Molecular Dynamic Simulations On Strengthening Mechanism Of W/Cu Joining Interface In First Wall Of Fusion Reactor

As the plasma-facing component,the first wall of the fusion reactor has attracted many concerns to its thermal shock resistance and thermal fatigue resistance.However,due to technical limitations,submicron or nanoscale defects remain on the interface between different materials,which are potential threats to interface cracking and fatigue.Because this kind of micro-defects is difficult to detected online and the engineers put their focuses on satisfying macroscopic performance,researches in these aspects have not received enough attention.In this study,on the joining interface between the tungsten layer(plasma facing material)and the copper layer(heat sinking material)in the first wall of the fusion reactor which requires high safety,a series of molecular dynamics simulations were conducted to study the hot isostatic pressure joining parameters,interface strengthening mechanisms,shock wave in-situ elimination of submicron/nanoscale defects on interface and the microscopic propagation characteristics of shock waves across polycrystalline copper.The main research progresses are listed as follows:1、Under the condition of hot isostatic pressure joining,increasing the temperature can accelerate the atomic diffusion rate on interface;while at constant isostatic temperature,increasing the pressure will inhibit the diffusion rate on interface.In a high static pressure environment,increasing the temperature has more dramatic influence on the diffusion properties of the interface atoms.2、The nano-crystallization on interface can affect the atomic diffusion process of the hot isostatic pressure joining interface,but the final diffusion depth depends on the welding temperature.Currently hot isostatic pressure and temperature conditions can hardly eliminate micro/nano defects on the interface.3、At lower impact velocity,the shock wave generated within the single crystal material is clearly presented as dual-wave structure of the precursor elastic wave and the subsequent plastic wave.As the impact strength increases,the plastic wave gradually catches up to the elastic wave and the dual-wave structure disappears.The stress differences induced by the crystal orientation occurs in are mainly indicated in the elastic stress wave range,which is result from differences of the lattice atoms arrangement and the interatomic force acting mechanism.4、On the basis of the foregoing research,the microscopic propagation characteristics of the impact stress wave at the interface of polycrystalline copper materials are further studied.It is found that at the microscopic grain boundary interface,the propagation of the shock wave across the grain boundary is anisotropic,and the stress distribution difference is closely related to the arrangement characteristics of the lattice atoms.After a large number of statistical analysis,a stress distribution tensor only associated with the crystal lattice angle in the elastic stress wave range is obtained.This tensor is characterized by consistent predictability for the FCC lattice metals.5、Finally,a comparative simulation of the process of eliminating micro/nano defects by shock waves on the polycrystalline interface of materials shows that the required stress conditions are significantly reduced.