An in-situ grown mullite whisker reinforced low-temperature ceramic binder, its preparation method and application

Abstract

This invention relates to an in-situ grown mullite whisker-reinforced low-temperature ceramic binder and its preparation method: 35–45 wt% metakaolin, 10–15 wt% Al(OH)3, and 15–25 wt% silica sol are used as precursors for in-situ growth of mullite whiskers; 0.3–1.5 wt% NH4VO3 and 0.5–2.0 wt% AlF3 are used as a whisker growth composite catalyst; and 25–30 wt% of a quaternary system B2O3-Al2O3-SiO2-ZnO low-melting-point borosilicate glass powder is used as the matrix. The process involves batching, ball milling, drying, sieving, molding, and sintering. The binder sample exhibits a three-point flexural strength of 120–132 MPa and a fracture toughness K0. IC 3.0–3.7 MPa·m 0.5 This invention eliminates the need for an external whisker dispersion step, allowing for in-situ precipitation of the reinforcing phase through a single firing process. The process is simple, with high batch consistency, making it suitable for mass production. The use of a low-boron, low-melting-point glass matrix free of alkali metal oxides avoids erosion and dissolution of the whisker-reinforcing phase. Through the synergistic reinforcement effect of in-situ whiskers and weak interfaces, the strength of the ceramic binder is increased by ≥50%, and its toughness by ≥58%.

Description

Technical Field

[0001] This invention belongs to the field of inorganic non-metallic materials technology, specifically relating to a ceramic binder that can be sintered without pressure below 950℃, and particularly to a low-temperature ceramic binder that achieves high strength and high toughness through in-situ growth of mullite whiskers, its preparation method, and its application in superhard abrasives. Background Technology

[0002] Ceramic-bonded superhard abrasives have become one of the most promising tools in modern grinding processes due to their advantages such as high strength, high elastic modulus, good self-sharpening properties, high cutting sharpness, resistance to clogging, and good thermal stability. They are increasingly widely used in high-speed, high-efficiency, and precision grinding. To avoid thermal damage to diamond / cBN superhard abrasives and fully utilize their cutting capabilities, ceramic binders must possess the characteristics of "low melting point, high strength, and high toughness." Traditional ceramic binders suffer from problems such as high sintering temperature, high brittleness, and low tensile strength. Introducing fluxes such as B2O3 / alkali metal oxides to lower the sintering temperature, along with the introduction of reinforcing phases, is a common solution. However, excessive flux introduction can lead to the glassy phase formed at high temperatures eroding / dissolving the reinforcing phase, severely weakening or even completely destroying the reinforcing effect. Furthermore, excessively strong interfacial bonding between the reinforcing phase and the glass matrix can prevent whisker pull-out, resulting in a decrease in binder toughness instead of an increase. Therefore, there is an urgent need to develop new processes for reinforcing binders.

[0003] Currently, to improve the toughness of ceramic binders, the technical route of "adding whiskers / fibers + mechanical dispersion" is often adopted (such as patent technologies CN106737255B, CN102399084A, CN105252433A, etc.). However, this method suffers from drawbacks such as difficulty in dispersing the reinforcing material, the formation of stress concentration points after agglomeration, and large fluctuations in mechanical properties. The patent technology "A method for toughening and reinforcing ceramic binders for superhard abrasives" (CN109048693A) discloses a method of "adding fiber-whisker-graphene oxide composite toughening and reinforcing ceramic binder". Carbon fibers, SiC whiskers and graphene oxide are placed in three beakers respectively, and dispersed through a "three-step dispersion" process of magnetic stirring-ultrasound-re-stirring. Then, they are mixed with ceramic binder slurry, gel-molded, and sintered at 700℃. While this technology achieves a certain degree of toughening, it has the following inherent drawbacks: ① Long process chain: It requires pre-dispersing the three reinforcing phases separately, taking a total of 6-8 hours, with the dispersion process alone accounting for more than 40% of the entire production cycle; ② Poor dispersion uniformity: Micron-nano-scale whiskers are extremely prone to agglomeration. Even after prolonged ultrasonication, "whisker-rich areas" and "whisker-free areas" will still form in the slurry, resulting in a density gradient in the green blank and local stress concentration after sintering; ③ High equipment investment: It requires high-power ultrasonic equipment, multiple sets of magnetic stirring and defoaming devices, and is sensitive to slurry viscosity, pH, and temperature, resulting in poor batch stability during scale-up production; ④ Risk of interface contamination: Commercial dispersants or organic activators often remain on the surface of the added whiskers. These impurities cannot be completely removed at 700℃, and residual carbon easily reacts with alkali metal oxides in the binder to generate CO / CO2, causing an increase in interfacial porosity and reducing the bonding strength.

