IL45848A

IL45848A - Corrosion resistant coating system for ferrous metal articles

Info

Publication number: IL45848A
Application number: IL45848A
Authority: IL
Original assignee: Chromalloy American Corp
Priority date: 1974-10-14
Filing date: 1974-10-14
Publication date: 1976-10-31
Also published as: IL45848A0

Claims

1. 45848/2 CIAIMS ·κ·* X. A ferrous metal article having at least one brazed joint, the braze of said joint being formed of a non-ferrous bra¾ing ¾llo of melting point ranging from about 1,125° ■ - to 1,925°F, ■ said article being characterized by a di fusion-bonded laye of a metal aluminide selected from the group consisting of iron aluminide, nickel aluminide, cobalt aluminide, and chromium aluminide over the entire surface thereof including the surface of the brazed joint, the corresponding metal of said metal aluminide selected from the group consisting of iron, nickel, cobalt and Chromium bein di usion-bonded as a first layer into, the surfaces of both the braze and the ferrous metal and being enriched outward therefrom in the corresponding metal aluminide by virtue of aluminum diffused into said diffused f rs metal layer, the thermally diffused aluminum coating also having bonded thereto a cured non-metallic barrier laye formed from a silicate selected from the group consisting of sodium silicate, potassium silicate, lithium silicate and ethyl silicate, whereby the alumlnized brazed joint is characterized b an improved combination of resistance to corrosio and fatigue-.

2. The ferrous metal article of Clai 1, wherein the non-ferrous brazing alloy has a melting point of about 1,175° to 1,85G°F and wherein said brazing alloy is selected from the group consisting of a copper-base, silver-base or a gold-base alloy. 45848/2

3. The ferrous metal article of Claim 1, wherein said non-metallic barrier layer also includes a ehromate and phosphate of at least one metal.

4. The ferrous metal article of Claim 3, wherein said o¾roiaates and phosphates of said at least one metal are chromates and phosphates of aluminum and magnesium.

5. The ferrous article of Claim 4 , wherein the silicate of the non-metallic barrier layer is derived from sodium silicate.

6. The ferrous article of Claim 4, wherein the silicate of the non-metallic barrier layer is derived from potassium silicate.

7. A ferrous metal article having at least one brazed joint, the braze of said joint being formed of a non-ferrous brazing alloy of melting point ranging from about l,125e to 1,925°F, said article being characterized by a diffusion-bonded layer of a metal aluminide selected from the group consisting of iron aluminide, nickel aluminide, cobalt aluminide and chromium aluminide over the entire surface thereof including the surface of the brazed joint, the corresponding metal of the metal aluminide selected from the group consisting of iron, nickel, cobalt and chromium being diffusion-bonded as a first layer into the surfaces of both the braze and the ferrous metal and being enriched outward therefrom i the corre^6nding metal aluminide by virtue of aluminum diffused into said first metal layer, whereby the aluminized brazed joint is characterized by ah improved combination of resis ance to corrosio and fatigue. » 45848/2 i ■

8. The ferrous metal article of Claim 7, wherein the non-ferrous brazing alloy has a melting point of about 1,175° to l,850oF, and wherein said brazing alloy is selected from the group consisting of a copper-base, silver-base or gold-base alloy.

9. A method of aluminizing a brazed ferrous metal article characterized by at least one brazed joint, the braze of said joint being formed of a non-ferrous brazing alloy of melting point ranging from about 1125 °F to 1925 °F which comprises: coating the entire surface of said ferrous metal article with an adherent coating of an aluminide-forming metal selected from the group consisting of iron, nickel, cobalt and chromium, and thermally diffusing aluminum into the entire surface of said article including the coated braze, whereby a sacrificial coating comprising said aluminum is produced, the aluminum coating being characterized by the pre¬ sence, of an aluminide 45848/2 compound selected from the group consisting of iron aluminide, ^nickel aluminide, cobalt aluminii \ and chromium aluminide.

10. The method of claim 9, wherein said non- ferrous brazing alloy is either a copper-base, silver- base or gold-base alloy, and wherein said brazing alloy has a melting point ranging from about 1175 °F to 18503F.

11. The method of claim 9, wherein said coating of aluminide-forming metal is obtained by plating from an aqueous bath. -

12. The method of claim 9, wherein following the production of the thermally diffused aluminum sur¬ face, a non-metallic coating is applied to said surface comprising the steps of applying a coating of a solution of a soluble silicate salt selected from the group consist¬ ing of sodium silicate, potassium silicate, lithium sili¬ cate and ethyl silicate at a temperature ranging up to 100 °C, removing excess liquid from said surface so as to * 45848/2 <, ■ form a uniform layer of said silicate salt covering said surface and then, drying ahd curing said non-metallic « layer, said curing being carried out at a temperature of about 150 °C to 430 °C.

13. The method of claim 12, wherein the step of applying said silicate layer is repeated a plurality of times and "dried and wherein the layers are thereafter cured by heating at a temperature of about 150 °C to 430 °C.

14. The method of claim 12, wherein following the formation. of silicate coating on the aluminum surface, a conversion coating is applied comprising the steps of applying a solution containing by weight about 5% to 30% of phosphoric acid, about 3% to 8% chromic acid (CrO ) , 3 and at least about 0.5%of at ,least one chromate and phos¬ phate forming metal and the balance essentially water, drying said conversion coating "ahd then thermally curing said conversion coating.

15. The method of claim 14, wherein said chromate and phosphate-forming metals are aluminum in the amount of about 0.02% to 3% and magnesium in the amount of about 0.75% to 6%.