CN110465669B

CN110465669B - Gradient composite cubic boron nitride material and preparation process and application thereof

Info

Publication number: CN110465669B
Application number: CN201910847330.7A
Authority: CN
Inventors: 邹斌; 云昊; 邢宏宇; 王鹏; 丁守岭; 王军; 黄传真
Original assignee: Shandong University
Current assignee: Sichuan Yingnuo Aviation Technology Co ltd
Priority date: 2019-09-09
Filing date: 2019-09-09
Publication date: 2020-06-26
Anticipated expiration: 2039-09-09
Also published as: CN110465669A

Abstract

The invention provides a gradient composite cubic boron nitride material and a preparation process and application thereof, the material is prepared by sintering cubic boron nitride, titanium carbide, aluminum and cobalt which are used as raw materials, and has a symmetrical gradient structure with 3 layers which are symmetrical by taking an intermediate layer as a symmetrical structure; wherein the raw materials comprise the following components in percentage by volume: cubic boron nitride 70-80 vol.%, titanium carbide 10 vol.%, aluminum 5-10 vol.% and cobalt 5-10 vol.%; wherein, cubic boron nitride is used as a substrate, titanium carbide is used as a ceramic bonding agent, and aluminum and cobalt are used as metal bonding agents; and the symmetrical layers which are symmetrical relative to the middle layer have the same raw material component content and symmetrically distributed thickness. The material has higher toughness and wear resistance, so that the cutter is better suitable for high-speed cutting and machining of wear-resistant parts, and has wider application prospect.

Description

Gradient composite cubic boron nitride material and preparation process and application thereof

Technical Field

The invention relates to the technical field of manufacturing of mechanical cutting tools, in particular to a gradient composite cubic boron nitride material and a preparation process and application thereof.

Background

The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.

With the development of science and technology, wear-resistant materials and high-hardness and difficult-to-machine alloys are used in large quantities, and common cutters for machining the materials are difficult to be sufficient. The application of the superhard cutter can realize high efficiency and high stability of processing, the processing cost of a workpiece can be greatly reduced, and the superhard cutter becomes an indispensable tool in modern cutting processing. The hardness of the polycrystalline cubic boron nitride can reach HV3000-5000, is second to diamond, has very high chemical inertia and thermal stability, and is widely applied to the processing of quenched steel, high-hardness cast iron and wear-resistant alloy in industry. However, the inventors have found that the overall properties of the homogeneous cubic boron nitride material are still not ideal, especially the mechanical properties of the material such as flexural strength, wear resistance and toughness.

Disclosure of Invention

Therefore, the invention aims to provide a gradient composite cubic boron nitride material, a preparation method thereof and application of the material in the field of cutter preparation or the field of wear-resistant part processing. According to the invention, a Cubic Boron Nitride (CBN) material is introduced into the gradient structure, and residual compressive stress is formed on the surface layer by utilizing the gradient structure, so that the hardness, wear resistance and toughness of the material are improved, and the comprehensive mechanical property of the Cubic Boron Nitride cutter is further improved on the basis of keeping the original advantages of the Cubic Boron Nitride cutter.

Specifically, the invention has the following technical scheme:

in a first aspect of the invention, the invention provides a material which is made by sintering cubic boron nitride, titanium carbide, aluminum and cobalt as raw materials and has a three-layer gradient structure with an intermediate layer as a symmetry.

Wherein the raw materials comprise the following components in percentage by volume: cubic boron nitride 70-80 vol.%, titanium carbide 10 vol.%, aluminum 5-10 vol.% and cobalt 5-10 vol.%; wherein, cubic boron nitride is used as a substrate, titanium carbide is used as a ceramic bond (as a ceramic phase), and aluminum and cobalt are used as metal bonds (as metal phases).

The symmetric layer (also referred to as a surface layer in the present invention) having a symmetric position with respect to the intermediate layer has the same raw material component content and thickness, and has a symmetric thickness distribution.

In some embodiments of the present invention, the raw materials comprise the following components in percentage by volume: cubic boron nitride is optionally in the range of 70-80 vol.%, such as 72-80 vol.% or 74-80 vol.% or 76-80 vol.% 70-78 vol.%, or 72-76 vol.% or 72 vol.%, 74 vol.%, 76 vol.% or 80 vol.%, titanium carbide 10 vol.%, aluminum and cobalt are each independently optionally in the range of 5-10 vol.%, such as 5-10 vol.%, 5-9 vol.%, 5-8 vol.%, 7-9 vol.% or 5-7 vol.%, or 5 vol.% or 7 vol.% or 8 vol.% or 9 vol.%.

