Bonded abrasive article

CONNECTED ABRASIVE ARTICLE

FIELD OF THE INVENTION

The present invention relates to bonded abrasive articles, and particularly addressed to bonded abrasive articles that have a crystalline bonding matrix.

BACKGROUND OF THE INVENTION

In general, abrasives are used in various machining operations, ranging from fine polishing to the removal and cutting of raw material. For example, free abrasives composed of loose particles are used in suspensions for polishing applications, such as mechanical chemical polishing (CMP) in the semiconductor industry. Alternatively, the abrasives may be in the form of fixed abrasive articles, such as bonded and coated abrasives, which may include devices such as wheels, belts, rollers, discs and the like. In general, fixed abrasives differ from free abrasives in that fixed abrasives use abrasive grains or sand within a material matrix that fixes the position of the abrasive grains relative to each other. Common fixed abrasive sands may include alumina, silicon carbide, various minerals, such as garnet, as well as superabrasives such as diamond and cubic boron nitride (cBN). With particular reference to bonded abrasive articles, the abrasive sands are fixed in relation to each other in a bonded material. Although many different bonding materials can be used, vitrified bonding materials, such as amorphous phase glass materials, are common. However, the performance properties of conventional bonded abrasives such as, for example, aluminum oxide, silicon carbide, diamond and cubic boron nitride having vitrified bonds are limited by the nature of the bond and the composition of the abrasive grains. In particular, the connection between the bonding matrix and the abrasive grains may be insufficient such that during grinding the abrasive grains are easily removed from the bonding matrix, reducing the efficiency of the grinding process or

Petition 870180124254, of 08/31/2018, p. 21/45 polishing.

The industry continues to need bonded abrasives with improved properties. The properties of interest include mechanical stability, strength, service life and improved grinding performance.

DESCRIPTION OF THE INVENTION

According to a first aspect, a bonded abrasive article is provided which includes abrasive grains including cubic boron nitride (cBN) in a bonding matrix. The binding matrix includes a polycrystalline ceramic phase. The bonded abrasive has a porosity of not less than about 5.0% by volume and a rupture modulus (MOR) of not less than about 40 MPa.

According to a second aspect, a bonded abrasive is provided that includes abrasive grains including cubic boron nitride (cBN) 15 in a bonded matrix that includes a polycrystalline ceramic phase. The bonded abrasive has a porosity of not less than about 20% by volume and a rupture module (MOR) of not less than about 30 MPa.

According to another aspect, a method is provided which includes providing a glass powder, and combining the glass powder with non-stick grains including cubic boron nitride to form a mixture. The method further includes forming the mixture to form an unfinished article and sintering the unfinished article at a temperature of not less than about 1200 ° C to form a bonded abrasive comprising abrasive grains within a bonding matrix. The bonding matrix includes no less than about 25-50% by volume of a polycrystalline ceramic phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The present description can be better understood, and its numerous characteristics and advantages can become more evident to those skilled in the art through reference to the associated drawings.

Figure 1 is a flow chart illustrating a process for forming an abrasive article bonded according to an embodiment.

Figures 2a-2b are two micrograph images that illustrate portions of an abrasive article bonded according to one embodiment.

Figures 3a-3e are five micrograph images illustrating portions of bonded abrasive articles, each of the illustrated portions are taken from bonded abrasive articles burned at different temperatures.

Figure 4 is a graph that illustrates properties of a bonded abrasive as a function of the firing temperature according to a modality.

Figure 5 is a graph that illustrates the modulus of elasticity (MOE) of bonded abrasive articles formed according to the modalities described here.

Figure 6 is a graph that illustrates the rupture module (MOR) of bonded abrasive articles formed according to the modalities described here.

Figure 7 is a graph illustrating the hardness of bonded abrasive articles formed according to the modalities described herein.

Figure 8 is a graph that illustrates the wear of bonded abrasive articles formed according to the modalities described here.

The use of the same reference symbols in different drawings indicates similar or identical items.

DESCRIPTION OF THE MODE (S)

With reference to Figure 1, a flow chart is provided that illustrates a process by which a bonded abrasive is formed according to one embodiment. The process is started at step 101 by providing a glass powder. The powder is generally glassy (amorphous), so that no less than about 80% by volume of the glass is amorphous. According to a particular embodiment, the glass powder can include a higher content of amorphous phase, for example, not less than about 90% by volume, or even not less than about 95% by volume of amorphous phase. In general, the formation of a glass powder can be completed by mixing an appropriate proportion of raw materials and melting the mixture of raw materials to form a glass at high temperatures. After sufficient melting and mixing of the glass, the glass can be cooled (tempered) and ground to a powder.

In general, the glass powder can be further processed, for example by a grinding process, to provide a glass powder having a suitable particle size distribution. Typically, the glass powder has an average particle size of no more than about 100 microns. In a particular embodiment, the glass powder has an average particle size of not more than 75 microns, for example, not more than about 50 microns, or even not more than about 10 microns. However, the average particle size of the glass powder is typically in the range of about 5.0 microns to about 75 microns.

The composition of the glass powder can be described using the equation aM2O-bMO-cM₂O3-dl / 10O2. As illustrated by the equation, the composition of the glass powder can include more than one metal oxide, such that the oxides are present together as a compound of oxide material. In a particular embodiment, the glass includes metal oxide compounds having monovalent (1+) cations, such as, for example, the metal oxide compounds represented by the generic formula M₂O. Suitable metal oxide compositions represented by M₂O may include compounds such as L12O, Na2O, K₂O and CS2O.

