Effect of Cr Addition on the Phase Equilibria and Oxidation Behavior of NbSi2
2019 年 60 巻 5 号 p. 666-673
詳細
2019 年 60 巻 5 号 p. 666-673
Effect of Cr addition on the phase equilibria and oxidation behavior of NbSi2 was investigated. Although the crystal structures of NbSi2 and CrSi2 are both C40, they form separated ranges of homogeneities in the Nb–Cr–Si ternary system. The vertical section passing through the NbSi2 and CrSi2 binary edges were experimentally determined. A binary NbSi2 alloy exhibited poor oxidation resistance, showing pest-like behavior upon cyclic oxidation at temperatures from 800 to 1200°C. On the other hand, Cr addition significantly improved the oxidation resistance of NbSi2. The oxide layers that developed on the Nb–Cr–Si ternary alloys consisted of NbCrO4, Cr2O3, and SiO2, and the formation of Cr2O3 and NbCrO4 suppresses the Nb2O5 formation, and thereby suppresses the pest-like behavior of the binary NbSi2 alloy. However large Cr additions that exceed the solubility limit of NbSi2 should not be suitable, because NbSi2/CrSi2 alloys were susceptible to spalling and disintegration of the oxide scales upon cyclic oxidation.
