Halide Activated Pack Cementation (HAPC) is a cost-effective and efficient surface modification process that increases the durability of a metallic alloy. This technique has been utilized to protect alloys operating in a wide variety of high temperature environments. The method can create a hard, corrosion-resistant, diffusional coating through chemical reactions that occur in a “pack” consisting of an inert filler (typically aluminum oxide), a master alloy, and a halide activator.

A study was conducted in which pure nickel, Ni-5 wt% Cr and Ni-10 wt% Cr were aluminized at 750, 850 and 950°C for 9 h using sodium halides (sodium fluoride, chloride and bromide) as activators. The effects of the chromium content of the alloy and the type of activator on the aluminization process were studied by characterizing the substrate using optical microscopy, X-ray diffraction, scanning electron microscopy and microhardness measurements.

Results indicate that the thickness of the surface modified layer is strongly dependent upon the halide activator and process temperature used, with little to no apparent dependence on the chromium content of the alloy. The sodium fluoride activator produced the thickest coating for a given temperature and substrate. XRD analysis revealed that NiAl and Ni2Al3 surface phases were the most dominant and frequently observed for all activators and chromium contents. Microhardness analysis on coatings showed that the coating layers were consistently harder than the substrate for each activator, with an especially hard mid-layer in some cases.

Subject
Scanning electron microscopy, X-ray diffraction, Nickel coatings, Coatings, Substrates, Diffusion, Nickel based alloys, Chromium, Coating thickness, Nickel, Aluminum alloys, Activators, Samples
Keywords:
Halide Activated Pack Cementation, nickel chromium, aluminizing, HAPC, protective coatings, aluminide coatings
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2016
Association for Materials Protection and Performance (AMPP)
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