Bonded abrasive article and method of making

(54) Title: CONNECTED ABRASIVE ARTICLE AND METHOD (57) Summary: MANUFACTURING (30) Unionist Priority: 14/03/2007 us 60 / 894,873 (73) Holder (s): Saint-Gobain Abrasifs, Saint-Gobain Abresives, INC.

(72) Inventor (s): Cecile Jousseaume, Gilles Querei, Paul S. Dando, Richard W. Hall (74) Attorney (s): Dannemann .Siemsen, Bigler & Ipanema Moreira (86) International Request: pct us2008056884 of 13 / 03/2008 (87) International Publication: wo 2OO8 / H29i4de 18/09/2008

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Cool the Cgado abrasive article to form a polycrietalin binding matrix

Descriptive Report of the Invention Patent for ABRASIVE LINKED ARTICLE AND MANUFACTURING METHOD.

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 TECHNIQUE

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 in such a way that during grinding the abrasive grains are easily removed from the bonding matrix, reducing the efficiency of the grinding or polishing process.

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 embodiment, a bonded abrasive article is provided which includes abrasive grains including cubic boron nitride within a bonding matrix which is made of a silicate. The bonded abrasive also includes a reaction product at the interface between the abrasive grains and the bonding matrix comprising a transition metal nitride.

According to a second embodiment, a method is provided for making a bonded abrasive which includes providing a glass powder made of a transition metal oxide compound. The method further includes combining the glass powder with abrasive grains having cubic boron nitride and forming the glass powder and the abrasive grains to form an unfinished article. The method further includes sintering the unfinished article at a transformation temperature to form abrasive grains in a glassy bonding matrix, such that at the transformation temperature the transition metal oxide compound changes to a transition metal nitride compound at the interface of the abrasive grains and the vitreous bonding matrix. BRIEF DESCRIPTION OF THE DRAWINGS

The present description can be better understood, and its innumerable 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.

Figure 2a is an image illustrating a portion of a bonded abrasive article formed in accordance with embodiments described herein.

Figure 2b is an image illustrating a portion of a bonded abrasive article formed according to conventional techniques.

Figure 3 is a graph showing the modulus of elasticity (MOE) of bonded abrasive articles formed according to the modalities described here in comparison with a Comparative Sample.

Figure 4 is a graph illustrating the rupture module (MOR) of bonded abrasive articles formed according to the modalities described here in comparison with a Comparative Sample.

Figure 5 is a graph illustrating the hardness of bonded abrasive articles formed according to the modalities described here in comparison with a Comparative Sample.

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 an abrasive bonded according to an embodiment is formed. The process is started at step 101 providing a glass powder that includes a transition metal oxide reagent. 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 may 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-dMO₂-in₂O₅. As illustrated by the equation, the composition of the glass powder can include metal oxides and, in particular, more than one metal oxide, such that the oxides are present together as a compound of oxide material. In a particular embodiment, the glass powder includes metal oxide compounds having monovalent cations (M¹⁺), with, for example, the metal oxide compounds represented by the generic formula M₂O. Suitable metal oxide compositions represented by M₂O may include compounds such as Li₂O, Na₂OK₂O 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 may include metal oxide compounds having divalent cations (M²⁺), 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 cations (M³⁺), 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, Y₂C&gt; 3, Fe₂O₃, BÍ2O3 and l_a₂C&gt; 3.

In particular, as indicated in the general equation above, the glass powder can include metal oxide compounds having cations of a valence state M⁴⁺, as represented by MO₂. MO compositions₂ particularly suitable include SiO₂, ZrO₂ and TiO₂.

In addition, the glass powder can include metal oxide compounds having cations of an M valence state⁵⁺, particularly those metal oxide compounds represented by the generic formula M2O5. Suitable metal oxide compositions represented by M2O5 can include compounds, for example, V₂O₅ and Nb2Os.

Also with reference to the composition of the glass powder represented by the generic equation aM2O-bMO-cM₂O3-dMO2-eM₂O5, the coefficients (a, b, c, d, e) are provided to indicate the amount (in mol%) of each of the different types of metal oxide compounds (M₂O, MO, M2O3, MO₂ and M2O5) 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 (molar fraction) of the metal oxide compounds M₂Glass powder is generally in the range of about 0.30 &lt;to &lt;0. According to a particular embodiment, the amount of the metal oxide compounds M₂Glass powder is in the range of about 0.15 &lt;to &lt;0 and, more particularly, in the range of about 0.10 &lt;to &lt;0.

