用于第四代先进核能系统的氧化物弥散强化合金的研究

发布时间：2018-06-27 19:01

本文选题：氧化物弥散强化 + 铁素体钢　；参考：《北京科技大学》2016年博士论文

【摘要】：目前为止,人类面临的最大问题就是日趋增长的能源需求问题,对这一问题的解决需要综合考虑新能源的开发利用以及环境污染等诸多因素。在新能源中,核裂变能(Fission Energy)很可能在未来的低碳环保能源系统中继续扮演非常重要的角色。根据国家政策要求,当今核裂变反应堆需要朝着更高效以及服役寿命更长的方向发展。由于超临界水堆(Supercritical Water Reactor, SCWR)具有很高的经济性、优异的热效率、以及简单的设计理念,因此成为了第四代先进核裂变系统中的重要候选堆型之一。由于超临界水堆需要在强中子辐照、高瞬变应力、以及强腐蚀性介质这样极端的环境下运行,因此,材料问题成为制约其工程应用的一个关键性问题。因为纳米氧化物弥散强化(Oxide Dispersion Strengthened, ODS)铁素体钢(Ferritic Steels)具有优异的抗辐照损伤性能、高温力学性能、以及抗腐蚀潜力,被认为是超临界水堆包壳管的主要候选材料之一。ODS铁素体钢具有如此优异的性能主要是源自于它特殊的显微组织结构。通常情况下,ODS铁素体钢内部存在着大量尺寸极为细小的纳米氧化物弥散粒子,它们可以作为钉扎质点有效地阻止基体内位错和晶界的移动,从而提高材料的力学性能以及热稳定性能。同时,这些纳米氧化物弥散粒子还可以作为稳定的“池子”对辐照后的ODS铁素体钢中产生的缺陷进行捕获和钉扎,从而提高材料的抗辐照性能。众所周知,Cr含量对ODS铁素体钢的性能起着重要的作用。一般而言,由于低Cr含量的ODS铁素体钢的抗腐蚀性能不够优异,这使得它们在超临界水堆中的应用受到一定限制。然而,如果ODS铁素体钢中的Cr含量过高,长时间服役之后基体内部可能会产生大量的富Cr相从而引起材料的时效脆化。因此,通过实验研究找到一个合适的Cr含量值对于服役于超临界水堆中的ODS铁素体钢是至关重要的。在本研究中,通过机械合金化和热等静压的方法制备了Cr含量分别为12%、14%、16%、以及18%(质量分数)的四种ODS铁素体钢样品。采用热加工(锻造／轧制)的方法提高烧结后材料的力学性能,再通过热处理工艺消除热加工给材料带来的残余应力。采用光学显微镜(Optical Microscope, OM)、扫描电子显微镜(Scanning Electron Microscopy, SEM)、以及透射电子显微镜(Transmission Electron Microscopy, TEM)等先进表征手段对不同Cr含量的ODS铁素体钢样品的显微组织结构进行了系统地研究。结果表明不同Cr含量的ODS铁素体钢的晶粒尺寸都呈现出一种双峰分布的特征。所有样品的基体中都可以观察到大量均匀分布的Y-Ti-O型的纳米氧化物弥散粒子,这些弥散粒子的尺寸几乎都在几个纳米至五十个纳米之间。对不同Cr含量ODS铁素体钢样品的维氏显微硬度、拉伸性能、冲击韧性等力学性能进行测试,分析结果表明Cr含量的变化对于ODS铁素体钢的力学性能的影响并不是非常明显。此外,我们对不同Cr含量的ODS铁素体钢的其它服役性能也进行了测试和对比,包括材料在600℃/25 MPa条件下抵抗超临界水介质腐蚀的性能,材料在700℃的长期时效稳定性,以及材料在500℃条件下进行双束离子辐照(1 MeV Kr+ and 15 keV He+)后的显微组织变化等。最终,根据结果对比优选出综合性能较为优异的Cr含量为16%的ODS铁素体钢作为未来研究和生产的主要材料。在本次研究中除了制备了不同Cr含量的ODS铁素体钢样品之外,我们还尝试通过机械合金化(MA)和热挤压(Hot Extrusion, HE)的方法制备了一种可以适用于超临界水堆以及超高温反应堆(Very High Temperature Reactor, VHTR)的新型Hastelloy XR-ODS镍基合金。相比传统的Hastelloy XR型镍基合金而言,经过纳米氧化物弥散强化之后的Hastelloy XR-ODS镍基合金在强度方面得到了明显的提高,但是其塑性却发生了严重地下降。通过装备有能谱分析仪(X-ray Energy Dispersive Spectroscopy, EDS)的高分辨透射电子显微镜(High-Resolution Transmission Electron Microscopy, HRTEM)结合选区电子衍射分析技术(Selected Area Electronic Diffraction, SAD)对Hastelloy XR-ODS镍基合金样品的显微组织结构进行系统地研究,根据实验分析结果发现造成材料塑性不佳的主要原因是其内部存在着大量的尺寸在微米级的晶界第二相析出物、相连化合物、以及非晶态二氧化硅。
[Abstract]:So far, the biggest problem facing mankind is the growing energy demand problem. The solution of this problem requires a comprehensive consideration of the development and utilization of new energy and environmental pollution. In the new energy, nuclear fission energy (Fission Energy) is very likely to continue to play a very important role in the future low carbon environmental energy system. Role. According to national policy, nuclear fission reactors need to develop in the direction of more efficient and longer service life. Because the Supercritical Water Reactor (SCWR) has high economic, excellent thermal efficiency and simple design concepts, it has become the weight of the fourth generation of advanced nuclear fission systems. One of the candidate reactor types. Because the supercritical water reactor needs to be operated in extreme conditions such as strong neutron irradiation, high transient stress, and strong corrosive medium, the material problem becomes a key problem that restricts its engineering applications. Because of the nano oxide dispersion strengthening (Oxide Dispersion Strengthened, ODS) ferrite steel (Ferriti C Steels) has excellent resistance to radiation damage, high temperature mechanical properties and corrosion resistance. It is considered to be one of the main candidate materials for the supercritical water reactor shell tube,.ODS ferrite steel has such excellent properties mainly from its special microstructure. Under ordinary conditions, there are a large number of rulers inside the ODS ferrite steel. The nanometer oxide dispersion particles are very small, which can effectively prevent the dislocation and grain boundary movement in the matrix as the pinning particles, thus improving the mechanical properties and thermal stability of the materials. At