"Wetting" And Brazing Of AlN By Sputtered Al

Brazing is the main method of joining ceramics with themselves or metals,semi-conductors.Due to the poor wettability of molten metals,the usage of metallization or active brazing methods are employed,to form reaction layers which can be wetted by molten metals.However,the reaction layers will cause adverse effects on brazing joints.In order to realize the wetting of molten metals on AIN without reaction layers,this paper proposed a method of directly brazing AIN,based on the investigation on the wetting molten A1 on AIN above 850’C.By utilizing sputtered A1 films deposited on AIN as fillers,the AlN/AlN and AlN/Al based composite were directly brazed.The microstructure and morphologies are characterized with scanning electron microscopy,energy disperse spectrometer and large depth field optical microscopy.The results indicated that:1)The received Al/AlN brazing joints represented strong interface connection,with the shear strength of 104 MPa.An addition of 3.8at.%Cu to fillers further promoted shear strength to 165 MPa.When Cu content reached to 9.4at.%,fracture surfaces occurred near the region between brazing seam and ceramic substrate with lower strength of 95 MPa since Cu tended to segregate along the interface.2)The addition of 20at.%Ge and 28.Oat.%Ge decreased the brazing temperature to 510℃ and 430℃ respectively.Similarly however,the significant segregation of Ge alone the interface cause greater decline of shear strength to 48 MPa of Al-20.0at.%Ge and 39 MPa of Al-28.0 at.%Ge;3)After being brazed at 580 for 30 min with Al-15.Oat.%Ge film fillers,the joints of AlN/Al based composites are received,with few pores or un-jointed region,and Ge fully diffused through xoide film into Al matrix,thus causing the melting of matrix and the mixing with molten fillers.The brazing of AIN and Al based composites are achieved by two kinds of effects of sputtered Al particles:1)The wetting of sputtered Al particles on AIN:The impact of high-energy sputtered Al particles on AIN surface would induce the formation of Al-N bonds on Al/AlN interface,thus resulting in the "wetting" of Al on A1N,though the wetting between molten aluminum and AIN usually required a high systematic temperature over 850℃.The energy of Al-N covalent bonds are far more above that of Al-Al metallic bonds,and will sustain after the molting of film fillers.This kind of interfaces will receive smaller liquid/solid interfacial tension.2)The "in-stu" depletion of oxide films by sputtered Al particles:The magnetron sputtered Al particles would induce the formation of chemical bonding between Al-based film fillers and oxide film of Al matrixes,and such connection could prevent the diffusion of oxygen into the fillers/composites interface.During brazing,the oxide film will be broken under thermal stress,then the molten fillers diffuse through the cracks of oxide film into Al matrixes.The oxide film will then be further broken by liquid tension and viscous force of molten alloys and be separated in the molten alloy.