New routes for improving adhesion at the metal/α-Al₂O₃(0001) interface

Abstract

With the advent of new steel grades, galvanic protection by zinc coating faces a new paradigm. Indeed, enrichment in strengthening elements prone to oxidation, such as Al, Mn, and Si, leads to the formation of oxide films that are poorly wet by zinc. We study herein routes for the improvement of adhesion at the model Zn/α-Al2O3 interface by the addition of metals. As a first step, with the help of ab initio results on the adsorption characteristics of transition metal adatoms at α-alumina surfaces, we establish and rationalize clear trends in both the behavior of metal-alumina interaction strength and the relative thermodynamic stability of configurations with weakly and strongly bound metal adatoms. The reasons for the enhanced binding strength of transition metals, such as Cr, maintained regardless of the precise alumina termination and the surface charge state are pointed out. On these grounds, possible improvements of adhesion under realistic conditions are discussed. It is predicted that enrichment in transition metals, such as Cr, may produce strongly adhesive interfaces that lead to cohesive cleavage.

Structural, electronic and adhesion characteristics of zinc/silica interfaces: ab initio study on zinc/β-cristobalite

“…Before concluding, let us note that the overall pattern of zinc interaction at various terminations of silica shows clear similarities with zinc interaction at the α-alumina(0001) surfaces 44 . This suggests that, similarly to the case of alumina, adhesion improvement of zinc/silica interfaces may require the presence of interfacial buffers made of more reactive elements [45][46][47] . However, we stress that surface siloxane rings, which are a structural peculiarity of the non-polar silica surfaces, may require specific treatment to break them.…”

Effects of surface hydroxylation on adhesion at zinc/silica interfaces

“…Let us stress, however, that the calculated decohesion effect is small and likely inferior to the precision of the present approach, due to both an approximate treatment of exchange and correlations and to the structural constraints imposed by the supercell geometry. Alternative routes for adhesion improvement of zinc/silica interfaces, based, e.g., on interfacial buffers made of more reactive elements [56][57][58] , could be envisioned and are presently under study in our group.…”

Al-rich Fe0.85Al0.15(1 0 0), (1 1 0) and (1 1 1) surface structures

“…2. While commensurability is verified along the [01] S direction (the superstructure involving five substrate unit cells), peaks appear at h S = ±0.12, ±0.56 along the [10] S direction that is to say at a distance of ∆h S = 0.44 from the surface Bragg peaks. Whatever the beam energy, the superstructure spots are found only around Bragg spots.…”

“…The integrated line cuts along the [10] S and [01] S directions through the (11) S reflection of the LEED pattern of Fig. 1-a are shown in Fig.…”

“…These so-called Advanced High-Strength Steels (AHSS), that allow weight reduction of cars, are among the means used by the automotive industry to face the global challenge of CO 2 emission decrease. However, a drawback of alloying steel with highly electropositive elements such as aluminum is the tendency of these to segregate and to form a surface oxide film, which then degrades the quality of the zinc-based anticorrosive coating during the galvanization process [6,7,8,9,10,11,12].…”