Effects of Si, W and W–Mo on isothermal oxidation behaviors of Nb/Nb5Si3 in situ composites at high temperature

The effects of Si, W and W–Mo on the isothermal oxidation behaviors of Nb/Nb5Si3 in situ composites in static air at 1000 and 1200 °C for 20–100 h were investigated on as-cast materials. The results show that the oxidation kinetics of each alloy was not changed whether at 1000 or 1200 °C, and the oxidation mechanism were not changed. The oxidation resistance of Nb/Nb5Si3 in situ composites was sensitive to Si content, and the oxidation rate of Nb-10Si alloy was more than twice as many that of Nb–20Si alloy. By alloying of W, the oxidation resistance of Nb–20Si–10W alloy was improved significantly, because the WO3 scale can provide the adherence for the creaked Nb2O5 scale and reduce the diffusion of oxygen through the scale. Comparing to alloying with W, the poor oxidation resistance of Nb–20Si–10W–10Mo alloy was attributed to the evaporation of MoO3 and highly porous scale.