THE MICROSTRUCTURE OF DIFFUSION-BONDED TI/NI INTERFACE

The microstructure of the diffusion-bonded Ni/Ti interface has been investigated by secondary electron microscopy, electron probe microanalysis and transmission electron microscopy. The alpha -Ti in the vicinity of the bonding interface is transformed into beta -phase by the penetration of Ni atoms at temperatures between the beta -transus and eutectoid point. This transformation enhances the diffusivity of Ni atoms into Ti and results in microvoid formation due to the Kirkendall effect. Across the Ni/Ti bonded interface, intermetallic compound layers, i. e. , hexagonal TiNi//3 left bracket and Ti(Ti//0//. //1//lNi//0//. //8//9)//3 right bracket , cubic TiNi, monoclinic TiNi, and hexagonal Ti//2Ni are formed. The region where the alpha -Ti transforms into bcc beta -phase without intermetallic compound formation decomposes into the lamellar Ti//2Ni eutectoid structure directly or after proeutectoidal alpha -lath formation during cooling to romm temperature.