STUDIES OF OXIDATION OF NIOBIUM ALLOYS AT VERY HIGH TEMPERATURES.
Final rept., 1 Oct 65-30 Sep 66,
CENTRAL INST FOR INDUSTRIAL RESEARCH OSLO (NORWAY)
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Oxidation of binary Hf-Nb alloys with 10-50wtNb and a few corresponding alloys with ternary additions of Cr, Ti, V, and W has been studied in the temperature range 800-1300 C. Most of the studies were carried out at 10 torr O2, but the oxidation of one binary alloy Hf-34wtNb was also studied as a function of oxygen pressure. The major reaction products are HfO2, Nb2O5, and Nb2O5 6HfO2. At and above 10 torr O2 the oxidation of the binary alloys increase with temperature up to 900-1000 C, where the oxidation goes through a maximum and then decreases up to about 1100 C. Above 1100 C the oxidation again increases with temperature. This maximum is interpreted as a result of an interplay between relative rates of formation of HfO2 and Nb2O5 and their subsequent reaction to form Nb2O5 6HfO2. The ternary alloy additions of Cr, Ti, and W did not significantly change the oxidation rates. Catastrophic oxidation was observed for Hf-25woNb-52oV and Hf-20woNb-10woV alloys above 1000 and 900 C, respectively. The binary Hf-Nb alloys showed poor oxidation resistance, and at 900-1000 C the oxidation is as fast as for unalloyed niobium. Author
- Properties of Metals and Alloys