Plasma Oxidation of Alloys

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In order to make clear a possibility and the mechanism of plasma oxidation of alloys, Cu-Al, Ag-Cd and Ag-Al alloys were oxidized by low temperature plasma. For comperison, oxidation behavior of Ag-Al alloys in air by the usual oxidation method was also studied in the temperature range of 400-900 c.In Ag-0.5-4.5at%Al alloys oxidized in air at 400-900 C a marked increase in hardeness due to oxidation was confirmed. This results from dispersion of Al oxide precipitates small in size. In these alloys, two types of oxidation behavior were found : high temperature oxidation and low tempature oxidation. On the high temperature oxidation the electrical resistivity R decreases, while R increases at low temperatures. This is because Al_2O_3 precipitates have an excess amount of oxygen for the low temperature oxidation, and stoichiometric Al_2O_3 particles are formed at hith temperatures.Low temperature plasma was found to be enable to oxidize both Cu and Ag alloys. In adequate conditions of plasma oxidation, only the internal oxidation layer was formed without the formation of an external oxidation layer. The oxidation rate and the hardeness are much higher for plasma oxidation than for the usual gas oxidation.