For example, in some embodiments of the present invention, the volume percentage of each component in the raw material of each layer is as follows: cubic boron nitride 72-80 vol.%, titanium carbide 10 vol.%, aluminum 5-9 vol.% and cobalt 5-9 vol.%; the two surface layer structures in the three-layer structure are symmetrical relative to the middle layer, and the raw material component content and the thickness of the two surface layers which are symmetrical to each other are the same. Particularly, under the composition, the cubic boron nitride material has better mechanical property, microstructure and sintering property improvement degree.

The addition of the metal phase and the ceramic phase can improve the mechanical property of the cubic boron nitride and improve the microstructure and the sintering property of the material. Al is melted into a liquid phase at high temperature, thereby being beneficial to the diffusion flow of CBN particles and the bonding between the CBN particles, and the Al reacts with the CBN to generate AlN in the sintering process to promote the sintering. AlN can inhibit the reverse conversion of CBN to h-BN, and has important significance for improving the content and density of cubic boron nitride in a sintered body; the addition of the hard phase TiC can reduce bonding among CBN, inhibit grain growth and effectively improve the heat resistance and impact resistance of a PCBN (polycrystalline cubic boron nitride, which can be formed by CBN sintering) sintered body; co mainly has the purification function of deoxidizing and degassing the surface of cubic boron nitride, activates cubic boron nitride particles, promotes direct bonding between cubic boron nitride, and improves the performance of a sintered body.

In addition, the invention also introduces a gradient structure into the composite cubic boron nitride material, so that the components, the performance and the functions of the material present gradient changes, the thermal expansion coefficient is increased from the outside to the inside, the surface layer of the material is ensured to form favorable residual compressive stress in the preparation process, and the tensile stress formed in the cutting process can be counteracted; meanwhile, the generation of residual tensile stress is reduced as much as possible, and the toughness and the wear resistance of the material are improved; the heat conductivity coefficient is increased from the outside to the inside, so that the heat transfer of cutting is facilitated, and the prepared gradient composite cubic boron nitride material is suitable for high-speed cutting and quenching of steel materials when being used for manufacturing cutters.

In an embodiment of the invention, the symmetric gradient of the invention symmetric to the intermediate layer comprises a content gradient.

In the embodiment of the invention, the volume percentage content of the cubic boron nitride increases layer by layer from the middle layer to the surface layer; and the content of at least one component selected from the group consisting of aluminum and cobalt in percentage by volume decreases layer by layer from the intermediate layer to the surface layer.

In certain embodiments, the feedstock composition gradient between the intermediate layer and the skin layer is optional in the range of 4 vol.% to 10 vol.%.

For example, in some embodiments, the gradient of the raw material composition cubic boron nitride between the intermediate layer and the top layer is selected in a range of 4 vol.% to 10 vol.%, e.g., the gradient is 4 vol.% to 10 vol.%, 4 vol.% to 8 vol.%, or 4 vol.% to 6 vol.%; or the gradient is 4 vol.% or 6 vol.% or 8 vol.% or 10 vol.%.

For example, in still other embodiments, the gradient of at least one raw material component selected from aluminum and cobalt between the intermediate layer and the surface layer is selectable in a range of 2 vol.% to 5 vol.%, such as 2 vol.% to 5 vol.%, 2 vol.% to 4 vol.%, 2 vol.% to 3 vol.%, 3 vol.% to 4 vol.%, or 2 vol.%, 3 vol.% or 4 vol.%.

Particularly, the gradient change among the components, the properties and the functions of the material and the increase of the thermal expansion coefficient from the outside to the inside can better ensure the formation of favorable residual compressive stress on the surface layer of the material and the offset of the tensile stress formed in the cutting process; the toughness and the wear resistance of the material are improved; the heat conductivity coefficient is increased from the outside to the inside, which is beneficial to the transfer of cutting heat.

In an embodiment of the present invention, the intermediate layer thickness is equal to or greater than the skin layer thickness; for example, in some embodiments of the present invention, the thickness of the intermediate layer is larger than the thickness of the symmetrical layer, and the ratio of the thicknesses of the surface layer and the intermediate layer is selectable in the range of 0.2 to 0.6, and in some embodiments of the present invention, the ratio of the thicknesses is preferably 0.3, and the material as a whole exerts a good effect on the performance.

In an embodiment of the invention, the components in the raw material are powders, wherein the powder particle sizes of cubic boron nitride, titanium carbide, aluminum and cobalt are 5-10 μm, 1-5 μm, 3-5 μm and 0.5-1 μm, respectively.

