Abrasive tool making process – material – or composition – With inorganic material – Metal or metal oxide
Reexamination Certificate
2000-12-07
2003-04-01
Marcheschi, Michael (Department: 1755)
Abrasive tool making process, material, or composition
With inorganic material
Metal or metal oxide
C051S295000, C051S293000, C051S307000
Reexamination Certificate
active
06540800
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to abrasive core particles metallurgically bonded to a metal deposit, and, in particular, to core abrasive particles metallurgically bonded to encapsulating coatings comprising ruthenium, rhenium, osmium, alloys, and mixtures thereof, and to composites and abrasive compacts containing such coated abrasive particles, and to methods of preparing such coated abrasive particles, composites and abrasive compacts.
2. Description of the Prior Art
Abrasive particles have long been embedded in various matrix/binder materials for use as cutting tools, grinding wheels, and the like. Abrasive particles have also been utilized to lend hardness to articles where no abrasion is involved. Difficulty had been experienced in retaining the abrasive particles in the matrix/binder materials. Various expedients had been proposed to improve the retention and/or wetting of the abrasive core particles in the matrix/binder materials. It is well known to coat abrasive core particles with metal coatings so as to, inter alia, improve the retention of the abrasive core particles in a matrix/binder material. Typically, such metal coatings had relied on the formation of a chemical bond with the abrasive core particles for their retention properties. For example, with carbon containing abrasive core particles such as diamond or metal carbides, metal coatings had been selected for their ability to form carbides, or for their ability to wet carbon at high temperatures. Titanium, chromium, zirconium, and tungsten, for example, react to form a carbide with the carbon in diamond or carbide, which results in the formation of a chemical bond between the carbide forming element and a diamond or carbide abrasive core particle. Metals that form chemical bonds in this manner are typically described as active metals. Generally, the active metals also exhibited good adhesion reception with respect to the common metallic, resin, ceramic, or the like matrix/binder materials. It had previously been proposed that as an alternative to active metals and carbide formers, non-carbide forming cubic metals, such as cobalt, nickel, palladium, and platinum could be used to improve wettability and retention of diamonds and carbide materials. Such cubic materials are isostructural with cubic metal carbides and diamond. Such cubic materials also have high solubilites for carbon at elevated temperatures (typically at temperatures above one half the melting point of the cubic metals). A combination of metallurgical and mechanical bonds is typically formed between such cubic metals and diamond, cubic metal carbides, borides, nitrides, oxides, and the like. Other metals, such as copper, have also been used solely to promote wetting while only providing a mechanical bond to the abrasive grains.
Other prior proposed expedients for improving the retention of abrasive particles had included, for example, etching or otherwise modifying the surface of the abrasive particle to improve mechanical bonding.
Abrasive core particles generally comprise, for example, diamond, cubic metal carbides, cubic metal borides, cubic metal nitrides, cubic metal oxides, other ceramics, and the like, of various elements. Abrasive core particles, whether in compact or discrete form, are generally used to form tools, wear components, hardfacing alloys, and the like. Earth or rock drilling and boring tools such as are used, for example, in the mining and oil production fields are particularly benefited from the present invention. Metal working tools also benefit from the present invention. Typically, coated abrasive particles made according to the present invention are mounted to a tool holder, the nature of which is dictated by the intended use. Typical mounting procedures include, for example, sintering, brazing, casting, plasma spraying, thermal spraying, or the like to form coatings or compacts. Single particles can be mounted, if desired. Often, the particles are formed into a composite of a desired configuration, and the preformed composite is then mounted to the tool holder. For some applications a binder/matrix that incorporates the abrasive particles is formed to the desired configuration in situ on the tool holder.
Reliance on chemical bonding for abrasive core particle retention limits the elements that can be employed for retention purposes. Chemical bonds form interfacial materials at the boundary between the surface of the particle and the overlaying deposit. Such materials are generally not ductile so the chemical bonds are susceptible to being broken by thermal and mechanical shock, which undesirably reduces the particle retentive capacity of the coating system.
Those concerned with these problems recognize the need for improvement.
BRIEF SUMMARY OF THE INVENTION
A preferred embodiment of the coated abrasive core particles according to the present invention comprises a deposit formed in situ on the surface of an abrasive core particle, which deposit forms a metallurgical bond, rather than a chemical bond with the abrasive core particle. The deposit comprises a non carbide forming hexagonal metal, which has a melting point above about 1,000 degrees centigrade, and forms a metallurgical bond with the abrasive particle. The metals that meet these criteria are ruthenium, rhenium and osmium. Cobalt, which had previously been proposed for use in bonding diamonds, has a hexagonal polymorph, however, the stable structure above 450 degrees centigrade is the cubic phase. In this cobalt is analogous to nickel.
The use of a hexagonal refractory metal from the group ruthenium, rhenium and osmium unexpectedly results in stabilization of the diamond, metal carbide, boride, nitride, oxide, or the like, structure, even though the hexagonal lattice is not isomorphous with the cubic diamond structure. This is contrary to what previous understandings of these materials generally suggested. For example, cubic metals are isostructural with diamond, while hexagonal metals are isostructural with graphite. This would seem to suggest that the hexagonal metal would destabilize cubic structures such as diamond, carbide or other abrasives. Also, cubic metals such as nickel, and the high temperature allotrope of cobalt, tend to be more ductile and have higher solubility for carbon than do the hexagonal metals. This also would seem to suggest away from the use of refractory hexagonal metals to retain diamonds, carbides and other abrasives in binder/matrix materials. Unexpectedly, it has been found that these hexagonal refractory metals are particularly effective in retaining diamonds, metallic carbides, borides, nitrides, oxides, and the like abrasive particles. The high temperature capabilities, strengths and other inherent characteristics of the refractory metals contribute substantially to the retention of the abrasive particles, and to other desirable properties of the abrasive loaded binder/matrix articles that are made with such abrasive particles.
The use of hexagonal refractory metals to retain cubic nitride, boride and oxide abrasive particles provides very satisfactory results. Without wishing to be bound by any theory, the following is believed to be one possible explanation for this. The borides, nitrides (if formed), and oxides of ruthenium, rhenium and osmium are much less stable than the borides, nitrides and oxides of which the abrasive particles are formed. The abrasive borides, nitrides or oxides (non-carbides) are slightly soluble in the hexagonal refractory metal. Thus, a small amount of these non-carbides dissolves in the hexagonal refractory metal without the formation of brittle intermetallics, or the like. This provides a very good metallurgical bond.
Metallurgical bonds are formed between different materials when one material is soluble-in the other, without any significant chemical reaction. That is, a metallurgical bond is formed when the materials form solid solutions at the interface between them without forming intermediate compounds. Metallurgical bonds or solid solu
Bose Animesh
Sherman Andrew J.
Jagger Bruce A.
Marcheschi Michael
Powdermet, Inc.
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