With reference to the presence of the metal oxide compounds MO containing a divalent cation M²⁺, 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 between about 0.60 &lt;b &lt;0. According to a particular embodiment, the amount of metal oxide compounds MO is comprised in a range between about 0.45 &lt;b &lt;0 and, more particularly, in a range between about 0.35 &lt;b &lt;0, 15.

In addition, the amount of M2O3 metal oxide compounds containing a trivalent cation M³⁺ in glass powder it is represented by the coefficient c. In this way, the total amount (molar fraction) of the M2O3 oxide compounds is generally within the range of about 0.60 &lt;c &lt;0. According to a particular embodiment, the amount of M2O3 metal oxide compounds in the glass powder is generally in the range of about 0.40 &lt;c &lt;0 and, more particularly, in the range of about 0, 30 &lt;c &lt;0.10.

The amount of MO metal oxide compounds₂ containing an M cation⁴⁺ as described in the general equation aM2O-bMO-cM₂O3-dMO2-eM₂O5 is represented by the coefficient d. In general, the total amount (molar fraction) of the MO2 oxide compounds in the glass powder is between about 0.80 &lt;d &lt;0.20. In a particular embodiment, the amount of MO2 metal oxide compounds in the glass powder is in the range of about 0.75 &lt;d &lt;0.30 and, more particularly, in the range of about 0.60 &lt; d &lt;0.40.

The presence of M2O5 metal oxide compounds containing an M⁵⁺ as described in the general equation aM2O-bMO-cM₂O3-dl \ / IO2-eM2O5 is represented by the coefficient e. In general, the total amount (molar fraction) of the M2O5 oxide compounds in the glass powder is between about 0.20 &lt;d &lt;0. In a particular embodiment, the amount of M2O5 metal oxide compounds in the glass powder is comprised in a range between about 0.15 &lt;d &lt;0 and, more particularly, in a range between about 0.10 &lt;d &lt; 0.01.

With reference to metal oxide compounds MO2 and as described above, a particularly suitable metal oxide compound MO2 is silicon oxide (S1O2), 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 no more than about 70 mol%, or even no 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%. Thus, the amount of silicon oxide in the glass powder is generally between about 30 mol% and about 70 mol% and, particularly, between about 40 mol% and about 60 mol%.

With particular reference to other metal oxide compounds, 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 reference to modalities that use 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% to about 30% mol mol.

According to other modalities, the glass powder includes at least one of magnesium oxide (MgO) and lithium oxide (Li₂O), particularly 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% to 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, particularly in addition to silicon oxide and, more particularly, in addition to aluminum oxide and silicon 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 a composition of aluminum silicate and lithium.

In other embodiments, the glass powder may include a certain content of barium oxide (BaO), particularly in addition to silicon oxide and, in some embodiments, in addition to a system containing aluminum oxide and silicon oxide. Thus, the amount of barium oxide in the glass powder is generally not more than about 45 mol%, such as 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 a composition of barium and aluminum silicate.

In other embodiments, the glass powder contains a certain amount of calcium oxide (CaO), as for example in addition to a glass powder containing silicon oxide and in particular modalities, in a glass powder containing aluminum oxide and aluminum oxide. silicon. 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 ranging from about 0.5 mol% to about 20 mol% and, particularly in a range between 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. Thus, calcium oxide can form an oxide compound, for example, magnesium aluminum calcium calcium silicate (CMAS) or barium magnesium aluminum calcium silicate (CBAS).

As described above, glass compositions can include other metal oxide compounds. According to a particular embodiment, the glass powder composition includes boron oxide (B2O3). 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%.

With particular reference to the transition metal oxide reagents in the glass powder, as used in this context, the term transition metal oxide reagent refers to a selected group of transition metal oxide compounds that are provided in the powder glass and react during the sintering of the bonded abrasive to form a metal nitride compound. Accordingly, suitable transition metal oxide reagents include TiO₂, Cr₂O₃, V₂O_5l ZrO₂ and Nb₂O₅ and their combinations or complex oxides.

