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

要开发在电放电机器（EDM）中由硬陶瓷制成的模具材料，TiB_2-B_4C陶瓷复合材料中含有0至100摩尔%B_4C（20摩尔%步）的TiB_2和B_4C粉末混合而成的方法可能是有效地生产的。SPS条件为1680-1750摄氏度，在真空中40.0兆帕的压力下为720秒，并对复合材料揭示的机械和电气性能和电火花加工特性进行了试验，作为TiB_2到B_4C的复合变化的一个功能。优化添加剂以改善机械性能，也对该复合物的含量40mol%B_4C进行了调查。（1）衍生出的TiB_2-B_4C复合物含有40-60摩尔%B_4C，无添加物具有高性能。相对密度可以超过96%，维克斯硬度30 GPa，柔性强度730 MPa，年轻的模块450 GPa，分形硬度（Kic） 5.4 MPa·m^<1/2>或更多，尊重。平均表面粗糙度（Ra）低于25纳米，电导电性在0.25-1.32 MS·m^<->1。（2）该组合物提供的高机械性能与那些用于TiB_2或B_4C单相位的高机械性能相比较，并在1950°C的相同组合物中采用热压方法制造的可比较性能。（3）该复合材料是可机械化的，并以高速使用钢铁条件进行电气放电。汉斯，这个复合物是用陶瓷模具材料用的。在EDM处理后，机械性能约占70%。（4）AIN是一种最佳补充剂，以提高TiB_2-B_4C陶瓷复合物的机械性能。特别是将复合陶瓷作为模具材料采用复合陶瓷，从而使模具的长期寿命、耐高温和耐腐蚀的改进成为8.OMpa·m^<1/2>。

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.