According to another embodiment, and as provided in the general equation, the glass powder can include other metal oxide compounds. In particular, the glass powder can include metal oxide compounds having divalent (2+) cations, such as those metal oxide compounds represented by the generic formula MO. Suitable metal oxide compositions represented by MO can include compounds, for example, MgO, CaO, SrO, BaO and ZnO.

In addition, the glass powder may include metal oxide compounds having trivalent (3+) cations, particularly those metal oxide compounds represented by the generic formula M₂O₃. Suitable metal oxide compositions represented by M2O3 can include compounds, for example, AI2O3, B2O3, Y2O3 · Fe2C> 3, B2O3 and La2O3.

Particularly, as indicated in the general equation above, the glass powder may include metal oxide compounds having cations of a 4+ valence state, as represented by MO₂. In this way, the MO compositions₂ suitable ones include SiO₂, Uncle₂ and ZrO₂.

With reference also to the composition of the glass powder represented by the generic equation aM₂O-bMO-cM₂O3-dMO₂, the coefficients (a, b, c and d) are provided to indicate the quantity (molar fraction) of each of the different types of metal oxide compounds (M₂O, MO, M₂O₃, and MO₂) that may be present in the glass powder. Thus, coefficient a in general represents the total amount of metal oxide compounds M₂The glass powder. The total amount of the metal oxide compounds M₂Glass powder is generally in the range of about 0.30 <to <0. According to a particular embodiment, the total amount of the metal oxide compounds M₂Glass powder is in the range of about 0.15% to 0% and, more particularly, in the range of about 0.10% to 0%.

With reference to the presence of the metal oxide compounds MO containing a divalent cation, the total amount (molar fraction) of these compounds can be defined by the coefficient b. In general, the total amount of MO metal oxide compounds in the glass powder is in the range of about 0.60% b ^ 0. According to a particular embodiment, the amount of MO metal oxide compounds is in the range of about 0.45% b, 0 and, more particularly, in the range of about 0.35% b, 0, 15.

In addition, the amount of metal oxide compounds M₂O₃containing a kind of trivalent cation in the glass powder is represented by the coefficient c. Thus, the total amount (molar fraction) of the oxide compounds M₂O₃ it is, in general, comprised in a range between about 0.60 <c <0. According to a particular embodiment, the amount of metal oxide compounds M₂O₃ in glass powder it is, in general, comprised in a range between about 0.4Ctéc ^ 0 and, more particularly, in a range between about 0.30 <c <0.10.

The presence of metal oxide compounds MO₂ containing a kind of 4+ cation as described in the general equation aM₂O-bMOcM₂O₃-dMO₂ is represented by the coefficient d. In general, the total amount (molar fraction) of the oxide compounds MO₂ in the glass powder it is between about 0.80 ^ d £ 0.20. In a particular embodiment, the amount of metal oxide compounds MO₂ in the glass powder it is comprised in a range between about 0.75 £ d ^ 0.30 and, more particularly, in a range between about 0.60 <d <0.40.

With particular reference to metal oxide compounds MO₂, particular modalities use a glass powder that includes silicon oxide (SiO₂) such that the glass powder is a silicate-based composition. With particular reference to only the presence of silicon oxide in the glass powder, the glass powder typically includes no more than about 80 mol% of silicon oxide. According to another embodiment, the glass powder includes not more than about 70 mol%, or even not more than about 60 mol% of silicon oxide. Also, in particular embodiments, the amount of silicon oxide in the glass powder is not less than about 20 mol%. In this way, the amount of silicon oxide in the glass powder is, in general, comprised in a range between about 30 mol% and about 70 mol% and, particularly, in a range between approximately 40 mol% and about 60 mol%.

With additional reference to metal oxide compounds M₂C> 3, certain glass powder compositions include aluminum oxide (AI₂O₃) particularly in addition to silicon oxide, such that the glass powder is an aluminum silicate. Thus, with particular reference to only the presence of aluminum oxide, in general, the glass powder includes no more than about 60 mol% of AI₂O₃. In other embodiments, the glass powder may include aluminum oxide in smaller amounts, such as, for example, not more than about 50 mol% or even not more than about 40 mol%. Typically, the glass powder incorporates aluminum oxide in a range between about 5.0 mol% to about 40 mol% and, particularly in a range between about 10 mol% and about

30 mol%

According to a particular embodiment, the glass powder includes at least one of magnesium oxide and lithium oxide in addition to silicon oxide and, more particularly, in addition to silicon oxide and aluminum oxide. Thus, the amount of magnesium oxide in the glass powder is generally not more than about 45 mol%, such as not more than 40 mol%, or even not more than 35 mol%. Typically, glass powder compositions containing magnesium oxide use an amount in the range of about 5.0 mol% to about 40 mol% and, particularly, in the range of about 15% and about 35 mol%. Magnesium-containing aluminum silicate glasses can be referred to as MAS glasses having an aluminum and magnesium silicate composition.

According to another embodiment, the glass powder includes lithium oxide. Thus, the amount of lithium oxide in the glass powder is generally not more than about 45 mol%, such as not more than 30 mol% or even not more than 20 mol%. Typically, glass powder compositions containing lithium oxide use an amount in the range of about 1.0 mol% to about 20 mol% and, particularly, in the range of about 5.0 mol% mol and 15 mol%. Aluminum silicate glasses containing lithium can be referred to as LAS glasses having an aluminum and lithium silicate composition.