Although the above description was directed to the presence of generic oxide compounds, such as MO, M₂O, M₂O₃, M₂O₅ and MO₂, the following description is particularly directed to the presence of these metal oxide compounds which are used herein as transition metal oxide reagents as described above. In general, the total amount of the transition metal oxide reagents in the glass powder is not more than about 25 mol%. According to a particular embodiment, the total amount of the transition metal oxide reagents in the glass powder may be less, such as not more than about 20 mol%, for example not more than 15 mol% or even not more than about 10 mol%. Typically, the total amount of the transition metal oxide reagents is in the range of about 1.0 mol% to about 20 mol%, and particularly in the range of about 2.0 mol% and about 15 mol%.

With particular reference to the TiO transition metal oxide reagent₂, this reagent may be present in addition to other oxides, particularly in addition to silicon oxide and, in particular, in addition to aluminum oxide and silicon oxide. In general, the glass powder contains an amount of titanium oxide of not more than about 20 mol%. According to another embodiment, the glass powder includes an amount not exceeding 15 mol% of TiO₂. Typically, glass powder compositions containing TiO transition metal oxide reagent₂ use an amount in the range of about 1.0 mol% to about

15 mol% and, more particularly, in a range between about 2.0 mol% and about 10 mol%.

With particular reference to the Cr transition metal oxide reagent₂O₃, this reagent may be present in addition to other oxides, particularly in addition to silicon oxide and, in particular, in addition to aluminum oxide and silicon oxide. In general, the amount of chromium oxide in the glass powder is not more than about 20 mol%. Furthermore, the glass powder may contain less, for example, not more than about 15 mol% of Cr₂O₃. Typically, glass powder compositions containing the Cr transition metal oxide reagent₂O₃ they use an amount in the range of about 1.0 mol% to about 15 mol% and, more particularly, in the range of about 2.0 mol% to about 10 mol%.

With particular reference to the transition metal oxide reagent ν₂Οδ, in general, this reagent is present in addition to other oxides, particularly in addition to silicon oxide and, in particular, in addition to aluminum oxide and oxide and silicon. In general, the glass powder includes no more than about 20 mol% of V₂O₅. According to another embodiment, the glass powder includes not more than 15 mol% of V₂The. Typically the transition metal oxide reagent V₂O₅ it is used in an amount ranging from about 1.0 mol% to about 15 mol% and, more particularly, in a range between about 2.0 mol% and about 10 mol%.

With particular reference to the presence of ZrO₂, this reagent may be present in addition to other oxides, particularly in addition to silicon oxide and, in particular, in addition to aluminum oxide and silicon oxide. As a transition metal oxide reagent in glass powder, glass powder generally contains no more than about 20 mol% of ZrO₂. According to another embodiment, the glass powder includes no more than 15 mol% of ZrO₂. Typically, the transition metal oxide reagent is present in an amount in the range of about 1.0 mol% to about 15 mol% and, more particularly, in the range of about 2.0% in mol and about 10 mol%.

With particular reference to the Nb2O transition metal oxide reagent₅, this reagent may be present in addition to other oxides, particularly in addition to silicon oxide and, in particular, in addition to aluminum oxide and silicon oxide. In general, the glass powder contains an amount of Nb₂O5 not more than about 20 mol%. According to another embodiment, the glass powder includes not more than 15 mol% of Nb₂O5. Typically, glass powder compositions containing the Nb transition metal oxide reagent₂O₅ they use an amount between about 1.0 mol% and about 15 mol% and, more particularly, between about 2.0 mol% and about 10 mol%.

After providing the glass powder in step 101, the process continues in step 103 by combining the glass powder with the abrasive grains comprising cubic boron nitride 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 in such a way 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 60% by volume.

With reference to abrasive grains, abrasive grains include hard, abrasive materials and, particularly, include superabrasive materials such as cubic boron nitride. In addition, according to a particular embodiment, the abrasive grains include cubic boron nitride and, more particularly, the abrasive grains consist essentially of cubic boron nitride. In certain embodiments, a certain percentage of abrasive grains, which are usually 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 the total abrasive grains, such as not more than about 25% by volume or even not more than about 10% by volume. volume.

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.

