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Pack aluminization process of heat resistant FeCrAl and NiCr alloys

Pack aluminization process is one of the possible production methods to improve oxidation resistance at high temperatures of various types of metallic materials. It is a chemo-thermal process where products are embedded in the powder mixture, consisting of Al powder, halide activator NH4Cl, and inert diluent Al2O3 powder, and annealed at high temperature. This exposure to high temperature causes the Al diffusion into the base material and formation of the aluminide surface layer. During the component service at elevated temperatures, the oxidation resistance is obtained due to the constant formation of an aluminium oxide film that forms on the aluminide surface layer and acts as an oxygen impermeable barrier. In the present study, FeCrAl and the NiCr heat resistant alloys in the form of 1mm thick sheet were aluminized at various process parameters. The effect of time, temperature, concentration of aluminium and halide activator in the powder mixture as well as the influence of furnace atmosphere on coating formation mechanism, mass gain and the thickness of the aluminide diffusion layer was evaluated by scanning electron microscopy, X- ray photoelectron spectroscopy and micro hardness analytic techniques. Isothermal exposure tests at 1200 °C for 24h in air were conducted and compared with untreated samples for high temperature oxidation resistance estimation.

Aluminizing, heat resistant alloys, FeCrAl, NiCr, high temperature oxidation

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