Study On Process And Microstructure Properties Of TLP Bonded GH99 Superalloy

Aiming at the application of nickel-based superalloys GH99 in the field of aerospace, in this paper the welding experiment was carried out on nickel-based superalloys GH99 by using transient liquid phase bonding technology(TLP), with high temperature solder BNi2 and three kinds of self-designed solders as interlayer metal separately. We systematicly investigated the influences of technical parameters on joint microstructure and mechanical properties, and discussed the diffusion solidification mechanism of joint formation basing on experiments.When used high temperature solder BNi2 as interlayer, we found that improving the welding temperature and holding time could help to reduce the precipitation of compounds in welding precipitation zone. Especially the holding time was important for obtaining the joints whose structure and composition were relatively uniform. After isothermal holding at 1170℃for 24 hours,the joint structure and composition was basically the same with base metal, but the base metal tensile strength declined greatly caused by the welding thermal cycle. Through the room temperature shear strength and high temperature shear strength in 900℃, we found that welding parameters, especially holding time, had much greater influences on the joint high temperature strength than the room temperature strength.When used the three kinds of self-designed solders as interlayer, we found that B element as melting point depressant, its content directly impacted on the formation of joint compounds. Since Si element solid solubility in base metal was relatively higher, it wasn't easy to precipitate compounds during the welding process. However, relative to B, Si diffusion speed in the base metal was slower, so required longer homogenization time. If Si content was too high, it was easy to produce regional segregation in isothermal solidification process, resulting zonal distribution silicides in weld center.By calculating, at 1170℃under the GH99 to TLP connection, when the thickness of the interlayer BNi2 was 50μm, the required isothermal solidification time was about 30min. So the long isothermal time needed in TLP connection process was mainly in the homogenization stage after the liquid phase solidification.