Simultaneous chromizing-aluminizing of an iron-2.5 chromium-1molybdenum steel and cobalt-base alloys by halide-activated pack cementation

A method for simultaneously chromizing and aluminizing an Fe-2.25Cr-1Mo-0.15C steel and Co-base alloys by halide-activated pack cementation is described. The equilibrium partial pressures of the gaseous species in the pack responsible for Al and Cr deposition have been calculated with the computer program SOLGASMIX-PV. These calculations are used as a means of predicting the relative chromizing/aluminizing potential of packs containing various Cr-Al masteralloys and activators. These predictions are compared to coatings produced in the laboratory.;A two-step coating treatment has been developed to produce Kanthal-like (Fe-20 wt.% Cr-4.5 wt.% Al) coating compositions on an Fe-2.25Cr-1Mo steel. This treatment entails heating an AlCl;The high carbon-content of the Co-base superalloys X-40 and MAR-M509 resulted in the formation of surface carbides during the coating treatment. These carbides act as a diffusion barrier and severely hinder the coating process. The formation of effective diffusion coatings by chromizing/aluminizing of Co-base superalloys does not appear to be feasible.