放電プラズマ焼結法によって作製したHfC-Wの高温強度特性に及ぼす焼結条件の影響

抄録

Thoriated tungsten alloy (ThO2-W) has been used as cathode material in discharge lamp and for TIG welding rod because of its excellent thermoelectric emission properties. However, ThO2 is one of radioactive substances, therefore development of thoria free tungsten is desired. In this study, hafnium carbide (HfC) was used as an alternate material of ThO2. The material used, HfC-W alloys was produced with spark plasma sintering (SPS) and tensile strength of the alloy at elevated temperature was evaluated. Tensile strengths at 1300 and 1500°C increased with increasing sintering temperature. Increase of sintering pressure also enhanced tensile strength from 250 MPa to 281 MPa at 1300°C. According to microstructure observation by SEM-EDS in the materials used, coarse aggregates of HfC were observed in HfC-W sintered by SPS. It is considered that aggregate of HfC with lower relative density affects tensile strength of the materials used. Therefore, the high temperature strength is possibly improved by increasing sintering temperature and pressure due to dense aggregate of HfC. Moreover, strength may be improved by dispersing small HfC particles in the W-matrix to avoid formation of aggregate of HfC.