Abstract:
Ni-20Cr coating offers superior resistance against high temperature oxidation and
corrosive salts. Therefore it is widely used in several industries for the protection of
metallic components. In present study, Ni-20Cr coating was deposited on stainless
steel (AISI-304) substrate by using air plasma spraying system. The inherent features
of air plasma spray coating, for example, porosity, oxides and splat boundaries, act as
channels for the diffusion of oxygen during high temperature exposure. The coating
was re-melted using CO2 laser varying laser power and defocus distance while
keeping the remaining parameters constant. The laser tracks applied on the coating at
different powers and defocus distances were characterized with the help of optical
microscope, SEM and XRD. After optimizing the CO2 laser parameters the coated
surface was completely cladded. Considerable reduction in the defects was observed
after cladding the plasma sprayed surface. The (1) uncoated, (2) air plasma sprayed
and (3) laser re-melted specimens, were exposed to cyclic oxidation at 900°C for a
100 cycles run. The oxidation products were characterized using XRD and SEM.
Weight changes were determined after every 4th cycle; uncoated samples showed
severe oxidation indicated by substantial weight loss, whereas air plasma coated
samples demonstrated noticeable weight gain. However, oxidation resistance of
laser-cladded samples was found to be significantly improved as the samples showed
negligible weight change; porosity within the coating was minimized with an
improvement in interface quality causing reduction in delamination damage
