| Budget Amount *help |
¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 2000: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 1999: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
In order to improve the resistance to radiation embrittlement that is the major concerns in the use of vanadim and its alloys for fusion structural applications, it is necessary to introduce the microstructure with fine grains and dispersed particles. The microstructure can be introduced by power metallurgy (P/M) method including mechanical alloying (MA) and hot isostatic pressing (HIP). For the P/M methods, however, there is a critical issue that solute oxygen and nitrogen contained in the starting powder and introduced through the fabrication processes cause a serious loss of ductility. In this study, first, a process for microstructural control to solve the issue was proposed and applied to fabricate vanadium alloys of V-(1.6-2.6)wt%Y. Then, the microstructure and mechanical properties of the fabricated alloys were evaluated with emphasis on the effects of vacuum annealing at 1273-1573 K and cold rolling up to 80%. Neutron irradiation was performed in JMTR to 0.7 dpa at 563 to 1073 K. Irradiated specimens were subjected to Vickers microhardness testing and TEM microstructural observation.
The essential point of the process is that solute oxygen and nitrogen is consumed to form yttrium compounds as finely dispersed particles (Y_2O_3 and YN). It is shown that the vanadium matrix in the alloys is free from solute oxygen and nitrogen and the alloys exhibited good ductility even at 77K, as measured by impact three-point bending and dynamic tensile testing. The effect of annealing on the microstructure and mechanical properties is significant, but that of cold rolling is insignificant, indicating that the alloys in the annealed conditions show good ductility and strength without plastic working after HIP. The irradiated specimens showed radiation induced <110> twinning and much less radiation hardening than commercially available pure vanadium, indicating that the fabricated alloys have much improved radiation resistance.
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