Influence of building directions on the impact properties of NiTi fabricated via laser powder bed fusion

The Charpy impact toughness is a crucial mechanical parameter in the application of materials within the realm of engineering. This study represents the pioneering investigation into the influence of different building directions on the Charpy impact toughness of NiTi shape memory alloys (SMAs) produced via laser powder bed fusion (LPBF). Texture analysis reveals that C0 and C90 exhibit a pronounced // building direction (BA), while C45 demonstrates a strong texture along and . The impact test results demonstrate that C0 exhibits superior impact toughness with an absorbed energy of 12.87 J. The fractured surfaces are examined using the scanning electron microscope (SEM) and transmission electron microscope (TEM). Among them, the electron backscatter diffraction (EBSD) results indicate that the samples with higher geometrically necessary dislocation (GND) and kernel average misorientation (KAM) values can effectively reflect superior impact toughness. In contrast, fewer high-angle grain boundaries (HAGBs) are preferable. Due to the adiabatic effect, the phase transformation of the samples from austenite to martensite doesn't appear under the impact loading. Additionally, this paper discusses the impact of texture orientation, defects, and the relationship between loading direction and deposited layers on the impact toughness of the samples. These findings on impact properties would provide valuable guidance for engineering applications of NiTi SMAs.