Modeling Microstructure Formation in Yttria-Stabilized Zirconia (YSZ) Droplet with High Impact Velocity in Supersonic Pl
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Modeling Microstructure Formation in Yttria-Stabilized Zirconia (YSZ) Droplet with High Impact Velocity in Supersonic Plasma Spray Mingguang Shen1 • Ben Q. Li2 • Yu Bai3
Submitted: 18 September 2019 / in revised form: 3 May 2020 Ó ASM International 2020
Abstract In plasma spraying, copious heterogeneous nucleation starts when a molten ceramic droplet spreads on a cold surface under rapid cooling. Some nuclei will survive and grow, eventually forming a splat of grains of distinct crystalline orientations. This paper aims to predict the dynamic process of yttria-stabilized zirconia (YSZ) droplet impact with solidification microstructure formation under various plasma spray conditions. A diffuse interface model was developed to track the evolving liquid–gas and solid–liquid interfaces. Continuously dense YSZ droplet impacts with different impacting angles were conducted, along with a hollow droplet impact. Results reveal that competitive growth among crystals is limited in the planar solidification, and that columnar structure dominates all the tests performed owing to a large thermodynamic driving force, and that given the rapid spreading of YSZ droplets along a solid surface, solidification may be safely assumed to take place mostly after spreading. Besides, typical crystal growth velocities are around 1 m/s, and local equilibrium can be assumed in the bulk.
& Ben Q. Li [email protected] Mingguang Shen [email protected] 1
State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, People’s Republic of China
2
Department of Mechanical Engineering, University of Michigan, Dearborn, MI 48128, USA
3
State Key Laboratory for Mechanical Behavior of Materials, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, People’s Republic of China
Keywords droplet impact hollow droplet plasma spray polycrystalline growth solidification List u t p q r g G c cP T ql Ll / l M f n c s/ u s h eh P sh d Fl fw d0
of Symbols Velocity (m/s) Time (s) Pressure (Pa) Density (kg/m3) Newtonian stress tensor (Pa) Gravitational acceleration (m/s2) Chemical potential (J/m3) Order parameter for the flow field Specific heat (J/kg K) Temperature (K) Liquid density (kg/m3) Latent heat of fusion (kJ/kg) Order parameter for the solidification field Dynamic viscosity (Pa s) Phase field mobility (m3 s/kg) Bulk free energy density (J/m3) Interface thickness (m) Surface tension (N/m) Kinetic time constant (s) for the solidification field Reduced temperature Coupling strength (m) Orientation field Gradient energy coefficient (m) for the orientation field Kinetics of h Kinetic time constant (s) for the orientation field Mushy region constant Liquid fraction Wall free energy density (J/m2) Thermal capillary length (m)
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J Therm Spray Tech
D e4 l b Cn le k e~/
Thermal diffusivity (m2/s) Antistrophic strength Rotation rate of grains (m) Grain boundary mobility Cahn number Effective viscosity (Pa s) Thermal conductivity (W/m K) Gradient energy coefficient (m) for the solidificatio
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