ELECTRO-CONDUCTIVE B4C-TiB2 COMPOSITE CERAMIC AND PREPARATION METHOD THEREOF

Information

  • Patent Application
  • 20230271886
  • Publication Number
    20230271886
  • Date Filed
    April 15, 2023
    a year ago
  • Date Published
    August 31, 2023
    a year ago
Abstract
An electro-conductive B4C—TiB2 has a microstructure in which large B4C grains are coated by small TiB2 grains. The composite ceramic includes 10˜30% by volume of TiB2. A method for preparing the electro-conductive B4C—TiB2 composite ceramic includes: (1) weighing B4C, TiC, and amorphous B powder; (2) mixing evenly and drying thoroughly the powders; and (3) loading the mixed powder into a graphite mold; and placing the graphite mold in a spark plasma sintering furnace for sintering under vacuum, where the sintering is performed at 2000° C. and 50 MPa for 5˜20 min.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from Chinese Patent Application No. 202210485924.X, filed on May 6, 2022. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference in its entirety.


TECHNICAL FIELD

This application relates to ceramic materials, and more particularly to an electro-conductive B4C—TiB2 composite ceramic and a preparation method thereof.


BACKGROUND

B4C has been widely used in bulletproof armor, wear-resistant devices, aerospace and nuclear industries because of its high hardness, low density, good chemical stability, and large neutron-absorption cross section. Due to the presence of covalent bonds, B4C has poor sintering performance, which makes it difficult to achieve densification. Furthermore, the low fracture toughness of monolithic B4C ceramic leads to poor machining efficiency and accuracy and high cost, which limit the application of the monolithic B4C ceramic.


The introduction of a second phase TiB2 into the B4C matrix to form B4C—TiB2 composite ceramics can not only significantly improve the sintering performance and mechanical properties of B4C ceramics, but also greatly reduce the electrical resistivity thereby meeting the requirements of electrical discharge machining (EDM). Usually, a material with lower electrical resistivity is more suitable for the EDM processing. Therefore, a key to improving the EDM processing performance of B4C—TiB2 composite ceramics is reducing the electrical resistivity. The most effective way to reduce the electrical resistivity is increasing the conductive phase content in composite ceramics. However, the increased content of TiB2 conductive phase in the B4C—TiB2 composite ceramics will bring the following problems: (1) increasing the overall density of the composite ceramics (the density of TiB2 is about 1.8 times that of B4C); (2) reducing the hardness of composite ceramics (the hardness of TiB2 is lower than that of B4C); and (3) increasing the raw material cost. The above problems limit the application of B4C—TiB2 composite ceramic in lightweight armor. In conventional methods, a lower electrical resistivity of B4C—TiB2 composite ceramics is achieved mainly at the expense of other properties or cost.


SUMMARY

In view of the deficiencies in the prior art, this application provides an electro-conductive B4C—TiB2 composite ceramic having a high electrical conductivity at low TiB2 content and a preparation method thereof In the microstructure of the B4C—TiB2 composite ceramic provided herein, the large B4C grains are coated by small TiB2 grains.


Technical solutions of this application are described as follows.


In a first aspect, this application provides an electro-conductive B4C—TiB2 composite ceramic, wherein the electro-conductive B4C—TiB2 composite ceramic has a microstructure in which B4C grains are coated by TiB2 grains; a grain size of the B4C grains is much larger than that of the TiB2 grains; and a TiB2 volume percentage in the electro-conductive B4C—TiB2 composite ceramic is 10˜30%;


wherein the electro-conductive B4C—TiB2 composite ceramic is prepared through steps of:

    • (1) weighing a B4C powder, a TiC powder, and an amorphous B powder according to a preset weight ratio;
    • wherein a particle size of the B4C powder is 3.0˜20.0 μm; a particle size of the TiC powder is 0.05˜3.0 μm; a particle size of the amorphous B powder is 0.5˜1.0 μm; a molar ratio of TiC to B is 1:6.6; and a weight ratio of the B4C powder to the TiC powder to the amorphous B powder is 21-69:14-36:16-43;
    • (2) mixing the B4C powder, the TiC powder and the amorphous B powder evenly followed by drying to obtain a mixed powder; and
    • (3) loading the mixed powder into a graphite mold; and transferring the graphite mold to a spark plasma sintering (SPS) furnace followed by sintering under vacuum.


In a second aspect, this application further provides a method for preparing the electro-conductive B4C—TiB2 composite ceramic, including:

    • (1) weighing a B4C powder, a TiC powder, and an amorphous B powder according to a preset weight ratio;
    • wherein a particle size of the B4C powder is 3.0˜20.0 μm; a particle size of the TiC powder is 0.05˜3.0 μm; and a particle size of the amorphous B powder is 0.5˜1.0 μm; a molar ratio of TiC to B is 1:6.6; and a weight ratio of the B4C powder to the TiC powder to the amorphous B powder is 21-69:14-36:16-43;
    • (2) mixing the B4C powder, the TiC powder and the amorphous B powder evenly followed by drying to obtain a mixed powder; and
    • (3) loading the mixed powder into a graphite mold; and transferring the graphite mold to a spark plasma sintering (SPS) furnace followed by sintering under vacuum.