In other embodiments, the glass powder particularly includes barium oxide. Thus, the amount of barium oxide in the glass powder is generally not more than about 45 mol%, for example not more than 30 mol% or even greater than 20 mol%. Typically, glass powder compositions having barium oxide use an amount in the range of about 0.1 mol% to about 20 mol% and, more particularly, in the range of about 1.0 mol% mol and about 10 mol%. Barium-containing aluminum silicate glasses can be referred to as BAS glasses having an aluminum silicon and barium composition.

In other embodiments, the glass powder includes calcium oxide. Thus, the amount of calcium oxide in the glass powder in general is not more than about 45 mol%, for example, not more than 30 mol% or even more than 20 mol%. Typically, glass powder compositions having calcium oxide use an amount in the range of about 0.5 mol% to about 20 mol%, and particularly in the range of about 1.0 mol% and about 10 mol%. In some embodiments, calcium oxide is present in systems that use other metal oxide compounds mentioned above, particularly in combination with MAS and BAS glasses. Calcium oxide can form an oxide compound, for example, aluminum magnesium and calcium silicate (CMAS) or aluminum magnesium barium and calcium silicate (CBAS).

As described above, glass compositions can include other metal oxide compounds. According to a particular embodiment, the glass powder includes boron oxide. In general, the amount of boron oxide in the glass powder is not more than about 45 mol%, for example not more than 30 mol% or even not more than 20 mol%. Typically, glass powder compositions containing boron oxide use an amount ranging from about 0.5 mol% to about 20 mol% and, particularly in a range between about 2.0 mol% and about 10 mol%.

In another particular embodiment, the glass powder may include other metal oxides, as described above, for example, Na₂OK₂O, Cs₂O, Y₂O₃, Fe₂O₃, Bi₂O₃, There₂O₃, SrO, ZnO, TiO₂, P₂O₅ and ZrO₂. These metal oxides can be added as modifiers to control the properties and processability of the glass powder and the resulting bonding matrix. Typically, these modifiers are present in the glass powder in an amount not exceeding about 20 mol%. According to another embodiment, these modifiers are present in the glass powder in an amount not exceeding about 15 mol%, for example, not exceeding about 10 mol%. Typically, glass powder compositions with modifiers use an amount in the range of about 1.0 mol% to about 20 mol% and, more particularly, in the range of about 2.0 mol% and about 15 mol%.

After providing the glass powder in step 101, the process continues in step 103 by combining the glass powder with the abrasive grains to form a mixture. With reference to the composition of the mixture, in general the mixture includes not less than about 25% by volume of abrasive grains. According to a particular embodiment, the mixture includes not less than about 40% by volume of abrasive grains, for example not less than about 45% by volume, or even not less than about 50% by volume of abrasive grains . In addition, the amount of abrasive grains is limited such that the mixture generally includes no more than about 60% by volume of abrasive grains. In particular, the abrasive grains in the mixture are generally present in an amount ranging from about 30% by volume to about 55% by volume.

With reference to abrasive grains, in general, abrasive grains include hard, abrasive materials and, particularly, include superabrasive materials. According to a particular modality, in general, abrasive grains are superabrasive grains, such that they are diamond or cubic boron nitride (cBN). In a particular embodiment, the abrasive grains include cubic boron nitride and, more particularly, the abrasive grains consist essentially of cubic boron nitride.

In general, abrasive grains have an average grain size of no more than about 500 microns. In particular, the average grain size of the abrasive grains is not more than about 200 microns or even not more than about 100 microns. In general, the average grain size is in the range of about 1.0 microns to about 250 microns and, particularly, in the range of about 35 microns to about 180 microns.

According to one embodiment, abrasive grains have a major component of cubic boron nitride. In certain embodiments, a certain percentage of abrasive grains, which in general are normally cubic boron nitride, can be replaced by abrasive grains, such as aluminum oxide, silicon carbide, boron carbide, tungsten carbide and silicate. zirconium. Thus, the amount of abrasive grains replaced is, in general, not more than about 40% by volume of total abrasive grains, such as not more than about 25% by volume or even not more than about 10% by volume. volume.

With reference to the amount of glass powder combined with the abrasive grains in the mixture, the mixture may include not less than about 10% by volume of glass powder, for example, not less than about 15% by volume of glass powder. glass. In addition, the amount of glass powder is limited, so that the mixture includes no more than about 60% by volume of glass powder, such as no more than about 50% by volume of glass powder, or even not more than about 40% by volume of glass powder. In particular, the mixture in general includes an amount of glass powder ranging from about 10% by volume to about 30% by volume.

The mixing process can include a dry mixing process or a wet mixing process. In particular, the mixing process includes a wet mixing process, such that at least one liquid is added to facilitate the mixing of the glass powder and the abrasive grains. According to a particular embodiment, the liquid is water. In these embodiments, water is added in an adequate amount to facilitate proper mixing and, therefore, the mixture in general contains at least about 6.0% by volume of water, for example, at least about 10% by volume . In addition, the mixture generally includes no more than about 20% by volume of water, such as no more than about 15% by volume of water.

The mixture can include other additives, for example, a binder. In general, the binder is an organic material. Suitable binder materials can include materials that contain glycol (for example, polyethylene glycol), dextrin, resin, glue or alcohol (for example, polyvinyl alcohol), or combinations thereof. In general, the mixture includes not more than about 15% by volume of a binder, such as, for example, not more than about 10% by volume. According to a particular embodiment, the binder is provided in the mixture in a range comprised between about 2.0% by volume and about 10% by volume.

