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

点击翻译按钮获取中文摘要

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.