Study on Heavy Neutron Irradiation Effects of Refractory-Metal-Base, High-Z and High-Heat-Flux Materials for Fusion Power Reactors

用该程序研究了难熔金属、钼、钨及其合金的中子辐照效应。目的是提出高z材料在高热负荷和重中子辐照下的可用性，如在核聚变反应堆中。在动力反应堆中，高热流密度材料必须在高温中子照射后存活。在这些材料中，控制辐照过程中的微观结构是抑制中子辐照脆化的关键。本研究采用Mo、TZM、Mo- re和W-Re合金。这些材料中加入钛、锆（用于TZM合金）和铼，以提高再结晶后的可焊性和延展性。这些合金在高通量中子重辐照后的材料性能还没有得到很好的研究。研究了辐照条件和材料参数对材料力学性能的影响。样品在快速通量测试设备（FFTF）中辐照，温度从360℃到800℃，通量高达34 dpa。利用这些试样进行了显微组织观察、拉伸试验和弯曲试验。发现辐照前的热处理对中子辐照引起的延性变化有影响。特别是，应力消除处理可以有效地抑制辐照引起的脆化。在800C以上的高温下辐照时，添加稀土能有效抑制再结晶。过量的稀土含量会增强辐照诱导沉淀，导致明显的辐照硬化和脆化。在大功率聚变反应堆等高温辐照环境中，Mo和W合金必须具有最佳的Re含量，以抑制晶界的生长，延缓辐照诱导析出。

Neutron irradiation effects of refractory metals, molybdenum (Mo), tungsten (W) and their alloys were studied in the program. The aim is to propose the availability of high-Z materials in the condition of high thermal load and heavy neutron irradiation as in fusion power reactors. In power reactors, high-heat flux materials must be survived after neutron exposure at high temperatures. In these materials, it is important to control the microstructure during irradiation in order to suppress the neutron-irradiation embrittlement.In this study, Mo, TZM,Mo-Re and W-Re alloys were used. These materials are added with titanium and zirconium (for TZM alloy) and rhenium to improve the weldability and ductility after recrystallization. Material properties of these alloys after neutron heavy irradiation up to high fluence have not been studied well. The influence of irradiation conditions and materials parameters on the mechanical properties was studied.The specimens were irradiated in the Fast Flux Test Facility (FFTF) at temperatures from 360C to 800C and fluence up to 34 dpa. With these specimen, the observations of microstructure, tensile tests and bend tests were carried out. It was found that heat treatments before irradiation affect the ductility change caused by neutron irradiation. Especially, stress-relieved treatment is found to be effective to suppress irradiation-induced embrittlement. Re addition is effective for suppression of recrystallization during irradiation at high temperatures over 800C.But excessive Re content enhances irradiation-induced precipitation, which results in conspicuous irradiation hardening and embrittlement.As used in irradiation environment at high temperatures, such as in power fusion reactors, the alloys of Mo and W must be required with optimum Re content, as much as to suppress the growth of grain boundary and retard irradiation-induced precipitation.