Additive Manufacturing of Ni-Rich NiTiHf20: Manufacturability, Composition, Density, and Transformation Behavior

In this work, the effects of process parameters on the fabrication of NiTiHf alloys using selective laser melting are studied. Specimens were printed using bidirectional scanning pattern and with various sets of process parameters of laser power (100–250 W), hatch spacing (60–140 µm), and scanning speed (200–1000 mm/s). Cracking and delamination formation, dimensional accuracy, density, and transformation temperatures were examined. Despite the brittle nature of the alloy, fully dense parts have been produced. Laser scanning speed and volumetric energy density were found to be the most influential process parameters on fabricating defect-free samples. It was shown that transformation temperatures are highly dependent on the process parameters. By proper choice of parameters, it is possible to tailor the austenite finish temperature from 100 to 400 °C. The most influential factors on transformation behavior were found to be the laser power and energy density. It is worth noting that these two parameters at higher levels resulted in high process temperatures and therefore a larger level of Ni evaporation. Among the four parameters that constitute the energy density, the hatch spacing does not significantly affect the transformation temperatures. These findings serve as the foundation of developing HTSMA devices with desired geometrical and functional properties.