The sessile drop method coupled with contact heating procedure was applied for testing high temperature interaction of MgO(100) single crystalline substrates with liquid pure Ni, NiCr5 and NiCr10 alloy at 1500°C under flowing gas (Ar) of 900 mbar. After 15 min contact at the test temperature, the drop/substrate interface was opened by moving the drop to another position using a special manipulator. The solidified sessile drop samples were used for detailed structural characterization of interfaces using optical, SEM+EDS, HRTEM and scanning probe microscopy techniques.
Contrary to available data on wetting properties of Ni-based alloys on oxide-based ceramics, the NiCr10 alloy exhibits a good wetting and unusual wetting behavior on MgO single crystal: after reaching the lowest value of 68°, the contact angle increases up to 104° and wetting-dewetting phenomenon periodically repeats a few times during 15 min contact, both for the first and the second position of the drop on the substrate (after drop pushing to a new position).
The results obtained are analyzed from point of view of thermodynamic stability and reactivity in the NiCr-MgO system as well as of practical applications, particularly taking into account the reasons for the formation of such casting defects in Ni-superalloy castings as oxide-based inclusions and porosity.