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

Abstract

An electro-conductive B.sub.4C—TiB.sub.2 has a microstructure in which large B.sub.4C grains are coated by small TiB.sub.2 grains. The composite ceramic includes 10˜30% by volume of TiB.sub.2. A method for preparing the electro-conductive B.sub.4C—TiB.sub.2 composite ceramic includes: (1) weighing B.sub.4C, 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.

Claims

1. An electro-conductive B.sub.4C—TiB.sub.2 composite ceramic, wherein the electro-conductive B.sub.4C—TiB.sub.2 composite ceramic has a microstructure in which B.sub.4C grains are coated by TiB.sub.2 grains; a grain size of the B.sub.4C grains is larger than that of the TiB.sub.2 grains; and a TiB.sub.2 volume percentage in the electro-conductive B.sub.4C—TiB.sub.2 composite ceramic is 10˜30%; wherein the electro-conductive B.sub.4C—TiB.sub.2 composite ceramic is prepared through steps of: (1) weighing a B.sub.4C powder, a TiC powder, and an amorphous B powder according to a preset weight ratio; wherein a particle size of the B.sub.4C 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 B.sub.4C 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 B.sub.4C—TiB.sub.2 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 B.sub.4C—TiB.sub.2 composite ceramic of claim 1, wherein a molar ratio of TiC to B is 1:6.6; and a weight ratio of the B.sub.4C 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 B.sub.4C—TiB.sub.2 composite ceramic, comprising: (1) weighing a B.sub.4C powder, a TiC powder, and an amorphous B powder according to a preset weight ratio; wherein a particle size of the B.sub.4C 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 B.sub.4C 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 B.sub.4C powder to the TiC powder to the amorphous B powder is 21-69:14-36:16-43.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] FIG. 1 schematically shows a fabrication principle of an electro-conductive B.sub.4C—TiB.sub.2 composite ceramic according to an embodiment of the present disclosure;

[0029] FIGS. 2a-2c show microstructure changes of a polished surface of a B.sub.4C—TiB.sub.2 composite ceramic prepared in Example 1 of the present disclosure; and

[0030] FIG. 3 is a microstructure diagram of a fracture surface of the B.sub.4C—TiB.sub.2 composite ceramic prepared in Example 1 of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0031] 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

[0032] 5.03 g of B.sub.4C 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 B.sub.4C-15 vol % TiB.sub.2 composite ceramic. As demonstrated by the performance test, the prepared B.sub.4C-15 vol % TiB.sub.2 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.Math.m.sup.1/2, and an electrical conductivity of 2.8×10.sup.4 S/m.

[0033] A B.sub.4C-15 vol % TiB.sub.2 composite ceramic prepared from 10.3 μm B.sub.4C powder and 2.5 μm TiB.sub.2 powder through the same mixing and sintering process was used as comparison. As demonstrated by the performance test, the obtained B.sub.4C-15 vol % TiB.sub.2 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.Math.m.sup.1/2, and an electrical conductivity of 4.3×10.sup.3 S/m.

[0034] FIG. 1 illustrated the construction of the B.sub.4C—TiB.sub.2 composite ceramic of the present disclosure, where (a) mixing of raw materials B.sub.4C, TiC, and B powder; (b) during the sintering process, TiC and B first underwent an in-situ reaction to form B.sub.4C—TiB.sub.2 ultrafine composite powder; (c) large B.sub.4C particles selectively absorbed ultrafine B.sub.4C particles in the B.sub.4C—TiB.sub.2 composite powder to experience grain growth; and (d) small TiB.sub.2 grains are distributed around the large B.sub.4C grains to form an enveloped microstructure.

[0035] FIGS. 2a-2c show microstructure change of the polished surface of the B.sub.4C—TiB.sub.2 composite ceramic prepared in Example 1, where FIG. 2a: in the early stage of the sintering process, the large B.sub.4C particles and the in-situ formed B.sub.4C—TiB.sub.2 ultrafine composite powder coexisted; FIG. 2b: with the extension of the sintering time, the large B.sub.4C particles selectively absorbed the ultrafine B.sub.4C particles in the B.sub.4C—TiB.sub.2 composite powder to experience grain growth; and FIG. 2c: after holding for a certain time, the ultrafine B.sub.4C particles in the B.sub.4C—TiB.sub.2 composite powder were completely absorbed by the large B.sub.4C particles, and the small TiB.sub.2 grains are distributed around the large B.sub.4C grains to form an enveloped microstructure. During this process, TiB.sub.2 also underwent grain growth. However, due to the small initial grain size and limited growth, the TiB.sub.2 grain was still much smaller relative to the B.sub.4C grain.

[0036] As shown in FIG. 3, the small TiB.sub.2 grains were distributed around the large B.sub.4C grains.

Example 2

[0037] 5.99 g of B.sub.4C 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 B.sub.4C-15 vol % TiB.sub.2 composite ceramic. As demonstrated by the performance test, the prepared B.sub.4C-15 vol % TiB.sub.2 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.Math.m.sup.1/2, and an electrical conductivity of 3.3×10.sup.3 S/m.

[0038] B.sub.4C-15 vol % TiB.sub.2 composite ceramic prepared from 3.1 μm B.sub.4C powder and 2.5 μm TiB.sub.2 powder through the same mixing and sintering method was used as comparison. As demonstrated by the performance test, the obtained B.sub.4C-15 vol % TiB.sub.2 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.Math.m.sup.1/2, and an electrical conductivity of 2.1×10.sup.3 S/m.

Example 3

[0039] 4.07 g of B.sub.4C 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 B.sub.4C-20 vol % TiB.sub.2 composite ceramics. As demonstrated by the performance test, the prepared B.sub.4C-20 vol % TiB.sub.2 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.Math.m.sup.1/2, and an electrical conductivity of 6.9×10.sup.4 S/m.

[0040] B.sub.4C-20 vol % TiB.sub.2 composite ceramic prepared from 10.3 μm B.sub.4C powder and 2.50 μm TiB.sub.2 powder by the same mixing and sintering method was used as comparison. As demonstrated by the performance test the obtained B.sub.4C-20 vol % TiB.sub.2 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.Math.m.sup.1/2, and an electrical conductivity of 1.6×10.sup.4 S/m.