HK1069606B - Metallic diffusion process and improved article produced thereby - Google Patents

Description

Metal diffusion coating method and improved product manufactured by using same

Statement of government rights

The U.S. government has rights in this invention pursuant to a contract (contract number: DE-AC05-00OR22800) signed between the department of energy and BWXY Y-12, l.l.c.

Technical Field

The invention mainly relates to the technical field of alloy materials, in particular to the technical field of diffusion coating modification treatment of a surface area of a metal part.

Background

The conventional modification treatment of the metal part based on the prior art can ensure that the surface area of the metal part obtains excellent characteristics, and the internal area of the metal part is basically not influenced. Examples of such processing techniques include electroplating, i.e., plating the surface of the metal part with zinc or other alloying constituents to enhance its resistance to the surrounding environment. Another embodiment of this prior art involves the use of anodizing techniques to form a thin oxide layer of aluminum on the surface of the metal part, which also provides better resistance to the ambient environment.

More advanced process technologies involve the treatment of diffusion plating of various metallic materials into the surface of the formed metal part. The conventional process is carried out in a heated environment, which is heated throughout by the use of various heating elements to a temperature sufficient to cause diffusion of the metallic material into the surface of the formed metal part. One such treatment is a retort process in which the metal part is welded in a retort and the retort is surrounded by the metal material to be infiltrated into the surface of the metal part. Typically, this process involves slow heating to about 2100 ° f followed by slow cooling for an extended period of time. Known methods for both stack and blank diffusion plating are similar, but require longer heating and cooling times for larger volumes of material, including metal parts and metal materials that affect changes in the metal parts. Generally these diffusion coating process techniques involving slow heating and cooling cause considerable variation not only in the surface of the metal part, but also in the internal volume regions of the metal part where grain growth and refinement are a natural consequence of the heating.

Summary of The Invention

It is therefore an object of the present invention to provide an improved method for the surface modification treatment of shaped metal parts.

It is another object of the present invention to surface modify a formed metal part by a metal diffusion coating process to provide improved corrosion resistance and improved resistance to physical wear and abrasion.

It is another object of the present invention to modify the surface of a metal part by providing an improved method that does not cause significant grain growth or refinement of the internal volume of the shaped metal part.

It is another and still more specific object of the present invention to provide an improved process with a time period that is significantly shorter than the time periods of the prior art.

These and other objects are achieved by infiltrating the metal into the surface of a formed metal part by enclosing the formed metal part in an enclosure of thermally insulating material having the desired metal dispersed therein. Microwaves are directed into the enclosure for heating the shaped metal part and the surrounding enclosure to a temperature sufficient to cause diffusion of the desired metal material into the surface portion of the desired shaped metal part.

Drawings

FIG. 1 is a schematic diagram of an apparatus for carrying out the process of the present invention.

Fig. 2-5 are photomicrographs showing various embodiments of the invention.

Detailed description of the invention

In accordance with the present invention, it has been discovered that microwave energy can be used in a process for diffusion coating a desired metal into a surface region of a formed metal part. The method of the present invention has many advantages over the prior art. The heating and cooling cycle process is significantly shortened thereby minimizing grain growth and grain refinement within the volume of the formed metal part. Moreover, the method of the present invention causes little dimensional change in the metal parts. The diffusion coating method of the present invention can produce a variety of surface enhancements including corrosion resistance and appearance as well as specific resistance to ambient. The method has wide application in boiler and automobile parts industries. Various other advantages and features of the present invention will become apparent from the following description, which proceeds with reference to the accompanying figures.

The method of the present invention relates to the improvement of the properties of the formed metal part. The formed metal part may be constructed from a variety of steels, including some steels that have been previously corroded. The formed metal part is preferably carbon steel and a plurality of desired metal materials may be infiltrated into the surface of the formed metal part to enhance the exterior corrosion resistance of the metal part and the specific resistance of the different surroundings. Typically, the formed metal part is surrounded by an insulating material having the desired metal or metals therein, and the formed metal part and its surrounding enclosure including the desired metal are then heated by microwave energy to a temperature sufficient to cause the designed metal to plate into the surface area of the formed metal part. The method is preferably practiced by placing the formed metal part within insulation and a metal enclosure within a cavity of a microwave generator. The method can optionally be applied in such a way that only the surface area where the profiled metal part needs to be infiltrated is surrounded by a surround rich in metal to be infiltrated into the part. In this alternative process, only those portions of the formed metal part that are in contact with the enriched regions of the desired metal undergo the surface diffusion reaction.