With reference to still other additives, the mixture may include pore builders or a pore-inducing material to facilitate the formation of a porous final bonded abrasive structure. Accordingly, pore builders, in general, include inorganic or organic materials.

Typically, suitable organic materials can include polyvinyl butyrate, polyvinyl chloride, wax (e.g., polyethylene wax), plant seeds, plant husks, sodium diamyl sulfosuccinate, methyl ethyl ketone, naphthalene, polystyrene, polyethylene, polypropylene , acrylic polymers, p-dichlorobenzene and combinations thereof. These pore formers are typically provided in particulate form such that upon heating the particulate material is developed and a pore is left behind. Accordingly, the pore former has an average particle size of no more than about 0.5 mm, or even no more than about 0.05 mm. In addition, suitable inorganic materials can include spheres of inorganic material, particularly hollow spheres of materials such as glass, ceramic or ceramic glass or combinations thereof.

Typically, the amount of pore former provided in the mixture is not more than about 35% by volume. In another embodiment, the mixture includes no more than about 30% by volume of the pore former, such as no more than about 20% by volume, or even no more than about 15% by volume of the pore former. pore. According to a particular embodiment, the mixture includes an amount of pore former ranging from about 1.0% by volume to about 35% by volume and, more particularly, from about 5% , 0% by volume and about 25% by volume.

In addition, it will be understood that the mixture may include natural porosity or the existence of bubbles or pores within the mass of the abrasive grain mixture, glass powder and other additives. Accordingly, this natural porosity can be maintained in the final bonded abrasive article depending on forming techniques. Thus, in particular embodiments, pore formers may not be used and the natural porosity in the mixture can be used and maintained throughout the forming and sintering process to form a final bonded abrasive article with the desired amount of porosity. In general, the natural porosity in the mixture is not more than about 40% by volume. Although, in particular modalities, the natural porosity in the mixture is less, for example, not more than about 25% by volume or not more than about 15% by volume. In general, the amount of natural porosity in the mixture is between about 5.0% by volume and about 25% by volume.

Although the mixing step may include mixing the glass powder, abrasive grains and other components described above, according to a particular embodiment, the binder and abrasive grains can first be mixed in the water. The water with the additional components (ie the abrasive grains and the binder) can then be combined with the glass powder and, if present, the pore former.

Referring once again to Figure 1, after mixing the glass powder with the abrasive grains in step 103, the method continues in step 105, forming the mixture to form an unfinished article. The formation of the mixture in an unfinished article includes forming processes that give the unfinished article the desired final contour or substantially the desired final contour. As used in this context, the term unfinished article refers to a part that is not fully sintered. Accordingly, forming processes can include processes such as, for example, casting, molding, extrusion and pressing, or combinations thereof. According to one embodiment, the forming process is a molding process.

After forming the unfinished article, the process continues on and covers 107 and includes a pre-firing step. In general, the pre-firing step includes heating the unfinished article to facilitate the development of volatiles (for example, water and / or organic materials or pore-forming). Thus, heating the mixture, in general, includes heating to a temperature higher than about room temperature (22 ° C). According to one embodiment, the pre-firing process includes heating the unfinished article to a temperature of not less than about 100 ° C, for example, not less than about 200 ° C, or even not less than about 300 ° Ç. According to a particular embodiment, the heating is complete between a temperature of about 22 ° C and about 850 ° C.

After pre-firing the unfinished article in step 107, the process continues in step 109, by sintering the unfinished article at a temperature of not less than about 1200 ° C, to form a densified bonded abrasive article having abrasive grains within the matrix binding. In particular, the unfinished article is sintered at a temperature of not less than about 1200 ° C, such that, in one embodiment, sintering is carried out at a temperature of not less than about 1250 ° C. More particularly, sintering can be carried out at higher temperatures, for example, not less than about 1300 ° C or even not less than about 1350 ° C. In general, sintering is carried out at a temperature between about 1200 ° C and about 1600 ° C and, particularly, in a temperature range between about 1300 ° C and about 1500 ° C .

In addition to sintering at high temperatures, sintering is generally carried out in a controlled atmosphere. According to one embodiment, this controlled temperature can include a non-oxidizing atmosphere. Examples of a non-oxidizing atmosphere can include an inert atmosphere, such as one that uses a noble gas. According to a particular modality, the atmosphere consists of nitrogen, for example, not less than about 90% by volume of nitrogen. Other modalities use a higher concentration of nitrogen, for example, not less than about 95% by volume, or even not less than 99.99% by volume of the nitrogen atmosphere. According to one embodiment, the sintering process in a nitrogen atmosphere begins with an initial evacuation of the ambient atmosphere to a reduced pressure of no more than about 5 kPa (0.05 bar). In a particular embodiment, this process is repeated 5 so that the sintering chamber is evacuated numerous times. After evacuation, the sintering chamber can be purged with oxygen-free gaseous nitrogen.

With reference also to the sintering process, in general, this process is carried out for a particular duration. In this way, sintering10 is carried out, in general, for a duration of not less than about 10 minutes, for example, not less than about 60 minutes or even not less than about 240 minutes at the sintering temperature. In general, the sintering takes place between about 20 minutes and about 4 hours and, in particular, between about 30 minutes and about 15 hours.

Referring once again to Figure 1, after the sintering step at 109, the process continues at step 111, which includes controlled cooling and in some systems a controlled crystallization process. In general, after sintering, the bonded abrasive article is processed by means of controlled cooling. In this way, the gradient from the sintering temperature can be controlled to facilitate crystallization of the bonding matrix material. Typically, the cooling rate is not more than about 50 ° C / minute, for example, not more than about 40 ° C / minute, or even not more than about 25-30 ° C / minute. According to a particular modality, cooling is carried out at a rate not exceeding about 20 ° C / minute.