In a second aspect of the invention, there is provided a method of preparing a material as described in the first aspect above, comprising: ball-milling the raw materials respectively, drying and sieving the raw materials after ball-milling; preparing 3 groups of raw materials according to the composition and mixing; and 3 groups of raw materials are paved and filled in layers, and are subjected to vacuum treatment and sintering after being pre-pressed.

In some embodiments, the ball milling is performed by using absolute ethyl alcohol as a medium, and the mass ratio of the grinding balls to the raw materials in the ball milling process is 10-25: 1, ball milling for 24-50 h; in the embodiment of the invention, when the mass ratio of the grinding balls to the raw materials is 20: 1. the ball milling time is 48h, so that a better ball milling effect can be obtained, and the uniform dispersion of the raw material powder is realized.

In some embodiments, the post-pre-compaction vacuum treatment comprises: the pre-pressing pressure is 10-20MPa, and the vacuum treatment condition is 450-600 ℃ vacuum treatment for 10-15 h. In the embodiment of the invention, when the prepressing pressure is 15MPa and the vacuum treatment condition is 500 ℃ for vacuum treatment for 12 hours, the prepressing effect is better, the compactness after prepressing is proper, and the dispersion among layers is good.

In certain embodiments, the sintering comprises: sintering at 1350-1500 deg.c for 5-20min and sintering pressure of 5.5-6 GPa. Particularly, when the sintering temperature is in the range of 1350-1500 ℃, particularly 1500 ℃ and the sintering pressure is in the range of 5.5-6 GPa, particularly 5.8GPa, the heat preservation treatment is carried out for 10min, and the sintering effect is excellent. Under the sintering condition, the method is more beneficial to the exertion of the functions of the metal phase and the ceramic phase and promotes the improvement of the mechanical property, the microstructure and the sintering property of the cubic boron nitride.

Specifically, under the sintering condition, Al is melted into a liquid phase, which is particularly beneficial to the diffusion flow of CBN particles and the bonding between the CBN particles, more AlN is generated, the sintering is promoted, the reverse conversion of CBN to h-BN is inhibited, and the sintered body has higher content of cubic boron nitride and better compactness; under the condition, TiC can better reduce bonding among CBN, inhibit grain growth and effectively improve the heat resistance and impact resistance of the PCBN sintered body; under the condition, Co has good activation effect on cubic boron nitride particles, direct bonding between cubic boron nitrides can be better promoted, and the performance of a sintered body is improved.

The material prepared by the invention has excellent mechanical property, in some embodiments of the invention, the hardness HV of the material prepared by the invention can reach 2800-. In some preferred embodiments of the invention, the hardness HV of the prepared material is as high as 4000, and the bending strength is as high as 1000 MPa.

In a third aspect of the invention, the invention also provides the use of the material described in the first aspect above in the field of tool preparation or in the field of machining of wear-resistant parts; preferably, the tool is a mechanical cutting tool, particularly suitable for high speed cutting of quenched steel-like materials.

The invention reasonably optimizes the process parameters such as layer thickness ratio, interlayer component gradient, sintering temperature, sintering pressure, heat preservation time and the like, and reasonably adjusts the thermal expansion coefficient to enable the material surface layer to have residual compressive stress, thereby improving the hardness, toughness and wear resistance of the surface layer material. Compared with homogeneous cubic boron nitride cutters, the material prepared by the invention has higher toughness and wear resistance, so that the cutters are better suitable for high-speed cutting and machining of wear-resistant parts, and have wider application prospects.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein:

fig. 1 is a schematic diagram of the definition of the layer thickness ratio of the 3-layer gradient cubic boron nitride material (e ═ d1/d2 ═ d3/d2) in the embodiment of the present invention, where d1, d2, and d3 are the thicknesses of the 1 st layer, the 2 nd layer, and the 3 rd layer in this order from top to bottom.

Fig. 2 is a schematic structural diagram of a 3-layer gradient cubic boron nitride material in example 1, in which a surface layer C1, an intermediate layer C2, and a surface layer C1 are arranged in sequence from top to bottom, and 2C 1 layers are symmetrical with respect to the intermediate layer C2.

Detailed Description

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out according to conventional conditions or according to conditions recommended by the manufacturers.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or starting materials used in the present invention can be purchased from conventional sources, and unless otherwise specified, the reagents or starting materials used in the present invention can be used in a conventional manner in the art or in accordance with the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present invention. The preferred embodiments and materials described herein are intended to be exemplary only.

