Simultaneous chromizing-aluminizing of nickel and nickel base alloys by halide activated pack cementation.

摘要

A method for simultaneously chromizing-aluminizing Ni and Ni-base alloys via halide-activated pack cementation is described. Equilibrium partial pressures of the gaseous species in halide-activated cementation packs have been determined with the computer program SOLGASMIX. The effect of the activator and the composition of the masteralloy on the coating process has been predicted. The activities of Al and Cr have been incorporated into the calculations and the results indicate that codeposition of Al and Cr is possible using NaCl, CrCl;The thermodynamic predictions were used as guidelines in choosing pack chemistries to attain the desired corrosion resistant coating composition of 18-30 Cr and 5-10 Al (a/o) in Ni-base alloys. CrCl;Diffusion profiles for Cr and Al into Ni, coated under different conditions, have been obtained. A finite element program which predicts diffusion profiles for a given surface concentration was developed and evaluated, using diffusion coefficients from literature. Very good agreement between predicted and experimental profiles were obtained.;Low temperature hot corrosion tests of the coated Rene 80 coupons show excellent corrosion protection for exposure times up to 16 hours at a temperature of 730