[0004] The existing "addition-dispersion" route for reinforcing ceramic binders has encountered bottlenecks in terms of large-scale production, low cost, and high consistency. There is an urgent need for a new process for reinforcing low-temperature ceramic binders that "does not require the addition of whiskers, does not require lengthy dispersion, and can form a uniform whisker-reinforcing phase in situ in one step of firing."

[0005] Based on this, this application was developed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and address the technical problems in current reinforced ceramic binder technologies, such as "difficulty in dispersing the added reinforcing phase, erosion of the reinforcing phase by the glass matrix, and poor reinforcement and toughening effects." This invention provides a method for preparing an in-situ grown mullite whisker-reinforced low-temperature ceramic binder. This method generates a uniform whisker reinforcing phase through in-situ reaction, avoiding whisker erosion. A weak interface layer exists on the whisker surface, resulting in high reinforcement and toughening efficiency. Furthermore, the process is simple and suitable for large-scale production.

[0007] This invention also provides an in-situ grown mullite whisker-reinforced low-temperature ceramic binder prepared by the above method and its application.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: An in-situ grown mullite whisker-reinforced low-temperature ceramic binder, comprising a main material and auxiliary materials; the main material is primarily composed of the following raw materials by weight percentage: Metakaolin 35–45 wt%, Al(OH)3 10–15 wt%, silica sol 15–25 wt%, glass powder 25–30 wt%; The excipients include NH4VO3 and AlF3, wherein NH4VO3 accounts for 0.3–1.5 wt% of the main material and AlF3 accounts for 0.5–2.0 wt% of the main material.

[0009] Specifically, the SiO2 content of the silica sol can be 30–40%.

[0010] This invention provides a method for preparing the above-mentioned in-situ grown mullite whisker-reinforced low-temperature ceramic binder, which includes the following steps: (1) Ingredients: Weigh each ingredient according to the proportions; (2) Ball milling: The weighed raw materials are placed in a polyurethane ball mill jar for ball milling to obtain a slurry after ball milling; (3) Drying and sieving: The slurry is vacuum dried and sieved to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under a pressure of 80–100 MPa for 30–60 s to obtain a ceramic green body; (5) Sintering: The ceramic green body is heated to 850–950℃ in air atmosphere and held for 0.5–1.5 h for pressureless sintering, followed by furnace cooling, to obtain the in-situ grown mullite whisker-reinforced low-temperature ceramic binder sample strip. The sample strip was tested, and the performance indicators are as follows: Three-point flexural strength: 120–132 MPa; fracture toughness K IC 3.0–3.7 MPa·m 0.5 .

[0011] Specifically, in step (2), alumina balls are used for ball milling in the presence of anhydrous ethanol, with a rotation speed of 200–400 rpm and a milling time of 3–6 h.

[0012] Furthermore, in step (3), the slurry is vacuum dried at 80–90°C for 10–12 hours and then passed through a 300–400 mesh sieve.

[0013] This invention also provides a superhard abrasive tool, which is prepared from the aforementioned in-situ grown mullite whisker-reinforced low-temperature ceramic binder and superhard abrasive. The superhard abrasive tool has a firing temperature ≤950℃ and a grinding ratio ≥130.

