spraying parameters optimization for wear and abrasion resistance of Cr2O3 coating deposited with cascaded plasma torch

Abstract

Atmospheric plasma sprayed (APS) chromia coating provides excellent wear behaviour combined with corrosion resistance even in aggressive environments. In this paper, the influence of variable spraying parameters on the mechanical properties and microstructure of chromia coatings is investigated. Main goal for this optimization is to achieve high wear and abrasive resistance. APS ceramic coatings such as chromia could perform in some industrial applications as well as more commonly used HVOF (high velocity oxygen fuel) cermet coatings, especially in wear and abrasion resistance. In order to be able to compete with hard and wear resistant cermet HVOF coatings, optimization of spraying parameters for this particular chromia powder is required. High throughput cascaded plasma troch is used for the spraying process. Set of five different spraying parameters is used varying only primary plasma gas flow rate and input electrical current with rest of spraying parameters set constant, including carrier gas flow. Critical plasma spraying parameter or CPSP is also utilized in the design stage of experiment. Coatings sprayed on low carbon steel substrate underwent superficial Rockwell indentation, optical microscopy on polished cross section, adhesion strength testing and dry sand abrasion test. No significant correlation between CPSP values and hardness, adhesive strength or abrasion resistance was observed. High input electrical current combined with rather high plasma gas flow provided better abrasion resistance than lower input electrical current and flow rates. Coating performing best in abrasion test also displayed by far the highest adhesive strength to substrate material, so presumably having also the highest cohesion strength between splats may lead to less inter splat decohesion or chipping during dry sand abrasion.