两种Co-Nb合金在60O℃～800℃1大气压纯氧中的氧化

OXIDATION OF TWO Co-Nb ALLOYS UNDER 1 ATM O2 AT 600℃～800℃

研究了含Ｎｂ１５和３０ｗｔ％的Ｃｏ－Ｎｂ二元合金在ｌａｔｉｎ纯氧中６００～８００℃的氧化特性。它们的氧化动力学近似地遵循抛物线规律，而其瞬时氧化速率常数随时间而减低、且以６００℃氧化者尤甚。两合金的氧化速率均高于纯Ｃｏ，但其速率增量颇低。在所有的实验条件下，两合金都发生了外氧化与内氧化，外氧化膜的外侧为连续的纯氧化钴带，其下为两个二元Ｃｏ－Ｎｂ氧化物（ＣＯＮｂ２Ｏ６和ＣＯ４Ｎｂ２Ｏ９）与基金属氧化物的混合。内氧化带为氧化钴、氧化铌（Ｎｂ２Ｏ５或／和ＮｂＯ２）的混合，而在该带的最外侧还有源于富Ｎｂ合金相的二元氧化物。在合金－氧化膜界面处都没有观察到贫铌带。从合金的和所生成氧化膜的显微组织特征，尤其是从铌在钴中溶解度低的角度，对合金的氧化行为进行了讨论。

The oxidation behavior of two Co-Nb alloys containing 15 and30 Wt.%Nb respectively was studied at 600-800℃ under 1 atm of pure oxygen. The oxidation kinetics followed parabolic law only approximately, whilst, especially at 600℃, the transient rate constant decreased with time. The oxidation rates of the two alloys were faster than that of pure cobalt, but the increment was rather small. The two alloys underwent both external and internal oxidation under all the conditions tested. The external scales were composed of a continuous layer of pure cobalt oxide close to the scale/gas interface, followed by an inner layer containing a complex mixture of two double Co-Nb oxides (CoNb2O6 and Co4Nb2O9) with the basemetal oxide. The region of internal oxidation contained a mixture of cobalt metal, niobium oxides (Na2O5or/and NbO2) and in the outermost region there was a double oxide formed from the Nb-rich metal phase.No niobium depletion region was observed at the alloy/scale interface. The oxidation behavior of these alloys was discussed in terms of the low solubility of niobium in cobalt and the microstructure of the alloys and the oxide scales.