Thermodynamic ripening induced multi-modal precipitation strengthened NiTi shape memory alloys by directed energy deposition

The functional properties of shape memory alloys made by additive manufacturing can be used in numerous applications. Adjusting the precipitation can be one way to tailor the functional properties. In this work, the NiTi shape memory alloys are fabricated through Directed Energy Deposition (DED) technology and facilitate Ni4Ti3 and NiTi2 precipitates by heat treatment. Experimental results show that increasing the heat treatment temperature can switch the precipitates distributed from the grain boundaries to the interior of the grains, accompanied by the increasing size and content of precipitates. The results pressent that the tailored microstructure affects the mechanical performance, manifested by the tensile recovery strain of ∼2 %, the tensile strength of ∼749 MPa, and the strain of ∼11 %. Our findings can provide information for designing enhanced shape memory properties and further microstructural studies of NiTi shape memory alloys.