In an embodiment, the sintering is performed at 2000° C. and 50 MPa for 5˜20 min.


Compared to the prior art, this application has the following beneficial effects.

    • (1) A microstructure, in which the large B4C grains are coated by the small TiB2 grains, is constructed, which is conducive to the formation and improvement of the electro-conductive network.
    • (2) The spark plasma sintering (SPS) technology can effectively inhibit the growth of TiB2 grains, which is conducive to improving the electrical properties of the B4C—TiB2 composite ceramic.
    • (3) In the case of the same TiB2 content, the B4C—TiB2 composite ceramic prepared herein has higher electrical conductivity.
    • (4) In the case of the same resistivity, the B4C—TiB2 composite ceramic provided herein has lower TiB2 content.
    • (5) The larger the particle size of B4C, the higher the conductivity of the composite ceramic, which helps to reduce the cost of raw materials.
    • (6) Compared with the traditional method, the mechanical properties of the B4C—TiB2 composite ceramic prepared in the present application are comparable or better.
    • (7) The preparation process of the present application is simple, including only mixing and sintering of raw powders, without any complex operations.





BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains FIG. 1 executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.



FIG. 1 schematically shows a fabrication principle of an electro-conductive B4C—TiB2 composite ceramic according to an embodiment of the present disclosure;



FIGS. 2a-2c show microstructure changes of a polished surface of a B4C—TiB2 composite ceramic prepared in Example 1 of the present disclosure; and



FIG. 3 is a microstructure diagram of a fracture surface of the B4C—TiB2 composite ceramic prepared in Example 1 of the present disclosure.





DETAILED DESCRIPTION OF EMBODIMENTS

The technical solutions of the present disclosure will be further described in detail below in conjunction with the accompanying drawings and embodiments, but the embodiments below are not intended to limit the disclosure.


Example 1

5.03 g of B4C powder with a particle size of 10.3 μm, 1.83 g of TiC powder with a particle size of 0.05 and 2.19 g of amorphous B powder with a particle size of 0.9 μm were weighed, mixed uniformly, and dried to obtain a mixed powder. The mixed powder was loaded into a graphite mold, subjected to sintering in a spark plasma sintering furnace under vacuum at 2000° C. and 50 MPa for 16 min, and cooled naturally to obtain an electro-conductive B4C-15 vol % TiB2 composite ceramic. As demonstrated by the performance test, the prepared B4C-15 vol % TiB2 composite ceramic had a relative density of 98.7%, a three-point flexural strength of 676 MPa, a Vickers hardness of 29.0 GPa, a fracture toughness of 5.3 MPa·m1/2, and an electrical conductivity of 2.8×104 S/m.


A B4C-15 vol % TiB2 composite ceramic prepared from 10.3 μm B4C powder and 2.5 μm TiB2 powder through the same mixing and sintering process was used as comparison. As demonstrated by the performance test, the obtained B4C-15 vol % TiB2 composite ceramic had a relative density of 95.3%, a three-point flexural strength of 552 MPa, a Vickers hardness of 27.5 GPa, a fracture toughness of 4.4 MPa·m1/2, and an electrical conductivity of 4.3×103 S/m.



FIG. 1 illustrated the construction of the B4C—TiB2 composite ceramic of the present disclosure, where (a) mixing of raw materials B4C, TiC, and B powder; (b) during the sintering process, TiC and B first underwent an in-situ reaction to form B4C—TiB2 ultrafine composite powder; (c) large B4C particles selectively absorbed ultrafine B4C particles in the B4C—TiB2 composite powder to experience grain growth; and (d) small TiB2 grains are distributed around the large B4C grains to form an enveloped microstructure.



FIGS. 2a-2c show microstructure change of the polished surface of the B4C—TiB2 composite ceramic prepared in Example 1, where FIG. 2a: in the early stage of the sintering process, the large B4C particles and the in-situ formed B4C—TiB2 ultrafine composite powder coexisted; FIG. 2b: with the extension of the sintering time, the large B4C particles selectively absorbed the ultrafine B4C particles in the B4C—TiB2 composite powder to experience grain growth; and FIG. 2c: after holding for a certain time, the ultrafine B4C particles in the B4C—TiB2 composite powder were completely absorbed by the large B4C particles, and the small TiB2 grains are distributed around the large B4C grains to form an enveloped microstructure. During this process, TiB2 also underwent grain growth. However, due to the small initial grain size and limited growth, the TiB2 grain was still much smaller relative to the B4C grain.


As shown in FIG. 3, the small TiB2 grains were distributed around the large B4C grains.


