Abstract: Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti₂Cu and α-Ti after additive manufacturing, they are potential candidates for high-performance materials. To reveal the deformation and strengthening mechanisms, the molecular dynamics (MD) simulations and experimental analysis were carried out upon Ti-Ti₂Cu lamellae. In this work, we focused on revealing the interface dislocations (IDs) pattern and its effects on the dynamic evolution of the lattice dislocations (LDs) at the Ti/Ti₂Cu interface with (0001)_a//(013)_Ti2Cu orientation relationship. Atomistic simulations depicted that the equilibrium Ti/Ti₂Cu interface contains three groups of partial dislocations which dictate two interfacial coherent structures with low stacking fault energy. Each ID consists of several segments, connected by atomic steps with identical direction. The nucleation sites of LDs under external loading locate at the intersection between the dislocation segment and the atomic step, which is related to the local high atom strain. Under compression deformation, the <100> {011} and <331> {103} slip systems in Ti₂Cu, and the <1123> {1011} slip system in α-Ti are activated, achieving a co-deformation mechanism in the Ti-Ti₂Cu multilayers. The dislocation-interface interactions are responsible for the deformation plasticity and in turn governs the mechanical strengthening. During nanoindentation tests, larger hardness (∼6.2 GPa) and smaller activation volume (∼12b³) were found in the Ti-Ti₂Cu lamellae, which is mainly ascribed to the presence of high-density lamellae interface and confined layer slip, resulting in interface-mediated dislocation annihilation/deposition and consequent high strain hardening. The MD simulations, nanoindentation tests and TEM investigations of interlayer dislocation activity support the strengthening mechanism of dislocation-interface interactions.

Key words: Ti-Ti₂Cu eutectoids, Interface, Dislocation, Molecular dynamics