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

• Published in: Surface & coatings technology Vol. 260; pp. 9 - 16
• Main Authors: Audigié, Pauline, Rouaix-Vande Put, Aurélie, Malié, André, Bilhé, Pascal, Hamadi, Sarah, Monceau, Daniel
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.12.2014; Elsevier
• Subjects: Bonding; Chemical engineering; Chemical Sciences; Coating; Diffusion; Engineering Sciences; Foils (structural shapes); Interdiffusion; Kirkendall voids; Materials; Mathematical models; Modeling; Nickel base alloys; Platinum; TBC; Voids; α-NiPtAl; α-NiPtAl; Interdiffusion; TBC; Kirkendall voids; Modeling
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2014.08.083

During the last 15years, Pt-rich γ–γ′ bond-coatings have been studied extensively for their corrosion and oxidation resistance, and as a lower cost alternative to β-(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/γ-(Ni-13Al) alloy system. Pt coatings were deposited either by electroplating or by spark plasma sintering using a Pt foil. Heat treatments at 1100°C for 15min to 10h were performed either in a high-temperature X-ray diffraction device under primary vacuum or in a furnace under argon secondary vacuum. The α-NiPtAl phase with L10 crystal structure formed very rapidly, implying fast uphill Al diffusion toward the surface. For Pt electroplating, α-phase transformed to γ′-(Ni,Pt)3Al after only 45min–1h at 1100°C. The resulting two-phased γ–γ′ microstructure remained up to 10h. When using a Pt foil coating, the continuous layer of α-NiPtAl phase disappeared after 10h and the γ′-(Ni,Pt)3Al or γ-(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 1h 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 γ-phased systems. •L10 α-NiPtAl phase was observed during the interdiffusion of Pt/γ-(Ni,Al) at 1100°C.•α-NiPtAl phase nucleated in the early stage of interdiffusion and dissolved after 1h.•The diffusion path Pt–α-NiPtAl–γ-(Ni,Pt,Al)–Ni-13Al was observed.•Voids formed at the Pt diffusion front in the Al-depleted zone after 1h at 1100°C.•Concentration profiles evolutions were calculated for the Pt/Ni-13Al diffusion couple.