Electron localization governed plasticity in nanotwinned metals beyond the Hall-Petch type limit
JW Xiao and N Wu and O Ojo and C Deng, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 797, 140251 (2020).
While nanotwinned metals have been widely reported to show a strengthening-softening transition as the twin spacing decreases below a critical size, which is similar to the Hall-Petch limit in nanocrystalline materials, a recent study has suggested that some nanotwinned high entropy alloys (HEAs) could show continuous strengthening as long as the twin spacing decreases. Here we investigate the physical origin of the contrasting plasticity in nanotwinned face- centered-cubic (FCC) metals beyond the Hall-Petch type limit by using atomistic simulations based on density functional theory. Our results indicate that the degree of electron localization among atoms at the FCC sites and the stacking faults, which have a hexagonal-closed-packed (HCP) structure, governs the plasticity in nanotwinned metals with extremely fine twin spacing. Specifically, metals whose electrons are more localized at FCC atoms than those at stacking faults, such as conventional FCC metals, are associated with positive stacking fault energy and accordingly detwinning and strengthening-to-softening transition beyond the Hall-Petch type limit. In contrast, metals in which electrons are more localized at stacking faults than at FCC sites as found in some HEAs exhibit negative stacking fault energy and continuous strengthening by the unconventional FCC-to-HCP martensite transformation when the Hall-Petch type limit is reached. This work provides a new microscopic aspect from the electron properties to understand the macroscopic mechanical behavior of nanotwinned FCC metals which can shed some light on designing novel complex alloys.
Return to Publications page