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Surface Modification and Characterization of Plasma Sprayed Alumina Coatings using Lasers

  • R. Krishnan (a1), S. Dash (a1), R. Kesavamoorthy (a1), C. Babu Rao (a1), A. K. Tyagi (a1) and Baldev Raj (a1)...


A synergetic way of combining superior properties of ceramics with that of metals is to apply ceramic coatings over metallic substrates. Also, ceramic coatings provide better protection of the covered metal under concomitant corrosion and wear conditions. Of all the advanced ceramic materials, Al2O3 is widely used due to its low cost and availability in high purity forms. But the alumina coatings made through Air Plasma Spray suffers from major disadvantages such as presence of metastable γ-Al2O3 phase, high surface roughness and porosities. In this paper, we have shown the feasibility of transforming the γ-Al2O3 phase present in the as-sprayed coatings to a thermodynamically stable α-Al2O3 phase. A continuous wave CO2 laser having maximum power of 500W was used to provide a surface specific heating without affecting the metallic substrate. In addition to XRD, Raman scattering and photoluminescence investigations were carried out using a Ar+ laser to confirm the restoration of alpha phase and the reduction in porosity respectively. Also, 1 mW He-Ne laser operating in TEM00 mode was used to examine the reduction of surface roughness using laser scattering technique. The intensity of the specular reflection was used to quantify the surface roughness. Both reduction in surface roughness and porosity were evaluated using SEM micrographs taken on the surface and cross section of the coatings.



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