Co-20Re-25Cr-7Al合金在3.0×10^(-5)Pa低氧压下的氧化行为研究

Study on Oxidation Behavior of Co-20Re-25Cr-7Al Alloy at Low Oxygen Pressure of 3.0×10^(-5) Pa

为探究在低氧压高温环境中添加少量的Al是否对Co-Re基高温合金形成保护性的Cr_(2)O_(3)氧化膜具有协同效应,研究了Co-20Re-25Cr-7Al合金在1100~1300℃,3.0×10^(-5)PaO_(2)下氧化24 h的恒温氧化行为。结果显示:合金的氧化动力学曲线完全符合抛物线规律,其氧化激活能为242.3 kJ/mol。合金在1100~1300℃形成的氧化膜很类似,主要由连续致密的Cr_(2)O_(3)层组成,其上分布着少量的CoO和CoCr_(2)O_(4)尖晶石。与相应的Co-20Re-25Cr三元合金相比,Co-20Re-25Cr-7Al四元合金形成的具有保护性的Cr_(2)O_(3)层在氧化过程中可以防止合金中的Re元素以ReO_(3)的形式挥发,从而为合金提供更好的保护。7%Al的添加不足以使Co-20Re-25Cr-7Al合金发生Al的选择性外氧化,因此在外氧化膜下面形成了Al的内氧化区。但Al的添加明显促进了连续而致密的Cr_(2)O_(3)层的形成,大大提高了合金的抗高温氧化性能。Al的添加和低氧压对于形成保护性的Cr_(2)O_(3)层具有协同效应。

In order to investigate whether adding a small amount of Al in a low oxygen pressure and high temperature environment has a synergistic effect on the formation of a protective Cr_(2)O_(3) oxide film on Co-Re based high temperature alloys, the isothermal oxidation behavior of the Co-20Re-25Cr-7Al alloy was studied under 3.0×10^(-5) PaO_(2) at 1 100~1 300 ℃ for 24 h. Results showed that the oxidation kinetics curve of the alloy conformed to parabolic law quite well, with the value of oxidation activation energy of 242.3 kJ/mol. The oxidation film formed at 1 100~1 300 ℃ were very similar and mainly composed of continuous and dense Cr_(2)O_(3) layer, covered by a small amount of CoO and CoCr_(2)O_(4) spinelle. The protective Cr_(2)O_(3) layer could prevent the evaporation of Re element of alloy in the form of ReO_(3) during the oxidation process, and thus provided better protection for the Co-20Re-25Cr-7Al quaternary alloy, as compared with the corresponding Co-20Re-25Cr ternary alloy, thus providing better protection for the alloy. The addition of 7% Al was not enough to result in the selective external oxidation of Al in Co-20Re-25Cr-7Al alloy, thus forming an internal oxidation zone of Al below the outer oxidation film. However, the addition of Al promoted the formation of continuous and dense Cr_(2)O_(3) layer, and improved the high temperature oxidation resistance of the alloy greatly. The addition of Al and low oxygen pressure showed a synergistic effect on the formation of a protective Cr_(2)O_(3) layer.