[0014] Furthermore, the superhard abrasive can be CBN, with a particle size of 100 / 120 or 120 / 140, and an abrasive concentration of 25–35 vol%.

[0015] The present invention also provides a method for preparing the above-mentioned superhard abrasive, which involves mixing the in-situ grown mullite whisker-reinforced low-temperature ceramic binder powder with superhard abrasive, dry pressing at 90±10 MPa for 40±10 s to obtain a grinding wheel blank; heating the grinding wheel blank to 850-950℃ in air atmosphere and holding it at that temperature for 0.5-2 h for pressureless sintering, and then cooling it in the furnace to obtain the final product.

[0016] The present invention also provides the application of the above-mentioned superhard abrasive in precision grinding of quenched steel, high-speed steel, cast iron, titanium alloy, high-temperature alloy, etc., that is, the superhard abrasive can be used for efficient precision grinding of quenched steel, high-speed steel, cast iron, titanium alloy, high-temperature alloy, etc.

[0017] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder of this invention has the following material design concept: Low melting glass matrix: The matrix is ​​based on low melting point glass powder of the B2O3-Al2O3-SiO2-ZnO quaternary system, wherein the B2O3 content is ≤12wt%, the ZnO content is 8–15wt%, and the glass softening point is 620–650℃. In-situ mullite whiskers: using metakaolin, Al(OH)3, and silica sol as precursors, and adding NH4VO3+AlF3 as a composite catalyst for whisker growth, mullite whiskers are precipitated by in-situ reaction with pressureless sintering at ≤950℃. Weak interface layer: By introducing vanadium to form a weak interface transition layer of a certain thickness on the surface of in-situ mullite whiskers, a synergistic enhancement mechanism of crack deflection and whisker pull-out is achieved.

[0018] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder of this invention uses metakaolinite, Al(OH)3, and silica sol as reaction precursors, and NH4VO3+AlF3 as a whisker growth composite catalyst, and is generated through an in-situ reaction by pressureless sintering at ≤950℃. The binder, after pressureless sintering at 850–950℃, exhibits a three-point flexural strength ≥120MPa and a fracture toughness K0. IC ≥3.0MPa·m 0.5 .

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1) This invention eliminates the need for an external whisker dispersion step, allowing for in-situ precipitation of the reinforcing phase through a single sintering process. The process is simple, with high batch consistency, making it suitable for mass production. 2) This invention uses a low-boron, low-melting-point glass matrix that does not contain alkali metal oxides, thus avoiding the erosion and dissolution of the whisker-reinforcing phase; 3) This invention achieves the crack deflection and pull-out toughening mechanism of whiskers through the synergistic effect of in-situ whiskers and weak interfaces, which improves the strength of ceramic binders by ≥50% and the toughness by ≥58%. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] An in-situ grown mullite whisker-reinforced low-temperature ceramic binder and its preparation method are disclosed. The specific steps of the preparation method described in this embodiment are as follows: (1) Ingredients: Weigh each of the main raw materials according to the following weight percentages: metakaolin 35–45 wt%, Al(OH)3 10–15 wt%, silica sol (30–40% SiO2) 15–25 wt%, and glass powder 25–30 wt%. Add 0.3–1.5 wt% of NH4VO3 and 0.5–2.0 wt% of AlF3 by weight of the main material. (2) Ball milling: The weighed raw materials are placed in a polyurethane ball milling jar and mixed with "alumina balls + anhydrous ethanol" in a ball milling process. The speed is set to 200-400 rpm and the time is 3-6 h to obtain the ball milled slurry. (3) Drying and sieving: The ball-milled slurry is vacuum dried at 80–90℃ for 10–12 hours and then passed through a 325-mesh sieve to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under pressure of 80–100 MPa for 30–60 s to obtain a ceramic blank with dimensions of 50×10×4 mm; (5) Sintering: The ceramic blank is heated to 850–950℃ in air atmosphere and sintered without pressure for 0.5–1.5h. It is then cooled in the furnace to obtain the in-situ grown mullite whisker reinforced low temperature ceramic binder sample strip.

