Nairen Zhao

Bonding behaviour of nickel base single crystal to polycrystal superalloys by transient liquid phase method

Abstract Transient liquid phase bonding between single crystal superalloy DD98 and polycrystal superalloy M963 has been characterised in terms of microstructure, crystallographic orientation analysis and stress rupture test. Result shows that during isothermal solidification (IS), with increasing bonding time, the liquid interlayer thickness decreases. As a result of incomplete IS, many compounds formed in the centreline. After 1190°C/4 h bonding, the IS process has been complete. It is notable that an interface formed in the bonding zone due to crystallographic orientation difference between parent metals. Result of stress rupture test shows that the rupture life of the bonded joint is more than 140 h at 800°C/350 MPa, which is comparable to that of the M963 alloy. Failure of the joint occurs in the segment of M963 alloy.

Effect of Temperature on Formation of Borides in TLP Joint of a Kind of Nickel-Base Single Crystal Superalloy

a kind of as-cast nickel-base single crystal superalloy was TLP bonded using Ni-Cr-B amorphous foil at different temperatures. Special attention is paid to the formation of boride in diffusion zone of TLP joints at different conditions. The chemical composition and microstructure of borides were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). At different bonding temperature, M3B2 precipitates appear distinct morphologies. At 1200°C, both blocky and plate-like borides formed owing to the diffusion of boron atoms into base metal and precipitation during the cooling process. At 1230°C or above, due to the diffusion of boron atoms the constitutional liquation of original γ/γ′ eutectics in the base metal occurs and borides formed when the system was cooled to room temperature. The analysis of TEM results reveals that M3B2 has a tetragonal structure and is rich in Mo, W, and Cr elements.

Temperature dependence of deformation mechanism in bonding zone of TLP joint of nickel base single crystal superalloy after tensile test

Abstract A nickel base single crystal superalloy was transient liquid phase (TLP) bonded using Ni–Cr–B amorphous foil at 1230°C for 4 h. Tensile tests of the TLP joint were carried out at different temperatures under constant strain rate. The microstructures and the deformation substructures in the bonding zone of the joint were investigated. The results show that the deformation mechanism of bonding zone depends on test temperature greatly. At low temperatures, the deformation is dominated by γ′ shearing; at high temperatures, the deformation occurs by means of γ′ bypass; at intermediate temperatures, the deformation exhibits a transitional behaviour. The deformation mechanism of different parts of TLP joint is identical.