The present invention relates to a tool for grinding and polishing diamond and a method for polishing diamond and/or the materials containing diamond without causing cracks and fractures therein. The diamond can be a polycrystalline diamond, a single crystal diamond, a sintered diamond compact, or a diamond thin film including a diamond thin film formed on a substrate by a gas phase synthetic method or a diamond self-standing film, foil or plate. The present invention also relates to a polished diamond including a diamond thin film, a polycrystalline diamond, etc., a polished single crystal diamond, and a polished sintered diamond compact obtained by the grinder and polishing method.
Diamond thin films which have recently attracted considerable attention are one of the materials which utilize diamond. Diamond thin films (ie. a diamond thin film formed on a substrate and a diamond thin-film coating member) and diamond self-standing films each consist of diamond polycrystalline grains that have been produced industrially (artificially) by a gas phase synthetic method (CVD method) or the like. However, diamond thin films obtained by the above synthetic method consist of a great number of crystal grains and have a rough surface.
Thus, the rough surface of a diamond thin film formed by a gas phase synthetic method must be planarized before its use in, for example, electronic parts, optical parts, super precision parts, or machining tools.
Further, although a natural single crystal diamond and an artificial single crystal diamond formed by, for example, a high pressure synthetic method or a gas phase synthetic method are currently being used as various kinds of industrial materials, such as a grinder dresser, cutting tool, die, heat sink, and x-ray window, or used as a jewel, the diamonds require finishing to an appropriate shape suitable for their respective applications.
As for a sintered diamond compact utilizing diamond, its characteristics are being made full use of and are becoming widely used in tools for high-speed precision grinding or polishing of automobile engines, tools for precision grinding or polishing of cemented carbide, grinding or cutting tools, wear-resistant parts, heat sinks or packages for communication instruments, etc.
The sintered diamond compacts usually contain Co, WC, TiC, etc. as a binder additive; however, some contain little or no binder additive. Unless otherwise specified, xe2x80x9cdiamond sintered compactsxe2x80x9d used herein include sintered compacts containing Co, WC, TiC, etc. as a binder additive or sintered compacts containing little or no binder additives.
It is easily understood that polishing diamond is not easy since diamond is extremely hard. It is so hard that it is commonly used for polishing other hard materials such as metals and ceramics or for fine-polishing jewelry.
As a method for planarizing a polycrystalline diamond thin film or a free-standing diamond film which each have a large amount of roughness on their surfaces, a Scaife method is utilized in which the diamond films are polished with diamond powders intervened between the diamond film and a hard cast iron plate rotating at a high speed (ie. grinding and polishing using a diamond).
This method has been used for polishing diamond as a jewel; however, as a method for polishing the foregoing artificial diamonds, its processing efficiency is extremely low and it is therefore not used.
In particular, for the foregoing diamond single crystal, its hardness varies dramatically from crystal plane to crystal plane or from orientation to orientation. The crystallographic planes which can be polished are limited to, for example, the (100) and (110) planes under present conditions, and it is extremely difficult to polish the (111) plane which is superior to any other planes in hardness and thermal conductivity. In actuality, it has been considered that it is substantially impossible to polish that crystal plane.
Thus, polishing a diamond single crystal requires such great skill that polishing is carried out while examining the crystallographic planes and orientation to locate the plane to be possibly polished. This has led to making diamond polishing complicated and expensive.
As for the sintered diamond compacts, when employing a polishing method using a diamond grinder (ie. grinding and polishing using a diamond) described above, an intense step (about several xcexcm) is likely to occur due to a difference in hardness at grain boundaries between diamond and binder or between neighboring diamond grains, or due to a falling of many diamond grains in the sintered compact. Thus, when using a sintered diamond compact as a machining tool as described above, grinding accuracy decreases. When using the same as a wear-resistant part, the problem of deterioration in fracture properties arises, and even the problems of damage to the sintered diamond compact and falling of diamond grains in the sintered diamond compact arise.
As described above, a diamond is so hard a material that there is no substitute for it; therefore, it is only natural to consider that there is no abrasive for diamond except diamond itself (ie. grinding and polishing using diamond). Thus there have been devised grinders for polishing diamonds in which a diamond abrasive for grinding and polishing using a diamond are embedded in different kinds of binders.
