Microstructure evolution and interdiffusion of PtAl coated a third generation single crystal superalloy during thermal exposure

Abstract

Microstructure evolution and elemental interdiffusion of PtAl coated third generation single crystal superalloy at 1000 °C and 1100 °C have been investigated. Interdiffusion coefficients and elemental diffusion fluxes are determined by HitDIC software based on the numerical inverse method. The interdiffusion zone (IDZ) with σ and R topologically close-packed (TCP) phases and secondary reaction zone (SRZ) with σ and P phases are formed after exposure at 1000 °C and 1100 °C. Interdiffusion flux of Al is the largest, followed by Pt, Ni, Co and Ta. However, most of the inward diffused Al is absorbed by IDZ, and the enrichment of Ta in IDZ/SRZ primarily accounts for the formation of SRZ. The increasing outward diffusion of refractory elements, such as Re, W and Ta mainly leads to larger thickness of SRZ at 1100 °C. Moreover increasing interdiffusion of Al and Ni further promotes the growth of SRZ and transformation from β-NiAl to γ′-Ni3Al phases. The content of reserved Al in the β layer is the same after thermal exposure at both temperatures, due to the effect of Pt.