Influence of Cr₂O₃-Al₂O₃ composite oxide scale on oxidation resistance of ZG40Cr24

Abstract

Test alloys ZG40Cr24 with alloying of 3 wt% aluminium were cast by intermediate frequency induction furnace. The oxidation resistance of test alloys at 1 000 °C for 500 hours was examined according to oxidation weight gain method. The scale morphology and composition were studied using scanning electron microscope (SEM) and X-ray diffraction (XRD) respectively. By energy dispersive spectroscopy (EDS) studies, a kind of composite oxide scale compounded highly by Cr₂O₃, Al₂O₃ and spinel MCr₂O₄ in molecule scale came into being at high temperature. With flat and compact structure, fine and even grains, such composite scale granted complete oxidation resistance to alloy ZG40Cr24. The oxidation resistance mechanism was studied deeply in electrochemistry corrosion. The P+N semiconductor composite scale composed plenty of inner PN junctions, of which the unilateral conductive and the out-of-order arrangement endowed itself insulating in all directions. The positive and negative charges in scale could not move, and the mobile number and transferring rate of them both dropped enormously, as a result, the oxidation rate of the matrix metal was cut down greatly. So the composite scale presented excellent oxidation resistance.

Keywords

oxide scale / oxidation resistance / Cr₂O₃ / Al₂O₃ / semiconductor

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