Molecular dynamics study of the effect of alloying elements and imperfections on linear friction welding of Cu and Ni metals

Probing Friction Properties of Hydrogen-Free DLC Films in a Nitrogen Environment Based on ReaxFF Molecular Dynamics

In this paper, ReaxFF molecular dynamics simulations were used to look at how load and the number of nitrogen molecules affect how friction behavior in hydrogen-free diamond-like carbon (DLC). The presence of nitrogen molecules will inhibit the formation of C-C covalent bonds between the contact surfaces of the upper and lower DLC, thereby effectively suppressing the increase in friction during the initial friction phase. After the initial friction stage, the mechanical mixing of the contact surfaces brought on by the diffusion of nitrogen molecules results in considerable shear stress, which has significant impacts on the friction force. In addition, due to the existence of nitrogen molecules, the effect of graphitization of hydrogen-free DLC on friction is almost negligible.

Research on the Diffusion Behavior of Cu in Low-Carbon Steel under High Temperatures

The effective diffusion of Cu in Fe is the key to forming a stable transition layer between copper and low-carbon steel, but it is seriously affected by several factors, especially temperature, and the diffusion of Cu can only be completed at high temperatures. In order to analyze the diffusion coefficient of Cu in low-carbon steel under high temperatures, and to obtain the best diffusion temperature range of Cu in steel, the electrodeposition method was used to prepare the diffusion couple of copper and low-carbon steel, which would be annealed under different temperatures for 6 h; meanwhile, the MD models were also used to analyze the diffusion behavior of Cu in Fe at different temperatures. The results show that the diffusion of Cu in low-carbon steel could be realized by high-temperature annealing, and as the temperature increases, the thickness of the Cu/low-carbon steel transition layer shows an increasing trend. When the annealing temperature is between 900 °C and 1000 °C, the thickness of the transition layer increases the fastest. The results of the MD models show that, when the temperature is in the phase transition zone, the main restrictive link for the diffusion of Cu in Fe is the phase transition process of Fe; additionally, when the temperature is higher, the main restrictive link for the diffusion of Cu in Fe is the activity of the atom.