Sc对CoNiCrAl合金高温氧化性能的影响

High Temperature Oxidation Performance of CoNiCrAl Alloy with Different Sc Contents

通过等温氧化及循环氧化实验研究了活性元素Sc对CoNiCrAl合金高温氧化动力学、氧化层/基体界面结合力的影响。在1150℃温度下进行了100次1 h循环氧化实验及5,30,50,640,1000 h等温氧化实验。结果表明:添加活性元素Sc能明显降低氧化膜的生长速度,改善氧化层/基体界面结合力,Sc元素添加量的不同对合金高温氧化行为的影响也不同。等温氧化中,原始合金的氧化速率常数为2.5×10-5μm2·s-1,添加0.1%Sc(原子分数,下同)的合金的氧化速率常数降低到原始合金的22.2%,添加0.2%Sc元素的合金的氧化速率常数降低到原始合金的44.4%。原始合金经过5 h等温氧化后的剥落比例就达到35%,经过30 h等温氧化后剥落比例达到95%;添加Sc元素之后,在氧化时间低于640 h时,氧化层的最大剥落比例为11.6%;当氧化时间达到1000 h时,添加0.1%Sc元素的合金的氧化层剥落比例增加到23.6%,添加0.2%Sc元素的氧化层剥落比例增加到68.5%。在循环氧化实验中,原始合金在循环氧化实验中经过1次循环之后重量就出现下降,而添加0.1%Sc及0.2%Sc元素的合金分别经过25和53次循环之后重量才开始下降。相对于原始合金在循环氧化过程中观察到的氮化现象,添加Sc元素的合金基体组织完好,没有受到破坏。

The effect of Sc on oxidation kinetics and scale/alloy interface bonding of a CoNiCrA1 alloy was investigated by isothermal and cyclic oxidation experiments. Cyclic oxidations were carried out for 100 1-h cycles at 1150℃. Isothermal oxidation experiments were conducted at 1150 ℃ for 5, 30, 50, 640 and 1000 h. The results revealed that Sc addition decreased the oxide growth rate and improved the scale/alloy interface bonding of investigated alloys. The steady-state oxidation rate of Sc-free alloy was 2.5 × 10-5 μm2 ·s ^-1. The oxidation rate decreased to 22.2% and 44.4% of the original value with 0.1% and 0.2 % （ atom fraction） additions of Sc. Under isothermal heating, spallation fraction of Sc-free alloy was measured to be 35% after 5 h which increased to 95% after 30 h. In contrast, the spallation fraction of Sc-doped alloys was 11.6% within the first 640 h and later increased to 23.6% and 68.5% respectively for 0.1% and 0.2% Sc-doped alloys. Moreover, the Sc-free alloy suffered heavy weight loss under thermal-cycling while the 0.1% and 0.2% Sc doped alloys showed mass increase for the initial 25 and 53 cycles. In addition, nitrides were seen in region beneath the oxide of Sc-free alloy. On the contrary, alloy doped with Sc was protected from any nitrogen attack.