P. Ctibor, B. Kolman, P. Chraska, Institute of Plasma Physics, Praha, Czech Republic; J. Dubsky, Institute of Plasma Physics ASCR, Praha 8, Czech Republic; A. Jancarek, Faculty of Nuclear Science and Engineering CTU, Praha, Czech Republic
Chromia admixture to Alumina feedstock is used to block formation of γ-Al2O3 in plasma sprayed coatings. In this work a mechanical blend of Alumina-Chromia powders was used with the water stabilized plasma to make thick coatings. The resulting structure contained less of corundum type α-(Al,Cr)2O3 phase than for the fused feedstock. When additional post-treatment by a quasi-continuous laser was applied to the surface, amount of the corundum phase substantially increased. Careful examination of the treated surface revealed that the individual splats at and near the surface were fully remelted and the structure is formed by a homogeneous phase with no visible splat boundaries. Segregation of Chromium has been detected in the remelted zones which strongly affects the final properties of coatings. Fast melting and cooling of the ceramic material under certain spray conditions may result in formation of undesirable cracks between traces of individual passes of the laser beam.
Summary: Using the water stabilized plasma thick coatings were made of Alumina-Chromia feedstock. Quasi-continuos laser was used at two power levels to modify the as-sprayed surface. A homogeneous phase at the surface was produced with certain segregation of Chromia and under certain conditions with cracks.
