The effects of platinum concentration on the oxidation resistance of superalloys coated with single-phase platinum aluminide

Superalloy samples were coated with a low activity platinum aluminide applied by chemical vapor deposition (CVD). Different platinum thickness values were obtained on each group of samples by electroplating prior to CVD aluminizing and resulted in an array of platinum concentrations in the product coatings. The platinum aluminide coatings were single phase, (Ni,Pt)Al, with platinum concentrations varying from 8 to 38 wt.%. The coated samples were subjected to cyclic oxidation testing at 1175°C until failure. As expected, it was discovered that higher concentrations of platinum resulted in a coating more resistant to degradation during the cyclic oxidation testing. Electron microprobe composition profiles across the coatings for aluminum, platinum and substrate alloying elements were performed before and after oxidation testing. The results were compared to classical literature on two-phase platinum aluminide coatings. The ramifications of diffusion of many substrate alloying elements are discussed with regard to their relative effects on oxidation resistance of the coating.