[0022] The binder uses a low-melting-point glass of the B2O3-Al2O3-SiO2-ZnO quaternary system as the matrix, wherein the B2O3 content is ≤12wt%, the ZnO content is 8–15wt%, and the glass softening point is 620–650℃.

[0023] The mullite whiskers are generated by in-situ reaction through pressureless sintering at ≤950℃, using metakaolin, Al(OH)3 and silica sol as reaction precursors and NH4VO3+AlF3 as a whisker growth composite catalyst.

[0024] The details will not be repeated in the examples.

[0025] In the following examples, all raw materials used are commercially available products that can be purchased directly, or can be prepared using conventional techniques in the art. For example, silica sol, with a SiO2 content of 30–40%, is a commercially available product.

[0026] Glass powder: a quaternary system of B2O3-Al2O3-SiO2-ZnO, wherein the B2O3 content is ≤12wt%, the ZnO content is 8–15wt%, and the glass softening point is 620–650℃. It can be purchased directly from ordinary commercial products or prepared using conventional melt-water quenching processes in this field. Example 1

[0027] A method for preparing an in-situ grown mullite whisker-reinforced low-temperature ceramic binder. The steps of the preparation method described in this embodiment are as follows: (1) Ingredients: Weigh the raw materials according to the following proportions: 35g metakaolin, 15g Al(OH)3, 25g silica sol (30% SiO2), 25g glass powder, 1.5g NH4VO3, and 0.5g AlF3. (2) Ball milling: The weighed raw materials are placed in a polyurethane ball milling jar and mixed with "alumina balls + anhydrous ethanol" in a ball milling process. The speed is set to 200 rpm and the ball milling time is 6 hours to obtain the ball milled slurry. (3) Drying and sieving: The ball-milled slurry is vacuum dried at 90°C for 10 hours and then passed through a 325-mesh sieve to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under 80MPa pressure for 30s to obtain a ceramic blank with dimensions of 50×10×4mm; (5) Sintering: The ceramic blank is heated to 950°C in air atmosphere and sintered without pressure for 0.5 h. It is then cooled in the furnace to obtain the in-situ grown mullite whisker reinforced low temperature ceramic binder sample strip.

[0028] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder sample prepared in this embodiment was tested and found to have a three-point flexural strength of 129 MPa and a fracture toughness of 3.4 MPa·m. 0.5 . Example 2

[0029] A method for preparing an in-situ grown mullite whisker-reinforced low-temperature ceramic binder. The steps of the preparation method described in this embodiment are as follows: (1) Ingredients: Weigh the raw materials according to the following proportions: 40g metakaolin, 12g Al(OH)3, 20g silica sol (30% SiO2), 28g glass powder, 1.0g NH4VO3, and 1.0g AlF3. (2) Ball milling: The weighed raw materials are placed in a polyurethane ball milling jar and mixed with "alumina balls + anhydrous ethanol" in a ball milling process. The speed is set to 300 rpm and the time is 4 hours to obtain the ball-milled slurry. (3) Drying and sieving: The ball-milled slurry is vacuum dried at 80°C for 12 hours and then sieved through a 325-mesh sieve to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under a pressure of 90MPa for 40s to obtain a ceramic blank with dimensions of 50×10×4mm; (5) Sintering: The ceramic blank is heated to 900°C in air atmosphere and sintered without pressure for 1.0 h. It is then cooled in the furnace to obtain the in-situ grown mullite whisker reinforced low temperature ceramic binder sample strip.