With reference to the amount of glass powder combined with the abrasive grains in the mixture, the mixture can include not less than about 10% by volume of glass powder, such as, for example, not less than about 15% by volume of glass powder. glass. In addition, the amount of glass powder is limited, such 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 400% 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 binding materials may 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 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 (for example, 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, for example, not more than about 20% by volume, or even no more than about 15% by volume of the pore former . According to a particular embodiment, the mixture includes an amount of pore former comprised in a range between about 1.0% by volume and about 35% by volume and, more particularly, comprised in a range between 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 mixture of abrasive grains, 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 abrasive grains and 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 the formation of the unfinished article in step 105, the process continues in step 107 and includes pre-firing of the unfinished article. 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 above 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 ° C. According to a particular embodiment, the heating is complete between a temperature of about 22 ° C and about 850 ° C.

After pre-burning the unfinished article in step 107, the process continues in step 109, by sintering the unfinished article at a transformation temperature to form a bonded abrasive article including abrasive grains in a bonding matrix and a compound reaction product of transition metal nitride at the interface of the abrasive grains and the bonding matrix. In general, the transformation temperature is a temperature that is sufficient to change a substantial portion of the transition metal oxide reagent present in the glass powder to a transition metal nitride compound. Accordingly, the transformation temperature is, in general, not less than about 800 ° C. Other embodiments use a higher transformation temperature, for example, not less than about 1000 ° C, or not less than about 1200 ° C, or even not less than about 1300 ° C. The transformation temperature is, in general, in the range between about 1000 ° C and about 1800 ° C and, particularly, in the range between about 1100 ° C and about 1500 ° C.

In general, sintering takes place 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 one 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, such that the atmosphere essentially consists of nitrogen. 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 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, this process is carried out for a particular duration. In general, the sintering is carried out for a duration of not less than about 10 minutes. According to another embodiment, the sintering is carried out for a duration, for example, not less than about 60 minutes, or even not less than about 240 minutes at the sintering temperature. Typically, sintering takes place between about 20 minutes and about 4 hours, and particularly between about 30 minutes and about 2 hours.

In addition, during sintering at the transformation temperature, the bonding matrix, in general, has a high content of an amorphous phase, for example, not less than about 50% by volume of amorphous phase. More typically, the binding matrix has a higher content of amorphous phase, such as not less than about 60% by volume or not less than about 70% by volume, or even not less than about 80% by volume . The high content of amorphous phase facilitates the transformation of the transition metal oxide reagent into a transition metal nitride compound at the interface of the abrasive grains and the bonding matrix.

After sintering step 109, the bonded abrasive can be subjected to an additional optional processing in step 111, which includes a cooling operation to form a bonding matrix having a polycrystalline ceramic phase. For example, the bonded abrasive can be subjected to controlled cooling and optional controlled crystallization to facilitate crystallization of the bonding matrix material. In these operations, in general, the cooling rate of the sintering temperature does not exceed about 50 ° C / minute. Other modalities may use a smaller gradient, such as, for example, not exceeding about 40 ° C / minute, or even not exceeding about 30 ° C / minute. According to a particular mode, 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.

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 crystallization temperature for not less than about 20 minutes, 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 particularly in the range of about 1 hour to about 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 these embodiments using a cooling operation, the bonding matrix can have a significant crystalline ceramic phase, such that no less than 50% by volume of the bonding matrix is ​​crystalline. According to a particular embodiment, not less than about 60% by volume, or not less than about 75% by volume, or even not less than about 90% by volume of the binding matrix can be crystalline.

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 in the range of about 1.0 microns to 100 microns.

In general, the composition of the crystallites of the polycrystalline ceramic phase can include silicon oxide, aluminum oxide or a combination of both. Thus, crystallites from the polycrystalline ceramic phase may include crystals such as beta quartz, which may incorporate other metal oxides incorporated into the initial glass powder, 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 cordierite, enstatite, safirine, anortite, celsian, diopside, spinel and beta spodumene, where beta spodumene in particular is found in a solid solution.

In addition, a portion of the binding matrix can also include an amorphous phase. The amorphous phase, like the polycrystalline ceramic phase, 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 quantity, such that it is present in an amount not exceeding about 40% by volume, such as, 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 from about 0% by volume to about 40% by volume and, more particularly, in a range between about 5.0% by volume and about 20% by volume.

