Oxidation of two ternary Fe-Cu-5 at.% al alloys in 1 atm of pure O-2 at 800 degrees C

The oxidation of two two-phase ternary Fe - Cu - Al alloys containing about 5 at.% aluminium, one Fe-rich and one Cu-rich, has been studied at 800degreesC under 1 atm O-2. The Fe- rich alloy (Fe - 15Cu - 5Al) shows two parabolic stages, with a large decrease of the parabolic rate constant after about 2 hr. The presence of 5 at.% Al reduces significantly the oxidation rate of this alloy with respect to a binary Fe- Cu alloy of similar composition by forming an external alumina scale. Moreover, the addition of 15 at.% Cu is able to reduce the critical aluminium content needed to form alumina scales with respect to binary Fe - Al alloys. On the contrary, the Cu-rich Fe - 85Cu-5Al alloy presents a single parabolic stage and forms a thick and porous external scale composed of an outermost layer of copper oxides and an inner region containing a mixture of copper and Fe - Al oxides, coupled to the internal oxidation of iron and aluminium. As a result, the oxidation of the Cu-rich ternary alloy at 800degreesC is much faster than that of the Fe- rich ternary alloy.