国产B_4C颗粒增强铝基复合材料的耐辐照性能研究

采用粉末冶金工艺制备的国产B4C颗粒增强铝基复合材料中子吸收板开展辐照试验研究,中子吸收板经受累积快中子注量4.22×1019n/cm2、γ射线剂量为4.75×1011rad的辐照后,对材料各项性能进行测试,包括表面形貌、尺寸、质量、密度、力学性能(抗拉强度、硬度和伸长率)及10B面密度,并与辐照前的测试结果进行对比分析。结果表明,在中子和γ射线的辐照作用下,复合材料试样的抗拉强度和硬度提高,伸长率下降,表面形貌未发生明显变化,尺寸、质量、密度及10B面密度均无显著改变。     

钒合金抗高温氧化腐蚀研究进展

以V?(4?5)Cr?(4?5)Ti合金为代表的钒合金具有高温性能优异、抗辐照肿胀性能好、中子辐照活化性低等诸多优点,被视为先进核聚变反应堆最有潜力的候选包层结构材料之一。然而,钒合金在较高温度下的氧化腐蚀及吸氧脆化问题仍是目前制约其实际应用和长寿命服役的重要因素。因此,提升钒合金的抗高温氧化腐蚀性能,对于提高其服役温度、延长其服役寿命以及拓宽其应用领域均具有重要意义。本文综述了国内外有关提升钒合金抗高温氧化腐蚀性能的三种主要方案,即添加抗氧化性元素、应用扩散型涂层和包覆型涂层,并对这些方案的主要特点、应用实例以及存在的问题进行了分析和讨论。上述三种方案中,包覆型涂层由于可以将钒合金基体和服役环境完全隔离,因而具备更大的应用潜力。根据钒合金的应用特点,对先进包覆型抗氧化腐蚀涂层的发展趋势和技术需求进行了展望,以期为钒合金抗高温氧化腐蚀研究工作的深入开展提供借鉴。      

铁基非晶合金的辐照性能

铁基非晶合金由于成本低较、易制备、较好的温度稳定性等优点,并具优异的机械性能、磁性能和耐腐蚀性能而被广泛研究.并且其固有的无序结构有助于抵抗辐照导致的损伤,使得铁基非晶合金可作为抗辐照材料使用.辐照既可以试验铁基非晶合金的性能也是优化铁基非晶合金结构和性能的有效方法.本文综述了铁基非晶合金中子辐照、离子辐照和电子辐照性能的研究进展,探讨了铁基非晶合金的结构和性能与非晶合金的成分以及辐照粒子的类型、能量、注量之间的关系,以及辐照晶化的机制,为进一步促进高性能铁基非晶合金的研究提供了有价值的参考.      

作用应力对2.25Cr-1Mo合金钢回火脆性的影响

在146.7MPa的作用应力下,对加氢反应器材料2.25Cr-1Mo合金钢(%:0.15C、2.32Cr、0.95Mo、0.011S、0.009P、0.0068As、0.0035Sb、0.0079Sn、0.01V)进行468℃125h和400h的等温回火脆化试验。根据加氢反应器母材试块脱脆、脆化和应力作用3种状态冲击功和温度关系曲线,得出各状态回火脆性转变温度VTr54.2(℃)值和回火脆化度ΔVTr54.2(℃)。结果表明,温度和等温时间是导致材料回火脆化的主要因素,作用应力对2.25Cr-1Mo钢回火脆性的影响不显著。     

快中子反应堆核心结构材料的辐照损伤

快中子反应堆(快堆)的核心结构材料(如燃料包壳等)在服役过程中将承受长期的高通量的中子辐照、高温和嬗变反应产生的He的作用,引起的合金微观结构的改变,导致材料力学性能的严重恶化.高性能抗辐照材料成为快堆发展的关键前提条件之一.本文介绍快堆中辐照引起的金属材料微观结构的变化.     

浅谈铬钼钢的回火脆性及控制

铬钼钢在化工设备高温抗氢方面应用十分广泛,然而由于回火脆化敏感性的影响,对于长期在一定温度范围内运行的压力容器还是存在一定的风险。本文进一步指出了铬钼抗氢钢的回火脆化的主要特征,分析了化学成分和热处理工艺两个影响回火脆化敏感性的因素,得出回火脆化的评定以及为了获得材料的最佳综合性能应采取的控制措施。     

奥氏体耐热钢 HP40 离心铸造辐射管的失效分析

HP40钢(%:0.35～0.45C、24～27Cr、34～37Ni、≤0.5Mo)辐射管在≤980℃服役2年9个月后开裂失效.分析结果表明,服役过程σ-相的析出导致材料脆化是辐射管开裂的主要原因,开裂区服役温度高于未开裂区,开裂区析出σ-相粗大、数量增多、塑韧性显著降低,致使该区开裂失效.     

