Processing Considerations of Nitinol Powders for LPBF

Additive manufacturing (AM) has become an emerging domain for metal powders. With the advancing progress in AM, there is a growing emphasis on powder manufacturing for reliable AM-built parts. Atomization technologies are well established for metal powder preparation, dominating the market for laser powder bed fusion (LPBF). They allow for producing powders with high purity, adequate particles size distribution and without satellites from a variety of metallic materials.

In this panorama, considerable research work has been devoted to tailor NiTi powder AM processing. Material and energy savings, process automation, as well as precise control of chemical compositions could be achieved while avoiding problems associated with melting procedures and limited machinability. However, little attention was devoted to the powder itself as key factor for a successful manufacturing process.

Due to the sensitivity of the functional properties to the alloy chemistry of NiTi, the conversion from solid metal to powder is more challenging than in other alloy systems. The increase in surface area by the formation of particles during atomization leads to higher oxidation. Furthermore, the oxygen content depends on the particle size distribution requirements of distinct AM processes, and also pick up of other impurities during melting and atomizing such as carbon and nitrogen needs to be controlled as they impact on the transformation of final NiTi AM components.

In this study, Ni-rich and Ti-rich NiTi powders prepared by different gas atomization technologies are characterized and compared. Advantages and disadvantages of each approach for LPBF processing will be highlighted and discussed.