Ni23Cr6Al0.4Y plasma sprayed coating on nimonic75 substrate was remelted using a 1
kW continues CO2 laser. The topography, microstructure, phases and chemical analysis
of plasma sprayed and laser melted regions were examined using various techniques
including scanning electron microscope (SEM), electron probe microanalysis (EPMA),
energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The plasma
sprayed coatings consisted heterogeneous microstructure of lamella with unmelted
particles, voids, porosity and cracks. It was found that the depth of melting increased
with increasing the specific energy. Homogenous and shiny melted regions were
achieved without voids, porosity and cracks after laser melting. Thin upper surface
layers with shallow cracks were observed due to the rich layer of α-Al2O3 and YAlO3.
No phases changed were found before and after laser melting of plasma sprayed layers.
The phases formed are mixtures of γ’, β, YAlO3 in the matrix γ. The microstructure
formed after laser melting is fine cells.
Keywords: Plasma sprayed coating; Laser melting, Ni solid solution; YAlO3; α-Al2O3