Comparison of slurry and dry erosion behaviour of some HVOF thermal sprayed coatings

Abstract

The performance of 10 high velocity oxy-fuel (HVOF) sprayed coatings has been evaluated under both dry particle and slurry erosion conditions at 90° and 20° impingement angles. The coatings were six WC cermets with Co- or Ni-based matrices, a Cr 3C 2–NiCr composite and three metallic alloys. Slurry jet erosion experiments were carried out using a 9 wt.% alumina/water slurry with 35 and 200 μm angular alumina particles, at an impingement velocity of 15 m/s and flow rate of 18 l/min in a re-circulating loop apparatus. Dry erosion was effected in a once-through mode with 50 μm diameter alumina particles at a velocity of 84 m/s and feed rate of 2 g/min. Dry erosion rates three orders of magnitude greater than slurry erosion rates were due mainly to the differences in actual particle-target impact velocities. Coating composition, microstructural integrity and hardness were the major determinants of relative erosion resistance in all tests, with matrix corrosion resistance influencing the surface damage resistance of cermets in longer duration aqueous slurry tests.