Wettability Of Molten Ni(-Cr, W) Alloys On Alumina Ceramic Substrate

Ni-based alloys are used in space and medical fields as important parts because of its high heat strength, thermal shock resistance and the oxidation resistance. Alumina is especially used as a structural material in high temperature applications or as reinforcement in metal matrix composites because of its good mechanical properties, high thermal conductivity, good thermal shock behavior and high oxidation resistance. Wettability of molten Ni-based alloy / alumina system determines the property of metal matrix composites.Wettability of molten Ni-(Cr, W) alloy on polycrystal and single crystal alumina substrate was observed at 1773-1873 K in an Ar+3%H2 atmosphere, vacuum using an improved sessile drop method. The interface of Ni-based alloy / alumina and the surface of alumina substrate were observed and analyzed using X-ray diffraction (XRD), environment scanning electron microscopy (ESEM), scanning electron microscopy (SEM) and 3-D rotational microscope. The effects of temperature, alloy element, crystal type of substrate and protective atmosphere on the wettability and interface reaction were analyzed, and the thermodynamics analysis of interface reaction was also studied.Molten Ni / polycrystal alumina system is the base of Ni-based alloy / alumina system, Wettability of molten Ni on polycrystal alumina substrate was observed at 1773-1873 K in an Ar+3%H2 atmosphere. The contact angle of molten Ni on alumina substrate changes through rapid decrease stage and slow decrease stage, and tends to be equilibrium. Based on detection results and thermodynamic calculation, the interface reaction products include NiO, NiAl2O4, Al2O and Ni-Al intermetallic compounds. The initial contact angle and equilibrium contact angle of molten Ni tend to be smaller with increasing temperature, the time to be equilibrium becomes shorter. Reaction become stronger and interface product become more with increasing temperature.Adding alloy element Cr to Ni, the effect of Cr on wettability of Ni-Cr / alumina was analyzed. The initial contact angle and the equilibrium contact angle decreased and the decreasing rate of contact angle become larger with adding 5%-10%Cr. Adding Cr can enhance interface reaction and increase the interface adhesion, improve the wettability.The wetting of molten Ni-10%W alloy on single crystal alumina substrate was observed at 1823-1873 K. Due to anisotropies of the single crystal, the difference between the contact angles in two directions is large. The effect of anisotropies increases with increasing the temperature. Compared with polycrystal alumina, the effect of substrate crystal type on wettability of molten Ni-W/Al₂O₃ was analyzed.The wetting of molten Ni-10%W alloy on polycrystal alumina was observed in two protect atmospheres. Compared with Ar+3%H2 atmosphere, the decreasing rate of contact angle is larger, the time to be equilibrium is shorter and the equilibrium contact angle is smaller in vacuum. The interface reaction both occurred in the two protect atmospheres, the reaction is stronger in vacuum.