利用小冲孔试验预测低合金贝氏体钢的拉伸性能和韧脆转变温度

利用小冲孔试验可预测各种具有贝氏体组织的反应压力容器 (RPV)钢在室温至 196℃范围内的拉伸性能和韧脆转变行为。在用不同工艺生产的一种 RPV钢的焊缝处和 6种锻造 RPV钢的 1/ 4t位置处切取试样并切削加工至尺寸 10 mm× 10mm× 0 .5 m m。用所有温度范围的屈服强度和 SP能与温度曲线的上平台区的拉伸强度非常成功地修正了 SP试验屈服强度和抗拉强度。即使在 SP试样非常少的情况下 ,韦氏统计分析仍是测定韧脆转变区平均 SP能值和转变温度的有效方法。利用在上下 SP能 (TSP)的中点测得的转变温度成功地校正了夏比冲击试验中的韧脆…     

长期热老化后核电站主管道材料的力学行为

大型压水堆核电站主管道多采用综合性能优良的铸造奥氏体不锈钢,但该材料在中温下长期服役会发生热老化脆化现象。总结了国内外的最新研究成果,主要综述了长期热老化过程中主管道材料的相变规律及其影响因素,以及长期热老化后材料的纳米硬度、拉伸、冲击和疲劳行为。     

IF钢二次加工脆化性能的评定与研究

针对IF钢板成形后出现的加工脆化现象,对马钢生产的冷轧IF钢二次加工脆化进行检验评定。试验结果表明:马钢IF钢的韧脆转变温度为-60℃,冲杯破裂断口为沿晶与解理混合脆性断口,并对影响IF钢二次加工脆性的因素进行了阐述。     

Magnetic Properties of Thermally Aged Fe-Cu Alloys with Pre-deformation

Magnetic properties of thermally aged Fe-Cu alloys with pre-deformation have been evaluated to improve the understanding of using magnetic technology for the nondestructive evaluation(NDE)of irradiation embrittlement in reactor pressure vessel(RPV)steels.Fe-Cu alloys with and without pre-deformation were thermally aged at 500 ℃ and the changes in microstructure,mechanical properties and magnetic properties were determined.It is found that the strain-induced dislocations recover and the Cu-rich particles precipitate during the aging process,and the magnetic properties variation depends on the combined influence of these two factors.From the point of view of NDE,a fully tempered or annealed microstructure is favorable before RPV is put into service.These results improve the understanding of magnetic property evolution in actual RPV steels and help to develop NDE theory for irradiation embrittlement.     

A bayesian analysis of the influence of neutron irradiation on embrittlement in ferritic submerged arc weld metal

The effect of neutron irradiation and temperature on Charpy-impact-energy properties has been studied to assess the irradiation embrittlement of submerged-arc-weld metal. Measurements of Charpy-impact-energy data are available from irradiation exposures carried out under surveillance conditions at 190 °C and 198 °C and from irradiation at accelerated dose rates carried out over a temperature range from 186 °C to 292 °C. Neutron irradiation at accelerated dose rates was carried out on specimens which were previously subjected to surveillance irradiation. The test-temperature dependence of Charpy impact energy was represented by a relationship based on the Burr distribution function in which some of the parameters were dependent on the neutron dose, irradiation dose rate, and temperature. The analysis of the data was carried out in the Bayesian framework. The posterior probability distributions of the model parameters were computed using Markov chain Monte Carlo based techniques. It has been found that the upper-shelf Charpy impact energy changes by a constant amount, neutron dose independent, between the unirradiated, surveillance-irradiated, and double-irradiated conditions. The temperature shift in the Charpy-impact-energy curves is independent of dose rate but decreases with increasing irradiation temperature. The remaining model parameters were found to be unaffected by neutron irradiation. It has been found that accelerated reirradiation experiments can be used to extend the range of applicability of the surveillance-monitoring scheme.     

Benchmarking the MCNP code for Monte Carlo modelling of an in vivo neutron activation analysis system

The Monte Carlo computer code MCNP (version 4A) has been used to develop a personal computer-based model of the Swansea in vivo neutron activation analysis (IVNAA) system. The model included specification of the neutron source (252Cf), collimators, reflectors and shielding. The MCNP model was 'benchmarked' against fast neutron and thermal neutron fluence data obtained experimentally from the IVNAA system. The Swansea system allows two irradiation geometries using 'short' and 'long' collimators, which provide alternative dose rates for IVNAA. The data presented here relate to the short collimator, although results of similar accuracy were obtained using the long collimator. The fast neutron fluence was measured in air at a series of depths inside the collimator. The measurements agreed with the MCNP simulation within the statistical uncertainty (5-10%) of the calculations. The thermal neutron fluence was measured and calculated inside the cuboidal water phantom. The depth of maximum thermal fluence was 3.2 cm (measured) and 3.0 cm (calculated). The width of the 50% thermal fluence level across the phantom at its mid-depth was found to be the same by both MCNP and experiment. This benchmarking exercise has given us a high degree of confidence in MCNP as a tool for the design of IVNAA systems.     