In addition, controlled cooling and the crystallization process may include a waiting process where the bonded abrasive article is maintained at a crystallization temperature above the glass transition temperature (T_g) of the bonding matrix material. Typically, the bonded abrasive article can be cooled to a temperature of not less than about 100 ° C above T_g, for example, not less than about 200 ° C above T_g, or even not less than about 300 ° C above T_g. In general, the crystallization temperature is not less than about 800 ° C, for example, not less than about 900 ° C, or even not less than about 1000 ° C. In particular, the crystallization temperature is in the range of about 900 ° C to about 1300 ° C and, more particularly, in the range of about 950 ° C to about 1200 ° C.

During the crystallization and controlled cooling process, the bonded abrasive article is, in general, kept at the crystallization temperature for a duration of not less than about 10 minutes. In one embodiment, the bonded abrasive article is maintained at the temperature of crystallization for not less than about 20 minutes, such as, for example, not less than about 60 minutes or less not less than about 2 hours. Typical durations for keeping the abrasive bonded to the crystallization temperature are in the range of about 30 minutes to about 4 hours and, in particular, in the range of about 1 hour to about 2 hours. It will be understood that the atmosphere during this optional cooling and crystallization process is the same as the atmosphere during the sintering process and accordingly includes a controlled atmosphere, particularly an oxygen-rich, nitrogen-free atmosphere.

In the final formed bonded abrasive article, the abrasive grains generally comprise not less than about 25% by volume of the total volume of the bonded abrasive article. According to the modalities, in general, abrasive grains comprise not less than about 35% by volume, for example, not less than about 45% by volume, or even not less than about 50% by volume. total volume of the final formed bonded abrasive article. According to a particular embodiment, the abrasive grains comprise between about 35% by volume and about 60% by volume of the total volume of the final formed abrasive article.

In general, the bonding matrix is ​​present in an amount not exceeding about 60% by volume of the total volume of the final formed bonded abrasive article. Thus, the bonded abrasive, in general, includes no more than about 50% by volume of the bonding matrix, such as, for example, no more than about 40% by volume, or even no more than about 30% by volume . Accordingly, the bonding matrix is ​​generally present in an amount of between about 10% by volume and about 30% by volume of the total volume of the formed abrasive bonded article.

It will be understood that the binding matrix includes those compounds and particularly the proportion of the compounds in the initial glass powder as described above. That is, the bonding matrix comprises substantially the same composition as the glass powder, particularly, this includes metal oxide compounds, particularly complex metal oxide compounds and, more particularly, silicate-based compositions, such as a composition of aluminum silicate, MAS, LAS, BAS, CMAS or CBAS.

With reference also to the bonding matrix, in general, the bonding matrix includes a polycrystalline ceramic phase and, particularly, the bonding matrix includes not less than about 50% by volume of polycrystalline ceramic phase. According to a particular embodiment, the bonding matrix includes not less than about 75% by volume of the polycrystalline ceramic phase, such as, for example, not less than about 80% by volume or even not less than about 90% by volume. volume. According to a particular embodiment, the bonding matrix is ​​essentially comprised of a polycrystalline ceramic phase. Typically, the polycrystalline ceramic phase of the bonding matrix is ​​present in an amount between about 60% by volume and about 100% by volume.

In general, the polycrystalline ceramic phase includes a plurality of crystallites or crystalline grains that have an average size of not less than about 0.05 microns. In a particular embodiment, the average crystallite size is not less than about 1.0 microns, such as, for example, not less than about 10 microns or even not less than about 20 microns. In addition, the average crystallite size is generally no more than about 100 microns, such that the average crystallite size is comprised in a range between about 1.0 microns and 100 microns.

In general, the composition of the crystallites from the polycrystalline ceramic phase can include silicon oxide, aluminum oxide or a combination of both. In this way, crystallites from the polycrystalline ceramic phase may include crystals such as beta quartz, which may incorporate other metal oxides incorporated in the initial glass powder such as Li₂OK₂O, MgO, ZnO and AI₂O₃, in a solid solution. In particular, the polycrystalline ceramic phase can include an aluminum silicate phase. According to another particular embodiment, crystallites from the polycrystalline ceramic phase may include compounds of oxide crystals, such as, for example, cordierite, enstatite, safirine, anortite, celsian, diopside, spinel and beta spodumene, where beta spodumenium in particular it is found in a solid solution.

In addition to the polycrystalline ceramic phase, the bonding matrix also includes an amorphous phase. The amorphous phase, like the polycrystalline ceramic phase 15, can include silicon oxide and aluminum oxide and additional types of metal oxide that may be present in the original glass powder. Typically, the amorphous phase is present in an amount not exceeding about 50% by volume of the total volume of the binding matrix. Thus, an amorphous phase is present, in general, in a minority amount, 20 such that it is present in an amount not exceeding about 40% by volume, for example, not exceeding about 30% by volume , or less, such as not more than about 15% by volume. According to a particular embodiment, an amorphous phase is present in an amount between about 0% by volume to about 25 40% by volume and, more particularly, in a range between about 5.0% by volume and about 20% by volume.

