Effect of hatch spacing and laser power on microstructure, texture, and thermomechanical properties of laser powder bed fusion (L-PBF) additively manufactured NiTi. (May 2022)

• Record Type: Journal Article
• Authors: Ehsan Saghaian, Sayed; Nematollahi, Mohammadreza; Toker, Guher; Hinojos, Alejandro; Shayesteh Moghaddam, Narges; Saedi, Soheil; Lu, Charles Y.; Javad Mahtabi, Mohammad; Mills, Michael J.; Elahinia, Mohammad; Karaca, Haluk E.
• Is Part Of: Optics & laser technology. Volume 149(2022)
• Publication Date: 2022-05
• Subjects: Shape Memory Alloys -- NiTi -- Additive Manufacturing -- Laser Powder Bed Fusion -- Effect of Process Parameters -- Texture; Optics -- Periodicals; Lasers -- Periodicals; Electronic journals; 621.366
• DOI: 10.1016/j.optlastec.2021.107680
• Languages: English
• ISSNs: 0030-3992

Abstract

Highlights: Expand optimum L-PBF-AM process parameters (PPs) threshold for SMAs fabrication. Evaluate the texturing advantage of L-PBF-AM to fabricate highly textured NiTi. Clarify the impact of linear and volumetric energy densities on NiTi product quality. Customize the temperature functionality of NiTi by altering the hatch spacing. Present the impacts of PPs on superelastic stability and recovery ratio of AM NiTi. Abstract: This study systematically evaluates the effects of laser powder bed fusion additive manufacturing (L-PBF-AM) parameters (hatch spacing and laser power) on the thermomechanical behavior and microstructure of Ni50.8 Ti49.2 shape memory alloy. The samples were fabricated with hatch spacings from 40 to 240 µm and laser powers of 50 and 100 W at a constant scanning speed of 125 mm/s, resulting in parts with volumetric energy density levels from 55 to 666 J/mm 3 and two sets of linear energy densities of 0.4 and 0.8 J/mm. The results showed a reduced melt pool size and discontinuity of scan tracks with decreased laser power. Additionally, the porosity level was increased with larger hatch spacing and lower laser power. More notably, the transformation temperatures increased, and the critical stress, recoverable strain, and functional stability of samples improved with lower hatch spacing, where the recovery ratio of up to 90% was observed, regardless of the employed laser power. This study also discussed the relationship between the fabrication process and texture formation in the L-PBF-AM process. The advantage of L-PBF-AM was revealed in tailoring the microstructure from highly textured samples in [1 1 1] or [0 0 1] direction when hatch spacing lower than laser beam focused was employed, to the appearance of equiaxed solidification front with island grains and random orientations.