Effects of scanning strategy and scanning speed on microstructures and mechanical properties of NiTi alloys by laser powder bed fusion

Abstract

In this work, the influence of processing parameter including laser scanning strategy and scanning speed on grain morphology and crystalline orientation of NiTi alloys fabricated by laser powder bed fusion (L-PBF) was comprehensively investigated from the perspective of crystal growth. The results show that as the interlayer rotation angle increases from 0 to 90°, the grain morphology changes from the coarse columnar to columnar-and-equiaxed shapes, accompanied by the texture intensity first rising then reducing. Besides, increasing the scanning speed leads to a transition in grain morphology from columnar to equiaxed crystals, as well as a reduction in grain size and texture intensity. The recovery mechanism caused by different thermal histories under various scanning speeds was discussed, with a particular focus on dislocation density and its distribution. The results demonstrate that the dislocation density gradually increases with the increase of scanning speed, leaving behind more dislocations within the matrix. Furthermore, the effects of scanning speed and building direction on the compressive behavior were investigated through identifying the difference of microstructure in the NiTi alloys by L-PBF. This study highlights the relationship among processing, microstructure, and mechanical performance, paving the way for tailoring and designing microstructures and mechanical properties for the NiTi alloys by L-PBF.