Микроструктура и коррозионная стойкость сплавов Mo – 15 ат. % Si – РЗЭ (Sc, Nd) на воздухе и в паровоздушной среде

Abstract

The research results of the REEs effect, in particular, Sc and Nd, on the structural-phase state and behavior of a high-temperature Mo – Si composite with a hypereutectic composition, which crystallizes from the melt with the formation of a two-phase natural (in situ) composite during oxidation in dry and moist air were presented. Samples of model alloys with different REE concentrations were obtained by vacuum-arc melting of a mixture consisting of the Mo – 15 Si (at. %) binary alloy and additives of alloying elements. Phase composition, microstructure features and distribution pattern of alloying components in Mo – Mo3Si metal-silicide composites containing from 0,5 to 3,0 at. % Sc or Nd were identified by X-ray diffraction and electron microscopy. Corrosion resistance of Mo – 15 at. % Si – REE (Sc, Nd) alloys during continuous heating to 700 and 850 °C in air and in a vapor-air medium was evaluated by thermal analysis methods (DSC and DTA). It was shown that microalloying of the Mo – 15 at. % Si with scandium or neodymium within 0,5 at. % leads to decrease in the oxidation rate when heated in air to 850 °C. Increasing the concentration of alloying elements to 3,0 at. % REE during oxidation in air adversely affects the corrosion resistance of samples, moreover the oxidation of alloys with neodymium proceeds at a higher rate than with scandium. During non-isothermal heating in a vapor-air medium, the alloy doped with scandium oxidizes more slowly than the binary one, and the sample with neodymium, by way of contrast, oxidizes at a much higher rate compared to dry air.