Effect of micro-strain and (100) texture intensity on corrosion behaviors of NiTi alloy via laser powder bed fusion

Abstract

We report the effect of micro-strain and (100) texture intensity on corrosion behaviors of NiTi shape memory alloys (SMAs) subjected to laser powder bed fusion (LPBF) and further elucidate their underlying pitting mechanism in a 3.5 wt% NaCl solution. Our findings reveal that the low micro-strain and simultaneous the high (100) texture intensity result in outstanding corrosion resistance featuring the low corrosion current density in the NiTi SMA sample (S_MM) with the middle LPBF power and scan speed, outperforming the corresponding current ones reported in NiTi SMAs via various materials processing approaches. Essentially, this is attributed to the minimized diffusion channels by the low micro-strain and the dense uniform passivation film by the high (100) texture intensity. Two additional samples, S_LL (low LPBF power and scan speed) and S_HH (high LPBF power and scan speed), exhibit different corrosion behaviors. Based on the high micro-strain and low (100) texture intensity, the S_LL sample shows transverse corrosion with numerous shallow pits, while the S_HH sample experiences longitudinal corrosion with deeper pits. These variations may stem from Cl⁻ penetration hindered by compressive stress in S_LL and faster diffusion channels in the S_HH due to a higher proportion (18.8%) of fine grains. These findings offer valuable insights for optimizing microstructure design to improve the corrosion resistance of metallic materials produced by LPBF.