The gradient cubic boron nitride cutter material is exemplarily illustrated by taking a 3-layer symmetrical gradient structure (as shown in figure 2), the invention provides some implementation modes, and the volume percentages of the raw materials of the components are as follows: CBN 70-80 vol.%, TiC10 vol.%, Al 5-10 vol.% and Co 5-10 vol.%. The layer thickness ratio is selected to be 0.2-0.6, the gradient of interlayer composition is 2-10 vol.%, for example, the gradient of cubic boron nitride is 4-10 vol.%, and the gradient of aluminum and cobalt is 2-5 vol.%. The powder is filled into a molybdenum cup in a layered paving and filling mode, and the cubic boron nitride cutter material is synthesized by utilizing high temperature and high pressure. The preparation method comprises the following steps:

respectively filling TiC, Al and Co into a ball milling tank, taking a hard alloy ball as a grinding ball and absolute ethyl alcohol as a medium, wherein the mass ratio of the grinding ball to powder is 20: 1, ball milling for 48 hours; drying the suspension subjected to ball milling in a vacuum drying oven at 110 ℃, sieving with a 200-mesh sieve after drying, and packaging for later use; mixing all the powder according to a volume ratio, controlling the thickness of the layer by quality, putting the weighed powder into a molybdenum cup layer by layer, and filling according to the sequence of C1/C2/C1, wherein the powder needs to be compacted and paved every time one layer of powder is added until all the powder is filled; pre-pressing the filled powder under 15MPa, and then carrying out vacuum treatment on the powder at 500 ℃ for 12 h; and putting the powder subjected to vacuum treatment into a pyrophyllite die, and starting pressing and sintering. The sintering temperature is 1350-1500 ℃, the heat preservation time is 10min, and the sintering pressure is 5.5GPa-6 GPa.

Example 1

The preparation of a gradient cubic boron nitride cutting tool with a layer thickness ratio of 0.3, 3 layers, a CBN composition gradient of 6 vol.% between layers and an Al and Co composition gradient of 3 vol.% was carried out, and the ingredients are shown in table 1, giving the composition in volume percent (vol.%) of the mixed powders of C1 (surface layer) and C2 (middle layer).

TABLE 1

Respectively filling TiC, Al and Co into a ball milling tank, taking a hard alloy ball as a grinding ball and absolute ethyl alcohol as a medium, wherein the mass ratio of the grinding ball to powder is 20: 1, ball milling for 48 hours; drying the suspension subjected to ball milling in a vacuum drying oven at 110 ℃, sieving with a 200-mesh sieve after drying, and packaging for later use; mixing all the powder according to a volume ratio, controlling the thickness of the layer by quality, putting the weighed powder into a molybdenum cup layer by layer, and filling according to the sequence of C1/C2/C1, wherein the powder needs to be compacted and paved every time one layer of powder is added until all the powder is filled; pre-pressing the filled powder under 15MPa, and then carrying out vacuum treatment on the powder at 500 ℃ for 12 h; and putting the powder subjected to vacuum treatment into a pyrophyllite die, and starting pressing and sintering. The sintering temperature is 1450 ℃, the heat preservation time is 10min, and the sintering pressure is 5.5 GPa. The material was ground and polished to give a sample bar having a flexural strength of 500MPa and a hardness of HV 2800.

Example 2

A gradient cubic boron nitride cutting tool with a layer thickness ratio of 0.3, 3 layers, an interlayer CBN composition gradient of 4 vol.% and an Al and Co composition gradient of 2 vol.% was prepared, and the ingredients are shown in Table 2, which gives the volume percentages (vol.%) of the components of three sets of mixed powders, C1 (surface layer) and C3 (intermediate layer)

TABLE 2

Respectively filling TiC, Al and Co into a ball milling tank, taking a hard alloy ball as a grinding ball and absolute ethyl alcohol as a medium, wherein the mass ratio of the grinding ball to powder is 20: 1, ball milling for 48 hours; drying the suspension subjected to ball milling in a vacuum drying oven at 110 ℃, sieving with a 200-mesh sieve after drying, and packaging for later use; mixing all the powder according to a volume ratio, controlling the thickness of the layer by quality, putting the weighed powder into a molybdenum cup layer by layer, and filling according to the sequence of C1/C3/C1, wherein the powder needs to be compacted and paved every time one layer of powder is added until all the powder is filled; pre-pressing the filled powder under 15MPa, and then carrying out vacuum treatment on the powder at 500 ℃ for 12 h; and putting the powder subjected to vacuum treatment into a pyrophyllite die, and starting pressing and sintering. The sintering temperature is 1500 ℃, the heat preservation time is 10min, and the sintering pressure is 5.8 GPa. The material was polished to obtain a sample strip having a flexural strength of 780MPa and a hardness of HV 3600.

