Investigation on the interface of additively manufactured bimetallic structure: A molecular dynamics simulation

In this study, • A molecular dynamics (MD) simulation analyzes Ti-Nb interfaces in wire-arc DED deposits. • Point defects at Ti-Nb interfaces are quantified under varying heat input. • Cluster counts drop in lower layers but rise in upper layers at high heat inputs. • Atomic size-mismatch-induced lattice distortion drives residual stress and loop formation. • Substrate and layers demonstrated compressive and tensile biaxial stresses, respectively. Multilayer depositions with varying interface behaviors affect the mechanical properties of deposited materials, so atomic-scale deposition mechanisms provide a better understanding of material behavior under multiple diffusion conditions. In this research, molecular dynamics is applied to investigate the behavior of the interface in Ti6Al4V-NbZr1 bimetallic structure deposited by wire-arc directed energy deposition (W-DED) in various heat input conditions. In addition, the interactions between the bimetallic structure and the distribution and size of dislocation loops are studied during deformation. It was found that the nano-melting pool forms before solidification, and the crystal growth proceeds by directional solidification, which can be equiaxed or columnar. Interdiffusion of the system shows asymmetrical diffusion behavior, and Nb atoms show a greater tendency to diffuse into the matrix in higher heat input conditions. According to the cluster analysis, the cluster number decreases from 76138 to 75720 for the first deposited layer, whereas it increases from 88046 to 90309 for the final deposited layer as heat input increases. Surface roughness decreases from 1.6 to 0.9 Å while the interface width increases from 30 to 50 Å as the heat input increases. It was concluded that atomic-size mismatch-induced lattice distortion enhances residual stress, resulting in dislocation loops. The formation of numerous 1/6 Shockley and 1/2 interstitial dislocation loops, along with a low amount of and mixed loops, was also observed. At the substrate-interface, the biaxial stress is compressive, whereas the deposited layers exhibit tensile behavior.