Oxidation resistant NbCr2 phase in Nb–W–Cr system

Alloys of Nb–20W–5Cr and Nb–20W–10Cr (in weight percents) have been subjected to oxidation in air for 24 h at temperatures ranging from 700 to 1400 °C. Oxidation resistance revealed by weight gain per unit area after each oxidation treatment shows better oxidation resistance for 10Cr alloy. However, the alloy system shows phase transformations that may be directly affecting the oxidation resistance. 5Cr alloy becomes single phase around 1100–1200 °C and remains single phase until 1400 °C. It is anticipated that the second phase NbCr2 provides the resistance to oxidation in these alloys since 10Cr alloy has less weight gain in the temperature range from 1000 to 1300 °C. Isothermal sections of the ternary Nb–W–Cr phase diagram allow us to make such analysis.