Boronized wear-resistant materials and methods thereof

Details Boronized wear-resistant materials and methods thereof Boronized wear-resistant materials and methods thereof

1998-12-16

2002-11-12

Jenkins, Daniel J. (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Processes of coating utilizing a reactive composition which...

C175S374000

Reexamination Certificate

active

06478887

ABSTRACT:

FIELD OF THE INVENTION
This invention generally relates to wear-resistant materials and methods of making such materials. More particularly, the invention relates to a boron-containing wear-resistant material and methods of making the material.
BACKGROUND OF THE INVENTION
Cemented carbides, such as cemented tungsten carbide, possess a unique combination of hardness, strength, and wear resistance. Accordingly, they have been extensively used for such industrial applications as cutting tools, drawing dies, and wear parts. Additionally, cemented tungsten carbide has been widely used as cutting inserts on a rock bit for petroleum and mining drilling.
For abrasive wear and nonferrous metal-cutting applications, cemented tungsten carbide in a cobalt matrix (i.e., WC/Co composition) is preferred because of its high strength and good abrasion resistance. For steel machining applications, WC/Co compositions are not suitable because they react to some extent with steel work pieces at high machining speeds. Instead, compositions such as WC/TiC/TaC/Co, TiC/Ni, and TiC/Ni/Mo, are used. However, the use of carbides other than tungsten carbide generally results in a significant strength reduction. As to inserts formed of cemented tungsten carbide, excessive wear and fracture of the inserts frequently occur under severe drilling conditions. Therefore, various attempts have been made to increase the toughness, strength, and wear resistance of cemented carbides for rock drilling and metal machining.
To increase wear resistance in machining and metal-turning applications, carbide, nitride, and carbonitride coatings have been applied to cemented carbide. The coating materials, for example, include titanium nitride (TiN), titanium carbonitride (TiCN), titanium carbide (TiC), titanium aluminum nitride (TiAlN), and aluminum oxide (Al
2
O
3
). These coating materials may be applied to a cemented carbide substrate by physical vapor deposition (PVD) or chemical vapor deposition (CVD). In a CVD coating process, a carbide substrate is heated in a reactor filled with a gas, e.g., hydrogen, at atmospheric or lower pressure. Volatile compounds are added to the reactor to supply the metallic and nonmetallic constituents of the coating. For example, TiC coatings are produced by reacting TiCl
4
vapors with methane (CH
4
) and hydrogen (H
2
) at 900 to 1100° C. (1650-2000° F). In contrast, in a PVD coating process, the desired coating material is transported from the source to the substrate without involving chemical reactions. Generally, the thickness of the coatings obtained by a PVD or CVD process is less than about 10 microns. Although these thin coatings deposited on carbide cutting inserts have resulted in significant increases in service life, such thin coatings are not suitable for rock drilling applications due to the inadequate thickness. To survive the severe wear and erosion conditions experienced by inserts on a rock bit, a coating preferably should have a thickness greater than 10 microns.
Apart from CVD and PVD, a different method known as “boronizing” has been developed. In contrast to PVD and CVD, boronizing (or boriding) is a thermochemical surface hardening process, in which a boride surface layer is produced via boron diffusion into the surface of a work piece. The process typically involves heating a cleaned substrate to an elevated temperature, preferably for one to twelve hours, in contact with a boronizing compound in the form of a solid powder, paste, liquid, or gaseous medium. The boride surface layer (or boronized layer) typically ranges from about 1.2 microns to 15 microns, depending on the substrate metal, boronizing time, and temperature.
Because ferrous metals and nonferrous metals may be readily boronized, metal boronizing has been applied to make metal components for pneumatic transport systems, plasticating units in plastics processing, automobile gear systems, components for mills, and pumps and valves for chemical plants.
On the other hand, boronized cermet material (e.g., cemented carbides) has only limited use due to the limited thickness obtainable by existing boronizing techniques. For example, boronizing has been used to manufacture extrusion dies and cutting tools (which require a relatively thin boride layer). However, inserts formed of boronized carbide have not been successfully employed for petroleum and mining drilling applications due to the inadequate thickness of, and inconsistent quality in, the boride layer.
For the foregoing reasons, the benefits of boronizing cemented carbides to produce a relatively thick boride layer have not been fully realized. Therefore, there is a need to explore a method of obtaining a relatively thick boride layer by boronizing cemented carbides. Furthermore, it also is desirable to obtain a boronized wear-resistant material with improved wear resistance, toughness, and/or fracture strength.
SUMMARY OF THE INVENTION
In one aspect, the invention relates to a boron-containing composition which comprises tungsten carbide and one or more compounds represented by the formula W
3
MB
3
, where M is selected from the group consisting of iron, nickel, and cobalt. In some embodiments, the boron-containing composition includes a compound represented by the formula W
3
CoB
3
. The boron-containing composition may further comprise CoB, W
2
CoB
2
, and WB.
In another aspect, the invention relates to a boron-containing composition obtained by the following method. The method includes: (a) providing a substrate formed of cemented tungsten carbide in a cobalt matrix; (b) contacting the substrate with a boron-yielding material; and (c) heating the substrate and the boron-yielding material to at least 800° C. to form a compound having the formula W
3
CoB
3
.
In still another aspect, the invention relates to a wear-resistant body which includes a substrate and a boride layer over the substrate. The boride layer includes a compound represented by the formula W
3
CoB
3
. In some embodiments, the boride layer of the wear-resistant body also may include CoB, W
2
CoB
2
, and WB. It may further include tungsten carbide. Preferably, the weight percent of W
3
CoB
3
in the boride layer in the boride layer should be in the range of about 2% to about 16%. The weight percent of the tungsten carbide in the boride layer preferably should exceed about 60%. The weight percent of CoB in the boride layer preferably should be in the range of from about 8% to 20%. Furthermore, the weight percent of WB in the boride layer preferably should be up to about 2%. In some embodiments, the substrate of the wear-resistant body may be formed of a carbide in a metallic matrix selected from the group consisting of iron, nickel, cobalt, and alloys thereof. The substrate may further include one or more of WC, TaC, VC, and TiC. For example, the substrate of the wear-resistant body may be formed of cemented tungsten carbide in a cobalt matrix. The average grain size of the tungsten carbide in the substrate preferably should be in the range of about 1 micron to about 6 microns. The wear-resistant body may be used to form a face seal, a bearing surface, a thrust plug, and a nozzle. It also may be used to form a component of a rock bit.
In yet another aspect, the invention relates to a wear-resistant body which comprises a substrate formed of cemented tungsten carbide in a cobalt matrix and a boride layer over the substrate. The boride layer includes WC, W
3
CoB
3
, CoB, W
2
CoB
2
, and WB.
In yet still another aspect, the invention relates to a wear-resistant body obtained by the following method. The method comprises: (a) providing a substrate formed of cemented tungsten carbide in a cobalt matrix; (b) contacting the substrate with a boron-yielding material; and (c) heating the substrate and the boron-yielding material to at least 800° C. to form a boride layer over the substrate. The boride layer includes tungsten carbide and a compound having the formula W
3
CoB
3
.
In one aspect, the invention relates to a hard material insert for an earth-boring bit. The insert comprises an inner co

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