The influence of cooling rate on the microstructure and phase fraction of gas atomized NiAl3 alloy powders during rapid solidification

NiAl3 alloy powders were produced by nitrogen gas atomization in this paper. The microstructure and phase compositions of different particle size powders were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron backscattered diffraction (EBSD). The atomized powders are composed of Ni2Al3, NiAl3 and Al-eutectic phases, and three main types of solidification microstructures were identified: dendrites, refined dendrites, and compounds. Phase fraction of three representative particles with diameter of 60, 140 and 220 mu m were measured. Moreover, the Newtonian heat transfer formulation coupled with the classical heterogeneous nucleation was used for analyzing the influence of heat transfer coefficient and cooling rate on the thermal history of droplets. Therefore, this work highlights the experimental results matched well with the theoretical calculation and guides the further production of high NiAl3 phase Raney nickel catalytic powders.