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

本项目研究了难熔金属钼、钨及其合金的中子辐照效应。其目的是提出高Z材料在聚变动力堆高热负荷和重中子辐照条件下的可用性。在动力反应堆中，高热通量材料必须在高温中子暴露后存活。在这些材料中，重要的是控制辐照过程中的微观结构，以抑制中子辐照脆化。这些材料中添加了钛和锆（对于TZM合金）和镁，以改善再结晶后的可焊性和延展性。这些合金的材料性能后，中子重辐照高通量尚未得到很好的研究。在快通量试验装置（FFTF）中，在360 ~ 800 ℃，能量密度达34 dpa的辐照条件下，研究了辐照条件和材料参数对材料力学性能的影响。对试样进行了显微组织观察、拉伸试验和弯曲试验。结果表明，辐照前的热处理影响中子辐照引起的塑性变化。特别是，应力消除处理被发现是有效的，以抑制辐照诱发脆化。Re的加入对抑制800 ℃以上高温辐照再结晶是有效的，但过量的Re含量会促进辐照诱导析出，导致明显的辐照硬化和脆化。在高温辐照环境下，如在动力聚变堆中使用，必须要求Mo和W合金具有最佳的Re含量，从而抑制晶界的生长和延迟辐射诱导的沉淀。

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.