In the final formed bonded abrasive article, the abrasive grains generally comprise no 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 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 bonded abrasive article includes a degree of porosity that is not less than about 5.0% by volume 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 not at all less than about 30% by volume of the total volume of the bonded abrasive. Furthermore, 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 not more than about 250 microns, for example, not more than about 100 microns, or even not more than about 75 microns. According to a particular embodiment, the average pore size is comprised in a range between about 1.0 microns and about 500 microns and, particularly, in a range between about 10 microns and about 250 microns.

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 that were initially present in the initial glass powder, with the exception of the transition metal oxide reagents. That is, the bonding matrix comprises substantially the same composition as the glass powder, particularly, this includes the metal oxide compounds described above and, particularly, complex metal oxide compounds and, more particularly, silicate based compositions, such as, for example, an aluminum silicate composition, MAS, LAS, BAS, CMAS or CBAS.

As described above, the bonding matrix has substantially the same metal oxide compounds as the initial glass except for the transition metal oxide reagent, which, during sintering, is transformed in situ into a metal nitride compound. . As used in this context, transition metal nitride compounds include those compounds that have been added to the initial glass powder as a transition metal oxide reagent and exist in the final formed bonded abrasive as a transition metal nitride. Accordingly, transition metal nitride compounds include TiN, CrN, VN, ZrN and NbN or their combinations or complex nitride compounds.

In particular, the total amount of the transition metal nitride compounds in the bonded abrasive is, in general, not more than about 20 mol%. According to another embodiment, the total amount of one or more transition metal nitride compounds is not more than about 15 mol%, such as, for example, not more than about 10 mol%. The total amount of the transition metal nitride compound in the bonded abrasive is typically in the range of about 1.0 mol% to about 20 mol% or, particularly, in the range of about 4 mol, 0 mol% and about 15 mol%.

With reference to a particular transition metal nitride compound, the bonded abrasive generally includes no more than about 15 mol% of TiN. According to another embodiment, the bonded abrasive includes not more than about 10 mol% of TiN, for example, not more than about 8.0 mol% or even not more than about 6.0 mol% of TiN. The TiN content in the final bonded abrasive formed is between about 1.0 mol% and about 15 mol% and, particularly, between about 4.0 mol% and about 10 mol% mol%

The final formed bonded abrasive can include other transition metal nitrides, for example, CrN. In general, the bonded abrasive, in general, includes no more than about 15 mol% CrN. According to another embodiment, the bonded abrasive includes not more than about 10 mol% of CrN, for example, not more than about 8.0 mol% or even not more than 6.0 mol% of CrN. The content of CrN in the final bonded abrasive formed is generally between about 1.0 mol% and about 15 mol% and, particularly, between 4.0 mol% and about 10 mol%.

Other transition metal nitrides, such as VN, may be present in the bonded abrasive article and, in general, the bonded abrasive 22 includes no more than about 15 mol% of VN. According to another embodiment, the bonded abrasive includes not more than about 10 mol% of VN, for example, not more than about 8.0 mol% or even not more than 6.0 mol% of VN. The content of VN in the final formed bonded abrasive is generally between about 1.0 mol% and about 15 mol% and, particularly, between 4.0 mol% and about 10 mol%.

The final formed bonded abrasive article may include other transition metal nitrides, for example, ZrN. In general, the bonded abrasive, in general, includes no more than about 15 mol% of ZrN. According to another embodiment, the bonded abrasive includes no more than about 10 mol% of ZrN, such as, for example, no more than about 8.0 mol% or even no more than about 6.0 mol% of ZrN. The ZrN content in the final formed bonded abrasive is generally between about 1.0 mol% and about 15 mol% and, particularly, between about 4.0 mol% and about 10 mol%.

Other transition metal nitrides, for example, NbN, may be present in the bonded abrasive article, and in general, the bonded abrasive includes no more than about 15 mol% NbN. In general, the bonded abrasive, in general, includes no more than about 15 mol% NbN. According to another embodiment, the bonded abrasive includes no more than about 10 mol% of NbN, such as, for example, no more than about 8.0 mol% or even no more than about 6.0 mol% of NbN. The content of NbN in the final formed bonded abrasive is generally between about 1.0 mol% and about 15 mol% and, particularly, between 4.0 mol% and about 10 mol%.

