The Element Segregation Between γ/γʹ Phases in a Ni-Based Single Crystal Superalloy Studied by 3D-APT and Its Potential Impact on Local Interfacial Misfit Strain

Abstract

Three-dimensional atom-probe tomography was used to characterize the γ/γʹ interface structure in a third-generation Ni-based single crystal superalloy with Re addition. It was found that an element-segregation layer with Re, Co and Cr was formed in the γ phase close to the γ/γ′ interface, resulting in a more negative local interface misfit (− 0.29%) compared to the measured result (− 0.16%) from high-resolution X-ray diffraction. Furthermore, the total reduction of interfacial free energy due to the solute atom segregation based on the Gibbsian interfacial excess was calculated to indicate that Re element was the most beneficial element in producing this more negative local misfit with the largest interfacial free energy reduction (13.67 ± 0.21 mJ/m2). Simultaneously, because of the co-segregation of Re, Co and Cr, and the depletion of Ni in the γ phase close to the γ/γ′ interface, it was also deduced that some harmful topologically close-packed phases might be easier to nucleate and grow in the γ phase close to the γ/γ′ interface in service. The element-segregation layer across γ/γ′ interface resulted in a more negative local interface misfit (− 0.29%), compared to the measured result (− 0.16%) from highresolution X-ray diffraction, and the total reduction of interfacial free energy due to the solute atom segregation was calculated to indicate that Re element was the most beneficial element in producing this more negative local misfit with the largest interfacial free energy reduction (13.67 ± 0.21 mJ/m2).