A polycrystalline cubic boron nitride blade material and a method of making the same

Abstract

The application discloses a polycrystalline cubic boron nitride blade material and a preparation method thereof, and relates to the technical field of superhard cutter materials. The material is composed of cBN particles, Cu-Ti-Sn alloy powder, Al powder and CaF2@Ni particles with a core-shell structure. The Ni layer is coated on the surface of CaF2 through chemical plating, so that the wettability of CaF2 with the metal matrix is improved, and the agglomeration is inhibited. The Al powder is added to react with the in-situ generated Ni layer during sintering to form a high-temperature-resistant Ni3Al strengthening phase, so that the interfacial bonding force is improved. The high densification is realized by combining the transient liquid phase sintering, and the material has excellent mechanical properties and wear resistance.

Description

Technical Field

[0001] This invention relates to the field of superhard cutting tool materials technology, and in particular to a polycrystalline cubic boron nitride (PcBN) cutting tool material and its preparation method. Background Technology

[0002] Polycrystalline cubic boron nitride (PcBN) inserts are widely used for precision cutting of difficult-to-machine materials such as hardened steel and powder metallurgy parts due to their high hardness, high thermal stability, and low chemical reactivity with ferrous metals. PcBN inserts are typically made by sintering cBN particles and a binder under high temperature and high pressure conditions. The overall performance of the material largely depends on the composition design of the binder system and the degree of densification achievable by the sintering process.

[0003] In metal-bonded systems, Cu-Ti based alloys have attracted attention due to the ability of Ti to react with the surface of cBN particles to form transition phases such as TiN, creating a chemical bond between the hard particles and the metal matrix, which is beneficial for improving interfacial bonding strength. Adding an appropriate amount of Sn to Cu-Ti alloys can utilize the characteristic of the Cu-Sn system forming a liquid phase at relatively low temperatures to achieve transient liquid phase sintering (TLPS), obtaining high density under milder sintering conditions. However, under high-speed dry cutting conditions, the temperature of the tool-chip contact zone in Cu-Ti-Sn based PcBN inserts is too high. The instantaneous thermal shock generated by intense friction easily leads to the initiation and propagation of surface microcracks, and in severe cases, can cause brittle spalling of the material, limiting the cutting life of the insert.

[0004] To improve the frictional properties and thermal shock stability of PcBN cutting tools under high-temperature cutting conditions, researchers have attempted to introduce a solid lubricating phase into the binder, with common materials including CaF2 and hBN. CaF2 exhibits low shear strength above 400℃ and can spread to form a lubricating transfer film on the wear surface. However, CaF2 has poor wettability with Cu-based metal matrices. When directly added as powder, CaF2 particles tend to form local agglomerates in the metal phase during sintering. These agglomerated areas become weak points in mechanical properties after solidification, leading to a decrease in the material's flexural strength and fracture toughness. Furthermore, the agglomerated distribution limits the uniformity and persistence of the lubricating film formation, making it difficult to fully realize the lubrication effect. Achieving a uniform and dispersed distribution of the solid lubricating phase in the PcBN binder matrix without significantly sacrificing mechanical properties is a pressing problem in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a polycrystalline cubic boron nitride (cBN) blade material, comprising the following raw materials in parts by weight: 70-85 parts cBN particles, 10-25 parts Cu-Ti-Sn alloy powder, 0.1-0.5 parts Al powder, and 3-5 parts core-shell structured particles.

[0006] Preferably, the core-shell structured particle is a CaF2@Ni particle with a core-shell structure, wherein the core layer is a CaF2 particle and the shell layer is Ni.

[0007] Preferably, the Al powder is pure Al powder with a particle size ≤ 5 μm, and the mass ratio of Al powder to Cu-Ti-Sn alloy powder is (0.01~0.02):1.

[0008] This invention also provides a method for preparing polycrystalline cubic boron nitride blade material, comprising the following steps: S1. Preparation of core-shell structured particles: The CaF2@Ni particles with the core-shell structure were prepared by chemical plating. S2. Mixing: First, the Cu-Ti-Sn alloy powder, Al powder and CaF2@Ni particles prepared in step S1 are ultrasonically dispersed and mixed in a liquid medium, and then dried. Then, the dried powder and cBN particles are mechanically mixed evenly. S3. Sintering: The powder mixed in step S2 is loaded into a mold and sintered in a vacuum environment using a transient liquid phase sintering method. After cooling, the powder is obtained.

