Abstract:
Thermal spray coatings are widely used for
addressing erosion problems in fluid machineries. However,
the presence of splat boundaries, non-homogeneous
microstructure and element segregation limits their performance.
In this study, we developed Ni-Cr-40Al2O3
coatings on stainless steel (SS316L) substrate using highvelocity
flame spray followed by post-processing using
friction stir processing. The performance of as-sprayed and
processed coatings was evaluated in slurry erosion, erosion–
corrosion and pure corrosion in 3.5% NaCl solution.
As-sprayed coating showed lower erosion and erosion–
corrosion resistance compared to stainless steel. Friction
stir processing resulted in significant microstructure
refinement concurrent with enhanced hardness and fracture
toughness of the developed coating. At oblique impingement
angle, the processed coating showed nearly 30% to
twofold higher erosion and erosion–corrosion resistance
compared to stainless steel substrate. During pure erosion
at normal impingement, both as-sprayed and processed
coating showed higher volume loss. However, during
erosion–corrosion at normal impingement, the processed
coating was able to demonstrate similar volume loss as that
of the substrate. In addition, the processed coating showed
significant improvement in the corrosion performance as
well. The study showed that friction stir processing could
be a promising pathway to unravel the deleterious effects
of inherent non-homogeneities in thermal spray coatings.