In addition, the thermal expansion coefficient of the bonding matrix material is typically low, for example, no more than about 80x10 '⁷/ K '¹. According to a particular embodiment, the 30-connection matrix has a thermal expansion coefficient of not more than about 60x10⁷/ K '¹, for example, no more than about 50x10 '⁷/ K '¹, or even not more than about 40x10 '⁷/ K '¹. In this way, the thermal expansion coefficient of the bonding matrix is ​​typically comprised in a range between about 10x10 '⁷/ K '¹ and about 80x10 '⁷/ K '¹.

The post-sintering polycrystalline bonding matrix, in general, has a flexural strength of not less than about 80 MPa. In other embodiments, the flexural strength of the bonding matrix is ​​greater, for example not less than about 90 MPa, not less than about 100 MPa or, in some cases, not less than about 110 MPa. According to a particular embodiment, the flexural strength of the bonding matrix is ​​between about 90 MPa and about 150 MPa.

In addition to these characteristics, the post-sintering polycrystalline bonding matrix, in general, has a toughness of not less than about 0.8 MPa m^1/2. In other embodiments, the toughness of the bonding matrix can be higher, for example, not less than about 1.5 MPa m^1/2, or even not less than about 2.0 MPa m^1/2.

As described according to Figure 1, the forming process, in general, includes adding pore formers, such that the final bonded abrasive article includes a certain degree of porosity. Accordingly, the bonded abrasive article, in general, includes a degree of porosity that is not less than about 5.0% of the total volume of the bonded abrasive article. Typically, the amount of porosity is greater, such that the porosity is not less than about 10% by volume, for example, not less than about 15% by volume, about 20% by volume, or even not less than about 30% by volume of the total volume of the bonded abrasive. Also, the amount of porosity is limited, such that the porosity is not more than about 70% by volume, for example, about 60% by volume, or even not more than about 50% by volume . According to a particular embodiment, the porosity of the bonded abrasive article is in the range of about 20% by volume to about 50% by volume. This porosity, in general, is a combination of open and closed porosity.

With reference also to the porosity of the bonded abrasive article, the average pore size, in general, is not greater than about 500 microns.

In one embodiment, the average pore size is no more than about 250 microns, for example, no more than about 100 microns, or even no more than about 75 microns. According to a particular embodiment, the average pore size is comprised in a range between 5 about 1.0 microns and about 500 microns and, particularly, in a range between about 10 microns and about 250 microns.

With reference to the properties of the bonded abrasive article, in general the bonded abrasive article formed has a breaking modulus (MOR) of not less than about 20 MPa. However, the MOR can be greater, for example, not less than about 30 MPa, or not less than about 40 MPa, for example, not less than about 50 MPa, or even not less than about 60 MPa. In a particular embodiment, the MOR of the bonded abrasive article is not less than about 70 MPa and is typically in the range of about 50 MPa to about 150 MPa.

• 15 With reference to the properties of bonded abrasive articles, according to one modality, the abrasive articles have an elasticity modulus (MOE) of not less than about 40 GPa. In another modality, the MOE is not less than about 80 GPa, for example, not less than about 100 GPa, and even not less than about 140 GPa. In general, the MOE of the bonded abrasive article is comprised in a range between about 40 GPa and about 200 GPa and particularly in a range between about 60 GPa and about 140 GPa.

Referring to Figure 2a, a first image 201 is shown which includes a portion of an abrasive bonded according to a mode25. The first image 201 illustrates abrasive grains 205 within a bonding matrix 207. In particular, the bonded abrasive article shown in Figure 2a was sintered at 1320 ° C for a duration of 60 minutes. In particular, the first image 201 illustrates the bonding matrix 207 in a substantially uniform phase, superior wetting between the bonding matrix 207 and the abrasive grains 205, which in turn demonstrates a significant bond between the bonding matrix 207 and the grains abrasives 205.

Figure 2b further illustrates a second image 203 of a portion of an abrasive bonded according to an embodiment. In particular, the second image 203 is an enlarged image compared to the first image 201 and illustrates an abrasive grain 209 within a bonding matrix 211. As illustrated in the second enlarged image 203, the bonding matrix 211 includes a crystalline phase and, in particular, exhibits a plurality of crystalline grains 213 that form the polycrystalline ceramic phase of the bonding matrix.

With reference to Figures 3a-3e, five micrographs are provided that illustrate portions of bonded abrasive articles, where each bonded abrasive article was sintered at a different temperature. Figure 3a shows a portion of a bonded abrasive article sintered at 950 ° C for 60 minutes. Figure 3b shows a bonded abrasive article sintered at 980 ° C for 60 minutes. Figure 3c shows a bonded abrasive article sintered at 1060 ° C for 60 minutes. Figure 3d illustrates a portion of a bonded abrasive article sintered at 1200 ° C for 60 minutes. Figure 3e illustrates a portion of a bonded abrasive article sintered at a temperature of 1340 ° C for 60 minutes. As illustrated, portions of bonded abrasive articles burned at low temperatures, particularly Figures 3a-3c, illustrate a bonding matrix that is non-coalesced, non-uniform and dispersed in small droplets by the abrasive grains which indicates little wetting of the bonding matrix abrasive grains. Alternatively, bonded abrasive articles sintered at elevated temperatures, particularly in Figures 3d and 3e, exhibit a bonding matrix that has improved coalescence, increased uniformity and connectivity within the bonding matrix and superior wetting of the abrasive grains.