Example 2

5.99 g of B4C powder with a particle size of 3.1 μm, 1.22 g of TiC powder with a particle size of 0.8 μm, and 1.46 g of amorphous B powder with a particle size of 0.9 μm were weighed, mixed uniformly, and dried to obtain a mixed powder. The mixed powder was loaded into a graphite mold, subjected to sintering in a spark plasma sintering furnace under vacuum at 2000° C. and 50 MPa for 16 min, and cooled naturally to obtain an electro-conductive B4C-15 vol % TiB2 composite ceramic. As demonstrated by the performance test, the prepared B4C-15 vol % TiB2 composite ceramic had a relative density of 99.5%, a three-point flexural strength of 780 MPa, a Vickers hardness of 31.8 GPa, a fracture toughness of 5.8 MPa·m1/2, and an electrical conductivity of 3.3×103 S/m.


B4C-15 vol % TiB2 composite ceramic prepared from 3.1 μm B4C powder and 2.5 μm TiB2 powder through the same mixing and sintering method was used as comparison. As demonstrated by the performance test, the obtained B4C-15 vol % TiB2 composite ceramic had a relative density of 98.65%, a three-point flexural strength of 638 MPa, a Vickers hardness of 29.2 GPa, a fracture toughness of 4.9 MPa·m1/2, and an electrical conductivity of 2.1×103 S/m.


Example 3

4.07 g of B4C powder with a particle size of 10.3 μm, 2.45 g of TiC powder with a particle size of 0.8 and 2.91 g of amorphous B powder with a particle size of 0.9 μm were weighed, mixed uniformly, and dried to obtain a mixed powder. The mixed powder was loaded into a graphite mold, subjected to sintering in a spark plasma sintering furnace under vacuum at 2000° C. and 50 MPa for 16 min, and cooled naturally to obtain an electro-conductive B4C-20 vol % TiB2 composite ceramics. As demonstrated by the performance test, the prepared B4C-20 vol % TiB2 composite ceramic had a relative density of 98.1%, a three-point flexural strength of 701 MPa, a Vickers hardness of 28.5 GPa, a fracture toughness of 6.2 MPa·m1/2, and an electrical conductivity of 6.9×104 S/m.


B4C-20 vol % TiB2 composite ceramic prepared from 10.3 μm B4C powder and 2.50 μm TiB2 powder by the same mixing and sintering method was used as comparison. As demonstrated by the performance test the obtained B4C-20 vol % TiB2 composite ceramic had a relative density of 93.5%, a three-point flexural strength of 587 MPa, a Vickers hardness of 27.6 GPa, a fracture toughness of 5.1 MPa·m1/2, and an electrical conductivity of 1.6×104 S/m.

Claims
  • 1. An electro-conductive B4C—TiB2 composite ceramic, wherein the electro-conductive B4C—TiB2 composite ceramic has a microstructure in which B4C grains are coated by TiB2 grains; a grain size of the B4C grains is larger than that of the TiB2 grains; and a TiB2 volume percentage in the electro-conductive B4C—TiB2 composite ceramic is 10˜30%; wherein the electro-conductive B4C—TiB2 composite ceramic is prepared through steps of:(1) weighing a B4C powder, a TiC powder, and an amorphous B powder according to a preset weight ratio;wherein a particle size of the B4C powder is 3.0˜20.0 μm; a particle size of the TiC powder is 0.05˜3.0 μm; and a particle size of the amorphous B powder is 0.5˜1.0(2) mixing the B4C powder, the TiC powder and the amorphous B powder evenly followed by drying to obtain a mixed powder; and(3) loading the mixed powder into a graphite mold; and transferring the graphite mold to a spark plasma sintering (SPS) furnace followed by sintering under vacuum.
  • 2. The electro-conductive B4C—TiB2 composite ceramic of claim 1, wherein in step (3), the sintering is performed at 2000° C. and 50 MPa for 5˜20 min.
  • 3. The electro-conductive B4C—TiB2 composite ceramic of claim 1, wherein a molar ratio of TiC to B is 1:6.6; and a weight ratio of the B4C powder to the TiC powder to the amorphous B powder is 21-69:14-36:16-43.
  • 4. A method for preparing an electro-conductive B4C—TiB2 composite ceramic, comprising: (1) weighing a B4C powder, a TiC powder, and an amorphous B powder according to a preset weight ratio;wherein a particle size of the B4C powder is 3.0˜20.0 μm; a particle size of the TiC powder is 0.05˜3.0 μm; and a particle size of the amorphous B powder is 0.5˜1.0 μm;(2) mixing the B4C powder, the TiC powder and the amorphous B powder evenly followed by drying to obtain a mixed powder; and(3) loading the mixed powder into a graphite mold; and transferring the graphite mold to a spark plasma sintering (SPS) furnace followed by sintering under vacuum.
  • 5. The method of claim 4, wherein in step (3), the sintering is performed at 2000° C. and 50 MPa for 5˜20 min.
  • 6. The method of claim 4, wherein a molar ratio of TiC to B is 1:6.6; and a weight ratio of the B4C powder to the TiC powder to the amorphous B powder is 21-69:14-36:16-43.
Priority Claims (1)
Number Date Country Kind
202210485924.X May 2022 CN national