the same time, these nano oxide dispersion particles can also be used as stable "pool" to produce the irradiated ODS ferrite steel. It is well known that the Cr content plays an important role in the performance of the ODS ferrite steel. Generally speaking, the low Cr content of the ODS ferrite steel is not excellent in corrosion resistance, which makes their application in the supercritical water reactor limited. However, if ODS iron is used. The content of Cr in the plain body steel is too high. After a long time service, a large number of rich Cr phases may be produced in the matrix and thus cause the aging embrittlement of the material. Therefore, it is necessary to find a suitable value of the Cr content for the ODS ferrite steel in the supercritical water reactor. Four kinds of ODS ferritic steel samples with Cr content of 12%, 14%, 16%, and 18% (mass fraction) were prepared by isostatic pressure. The mechanical properties of the sintered materials were improved by hot working (forging / rolling), and the residual stresses produced by heat processing were eliminated by heat treatment. The optical microscope (Optical Microscope) was used. OM), scanning electron microscopy (Scanning Electron Microscopy, SEM), and transmission electron microscopy (Transmission Electron Microscopy, TEM) have been used to systematically study the microstructure of ODS ferrite steel samples with different Cr content. The results show that the grain size of the ferrite steel with different Cr content is all. A large number of uniformly distributed Y-Ti-O type nano oxide dispersion particles can be observed in the matrix of all samples. The size of these dispersion particles is almost between a few nanometers and fifty nanometers. The microhardness, tensile properties and impact toughness of the Vivtorinox with different Cr content of ODS ferrite steel samples are made. The mechanical properties of the ODS ferrite steel are not obviously affected by the change of Cr content. In addition, we also test and compare the other service properties of the ODS ferrite steel with different Cr content, including the resistance to the supercritical water medium corrosion under the condition of /25 MPa at 600. The properties, the long-term stability of the material at 700 C, and the microstructure change of the material at 500 C under the condition of double beam irradiation (1 MeV Kr+ and 15 keV He+). Finally, according to the results, the ODS ferrite steel with a better Cr content of 16% is selected as the main material for future research and production. In addition to the preparation of ODS ferrite samples with different Cr content, we have also tried to prepare a new type of Hastelloy nickel base alloy which can be applied to the supercritical water reactor and the ultra high temperature reactor (Very High Temperature Reactor, VHTR) by mechanical alloying (MA) and hot extrusion (Hot Extrusion, HE). Compared with the traditional Hastelloy XR nickel based alloy, the Hastelloy XR-ODS nickel base alloy after the nano oxide dispersion strengthening has been obviously improved in strength, but its plasticity has been severely reduced. The high resolution transmission electron with the energy spectrum analyzer (X-ray Energy Dispersive Spectroscopy, EDS) is equipped. High-Resolution Transmission Electron Microscopy (HRTEM) combined with electoral electron diffraction analysis (Selected Area Electronic Diffraction, SAD) to systematically study the microstructure of Hastelloy XR-ODS nickel base alloy samples. According to the results of the experimental analysis, the main reasons for the poor plasticity of the materials are found. There are a large number of micron sized grain boundaries, second phase precipitates, connected compounds and amorphous silicon.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.1

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