Observation and modeling of α-NiPtAl and Kirkendall void formations during interdiffusion of a Pt coating with a γ-(Ni-13Al) alloy at high temperature

[摘要] During the last 15 years, Pt-rich gamma-gamma' bond-coatings have been studied extensively for their corrosion and oxidation resistance, and as a lower cost alternative to beta-(Ni,Pt)Al bond-coatings in thermal barrier coating systems. To optimize their fabrication and durability, it is essential to investigate their interdiffusion with Ni-based superalloys. This study reports on experimental results and modeling of the interdiffusion of the model Pt/gamma-(Ni-13Al) alloy system. Pt coatings were deposited either by electroplating or by spark plasma sintering using a Pt foil. Heat treatments at 1100 degrees C for 15 min to 10 h were performed either in a high-temperature X-ray diffraction device under primary vacuum or in a furnace under argon secondary vacuum. The alpha-NiPtAl phase with L1(0) crystal structure formed very rapidly, implying fast uphill Al diffusion toward the surface. For Pt electroplating, alpha-phase transformed to gamma'-(Ni,Pt)(3)Al after only 45 min-1 h at 1100 degrees C. The resulting two-phased gamma-gamma' microstructure remained up to 10 h. When using a Pt foil coating, the continuous layer of alpha-NiPtAl phase disappeared after 10 h and the gamma'-(Ni,Pt)(3)Al or gamma-(Ni,Pt,Al) phase appeared, resulting in two different diffusion paths in the Ni-Pt-Al phase diagram. Voids also formed at the interdiffusion zone/substrate interface for both systems after 1 h or more. Composition analyses confirmed that voids were located at the Pt diffusion front corresponding to the Al-depleted zone. Experiments performed with the samples coated with a Pt foil confirmed that voids are due to a Kirkendall effect and not to the Pt deposition process. Numerical simulations including the cross-term diffusion coefficients in the diffusion flux equations reproduced the experimental concentration profiles for the gamma-phased systems. (C) 2014 Elsevier B.V. All rights reserved.

[发布日期] 2014-12-15

[效力级别]  Proceedings Paper

[关键词] TBC;Interdiffusion;Modeling;alpha-NiPtAl;Kirkendall voids