Effect of Laser Printing Mode on Surface Topography, Microstructure, and Corrosion Property of Additive-Manufactured NiTi Alloy

Laser powder bed fusion (LPBF) is an emerging metal additive manufacturing method that can pave a pathway for manufacturing NiTi shape memory alloys (SMAs) with high performance. Considering the unique characterizations of LPBF process, the position and sequence of laser irradiation are different under different laser scanning modes, which will affect the performance of as-built samples. Herein, four different chessboard sizes are utilized to fabricate NiTi parts. The surface quality and relative density first increase and then decrease with the increasing chessboard size, obtaining the optimal surface roughness of 9.95 & mu;m and relative density of 99.7%, respectively, at a chessboard size of 5 mm. As the chessboard size increases, the more pronounced precipitation of Ni4Ti3 with a higher quantity induces a strengthening effect, leading to a higher microhardness value of & AP;290 HV0.2 at a chessboard size of 9 mm. The electrochemical test shows a better corrosion resistance with a corrosion potential of 0.101 V and a corrosion current density of 1.670 x 10-5 A cm-2 at a chessboard size of 5 mm. The corrosion mechanism is further revealed. This work emphasizes the importance of chessboard size as a reference for optimizing the process of additive-manufactured NiTi SMAs. Appropriate choice of chessboard size improves the formability and corrosion properties of NiTi alloy. A coherent interface is observed between the B2 matrix and Ni4Ti3 precipitate phase inducing a strengthening effect. A dual-layer passive film composed of TiO2 and Ni(OH)2 enhances the corrosion resistance of the B2 matrix, and excellent corrosion resistance can be achieved at a chessboard size of 5 mm.image & COPY; 2023 WILEY-VCH GmbH