51316-7838-Effect of Process Parameters and Chromium Content in Pack Aluminizing of Nickel-Chromium Alloys

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Product Number: 51316-7838-SG

ISBN: 7838 2016 CP

Author: Vilupanur Ravi

Publication Date: 2016

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Halide Activated Pack Cementation (HAPC) is a cost-effective and efficient surface modification process that can increase the durability and corrosion resistance of a metallic alloys. This technique has been utilized to protect alloys operating in diverse high temperature environments. Pure nickel Ni-5 wt. % Cr and Ni-10 wt. % Cr were aluminized at 750 850 and 950°C for 9 h using halide activators (sodium fluoride chloride and bromide). The effects of chromium content and activator on aluminized nickel-based substrates were studied using various techniques. Mass change data for the coated samples were recorded and analyzed while optical microscopy of the coated cross-sections was used to measure coating thicknesses. The coated samples were also analyzed using X-ray diffraction scanning electron microscopy and microhardness. Results showed that the sodium fluoride activator produced the thickest coating for a given temperature and substrate. The effect of the chromium content of the alloy on overall coating thickness was insignificant. X-ray diffraction (XRD) analysis detected various surface phases e.g. Ni2Al3 peaks were the most frequently observed as well as the dominant ones. Microhardness analysis on samples coated at 850°C showed that the coating layers were consistently harder than the substrate for each activator with an especially hard mid-layer in some cases. The implications of the results thus far are that coating thicknesses are strongly dependent upon the type of halide activator and process temperatures whereas the dependence is more complex in regards to the chromium content of the nickel samples (for the range of alloy compositions studied).