| Faced with the increasingly prominent environment and resource issues, many countries gradually promote technological innovation to achieve targets of energy consumption reduction. The present energy structure dominated by powerplant forces the emphasis of technological breakthrough to transferred to how to effectively improve the efficiency of coal-fired generating units. The efficiency of coal-fired conversion mainly depends on the operating parameters of the units, namely steam temperature and pressure. Inconel740is usually used as pipe the materials of pipes in turbine reheater which is widely used in700℃advanced ultra-supercritical (A-USC) power plant. With the demand for increasing temperature Range of high temperature components unit, it requires that materials properties are improved to obtain a higher temperature strength and oxidation resistance, to meet the demand of the units in efficient and stable operation.Traditional preparation technology of Inconel740has several disadvantages, for instance, lower productivity, lower alloy purity, residue of inclusions, and so on. Baesd on the Inconel740superalloy prepared by electron beam melting(EBM). Its microstructure evolution, microhardness, and oxidation resistance at high temperature was analyzed in this thesis, to evaluate the advantages of EBM technology in terms of preparation of Inconel740superalloy. Eventually based on the clusters-plus-glue-atom model, composition of Inconel740alloy was interpretted and redesign. Through the view of alloy design, the high temperature properties of Inconel740is improved.Inconel740prepared by EBM were conducted to standard heat treatment. Microstructure evolution can be analyzed with OM, XRD, SEM and TEM. Mechanical properties and high temperature oxidation mechanism can be acquired with the microhardness test and oxidation experiments. Meanwhile, based on the clusters-plus-glue-atom model alloy, its composition will be redesigned and improved. The main conclusions are as follows:1) The matrix of Inconel740prepared by EBM mainly consists of single austenitic phase. There are a lot of twins existing with the grain size of2mm. After standard heat-treatment, a large number of spherical γ’phase whose average size was about30nm was distributed uniformly and finely in the matrix. The continuous distribution of carbides M23C6, and a small number of η phase could be observed in the grain boundary. G phase separated out with consumption of γ’phase in the matrix. The results showed that microhardness of Inconel740 prepared by EBM are higher than the traditonal method at the value of about12OHV0.1. The content of G phase significantly reduced with the increasing of solution temperature, so that the γ’phase were finely distributed in the grain.2) The oxidation kinetics of Inconel740in air at both950℃and1000℃obeyed parabolic law. The oxidation rate of Inconel740at1000℃remained one order of magnitude higher than the rate at950℃. It belonged to completely anti-oxidization at950℃and1000℃. Both inner and outer oxidation behavior occured during the process of oxidation.3) Based on cluster-plus-atom-model, composition of Inconel740was interpretated and designed. Microstructure observation and microhardness results showed precipitates in the grain boundary of alloy2#were the fewest, and y’phase was finely dispersed with the shape of sphere. The microhardness of the four alloys after solution and aging treatment were higher than the hardness in cast condition, Due to high content of cobalt in2#alloy, its microhardness was much higher than the other three alloys, which was twice as much as microhardness of Inconel740prepared by the traditional method. |
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