Application of the Master Curve Approach for the Irradiation Embrittlement Evaluation of Pressure Vessel Steels

The Master Curve (MC) approach and the associated reference temperature, T₀, as defined in the test standard ASTM E1921, is rapidly moving from the research laboratory to application in integrity assessment of components and structures. T₀ is the index temperature for the universal MC, which considers the toughness behaviour of a specific material. “The Structural Integrity Assessment Procedures for European Industry” (SINTAP) contain a MC extension for analysing the fracture behaviour of inhomogeneous ferritic steels. This paper presents the application of the MC approach to the T₀ determination of different types of Russian WWER‐type reactor pressure vessel (RPV) steels. In addition the SINTAP‐MC approach was applied to determine an alternative reference temperature, T_R. The influence of different microstructures and compositions within one type of RPV steel and the effect of irradiation with fast neutrons on T₀ are experimentally evaluated. In general the MC based T₀ is about 72 K below the Charpy V‐notch transition temperature related to an impact energy of 48 J. The paper demonstrates the application of MC based T₀ and T_R as an alternative reference temperature for neutron embrittled RPV steels used in the RPV integrity assessment.     

Effect of alloying and irradiation on the behavior of interstitial impurities in vanadium and V-Ga and V-Ti-Cr alloys

The effect of alloying and fast-neutron irradiation on the behavior of interstitial impurities in vanadium and V-Ga and V-Ti-Cr alloys is studied using low-frequency internal friction. It is found that, before irradiation, oxygen and nitrogen impurities in plain vanadium and V-Ga alloys are in a solid solution, whereas, in V-Ti and V-Ti-Cr alloys, they are predominantly fixed to form chemical compounds. Unlike the irradiation of plain vanadium, the irradiation of V-Ga alloys at 673 K to a neutron fluence of 4.24 × 10²⁵ m^?2 (E > 0.1 MeV) does not knock out oxygen and nitrogen impurities from interstitial positions in the lattice to the positions of radiation defects. In the V-5Ti-5Cr alloy, oxygen and nitrogen atoms are fixed before and after neutron irradiation according to these conditions.     

Influence of Fast Neutron Irradiation on Critical Current Densities of Bi-2223/Ag Tape

Experimental results on the magnetic field behavior of the critical current in silver sheathed Bi-2223 tapes are presented. The experiments consist of transport and magnetic measurements in a wide temperature range and in external magnetic field up to 6 T. Significant enhancement of the intragrain critical current densities Jc are observed after irradiation with fast neutron. This is attributed to an improvement of flux pinning capability by the neutron induced defects, but the weak link structure is somewhat damaged as evidenced by the small degradation of transport critical current at low field. According to the measurement of remanent magnetic moment before and after irradiation with fast neutron, the connectivity in Bi-2223 tapes is reduced by 50% after irradiated to a fluence of 2 × 1021 m-2, which resulted in the critical currents degradated by a factor of 10%.     

Review of Environmentally Assisted Cracking

Many efforts have been made in the past by several researchers to arrive at some unifying principles governing the embrittlement phenomena. An inescapable conclusion reached by all these efforts was that the behavior is very complex. Hence, recognizing the complexity of material/environment behavior, we focus our attention here only in extracting some similarities in the experimental trends to arrive at some generic principles of behavior. Crack nucleation and growth are examined under static load in the presence of internal and external environments. Stress concentration, either pre-existing or in-situ generated, appears to be a requirement for embrittlement. A chemical stress concentration factor is defined for a given material/environment system as the ratio of failure stress with and without the damaging chemical environment. All factors that affect the buildup of the required stress concentration, such as planarity of slip, stacking fault energy, etc., also affect the stress-corrosion behavior. The chemical stress concentration factor is coupled with the mechanical stress concentration factor. In addition, generic features for all systems appear to be (a) an existence of a threshold stress as a function of concentration of the damaging environment and flow properties of the material, and (b) an existence of a limiting threshold as a function of concentration, indicative of a damage saturation for that environment. Kinetics of crack growth also depends on concentration and the mode of crack growth. In general, environment appears to enhance crack tip ductility on one side by the reduction of energy for dislocation nucleation and glide, and to reduce cohesive energy for cleavage, on the other. These two opposing factors are coupled to provide environmentally induced crack nucleation and growth. The relative ratio of these two opposing factors depends on concentration and flow properties, thereby affecting limiting thresholds. The limiting concentration or saturation depends on the relative chemistry of environment and material. A dynamic dislocation model is suggested to account for crack growth.     

高剂量氦离子辐照对新型中子增殖铍钨合金表面结构的影响

为了确保未来核聚变反应堆的氘氚自持燃烧必需采用中子增殖材料来得到合适的氚增值比。金属铍被认为是最有前途的核聚变反应堆固态中子倍增材料,但其熔点低,高温抗辐照肿胀性能差,因此需要寻找和研发具有更高熔点和更耐辐照肿胀的新型中子增殖材料以满足更先进的聚变堆要求。本研究尝试提出并制备了一种更高熔点的铍钨合金（Be₁₂W）,通过X射线和扫描电子显微镜对它的相组成和表面结构进行分析。对新型铍钨合金进行高剂量的氦离子辐照,发现合金表面一次起泡的平均尺寸约为0.8 μm,面密度约为2.4×107 cm?2,而二次起泡的平均尺寸约为80 nm,面密度约为1.28×108 cm?2。分析氦辐照引起的表面起泡及其机制,并与纯铍和铍钛合金表面起泡的情况进行了对比。