[0009] Preferably, in step S1, the preparation of the CaF2@Ni particles by chemical plating specifically involves using nickel sulfate solution as a nickel salt and sodium hypophosphite solution as a reducing agent to carry out the reaction, controlling the pH value of the reaction to be 8~10, the reaction temperature to be 70~90℃, and the reaction time to be 20~40 min.

[0010] Preferably, step S2 is as follows: Cu-Ti-Sn alloy powder, Al powder and CaF2@Ni particles prepared in step S1 are first ultrasonically dispersed and mixed in anhydrous ethanol for 30-60 min, and then dried; then the dried powder and cBN particles are mixed evenly in a ball mill.

[0011] Preferably, when mixing in a ball mill, the weight ratio of the mixed powder to the grinding balls is 1:(3~5), the ball mill speed is controlled at 150~250 r / min, and the mixing time is 4~8 h.

[0012] Preferably, in step S2, the drying process after ultrasonic dispersion and mixing is as follows: drying in a vacuum drying oven at 40~80 ℃ for 8~12 h.

[0013] Preferably, in step S3, the conditions for the transient liquid phase sintering method are: a heating rate of 5~10 ℃ / min, and sintering for 30~60 min at a temperature of 1350~1450 ℃ and a pressure of 30~50 MPa.

[0014] Preferably, in step S3, the vacuum pressure under the vacuum conditions is <10 Pa.

[0015] The beneficial effects of this invention are: This invention forms a continuous Ni-P coating layer on the surface of CaF2 particles through chemical plating, giving it good metallurgical compatibility with the Cu-Ti-Sn metal matrix. When the coated CaF2@Ni particles are premixed with Cu-Ti-Sn alloy powder in anhydrous ethanol medium, the tendency for particle agglomeration is significantly reduced, laying the foundation for uniform transport of the lubricating phase during subsequent sintering.

[0016] This invention also employs a transient liquid phase sintering (TLPS) step. The transient liquid phase formed by the Cu-Ti-Sn system has low viscosity, enabling it to carry CaF2@Ni particles into the micropores. As Ti reacts with the cBN surface to form a TiN transition phase and the liquid phase gradually solidifies, CaF2 particles are in-situ sealed within the densified binder matrix. With the gradual renewal of the tool wear surface, the dispersed CaF2 particles sealed in the matrix are continuously exposed, spreading to form a solid lubricating film at high cutting temperatures, continuously reducing the tool-chip interface friction coefficient and suppressing cutting heat accumulation. Simultaneously, this invention adds Al powder. During the subsequent transient liquid phase sintering (TLPS) process, utilizing the in-situ reaction sintering principle, Al preferentially accumulates in the Ni layer on the CaF2 particle surface and undergoes a strong exothermic reaction, spontaneously forming Ni3Al intermetallic compounds. Ni3Al has high strength and high temperature resistance, allowing CaF2 to release the lubricating medium only when the tool surface wears, thus improving the tool's wear resistance and service life. Attached Figure Description

[0017] Figure 1 This is a SEM micrograph of the fractured surface of the blade material prepared in Example 2; Figure 2 This is a SEM image of the CaF2@Ni core-shell particles prepared in Example 2. Detailed Implementation

[0018] The amount of Al powder (pure Al powder with a particle size ≤ 5 μm) added in this invention is calculated based on the mass of the binder (Cu-Ti-Sn alloy powder). By maintaining the mass ratio of Al powder to Cu-Ti-Sn alloy powder within the range of 0.01 to 0.02, it is ensured that Al elements can accurately and sufficiently undergo in-situ alloying reactions with the Ni coating on the CaF2 surface to generate Ni3Al, which has mechanical protective properties. At the same time, it avoids the side reaction of excessive Al elements with Ti in the binder to generate the brittle TiAl3 phase, which would damage the matrix.

[0019] The Cu-Ti-Sn alloy powder described in this invention was purchased from Changsha Ruituomei New Material Co., Ltd., with Cu=60%~80%, Sn=10%~20%, and Ti=1%~10%.

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Example 1 The polycrystalline cubic boron nitride blade material of this embodiment includes the following raw materials in parts by weight: 70 parts cBN particles, 10 parts Cu-Ti-Sn alloy powder, 0.1 parts Al powder (at this time, the mass ratio of Al to Cu-Ti-Sn is 0.01:1), and 3 parts core-shell structure particles.

[0022] This embodiment describes a method for preparing a polycrystalline cubic boron nitride blade material, comprising the following steps: Preparation of S1, CaF2@Ni core-shell particles Take an appropriate amount of CaF2 powder (particle size 200~300 nm), place it in deionized water and ultrasonically clean it for 10 min, filter it and vacuum dry it at 60℃ for 1 h for later use.

