Simultaneous chromizing and aluminizing using chromium oxide and aluminum: (I) on low alloy steel

A new pack process of simultaneous deposition of chromium and aluminum onto metal components has been developed. This process is characterized by the pack composition using elemental Al and Cr2O3 powder as the Al and Cr sources. A series of pack cementation on a low alloy steel have been performed by varying the weight ratio of Cr2O3 to Al and the pack temperature. Cr2O3 is converted by aluminum halide (or Al) to Cr halide (or Cr) which is deposited along with aluminum on the metal surface. At a higher weight ratio of Cr2O3 to Al, the aluminum content in the coating layer decreases with increasing temperature, while the Cr content does the opposite. The decrease in aluminum content is mainly related to the activated conversion of Cr2O3 to chromium halide by aluminum in the diffusion layer.