Microstructure and high-temperature corrosion behaviors of aluminide coatings by low-temperature pack aluminizing process

Aluminide coatings were produced on carbon steel and Fe-5Cr-Mo alloy at a relatively lower temperature below 600 °C in shorter treatment time by a combination of surface refinement process and pack aluminizing process. Repetitive ball impact, generated by mechanical vibration, caused the top-layer refinement of substrates in a conventional pack aluminizing process. The effects of temperature and treatment time on the formation of aluminide coatings were analyzed. The microstructure of the coatings was investigated by SEM, AFM and XRD. The aluminide coatings were one-layer, compacted structure with ultrafine grains and uniform elemental distribution. High-temperature oxidation and sulphidation tests were carried out at 600 °C in air for 200 h and 10% SO₂ + Ar gas mixture atmosphere for 50 h, respectively. The mass gains and spallation indicated that the aluminide coatings significantly improved the high-temperature oxidation and sulphidation resistance.