The oxidation and rumpling behavior of overlay B2 bond coats containing Pt, Pd, Cr and Hf

The behavior of Hf-modified B2 nickel aluminide bond coatings, fabricated by ion-plasma deposition, has been investigated under thermal cycling conditions. The mass change, surface roughness, and microstructural evolution have been characterized. Variation in the Al, Cr, Pd and Pt concentrations did not affect the initial oxidation or rumpling behavior of these bond coats, but did influence oxide adherence as well as the surface roughness at failure. Both the Pt and, interestingly, the Pd-modified coatings displayed superior cyclic oxidation lifetimes compared to the state-of-the-art platinum aluminide coatings. The rate of surface roughening (rumpling) is discussed in terms of the B2 to L12 phase transformation and oxide spallation.