Ultra-high work hardening mediated by three-level precipitation in a Ni2CoCr0.5Si0.3Al0.2Ti0.2 medium entropy alloy

The three levels of precipitation with the primary Ni16Ti6Si7 intermetallic, the secondary large-sized L12 phase and the tertiary diffused distributed nanoscale L12 particles is achieved in an aged Ni2CoCr0.5Si0.3Al0.2Ti0.2 medium entropy alloy (MEA). The yield strength of 1222 MPa and ultimate strength of 1626 MPa as well as the uniform elongation of 16% and excellent work hardening rate exceeding 4.5 GPa are obtained. The precipitation strengthening model is employed to understand the comprehensive effect of the shearing and Orowan strengthening on yield strength. The synergistic strengthening mechanisms, including dislocation Orowan mechanisms for the Ni16Ti6Si7 intermetallic, the shearing and Orowan mechanisms of large-sized L12 precipitation, the shearing mechanism and pining effect from the small-sized L12 precipitation, together with Lomer-Cottrell (LC) locks and nano-spacing stacking fault (SF) networks, result in the ultra-high work hardening during plastic deformation, which provides a novel strategy for the design of excellent precipitation-strengthened alloys. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).