[0023] Sensitization treatment: The above CaF2 powder was added to an aqueous solution containing 15 g / L SnCl2 and 15 mL / L HCl, ultrasonically stirred for 20 min, filtered, and washed with deionized water until neutral.

[0024] Activation treatment: The sensitized powder was added to an aqueous solution containing 0.2 g / L PdCl2 and 10 mL / L HCl, ultrasonically stirred for 12 min, filtered, and washed with deionized water.

[0025] Electroless Ni plating: Activated CaF2 powder was added to an electroless plating solution (NiSO4·6H2O 25 g / L, NaH2PO2·H2O 25 g / L, Na3C6H5O7·2H2O 12 g / L), and the pH was adjusted to 9.0 with ammonia. The mixture was stirred at a constant temperature in an 80℃ water bath for 30 min. After the reaction was completed, the mixture was filtered, washed successively with deionized water and anhydrous ethanol, and dried under vacuum at 60℃ for 8 h to obtain CaF2@Ni core-shell particles.

[0026] S2, Mixing Weigh 25 parts of Cu-Ti-Sn alloy powder, 0.1 parts of Al powder, and 3 parts of CaF2@Ni core-shell particles, and add them together to an appropriate amount of anhydrous ethanol (enough to completely submerge the added alloy powder and core-shell particles). Disperse and mix ultrasonically for 45 min. Transfer the suspension to a vacuum drying oven and dry at 60℃ for 10 h. Sieve and grind to obtain a premixed powder. Take 70 parts of cBN particles and the above premixed powder, place them in a planetary ball mill, add alumina grinding balls (material-to-ball weight ratio 1:4), and ball mill at 200 r / min for 6 h to obtain the final mixed powder.

[0027] S3, sintering The mixed powder is loaded into a graphite mold and placed in a vacuum sintering furnace. The furnace pressure is evacuated to <10 Pa. The temperature is increased to 1350℃ at a rate of 5℃ / min, and a sintering pressure of 30 MPa is applied. The temperature and pressure are maintained for 30 min. After cooling to room temperature in the furnace, the product is demolded to obtain the finished product.

[0028] Example 2 The polycrystalline cubic boron nitride blade material of this embodiment includes the following raw materials in parts by weight: 78 parts cBN particles, 17 parts Cu-Ti-Sn alloy powder, 0.26 parts Al powder (at this time, the mass ratio of Al to Cu-Ti-Sn is about 0.015:1), and 4 parts core-shell structure particles.

[0029] This embodiment describes a method for preparing a polycrystalline cubic boron nitride blade material, comprising the following steps: Preparation of S1, CaF2@Ni core-shell particles The sensitization and activation steps were the same as in Example 1. Chemical plating conditions: plating solution composition was the same as in Example 1, pH 9.0, temperature 80℃, reaction time 30 min, and CaF2@Ni core-shell particles were obtained after vacuum drying.

[0030] S2, Mixing Weigh 17 parts Cu-Ti-Sn alloy powder, 0.26 parts Al powder, and 4 parts CaF2@Ni core-shell particles. Disperse and mix them ultrasonically in anhydrous ethanol (enough to completely submerge the alloy powder and core-shell particles) for 45 min, and then vacuum dry at 60℃ for 10 h to obtain a premixed powder. Mix this powder with 78 parts cBN particles in a ball mill at a material-to-ball weight ratio of 1:4, at 200 r / min for 6 h.

[0031] S3, sintering The temperature was increased to 1400℃ at a rate of 7℃ / min, the sintering pressure was 40 MPa, the holding time was 45 min, the vacuum pressure was <10 Pa, and the finished product was obtained after cooling in the furnace and demolding.

[0032] Example 3 The polycrystalline cubic boron nitride blade material of this embodiment includes the following raw materials in parts by weight: 85 parts cBN particles, 10 parts Cu-Ti-Sn alloy powder, 0.2 parts Al powder (at this time, the mass ratio of Al to Cu-Ti-Sn is 0.02:1), and 5 parts core-shell structure particles.

[0033] This embodiment describes a method for preparing a polycrystalline cubic boron nitride blade material, comprising the following steps: Preparation of S1, CaF2@Ni core-shell particles Same as Example 1, chemical plating conditions: pH 9.0, 80°C, 30 min, vacuum drying at 60°C for 8 h.

