Effect of Nb plus Ti coating on the wetting behavior, interfacial microstructure, and mechanical properties of Al/Al2O3 joints

The subject of the work was to study the effect of Nb + Ti thin film deposited by PVD method on alumina substrates on the wetting behavior, bond strength properties, and structure of interface in the Al/Al2O3 joints. Applying the sessile drop method, the wetting behavior of molten Al (99,999%) on coated alumina substrates was studied in the temperature range between 953 and 1373 K under a vacuum of 0.2 mPa for 30 min of contact. The sessile drop samples were used to examine the interface structure, shear strength, and interfacial fracture toughness under the concentrated load. The introduction of the thin Nb + Ti film layer of 900 nm thickness: (1) greatly improves the wettability of alumina by molten Al at above 1223 K and the shear strength of Al/Al2O3 joints produced at 1223 K, (2) has positive effect on structure transformation in the interface and leads to fabrication of reliable metal-ceramic joints. Microstructural investigations of the interface indicated that the precipitates of Nb and Ti-rich intermetallic phases were formed at the Al/Al2O3 interface, which influenced strengthening of these joints. Hence a conclusion can be drawn that the interface structure influences the durability increase in Al/Al2O3 joints.