Microstructure and torsional behavior of selective laser melted NiTi shape memory alloy

Wednesday, May 18, 2022: 11:30 AM
Sunset Ballroom (Westin Carlsbad Resort)
Mr. Keyvan Safaei Baghbaderani , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Mr. Mohammadreza Nematollahi , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Ms. Parisa Bayati , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Ms. Fatemeh Kordizadeh , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Mohsen Taheri Andani , University of Michigan, Ann Arbot, MI
Mr. Hossein Abedi , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Nasrin Taheri Andani , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Dr. Othmane Benafan , NASA Glenn Research Center, Cleveland, OH
Dr. Behrang Poorganji , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Prof. Mohammad Elahinia , Department of Mechanical Engineering, University of Toledo, Toledo, OH
Selective laser melting (SLM) is a free-form additive manufacturing (AM) method showing remarkable progress in fabricating shape memory alloys. The properties of the SLM NiTi parts have been investigated under compression and tension, however, no work has been reported on the torsional behavior of additively manufactured parts. In this study, a series of NiTi tubes with different thicknesses were fabricated via the SLM technique. The optical microscopy shows size deviation and micro defects on the boundaries. A large shift between transformation temperatures and microstructural phases of the starting powder and as-built tubes is observed. X-ray diffraction patterns show the existence of Ti-rich oxide precipitates that may have formed during the builds. Scanning electron microscopy confirms Ti-rich precipitates formation along the grain boundaries, attributed to some of the transformation temperature shifts. Tubes were subjected to mechanical testing and the measured strains (using digital image correlation) show strain-localization on the tube surface under pure torsion. A stable strain recovery of 2.3% is achieved after deforming and heating after 10 cycles.
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