Publication Details
Abstract
The present study theoretically analyzes the variation of GB absorption efficiency with grain size and temperature in order to elucidate the microscopic dynamics of irradiation-induced defects and their interactions with structural sinks in nanocrystalline nickel. A dual-defect reaction-diffusion model considering both vacancies and interstitials was developed. The governing equations were numerically solved by the Crank-Nicolson scheme and implicit Newton iterations to ensure that the numbers remained stable even under very high temperature and reaction rate. The Robin boundary condition is employed to explore the effect of the boundary kinetic coefficient, h, on the partial defect transfer at grain boundaries. The simulations indicate that the concentrations of defects increase rapidly after irradiation and then gradually saturate. The stabilization under low temperatures takes a very long time due to slow diffusion. However, at high temperatures (T > 700 K), it attains within seconds. A significant reduction in the concentration of both vacancies and interstitials near grain boundaries (GBs) confirms that they act as an effective sink; the interstitials are more easily absorbed than vacancies due to the relation (Di \ Dv). As the size of grains goes down from 200 nm to 20 nm, sink efficiency is increased by about 2-5 times. This is because the diffusion paths are shorter while the boundary area density is higher. However, it somewhat decreases below 10 nm due to the saturation of the boundary. Efficiency also increases with temperature up to 700 K and then decreases slightly beyond that with the movement of the system towards an interface-limited regime. Model predictions are in good agreement with the available analytical solutions and suggest that the nonlinear recombination term reduces the efficiency of sinks by 10–25%. The dependence of defects evolution on (h), grain size, and temperature introduces a tool for the design of radiation-resistant nanocrystalline materials.