Development of Testing Machine for Mechanical Properties at Ultra High Temperature using Impulse Electron Irradiation

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Testing machine for mechanical properties of ultra high-temparture refractory materials has been developed. Special vacuum chamber was built for impulse electron bombardment system. Electron irradiation was carried out at 30kV in vacuum. To hold the specimen during mechanical testing, ceramic holder was used. The maximum temperature which was obtained using this heating system was around 2000ﾟC.High heating rate of 500ﾟC/min was obtained. The thermal stability during mechanical test was less than 2ﾟC.Since test specimens of metallic materials were directly heated by electron irradiation, mechanical test at ultra high temperature could be done. For ceramic specimens the specimen surface was convered by tantalum tube and then high temperature was realozed. The thermal gradient between upper and bottom sides of specimens was very small. The displacement of specimens during tesile or comression tests was measured using laser light. Mechanical properties of transition metal silicides such as MoSi_2 and NbSi_2 which are attractive candidates for refractory materials operating around 2000ﾟC were investigated by means of this testing machine. MoSi_2 and NbSi_2 showed anomalous strengthening above 1200ﾟC and the anomalous peak was shifted to higher temperture by addition of small amounts of third element. Mechanical properties of TiAl alloys were also investigated. The temperature dependence of strength and ductility of these alloys was easily obtained using this machine.