Effects of substituting Mo for W and temperature on γ/γ′ lattice misfits of second generation Ni based single crystal superalloys

In this investigation, effects of substituting Mo for W and temperature on lattice constants of γ and γ′ phases and γ/γ′ misfits of second generation Ni based single crystal superalloys was investigated. The lattice constants of γ and γ′ phases in heat-treated W-rich and Mo-rich single crystal superalloys were measured by in-situ high temperature X-ray diffraction (HT-XRD) at temperature ranged from room temperature to 1150 °C. Meanwhile, both thermodynamic calculation and Vegard's law (considering thermal expansion coefficient) were used to calculate lattice constants of γ and γ′ phases and γ/γ′ misfits of two experimental alloys. Both experiment and calculation results indicated that substituting Mo for W obviously increased lattice constant of γ phase, while its influence on lattice constant of γ′ phase was limited, and thus substituting Mo for W significantly decreased γ/γ′ misfit. Meanwhile, the experimental results of HT-XRD indicated that absolute value of γ/γ′ misfits of two experimental alloys at 1100 °C were higher than those of at 1150 °C, which was in good agreement with evolution rule of γ/γ′ interfacial dislocation network spacings in two experimental alloys (after creep rupture at 1100 °C and 1150 °C).