Metal droplet breakup and rapid solidification behavior under multi-stage-controlled atomization process: NiTi alloys 3D printing special powder preparation

Abstract

In view of the problem of coordinated control of powder particle size distribution and surface quality during the preparation process of NiTi shape memory alloy 3D printing special metal powder EIGA method, a novel multi-stage-controlled gas atomization method is presented in this study to address the coordinated control of powder particle size distribution and surface quality. The process experiment, comprehensive powder performance test, and characterization of composition and microstructure were carried out, along with the construction of a theoretical model and mechanism research of metal droplet breakup and rapid solidification under multi-field coupling control. The results show that for the breaking behavior of metal droplets, the multi-stage-controlled gas atomization method can maximize the surface energy of metal droplets, which is beneficial to droplet breaking. For the spheroidization and solidification behavior, under the multi-stage-controlled gas atomization pressure, by adjusting the heating power and the feed rate of the bar, the mismatch between the solidification and spheroidization behavior of the droplets can be effectively improved (Ф = t_{spheroidization} / t_{solidification} ≈ 1). The sphericity and surface quality of the powder are improved. The NiTi alloy powder prepared by this method retained its main elements. The maximum increments of O and N elements are 310 ppm and 70 ppm, and D₉₀ is 50.3 μm. The powder sphericity is good, significantly reducing the number of hollow and satellite powders. This method plays a vital role in improving the application of NiTi alloy powder in 3D printing.