Lattice Distortion Promotes Incipient Plasticity in Multiprincipal Element Alloys

Multiprincipal element alloys usually exhibit earlier pop-in events than pure metals and dilute solid solutions during nanoindentation experiments. To understand the origin of this phenomenon, large-scale atomic simulations of nanoindentation were performed on a series of metallic materials to investigate the underlying physics of incipient plasticity at the nanoscale. Statistical result shows that lattice distortion δ and normalized critical pressure p_c/E_s follow a power-law relationship. Via quantitative analysis on the relative positions of the atoms within the nearest neighbor shell, the physical origin of premature incipient plasticity is revealed as severe lattice distortion induces large relative atomic displacement, so only a small indentation strain is required to meet the critical displacement threshold that triggers incipient plasticity. Therefore, for perfect crystals, lattice distortion is an intrinsic and determinative factor that affects the first pop-in event.