SEM and TEM studies of PtAl diffusion coatings under isothermal oxidation

Three commercial Pt modified aluminide coatings (RT22, SS82A and MDC150L) and one conventional aluminide diffusion coating (PWA73), applied to the same substrate (CMSX4), were oxidised in still laboratory air at 1,050 degrees C fur times up to 2,000 h. The samples were investigated by gravimetry, scanning electron microscopy, (SEM), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). It was found that among the three Pt modified coatings, RT22 produced the fastest growing oxide and that at about 500 h, a decrease in growth rate occurred for all three coatings. The oxide on RT22 started to spall after 1,000 h, while the oxide on SS82A and MDC150L remained adherent. The conventional aluminide diffusion coating suffered from severe spalling after 1,000 h. Furthermore, results from microstructural and compositional measurements of the Pt modified aluminide coatings are presented.