Cubic boron nitride particle group with highly eroded particle surface and high toughness index

Abstract

A group of cubic boron nitride particles having a highly corroded surface and a high toughness index is produced by blending a reactive metal powder with a plurality of cubic boron nitride particles to form a blended mixture. The blended mixture is compressed to form a compressed mixture. The compressed mixture is subjected to temperature and pressure, wherein the temperature is controlled to cause corrosion of the plurality of cubic boron nitride particles by reacting the cubic boron nitride with the reactive metal powder, thereby forming a plurality of corroded cubic boron nitride particles. In addition, the temperature and pressure are controlled to maintain the boron nitride in a cubic boron nitride phase. Thereafter, the plurality of corroded cubic boron nitride particles are recovered from the compressed mixture to form the group of particles. Preferably, the group of particles does not contain hexagonal boron nitride.

Description

Background Art

[0001] The present invention relates to cubic boron nitride (CBN) particles, and more particularly to a population of CBN particles having both a highly etched surface and a high toughness index (TI).

[0002] In many CBN applications, it is desirable to have a highly corroded (i.e., rough) particle surface. Such corroded surfaces can provide better particle retention in a bonding system and / or result in particles that self-sharpen during use. Although corroded CBN particle populations exist, they typically have a low TI. This low TI results in their poor performance in specific applications. Therefore, it is desirable to provide a CBN particle population that does not suffer from a low TI and is corroded. Summary of the invention

[0003] The present invention achieves the above-mentioned objects by providing a CBN particle group having both a highly corroded surface and a high TI. The surface is characterized by pits of approximately one micron size and submicron size, and the surface features are uniformly present on almost all CBN particle faces. However, the TI of the CBN particle group is only about 10 to 20 points lower than that of a typical smoothed (i.e., non-corroded, non-rough) CBN particle group having the same chemical composition, crystal structure and shape.

[0004] The CBN particle group of the present invention is manufactured by forming or obtaining a plurality of CBN particles. A reactive metal powder is blended with the plurality of CBN particles to form a blended mixture, and the blended mixture is compressed to form a compressed mixture. The compressed mixture is subjected to temperature and pressure, wherein the temperature is controlled to cause corrosion of the plurality of CBN particles by reacting the CBN with the reactive metal powder, thereby forming a plurality of corroded CBN particles. In addition, the temperature and pressure are controlled to maintain the boron nitride in a cubic phase. Thereafter, the plurality of corroded CBN particles are recovered from the compressed mixture to form a particle group. Preferably, the particle group does not contain hexagonal boron nitride (HBN).

[0005] Other objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings in which like reference numerals designate common parts throughout the several views. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a flow chart showing a method of manufacturing a CBN particle group according to the present invention.

[0007] Figure 2 is an image from a scanning electron microscope (SEM) showing multiple CBN particles before corrosion.

[0008] Figure 3 is an image from a SEM showing a Figure 2 One of the CBN particles.

[0009] Figure 4 is another image from a SEM showing the CBN particles after having been subjected to the etching process of the present invention.

[0010] Figure 5 It is for Figure 4 A conservative threshold analysis of the percentage of area covered by pits and grooves of an image of FIG.

[0011] Figure 6 It is for Figure 4 Moderate threshold analysis of the percentage of area covered by pits and grooves of an image.

[0012] Figure 7 It is for Figure 4 Aggressive threshold analysis of the percentage of area covered by pits and grooves of an image.

[0013] Figure 8 yes Figure 4 Size analysis of the pits and grooves in the images.

[0014] Fig. 9 is an image from a SEM showing a plurality of CBN particles before the etching process of the first experiment.

[0015] Fig.10 is an image from a SEM showing a plurality of CBN particles after the etching process of the first experiment.

[0016] Fig.11 is an image from a SEM showing a plurality of CBN particles after the etching process of the second experiment.

[0017] Fig.12 is an image from SEM showing a plurality of CBN particles before the etching process of the third experiment.

[0018] Fig.13 is an image from SEM showing a plurality of CBN particles after the etching process of the third experiment.

