Abstract:The oxidation of binary Ni-Al alloy containing 15%(mole fraction, the same below if not mentioned) Al (Ni-15Al), and of a ternary alloy with the same Al content but also containing 4% Si (Ni-4Si-15Al) has been studied at 1000℃ under 1.0×10⁵Pa O₂ to examine the effect of the addition of Si on the oxidation of Ni-15Al. Oxidation of Ni-15Al produces a duplex scale composed of an outer NiO layer and an inner layer riched in Al₂O₃. On the contrary, Ni-4Si-15Al forms an external alumina layer directly in contact with the alloy presenting only trace of NiO and the Ni-Al spinel. As a result, the kinetics of Ni-15Al shows a fast initial stage followed by two subsequent parabolic stages with decreasing rate constants, while Ni-4Si-15Al presents essentially a single nearly-parabolic behavior with a rate constant similar to that of the final stage of Ni-15Al. Therefore, the addition of 4% Si significantly reduces the oxidation rate during the initial stage by preventing the formation of Ni-riched scales and promoting an earlier development of an exclusive external alumina layer on the alloy surface. 

Key words: Ni-Si-15Al; ternary alloy; oxidation