With reference also to the presence of the transition metal nitride compound in the bonded abrasive, in general, the nitride compound is at the interface between the abrasive grains and the bonding matrix, so that it is in direct contact with the abrasive grains. According to one embodiment, no more than about 50% by volume of the total content of the transition metal nitride compound present in the bonded abrasive is in direct contact with the abrasive grains. Furthermore, the amount of transition metal nitride compound in direct contact with the abrasive grains can be greater, such as, for example, not less than about 60% by volume or not less than about 75% by volume, or even not less than about 95% by volume of the total volume of the transition metal nitride compound in the bonded abrasive.

Since the transition metal nitride compound can be formed in direct contact with the abrasive grains and at their interface and the bonding matrix, in general, the transition metal nitride compound covers no less than about 30 % of the total available surface area of ​​the abrasive grains. According to other embodiments, the transition metal nitride compound covers a larger amount of the abrasive grains, for example not less than about 40% or not less than about 50%, or even not less than about 75% of the total available surface area of ​​the abrasive grains.

In general, the bonding matrix is ​​a highly uniform phase such that it has an amorphous phase, crystalline phases or a combination of both as described above, but particularly the bonding matrix has limited porosity and bubbles. Typically, the binding matrix is ​​no more than about 10% by volume of bubbles compared to the total volume of the binding matrix. According to a particular embodiment, no more than about 5.0% by volume of the binding matrix is ​​comprised of bubbles, for example, no more than about 2.0% by volume or even no more than about 1 , 0% by volume.

The coefficient of thermal expansion of the bonding matrix material is typically low, such as not more than about 80x10 '⁷/ K '¹. According to a particular embodiment, the connection matrix has a thermal expansion coefficient of not more than about 60x10 '⁷/ 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/ K¹ and about 80x10 '⁷/ K '¹.

In general, the post-sintering bonding matrix 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 ​​in the range between about 90 MPa and about 150 MPa.

In addition to these characteristics, the post-sintering 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, such as not less than about 1.5 MPa m^1/2, or less not less than about 2.0 MPa m^1/2.

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 40 MPa or 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.

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 in a range between about 40 GPa and about 200 GPa and particularly in a range between about 60 GPa and about 140 GPa.

EXAMPLES

With reference to figure 2, the first image, figure 2a, illustrates a portion of an abrasive article bonded according to the modalities presented here. As shown in Figure 2a, the bonded abrasive portion includes abrasive grains 205 within a bonding matrix 207. This sample includes a polycrystalline ceramic phase bonding matrix having an aluminum and magnesium silicate composition. The sample shown in figure 2a was burned at 1320 ° C for 60 minutes in a nitrogen atmosphere and was cooled at a rate between 3.0 ° C / minute and 8.0 ° C / minute. The second image, figure 2b, illustrates a portion of a bonded abrasive article made according to other processes, particularly abrasive grains 209 within a matrix 211. This sample is a bonded abrasive article having a partially crystallized bonding matrix comprising an aluminum and lithium silicate. The bonded abrasive in figure 2b was burned at 1000 ° C for 4 hours in nitrogen. Each sample included 50% by volume of cubic boron nitride abrasive grains and 16% by volume of 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 as a binder. The mixture also included about 14% by volume of natural porosity. Each sample had approximately 34% by volume of porosity, 16% by volume of bonding matrix and 50% by volume of abrasive grains.

In comparison, the bonding matrix 211 of the abrasive bonded in Figure 2b illustrates a high degree of porosity and blistering, particularly among abrasive grains 209. In addition, bonding matrix 211 is not uniform in color, illustrating the presence of different phases, particularly an amorphous phase and a crystalline phase. It will be understood that the porosity and blistering between the abrasive grains 209 of the bonding matrix 211, defines stress concentration sites within the bonding matrix 211, thereby creating a bonding matrix more susceptible to fracture and breakage. By comparison, the bonding matrix 207 of figure 2a includes a uniform material having a high degree of crystallinity, a low degree of porosity and substantially no bubble formation between the abrasive grains, as well as effective wetting of the abrasive grains 205.

