The secret of the amorphous advantage begins at the atomic scale. In a crystalline alloy, grain boundaries, dislocations and other lattice defects act as chemically energetic hotspots where corrosion preferentially initiates. An amorphous alloy has no grains and no grain boundaries, presenting a chemically homogeneous surface to the environment. Combined with the right alloying recipe, typically iron blended with chromium, molybdenum, tungsten, boron, carbon and sometimes cobalt, nickel or phosphorus, this structural uniformity allows the coating to form dense, adherent passive films rich in chromium and molybdenum oxides. The review emphasizes that Fe-based AMCs consistently outperform conventional steels in aggressive chloride-rich environments such as seawater, where pitting corrosion normally drills microscopic pinholes through protective layers and eats into the underlying metal.

But chemistry alone does not tell the whole story, and the review is unusually candid about the gap between laboratory promise and field performance. The dominant way to make these coatings is thermal spraying: high-velocity oxy-fuel (HVOF), high-velocity air fuel (HVAF), detonation spraying, atmospheric plasma spraying and laser cladding all propel molten or semi-molten powder particles onto a substrate at extreme speeds. Each splat solidifies within microseconds, locking in the amorphous structure, but the process also stamps the coating with intrinsic defects. Porosity, unmelted particles, oxide inclusions, micro-cracks and splat boundaries thread through the deposit, and these are precisely where corrosion attacks first. Studies cited in the review show that pitting in sprayed Fe-based amorphous coatings frequently nucleates at pores and oxide inclusions rather than on the pristine amorphous matrix, meaning the coating’s Achilles heel is manufactured, not inherent.

Alloy composition remains the most powerful lever designers can pull. Chromium is the workhorse: it enriches the passive film and dramatically improves resistance in chloride solutions, with its benefit depending on having enough of it uniformly distributed. The review highlights work showing that eliminating chromium-depleted zones, which can form during spraying when oxidation selectively consumes elements, substantially enhances localized corrosion resistance. Molybdenum and tungsten act synergistically with chromium, improving the stability and repassivation behavior of the passive film, while boron and carbon promote glass formation, which is essential because a coating that crystallizes during deposition loses much of its corrosion advantage. Minor additions of nickel, cobalt, niobium or phosphorus tune glass-forming ability and electrochemical behavior, though the review notes that trade-offs exist, since elements that improve corrosion resistance can degrade the amorphous-forming capacity or mechanical properties if pushed too far.

Crystallization itself emerges as a nuanced theme. The amorphous structure is metastable, and thermal exposure during spraying or in service can trigger partial crystallization. The reviewed literature shows that the effect on corrosion is not uniformly negative: small amounts of nanoscale crystals can sometimes refine passivation, but solute-lean nanocrystals tend to deplete the surrounding amorphous matrix of chromium, creating galvanic couples that accelerate pitting. Structural relaxation, the subtle atomic rearrangement that occurs below the crystallization temperature, also shifts corrosion behavior. Recent work on thermal regulation of coatings demonstrates that carefully controlling the thermal history can actually be used as a strategy to enhance corrosion resistance, turning what was once seen purely as a degradation mechanism into a processing tool.

Environment matters as much as the material. The review surveys how temperature, hydrostatic pressure, applied electrochemical potential, and the identity of aggressive ions all reshape corrosion behavior. Elevated temperatures accelerate passive film dissolution and alter its semiconducting properties, while high hydrostatic pressure, relevant to deep-sea applications, changes both the thermodynamics and kinetics of pit initiation and growth. Chloride ions remain the primary villain, breaking down passive films and stabilizing pit growth, and sulfur-bearing species can compound the damage by interacting with oxide inclusions. The authors also point to tribo-corrosion, the coupled action of wear and corrosion, as a critical consideration for real components, since mechanical removal of passive films forces the surface into a continuous cycle of repassivation that not every coating chemistry can sustain.

Fortunately, the toolbox of enhancement strategies has grown impressively. Post-spray laser remelting re-fuses the coating surface, healing pores and splat boundaries and restoring a fully dense amorphous or amorphous-nanocrystalline layer. Sealing treatments, from traditional inorganic sealants to novel waterborne silicone-modified acrylics and eco-friendly rosin-based hybrid sealants loaded with functionalized silica and graphene oxide, plug the through-thickness porosity that would otherwise let electrolytes reach the steel substrate. Perhaps the most eye-catching strategy is superhydrophobicity: by combining micro-scale laser texturing or spray texturing with low-surface-energy chemistry, researchers have produced Fe-based amorphous coatings that repel water entirely, achieving self-cleaning, anti-fouling and dramatically enhanced anti-corrosion performance in a single surface.

Composite approaches push the concept further. Reinforcing the amorphous matrix with stainless steel powders, titanium nitride, aluminum oxide, titanium diboride or carbon nanotubes, sometimes delivered as core-shell structured powders or molybdenum-clad feedstock, simultaneously boosts wear resistance, impact toughness and corrosion performance. Reactive plasma spraying that forms titanium nitride phases in situ has produced coatings with improved multi-scale mechanical behavior and corrosion-abrasion resistance. These developments matter because in applications such as engine pistons, hydraulic rods, marine hardware and biomass-fired boiler tubes, coatings rarely face corrosion alone; they face corrosion combined with sliding, erosion, impact and heat, and the review argues that this coupled degradation, rather than pure electrochemical corrosion, defines the true service envelope of Fe-based AMCs.

Looking ahead, the authors identify clear development trends. Better control of feedstock oxidation and particle in-flight behavior during spraying should shrink the defect population at its source. Machine-assisted alloy design promises compositions that balance glass formation, passivation and cost more effectively. Standardized long-term testing under realistic conditions, including hydrostatic pressure, thermal cycling and tribocorrosion, is needed to close the credibility gap between electrochemical laboratory data and decades-long service life. And hybrid strategies that combine dense amorphous matrices, sealing layers and superhydrophobic topcoats point toward multi-functional surfaces that resist corrosion, wear and fouling at once. For a civilization whose infrastructure is steadily dissolving, these glassy iron coatings, born from a refusal of atoms to line up, may prove to be one of the most quietly consequential materials stories of the coming decade.

Subject of Research: Corrosion behavior and enhancement strategies of Fe-based amorphous metallic coatings

Article Title: Review: the factors influencing and the development trends of the corrosion behavior of Fe-based amorphous coatings

Article References: Cui, S., Zhang, X., Zhai, H., Kong, L., Zhang, J., Wang, B., Deng, L., Sun, W., Li, W., Liu, T., Zhao, X., & Liu, J. (2026). Review: the factors influencing and the development trends of the corrosion behavior of Fe-based amorphous coatings. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13750-4

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13750-4

Keywords: Fe-based amorphous coatings, metallic glass, corrosion resistance, thermal spraying, passive film, pitting corrosion, laser remelting, sealing treatment, superhydrophobic coating, tribocorrosion, alloying elements, crystallization