[0019] Fig.14Surface roughness vs TI for various CBN particle groups. DETAILED DESCRIPTION

[0020] Detailed embodiments of the present invention are disclosed below. However, it should be understood that the disclosed embodiments are merely examples of the present invention, which may be implemented in various alternative forms. The drawings are not necessarily drawn to scale, and some features may be enlarged or reduced to show the details of specific components. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to adopt the present invention.

[0021] In addition, as used herein, the term "about" refers to ±10% of the numerical value of the number with which it is being used. Thus, about 50% means within the range of 45% to 55%. The term "particle" refers to a discrete object. A particle is also considered a crystal or grain.

[0022] The CBN particles used in the present invention can be made from HBN at high pressure and temperature using a catalyst system such as nitrides of alkali metals and alkaline earth metals for a period of time sufficient to form a cubic structure. The reaction mass is maintained under pressure and temperature conditions that are thermodynamically favorable for the formation of CBN crystals. The CBN is then recovered from the reaction mass using a recovery method using a combination of water, an acidic solution or a caustic chemical. It should be noted that other methods for making CBN are known, for example, CBN can also be prepared by a temperature gradient method or a shock wave method.

[0023] Any combination of starting components can be used, the starting components providing both HBN and catalyst. The embodiment of the initial reaction mixture can contain a boron source, a nitrogen source and a catalyst metal source. The boron source can be a material of elemental boron, HBN or a boron hydride such as being decomposed into elemental boron under reaction conditions. The nitrogen source can be HBN or a nitrogen-containing compound of the catalyst metal that can provide a nitrogen source under reaction conditions. The catalyst metal can be used as an elemental metal or as a catalyst compound that can be decomposed into a catalyst metal or a catalyst metal nitride under reaction conditions.

[0024] The method is not limited to the catalytic conversion of HBN to CBN involving only one catalyst material. Thus, mixtures of two or more catalyst materials may be used. Those mixtures may contain one or more catalyst metals, one or more catalyst nitrides, or one or more combinations of metals and nitrides. The mixture may contain: a catalyst that inhibits the reaction, such as silicon nitride or aluminum nitride; and a catalyst that promotes the reaction, such as nitrides of alkali metals and alkaline earth metals. In addition, alloys may also be used in the practice of the present invention. These alloys include alloys of more than one catalyst metal and alloys of catalyst metals and non-catalyst metals. Other raw material combinations are also feasible.

[0025] The method can be implemented in any type of equipment capable of producing pressure and temperature for manufacturing superabrasives. The equipment that can be used is described in U.S. Patents 2,941,241 and 2,941,248, which are incorporated herein by reference. Examples of other equipment include belt presses, cubic presses, and split-sphere presses. The equipment comprises a reaction volume in which a controllable temperature and pressure are provided and maintained for a desired period of time. The equipment disclosed in the aforementioned patent is a high-pressure device inserted between the platens of a hydraulic press. The high-pressure device comprises: an annular member, which defines a roughly cylindrical reaction area; and two conical piston-type members or punches, which are designed to be assembled into the roughly cylindrical reaction area from either side of the annular member. The reaction vessel assembled into the annular member can be compressed by the two piston members to reach the desired pressure for manufacturing CBN particles. The desired temperature is obtained by suitable means, such as by induction heating, direct or indirect resistance heating or other methods.

[0026] In the present invention, after being formed by the above method, the CBN particles are corroded to obtain a rough surface. The method uses a nitride-forming metal such as titanium, magnesium, zirconium, aluminum or lithium as a reaction metal with CBN. For example, at high temperatures, CBN reacts with zirconium and forms zirconium nitride and zirconium boride. The reaction produces pits and grooves on the surface of the CBN. After the reaction occurs, the zirconium nitride and zirconium boride can be removed, thereby showing a significantly roughened CBN surface in which many complex pockets or pits are produced. Compared with what exists on typical CBN particles, this texture provides many sharper cutting edges on the particles. As a result, in the application of the CBN particles of the present invention, tool performance is improved. These applications include precision grinding, in which the CBN particles are introduced into a resin, metal or vitrified bond system. The CBN particles of the present invention also improve the performance of honing and superfinishing, especially when the bonding material comprises a resin, metal or glass batch. Additionally, the CBN particles of the present invention improve the performance of the tool when the particles are electroplated or electroformed onto the tool or when the particles are co-deposited into a coating.

