Fabrication and characterization of aluminide coating on V–5Cr–5Ti by electrodeposition and subsequent heat treating

Abstract

Preparation of aluminide coatings, AlxVy, is a key step for the formation of V-Al/Al2O3 as tritium permeation barrier (TPB) on V alloys. We firstly attempted to process aluminide coatings on V–5Cr–5Ti by a two-step process of electrochemical Al deposition (ECA) and heat treatment. Al deposition from AlCl3-1-ethyl-3-methyl-imidazolium chloride (AlCl3-EMIC) ionic liquid was performed at room temperature, with current density varying from 8 to 32 mA/cm2. Homogeneous and well adherent Al coatings on V–5Cr–5Ti were obtained by galvanostatic electrodeposition at 20 mA/cm2, with the deposition rates up to 21 μm/h. And then Al-coated specimens were heated in flowing Argon gas, forming aluminide coatings. The aluminide coatings exhibited a double-layer or almost a single-layer structure, and their thickness increased with temperature, time and Al-coating thickness, respectively. Main phase of coatings was Al3(V, Cr, Ti) at initial diffusion stage, and then gradually transformed into Al8(V, Cr, Ti)5, and next to V(Al, Cr, Ti) solid solution, with double-layer structure transforming into single-layer structure. The homogenous layer of Al8(V, Cr, Ti)5 is the appropriate aluminide for further selective oxidation. The optimum aluminized conditions and growth kinetics of Al8(V, Cr, Ti)5 were obtained.