Effect of Sintered Metal Powder Process Parameters on Strength of Alumina-Kovar Joint

For some applications, Alumina-Kovar joints are used to combine properties of both materials. Brazing is often the preferred method for joining process, but the critical problem is the poor wettability of ceramics by filler alloys. This problem is usually overcome by metallizing of ceramic surface. The most common process used for metallizing alumina ceramics is the sintered metal powder process (SMPP) which migration of glassy phase from ceramic into metallizing layer is responsible for bonding and is the most major issue of these joints. In this research, Alumina ceramic samples are fabricated by injection molding process and then sintered at high temperatures. These ceramics are metallized using SMPP then Nickel electroplated and finally brazed using silver filler. The affecting parameters on SMPP including Alumina particles size distribution and thickness of metallizing layer are investigated to improve the strength of ceramic-metal joint. The most probable mechanism for strengthening of joint is Glass Migration from Alumina substrate toward the metallizing layer due to different capillary pressure. Uniaxial tensile and leak tests are used to evaluate the strength and vacuum tightness of joint, respectively and the microstructure of joint area is studied using SEM. The results show that the joint strength for sample with bimodal particles size distribution is much higher than the unimodal one. In addition, this strength decreases by increasing in metallizing thickness.