Effect of modification by Pt and manufacturing processes on the microstructure of two NiCoCrAlYTa bond coatings intended for thermal barrier system applications

Few studies have already shown that Pt influences the diffusion of aluminium and therefore the microstructure of beta-NiAl or gamma-Ni/gamma'-Ni(3)Al materials. Besides, several works have revealed that the addition of Pt to MCrAlY (M = Ni and/or Co) improves the oxidation/corrosion behavior of the material. Nevertheless, very few data have been published on the microstructure of such modified MCrAlYs. Then, the present work deals with the addition of Pt to two NiCoCrAlYTa coatings that differ by their manufacturing process. Characterization is carried out in order to understand the influence of Pt diffusion but also the effect of the manufacturing process on the final microstructure. The collected data from XRD, SEM. EDS and TEM analyses reveal that an Al uphill diffusion occurs during heat treatment due to the presence of the Pt layer. The Al diffusion from the NiCoCrAlYTa bulk to the Pt-rich surface is so extensive that no more beta-phase remains within the core of the coating. Pt may also dissolve TaC, precipitates largely present in the non-modified NiCoCrAlYTa coatings. In addition to Pt, the microstructure of the NiCoCrAlYTa prior to Pt deposition and heat treatment, dependent on the NiCoCrAlYTa manufacturing process, greatly influences the final microstructure. (C) 2010 Elsevier B.V. All rights reserved.