Structural ordering governs stiffness and ductile-to-brittle transition in Al-Li alloys.

The trade-off of stiffness and ductility of metals has long plagued materials scientists. To address this issue, atomic structure designs of short-range ordering (SRO) to sub-nanometer and nanometer scales have received much interest in tailoring the atomic environment and electronic interaction between solute and solvent atoms. Taking an example of Al-Li alloy with high specific stiffness and reverse correlation of Young's modulus and melting point, in this work, we investigate the SRO-dependent stiffness and intrinsic ductile-brittle properties by performing a full-configuration strategy containing various structural ordering features. It suggests that the short-range ordered arrangement of Li atoms can effectively enhance the stiffness while keeping ductility, playing a hydrostatic pressure-like role. Our findings present fundamental knowledge to enable high stiffness and ductility for solvent phases with low modulus through designing local short-range ordered cluster structures.

Towards quantum corrosion chemistry: screening perfect Cr, Ni sites and stoichiometry on top of an Fe(110) surface using DFT.

For decades, corrosion has been classified into many categories according to the microstructural morphology of the chemical reaction products. Until recently, the development of quantum chemistry has simplified the fundamental corrosion mechanism into only two processes: electrochemical dissolution and hydrogen evolution reaction (HER). Although Cr and Ni elements have been found to segregate towards the surface of stainless steel to form a protective layer and prevent Fe dissolution, the understanding of the exact chemistry on top of the Fe surface has not been reported in previous studies. In this study, we have identified suitable doping sites for simultaneous doping of several Cr and Ni atoms, and quantified the effects of different alloy compositions (Fe12Cr3Ni1, Fe11Cr4Ni1, Fe11Cr3Ni2, Fe10Cr4Ni2, Fe10Cr3Ni3) on the stability from two aspects: electron transfer and atomic dissolution. It was found that the doping atoms are more likely to be dispersed rather than aggregated in solid solution. When Cr atoms are symmetrically distributed and Ni atoms are located in the center, it is the site arrangement with the highest work function and stability. Fe10Cr4Ni2 has been found to possess a higher electron binding capacity and thus higher electrode potentials. This is determined by the change of dipole caused by both electronegativity difference between atoms and polarization between the doped layer and the substrate layer. By calculating the vacancy formation energy, it is shown that Fe11Cr4Ni2 is the perfect chemistry on top of the Fe(110) surface due to its high ability of preventing atomic dissolution.