Examples of such grinders include a resin bonded diamond wheel utilizing phenol resin, a metal bonded diamond wheel, a vitrified bonded diamond wheel utilizing feldspar/quartz, and an electroplated diamond grinding wheel.
The basic concept of the above methods is to scratch the surface of the diamond subject to polishing with diamond abrasive. Unless otherwise specified, xe2x80x9cdiamondxe2x80x9d used herein means diamond itself as well as materials containing diamond, such as, diamond thin films, free-standing diamond films, single crystal diamonds, sintered diamond compacts, and polycrystalline diamonds other than the above. Thus, the wear resistance of the diamond abrasives and the amount of diamond abrasives are the points determining the processing efficiency of the grinders. In addition, any type of binder used as the holder of diamond grains must not present an obstacle to the polishing, and a new cutting edge diamond abrasive grain must appear on the polishing surface every time an old one becomes worn.
One example of the above methods is such that a new cutting edge of diamond abrasive appears automatically according to the amount of the diamond abrasive worn out in a grinder by anodic oxidation of the bond, the grinder binder such as cast iron, with the development of the wear of the diamond abrasive. In this case, as long as the diamond abrasive exists which can effectively polish the subject of polishing, iron oxide is formed on the surface of the binder so as to prevent it from being electrolyzed.
This method is considered to be the most efficient among the foregoing. However, even this method still gives rise to problems, such as complicated operation, high cost and unstable polishing quality. For high-quality diamond powders to be suitable for use as an abrasive in the above method, a suitable binder must be selected. The selected binder must be embedded in the grinder and the quality of the same must be maintained; electrolysis equipment and setting of its conditions are required; and polishing operation and its control are also required. The quality of polishing is determined by all of the above.
When the material being polished is a diamond thin film, the polishing rate and the polishing efficiency are limited due to the number of diamond grains in the material being polished being overwhelmingly large compared with the number of diamond grains of the abrasives applied during the polishing process.
As described above with the method for polishing diamond utilizing a grinding and polishing tool for diamond, problems have still persisted involving the intensive wear of the grinder and the need of an expensive polishing apparatus which is extremely accurate and which can withstand elevated pressures.
There is proposed a method, other than the foregoing, of polishing diamond by pressing iron or stainless steel against it. Although diamond is chemically stable at room temperature, it is graphitized and begins to bum when heated to 700xc2x0 C. in the air, and even in an evacuated atmosphere, it is graphitized when heated to 1400xc2x0 C. or higher. The above method for polishing diamond utilizes the reaction of diamond with iron at such high temperatures.
It has been understood that the reaction of diamond with iron (carbon, which is the component of diamond, decompose into melts) begins to occur at about 800xc2x0 C. to form Fe3C (cementite) which is peeled off at a polished plane during the polishing process, and the peeling of Fe3C causes the development of the polishing.
This reaction is further facilitated at elevated temperatures, at which the formation/decomposition of Fe3C occurs, diamond begins to take a form of carbon dioxide, and polishing is developed. Generally, the reaction temperature needs to be 900xc2x0 C. or higher taking into account the polishing efficiency.
This method has been considered to be acceptable in that it can use iron or iron-based materials which provide an inexpensive abrasive. The most serious problem in this method, however, is that an efficient polishing can be achieved only by heating the polishing tool or material to be polishing to high temperatures. Stainless steel and iron-based materials are softened at high temperatures and their strength is markedly deceased, which makes stable polishing impossible.
Polishing must be carried out in an evacuated atmosphere or in a reductive atmosphere so as to prevent the iron from being oxidized, especially when using iron at high temperatures. Thus, other problems arise relating to the facilities and to complicating the polishing process (ie. polishing cannot be carried out freely and easily).
In addition, such high temperature heating as described above affects even the diamond which is the subject of polishing and causes cracks and fractures in the subject diamond due to the thermal stress caused by an abrupt temperature gradient during fracture and heating.
An attempt has been made to replace iron with chromium and titanium, both of which have a strong affinity with carbon. However, chromium is too brittle to be subjected to polishing, and titanium is too soft and, like iron, easily oxidized to form titanium oxides. Thus, both cannot be used as an abrasive.
