Most research to date in the field of L-PBF of nitinol has been with near equiatomic nickel-titanium binary pre-alloyed powders. Significant understanding over the last 10 years has been gained in relation to aspects such as microstructural evolution, control of elemental composition, phase transformation behaviour, control of defects and mechanical properties. Challenges with the use of pre-alloyed nitinol powders include expense and time constraints in producing new blends. Elemental blending with in-situ alloying of nickel, titanium and other constituents at the point of additive manufacture offers the opportunity to significantly accelerate the pace of research of nitinol material and part geometry design. Other potential advantages of elementally blended over pre-alloyed powders include reduced process costs, energy savings, and improved control over final part macroscopic properties as well as local microscopic composition and properties. The relationship between elemental and pre-alloyed powder characteristics, the nitinol L-PBF process parameters and the resulting melt homogeneity has not previously been examined. This paper addresses this gap by examining, for in-situ alloyed nitinol, the relationship between laser power, scanning speed, powder properties and the resulting solidification track characteristics, and comparing results to those from pre-alloyed powder.

The properties of nitinol, an alloy of nickel and titanium, include its good biocompatibility, corrosion resistance, damping capacity, fatigue strength, superelasticity, and shape memory characteristics. With other conventional methods, it has been challenging to achieve high precision and accuracy of the produced parts; however, laser powder bed fusion (L-PBF) has provided a useful new route for the processing of nitinol. While L-PBF offers many advantages, it also has drawbacks, including the potential for the formation of different phases and residual stress during rapid solidification. Post L-PBF heat treatment conditions aid in the generation of targeted stable phases. As reported by Lee et. al., the mechanical properties and transformation temperatures of the manufactured nitinol samples were largely influenced by the heat treatment. Fan et. al. showed an increase in the transformation temperatures by increasing the heat treatment temperatures after a solution heat treatment. Heat treatments that help in achieving the desired properties are two-step heat treatment processes. This study investigates the feasibility of applying a single-step solution heat treatment to Ni-rich nitinol and reports its effects on density, transformation temperatures, microstructures and microhardness for intended applications.