Fabrication And Characteristics Of TiB₂-AlN Composite Ceramics

TiB₂ ceramics have excellent physical-chemical properties and mechanical properties. Apart from its extremely high hardness and elastic modulus, TiB₂ exhibits high electrical conductivity; melting temperature and wear resistance, low specific weight and relatively good chemical stability. TiB₂ ceramics are very promising in modern industry. The main problems that the application of TiB₂ ceramics include: high price of TiB₂ raw materials, low sintering activity and the inherent brittleness. Adding of secondary phase is an important way to improve the mechanical properties of ceramics.In this paper, TiB₂-AlN multiphase ceramics were prepared by hot pressing technology with A1N as an additive. The effects of aid content, sintering temperature and holding time on mechanical properties of TiB₂ ceramics were studied, the relationship between microstructure and mechanical properties was analyzed. And the effect of other aid to TiB₂-AlN ceramics was discussed.It improved the sintering ability that AlN was added. Relative density of the ceramic got above 96%, compared with 90% when added none into TiB₂. And materials showed the high relative density (97.2%) when A1N content was 5vol.%. With the increasing of A1N content, mechanical properties increased to max. at 5vol. % and then decreased.The effects of the sintering temperature (1700°C-1900°C) and holding time (0.5h- 3h) to properties were studied at the same A1N content. With the prolong of soaking time, the hardness and the blending strength of the materials increased to max. and then decreased. The same trend was found at sintering temperature increased. It was found that the better properties were got when sintered at 1800°C for holding 1h. The specimen sintered at this condition gave 23.3GPa for Vickers hardness, 461GPa for bending strength, 648MPa for young's modulus and 6.91 MPa·m ^1/2 for fracture toughness.Adding Y₂O₃ & NbB₂ could improve the relative density of TiB₂-5vol.% A1N composites. The mechanical properties decreased if Y₂O₃ was added, but they increased with NbB₂ as an aid. The samples with 5vol.% NbB₂ showed the good properties, exhibiting the bending strength of 682 MPa and fracture toughness of 7.06 MPa·m ^1/2.Microstructure observation displayed that AlN grains were randomly dispersed in TiB₂ matrix had the same sizes. TiN and BN formed in grain-boundary because of the reactions between AlN and the oxide-layer of TiB₂ powder. It got smaller gains and better relative density after Y₂O₃ and NbB₂ added. And the ceramics gave excellent mechanical properties with NbB₂ as an additive, because of excellent microstructure and density increasing.