On the effect of steel substrate alloying elements on the in-situ formation of intermediate thermal diffusion barrier layers

• Published in: Materials chemistry and physics 2020-01, Vol.240, p.122231, Article 122231
• Main Authors: Rosa, Roberto, Veronesi, Paolo, Casagrande, Angelo
• Format: Article
• Language: English
• Subjects: Alloying effects; Alloying elements; Aluminide coatings; Aluminum oxide; Barrier layers; Depletion; Diffusion barriers; Diffusion coating; Diffusion coatings; Diffusion layers; Diffusion rate; Electronic characterization; Enthalpy; Hot dip aluminizing; Interdiffusion reactions; Intermetallic compounds; Iron aluminides; Iron and steel making; Manganese; Multiphase formation; Nickel; Protective coatings; Spectroscopic characterization; Substrates; Thermal diffusion; Transition metals
• ISSN: 0254-0584; 1879-3312
• DOI: 10.1016/j.matchemphys.2019.122231

The aim of this work was to evaluate the feasibility of a hot-dipping aluminizing process, for the simultaneous production of an iron aluminide coating, a protective alumina topcoat layer and an intermediate thermal diffusion barrier layer, at the aluminide coating/steel substrate interface, the latter being thought in order to limit the detrimental depletion of Al content in the coating layer as a consequence of its inward diffusion towards the substrate. Indeed, the steel substrates were opportunely selected for their high weight percentages of alloying elements (namely Ni, Cr, Mn and Co) potentially able to diffuse from the substrate and react with the inward diffusing Al at the temperatures employed in the coating preparation, thus forming transition metal aluminides able to stop Al depletion, thus potentially prolong the lifetime of iron aluminide coatings in service. The effective in-situ growth of this intermetallic thermal diffusion layer was found to be strictly dependent on several factors, including the enthalpy of formation of the alloying-element aluminides, together with the atomic percentages of the selected alloying element in the steel substrate as well as its diffusion rate. The obtained results, can be considered an important contribution to the selection criteria of iron aluminides-coated steel substrates, to be employed in burdensome scenarios at high temperatures. •Diffusion barrier layers prepared by hot-dipping aluminizing and heat treatment.•An Al2O3/FeAl/diffusion barrier layer coating structure was simultaneously obtained.•Concurrent diffusion of Al from the coating and alloying elements from the substrate.•Substrate alloying element and its amount affect diffusion barrier layer formation.