Mechanisms of plastic deformation and mechanical strengthening in nano-scale Ti-Ti2Cu eutectoids: A study combined molecular dynamics simulation and experiment

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)α//(01‾3)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 〈112¯3〉{101¯1} 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.