A PROCESS MODEL FOR LASER SURFACE TREATMENT OF PLASMA SPRAYED COATINGS

摘要

Advanced ceramics are not easily fabricated and consolidated by the plasma spray technique because of their extremely high melting temperature. Zirconium diboride (ZrB_2) has been successfully plasma sprayed, but the coatings are quite porous. The high levels of porosity are usually a result of unmelted ZrB2 particles that have been incorporated into the coating during deposition. Applying a laser surface treatment to reduce both the porosity and the coating surface roughness, and to improve the coating quality, is of great interest. A laser based surface treatment technique provides a well-controlled heat input, with minimal or no distortion. In this study, a two dimensional mathematical model is developed to investigate the effects of laser power, beam diameter and level of porosity on the coating quality, incorporating melting, solidification, and evaporation phenomena. A continuum model is used to solve Navier-Stokes equations for both solid and liquid phases. Volume-of-Fluid (VOF) is incorporated to track the free surface. The surface force is incorporated as a body force instead of a boundary condition. The porosity level and surface roughness before and after the laser surface treatment are simulated and compared with experimental results.