Process Measurements in A vacuum Microplasma Spray System

Summary form only given. A system has been developed and refined for small-scale vacuum plasma spraying of metals. This system operates at arc power 1-3 kW and deposition rates below 0.1 g min^-1. The plasma is an argon-hydrogen mixture expanded through a Laval nozzle into chamber pressures in the range 5.3-13 kPa (40-100 torr). The vacuum spray environment, which distinguishes this work from other published plasma spray work at similar power levels, helps to enable the deposition of titanium or tungsten. These materials and others may also be deposited simultaneously with vapor-deposited material in order to synthesize composite materials. This hybrid processing is made possible by the reduction of spray deposition rate to be comparable to vapor deposition rates. Other potential applications include small-scale, reduced-cost versions of conventional plasma spray, such as barrier coatings and biomedical coatings. Sprayed materials and system behavior are discussed in terms of system measurements for tuning of particle trajectory, particle impact state, and coating microstructure. Planar laser Mie scattering was used to visualize particle trajectory fields in order to align them with the plasma jet´s core. In stainless steel coatings, spray deposition efficiency (DE) is seen to correlate well with such trajectory alignment.