[0034] S2, Mixing Weigh 10 parts of Cu-Ti-Sn alloy powder, 0.2 parts of Al powder, and 5 parts of CaF2@Ni core-shell particles. Disperse and mix them ultrasonically in anhydrous ethanol (enough to completely submerge the added alloy powder and core-shell particles) for 45 min, and then vacuum dry them at 60℃ for 10 h. Mix them with 85 parts of cBN particles in a ball mill at a material-to-ball ratio of 1:4, 200 r / min, for 6 h.

[0035] S3, sintering The temperature was increased to 1450℃ at a rate of 10℃ / min, the sintering pressure was 50 MPa, the holding time was 60 min, the vacuum pressure was <10Pa, and the finished product was obtained after cooling in the furnace and demolding.

[0036] Comparative Example 1 The raw material ratio for this comparative example is 78 parts cBN particles, 21 parts Cu-Ti-Sn alloy powder, and 0.32 parts Al powder (maintaining a mass ratio of approximately 0.015:1 with Cu-Ti-Sn alloy powder).

[0037] The only difference between this comparative example and Example 2 is that an equal amount of Cu-Ti-Sn alloy powder is used instead of CaF2@Ni core-shell particles.

[0038] Comparative Example 2 The raw material ratio for this comparative example is as follows: 78 parts cBN particles, 17 parts Cu-Ti-Sn alloy powder, 0.26 parts Al powder (maintaining a mass ratio of approximately 0.015:1 with Cu-Ti-Sn alloy powder), and 4 parts untreated CaF2 powder.

[0039] The only difference between this comparative example and Example 2 is that an equal amount of CaF2 powder (without Ni coating) is used instead of CaF2@Ni core-shell particles.

[0040] Comparative Example 3 The raw material ratio for this comparative example is: 78 parts cBN particles, 17 parts Cu-Ti-Sn alloy powder, and 4 parts CaF2@Ni core-shell particles.

[0041] The only difference between this comparative example and Example 2 is that no aluminum powder was added.

[0042] Actual test Vickers hardness: Following GB / T 7997-2014, a Vickers hardness tester was used. The test force was 196 N, and the holding time was 15 s. Five test points were taken for each sample, and the average value was calculated. The test results are shown in Table 1.

[0043] Fracture toughness: The Vickers indentation method was used, and the average value of 5 indentations was taken for each sample. The test results are shown in Table 1.

[0044] Bending strength: The three-point bending method was used, with a span of 20 mm and a loading rate of 0.5 mm / min. The average value of 5 specimens in each group was taken. The test results are shown in Table 1.

[0045] Rake face wear: The tool materials of the examples and comparative examples were used to a certain extent. The workpiece material was a round bar of FCD70 (ductile iron). The cutting speed was 400 m / min. The cutting method was a wet continuous high-speed cutting test of cast iron at a depth of 0.35 mm, with a feed rate of 0.15 mm / rpm and a time of 20 minutes. The workpiece material was SCM415 carburized and quenched round steel, with a cutting speed of 200 m / min. A dry continuous high-speed cutting test of steel was conducted under the following conditions: depth of cut: 0.1 mm, feed rate: 0.1 mm / rpm, time: 20 minutes. The flank wear width of the cutting edge was measured. The test results are shown in Table 1. Table 1 Example 2 showed the best performance in both mechanical and cutting properties, indicating that the cBN content was moderate, the amount of binder liquid phase was sufficient, and the CaF2@Ni particles were uniformly dispersed, thus comprehensively exerting the synergistic effects of densification, interface strengthening, and self-lubrication. Example 3 had the highest cBN content (85 parts), and the Vickers hardness reached 34.0 GPa, the highest among the three examples. However, the proportion of metal binder was reduced accordingly, weakening the bridging and deflection effect on crack propagation, resulting in lower fracture toughness and bending strength than Example 2. Comparative Example 1 replaced the CaF2@Ni core-shell particles with an equal amount of Cu-Ti-Sn alloy powder, resulting in tool wear after cutting cast iron (0.181 mm) and hardened steel (0.172 mm) being 2.87 times and 3 times that of Example 2, respectively. This fully demonstrates that the introduction of a solid lubricating phase is a key factor in suppressing the accumulation of frictional heat at the tool-chip interface and slowing down the initiation and propagation of thermal shock cracks; Comparative Example 2 directly replaced CaF2@Ni core-shell particles with untreated CaF2 powder. Due to the poor wettability between CaF2 and Cu-based metal matrix, CaF2 particles locally agglomerate in the binder during sintering, forming a mechanically weakened zone in the matrix after solidification. This results in the lowest fracture toughness (4.9 MPa·m1 / 2) and bending strength (520 MPa) among all groups. Although the CaF2 lubricating phase still exists in the matrix, its uneven distribution leads to significantly higher flank wear (0.154 mm for cast iron and 0.150 mm for hardened steel) compared to Example 2. This indicates that the uneven lubricating film is difficult to continuously and effectively reduce the coefficient of friction, and the material as a whole accelerates wear failure due to insufficient toughness. In Comparative Example 3, Al powder was removed while retaining the CaF2@Ni core-shell particles. The Ni3Al interface strengthening phase could not be generated in situ on the Ni coating surface, resulting in a decrease in the metallurgical bonding strength between the CaF2@Ni particles and the metal matrix. Its bending strength and fracture toughness were both lower than those of Example 2. The wear on the back face (0.118 mm for cast iron and 0.109 mm for hardened steel) was also significantly higher than that in Example 2, but the overall performance was significantly better than that in Comparative Example 2, indicating that the core-shell structure itself had improved the dispersibility of CaF2, and the introduction of an appropriate amount of Al powder further strengthened the interfacial bonding.

