Progress in Understanding the Origins of Excellent Corrosion Resistance in Metallic Alloys: From Binary Polycrystalline Alloys to Metallic Glasses and High Entropy Alloys

Abstract

Some of the factors responsible for good corrosion resistance of select polycrystalline and emerging alloys in chloride solutions are discussed with a goal of providing some perspectives on the current status and future directions. Traditional metallic glass alloys, single phase high entropy alloys (HEAs), early metallic glasses, and high entropy metallic glasses are all emerging corrosion-resistant alloys (CRAs) that utilize traditional strategies for improved corrosion resistance as well as take advantage of some other novel beneficial attributes. These materials enjoy many degrees of freedom as far as choice of both composition and structure, providing great flexibility in the pursuit of superior corrosion resistance. The new materials depart from classical solvent-solute type polycrystalline binary or ternary alloys. Thus, such emerging materials provide significant opportunities to achieve even greater improvements in corrosion resistance in harsh environments. Several examples of the unique corrosion properties of selected materials in the context of modern theories of corrosion are discussed herein. Discussion is restricted to solid-solution binary or ternary polycrystalline alloys, several metallic glass alloys, and single phase HEAs. A common feature of many CRAs is that composition and microstructure often affect both passivity and resistance to localized corrosion that can be divided into initiation, stabilization, and propagation stages. Enormous complexities in protective oxide structures and chemistries and the large number of combinatorial possibilities in newer materials such as HEAs preclude trial-and-error approaches and perhaps even combinatorial experimental design. Computational materials methodologies will be required in the search for new corrosion-resistant alloys in these material classes. The search must consider the best scientific insights available regarding how major and minor alloy additions, as well as various microstructural attributes, contribute to corrosion mitigation. Additional scientific insights, as they emerge, will enable choices beyond the reliance on high concentrations of alloying elements that are known to affect passivity breakdown and pit stabilization. A challenge is to connect the “basic attributes” of an alloy with its properties. The strength of this connection will likely require new scientific principles enabling deep multiphysics insights in order to link feature(s) such as composition and metallurgical phases to the desired corrosion properties. Application of data informatics will likely also play a role given the plethora of variables that are important in corrosion and the difficulty in assessing all relationships. The opportunity exists to accelerate the design of emerging materials for high corrosion resistance.

Bond Synergy Model for Bond Energies in Alloy Oxides

“…2 By now it has been found that this is probably not the case and many of the alloys do not represent their thermodynamic ground state, but are rather kinetically inhibited from phase decomposition and do so upon annealing. 1,5,6 Thus, in this paper, we understand the term HEA not just as entropymaximizing alloys with equiatomic composition, but rather in the modern sense of multiprincipal-element alloys (MPEA) where concentrations do not need to be equiatomic 3,[7][8][9][10][11] . Their oxide equivalents, either high-entropy ceramics 12 or perovskite oxides 13 , are also a currently very actively researched field.…”

Recent insights in corrosion science from atomic spectroelectrochemistry

“…Similar to stainless steel, the passivity of such alloys are attributed to Cr 2 O 3 ‐rich passive film formed on the surface. [ 39 ] However, understanding the role of secondary alloying elements Mo and Fe on Cr‐based passivity was inadequate without the real‐time dissolution analysis. As indicated by the ASEC‐PDP curve (Figure 5b), both the oxidation rate and dissolution rate of Ni‐22Cr were significantly lower than that of pure Ni in 2 M H 2 SO 4 , reflecting the improved passivity due to Cr alloying.…”

Influence of microstructure of CoCrNi medium entropy alloy on its corrosion behavior

“…Ternary CoCrNi MEA shows better mechanical properties at low temperatures than some typical HEAs and most phase alloys (Gerard et al, 2020;Yeh et al, 2004). In the future, it will be a new type of high-performance structural material, making it have broad potential application prospects (Shin et al, 2014;Yoo et al, 2006).…”