Development of Radiation Resistant Vanadium Alloys with Extra-fine Grains and Dispersed Particles

为了提高钒及其合金在熔合组织应用中的抗辐射脆化性能，有必要引入细晶粒和分散颗粒的显微组织。通过动力冶金（P/M）方法，包括机械合金化（MA）和热等静压（HIP），可以引入微观组织。然而，对于P/M方法，存在一个关键问题，即起始粉末中含有溶解氧和氮，并通过制造过程引入，导致延展性严重损失。本文首先提出了一种显微组织控制工艺，并将其应用于V-(1.6-2.6)wt%Y钒合金的制备。在此基础上，研究了1273 ~ 1573 K真空退火和80%冷轧对合金组织和力学性能的影响。在563 ~ 1073 K的JMTR中进行0.7 dpa的中子辐照。对辐照后的试样进行维氏显微硬度测试和透射电镜显微组织观察。该工艺的要点是溶质氧和氮被消耗，形成以细小分散颗粒（Y_2O_3和YN）形式存在的钇化合物。冲击三点弯曲和动态拉伸试验表明，合金中的钒基体不含溶质氧和溶质氮，即使在77K时合金仍具有良好的延展性。退火对合金组织和力学性能的影响显著，而冷轧对合金组织和力学性能的影响不显著，说明退火条件下的合金在非塑性加工条件下具有良好的塑性和强度。辐照后的样品显示出辐射诱导的<110>的孪晶和比市购纯钒少得多的辐射硬化，这表明制备的合金具有更强的抗辐射性。

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.