[0027] The method of the present invention can be used with different forms of CBN, including single crystal and polycrystalline CBN, but it is preferred to use the method of the present invention with single crystal CBN. The present invention is applicable to a wide range of CBN sizes from hundreds of microns in diameter to micron-sized powders. In an exemplary embodiment, CBN particles having a size of less than about 100 μm are used. However, CBN particles having a size of more than about 100 μm can also be used. In an exemplary embodiment, the size of the CBN particles is in the range of about 10 μm to about 1000 μm.

[0028] Usually, if Figure 1 As shown, the method for manufacturing a group of CBN particles according to the present invention includes: forming or obtaining a plurality of CBN particles in step 100; blending a reactive metal powder made of materials such as lithium, beryllium, calcium, strontium, magnesium, titanium, zirconium, aluminum, gallium, indium, tungsten, hafnium, chromium, cobalt, nickel, vanadium, tantalum, niobium and iron with the CBN particles in step 105; compressing the blended mixture in step 110; subjecting the compressed mixture to high pressure and high temperature in step 115; and recovering the corroded CBN particles in step 120. The CBN particles are preferably single crystal CBN particles. The reactive metal powder may be, for example, zirconium. For example, the ratio of reactive metal powder to CBN particles may be 1:10 to 10:1. Due to the method, the average weight loss experienced by the CBN particles may be greater than about 5%. In step 115, the temperature may be above about 1300°C, and the pressure may be above about 3 GPa.

[0029] More specifically, to produce the eroded CBN particles of the present invention, about 10 to about 80 weight percent CBN particles and about 20 to about 90 weight percent zirconium particles are mixed using any suitable mixing method that achieves a homogeneous mixture. For example, the weighed zirconium portion and the CBN particle portion can be placed in a jar, sealed, and inserted into a mixing device for at least about 1 hour, or about 30 minutes to about 1 hour. A binder can be optionally added to the mixture prior to mixing. The binder provides lubricity to the particle surface, thereby enabling a denser packing and closer contact between the metal powder and the CBN. The binder also helps to hold the compact together as a green body.

[0030] The mixture is then compressed to produce a close mixture of CBN particles and zirconium particles. Any method can be used to compress the CBN particles and zirconium particles, as long as they form a close mixture and the particles are in very close contact with each other. One method for compressing the mixture can be to place the mixture in a fixed mold set on a press. In the mold pressing, the mixture is subjected to a pressure between about 5000 and about 50000 psi, between about 10000 and about 40000 psi, or between about 15000 and about 30000 psi to form pellets. Isostatic pressing with deformable tooling can also be used to achieve close contact. Alternatively, the mixture can be compressed by, for example, pressing the mixture into a thin sheet of a few millimeters to a few inches thick by a high-pressure compaction roller or a briquetting roller. The formed sheet can then be cut into smaller parts for further processing. Another method of compressing the mixture of zirconium and CBN particles includes mixing and extruding the mixture under pressure. Granulating the mixture of CBN and zirconium particles via a granulator or tumbling the mixture in a tumbling device is also an alternative method that can be used to compress the mixture. Other methods of compressing a mixture of zirconium and CBN particles include injection molding, pressing the mixture into a container, and tape casting. The pellets, bricks, briquettes, or cakes formed by these methods can then be further processed as described below. Alternatively, a single CBN particle can be coated with metal particles by ion implantation, sputtering, spray drying, electrolytic coating, electroless coating, or any other suitable method, as long as the zirconium and CBN particles are in close contact with each other.

