Insight into the strengthening mechanism of α-Al2O3/γ-Fe ceramic-metal interface doped with Cr, Ni, Mg, and Ti

Corrosion prevention is an important issue in thermal energy storage. The poor bonding strength between the ceramic coatings and substrates in these energy storage devices arises because of the high corrosivity of the energy storage materials at high temperatures, which reduces the service life of the devices. In this study, an alloy element x (Cr, Ni, Mg, or Ti) was innovatively doped into the α-Al2O3 (0001)/γ-Fe (111) interface to enhance the interfacial bonding strength, and the strengthening mechanism of the doped interface was quantitatively analysed by first-principles calculations at the electronic level. The results show that Ti and Mg doping can clearly increase the bonding strength of the Al2O3/Fe interface, whereas doping with Ni and Cr is ineffective. More importantly, the micro-mechanism was revealed by discussing the segregation behaviour, where the Ti and Mg dopants readily segregated to the interface and then combined with Al or O atoms to form new compounds (Ti2O3, TiAl2, MgO, and MgAl3), whereas the Cr and Ni dopants were preferentially and stably localized in the Fe sites. Therefore, Mg and Ti atoms appear to play the enhancement effect as interfacial binders. Furthermore, evaluation of the electronic structure confirmed that all doped interfaces exhibited metallic and covalent characteristics at the interfaces, whereas greater hybridisation of the electron orbitals was found at the doped Ti and Mg interfaces than at the other interfaces, such as between Al-s and Mg-p, between Al-p and Mg-p, between Ti-p and Al-p, between Ti-s and Al-s, and between Ti-p, d and O-s. The more electron orbitals hybridizing, the larger the bonding strength is.