Abstract:
Cavitation erosion is a huge problem in engineering
structures working under hydrodynamic conditions.
The synergistic effect of erosion and corrosion can
aggravate the material removal by several orders of magnitude.
Surface coatings are widely used to address material
degradation by erosion–corrosion. However, nonhomogenous
microstructure and presence of defects leads
to premature coating failure under erosion–corrosion conditions.
Thus, it is imperative to identify plausible solutions
to address cavitation-related material degradation. In this
study, Ni-Cr-5Al2O3 coatings were deposited on stainless
steel substrate using high-velocity-oxy-fuel technique. The
as-sprayed coating showed highly non-homogeneous
microstructure comprising splats, pores, intermetallic
compounds and elemental segregation. A new thermomechanical
processing technique, stationary friction processing
(SFP), was utilized for achieving through-thickness
microstructural refinement in as-sprayed coating. Assprayed
and SFP-treated coatings were tested in pure
cavitation erosion, corrosion in 3.5% NaCl solution and
erosion–corrosion. SFP treatment resulted in 5-times
enhancement in the erosion and corrosion resistance compared
to as-sprayed coating. The remarkable performance of Ni-Cr-5Al2O3 coatings after SFP treatment is attributed
to significant enhancement in the mechanical properties
including hardness and fracture toughness which is the
consequence of complete removal of splat boundaries,
pores, intermetallic compounds and uniform element distribution
up to the coating–substrate interface.
