Abstract
The microstructure of diffusion-bonded Ni/Ti interface has been investigated by means of secondary electron microscopy, electron probe microanalysis and transmission electron microscopy. The α-Ti in the vicinity of the bonding interface is transformed into β-phase by the penetration of Ni atoms at temperatures between β-transus and eutectoid point. This transformation enhances the diffusivity of Ni atoms into Ti and results in the microvoid formation due to Kirkendall effect. Across the Ni/Ti bonded interface from the Ni- to Ti-side, the intermetallic compound layers, i.e., hexagonal TiNi3 [and Ti(Ti0.11Ni0.89)3], cubic TiNi, monoclinic TiNi, and hexagonal Ti2Ni are formed. The region where the α-Ti transforms into bcc β-phase without intermetallic compound formation at the bonded temperatures decomposes into the lamellar Ti2Ni eutectoid structure directly or after the proeutectoidal α-lath formation during cooling to room temperature.