[0031] After compressing the mixture of CBN and zirconium particles, the compressed mixture, which may be pellets, aggregates, or other compressed forms, is placed in a furnace and heated to a temperature in the range of about 900° C. to about 2300° C. in a hydrogen atmosphere, a vacuum atmosphere, or an inert gas atmosphere. For example, a temperature of about 1000° C. to about 1400° C., about 1100° C. to about 1400° C., or about 1300° C. may be used. The compressed mixture may be heated for a time period in the range of about five minutes to about five hours. For example, a time period in the range of about thirty minutes to about two hours or about one hour to about two hours may be used.

[0032] Unlike the prior etching process, the compressed mixture is also subjected to high pressure during this heating. For example, the compressed mixture can be subjected to pressures in the range of about 3 to about 6 GPa. The reason for this is related to the thermodynamic properties of boron nitride. CBN is thermodynamically unstable under normal atmospheric temperature and pressure conditions. Instead, it is kinetically trapped in the CBN phase. When heated during the prior etching process, at least some of the CBN can be transformed into HBN (which is the thermodynamically preferred phase of boron nitride under such conditions), thereby significantly reducing the TI of the CBN particle group. Specifically, the TI reduction obtained in such a process is generally about 30. In the present invention, the use of high pressure during etching prevents the CBN from being transformed into HBN because CBN is the thermodynamically preferred phase of boron nitride under the selected temperature and pressure conditions. This reduces the TI reduction caused by the etching process, but cannot completely eliminate it because the etching itself reduces the TI of the CBN particle group. Specifically, the TI reduction in the etching process of the present invention is only about 10 to 20. As a result, the present invention can provide an etched CBN particle group with a high TI.

[0033] Although specific exemplary temperatures and pressures have been provided, any temperature and pressure combination that meets the following two objectives can be used. First, the temperature should be high enough to cause the desired corrosion of the CBN particles by the reaction of the CBN with the nitride-forming metal. Second, the temperature and pressure should be selected to ensure that the boron nitride remains in the CBN phase and does not re-enter the HBN phase (or enter a third phase). In other words, the temperature and pressure should be selected to keep the boron nitride in the CBN phase. Preferably, this second objective is met throughout the etching process to prevent any conversion of CBN to HBN.

[0034] After etching is complete and the compressed mixture of CBN and reactive metal particles has cooled, the etched CBN particles are recovered by dissolving the compressed mixture in a common acid. Acids that may be used include hydrochloric acid, hydrofluoric acid, nitric acid, and specific combinations thereof. The acid is added in an amount ranging from 100:1 to 1000:1 (by volume) of acid to the compressed mixture. The mixture is then heated to, for example, between about 100° C. and about 120° C. for a time of about 6 hours to about 8 hours. Next, the solution is cooled, the released CBN particles are settled, and the solution is decanted. These recovery steps are repeated until substantially all of the reactive metals, metal nitrides, and metal borides are digested.

[0035] Depending on the furnace conditions selected, a greater or lesser reaction can occur between the metal and the CBN. The more the metal powder corrodes into the CBN, the more nitrides and borides are formed, and the more weight the CBN loses. In order to completely dissolve the nitrides and borides, a larger amount of acid or other dissolution treatment can be used. The CBN particles are then washed, for example in water, to remove the acid and residues. Subsequently, the CBN particles are dried in an oven, air-dried, microwave-dried or by other drying methods known in the art.

[0036] CBN particles of the present invention can be used in many applications, including polishing, grinding, cutting, polishing, dicing, sintering abrasive or abrasive compacts, wires for wire saws and honing. Typically, the roughened surface of the CBN particles helps to retain the particles in a tool or resin bond system. The roughened surface can also provide a higher material removal rate and better free cutting ability. In a specific exemplary embodiment, for example, the CBN particles are introduced into tools such as grinding wheels, fixed abrasive wires, honing tools, cutting blades, polishing films, chemical mechanical polishing (CMP) pad dressers, polishing agents and composite CBN wear-resistant coatings.

