Oxidation response of three Nb-Cr-Mo-Si-B alloys in air

The oxidation behavior in air of three alloys from the Nb-Cr-Mo-Si-B system has been evaluated in the temperature range of 700-1400 °C. The alloy compositions in atomic percent are Nb-25Cr-15Mo-20Si-15B (2015), Nb-25Cr-15Mo-20Si-10B (2010), and Nb-25Cr-15Mo-15Si-15B (1515). Increased oxidation resistance has been obtained for the 2015 alloy at high temperatures. Low temperature pest oxidation is not observed for the 2010 and 2015 alloy and only minimal pest products are obtained in the 1515 alloy. Analysis indicates the oxide scale includes Nb2O5 (monoclinic), CrNbO4, and SiO2. As-cast microstructural phases include Si-rich C14-NbCr2 Laves phase, (Nb, Mo)5Si3 silicide and (Nb, Mo)3Si silicide.