Resistance of Aluminide Coatings on Austenitic Stainless Steel in a Nitriding Atmosphere.

A new slurry cementation method was used to produce silicide-aluminide protective coatings on austenitic stainless steel 1.4541. The slurry cementation processes were carried out at temperatures of 800 and 1000 °C for 2 h with and without an additional oxidation process at a temperature of 1000 °C for 5 min. The microstructure and thickness of the coatings were studied by scanning electron microscopy (SEM). The intention was to produce coatings that would increase the heat resistance of the steel in a nitriding atmosphere. For this reason, the produced coatings were subjected to gas nitriding at a temperature of 550-570 °C in an atmosphere containing from 40 to 60% of ammonia. The nitriding was carried out using four time steps: 16, 51, 124, and 200 h, and microstructural observations using SEM were performed after each step. Analysis of the chemical composition of the aluminide coatings and reference sample was performed using wavelength (WDS) and energy (EDS) dispersive X-ray microanalysis, and phase analysis was carried out using X-ray diffraction (XRD). The resistance of the aluminide coatings in the nitriding atmosphere was found to depend strongly on the phase composition of the coating. The greatest increase in resistance to gas corrosion under nitriding atmosphere conditions was achieved using a manufacturing temperature of 1000 °C.