| Ru is a crucial element in the development of Ni-based superalloys and the effect of Ru in the Ni-based superalloys has become a hot discussion. Numerous investigations of the effect of Ru in the Ni-based superalloys focus on single crystal superalloys, but a few articles investigate on Ru effect of equiaxed superalloys. The microstructure, segregation of the elements, solidification behavior, hardness and the hot corrosion resistance of Ni-based equiaxed superalloys with various Ru content were investigated in the thesis.Mature alloys were prepared by investment casting technology and the hot corrosion property was investigated by a method of coating salt. Microstructure, segregation of the elements, solidification behavior and hot corrosion mechanism are detected by means of scanning electron microscopy(SEM), optical microscopy(OM), differential scanning calorimetry(DSC), electron probe microanalysis(EPMA), X-ray diffractometry(XRD) and so on.The microstructure of the as-cast alloys is mainly composed of γ, γ’, γ/γ’ eutectic and MC carbides. The γ/γ’ eutectic phase was completely dissolved after the heat treatment. The morphology of γ’ was more cuboidal in heat-treated alloys with increasing of Ru. Furthermore, the volume fraction of γ’ in the as-cast and heat-treated alloys diminishes upon the increase of Ru. In addition, the hardness of alloys improves and the porosity of alloys reduces with Ru addition.Ru addition changes the segregation characteristic of Cr, Mo in the alloys from negative segregation element to positive segregation element and promotes the extent segregation of W. As the Ru content increased, the magnitude of segregation of the positive segregation elements Ta, Ti increased and that of Al decreased and Ru tends to segregate in the dendrite core. With the increase of Ru, the solidus temperature of the alloys and the γ’ solvus temperature decreases, respectively. At the same time, the liquidus temperatures of the alloys have no obvious change.The hot corrosion resistance of Ru-free alloy is worse than that of alloys with different Ru content in the same conditions of 75%Na2SO4+25%Na Cl molten salts at 900℃. The hot corrosion resistance of the alloys can enhance with the increases of Ru content. The hot corrosion of superalloys with different Ru content obey sulfideoxidation mechanism. Ru addition can improve the hot corrosion resistance of Ni-based equiaxed superalloy. |
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