Diffusion coating of ferrous metals
AssigneeChromalloy American Corporation
InventorsKenneth K. Speirs, Robert P. Bradley
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Abstract
A process is provided for the pack diffusion coating of ferrous metal articles with aluminum, wherein a small but effective amount of an energizer, aluminum chloride, is employed associated with a small but effective amount of a halide selected from the group consisting of an ammonium halide and an anhydrous metal chloride mixed in a pack containing particulate aluminum metal mixed with an inert material, e.g. refractory oxide, in which the ferrous article to be coated is embedded, the process being characterized by the fact that substantial outgassing of aluminum chloride is inhibited during the coating process by controlling in combination the total amount of halides employed not to exceed about 1 - 1/2% of the pack.
Claims11
A pack cementation process for diffusing aluminum into a ferrous metal article while inhibiting substantial outgassing of aluminum chloride fumes during said process which comprises the steps of:
- forming a dry aluminum pack containing by weight at least about 50% particulate aluminum, about 1/8 to 3/4% AlCl.sub.3 combined with about 1/8 to 3/4% of a halide salt selected from the group consisting of an ammonium halide and an anhydrous metal chloride as an energizer, the balance particulate inert material, and maintaining said pack at a relative humidity ranging up to about 50%,
- subjecting said dry pack to thermal pretreatment in a sealed retort at a temperature of about 750.degree. to 900.degree. F for at least about 10 hours at said temperature,
- subjecting said pretreated pack to at least one more thermal pretreatment by again mixing therewith said energizer under said dry conditions and reheating said pack to a temperature in said range of about 750.degree. to 900.degree. F for at least about 10 hours,
- thereafter again mixing with said further pretreated pack said energizer under said dry conditions the final total amount of said energizer not exceeding about 11/2% by weight of said final pack,
- embedding the ferrous metal article to be coated in said pack and sealing said pack and embedded article in a steel retort,
- and then subjecting said pack and embedded article to a diffusion coating cycle by heating said pack to a diffusion coating temperature in the range of about 750.degree. to 900.degree. F and maintaining said pack at said temperature until the desired aluminum coating thickness has been obtained.
A pack cementation process for diffusion aluminum into a ferrous metal article while inhibiting substantial outgassing of aluminum chloride fumes during said process which comprises the steps of:
- forming a dry aluminum pack containing by weight at least about 50% particulate aluminum, about 1/8 to 3/4% AlCl.sub.3 combined with about 1/8 to 3/4% NH.sub.4 Cl as an energizer, the balance particulate inert material, and maintaining said pack at a relative humidity ranging up to about 50%,
- subjecting said dry pack to thermal pretreatment in a sealed retort at a temperature of about 750.degree. to 900.degree. F for at least about 10 hours at said temperature,
- subjecting said pretreated pack to at least one more thermal pretreatment by again mixing therewith said energizer under said dry conditions and reheating said pack to a temperature in the range of about 750.degree. to 900.degree. F for at least about 10 hours,
- thereafter mixing with said further pretreated pack said energizer under said dry conditions the final total amount of said energizer not exceeding about 11/2% by weight of said final pack,
- embedding the ferrous metal article to be coated in said pack and sealing said pack and embedded article in a steel retort,
- and then subjecting said pack and embedded article to a diffusion coating cycle by heating said pack to a diffusion coating temperature in the range of about 750.degree. to 900.degree. F and maintaining said pack at said temperature until the desired aluminum coating thickness has been obtained.
Dependencies are inferred from the claim text.