阅读说明：本技术 高耐磨的氮化硅基陶瓷及其制备方法和应用 (High-wear-resistance silicon nitride-based ceramic and preparation method and application thereof ) 是由 不公告发明人 于 2020-07-06 设计创作，主要内容包括：本发明公开了一种高耐磨的氮化硅基陶瓷及其制备方法和应用,所述氮化硅基陶瓷是将α-Si<Sub>3</Sub>N<Sub>4</Sub>和烧结助剂进行球磨混合,干燥得到混合粉体,再将混合粉体干压成型得到生坯；将生坯在1300~1700℃下预烧,降温到室温后获得预烧体；将预烧体在1600~1800℃,轴向加压加至30~100 MPa下进行烧结得到高耐磨氮化硅基陶瓷。本发明的高耐磨氮化硅基陶瓷在高温下的塑性流动实现氮化硅基陶瓷的径向向心流动,从而实现晶粒径向定向织构化,从而获得高耐磨氮化硅基陶瓷。(The invention discloses a high-wear-resistance silicon nitride-based ceramic and a preparation method and application thereof, wherein the silicon nitride-based ceramic is prepared by mixing α -Si 3 N 4 Ball-milling and mixing the powder and a sintering aid, drying to obtain mixed powder, and dry-pressing the mixed powder to obtain a green body; pre-sintering the green body at 1300-1700 ℃, and cooling to room temperature to obtain a pre-sintered body; and sintering the pre-sintered body at 1600-1800 ℃ under axial pressurization and 30-100 MPa to obtain the high-wear-resistance silicon nitride-based ceramic. The plastic flow of the high-wear-resistance silicon nitride-based ceramic realizes the radial centripetal flow of the silicon nitride-based ceramic at high temperature, thereby realizing the radial directional texturing of crystal grains and further obtaining the high-wear-resistance silicon nitride-based ceramic.)

1. A preparation method of high wear-resistant silicon nitride-based ceramic is characterized in that α -Si is added₃N₄Ball-milling and mixing the powder and a sintering aid, drying to obtain mixed powder, and dry-pressing the mixed powder to obtain a green body; pre-sintering the green body at 1300-1700 ℃, and cooling to room temperature to obtain a pre-sintered body; and sintering the pre-sintered body at 1600-1800 ℃ under axial pressurization and 30-100 MPa to obtain the high-wear-resistance silicon nitride-based ceramic.

2. The method for preparing high wear-resistant silicon nitride-based ceramic according to claim 1, wherein the sintering aid is Al₂O₃And Re₂O₃The mixture of (1), the Al₂O₃And Re₂O₃Al in the mixture of₂O₃:Re₂O₃The volume ratio of (1-4) to (1-4), the Re₂O₃The Re can be replaced by Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

3. The method for preparing silicon nitride-based ceramic with high wear resistance according to claim 2, wherein α -Si is used₃N₄The purity of the alloy is 98-100 wt%, and the alloy is α -Si₃N₄Has a particle diameter of<5 mu m; the Al is₂O₃The purity of the Al is 99.8-99.99 wt%, and the Al is₂O₃Has a particle diameter of<500 nm; said Re₂O₃The purity of (2) is 99-99.9 wt%, and the Re₂O₃Has a particle diameter of<1 µm。

4. The method for preparing silicon nitride-based ceramic with high wear resistance according to claim 1, wherein the mixed powder further comprises a reinforcing agent, α -Si is added₃N₄Ball milling and mixing the sintering aid and the reinforcing agent, and drying to obtain a mixtureAnd (3) powder.

5. The method for preparing high-wear-resistance silicon nitride-based ceramic according to claim 4, wherein α -Si is contained in the mixed powder₃N₄The volume ratio of the sintering aid to the reinforcing agent is (60-95): (5-12): 1-35).

