Phase Equilibria and Diffusion in the Ni-Cr-Pt System at 1200 °C
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Pt modified NiAl, which is often simply called Pt aluminide, is widely used in jet engines as a protective coating against oxidation and hot corrosion as well as a bond coat for thermal barrier coatings. Phase equilibria and diffusion coefficients in the Ni-Cr-Pt ternary system are thus valuable data for modeling the behavior of Pt aluminide coatings on Ni-based superalloys in which Cr is an essential alloying element. A Ni-Cr-Pt diffusion multiple was made and annealed at 1200 °C for 100 h to obtain the first reliable isothermal section phase diagram for this ternary system. Interdiffusion coefficients were extracted from the measured diffusion concentration profiles using a forward simulation analysis for all the single-phase regions of the Ni-Cr, Ni-Pt and Cr-Pt binary systems. The impurity diffusion coefficient data obtained from this study are combined with literature data to assess reliable Arrhenius equations for the impurity diffusion coefficients of Pt in Ni, Ni in Pt, and Cr in Ni. An Arrhenius equation for the impurity diffusion coefficient of Cr in Pt is recommended for the first time by combining a fitted prefactor from experimental data and an activation energy value from first principles calculations.
Keywordsbinary diffusion diffusion couples diffusivity coefficient experimental phase equilibria impurity diffusivity phase diagram
The authors would like to thank Jay Tiley for arranging the EPMA measurements for this study. The authors also greatly appreciate Qiaofu Zhang and Zhangqi Chen for sharing their FSA programs and providing support in performing some of the diffusion coefficient extractions. This study was supported by the internal funds of The Ohio State University.
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