| 摘要 | 本文选择了Ni-30Al-xY、Ni-3Cr-25Al-xY、Ni-20Cr-13Al-xY（x=0, 0.2, 1.0，wt%,下同）合金等9种试样，研究了它们的1000℃高温氧化和900℃Na2SO4热腐蚀行为，目的在于探究Y对Ni基涂层材料抗热腐蚀性能的影响，提出适用于保护性涂层材料的热腐蚀动力学模型。
比较了Ni-30Al-xY、Ni-3Cr-25Al-xY、Ni-20Cr-13Al-xY(x=0, 0.2, 1.0)的1000℃氧化行为。实验结果表明，加入0.2wt%Y对Cr含量为0和3wt%的样品的氧化增重影响不大，但大大降低了Cr含量为20%的样品的氧化增重，并抑制了Cr2O3膜的形成，提高了氧化膜的粘附性；加入1%Y大大增加了试样氧化增重，原因是Y含量为1%的试样析出了大量的富Y相，它可快速氧化。
比较了Ni-30Al-xY、Ni-3Cr-25Al-xY、Ni-20Cr-13Al-xY(x=0, 0.2, 1.0)的900℃涂盐热腐蚀和浸盐热腐蚀行为。经过10h涂盐热腐蚀测试后，在Ni-30Al-xY和Ni-3Cr-25Al-xY表面氧化膜易剥落，主要是氧化铝和疏松NiO膜，Ni-30Al-0.2Y氧化膜中还有NiAl2O4尖晶石，含Y的Ni-30Al-xY合金还有内氧化；Ni-20Cr-13Al-xY 表面氧化膜均为Al2O3膜，只有Ni-20Cr-13Al-1.0Y表面氧化膜未出现剥落。只有加入0.2wt%Y 的Ni-30Al和Ni-20Cr-13Al的腐蚀增重低于无Y合金的腐蚀增重；无Y合金中，Ni-3Cr-25Al腐蚀增重最大，Ni-20Cr-13Al腐蚀增重最小。在浸盐热腐蚀过程中，也只有Ni-20Cr-13Al-1.0Y表面氧化膜未出现剥落。
基于氧化膜热生长和碱性溶解同时发生机制，提出NiCrAlY热腐蚀动力学模型。利用三个观测值，包括增重曲线最高点和最低点的氧化膜厚度以及增重曲线最低点的减重速率，计算了热腐蚀时氧化膜的生长速率和溶解速率以及增重曲线。计算得到的增重曲线、退化层增厚和涂层减薄值和实验数据吻合的很好。 |
| 其他摘要 | The present thesis aimed to reveal the effect of Y on the hot corrosion performance of protective Ni-Cr-Al-Y coating materials, and to model their hot corrosion mechanism. The oxidation at 1000 ºC and Na2SO4-induced hot corrosion at 900 ºC of 9 kinds of specimens, which included the alloys of Ni-30Al-xY, Ni-3Cr-25Al-xY, Ni-20Cr-13Al-xY (x=0, 0.2, 1.0, wt%) were carried out. The specimens after tests were characterized using XRD, SEM/EDS.
Comparative studies on the oxidation behavior of Ni-30Al-xY, Ni-3Cr-25Al-xY, and Ni-20Cr-13Al-xY in air at 1000 ºC were performed. The additions of 0.2% Y had little effect on the oxidation rates of the specimens either without Cr or with 3% Cr while decreased the oxidation rates of the specimens with 20% Cr and prohibited the formation of Cr2O3 and enhanced the adherence of the scales. On the other hand, the addition of 1% Y increased the oxidation rates of the three kinds of specimens, because it led to the formation of large amount of Y-rich precipitates which were prone to fast oxidation.
Comparative studies on the Na2SO4-induced hot corrosion behavior of Ni-30Al-xY, Ni-3Cr-25Al-xY, and Ni-20Cr-13Al-xY at 900 ºC were performed. In the presence of Na2SO4 films, spallation of the oxide scales on all the specimens except on Ni-20Cr-13Al-1Y occurred during cooling down to room temperature. That alumina scale grew on all specimens was confirmed. The formations of porous NiO besides alumina on Ni-30Al-xY and Ni-3Cr-25Al-xY, however, occurred. Besides, spinel NiAl2O4 was found on Ni-30Al-0.2Y. Internal oxidation on Y-containing Ni-30Al-xY was observed. It was true only for the specimens of Ni-30Al-0.2Y and Ni-20Cr-13Al-0.2Y that the addition of Y decreased the corrosion rates; Among the Y-free specimens, Ni-3Cr-25Al had the highest corrosion rates while Ni-20Cr-13Al the lowest. The immerse test in the molten Na2SO4 confirmed that only the oxide scales on Ni-20Cr-13Al-1Y did not spall.
A kinetics model for hot corrosion of NiCrAlY was proposed based on the concurrent of the thermal growth and the basic fluxing of the oxide scales. The growth rates of the alumina scale on Ni-20Cr-13Al-1.0Y, the growth rates of the degradation layer and the change of the thickness of the specimens during hot corrosion, as well as the mass gain vs. time curve, were evaluated, using the three observation values, including the thicknesses of scales for the highest and the lowest points of mass gains, and the mass gain of the specimen at the end of testing time. The calculated mass gain vs. time curve, the thickness of the degradation layer and of the specimens were in well agreement with the experimental data. |
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