Improving the Reactivity and Receptivity of Alloy and Tool Steels for Phosphate Conversion Coatings: Role of Surface Mechanical Attrition Treatment

Abstract

The role of surface mechanical attrition treatment (SMAT) in the phosphatability of EN8, EN19, and H11 steels using a zinc phosphating bath and the corrosion resistance of the resultant coatings are addressed. SMAT generated a uniform surface profile, increased the surface roughness, and decreased the grain size, which helped to increase the extent of metal dissolution during phosphating and the rate of growth of zinc phosphate coating. In spite of the similarity in phase composition, the phosphate crystal size is relatively large for the treated steels. The zinc phosphate coatings deposited on treated steels offer a corrosion resistance in 3.5% NaCl that is better than that of their untreated counterparts. Among them, the extent of corrosion protection is relatively higher for coatings deposited on EN8 steel. The difference in corrosion protective ability is a function of amount of phosphate coating weight, which is determined by the reactivity of steels in the phosphating bath.

A Facile Method to Modify the Characteristics and Corrosion Behavior of 304 Stainless Steel by Surface Nanostructuring toward Biomedical Applications

“…The ability to generate functionally gradient materials, with a nanocrystalline surface layer that provides the desirable surface properties and the matrix with a coarse-grained structure that offers the ductility, is a promising attribute of SMAT. Using this method, it is possible to produce thicker nanocrystalline and work-hardened surface layers, as well as deeper surface regions with larger residual compressive stresses. , The surface nanocrystallization and refinement of grain size after SMAT helps to increase the kinetics of diffusion of boron during pack boronizing and plasma nitriding of 304 grade stainless steel (304 SS). , In addition, they also accelerate the deposition of phosphate conversion coatings on EN8-grade medium carbon steel, EN19-grade alloy steel, and H11-grade tool steel …”

Influences of Surface Finishes on Properties of Biological Zinc Phosphate Conversion Coating on Titanium

“…Surface roughening by mechanical method such as sandpaper abrading increased the metal dissolution and hence the nucleation rate at the beginning of phosphating was also accelerated and thus a coating with fine granules could be obtained. This rule is the same for other kind of metals such as steel and non‐ferrous metals . However, the difference lays in the ease of corroding different substrates and this is the reason why granules on Ti are sparse and large whereas those on easily corroded metals are dense and showed fine flake or flower‐like shapes.…”

“…In this study, although the EDS analysis revealed the coexistence of O, Ti, P, and Zn in the coating, the XRD patterns excluded presence of Hopeite. Surface roughness determined the number and size of granule, whereas it was the acidity of convention solution that determined the phase composition of the PCC . If the pH is low, the volume fraction of Hopeite in the coating will be obviously decreased.…”

“…This rule is the same for other kind of metals such as steel and non-ferrous metals. [27,28] However, the difference lays in the ease of corroding different substrates and this is the reason why granules on Ti are sparse and large whereas those on easily corroded metals are dense and showed fine flake or flower-like shapes. In contrast, surface roughening by acid etching did not promote nucleation.…”

“…Surface roughness determined the number and size of granule, whereas it was the acidity of convention solution that determined the phase composition of the PCC. [27] If the pH is low, the volume fraction of Hopeite in the coating will be obviously decreased. In our study, the pH of solution was as low as 1.5, and it should be the reason for the single lipscombite-like phase.…”