Influence of an aluminized intermediate layer on the adhesion of a γ-Al2O3 washcoat on FeCrAl

To improve the combination performance of a γ-Al2O3 washcoat on a FeCrAl support in auto-catalysts, an aluminized intermediate layer was deposited on the surface of metallic foils by the powder embedded aluminizing technique. A heat treatment after aluminizing and an aging test after washcoating were carried out. The microstructure, phase structure, chemical composition and inter-coat adhesion of the as-coated and heat-treated aluminized layers were studied by means of scanning electron microscopy, X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDX) and ultrasonic vibration tests. The surface of the as-coated aluminized layer was inhomogeneous and a great number of nanowires were formed. Aluminum infiltrated into the support to form Al5(Fe,Cr)2 and/or other intermetallic compounds in the coat-support interface. After the heat treatment, aluminum segregated out and oxidized into homogeneous α-Al2O3 whiskers on the outer surface. The aluminized layer transformed into α-Fe(Cr,Al) diffusion zone after the aging test. After the aluminizing and heat treatments, no cracks were found on the successive alumina washcoat and the weight loss was only 4.0 wt.% under ultrasonic vibration for 30 min. This suggested an enhanced interface adhesion between the γ-Al2O3 washcoat and the FeCrAl support.