Interdiffusion in the Al-V System in the 800-1000 °C Temperature Range

Abstract

Vanadium and its alloys have potential for application as fuel cladding in new fast breeder reactors cooled by sodium. Diffusion aluminide coatings could be a solution of choice in providing protection against high-temperature corrosion by liquid sodium or residual oxygen for these materials. In this work, multilayered coatings were formed on V and V-44Al substrates by halide activated pack cementation, using CrCl₃ as transport agent and pure aluminum (high activity) as master alloy. Two types of diffusion couples, V/Al and V-44Al/Al, were investigated in order to determine the growth kinetics of the aluminide compounds in the 800-1000 °C temperature range. The growth of the saturated V_ss as well as of the VAl₃ and V₅Al₈ layers was controlled exclusively by solid state diffusion following a parabolic law, allowing the determination of the parabolic growth constants. Wagner’s analysis was adopted to calculate the integrated interdiffusion coefficients, resulting in values ranging approximately from 10⁻¹⁰ to 10⁻¹² cm²/s for temperatures between 800 and 1000 °C. In general, VAl₃ has the highest \({\widetilde{\text{D}}}_{\text{int}}\) values in relation to those of the other two layers, considering the nominal temperatures (except for 1000 °C).