Effects of Lattice Mismatch on Diffusion Bonding; A Molecular Dynamics Study

Diffusion bonding is a solid-state joining process, that proposes potential benefits over conventional welding processes, and it provides minimum surface deformation and low twist of faying surfaces. Principally the process involves simultaneously applying elevated temperature of 0.5~0.7 Tm (where Tm is the Melting point of faying surfaces), and high pressures (up to 300 MPa) [1]. This method is capable of joining a wide range of metal and ceramic combinations to produce both small and large components. On a whole, diffusion bonding contains three mechanisms; after removing asperities and contaminants from the surface of work pieces joining surfaces; first stage is performed by producing intimate contact – in atomic-scale – of surfaces. During the second stage, diffusion becomes more important and the crystallization occurs in the third stage. Temperature is an important diffusion welding process condition and its quantitative effects can be explained by means of kinetic theory, in which the diffusion can be stated as a function of temperature ( , K is Boltzmann’s constant). The diffusion length, x, is the average distance traveled by migrating atoms during diffusion in ,t, time steps and it can be approximated as ( ), this simple relation that describes the average distance travelled by atomic particles does not reflect the more complex behavior of atoms in microstructures in formation of weld. Diffusion bonding is largely used as a special technique to provide the active medium of the solid-state thin disk lasers. Thin disk lasers propose multiplicity techniques of pumping to scale output power in several kilo-watts range, one practical example of thin disk laser is the Yb:YAG/YAG composite and several researches recognized applications of these kinds of composite materials in thin disk laser concept