Pyrometer system for monitoring the particle impact on a substrate during a plasma spray process

A measurement system consisting of two high-speed two-colour pyrometers is described; the system is suitable for monitoring the flattening and cooling of particles on a substrate during plasma spray deposition. The first double-wavelength optical fibre pyrometer is focused 2 mm before the substrate and the other is focused on the substrate surface. The present instrument provides data on the temperature, the velocity and the size of a particle prior to its impact on a substrate and on its flattening and cooling when it impinges on the surface. Examples of results are given with plasma-sprayed zirconia particles impacting on bare steel substrates. Measurements are presented in terms of flattening time and 'apparent' degree of flattening as a function of the velocity, surface temperature and size of the impinging particles.