Why do EB-PVD NiCoCrAlY coatings oxidize faster than their LPPS counterparts?

Bead-peened unannealed EB-PVD and LPPS NiCoCrAlY coatings showed differing oxidation kinetics on isothermal heating at 1000 degreesC. The unoxidized starting materials were investigated by DTA, XRD, TEM and EDS. The differences in oxidation kinetics are attributed to the formation of different TGOs. Whereas alpha -Al2O3 formation is assumed to start on the LPPS coating at the beginning it is seemingly formed at a later stage on the EB-PVD coating. Early alpha -Al2O3 formation on LPPS coatings is hypothetically attributed to the beneficial nucleation conditions of the dominating gamma phase on the surface and to the advantageous fast diffusive transport conditions in the coating. The fast provision of elements for TGO formation originates from grain boundary diffusion provided by the small-grained LPPS coating, from accelerated diffusion through amorphous phases and by highly supersaturated phases and grains and along directed and narrowly spaced eutectic phase boundaries. The oxidation behavior of the EB-PVD coating is ruled by dominating beta particles in gamma and less diffusive supply of Al.