Diffusion bonding of Cu atoms with molecular dynamics simulations

Diffusion bonding of copper disks is an important step during the assembly of accelerating structures -the main components of power radio-frequency linear accelerators-. During the diffusion bonding copper disks are subjected to pressure at high temperatures. Finding the optimal combination of pressure and temperature will enable an accurate design of manufacturing workflow and machining tolerances. However, required optimization is not possible without good understanding of physical processes developed in copper under pressure and high temperature. In this work, the combined effect of temperature and pressure on closing time of intergranular voids is examined by means of molecular dynamics simulations. In particular, a nano-void of 3.5-5.5 nm in diameter representing a peak and a valley of surface roughness facing each other was inserted between identical copper grains. The simulations performed at T = 1250 K, the temperature used in experimental condition, and the 300-800 MPa pressure range indicated the dislocation-mediated enhancement of atomic diffusion leading to full void closure.