[0037] Figure 2 and 3 is a SEM image of CBN particles. Figure 2 shows multiple CBN particles before corrosion, while Figure 3 One of these CBN particles is shown after the etching process of the present invention. Figure 2 A plurality of CBN particles 200 can be seen in the figure, each of which includes a plurality of faces 205. The surface of the faces 205 is smooth. However, after etching, such a surface is shown to have pits and grooves. For example, in Figure 3 In the embodiment of the present invention, the eroded CBN particle 300 comprises a face 305 having a plurality of etch pits 310 and a plurality of grooves 315. In the present invention, these surface features are micron-scale and submicron-scale. That is, the width of the etch pits 310 is generally between about 500nm and about 1.5μm, and the width of the grooves 315 is generally between about 500nm and about 5μm and about 30μm in length. The depth of both the etch pits and the grooves is between about 100nm and 1μm.

[0038] Similar to Figure 3 , Figure 4 is a high magnification (5000x) SEM image of the surface of an etched CBN particle of the present invention. In this image, the dark areas extend deeper into the particle than the light areas. Again, the surface is characterized by pits 400 and grooves 405. Isolated pits 400 and grooves 405 are visible. Figure 4Analysis of the corroded CBN particles provides an estimate of the percentage of the particle that is covered by the etch pits 400 or grooves 405. A conservative estimate is that 20% of the particle surface is covered by the etch pits 400 or grooves 405, while a moderate estimate is 41% and an aggressive estimate is 60%. Figures 5 to 7 The analysis also provides information on the size of the pits 400 and the grooves 405. The widths of the pits 400 and the grooves 405 are both less than about 1 μm, and the length of the grooves 405 is up to about 6 μm. Figure 8 As shown. Preliminary cross-sectional scanning electron microscopy analysis shows that the depth of the etch pits 400 and the grooves 405 are both less than about 1 μm. Typically, a plurality of etched cubic boron nitride particles are produced, wherein each cubic boron nitride particle contains a plurality of etch pits and a plurality of grooves, and the toughness index of the particle group is about 10 to about 20 points lower than that of an unetched, non-rough cubic boron nitride particle group having the same chemical composition, crystal structure and shape.

[0039] experiment

[0040] In the development of the present invention, a variety of different CBN particle populations were produced. These different particle populations help illustrate the benefits provided by the present invention.

[0041] In the first experiment, a CBN particle population with an aggressively eroded surface and a low TI was produced. Although this particle population exhibited excellent wetting behavior and good crystal retention during grinding due to the eroded surface, the TI was considered too low. Fig. 9 and Fig.10 The CBN particle population of the first experiment is shown before and after corrosion, respectively.

[0042] In the second experiment, a CBN particle group with an actively corroded surface and a medium TI was produced. Again, this particle group exhibited excellent wetting behavior and good crystal retention during grinding due to the corroded surface. However, the TI was still considered too low. Fig.11 The CBN particle population of the second experiment after corrosion is shown.

[0043] In the third experiment, a CBN particle group with a slightly corroded surface and a relatively high TI was produced. This particle group exhibited acceptable wetting behavior, crystal retention, and TI during grinding. Fig.12 and 13 The CBN particle population of the third experiment before and after corrosion is shown respectively.

[0044] In each of the first three experiments, etching was performed at atmospheric pressure. In the fourth experiment, etching was performed at high pressure according to the present invention. The produced CBN particle population had an actively etched surface with a uniform sub-micron surface pattern and a high TI.

[0045] The results of these experiments are plotted in Fig.14 In the figure, experiments 1 to 4 are labeled as EXP1 to 4. In addition, two uncorroded CBN particle groups are plotted, labeled as CBN-400 and CBN-500. Fig.14 As can be seen, surface roughness and TI are generally inversely correlated. One outlier is the population of CBN particles of the present invention, which exhibit both a rough surface and a high TI.