With reference to Figure 4, a graph is provided that illustrates a graph of characteristics of bonded abrasive articles formed according to the modalities described herein. In particular, Figure 4 illustrates the modulus of elasticity (MOE), the rupture modulus (MOR), the hardness and the porosity of abrasive articles bonded as a function of the sintering temperature. As illustrated, each of the prepared samples has substantially the same porosity, such that the porosity is about 34% by volume. In addition, each sample was formed having the same composition of the binding matrix, such that the binding matrix comprised about 45% by weight of SiO₂, about 28 wt% AI2O3, 14 wt% MgO, about 5.0 wt% B2O3, about 8.0 wt% TIO2. Accordingly, each of the samples included about 16% by volume of bonding matrix, 34% by volume of porosity and about 50% by volume of abrasive grains.

With reference to the modulus of elasticity (MOE), Figure 4 illustrates a generic trend, that is, as the sintering temperature increases, the modulus of elasticity increases. In particular, as illustrated, at a sintering temperature of about 950 ° C the modulus of elasticity is 25 GPa. However, as the sintering temperature increases, the modulus of elasticity increases such that about 1320 ° C the modulus of elasticity is almost 130 GPa. Figure 4 also illustrates another trend in relation to the MOE, notably that the MOE decreases for the sintered samples at temperatures in excess of about 1340 ° C.

With reference to the hardness of the bonded abrasive articles as a function of the sintering temperature, in general, the hardness of the bonded abrasive articles increases as the sintering temperature increases with a relatively constant porosity level. As illustrated, at a sintering temperature of about 1280 ° C the hardness is about 82 on the H Rockwell Hardness scale. As the sintering temperature increases to a temperature of around 1320 ° C, the hardness increases to a value greater than 100. Hardness measurements below 1280 ° C were not completed, since the bonded abrasive article was too soft for accurate measurements. Figure 4 further illustrates the hardness value of the bonded abrasive article which is shown to decrease after sintering at temperatures in excess of 1320 ° C.

With reference to the rupture module (MOR), in general, the MOR values ​​increase with increased sintering temperatures. Particularly, at a sintering temperature of about 950 ° C, the MOR is around 10 MPa, however, with increased sintering temperatures, the rupture modulus increases. Thus, at a sintering temperature above 1300 ° C, the bonded abrasive article has a MOR in excess of 50, such that at a sintering temperature of 1360 ° C the MOR is above 60 MPa.

EXAMPLES

The following provides particular examples of bonded abrasive articles formed according to modalities provided herein in contrast to a comparative sample of bonded abrasive article. The Table below illustrates glass powder compositions (% by weight), or eight matrix bound matrix compositions (Samples 1-8) formed according to the modalities described herein.

Table 1

<td>Ο c N</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>the CN cd</td><td>co cd lo</td>

<td>ID O CXJ 0-</td><td>σ&gt; co T "</td><td></td><td>CD CN</td><td>t—</td><td></td><td></td><td></td><td></td><td></td>

<td>O cxl L ·. N</td><td></td><td>xf O'</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>CXJ O I—</td><td>O CD xt</td><td>IO bb- '</td><td>xf O o '</td><td>I'm oo</td><td>o σ&gt;</td><td>CN O o</td><td>co b-_ co</td><td></td><td>CN oo</td>

<td>CO o CXJ CD</td><td>The to</td><td>oo xT CN</td><td>Γ'o CXÍ</td><td></td><td>LO oo xf</td><td>OO co</td><td>oo CN</td><td>the IO co '</td><td>co co to</td>

<td>the cd ca</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>O CXJ ω o</td><td>CXJ 00</td><td></td><td></td><td></td><td></td><td></td><td></td><td>the boo '</td><td></td>

<td>O CXJ kr</td><td>CD CD o</td><td>CXI oo '</td><td></td><td></td><td></td><td>O o</td><td>σ&gt; oo</td><td></td><td></td>

<td>O 04 CD z</td><td>CD CD o '</td><td>bo o</td><td>00 oo</td><td>o σ&gt; o</td><td>O O</td><td>the CN T—</td><td>bo</td><td>oo</td><td>co o o '</td>

<td>O CXJ l_i</td><td>CD CXJ b-</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

<td>MgO</td><td>σ&gt; CO cxí</td><td>CXÍ</td><td>CD CXÍ CXI</td><td>r- CN</td><td>co xf</td><td>CN CN</td><td>co cd</td><td>the LO b- '</td><td>oo oo '</td>

<td>Dog</td><td>CD σ&gt; o '</td><td>CD oo</td><td>oo Ό *</td><td>IO co o</td><td>IO oo</td><td>IO O_</td><td>o co o</td><td>CD oo</td><td>LO το '</td>

<td>CO o CXI &lt;</td><td>CD LO σ&gt;</td><td>The CXI co</td><td>xf σ&gt;</td><td>CD CT&gt;</td><td>CD bJ CN</td><td>CO D&gt; T—</td><td>LO B-</td><td>bxl · CN</td><td>the color-</td>

<td>co O OI Φ LU</td><td>O</td><td>o CXI o '</td><td>CXI oo</td><td>CN O o</td><td>CN O o</td><td>CN O o</td><td>CN o_ o</td><td>CN O o</td><td>the το</td>

<td>CXJ o ώ</td><td>with the CD</td><td>IO 00 • ^ r</td><td>CN with LO</td><td>b · 1θ LO</td><td>bxf xl</td><td>CN with LO</td><td>bio IO</td><td>τ'- CD xf</td><td>00 the IO</td>

<td></td><td>v— (ü Lω o E &lt;</td><td>CXJ s tf o E &lt;</td><td>CO CD L_ tf o E &lt;</td><td>xJ · CD tf OE &lt;</td><td>LO E tf o E &lt;</td><td>CD CD Ltf OE &lt;</td><td>bs tf o E &lt;</td><td>00 CD ϊ— rf— &lt;ω o E &lt;</td><td>CD &gt; rf— · _ ^roCD 5 · 4 = ^rotf Qê ^ANDAnd the &lt;O</td>

Each of the glass compositions was ground to a powder with an average particle size of about 12 microns and a high amorphous phase content of about 100 volume%. The glass powder was then combined with the cubic boron nitride abrasive grains having an average grain size of about 115 microns. The mixture included 50% by volume of abrasive grains of cubic boron nitride and 16% of the glass powder. In general, each of the mixtures also included additives in amounts of 15% by volume of water and 5.0% by volume of polyethylene glycol for use with binder. The mixture also included about 14% by volume of natural porosity.