Up to a temperature of 2100 deg.f so quickly that only the surface area of the formed metal part is affected, typically without significant heating of the volume within the formed metal part. Any ceramic material that is not significantly affected by the microwave source may be used for the insulating material. Generally, alumina powder is the best choice for this effect. Metals that can be used in the cementation process are chromium, nickel, vanadium, boron, aluminum, iron and alloys and mixtures thereof. The heating method of microwave overcomes the defect of long heating and cooling time period in the prior art, so that the crystal grain structure is not influenced by the heating process, and the formed metal part subjected to surface modification by using the diffusion coating method has uniqueness. Thus, the products produced according to the method of the invention are also unique.

An activator is used in the process in combination with the insulation. The activator used is preferably ammonium chloride (NH), although other halides or chlorides may be used₄Cl). The activator functions as a getter, removing oxygen and simultaneously inducing the formation reaction of the divalent chromium halide.

An enclosure suitable for carbon steel diffusion coating treatment according to the present invention is such that: contains 30-45 wt% of chromium, 2-10 wt% of chloride (activating agent) and the balance of alumina powder. When the content of elemental chromium is 20-35 wt%, a content exceeding 30 wt% is most effective.

FIG. 1 depicts an environment in which the method of the present invention may be practiced. In the figure, inside the cavity 1 of the microwave generator there are: a profiled metal part 3 surrounded by a surround 5 of a thermally insulating material, for example alumina containing the desired metal to be infiltrated into the profiled metal part 3. The container 7, which is known in the art as a bucket, contains the enclosure 5 and the formed metal part 3. The bucket 7 is placed on the insulating plate 9, in turn on the plate 11, which plate 11 is placed for insertion and removal from the cavity 1 of the microwave generator. Two waveguides 15 and 17 are connected to the microwave generator 13 to provide microwave energy to the microwave generator cavity 1. The location holes 21 are used for temperature measurement using optical means such as optical pyrometers. The microwave generator cavity 1 can be evacuated with a pump 23 and the enclosure can be appropriately filled with an inert gas through an inlet 25 if desired.

Fig. 2 and 3 are photographs of 10-fold microscopic tissue of a cross section of a part treated by the disclosed method, and fig. 4 and 5 are photographs of 100-fold microscopic tissue of a cross section of a part treated by the disclosed method. To show the grain boundaries more clearly, the cross section of the part was treated with a nital bath (approximately 3% nitric acid in ethanol). In the presence of about 55 wt% Al₂O₃42% FeCr and 3% NH₄A plurality of carbon steel short bolts and nuts are embedded in the granular mixture of Cl. The mixture was placed in a boron nitride crucible. The crucible, granular mixture and bolts and nuts were placed in a 2.45Ghz microwave oven and heated at about 1kW power for about 30 minutes. This process is used to diffusion plate chromium into the surface of carbon steel as shown in fig. 2-5.

It can thus be seen that the method of the present invention provides a uniquely modified molded part that utilizes microwaves to produce a diffusion coating into the surface of the molded part. The foregoing description of exemplary embodiments of the invention shows some of the several advantages and features of the invention. Such variations are intended to be included within the spirit and scope of the invention as defined in the appended claims.

Claims (13)

1. A method of diffusion coating a metal into a surface of a formed metal part, comprising the steps of:

placing the formed metal part within a thermally insulating material having the diffusion coated metal dispersed therein,

microwaves are directed into the insulating material to a temperature sufficient to cause diffusion of the diffusion metal into the surface area of the formed metal part to produce a change in its properties.

2. The method of claim 1, wherein: the formed metal part is contained in a container containing the insulating material and the diffusion-coated metal.

3. The method of claim 1, wherein: the diffusion metal is selected from the group consisting of chromium, aluminum, nickel, vanadium, boron, iron, alloys and mixtures thereof.

4. The method of claim 1, wherein: the formed metal part is carbon steel.

5. The method of claim 1, wherein: the insulation material incorporates a halide activator.

6. The method of claim 5, wherein: the halide activator is a chloride.

7. The method of claim 6, wherein: the chloride is ammonium chloride.

8. The method of claim 2, wherein: the container was placed in a microwave generator cavity, wherein the gas atmosphere in the microwave generator cavity was a vacuum.

9. The method of claim 2, wherein: the vessel was placed in a microwave generator cavity, which was evacuated to vacuum and then appropriately filled with an inert gas.

10. The method of claim 2, wherein: the diffusion metal is selected from the group consisting of chromium, nickel, vanadium, boron, aluminum, iron, alloys and mixtures thereof.

11. The method of claim 2, wherein: the formed metal part is carbon steel.

12. The method of any one of claims 8-9, wherein: the insulating material comprises a halide activator.

13. The method of claim 12, wherein: the halide activator is a chloride.