[0030] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder sample prepared in this embodiment was tested and found to have a three-point flexural strength of 132 MPa and a fracture toughness of 3.7 MPa·m. 0.5 . Example 3

[0031] A method for preparing an in-situ grown mullite whisker-reinforced low-temperature ceramic binder. The steps of the preparation method described in this embodiment are as follows: (1) Ingredients: Weigh the raw materials according to the following proportions: 45g metakaolin, 10g Al(OH)3, 15g silica sol (40% SiO2), 30g glass powder, 0.3g NH4VO3, and 2.0g AlF3. (2) Ball milling: The weighed raw materials are placed in a polyurethane ball milling jar and mixed with "alumina balls + anhydrous ethanol" in a ball milling process. The speed is set to 400 rpm and the time is 3 hours to obtain the ball-milled slurry. (3) Drying and sieving: The ball-milled slurry is vacuum dried at 80°C for 12 hours and then sieved through a 325-mesh sieve to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under a pressure of 100MPa for 60s to obtain a ceramic blank with dimensions of 50×10×4mm; (5) Sintering: The ceramic blank is heated to 850°C in air atmosphere and sintered without pressure for 1.5 hours. It is then cooled in the furnace to obtain the in-situ grown mullite whisker reinforced low-temperature ceramic binder sample strip.

[0032] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder sample prepared in this embodiment was tested and found to have a three-point flexural strength of 120 MPa and a fracture toughness of 3.0 MPa·m. 0.5 .

[0033] Comparative Example

[0034] A method for preparing an in-situ grown mullite whisker-reinforced low-temperature ceramic binder. The steps of the preparation method described in this comparative example are (without adding the catalyst NH4VO3+AlF3, the rest are the same as in Example 2): (1) Ingredients: Weigh the raw materials according to the following proportions: 40g metakaolin, 12g Al(OH)3, 20g silica sol (30% SiO2), and 28g glass powder. (2) Ball milling: The weighed raw materials are placed in a polyurethane ball milling jar and mixed with "alumina balls + anhydrous ethanol" in a ball milling process. The speed is set to 300 rpm and the time is 4 hours to obtain the ball-milled slurry. (3) Drying and sieving: The ball-milled slurry is vacuum dried at 80°C for 12 hours and then sieved through a 325-mesh sieve to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under a pressure of 90MPa for 40s to obtain a ceramic blank with dimensions of 50×10×4mm; (5) Sintering: The ceramic blank is heated to 900°C in air atmosphere and sintered without pressure for 1.0 h. It is then cooled in the furnace to obtain the in-situ grown mullite whisker reinforced low temperature ceramic binder sample strip.

[0035] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder sample prepared in this comparative example was tested and found to have a three-point flexural strength of 80 MPa and a fracture toughness of 1.9 MPa·m. 0.5 .

[0036] Application examples A diamond grinding wheel reinforced with in-situ grown mullite whiskers and a method for its preparation is disclosed. The steps of the preparation method described in this application example are as follows:

[0037] (1) Ingredients: Weigh the raw materials according to the following proportions: 40g metakaolin, 12g Al(OH)3, 20g silica sol (30% SiO2), 28g glass powder, 1.0g NH4VO3, and 1.0g AlF3. (2) Ball milling: The weighed raw materials are placed in a polyurethane ball milling jar and mixed with "alumina balls + anhydrous ethanol" in a ball milling process. The speed is set to 300 rpm and the time is 4 hours to obtain the ball-milled slurry. (3) Drying and sieving: The ball-milled slurry is vacuum dried at 80°C for 12 hours and then sieved through a 325-mesh sieve to obtain ceramic binder powder; (4) Mixing and molding: The ceramic binder powder is mixed with 30 vol% of CBN superhard abrasive (particle size 120 / 140), and dry-pressed at 90 MPa for 40 s to obtain a grinding wheel blank with dimensions of Φ100 mm × 10 mm. (5) Sintering: The grinding wheel blank is heated to 900°C in air atmosphere and sintered without pressure for 1.0 h. It is then cooled with the furnace to obtain the in-situ grown mullite whisker reinforced low temperature ceramic binder CBN grinding wheel.

