Fabrication and Mechanical Properties of TiB_2-B_4C Composite Ceramics by Spark Plasma Sintering Method

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To develop the mold material made of hard ceramics in which the electrical discharge machining (EDM) is possible, the TiB_2-B_4C ceramic composites containing 0 up to 100 mol%B_4C (20mol%steps) were fabricated from a mixture of TiB_2 and B_4C powders by Spark Plasma Sintering(SPS) method that was possible to product efficiently. SPS condition was 1680-1750°C for 720s under a pressure of 40.0 MPa in a vacuum, and the examination of the composite revealed mechanical and electrical properties and EDM characteristics as a function of compositional change from TiB_2 to B_4C. Optimum additive to improve mechanical properties was also investigated for the composite with the content of 40mol%B_4C.(1)The derived TiB_2-B_4C composite containing 40-60 mol%B_4C with no additives had following high properties. A relative density could be attained more than 96%, Vickers hardness 30 GPa, flexural strength 730 MPa, Young's modulus 450 GPa, fracture toughness (Kic) 5.4 MPa・m^<1/2> or more, respectively. The mean surface roughness (Ra) was below 25 nm, and electrical conductivity in the range of 0.25-1.32 MS・m^<->1.(2)The composites presented high mechanical properties compared with those for TiB_2 or B_4C single phase, and possesed the comparable properties manufactured by hot-pressing method at 1950°C with the same composition.(3)The composites were machinable by electric discharge with high-speed using the conditions for steel. Hence, the composite was useful for ceramic mold material. The mechanical properties after processing of EDM were about 70% of those bofore.(4)AIN was the optimum additive to improve the mechanical properties of TiB_2-B_4C ceramic composite. AINpromoted especially the Kic up to 8.OMPa・m^<1/2>.By adopting the composite ceramics as mold materials, it is presumed that the long-term life of mold, improvement of heat-resistant and corrosion-resistant are attained.