Mechanism of forming interfacial intermetallic compounds at interface for solid state diffusion bonding of dissimilar materials

The formation of brittle intermetallic compounds at the interfaces of diffusion bonds is the main cause which leads to poor bond strength. Therefore, it is very important to study and establish the formation and growth model of intermetallic compounds at the interfaces for the control process of diffusion bonding. In this paper, according to the diffusion kinetics and the thermodynamics, the principle of formation of intermetallic compounds at interfaces in the multi-component diffusion couple, the flux-energy principle, is put forward. In the light of diffusion theory, the formation capacity of the phase at the interfaces is determined by specific properties of the composition in the diffusion couple and the composition ratio of the formed phase is in agreement with the diffusion flux. In accordance with the flux-energy principle, the microstructure of the Ni/TC4 interface is Ni/TiNi3/TiNi/Ti2Ni/TC4, the microstructure of the TC4/00Cr18Ni9Ti interface is 00Cr18Ni9Ti/TiFe2/TiFe/Ti2Fe/TC4, and the microstructure of the TiAl/40Cr interface is 40Cr/TiC/Ti3Al + FeAl + FeAl2/TiAl. Multi-intermetallic compounds with the equivalent flux-energy can be formed at the interfaces at the same time.