Diffusion annealing and laser surface alloying with aluminium to enhance oxidation resistance of carbon steels

The oxidation behaviour of a carbon steel was investigated after modifying the surface in three different ways, namely: (a) physical vapour deposition of aluminium by a resistance heating evaporation technique; (b) diffusion annealing of predeposited aluminium; and (c) laser surface alloying with pr edeposited aluminium. While diffusion annealing at a temperature of 1023 K was found to result in the formation of Al13Fe4 and Al5Fe2 phases, laser su rface alloying resulted in a case containing Al13Fe4 and Al2Fe phases. The oxidation behaviour of all the above specimens was studied at 873 K for a t otal duration of up to 200 h. The mass change and morphological modificatio ns to the surface were monitored at regular intervals of 25 h. It was obser ved that aluminising results in a substantial enhancement of the high tempe rature oxidation resistance in comparison with the untreated base material, by virtue of the superior oxidation resistance of the intermetallic phases formed on the surface. Furthermore, laser surface alloying was found to re sult in better oxidation resistance, in comparison with diffusion annealed and as deposited specimens. (C) 2001 IoM Communications Ltd.