The hot corrosion behavior of a Ni?20Cr?18W (mass fraction, %) superalloy in the mixture of 75%Na 2 SO 4?25%NaCl melts at 700 and 800 °C was studied. The results demonstrate that the alloy suffers from serious ho...The hot corrosion behavior of a Ni?20Cr?18W (mass fraction, %) superalloy in the mixture of 75%Na 2 SO 4?25%NaCl melts at 700 and 800 °C was studied. The results demonstrate that the alloy suffers from serious hot corrosion attack in the mixture molten salt. Meanwhile, the degradation of the substrate accelerates with increasing the corrosion temperature. The corrosion layer has an obvious duplex microstructure, and the Cr-depletion zone is detected obviously nearby the inner corrosion layer. The main corrosion products at 700 and 800 °C are almost the same and mainly include NiO, Cr2O3and Ni3S2, but a trace amount of NiCrO2 is detected at 800 °C for 20 h. The hot corrosion mechanism and formation mechanism of corrosion scales of the Ni?20Cr?18W superalloy in the molten salt are proposed.展开更多
Nickel-based superalloys with and without Co by partial replacement of W were prepared using double vacuum melting.A comparison of the oxidation in air and hot corrosion behaviors under molten 75 wt.%Na2 SO4+25 wt.%Na...Nickel-based superalloys with and without Co by partial replacement of W were prepared using double vacuum melting.A comparison of the oxidation in air and hot corrosion behaviors under molten 75 wt.%Na2 SO4+25 wt.%NaCl at 900℃were systematically investigated.The results showed that partial replacement of W with Co promoted the formation of chromia scale and consequently decreased the oxidation rate.Besides,the addition of Co also retarded the internal oxidation/nitridation of Al and consequently promoted the growth of Al_(2) O3 scale,which further decreased the scaling rate and improved the adhesion of scale.Moreover,the addition of Co also further improved the hot corrosion resistance under molten Na2 SO4-NaCl salts.展开更多
High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe cor...High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.展开更多
基金Project(51171150)supported by the National Natural Science Foundation of China
文摘The hot corrosion behavior of a Ni?20Cr?18W (mass fraction, %) superalloy in the mixture of 75%Na 2 SO 4?25%NaCl melts at 700 and 800 °C was studied. The results demonstrate that the alloy suffers from serious hot corrosion attack in the mixture molten salt. Meanwhile, the degradation of the substrate accelerates with increasing the corrosion temperature. The corrosion layer has an obvious duplex microstructure, and the Cr-depletion zone is detected obviously nearby the inner corrosion layer. The main corrosion products at 700 and 800 °C are almost the same and mainly include NiO, Cr2O3and Ni3S2, but a trace amount of NiCrO2 is detected at 800 °C for 20 h. The hot corrosion mechanism and formation mechanism of corrosion scales of the Ni?20Cr?18W superalloy in the molten salt are proposed.
基金financial supports from the Natural Science Foundation of Shandong Province,China(No.ZR2019MEE107)Shandong Jiaotong University“Climbing”Research Innovation Team Program,China(No.SDJTC1802)PhD Scientific Research Foundation of Shandong Jiaotong University,China(No.BS2018005)。
文摘Nickel-based superalloys with and without Co by partial replacement of W were prepared using double vacuum melting.A comparison of the oxidation in air and hot corrosion behaviors under molten 75 wt.%Na2 SO4+25 wt.%NaCl at 900℃were systematically investigated.The results showed that partial replacement of W with Co promoted the formation of chromia scale and consequently decreased the oxidation rate.Besides,the addition of Co also retarded the internal oxidation/nitridation of Al and consequently promoted the growth of Al_(2) O3 scale,which further decreased the scaling rate and improved the adhesion of scale.Moreover,the addition of Co also further improved the hot corrosion resistance under molten Na2 SO4-NaCl salts.
文摘High-temperature corrosion is a serious problem for the water-wall tubes of boilers used in thermal power plants. Oxidation, sulfidation and molten salt corrosion are main corrosion ways.Thereinto, the most severe corrosion occurs in molten salt corrosion environment. Materials rich in oxides formers, such as chromium and aluminum, are needed to resist corrosion in high-temperature and corrosive environment, but processability of such bulk alloys is very limited. High velocity electric arc spraying (HVAS) technology is adopted to produce coatings with high corrosion resistance. By comparison, NiCr (Ni-45Cr-4Ti) is recommended as a promising alloy coating for the water-wall tubes, which can even resist molten salt corrosion attack. In the study of corrosion mechanism, the modern material analysis methods, such as scanning electron microscopy (SEM), X-ray diffractometry (XRD) and energy dispersive spectrometry (EDS), are used. It is found that the corrosion resistances of NiCr and FeCrAI coatings are much better than that of 20g steel, that the NiCr coatings have the best anti-corrosion properties, and that the NiCr coatings have slightly lower pores than FeCrAI coatings.It is testified that corrosion resistance of coatings is mainly determined by chromium content, and the microstructure of a coating is as important as the chemical composition of the material. In addition, the fracture mechanisms of coatings in the cycle of heating and cooling are put forward. The difference of the thermal physical properties between coatings and base metals results in the thermal stress inside the coatings. Consequently, the coatings spall from the base metal.
