Altered phase transformation behaviors and enhanced bending shape memory property of NiTi shape memory alloy via selective laser melting

Selective laser melting (SLM) of NiTi shape memory alloys (SMAs) was studied systematically for the resulting density and surface roughness. It was found that high laser energy density could not guarantee dense SLM NiTi SMAs. Furthermore, the phase composition and transformation temperatures varied remarkably with delicate change of laser power and scanning speed. Mechanical tests suggested that the SLM NiTi alloys made under the optimal process parameters (70 Win laser power and 105 mm/s in laser scanning speed) had an ultimate tensile strength of 788 MPa, an elongation of 7.43% in austenite state. Bending shape memory test revealed that 100% recovery rate was obtained in a sequent bending test (45 degrees -> 90 degrees -> 180 degrees -> 270 degrees -> 360 degrees), and the bending deformation was fully recovered in ten-time cycle bending test at 180 degrees, and recovery rate was 97% after ten-time cycle bending test at 360 degrees. The excellent bending shape memory properties was attributed to high-density dislocations and Ti2Ni nanoprecipitates which impeded the occurrence of plastic deformation effectively. The findings in this study demonstrated that SLM NiTi parts had excellent shape memory properties and was promising for industrial applications.

Automated summary

This study systematically investigated the density, surface roughness, and properties of selective laser melted NiTi shape memory alloys (SMAs). The findings revealed that increasing laser energy density did not guarantee dense SMAs, and the phase composition and transformation temperatures varied with slight changes in laser power and scanning speed. Mechanical tests showed that the SLM NiTi alloys made under the optimal process parameters exhibited high tensile strength and elongation. Shape memory tests demonstrated excellent recovery rates and deformation recovery of the alloys due to the presence of high-density dislocations and Ti2Ni nanoprecipitates. These findings suggest that SLM NiTi parts have promising shape memory properties for industrial applications.