6. The method of claim 4, wherein the enhancer is β -Si₃N₄Diamond, WC, TiC, TiN, TiCN, TiB₂、ZrB₂、MoSi₂And one or more of SiC, β -Si₃N₄Diamond, WC, TiC, TiN, TiCN, TiB₂、ZrB₂、MoSi₂The purity of the SiC is 99-99.9 wt%, and the purity is β -Si₃N₄Diamond, WC, TiC, TiN, TiCN, TiB₂、ZrB₂、MoSi₂And SiC having a particle diameter of<5 µm。

7. The method for preparing silicon nitride-based ceramic with high wear resistance according to claim 1, wherein α -Si is added₃N₄Ball-milling and mixing the powder and a sintering aid, drying to obtain mixed powder, and dry-pressing the mixed powder to obtain a green body; pre-sintering the green body at 1300-1700 ℃ in a protective atmosphere, and cooling to room temperature to obtain a pre-sintered body; and heating the presintering body to 1200-1500 ℃ at a speed of 10-150 ℃/min under a protective atmosphere, axially pressurizing to 10-30 MPa, continuously heating to 1600-1800 ℃ at a speed of 10-150 ℃/min, preserving heat for 20-120 min, axially pressurizing to 30-100 MPa within 1-5 min of beginning heat preservation, cooling to 700-900 ℃ at a speed of 10-150 ℃/min, axially releasing pressure, and cooling to room temperature along with a furnace to obtain the high-wear-resistance silicon nitride-based ceramic.

8. A silicon nitride-based ceramic obtained by the method for preparing a highly wear-resistant silicon nitride-based ceramic according to any one of claims 1 to 7, wherein, in a cross section of the silicon nitride-based ceramic perpendicular to an axis of the silicon nitride-based ceramic, more than 80% of the number of the long columnar silicon nitride crystal grains has the characteristics that: the included angle between the long axis direction of any long columnar silicon nitride crystal grain and the central line of the external circle passing through the silicon nitride crystal grain and perpendicular to the silicon nitride-based ceramic section is less than 30 degrees.

9. The silicon nitride-based ceramic prepared by the preparation method of the high-wear-resistance silicon nitride-based ceramic according to any one of claims 1 to 7, wherein the relative density of the silicon nitride-based ceramic is 98 to 100%, the Vickers hardness of the silicon nitride-based ceramic is 15 to 21GPa in a plane vertical to a pressurizing direction, and the Vickers hardness of the silicon nitride-based ceramic is 14.5 to 19 GPa in the center of a tangent plane.

10. Use of the highly wear resistant silicon nitride based ceramic according to any of claims 1 to 7 in the field of cutting tools.

Technical Field

The invention belongs to the technical field of ceramic cutting tools, and particularly relates to high-wear-resistance silicon nitride-based ceramic and a preparation method and application thereof.

Background

The silicon nitride-based ceramic is made of Si₃N₄High-performance structural ceramic materials containing (or not containing) one or more carbides, nitrides and oxides as reinforcing phases. The material has good comprehensive mechanical properties of high hardness and high toughness, low thermal expansion coefficient and good thermal conductivity in all structural ceramicsThe densification of silicon nitride ceramics needs to add a certain content of sintering aids to realize liquid phase sintering, and the phase change of α → β is usually accompanied in the sintering densification process, α -Si₃N₄Belongs to a low-temperature stable crystal form, β -Si₃N₄Belongs to a high-temperature stable crystal form, the phase change process of α → β is an irreversible process, β -Si₃N₄Silicon nitride ceramics having a microstructure of random distribution of such grains, typically having long columnar or acicular crystal morphology, generally have higher strength, toughness and hardness in different directions, but due to β -Si₃N₄The crystal grains have anisotropy, and have obvious performance difference in the directions of a long axis and a short axis, so that a material with certain performance in a certain direction and particularly excellent performance can be prepared through structural design so as to meet more severe application conditions. Wherein grain-oriented texturing is one of the methods to achieve such strengthening.

The silicon nitride-based ceramic cutter has excellent red hardness and stable size, can be used for processing metal materials such as cast iron, hardened steel, heat-resistant steel, high-temperature alloy and the like at high speed, and can obtain more excellent cutting performance than a hard alloy cutter. At present, the optimized design and preparation of the silicon nitride-based ceramic cutting tool can be realized by adjusting the appearance and the size of crystal grains, changing the component content of a sintering aid, adding a reinforcing phase, forming a gradient structure, forming a textured structure and the like. The cutting tool requires that the rear tool face of the tool has good wear resistance, the whole tool has good strength, and the direction perpendicular to the cutting edge has excellent heat conductivity, so that the cutting tool has the characteristic of anisotropic optimization on the performance requirement. Among the various methods of optimizing silicon nitride based tools, the formation of textured structures is the most potential method.