The following provides particular examples of bonded abrasive articles formed according to modalities provided herein in comparison to a bonded abrasive article made according to other processes. Table 2 below illustrates glass powder compositions (% by weight), or matrix bond compositions of three samples (Samples 1-3) formed in accordance with the modalities described herein and a glass powder composition (Comparative Sample) formed according to other processes. Table 2

<td></td><td>S1O2</td><td>Fe2O3</td><td>AI2O3</td><td>Dog</td><td>MgO</td><td>At₂O</td><td>K₂O</td><td>B2O3</td><td>Uncle₂</td><td>Zr₂O</td><td>ZnO</td>

<td>Sample 1</td><td> 48,5</td><td> 0,20</td><td> 28,9</td><td> 0,09</td><td> 12,10</td><td> 0,07</td><td> 0,02</td><td> 2,48</td><td> 7,75</td><td> 0,14</td><td></td>

<td>Sample 2</td><td> 44,70</td><td> 0,02</td><td> 27,9</td><td> 0,05</td><td> 14,30</td><td> 0,10</td><td></td><td> 4,85</td><td> 7,90</td><td></td><td></td>

<td>Sample 3</td><td> 55,70</td><td> 0,02</td><td> 17,50</td><td> 0,30</td><td> 19,60</td><td> 0,17</td><td> 0,09</td><td> 2,90</td><td> 3,73</td><td></td><td></td>

<td>Sample Comparative</td><td> 50,80</td><td> 0,10</td><td> 18,9</td><td> 0,15</td><td> 18,8</td><td> 0,03</td><td></td><td> 5,36</td><td> 0,02</td><td></td><td> 5,93</td>

The formation of the Samples illustrated in Table 2 were formed using the same processes provided above according to the description for the Samples in Table 1. Each of the glass compositions was ground to a powder having an average particle size of about 12 microns and a high content of amorphous phase, in the order of at least 80% by 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. After formation, the unfinished articles were pre-burned at a temperature of about 850 ° C to develop organic and low volatility species and assist in the formation of the final bonded abrasive article.

After the pre-firing process, the unfinished articles were sintered. Samples 1-3 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. Samples 1-3 were cooled at a rate between 8.0 ° C / minute and 13 ° C / minute. The Comparative Sample was sintered at a temperature of 1050 ° C for about 60 minutes 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 3, a graph is provided that illustrates the modulus of elasticity for Samples 1-3 and the Comparative Sample. As illustrated by the graph in figure 3, Samples 1-3 demonstrate an improved modulus of elasticity 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 4, a graph is shown that provides the rupture module of Samples 1-3 and the Comparative Sample. In general, the bonded abrasive articles from Samples 1-3 demonstrate an improved breaking modulus over that of the Comparative Sample. Particularly, Samples 1-3 have a rupture modulus (MOR) greater than about 60 MPa, whereas the Comparative Sample has a MOR of 23 MPa. Particularly, Samples 1 and 2 have a MOR in excess of 70 and, particularly, Sample 1 has a MOR which is about 75, almost four times greater than the Comparative Sample.

With reference to figure 5, a graph is provided that illustrates the hardness of the bonded abrasive samples. In particular, each of Samples 1-3 demonstrates a greater hardness than that of the Comparative Sample. Samples 1-3 illustrate a hardness greater than 90 (Rockwell Hardness Scale H) and typically at least about 100. In particular, Samples 2 and 3 have a hardness in excess of 100 and Sample 3 has a hardness of almost 105. The Comparative Sample did not have enough hardness for accurate measurement but it is expected to have a hardness of less than 70.

According to the modalities presented here, bonded abrasive articles are provided which have improved properties. While certain references describe the formation of coated superabrasive particles in a vitreous bonding matrix, these descriptions are limited by their bonding matrix compositions, coating processes and forming processes. 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 with respect to the cost, effectiveness and reduced degradation of bonded abrasive components, i.e., abrasive grains. In addition, conventional coated superabrasives are typically cutting tools that have a metal bonding matrix, not bonded abrasive articles for grinding applications. In contrast, the embodiments presented here use a combination of different characteristics including bonding matrix compositions, sintering processes, in situ reactions and transformation of oxides to nitrides and crystallization processes. In addition, the final formed bonded abrasive articles presented here combine a variety of characteristics, particularly high porosity, superior wetting between the bond and the abrasive grains, a high strength bond matrix having low porosity and bubbles and reaction product of the compounds of transition metal nitride formed at the interface between the abrasive grains and the bonding matrix.

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.