Controllable preparation of YSZ-STHS in arc plasma spheroidization: Exploring the plasma flow characteristics' impact on powder quality

Abstract

Yttria-stabilized zirconia hollow spherical powder (YSZ-HOSP) is a widely utilized ceramic material in thermal barrier coatings (TBCs). Within the category of YSZ-HOSP, yttria-stabilized zirconia spherical thin-walled hollow-shell powder (YSZ-STHS) displays immense potential for producing TBCs with minimal inter-lamellar porosity and cracks. Arc plasma torch equipped with flow-shaping nozzle shows promise for preparing YSZ-STHS. However, there is limited research on the impact of the nozzle geometry on plasma flow field characteristics and the resulting effect on the quality of YSZ-HOSP, particularly in terms of spheroidization ratio, hollow-shell powder ratio, and shell thickness. To achieve controllable preparation of YSZ-STHS in arc plasma spheroidization, this paper proposed a novel model for the formation of YSZ-HOSP under different plasma flow characteristics, including high-speed compressing flow field, intermediate-speed critical flow field, and low-speed expanding flow field. These different plasma flow characteristics were achieved by changing the nozzle diameter and investigated by both numerical simulation and experiments in terms of plasma flow characteristics, electro-thermal characteristics, and the quality of the YSZ-HOSP. Results reveal that YSZ-HOSP prepared with high-speed compressing flow field resulted in a low hollow-shell powder ratio, while low-speed expanding flow field led to an over-thick shell. Conversely, the intermediate-speed critical flow field demonstrates relatively high thermal efficiency and enthalpy, along with moderate jet temperature and velocity, resulting in YSZ-STHS with a spheroidization ratio of 96.6 %, a hollow-shell powder ratio of 92.5 %, and a mean shell thickness of 3.49 μm. Therefore, it is evident that manipulating plasma flow characteristics allows for the controlled preparation of YSZ-STHS.