[0038] The in-situ grown mullite whisker-reinforced low-temperature ceramic binder CBN grinding wheel prepared in this application example was tested by grinding (wet grinding of Inconel 718 nickel-based superalloy, grinding wheel linear speed v). s =30m / s, workpiece velocity v w =8m / min, grinding depth ap=0.01mm): The grinding ratio is 132, and the workpiece surface roughness Ra=0.52µm; Using the raw material ratio described in the comparative example, under the same preparation process parameters and the same grinding test conditions, the grinding ratio of the ceramic bond CBN grinding wheel described in the comparative example is 98, and the workpiece surface roughness Ra=0.54µm. In comparison, the grinding ratio of 132 of the grinding wheel in this embodiment is much higher than that of 98 in the comparative example, indicating that the grinding wheel is more durable and the grinding effect is superior.

[0039] In summary, this invention addresses the technical problems in existing reinforced ceramic binder technologies, such as "difficulty in dispersing the added reinforcing phase, erosion of the reinforcing phase by the glass matrix, and poor reinforcement and toughening effects." It provides an in-situ grown mullite whisker reinforced low-temperature ceramic binder and its grinding wheel, which improves the grinding ratio of the grinding wheel, makes the grinding wheel more durable, and provides a better grinding effect, making it suitable for large-scale production.

Claims

1. An in-situ grown mullite whisker-reinforced low-temperature ceramic binder, characterized in that, It consists of main ingredients and auxiliary ingredients; the main ingredients are mainly composed of the following raw materials by weight percentage: Metakaolin 35–45 wt%, Al(OH)3 10–15 wt%, silica sol 15–25 wt%, glass powder 25–30 wt%; The excipients include NH4VO3 and AlF3, wherein NH4VO3 accounts for 0.3–1.5 wt% of the main material and AlF3 accounts for 0.5–2.0 wt% of the main material.

2. The in-situ grown mullite whisker-reinforced low-temperature ceramic binder according to claim 1, characterized in that, The silica sol has a SiO2 content of 30–40%.

3. The method for preparing the in-situ grown mullite whisker-reinforced low-temperature ceramic binder according to claim 1 or 2, characterized in that, Includes the following steps: (1) Ingredients: Weigh each ingredient according to the proportions; (2) Ball milling: The weighed raw materials are ball milled to obtain a slurry after ball milling; (3) Drying and sieving: The slurry is vacuum dried and sieved to obtain ceramic binder powder; (4) Molding: The ceramic binder powder is dry-pressed under a pressure of 80–100 MPa for 30–60 s to obtain a ceramic green body; (5) Sintering: The ceramic blank is heated to 850–950℃ in air atmosphere and held for 0.5–1.5h for pressureless sintering, and then cooled in the furnace to obtain the product.

4. The method for preparing the in-situ grown mullite whisker-reinforced low-temperature ceramic binder according to claim 3, characterized in that, In step (2), alumina balls are used for ball milling in the presence of anhydrous ethanol, with a rotation speed of 200–400 rpm and a milling time of 3–6 h.

5. The method for preparing the in-situ grown mullite whisker-reinforced low-temperature ceramic binder according to claim 3, characterized in that, In step (3), the slurry is vacuum dried at 80–90℃ for 10–12 hours and then passed through a 300–400 mesh sieve.

6. A superhard abrasive, characterized in that, It is prepared from the in-situ grown mullite whisker-reinforced low-temperature ceramic binder and superhard abrasive as described in claim 1 or 2.

7. The superhard abrasive according to claim 6, characterized in that, The superhard abrasive is CBN, with a particle size of 100 / 120 or 120 / 140, and the abrasive concentration is 25–35 vol.

8. The method for preparing the superhard abrasive according to claim 6 or 7, characterized in that, The in-situ grown mullite whisker-reinforced low-temperature ceramic binder powder is mixed with superhard abrasive and dry-pressed at 90±10 MPa for 40±10 s to obtain a grinding wheel blank. The grinding wheel blank is heated to 850-950℃ in air atmosphere and held for 0.5-2 h for pressureless sintering, and then cooled in the furnace to obtain the final product.

9. The application of the superhard abrasive as described in claim 6 or 7 in grinding hardened steel, high-speed steel, cast iron, titanium alloys, and high-temperature alloys.