DIFFUSION BONDING
In this process, union between specially prepared mating surfaces takes place as a result of diffusion, which occurs due to high temperature & pressure, exerted for a long time. The pressure is low enough to ensure that there is no plastic flow or deformation. The extended time of several minutes at elevated temperatures (which will cause oxidation) requires that the joint be made in protective atmosphere or vacuum. Sometimes thin inserts are placed between the mating surfaces to speed up diffusion and ensure strong welds.