Session BB1.6

10:45 AM BB1.6
PARTICLE TEMPERATURE MEASUREMENTS IN A HVOF THERMAL SPRAY BY TWO COLOR RADIANT EMISSION PYROMETRY. Weiduo Yu and Baki M. Cetegen, Mechanical Engineering Department, University of Connecticut, Storrs, CT.

Thermal spray process diagnostics is vital in facilitating an improved understanding of thermal spray processes and controlling of coating quality deposited by thermal sprays. Key process parameters such as temperature, size, and velocity of thermally sprayed particles have been known to influence coating deposition characteristics and their longevity at their operating environment of high temperature and high mechanical and thermal stresses. Within the work described here, a two-color pyrometer system was first custom-designed utilizing two emission wavelength bands centered around 600 and 700 nm. The pyrometer system was calibrated using a black-body radiation source and a tungsten ribbon lamp before its application to the thermal spray characterization The calibrated pyrometer was used to measure the particle temperatures of various materials sprayed by a commercial high-velocity oxygen-fuel (HVOF) spray system. In these experiments, chromium carbide, stainless steel, ordinary tungsten carbide-cobalt and nano-agglomerated tungsten carbide-cobalt particles were sprayed. Measurements show that the average particle temperatures decay with increasing axial distance away from the flame tip. Particle temperatures also vary with the flame stoichiometry (or the oxygen-fuel mixture ratio), with highest temperature levels being reached near stoichiometric conditions. Particle temperatures tend to have a wider range in the early stage of flight towards substrate, but this range narrows with increasing downstream distance. Nano-agglomerated WC-Co particles show somewhat different temperature behavior from those of ordinary micro-sized WC-Co particles which may be attributed to the differences in their micro-structure.