve application in many fields like aerospace, national defense, biomedicine, and others.

About IJEM:

International Journal of Extreme Manufacturing (IF: 10.036) is a new multidisciplinary, double-anonymous peer-reviewed and diamond open-access without article processing charge journal uniquely covering the areas related to extreme manufacturing. The journal is devoted to publishing original articles and reviews of the highest quality and impact in the areas related to extreme manufacturing, ranging from fundamentals to process, measurement and systems, as well as materials, structures and devices with extreme functionalities.

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