INFLUENCE OF PARTIAL REPLACEMENT OF TUNGSTEN BY MOLYBDENUM ON PROCESS OF OXIDATION OF ALLOYS NICKEL-CHROME-TUNGSTEN
Influence of additions of iron on oxidation resistance of nickel alloys with additions of molybdenum, tungsten and iron is shown which. This is leading to a number of anomalies in kinetics of process of their oxidation.
Influence of partial replacement of tungsten with a molybdenum on oxidation resistance of nickel alloys, containing about 14 -15 mass. % chrome and about 5 mass. % iron was investigated in this work. A study of six alloys is undertaken with the different concentration of additions. The binary alloy of Ni - 35 mass. % W is studied as an etalon. Contents of chrome and iron in alloys 3-6 resides in the interval of 14,1-15,4% and 5% accordingly, and the concentration of Мо increases, while the concentration of W decreases. The total concentration of Мо and W makes 12,9 - 14,1 mass. %
From the investigated alloys that are containing chrome, the best oxidation resistance is possessed by an alloy 5, that contains 15.4 mass. % Cr, 5.7 mass. % W, 7.7 mass. % Mo and 5.1 mass. % Fe. At 1473 K the rate of oxidization of this alloy below, than at other. Kinetics of that oxidization is described by the law of quadratic parabola throughout 3 hours, and after that- by a cube law. At lower temperatures it obeys the Evans law.
Chrome in amounts more than 15% creates a beneficial effect oxidation resistance of nickel based alloys. At such concentrations the continuous layer of oxide of Cr2O3 is formed along the grounds of oxide over which the layer of NiO is situated with including spinels of NiCr2O4. It is shown that the concentration of molybdenum ~ of 8% and tungsten ~ of 6% is the most optimal in the heat resistant nickel alloys with the concentration of chrome about 15% .
The optimal amount of iron for the increase of resistance of investigational alloys is set, in an amount about 5 mass. %.
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