The possible application of Nb-W-Cr alloys in high-temperature air

Alloys from the Nb-W-Cr system have been investigated for possible application at temperatures above 1,000°C. In this study, Nb-20W-5Cr (compositions are in weight percent) and Nb-20W-10Cr alloys were exposed to air for both 24 hours and 168 hours in a temperature range of 700°C to 1,400°C in order to determine the oxidation resistance. Although extensive powder formation at temperatures below 1,000°C has been observed, the alloys show improvement in oxidation resistance as the oxidation temperature increases from 1,200°C to 1,400°C. The formation of various oxides of niobium, chromium, and tungsten has been detected. The solubility of oxygen in niobium and large differences in percent linear thermal expansion of the oxides play an important role in the oxidation process.