Unraveling the correlation between Hall-Petch slope and peak hardness in metallic nanolaminates

Abstract

Interfaces often dominate plastic response of nanostructured metallic materials, e.g., nanolaminates (NLs), and thus engineering NLs to introduce controllable interfacial properties is a grand challenge. In this work, we comparatively studied the mechanical properties of both crystalline/crystalline NLs (C/CNLs) and crystalline/amorphous NLs (C/ANLs) in terms of the Hall-Petch slope (k) and the peak hardness (Hpeak). To characterize the interfacial properties of Cu-based NLs, we propose an energy factor (χ) in light of the interfacial residual dislocation energy determined by the coupling effects of lattice and moduli mismatch and the increased system energy caused by transmission slip determined by the mixing enthalpy (ΔHmix). It is found that this energy factor χ can quantitatively capture well the variation of Hall-Petch slope k and peak hardness Hpeak of NLs with different types of interfaces. There are linear relationships for both k – χ and Hpeak – χ plots. For the C/CNLs with positive ΔHmix, both k and Hpeak decrease with increasing χ, whereas for both the C/CNLs with negative ΔHmix and the C/ANLs, k decreases with decreasing χ while Hpeak decrease with increasing χ. The underlying mechanisms for the different mechanical properties of these NLs are elucidated from the perspective of diatomic interactions characterized by the ΔHmix of a given NL system. These experimental findings provide deep insights into designing tunable interfacial structures in metallic materials to realize their high performance.