Spraying Distance Dependence of Microhardness on HVOF WC-Co Coatings

Thermal sprayed WC-based coatings are widely used in modern industry, especially in excellent wear-resistant-demanding fields, due to their high hardness and superior mechanical properties. WC-Co is a typical representative of the coatings, usually used as the protective layers of shaft, pump sleeve intine, etc. WC-Co coatings were prepared on low carbon steel substrate using high velocity oxygen fuel (HVOF) technology, under different distance ranging from 160 to 240 mm. The influence of the spraying distance on coating hardness was investigated and discussed. The results reveal that, the cross-sectional hardness of the HVOF WC-Co coatings depend not only on the spraying distance, but also on the indentation position. The average microhardness for all the coatings was obviously enhanced. The highest one (1793.6 Hv) was produced with a distance of 240 mm. Due to the heat effect of the flame, the hardness for all coatings varies with the distance from indentation to coating/substrate interface.