Laser polishing has also been attempted as an alternative; however, its accuracy of dimension is poor and it is therefore not useable.
Accordingly, an object of the present invention is to provide a tool for grinding and polishing diamond and a method for polishing diamond which enables the polishing of diamond itself or the materials containing diamond, such as, single crystal diamond, diamond thin film including a diamond thin film formed on a substrate by a chemical-vapor deposition or a free-standing diamond film (foil or place), sintered diamond compact, and polycrystalline diamond other than the foregoing, at low temperatures (including room temperature) without causing cracks, fractures, or degradation in quality therein. The tool and method should enable the use of currently existing apparatus including surface grinding apparatus, lap grinding apparatus and other polishing apparatus while maintaining stable abrasive performance. The tool and method should further provide for ease of operation while providing a stable polishing quality at a low cost. Another object of the present invention is to provide a diamond, such as a single crystal diamond or a sintered diamond compact, having been subjected to the above stated grinder and method.
Another object of the present invention is to provide efficient and inexpensive grinding and polishing processing of diamond thin film components of three-dimensional shape and diamond thin film coating components which are expected to rapidly increase in the near future with the development of diamond thin film applications.
The present inventor found that special metal materials can react with diamond effectively, be polished at low temperatures or ordinary temperature or under heating, and control the wearing and deterioration of abrasives extremely even in the atmospheric air.
Based on this finding, the present invention provides a tool (ie. grinder) for grinding and polishing diamond. The main component of the grinder is an intermetallic compound consisting of one kind or more of elements selected from the group of Al, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir and Pt and one kind or more of elements selected from the group of Ti, V, Zr, Nb, Mo, Hf, Ta and W.
According to another aspect of the present invention, a tool for grinding and polishing diamond is provided according to the above description, and wherein the content of the intermetallic compound in the grinder is 90 percent by volume or greater.
According to another aspect of the present invention, a tool for grinding and polishing diamond is provided according to either of the above descriptions, and wherein a part of the grinder or the whole grinder is made of the above stated intermetallic compound.
According to another aspect of the present invention, a method for polishing diamond is provided. The diamond is polished on a grinder whose main component is an intermetallic compound consisting of one kind or more of elements selected from the group of Al, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir and Pt and one kind or more of elements selected from the group of Ti, V, Zr, Nb, Mo, Hf, Ta and W, while heating the portion subjected to polishing to 100-800xc2x0 C., or more preferably, to between 300-500xc2x0 C.
According to another aspect of the present invention, the content of the intermetallic compound in the grinder utilized in the above described method is 90 percent by volume or greater.
The present invention further provides a polished diamond, single crystal diamond, and sintered diamond compact. The diamond, single crystal diamond, and sintered diamond compact have each been subjected to a polishing process on a grinder whose main component is an intermetallic compound consisting of one kind or more of elements selected from the group of Al, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir and Pt and one kind or more of elements selected from the group of Ti, V, Zr, Nb, Mo, Hf, Ta and W.
According to another aspect of the present invention, a polished diamond is provided having a step at a grain boundary portion of 0.1 xcexcm or smaller when the thickness of the diamond thin film exceeds 300 xcexcm, and 0.02 xcexcm or smaller when the thickness of the same is 300 xcexcm or thinner.
According to another aspect of the present invention, a single crystal diamond polished on the above stated grinder is provided wherein the polishing plane of the single crystal diamond is a (111) plane.
According to another aspect of the present invention, a sintered diamond compact polished on the above stated grinder is provided wherein the surface roughness of the sintered diamond compact after polishing is 0.5 xcexcm or less.
According to yet another aspect of the present invention, a composite grinding and polishing tool for grinding and polishing diamond and a segment of the same, wherein the composite grinding and polishing tool and the segment of the same is a composite of an intermetallic compound consisting of one kind or more of elements selected from the group of Al, Cr, Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Os, Ir and Pt and one kind or more of elements selected from the group of Ti, V, Zr, Nb, Mo, Hf, Ta and W, diamond abrasive, and a cemented carbide or ceramics.
Unless otherwise specified, xe2x80x9cintermetallic compoundxe2x80x9d used herein includes a composite intermetallic compound.