Preparation Of TiC-TiB₂Ceramic Composites By Spark Plasma Sintering

TiC and TiB2ceramics possess excellent physical and mechanical properties of high melting point and hardness, excellent chemical stability, good electrical and thermal conductivity as well as relatively low coefficient of thermal expansion, so they are considered to be one of the most promising high temperature structural ceramic materials and have been widely used in various fields, such as special electrode, cutting tools, wear-resisting parts and other special industry. The preparation methods of TiC-TiB2ceramic composites reported at home and abroad are mainly self-propagating high-temperature combustion synthesis(SHS), non-pressure liquid-phase sintering, hot pressing method, in-situ synthesis, floating zone and arc melting methods. SHS is also known as combustion synthesis technology, which is the most reported method. Compared with conventional sintering method, spark plasma sintering (SPS) has the characteristics of high thermal efficiency, low sintering temperature, short sintering time and fast heating and cooling speeds. SPS technology possesses unique advantages for the densification of hard sintered materials. Present reports on the synthesis of TiC-TiB2ceramics composite prepared by SPS method are still rare. In this study, we focused on preparing TiC-TiB2ceramics composites with additives of Ni, Cu and Ti, respectively. The effects of the kind of additives, sintering temperature and holding time on the composition, microstructure, bulk density and mechanical properties of the materials were investigated in detail.The experimental results were shown as follows:(1) XRD analyses results showed that all the three series of TiC-TiB2ceramic composites consisted of TiC and TiB2, except the TiC-TiB2-Cu composites in which the Cu phase was identified.(2) SEM results showed that for the TiC-TiB2ceramic composites with different metal elements, TiC and TiB2were observed as the matrix phases, and the metal phases were distributed in the areas of both phase interface and grain boundary. Especially, for the TiC-TiB2-Ni composites, some nano particles were dispersed on the TiC matrix phase. It was a particular phenomenon only observed in the TiC-TiB2-Ni composites, which were identified as intermetallic NiTi2phase.(3) For the TiC-TiB2ceramic composites adding with Ni, Cu or Ni, the fracture microstructures showed a mixing mode of inter/transgranular fracture. The ductile fracture characteristics of TiC-TiB2composites with Ni or Cu were more obvious than that of TiC-TiB2-Ti ceramic composites.(4) When the SPS temperature was1400℃, the TiC-TiB2-Ni composites showed the optimized properties. The bulk density, Vickers hardness and fracture toughness of TiC-TiB2-Ni composites were4.92g/cm3,21.3GPa and4.85MPa-m1/2, respectively. Using TiC, TiB2and Cu as raw materials, the sample prepared by SPS at1600℃holding for5minutes showed the best comprehensive performance:the bulk density, Vickers hardness, fracture toughness of TiC-TiB2-Cu composites were4.91g/cm3,19.8GPa and4.28MPa-m1/2, respectively. Using TiC, TiB2and Ti as raw materials, the best sintering conditions were1600℃holding for5minutes. The optimum bulk density, Vickers hardness and fracture toughness of TiC-TiB2-Ti composites were4.81g/cm3,20.3GPa and3.91MPa-m1/2, respectively.