Disclosure of Invention

Based on the above, the invention provides a high-wear-resistance silicon nitride-based ceramic, and a preparation method and application thereof, aiming at realizing radial centripetal flow of the silicon nitride-based ceramic through plastic flow at high temperature, so as to realize radial directional texturing of crystal grains, and further obtain the high-wear-resistance silicon nitride-based ceramic.

The technical scheme of the method is that the preparation method of the high-wear-resistance silicon nitride-based ceramic is prepared by mixing α -Si₃N₄Ball-milling and mixing the powder and a sintering aid, drying to obtain mixed powder, and dry-pressing the mixed powder to obtain a green body; pre-sintering the green body at 1300-1700 ℃, and cooling to room temperature to obtain a pre-sintered body; and sintering the pre-sintered body at 1600-1800 ℃ under axial pressurization and 30-100 MPa to obtain the high-wear-resistance silicon nitride-based ceramic.

In a further scheme, the sintering aid is Al₂O₃And Re₂O₃The mixture of (1), the Al₂O₃And Re₂O₃Al in the mixture of₂O₃:Re₂O₃The volume ratio of (1-4) to (1-4), the Re₂O₃The Re can be replaced by Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

In a further scheme, the α -Si₃N₄The purity of the alloy is 98-100 wt%, and the alloy is α -Si₃N₄Has a particle diameter of<5 mu m; the Al is₂O₃The purity of the Al is 99.8-99.99 wt%, and the Al is₂O₃Has a particle diameter of<500 nm; said Re₂O₃The purity of (2) is 99-99.9 wt%, and the Re₂O₃Has a particle diameter of<1 µm。

In a further aspect, the α -Si₃N₄Has a purity of 98 to 100 wt% of α -Si₃N₄Has a particle diameter of<3µm。

In a further aspect, the α -Si₃N₄:Al₂O₃And Re₂O₃The volume ratio of the mixture of (1) to (5) is (45-47).

In a further scheme, the mixed powder also comprises a reinforcing agent, α -Si is added₃N₄And carrying out ball milling mixing on the sintering aid and the reinforcing agent, and drying to obtain mixed powder.

In a further aspect, the mixed powder is a mixed powderMiddle α -Si₃N₄The volume ratio of the sintering aid to the reinforcing agent is (60-95): (5-12): 1-35).

In a further scheme, the reinforcing agent is β -Si₃N₄Diamond, WC, TiC, TiN, TiCN, TiB₂、ZrB₂、MoSi₂And one or more of SiC, β -Si₃N₄Diamond, WC, TiC, TiN, TiCN, TiB₂、ZrB₂、MoSi₂The purity of the SiC is 99-99.9 wt%, and the purity is β -Si₃N₄Diamond, WC, TiC, TiN, TiCN, TiB₂、ZrB₂、MoSi₂And SiC having a particle diameter of<5 mu m. The reinforcing agent can be used for increasing the hardness and the wear resistance in any direction; the crack propagation resistance in the radial direction is improved, and the toughness is improved.

