Ternary Interdiffusion Analysis in β-(Ni,Pt)Al System Pertaining to Bond Coat Applications

Interdiffusion study was carried out in β-(Ni,Pt)Al system at 1100 °C by solid–solid diffusion couple technique. Using Kirkaldy’s approach, ternary interdiffusion coefficients were determined at 27 different compositions covering broad range of the β phase region. Zero flux planes (ZFP) and regions of uphill diffusion were manifested in several diffusion couples indicating presence of strong diffusional interactions in the system. Among the three components, Pt and Al were found to be the slowest and the fastest diffusing elements, respectively. For a given Al content, the main interdiffusion coefficients \({\widetilde{D}}_{\text{AlAl}}^{{\text{Ni}}}\) ${\tilde{D}}_{\text{AlAl}}^{\text{Ni}}$ and \({\widetilde{D}}_{\text{PtPt}}^{{\text{Ni}}}\) ${\tilde{D}}_{\text{PtPt}}^{\text{Ni}}$ increased with increase in Pt content but they decreased with increase in Al concentration at a given Pt-content. The cross interdiffusion coefficient \({\widetilde{D}}_{\text{NiAl}}^{{\text{Pt}}}\) ${\tilde{D}}_{\text{NiAl}}^{\text{Pt}}$ is negative and about one order magnitude higher than the main coefficient \({\widetilde{D}}_{\text{NiNi}}^{{\text{Pt}}}\) ${\tilde{D}}_{\text{NiNi}}^{\text{Pt}}$ which implies that the interdiffusion flux of Ni is enhanced up the Al concentration gradient. Based on the ternary interdiffusion coefficients, it is inferred that Ni and Al have stronger interaction than Pt and Al. The effect of Pt in reducing spinel oxide formation in TGO layer is explained based on the diffusional interactions of Al and Ni as determined in this study.