Example 3

A gradient cubic boron nitride cutting tool with a layer thickness ratio of 0.3, 3 layers, an interlayer CBN composition gradient of 8 vol.% and an Al and Co composition gradient of 4 vol.% was prepared, and the ingredients are shown in Table 3, which gives the volume percentages (vol.%) of the components of three sets of mixed powders, C1 (surface layer) and C4 (intermediate layer)

TABLE 3

Respectively filling TiC, Al and Co into a ball milling tank, taking a hard alloy ball as a grinding ball and absolute ethyl alcohol as a medium, wherein the mass ratio of the grinding ball to powder is 20: 1, ball milling for 48 hours; drying the suspension subjected to ball milling in a vacuum drying oven at 110 ℃, sieving with a 200-mesh sieve after drying, and packaging for later use; mixing all the powder according to a volume ratio, controlling the thickness of the layer by quality, putting the weighed powder into a molybdenum cup layer by layer, and filling according to the sequence of C1/C4/C1, wherein the powder needs to be compacted and paved every time one layer of powder is added until all the powder is filled; pre-pressing the filled powder under 15MPa, and then carrying out vacuum treatment on the powder at 500 ℃ for 12 h; and putting the powder subjected to vacuum treatment into a pyrophyllite die, and starting pressing and sintering. The sintering temperature is 1350 ℃, the heat preservation time is 10min, and the sintering pressure is 5.8 GPa. The flexural strength was found to be 525MPa and the hardness was HV 3200.

The sintered gradient cubic boron nitride material of examples 1-3 was cut, ground and polished to a 3 × 4 × 20mm pattern, and the bending strength was measured by three-point bending, the hardness of the layer was measured by vickers, and the fracture toughness was measured by indentation.

Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that changes may be made in the embodiments and/or equivalents thereof without departing from the spirit and scope of the invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A gradient composite cubic boron nitride material is prepared by sintering cubic boron nitride, titanium carbide, aluminum and cobalt as raw materials, and has a 3-layer symmetrical gradient structure with a middle layer as a symmetry;

wherein the raw materials comprise the following components in percentage by volume: cubic boron nitride 70-80 vol.%, titanium carbide 10 vol.%, aluminum 5-10 vol.% and cobalt 5-10 vol.%; wherein, cubic boron nitride is used as a substrate, titanium carbide is used as a ceramic bonding agent, and aluminum and cobalt are used as metal bonding agents;

the raw material components of the symmetrical layers which are symmetrical relative to the middle layer are the same in content, and the thicknesses of the symmetrical layers are symmetrically distributed;

the volume percentage content of the cubic boron nitride increases from the middle layer to the symmetrical layer by layer, and the volume percentage content of at least one component selected from aluminum and cobalt decreases from the middle layer to the symmetrical layer by layer;

the gradient of the raw material composition cubic boron nitride between the middle layer and the symmetrical layer is 4-10 vol%;

the aluminum and cobalt gradients between the interlayer and the symmetric interlayer are both 2 vol.% to 5 vol.%;

the thickness of the middle layer is not less than that of the symmetrical layer;

the raw materials are powder, wherein the grain diameters of the powder of cubic boron nitride, titanium carbide, aluminum and cobalt are respectively 5-10 μm, 1-5 μm, 3-5 μm and 0.5-1 μm.

2. The gradient composite cubic boron nitride material of claim 1, wherein the thickness of the intermediate layer is greater than the thickness of the symmetrical layer, and the ratio of the layer thickness of the symmetrical layer to the layer thickness of the intermediate layer is 0.2 to 0.6.

3. The method of preparing a gradient composite cubic boron nitride material of claim 1, comprising: ball-milling the raw materials respectively, drying and sieving the raw materials after ball-milling; preparing 3 groups of raw materials according to the composition and mixing respectively; 3 groups of raw materials are paved and filled in layers, and vacuum treatment and sintering are carried out after prepressing;

the ball milling takes absolute ethyl alcohol as a medium, and in the ball milling process, the mass ratio of the grinding balls to the raw materials is 10-25: 1, ball milling for 24-50 h;

the post-prepressing vacuum treatment comprises the following steps: the prepressing pressure is 10-20MPa, and the vacuum treatment condition is 450-600 ℃ vacuum treatment for 10-15 h;

the sintering comprises the following steps: sintering at 1350-1500 deg.c for 5-20min and sintering pressure of 5.5-6 GPa.

4. Use of the gradient composite cubic boron nitride material of claim 1 in the field of tool preparation or in the field of wear part machining, wherein the tool is a mechanical cutting tool.