[0046] In summary, this invention effectively solves the key problem of agglomeration and distribution of solid lubricating phase in Cu-based metal binders by constructing a CaF2@Ni core-shell structure through chemical Ni plating; the addition of an appropriate amount of Al powder promotes the in-situ generation of the Ni3Al interface phase, further enhancing the metallurgical bonding strength between the lubricating phase and the matrix; and the combination of transient liquid phase sintering process achieves high densification. The synergistic effect of these three factors enables the fabricated PcBN cutting tool to maintain good mechanical properties while reducing the flank wear compared to the formulation without a lubricating phase, thus improving cutting life.

[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A polycrystalline cubic boron nitride blade material, characterized in that, The raw materials include the following parts by weight: 70-85 parts cBN particles, 10-25 parts Cu-Ti-Sn alloy powder, 0.1-0.5 parts Al powder, and 3-5 parts core-shell structured particles.

2. The polycrystalline cubic boron nitride blade material according to claim 1, characterized in that, The core-shell structured particles are CaF2@Ni particles with a core-shell structure, wherein the core layer is CaF2 particles and the shell layer is Ni.

3. The polycrystalline cubic boron nitride blade material according to claim 1, characterized in that, The Al powder is pure Al powder with a particle size ≤ 5 μm, and the mass ratio of Al powder to Cu-Ti-Sn alloy powder is (0.01~0.02):

1.

4. A method for preparing the polycrystalline cubic boron nitride blade material as described in claim 1, characterized in that, Includes the following steps: S1. Preparation of core-shell structured particles: The CaF2@Ni particles with the core-shell structure were prepared by chemical plating. S2. Mixing: The Cu-Ti-Sn alloy powder, Al powder and CaF2@Ni particles prepared in step S1 are ultrasonically dispersed and mixed in a liquid medium, and then dried. The dried powder is then mixed with the cBN particles by mechanical mixing. S3. Sintering: The powder mixed in step S2 is loaded into a mold and sintered in a vacuum environment using a transient liquid phase sintering method. After cooling, the powder is obtained.

5. The preparation method according to claim 4, characterized in that, In step S1, the preparation of the CaF2@Ni particles by chemical plating specifically involves using nickel sulfate solution as the nickel salt and sodium hypophosphite solution as the reducing agent to carry out the reaction, controlling the pH value of the reaction to be 8~10, the reaction temperature to be 70~90℃, and the reaction time to be 20~40 min.

6. The preparation method according to claim 4, characterized in that, Step S2 is as follows: First, Cu-Ti-Sn alloy powder, Al powder and CaF2@Ni particles prepared in step S1 are ultrasonically dispersed and mixed in anhydrous ethanol for 30-60 min, and then dried; then the dried powder and cBN particles are mixed evenly in a ball mill.

7. The preparation method according to claim 4, characterized in that, When mixing in a ball mill, the weight ratio of the mixed powder to the grinding balls is 1:(3~5), the ball mill speed is controlled at 150~250 r / min, and the mixing time is 4~8 h.

8. The preparation method according to claim 4, characterized in that, In step S2, the drying process after ultrasonic dispersion and mixing is as follows: place it in a vacuum drying oven at 40~80℃ for 8~12 hours.

9. The preparation method according to claim 4, characterized in that, In step S3, the conditions for the transient liquid phase sintering method are: a heating rate of 5~10℃ / min, and sintering for 30~60min at a temperature of 1350~1450℃ and a pressure of 30~50MPa.

10. The preparation method according to claim 4, characterized in that, In step S3, the vacuum pressure under the vacuum conditions is <10 Pa.

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