Abstract
The effect of silicon on diffusion behavior of the carbide forming elements in Ni-Mo-Cr-Fe based corrosion-resistant alloy is studied by diffusion couple experiment. One group of diffusion couples are made of the alloy with a different silicon content, another group of diffusion couples are made of pure nickel and the alloy with different silicon content (0Si, 2Si). Two groups of alloys with same silicon content and different carbon content are also prepared, the microstructure of solution and aging state of these two groups alloys are analyzed, and their stress rupture properties are tested. The effect of silicon on the diffusion of alloy elements and the interaction effect of carbon and silicon on the microstructure and stress rupture properties of the alloy are analyzed. The mechanism of Si on the precipitation behavior of carbide phase in Ni-Mo-Cr-Fe corrosion resistant alloy is discussed. The results show that silicon can promote the diffusion of carbide forming elements and the formation of carbide. The precipitation behavior of the secondary phase is the result of the interaction effect of silicon and carbon, and is related to the thermal history of the alloy. Combined with the characteristic of primary carbides, it is confirmed that the precipitation of M12C type secondary carbide is caused by the relative lack of carbon element and the relative enrichment of carbide forming elements such as molybdenum. The stress rupture properties of two silicon-containing alloys with different carbon contents in solution and aging state are tested. The stress rupture life of low carbon alloy is lower compared with high carbon alloy at solution state, but after aging treatment, the stress rupture life of low carbon alloy is significantly improved, and higher than that of high carbon alloy. The main aim of this research is to reveal the influence mechanism of silicon on carbide phase precipitation of a Ni-Mo-Cr-Fe based corrosion-resistant superalloy, which provides theoretical basis and reference for later alloy design and engineering application.
Highlights
Ni-Mo-Cr-Fe based superalloy has excellent corrosion resistance and high temperature resistance, which is used as a structural material in nuclear power molten salt breeder reactor environments [1,2].The structural parts used in molten salt breeder reactors require long-term service, generally more than 30 years
The influence mechanism of Si on primary and secondary phase precipitation is studied, the results of this study reveal the precipitation mechanism of silicon and carbon on the carbide phase in the alloy, and provide theoretical support for further optimization and engineering application of the alloy
In the Ni-Mo-Cr-Fe alloy matrix, silicon has a faster diffusion rate than Cr, Fe, and Mo, and at the temperatures ranging from 800 ◦ C to 1000 ◦ C, silicon can promote the diffusion of Cr, Fe, and Mo
Summary
Ni-Mo-Cr-Fe based superalloy has excellent corrosion resistance and high temperature resistance, which is used as a structural material in nuclear power molten salt breeder reactor environments [1,2]. The structural parts used in molten salt breeder reactors require long-term service, generally more than 30 years. The alloy has the problem of corrosion resistance, irradiation resistance, and oxidation resistance, and these properties can be improved by adding Si [4,5,6]. Silicon was reported to have great effect on formation of carbides [1,2,9,10,11], and the silicon element can stabilize and improve the high temperature properties of the alloy [12,13,14]
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