초록 ▼

Cermets, particularly composition gradient cermets can be prepared starting with suitable bulk metal alloys by a reactive heat treatment process involving a reactive environment selected from the group consisting of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen and mixtures the

Cermets, particularly composition gradient cermets can be prepared starting with suitable bulk metal alloys by a reactive heat treatment process involving a reactive environment selected from the group consisting of reactive carbon, reactive nitrogen, reactive boron, reactive oxygen and mixtures thereof.

대표청구항 ▼

What is claimed is: 1. A process for preparing a composition gradient cermet material comprising the steps of: in a first step, heating a metal alloy containing from 18 to 60 wt % chromium at a temperature in the range of about 600�� C. to about 1150�� C. in a hydrogen environment to form a heated

What is claimed is: 1. A process for preparing a composition gradient cermet material comprising the steps of: in a first step, heating a metal alloy containing from 18 to 60 wt % chromium at a temperature in the range of about 600�� C. to about 1150�� C. in a hydrogen environment to form a heated metal alloy; in a second step, exposing said heated metal alloy to a reactive carbon gaseous environment comprising H2 and CH4, wherein the CH4 ranges from about 2 vol % to about 45 vol % in the range of about 600�� C. to about 1150�� C. for a time sufficient to provide a reacted alloy with a reacted layer of about 1.5 mm to about 30 mm thick on the surface or in the bulk matrix of the metal alloy; and in a third step, cooling said reacted alloy to a temperature below about 40�� C. to provide a composition gradient cermet material, wherein one surface of the cermet is ceramic-rich and a second unexposed surface is metal-rich, and wherein said cooling step further comprises cooling said reacted alloy to a temperature in the range of 500�� C. to 100�� C., holding the temperature at any temperature in the range of 500�� C. to 100�� C. for a time period between 5 minutes to 10 hours and thereafter cooling at a rate in the range of 0.5�� C. per second to 25�� C. per second to below about 40�� C. 2. The process of claim 1 wherein said metal alloy further comprises from 0 to 10 wt % titanium, and from 30 to 88 wt % of metals selected from the group consisting of iron, nickel, cobalt, silicon, aluminum, manganese, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum, tungsten, and mixtures thereof. 3. The process of claim 1 wherein said metal alloy further comprises from 0 to 10 wt % titanium, and from 30 to 88 wt % iron. 4. The process of claim 1 wherein said exposing step is for a time period of about 1 hour to 800 hours. 5. The process of claim 1 wherein said exposing step is for a time period wherein the reacted alloy is of thickness encompassing the entire depth of said metal alloy. 6. The process of claim 1 wherein said cooling step comprises cooling said reacted alloy at a rate in the range of 0.5�� C. per second to 25�� C. per second. 7. The process of claim 1 wherein said exposing step is for a time period to provide a reacted alloy wherein said reacted alloy comprises precipitated chromium-rich carbides, titanium carbides and mixtures of chromium-rich and titanium carbides. 8. The process of claim 7 wherein said chromium-rich carbides comprise Cr7 C3, Cr23C6 (Cr0.6Fe0.4)7C3 (Cr0.6Fe0.4)23C6 and mixtures thereof. 9. The process of claim 7 wherein said titanium carbides comprise TiC. 10. A process for preparing a composition gradient cermet material comprising the steps of: in a first step, heating a metal alloy containing from 18 to 60 wt % chromium at a temperature in the range of about 600�� C. to about 1150�� C. in a hydrogen environment to form a heated metal alloy; in a second step, exposing said heated metal alloy to a reactive nitrogen gaseous environment comprising H2 and ammonia, wherein the ammonia ranges from about 2 vol. % to about 70 vol. % in the range of about 600�� C. to about 1150�� C. for a time sufficient to provide a reacted alloy with a reacted layer of about 1.5 mm to about 30 mm thick on the surface or in the bulk matrix of the metal alloy; and in a third step, cooling said reacted alloy to a temperature below about 40�� C. to provide a composition gradient cermet material, wherein one surface of the cermet is ceramic-rich and a second unexposed surface is metal-rich, and wherein said cooling step further comprises cooling said reacted alloy to a temperature in the range of 500�� C. to 100�� C., holding the temperature at any temperature in the range of 500�� C. to 100�� C. for a time period between 5 minutes to 10 hours and thereafter cooling at a rate in the range of 0.5�� C. per second to 25�� C. per second to below about 40�� C. 11. The process of claim 10 wherein said exposing step is for a time period to provide a reacted alloy wherein said reacted alloy comprises precipitated chromium-rich nitrides, titanium nitrides and mixtures of chromium-rich and titanium nitrides. 12. The process of claim 11 wherein said chromium-rich nitrides comprise Cr2N. 13. The process of claim 11 wherein said titanium nitrides comprise TiN. 14. A process for preparing a composition gradient cermet material comprising the steps of: in a first step, heating a metal alloy containing from 18 to 60 wt % chromium at a temperature in the range of about 600�� C. to about 1150�� C. in a hydrogen environment to form a heated metal alloy; in a second step, exposing said heated metal alloy to a reactive carbon and nitrogen gaseous environment comprising H2 and ammonia and CH4, wherein the CH4 ranges from about 2 vol % to about 45 vol % and the ammonia ranges from about 2 vol. % to about 70 vol. % in the range of about 600�� C. to about 1150�� C. for a time sufficient to provide a reacted alloy with a reacted layer of about 1.5 mm to about 30 mm thick on the surface or in the bulk matrix of the metal alloy; and in a third step, cooling said reacted alloy to a temperature below about 40�� C. to provide a composition gradient cermet material, wherein one surface of the cermet is ceramic-rich and a second unexposed surface is metal-rich, and wherein said cooling step further comprises cooling said reacted alloy to a temperature in the range of 500�� C. to 100�� C., holding the temperature at any temperature in the range of 500�� C. to 100�� C. for a time period between 5 minutes to 10 hours and thereafter cooling at a rate in the range of 0.5�� C. per second to 25�� C. per second to below about 40�� C. 15. A method for protecting a metal surface exposed to an erosive material at temperatures in the range of up to 850�� C., the method comprising providing the metal surface with a cermet composition according to any one of claims 1, 10 or 14. 16. A method for protecting a metal surface exposed to an erosive material at temperatures in the range of 300�� C. to 850�� C., the method comprising providing the metal surface with a cermet composition according to claim 15. 17. The method of claim 15 wherein said surface comprises the inner surface of a fluid-solids separation cyclone.