Study on properties of SLM-NiTi shape memory alloy under the same energy density

Abstract

In recent years, selective laser melting (SLM)-NiTi had developed rapidly due to the ability to achieve the complex shape and internal features, as well as high dimensional accuracy. The choice of parameters was particularly critical to the forming and performance of SLM-NiTi. In this work, we had designed and prepared five sets of SLM-NiTi shape memory alloys with the same energy density (range of 40–90 J/mm3). The microstructure, phase transition characteristic, mechanical properties and shape memory effect of SLM-NiTi shape memory alloys were investigated through various characterization methods of X-ray diffraction, scanning electron microscopy, differential scanning calorimetry and stress-controlled cyclic tensile tests, etc. The results showed that the surface forming quality of SLM-NiTi was not only related to the energy density, but also related to the value of P/V, which higher than 0.3 or lower than 0.1 would lead to the formation of surface pores. Interestingly, the SLM-NiTi showed ultrahigh failure strength of 735 MPa and elongation of 10.88% under room temperature tensile conditions. In addition, stress-controlled cyclic tensile tests under 400 MPa indicated that the SLM-NiTi had excellent shape memory effect of 76.1% recovery ratio and 3.95% recoverable strain after ten times loading–unloading cycles. The design of multi-parameter variables can not only optimize the surface quality, but also provide a basis for the prediction of SLM-NiTi phase transition temperature.

Keywords

• Selective laser melting
• NiTi shape memory alloys
• Additive manufacturing
• Laser beam energy