Mechanisms of yttrium on the wettability, surface tension and interactions between Ni-20Co-20Cr-10Al-ξY alloys and MgO ceramics

The mechanisms of Y on the wettability, surface tension, and interactions between the Ni-20Co-20Cr-10Al-ξY alloys and MgO ceramics at 1873 K were investigated by sessile drop experiments. The results of nonlinear fitting showed that the equilibrium contact angles and Y concentrations were approximately in accord with the log-normal distribution law. The equilibrium contact angles changed from 101.5° to 140.5° with Y increasing from 0 wt.% to 1.23 wt.%. Cross-sectional microstructure observations revealed that the thermal dissociation of ceramics occurred and the released [O] atoms can react with Y to produce Y₂O₃ reaction layer along three-phase interphase area. Wetting kinetics analyses indicated that surface tension of the melt droplets had been positively correlated with the Y concentrations, and it increased from 737.8–1045.1 mN/m. Meanwhile, the pinning effect of the rough substrate surface on the three-phase line hindered the spreading of the liquid on ceramics. The change in total free energy of the alloys/ceramics system was considered as the key factor affecting the wettability. Moreover, the surface morphology and thermodynamic stability of ceramics also had some influence on the wettability.