Further scheme, α -Si₃N₄Ball-milling and mixing the powder and a sintering aid, drying to obtain mixed powder, and dry-pressing the mixed powder to obtain a green body; pre-sintering the green body at 1300-1700 ℃ under the protection of protective atmosphere, and cooling to room temperature to obtain a pre-sintered body; and heating the presintering body to 1200-1500 ℃ at a speed of 10-150 ℃/min under a protective atmosphere, axially pressurizing to 10-30 MPa, continuously heating to 1600-1800 ℃ at a speed of 10-150 ℃/min, preserving heat for 20-120 min, axially pressurizing to 30-100 MPa within 1-5 min of beginning heat preservation, cooling to 700-900 ℃ at a speed of 10-150 ℃/min, axially releasing pressure, and cooling to room temperature along with a furnace to obtain the high-wear-resistance silicon nitride-based ceramic. Variable temperature pressurization and gradient pressurization are adopted, so that the pressurization process before heat preservation has the advantage that the pressure is increased along with the increase of the temperature, and the mold is protected (the strength of the cold mold is low). The constant pressure process before heat preservation, along with the temperature increase and pressure maintenance, provides a sintering driving force and promotes densification. The pressurizing process after heat preservation can quickly provide plastic deformation and centripetal flow driving force and shorten the preparation time. And in the constant pressure process after heat preservation, the temperature and the pressure are kept, and proper plastic deformation power is kept, so that the radial orientation of crystal grains is realized. The densification and plastic deformation processes are not completely separated, the densification process at the early stage is accompanied by certain plastic deformation, and the plastic deformation process at the later stage can be further improvedDensity. Because the formation of the long columnar grains needs a certain temperature and time, the presintering body is possibly crushed due to excessive pressurization at the early stage, or plastic deformation filling is completed before the long columnar grains are not formed, so that the long columnar grains cannot be plastically deformed after phase transformation at the later stage, and the directions of the columnar grains are randomly distributed.

In a further scheme, the protective atmosphere is nitrogen or argon.

Further, the shape of the burn-in body may be a cylindrical or annular column.

According to the further scheme, the mixed powder is filled into a dry pressing die, and a cylindrical green body is obtained through dry pressing, wherein the forming pressure of the dry pressing is 100-300 MPa.

Further, the outer diameter of the cylindrical green body is 10-100 mm, the height is 3-80 mm, and the ratio of the outer diameter to the inner diameter is 1.25-2.

Further, the ratio of the outer diameter to the inner diameter of the cylindrical green body is 1.25-1.6. The external-internal diameter ratio influences the direction angle of the oriented crystal grains, and the external-internal diameter ratio is small, the plastic deformation degree is large, the orientation degree is good, and the orientation angle consistency is good; too small a cylindrical wall thickness and too large an aspect ratio can collapse inwardly upon pressurization.

Further, the green body is placed into an atmospheric pressure sintering furnace or an atmospheric pressure sintering furnace, the temperature is raised to 1300-1700 ℃ at the speed of 10-50 ℃/min under the protection of nitrogen or argon atmosphere, then the temperature is preserved for 20-120 min, the temperature is reduced to room temperature at the speed of 10-150 ℃/min, and the green body is taken out to obtain a pre-sintered body, wherein the density of the pre-sintered body is 60% -90%. The pre-sintering can provide a blank with certain strength, and the dry pressing blank is effectively prevented from cracking and breaking in a graphite die.

Further, the pre-sintered body is placed in a graphite mold, placed in a hot-pressing sintering furnace or a discharge plasma sintering furnace, heated to 1200-1500 ℃ at a speed of 10-150 ℃/min under the protection of nitrogen or argon atmosphere, axially pressurized to 10-30 MPa, then continuously heated to 1600-1800 ℃ at a speed of 10-150 ℃/min, then subjected to heat preservation for 20-120 min, axially pressurized to 30-100 MPa within 1-5 min of starting heat preservation, then cooled to 700-900 ℃ at a speed of 10-150 ℃/min, subjected to axial pressure relief, cooled to room temperature along with the furnace, and taken out to obtain the high-wear-resistant silicon nitride-based ceramic.

In a further scheme, the diameter of a die cavity of the graphite die is consistent with the outer diameter of the pre-sintering body, and the contact surfaces of the upper pressure head and the lower pressure head and the pre-sintering body are solid planes. At the position, because the pressure is too small in the early stage, the presintering body continues to be sintered and shrunk in the temperature rising process, the outer diameter of the presintering body is smaller than the inner diameter of the die, and the plastic deformation flows outwards in the later stage, so that the outer layer cannot form radial orientation; in addition, spark plasma sintering requires a certain contact pressure, and the contact pressure required at low temperature is small. Therefore, depending on the formulation (different temperatures at which shrinkage begins), different pre-sinter sizes, a suitable early and late stage pressure is required.

A high wear-resistant silicon nitride-based ceramic, wherein in a cross section of the silicon nitride-based ceramic, which is perpendicular to an axis of the silicon nitride-based ceramic, more than 80% of the number of long columnar silicon nitride crystal grains has the characteristics that: the included angle between the long axis direction of any long columnar silicon nitride crystal grain and the central line of the external circle passing through the silicon nitride crystal grain and perpendicular to the silicon nitride-based ceramic section is less than 30 degrees.