[0046] Based on the above, it should be readily apparent that the present invention provides a population of CBN particles having both a high TI and a highly corrosive surface. Although certain preferred embodiments of the present invention have been described, it should be understood that various changes or modifications may be made without departing from the spirit of the present invention. For example, oxides or metals such as nickel or titanium may cover the particles, or the particles may be coated with a layer of glass, wherein the percentage of glass weight is preferably less than 10% of the particle weight. In general, the present invention is intended to be limited only by the scope of the appended claims.

Claims

1. A plurality of etched single crystal cubic boron nitride particles, comprising: a compressed blended mixture etched at a temperature above 1300°C and a pressure of 3 GPa, the compressed blended mixture comprising 20 wt% to 90 wt% of a reactive zirconium powder, and 10 wt% to 80 wt% of a plurality of single crystal cubic boron nitride particles, one or more of the etched single crystal cubic boron nitride particles each having a plurality of etch pits and a plurality of grooves, wherein each of the plurality of etch pits has a width of 500 nm to 1.5 μm and a depth of 100 nm to 1 μm, wherein each of the plurality of grooves has a length of 5 μm to 30 μm and a depth of 100 nm to 1 μm, the etched single crystal particle group having an actively etched surface having a uniform submicron surface pattern and a high toughness index, the toughness index of the etched particle group being 10 to 20 points lower than that of an unetched, non-roughened cubic boron nitride particle group having the same chemical composition and crystal structure, and The etched particle group does not contain hexagonal boron nitride.

2. The etched single-crystal cubic boron nitride particles according to claim 1, wherein the particle size of the etched single-crystal cubic boron nitride particles is 10 μm to 1000 μm.

3. The etched single crystal cubic boron nitride particle of claim 1, wherein the particle surface covered by the etch pits and the grooves is 20% to 60%.

4. The etched single crystal cubic boron nitride particle of claim 1, wherein the etched single crystal cubic boron nitride particle is coated with a glass layer.

5. The etched single crystal cubic boron nitride particle of claim 4, wherein the weight percentage of the glass layer is less than 10% of the weight of the etched single crystal cubic boron nitride particle.

6. The etched single crystal cubic boron nitride particle of claim 1, wherein the etched single crystal cubic boron nitride particle is covered with an oxide.

7. The etched single crystal cubic boron nitride particle of claim 1, wherein the etched single crystal cubic boron nitride particle is covered with a metal.

8. The etched single crystal cubic boron nitride particle of claim 7, wherein the metal is nickel.

9. The etched single crystal cubic boron nitride particle of claim 7, wherein the metal is titanium.

10. A method of making a population of corroded single crystal particles, comprising: blending 20 to 90 weight percent of a reactive zirconium powder with 10 to 80 weight percent of a plurality of single crystal cubic boron nitride particles to form a blended mixture; compressing the blended mixture to form a compressed mixture; subjecting the compressed mixture to a temperature above 1300° C. and a pressure of 3 GPa, wherein the temperature is controlled to cause corrosion of the plurality of single crystalline cubic boron nitride particles by reacting the single crystalline cubic boron nitride particles with the reactive zirconium powder to form a plurality of eroded single crystalline cubic boron nitride particles, and the temperature and pressure are controlled to maintain the boron nitride in a cubic boron nitride phase; and recovering the plurality of etched single crystal cubic boron nitride particles from the compressed mixture to form the population of etched single crystal particles, wherein the corroded single crystal particle group has an actively corroded surface having a uniform submicron surface pattern and a high toughness index, the toughness index of the corroded particle group being 10 to 20 points lower than that of an uncorroded, non-roughened cubic boron nitride particle group having the same chemical composition and crystal structure, and The etched particle group does not contain hexagonal boron nitride.

11. The method of claim 10, wherein the etched single crystal cubic boron nitride particles have a particle size of 10 μm to 1000 μm.

12. The method of claim 10, wherein each of the plurality of etched single-crystal cubic boron nitride particles comprises a plurality of etch pits and a plurality of grooves, wherein each of the plurality of etch pits has a width of 500 nm to 1.5 μm and a depth of 100 nm to 1 μm, and wherein each of the plurality of grooves has a length of 5 μm to 30 μm and a depth of 100 nm to 1 μm.

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