Air-reactive cladding assisted brazing of Y₂O₃-MgO nanocomposite ceramic to TC4 alloy: Interfacial reaction mechanism and mechanical property

AbstractY₂O₃-MgO nanocomposite ceramic, as a novel infrared window material, exhibits superior properties compared to traditional infrared window materials. To realize its engineering application in high-speed aircraft such as unmanned aerial vehicles, the reliable joining between Y₂O₃-MgO nanocomposite ceramic and TC4 alloy is a key challenge. In this study, the surface of Y₂O₃-MgO nanocomposite ceramic was first clad in air using an Ag-CuO-Al₂O₃ filler, which achieved uniform spreading on the ceramic. Subsequently, vacuum brazing was successfully performed between the clad Y₂O₃-MgO nanocomposite ceramic and TC4 alloy using AgCu filler. The microstructure and mechanical properties of the brazed joints were studied in detail. The air-reactive cladding technique significantly improved wettability, reducing the wetting angle of the filler metal on Y₂O₃-MgO nanocomposite ceramic from 104° to 27°. The brazed joint interface treated with the Ag-CuO-Al₂O₃ cladding exhibited sound metallurgical bonding without defects. The main phases identified in the Y₂O₃-MgO ceramic-side reaction layer were Cu₂Y₂O₅, Mg_0.78Cu_0.22O, and Y₄Al₂O₉. Analysis and calculations reveal that Cu₂Y₂O₅ and Mg_0.78Cu_0.22O are respectively formed by the reaction of CuO with Y₂O₃ and MgO, while Y₄Al₂O₉ results from the reaction between Al₂O₃ and Y₂O₃. The typical interfacial microstructure was: Y₂O₃-MgO/Cu₂Y₂O₅+Mg_0.78Cu_0.22O + Y₄Al₂O₉/Cu_xTi_6-xO + Ag (s,s.)/Ti (s,s.) + Ti₂Cu/TC4. The joint achieved a maximum shear strength of 66 MPa under optimal parameters of 24 mol% CuO in the cladding layer and a brazing parameters of 860 °C for 20 min.