Hot Corrosion Resistance of Nickel Based Alloys Evaluated by a Molecular Orbital Calculation.

本课题的目的是获得评价镍基合金抗热腐蚀性能的电子参数，明确合金化过渡元素在合金抗热腐蚀性能中的作用。为了这些目的，DV-Xalpha簇方法，这是一种分子轨道计算，使用两种假设的原子簇。它们是MNi_<13>Na_2Cl_2团簇和MNi_<12>SO_4团簇，分别用于评价合金化对抗Cl和抗SO_4热腐蚀性能的影响。用于计算的合金元素是3d、4d和5d过渡元素。此外，还进行了一系列的热腐蚀试验工作，使用镍二元合金含有各种三维过渡金属。计算和实验结果表明：（1）根据用MNi_ Na_2Cl_2原子簇方法计算的Bo（M-Cl）/Bo（M-Ni）键级比<13>，认为Fe、Co和Cu是提高热氯腐蚀抗力的有效元素。这里，Bo（M-Cl）是M和Cl原子之间的共价键强度，Bo（M-Ni）是M和Ni原子之间的共价键强度。计算结果与在氩气气氛下使用熔融NaCl盐的实验结果一致。(2)根据MNil_2SO_4团簇的计算结果，提出氧硫键的结合程度影响了含合金元素的氧化镍的稳定性，从而改变了其耐蚀性。从这一点来看，建议Mo和Re都应提高抗硫热腐蚀性能。(3)氧势的大小对NaCl熔盐的实验结果有显著影响。

The purposes of this project are to obtain electronic parameters for evaluating the hot corrosion resistance of nickel based alloys and to make clear the role of alloying transition elements in hot corrosion resistance of the alloys. For these purposes, DV-Xalpha cluster method, which is a molecular orbital calculation, was employed using two kinds of hypothetical atom clusters. They are an MNi_<13>Na_2Cl_2 cluster and an MNi_<12>SO_4 cluster, which were used for evaluating the alloying effect on the hot corrosion resistance to Cl and to SO_4, respectively. The alloying elements for the calculation are 3d, 4d and 5d transition elements. Also a series of experimental work on hot corrosion tests was carried out using nickel binary alloys containing various 3d transition metals. The results obtained from the calculation and the experiment are summarized as follows ;(1) On the basis of the bond order ratio Bo (M-Cl) /Bo (M-Ni) which was calculated by the cluster method using the MNi_<13>Na_2Cl_2 cluster, Fe, Co and Cu were considered to be useful elements for increasing the hot corrosion resistance to chlorine. Here, Bo (M-Cl) is the covalent bond strength between M and Cl atoms, and Bo (M-Ni) is the covalent bond strength between M and Ni atoms. The results obtained from the calculation were consistent with the experimental results using molten NaCl salt in argon atmosphere.(2) On the basis of the calculation using the MNil_2SO_4 cluster, it was suggested that the degree of the bond strength between oxygen and sulfur affected the stability of nickel oxides containing the alloying element, resulting in changing the corrosion resistance. In this point view, it was suggested that both Mo and Re should improve the hot corrosion resistance to sulfur.(3) The magnitude of oxygen potential affected significantly the experimental results using molten NaCl salt.