【摘 要】
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The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings pro-duced by high velocity arc spray (HVAS) were s
【机 构】
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School of Material Science and Engineering
论文部分内容阅读
The oxidation and lower temperature hot corrosion (LTHC) processes occurring on the surface of Ni-Cr coatings pro-duced by high velocity arc spray (HVAS) were studied. Several different conditions were studied under simulated boiler conditions at 650 ℃. The protection effect of an A1 coating deposited by HVAS onto the Ni-Cr coating was also investigated. Microscope,X-ray diffraction and corrosion rate curves have been used to analyze corrosion mechanisms. The experimental results show that: 1)The oxidation rates are almost superposed in both air (no SO3) and in simulated coal-fired gas (containing SO) as long as no salt was present on the surface. These rate curves show a logarithmic relationship. 2) When the surface is coated with salt (75%K2SO3 +25%Na2SO3) the rate curve for LTHC of the Ni-Cr coated surface shows a parabolic shape in the simulated coal-fire flue gas. In air only the oxidation reaction takes place, the second type of LTHC was not seen. And 3) the AI over coating on the Ni-Cr enhances resistance to LTHC because an inter-metallic compound, AlNi, forms at the Al/Ni-Cr interface and because of the increase in coating thickness.
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