Research On Process And Mechanism Of Alumina Reactive Metallization And Its Brazing With Copper

Alumina-copper composite components have a significant potential for aerospace and electronical applications. To meet the brazing of alumina and copper, the new technique of alumina reactive metallization and its brazing with copper was put forward in this dissertation. The mechanism of alumina reactive metallization was expounded. Also, the effect of Ti content and brazing parameters on microstructure and mechanical properties of alumina/copper joint was investigated. Metallization powders was used as active filler metal to braze alumina with copper directly. Moreover, comparation was carried out between direct brazing and indirect brazing, which was focused on their effect on the microstructure and mechanical properties of brazed joint and cooper. The interconnection of fracture position, shear strength and microstructure of joint was analyzed comprehensively.Metallization powders Sn0.3Ag0.7Cu-x%Ti(wt.%, x=2, 4, 6, 8), which had a melting range from 219°C to 231°C, was prepared by mechanical ball milling process. And mechanical metallurgy was not occurred between metallization powders during ball milling. Alumina was metallized at 900°C for 30 min, and a metallization layer was well covered on the surface of alumina. The microstructure of metallization layer consisted of β-Sn matrix and scattered distributed Ti6Sn5 phase, whose amount grown with the increase of content of Ti. A Ti O reaction layer was formed on the interface of metallization layer and alumina.Metallized alumina was brazed with copper using solder Sn0.3Ag0.7Cu at the temperature range from 580°C to 660°C. The typical microstructure of brazed joint was Cu/Cu3Sn/Cu6Sn5/β-Sn consisting of Ti6Sn5 and alumina particles/alumina. Brazing parameter had an obvious effect on interfacial microstructure and shear strength of brazed joint. With the increase of brazing temperature or extension of brazing time, more element Cu of copper was dissolved into brazing seam and more Cu-Sn compound was formed. The joint brazed at 620°C for 5min possessed the highest shear strength of 32 MPa, and fracture was occurred in Cu6Sn5 and β-Sn layer during shear test. As the brazing parameter exceed the optimal process parameters(620°C/5min), kirkendall voids were formed in brazing seam, which resulted in the steep decrease of the shear strength of joint.Alumina was directly brazed with copper using active filler metal, which was the same as metallization powders, at 900°C for 10 min. The typical microstructure of directly brazed alumina/copper joint consisted of Cu(s,s), rich-Cu and Ti2 Cu phase, also a reaction layer containing of Ti O and Ti O2 was formed along alumina. With the increase of content of Ti, the reaction between filler metal and alumina was more sufficient, and the shear strength of joint increased gradually and reached the steady value. When the content of Ti was 6% and 8%, the highest shear strength of 52 MPa was obtained and the brazed joint was fractured in alumina thoroughly. Compared with indirect brazing, the shear strength of joint was increased, but direct brazing had much greater damage on the surface hardness of copper.