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| Hot Corrosion of Pure Nickel and Its Weld Joints in Molten Na2SO4-K2SO4 Salts |
Xijing WANG1( ), Boshi WANG1, Chao YANG1, Yan YANG2, Bin SHEN3 |
1 State Key Laboratory of Gansu Advanced Nonferrous Metal Materials, Lanzhou University of Technology, Lanzhou 730050, China
2 State Key Laboratory of Nickel and Cobalt Resources Comprehensive Utilization, Jinchuan Group Cooperation Ltd., Jinchang 737104, China
3 Jinchuan Nickel Industrial Cooperation Ltd., Jinchang 737104, China |
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Abstract Hot corrosion behavior of pure nickel and its joints, which were prepared by plasma arc welding (PAW) and plasma arc welding+tungsten inert gas (PAW+TIG) respectively, in molten Na2SO4-K2SO4 salts at 900 ℃ are investigated by means of weight loss measurements, X-ray diffractometer (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Experimental results show that the grain size and hot corrosion resistance of the welds obtained by the two welding methods have little difference, while the corrosion resistance of the joints is inferior to that of the base metal. The hot corrosion kinetics of the specimens follow linear power laws, and the corrosion products on the base metal and joints are mainly composed of NiO and Ni3S2. Cross-sectional morphologies and corresponding elemental maps indicate that corrosion product composed of an outer dense scale, beneath which there existed an internal zone of oxides and sulfides. According to these results, a mechanism of synergistic oxidation and sulfidation for hot corrosion of pure nickel is confirmed. That is, the distribution of internal oxides and sulfides, located beneath the outer oxide scale , extends to the substrate. In other words, the sulfidation-oxidation cycle process and sulfur play an important role in the process of hot corrosion. So,for pure nickel welding, PAW+TIG welding method meets the requirements of the actual industrial production and application.
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Received: 07 August 2017
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| Fund: Supported by State Key Laboratory of Nickel and Cobalt Resources Comprehensive Utilization (301170501) |
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