Microstructure, Mechanical Properties and Corrosion Performance of Laser-Welded NiTi Shape Memory Alloy in Simulated Body Fluid

• Published in: Materials Vol. 17; no. 19; p. 4801
• Main Authors: Kannan, A Rajesh, Shanmugam, N Siva, Rajkumar, V, Vishnukumar, M, Channabasavanna, S G, Oh, Junho, Dat, Than Trong Khanh, Yoon, Jonghun
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 29-09-2024; MDPI
• Subjects: Alloys; Base metal; Biocompatibility; Biomedical engineering; Biomedical materials; Body fluids; Corrosion; Corrosion environments; Corrosion potential; Corrosion rate; Corrosion tests; Discount coupons; Hardness; Heat affected zone; Influence; Intermetallic compounds; Intermetallic phases; Laser beam welding; laser-welding; Lasers; Localized corrosion; Mechanical properties; Medical electronics; Microstructure; Nickel base alloys; NiTi; Orthodontics; Performance evaluation; Pitting (corrosion); Pitting potential; Precipitates; shape memory alloy; Shape-memory alloys; simulated body fluid; Steel; Tensile strength; Tensile tests; Titanium compounds; Transplants & implants; Welding; India; Germany; laser-welding; shape memory alloy; corrosion; microstructure; NiTi; simulated body fluid
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma17194801

Laser-welding is a promising technique for welding NiTi shape memory alloys with acceptable tensile strength and comparable corrosion performance for biomedical applications. The microstructural characteristics and localized corrosion behavior of NiTi alloys in a simulated body fluid (SBF) environment are evaluated. A microstructural examination indicated the presence of fine and equiaxed grains with a B2 austenite phase in the base metal (BM), while the weld metal (WM) had a coarse dendritic microstructure with intermetallic precipitates including Ti
Ni and Ni
Ti
. The hardness decreased from the BM to the WM, and the average hardness for the BM was 352 ± 5 HV, while it ranged between 275 and 307 HV and 265 and 287 HV for the HAZ and WM, respectively. Uni-axial tensile tests revealed a substantial decrease in the tensile strength of NiTi WM (481 ± 19 MPa), with a reduced joint efficiency of 34%. The localized corrosion performance of NiTi BM was superior to the WM, with electrochemical test responses indicating a pitting potential and low corrosion rate in SBF environments. The corrosion rate of the NiTi BM and WM was 0.048 ± 0.0018 mils per year (mpy) and 0.41 ± 0.019 mpy, respectively. During welding, NiTi's strength and biocompatibility properties changed due to the alteration in microstructure and formation of intermetallic phases as a result of Ti enrichment. The performance and safety of welded medical devices may be impacted during welding, and it is essential to preserve the biocompatibility of NiTi components for biomedical applications.