Correlation of work function and stacking fault energy through Kelvin probe force microscopy and nanohardness in dilute α-magnesium

Abstract

Electronic interactions of the Group 2A elements with magnesium have been studied through the dilute solid solutions in binary Mg-Ca, Mg-Sr and Mg-Ba systems. This investigation incorporated the difference in the ‘Work Function’ (ΔWF) measured via Kelvin Probe Force Microscopy (KPFM), as a property directly affected by interatomic bond types, i.e. the electronic structure, nanoindentation measurements, and Stacking Fault Energy values reported in the literature. It was shown that the nano-hardness of the solid-solution α-Mg phase changed in the order of Mg-Ca>Mg-Sr>Mg-Ba. Thus, it was shown, by also considering the nano-hardness levels, that SFE of a solid-solution is closely correlated with its ‘Work Function’ level. Nano-hardness measurements on the eutectics and ΔWF difference between eutectic phases enabled an assessment of the relative bond strength and the pertinent electronic structures of the eutectics in the three alloys. Correlation with ΔWF and at least qualitative verification of those computed SFE values with some experimental measurement techniques were considered important as those computational methods are based on zero Kelvin degree, relatively simple atomic models and a number of assumptions. As asserted by this investigation, if the results of measurement techniques can be qualitatively correlated with those of the computational methods, it can be possible to evaluate the electronic structures in alloys, starting from binary systems, going to ternary and then multi-elemental systems. Our investigation has shown that such a qualitative correlation is possible. After all, the SFE values are not treated as absolute values but rather become essential in comparative investigations when assessing the influences of alloying elements at a fundamental level, that is, free electron density distributions. Our study indicated that the principles of ‘electronic metallurgy’ in developing multi-elemental alloy systems can be followed via practical experimental methods, i.e. ΔWF measurements using KPFM and nanoindentation.