The samples were then formed into unfinished articles by molding the mixture using a compression mold. Once formed, the unfinished articles were pre-burned at a temperature of about 850 ° C to develop organic substances and species with low volatility and assist in the formation of the final abrasive article.

After the pre-firing process, the unfinished articles were sintered. Sample 1 was sintered at a temperature of 1000 ° C for 4 hours. On the other hand, Samples 2-8 were sintered at elevated temperatures typically between 1320 ° C and 1380 ° C for 60 minutes, in an atmosphere rich in nitrogen at about 1.1 atm. Each of Samples 1-8 was cooled at a rate of between 8.0 ° C / minutes and 13 ° C / minutes. The Comparative Sample was sintered at a temperature of 1050 ° C for about 60 minutes in an atmosphere rich in nitrogen. All samples had approximately 34% by volume of porosity, 16% by volume of bonding matrix and 50% by volume of abrasive grains.

With reference to Figure 5, a graph is provided that illustrates the modulus of elasticity for Samples 1-8 and the Comparative Sample. As illustrated by the graph in Figure 5, Samples 1-8 demonstrate a modulus of elasticity greater than that of the Comparative Sample. Samples 1-8 each demonstrate an elastic modulus in excess of 100 GPa and typically at least 120 GPa and in some cases in excess of 140 GPa. By comparison, the Comparative Sample has an elastic modulus of approximately 63 GPa.

With reference to Figure 6, a graph is shown that provides the rupture module of Samples 1-8 and the Comparative Sample. In general, the bonded abrasive articles from Samples 1-8 demonstrate an improved breaking modulus over that of the Comparative Sample. Particularly, Samples 1-8 have a rupture modulus greater than about 60 MPa, while the Comparative Sample has a rupture modulus of 23 MPa. In addition, most Samples 1-8 have a rupture modulus greater than 65 MPa, and some exhibit a rupture modulus in excess of 70 MPa.

With reference to Figure 7, a graph is provided that illustrates the hardness of the bonded abrasive samples. In particular, each of Samples 1-8 demonstrates a greater hardness than that of the Comparative Sample. Particularly, Samples 1-8 illustrate a hardness greater than 80 (Rockwell Hardness Scale H), and typically a hardness in excess of 90 and some samples exhibit a hardness greater than 100. The hardness of the Comparative Sample was not measured since it was too soft, however, the hardness was expected to be less than 70.

In general, the bonded abrasive articles provided herein exhibit improved grinding performance, particularly improved wear. Accordingly, the present bonded abrasive articles exhibit improved wear that is not less than about 5.0% or even not less than about 10% compared to comparative samples obtained according to other techniques.

Figure 8 illustrates wear values ​​(cm³/ (N / mm²) s) for Samples 1 and 3-8, provided in Table 1. The wear data illustrated for Samples 1 and 3-8 were obtained by performing the following test procedure. Each of the tested samples was subjected to a grinding process using an abrasive coated with SiC (100 mesh). Each sample was subjected to 10-second grinding cycles at an initial load of 10 N, and increasing in increments of 10 N to 50 N (i.e., 20N, 30N, 40N and 50N). Each sample was subjected to three grinding cycles for each load and the abrasive pad coated with SiC was changed for each cycle. After each grinding cycle, the length loss and weight loss of the samples was recorded and the average wear values ​​for each of the samples was calculated. As illustrated, the wear data indicates that bonded abrasive articles formed according to the modalities described herein have improved grinding performance and, in particular, improved wear values.

According to the modalities presented here, bonded abrasive articles are provided which have improved properties. Although certain references describe the formation of a bonded abrasive article having a crystalline bonding matrix, these descriptions are limited by their bonding matrix compositions, forming processes, low porosity articles and the absence of cubic boron nitride. Typically, conventional bonded abrasives typically add fluxes to the bonding matrix composition to lower the required sintering temperature. Lower sintering temperatures are believed to be advantageous in terms of the cost, effectiveness and reduced degradation of bonded abrasive components, i.e., abrasive grains. In contrast, the processes described herein use a combination of different characteristics including controlled matrix compositions, sintering temperatures, controlled cooling and crystallization treatment and atmosphere. In addition, the bonded abrasive articles formed herein have high porosity, superior wetting between bonding and abrasive grains, high crystalline content in the bonding matrix and improved hardness and strength.

Although the invention has been illustrated and described in the context of specific modalities, it is not intended to be limited to the details presented, since various modifications and substitutions can be made without, in any way, departing from the scope of the present invention. For example, additional or equivalent substitutes can be provided and additional or equivalent production steps can be used. Thus, other modifications and equivalents of the invention described herein can occur to those skilled in the art using no more than routine experimentation, and it is believed that all these modifications and equivalents are within the scope of the invention as defined by the following claims.