HIGH TEMPERATURE OXIDATION OF COLD GAS SPRAYED BOND COATS FOR TBC APPLICATION

Plasma sprayed thermal barrier coatings (TBC) have been extensively employed in most aerospace and land based turbine engines, permitting gas temperatures to be raised substantially above those for uncoated systems. Traditional TBC systems are composed of a metallic bond coat and a ceramic top coat both applied by plasma spraying. New deposition techniques have been proposed mainly for the metallic bond coat, like HVOF and more recently Cold Gas Spray (CGS). CGS is an attractive technology that generates very dense coatings, without oxidation and maintaining the initial powder microstructure, characteristics that are potentially interesting for bond coat application. In the current study, TBCs with two sets of cold gas sprayed bond coatings were prepared and evaluated in high temperature isothermal oxidation tests. Measurements of sample mass as well as microstructure observations were carried out on the as sprayed and oxidized samples to compare the behavior of different bond coat chemical compositions. As sprayed oxidation degree, structural changes and bonding strength of the samples were also determined.