Wetting And Brazing Of Si₃N₄ By Sputtered Al-Ni Film Filler

Brazing is one of the most important ways to join ceramic to ceramic and ceramic to metal.Because most metals can not directly wet the ceramic,the reaction transition layer are needed to be able to wet on the surface of the ceramic surface in the present brazing technique.Al is rarely able to directly wet the Si₃N₄ ceramic metal,but the Al₂O₃ oxide film on the surface of the molten liquid impedes the study of its wetting behavior and the realization of brazing.This paper selects the Al/Si₃N₄ system,using the sputtering film as the filler to completely eliminate the interference of oxide film of molten Al.By the deposition sequence of the Al-Ni bilayer films,two aspects of contents were studied:In the case of sputtered Al films not deposited directly on the Si₃N₄ surface,the wetting behavior of Al melt on Si₃N₄ was studied and the direct brazing of Al to Si₃N₄ ceramic without reaction layers at the high temperature?850??was achieved by increasing the temperature of Al liquid;Besides,by using the"wetting"effect of the sputtering particles'bombardment when Al films were deposited directly on Si₃N₄,the direct brazing of Si₃N₄ ceramic using Al fillers without reaction layers near the Al melting point?680??was realized.The study of sputtered Al films not directly deposited on Si₃N₄ surface showed that:1.The results of heating brazing of Si₃N₄ ceramic with sputtered Al showed that the molten Al can not immediately wet Si₃N₄;it changed from non-wetting to wetting on the Si₃N₄ ceramic when the brazing temperature increased from 680?to 750?;while the temperature was 1050?,an obvious interface reaction between the molten Al and the Si₃N₄ ceramic occurred.2.In consistent with the three stages of the interface interaction of Al/Si₃N₄,when the brazing temperature was 680?,the fracture generated at the interface between the brazing seam and the ceramic due to the failed wettability,and the shear strength of Al/Si₃N₄ joint reached 81MPa.With the increase of brazing temperature and improvement of wettability,the fracture areas generated from the interface to the metallic brazing seam,the shear strength also gradually increased from 116 MPa at 750?to more than150 MPa when the temperature increased to 850-950?.When the brazing temperature reached to 1050?,the formation and fracture of the reaction layer between molten Al and Si₃N₄ reduced the shear strength of the joint to40MPa.The study of sputtered Al films directly deposited on Si₃N₄ surface showed that:3.The results of direct sputtered Al-Ni particels on Si₃N₄ ceramic surface showed that the direct bombardment of energetic sputtered Al particles enable Al to“wet”Si₃N₄,and relaized the brazing of Si₃N₄ceramic using Al and Al-Ni alloy film at the temperature of 680?.The seams of brazing joints were well-stacked and less defects,and formed well metallurgical bonding to ceramic without reactive transition layers.The shear strength of pure Al/Si₃N₄ joint reached 106MPa.The strength increased to 148 MPa with adding 1.0 at.%Ni into film filler and forming hypoeutectic structure in the seam.With further increasing Ni content to 3.0at.%,the strength of joint slightly decreased to 132 MPa due to the eutectic structure of the seam.The fractures of all joints generated in Al or Al-Ni alloy seams.The physics essence of sputtered Al wetting Si₃N₄ was revealed by comparing wetting and brazing effects of film fillers with different deposition sequence.The two fillers both contained Al-1.0 at.%Ni but their Al layers were directly or indirectly contacted with Si₃N₄.The film filler of Al layer in direct contact with Si₃N₄ wetted and the indirect one not wetted when molted.Comparing with the filler of Al layer in direct contact with Si₃N₄,the brazing joint using the filler of Al layer not direct contact with ceramic fractured at the interface between the seam and the ceramic instead of the seam and the shear strength also decreased from 148 MPa to 81 MPa.This comparison provided a strong indirect evidence that wettability improvement of sputtered Al film on Si₃N₄ was attributed to the direct bombardment of energetic sputtered Al particles.