Chromium-silicon diffusion coating

Details Chromium-silicon diffusion coating Chromium-silicon diffusion coating

1997-11-03

1999-10-26

Beck, Shrive

Coating processes

Coating by vapor, gas, or smoke

Metal coating

427252, 427229, C23C 1622

Patent

active

059724293

ABSTRACT:
A method of diffusion coating a surface of an alloy product containing at least 5 wt. % iron with a chromium-silicon coating uses a dual activator containing a fluoride salt and a chloride salt, at least one of those salts particularly being ammonium chloride or another ammonium halide salt. The pack mix contain at least 20% chromium and a chromium to silicon ratio of at least 10 to 1. The workpiece is heated to at least 2050.degree. F. to obtain a coating of at least 10 mils which contains at least 30% chromium. Upon heating the ammonium salt will form a reducing environment containing molecular hydrogen. The presence of molecular hydrogen speeds up the chemical reactions by an additional reduction reaction to create the surface coating which enables the coating reactions to occur shorter hold times.

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