In a further scheme, in a section of the silicon nitride-based ceramic, which is perpendicular to a certain axis of the silicon nitride-based ceramic, more than 80% of the long columnar silicon nitride crystal grains have the characteristics that: the included angle between the long axis direction of any long columnar silicon nitride crystal grain and the central line of the circumcircle passing through the silicon nitride crystal grain on the section vertical to the silicon nitride-based ceramic is less than 20 degrees.

In a further scheme, the relative density of the silicon nitride-based ceramic is 98-100%, the Vickers hardness of the silicon nitride-based ceramic is 15-21 GPa on a surface vertical to the pressurizing direction, and the Vickers hardness of the silicon nitride-based ceramic is 14.5-19 GPa at the center of a chord tangent plane. The silicon nitride-based ceramic is tested by adopting a method that a Vickers hardness pressure head is perpendicular to the surface and is pressed at the position, the load is 1 kilogram, and the pressure maintaining time is 10 seconds; the relative density here is a percentage of the actual density to the theoretical density, the relative density = (actual density/theoretical density) × 100%; the chord section is a section parallel to the pressurizing direction; the center of the chord section is the position of the center line parallel to the pressurizing direction on the chord section. The application of high wear-resistant silicon nitride-based ceramics in the field of cutting tools.

After the high-wear-resistance silicon nitride-based ceramic is prepared, the silicon nitride-based ceramic is mechanically edged to obtain the silicon nitride-based ceramic cutting tool.

In a further scheme, the silicon nitride-based ceramic cutting tool is in the shape of a disk, a square disk, a pentagram disk or a hexagon disk with a hole in the center.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

1. the high-wear-resistance silicon nitride-based ceramic has the advantages that the radial oriented texture structure of crystal grains has the differences of the radial and axial physical and mechanical properties, the surface vertical to the radial direction has high wear resistance, the optimal wear-resistant surface is in a 360-degree surrounding structure, the obtained ceramic is used for a cutting tool, particularly an indexing blade, the maximum utilization of a cutting edge can be realized, and the exposed wear-resistant surface with a high area can be kept, so that the high-wear-resistance silicon nitride-based ceramic has obvious application advantages compared with the existing one-dimensional or random two-dimensional texture.

2. The high wear-resistant silicon nitride-based ceramic is sintered by adopting a temperature-changing and different axial pressurization method after presintering, and the radial centripetal flow of the silicon nitride-based ceramic is realized by plastic flow at high temperature, so that the radial directional texturing of crystal grains is realized, more than 80 percent of long columnar silicon nitride crystal grains are in the section vertical to a certain axis of the silicon nitride-based ceramic, and the silicon nitride-based ceramic has the characteristics that: the included angle between the long axis direction of any long columnar silicon nitride crystal grain and the central line of the external circle passing through the silicon nitride crystal grain and perpendicular to the silicon nitride-based ceramic section is less than 30 degrees.

3. According to the preparation method of the high-wear-resistance silicon nitride-based ceramic, disclosed by the invention, the pre-sintering and texture sintering are combined, so that large-batch operation can be easily realized in the pre-sintering process, and the cost is effectively saved; due to the existence of the pre-sintering process, the time-consuming pre-sintering or early-stage heating time can be effectively reduced in the sintering and texturing process, the rapid densification and texturing are realized, the pre-sintering can provide a blank with certain strength, the dry-pressed blank is effectively prevented from cracking and breaking in a graphite mold, and compared with one-step sintering and texturing, the production efficiency is greatly improved.

4. According to the preparation method of the high-wear-resistance silicon nitride-based ceramic, the final texturing degree and the grain size are effectively and flexibly controlled by controlling the inner diameter and the outer diameter of the dry-pressed green body, the pre-sintering process and the sintering texturing process, so that the silicon nitride-based ceramic can be obtained in the same formula and applied to ceramic cutters.

Drawings

Fig. 1 is a micrograph of the solid body and its cross-sections at different positions of a silicon nitride-based ceramic cutting tool according to example 1 of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.