PROLONGED MCRALY COATING LIFETIME BY MEANS OF THE LPPS PROCESS

It is state of the art that MCrAlY powder is sprayed by LPPS or alternatively by HVOF either as an environmental protective coating or as a bond coat of the TBC on hot section parts of the turbine. The lifetime of the MCrAlY coating can be predicted by the two different losses of the Aluminum content causing a B-depletion of the beta NiAl-phase of MCrAlY: the Al loss by the oxidation on the surface and the Al loss by the interdiffusion into the substrate. These effects were analyzed with a NiCoCrAlYRe and a CoNiCrAlY coating sprayed by LPPS and HVOF. Long term oxidation tests demonstrate: the coatings sprayed by LPPS have less B-depletion by diffusion compared to the coatings sprayed by HVOF. This was evaluated for the tested alloy-coating combinations. The B-depletion caused by oxidation is dependent on the MCrAlY: the NiCoCrAlYRe coating has less B-depletion when sprayed by LPPS while in the CoNiCrAlY coating the B-depletion caused by oxidation is lower in the HVOF sprayed coating.