Aluminium based protective coatings produced on AISI 304 stainless steel

Abstract
The diffusion of Aluminium is one of the most promising methods to build superficial coatings for stainless steel protection. Heat treatments at 800 °C performed on rods of AISI 304 steel, Aluminium coated by means of electrodeposition, displayed the possibility of forming intermetallic compounds. Depending on the duration of the heat treatment and on the cooling kinetics, these compounds can be continuous. At high cooling kinetics (water cooling) a two-phase structure composed of [MATH] and [MATH] (substitutional solid solution) is obtained. At slow cooling rates (in furnace), a substitutional solid solution and some precipitates of [MATH] and [MATH] can be observed. At intermediate cooling rates (oil cooling and air cooling), only the substitutional solution and the [MATH] phase are present. Using furnace cooling from 800 °C until 500 °C, permanence at this temperature for 192 h and cooling furnace, the two-phase structure obtained is composed of the substitutional solid solution and the [MATH] phase. The existence of these phases and their composition have been reported by X-ray diffraction patterns and microanalysis. The possibility of forming a natural composite, constituted by a hard phase of aluminides diffused in a substitutional solid solution, has an important consequence on the mechanical and protection properties of these coatings. Moreover, the diffusion of Al improves the adhesion of coatings.