•B2- Cu-enriched precipitates exist in the studied model alloys.•The maximum contribution to precipitation hardening is attributed to Cu-enriched precipitates.•Ni addition led to relatively higher ...precipitation nucleation and growth of Cu-enriched precipitates.•Small-angle scattering could provide better details when analyzing nano-sized precipitates.
To better understand the mechanisms of thermally aged and embrittled reactor pressure vessel steels, the hardening behavior and microstructure evolution of different Fe-Cu and Fe-Cu-Ni model alloys were investigated using transmission electron microscopy (TEM) and small-angle neutron scattering (SANS) analysis methods. The effects of different aging conditions and alloy composition on the formation and growth of Cu-enriched precipitates were discussed. The results showed that the hardness of the Fe-Cu model alloys with low copper content continuously increased with aging, increasing to peak hardness and then decreasing for the Fe-Cu model alloys with high copper content. The aging time to reach peak hardness was greatly reduced due to the addition of Ni in the Fe-Cu model alloys. The TEM results showed that with increased aging temperature and copper content, the Cu-enriched precipitates with a B2 structure precipitated in the ferritic matrix following a direct relationship. Therefore, Ni addition led to relatively higher precipitation nucleation and growth, and the size distribution of the Cu-enriched precipitates derived from the SANS was in overall good agreement with the TEM observations for 6–25 nm regions. Therefore, small-angle scattering could provide better details when analyzing smaller, nano-sized precipitates.
17-4PH martensitic steel is usually used as valve stems in nuclear power plants and it suffers from thermal aging embrittlement due to long-time service in a high-temperature and high-pressure ...environment. Here, we characterized the evolution of microstructures at the nano-scale in 17-4PH steel by in situ small-angle neutron scattering (SANS) with a thermo-mechanically coupled loading device. The device could set different temperatures and tensile so that an in situ SANS experiment could dynamically characterize the process of nanoscale structural changes. The results showed that with increasing thermal aging time, the ε-Cu phase precipitates and grows as the temperature is 475 °C and 590 °C, and the ε-Cu phase is spherical at 475 °C but became elongated cylinders at 590 °C. Moreover, the loading stress could aid in the growth of the ε-Cu phase at 475 °C.
BackgroundThe study of irradiated samples is of considerable importance. Owing to these samples being radioactive, the applicability of conventional characterization methods is limited. Because of ...the high sensitivity of 3He detectors to neutrons, the small-angle neutron scattering (SANS) technique is nearly unaffected by radiation such as gamma, beta rays, and sample preparation is simple.PurposeThis study aims to develop a device for SANS measurement of nanostructures in radioactive samples.MethodsThe shielding thickness of the device was optimized through Monte Carlo simulations. Experimental efficiency and safety of the device were improved by combining remote-control functionality and automated sample switching among up to 12 samples loaded simultaneously. Finally, the device was used to carry out a SANS experiment for characterizing the radioactive A508-III steel sample.ResultsThe optimized thickness of the lead shielding layer of the device is 7.5 cm, the corresponding maximum dose rate of the measurab
O571.56; 管道焊接残余应力是影响管道安全和使用寿命的关键因素.中子衍射是唯一无损检测厚钢焊缝结构完整性的方法.本文主要采用中子衍射谱仪,辅以显微镜和硬度分析仪研究40 mm厚STE460钢管钨极惰性气体保护焊得的焊缝的残余应力分布、微观形貌、维氏硬度等.研究结果表明,焊缝的残余应力最高达670 M Pa,非常接近S T ...E460钢抗拉强度极限,而热影响区内的残余应力很小.全峰半高宽分析表明,焊缝区域塑性形变程度较低.整个焊缝不同区域的晶体显微照片表明其皆是均匀细晶.沿着焊缝方向和垂直焊缝方向的维氏硬度几乎一致,均在(200～250)HV0.2范围内.分析测试结果不仅满足工业应用里的电站基础结构建设和其他非破坏性残余应力评估装置校准的需求,并能增加对S T E460钢厚截面焊缝的认知.
In-situ Thermodynamic Coupling Device for Small-angle Neutron Scattering CHEN Zhong, LI Tianfu, WANG Zijun, YAN Shibo, LIU Rongdeng, LI Meijuan, HU Wenyao, ZOU Zhiquan, YANG Yuchen, LIU Yuntao, SUN Kai, CHEN Dongfeng
Yuanzineng kexue jishu,
01/2024, Letnik:
58, Številka:
1
Journal Article
Odprti dostop
The in-situ experimental study of the microstructure of materials under thermodynamic coupling under near-working conditions is very important for in-depth understanding of the evolution mechanism of ...material service performance. The microscopic distribution of nanostructures on the sample can be given. Based on the advantages of small-angle neutron scattering method with good statistics and large sampling volume, in-situ experiments can be carried out, based on the small-angle neutron scattering spectrometer of China Advanced Research Reactor, an in-situ experimental device with simultaneous loading of high temperature and tensile force was designed and developed, and the morphological changes of materials at the nanoscale were measured online at high temperature and high pressure. The test results of the inspection and calibration experiment show that the maximum load of the device can reach 20 kN, the maximum temperature is 800℃, and the temperature control accuracy is better than ±1℃. The device was used to carry out in-situ small-angle neutron scattering experiments on nickel-based single crystal superalloy samples, and the obvious changes in the internal nanostructure of the samples under temperature tension conditions were obtained, indicating that the device could carry out the experimental research ability of in-situ thermodynamic coupling loading small-angle neutron scattering. The device and its corresponding experimental methods can also be used for in-situ experimental research of various high-temperature structural materials such as nuclear power stainless steel to provide microstructure evolution data.
The advantages of time of flight method enable it to be widely used on stationary reactors. In this study, we reported several typical applications of time of flight method on the China Advanced ...Research Reactor (CARR). First, a new solution is designed to measure the beam characteristics including wavelengths, wavelength resolution rates and intensities of HOPG(002) monochromator for the unfiltered and filtered cases. Second, the changes in neutron wavelength spectra on the cross section of curved neutron guide CNGB end were examined and studied. It can be concluded that evident shape changes between neutron wavelength spectra along horizontal direction are mainly caused by the horizontal curving of curved neutron guide and dips at other wavelengths apart from 4 Å are mainly caused by small radius of curvature of curved neutron guide. Third, based on neutron velocity selector of small angle neutron scattering instrument at CARR, a calibration instrument is designed, and calibration experiments are conducted and simulated. The results indicate that the discrepancy between the experimental wavelength resolution rate and the theoretical one is caused by beam divergence linked with the critical reflection angle of neutron guide coating and the difference between experimental wavelength and the theoretical one is caused by the shape change of source neutron wavelength spectrum. These findings are reported here for the first time.
Microstructure evolution and mechanical properties in an Fe-17Cr-4Ni-4Cu alloy aged at 475 °C after different aging times were studied. Conventional transmission electron microscopy (TEM) and ...high-resolution electron microscopy (HREM) studies revealed the formation of 9R-structure Cu-rich precipitates and Cr-rich α’ phase by spinodal decomposition in the samples aged at 475 °C after 100–1000 h. The fine Cu-rich precipitates and Cr-rich α’ phase by spinodal decomposition lead to a significant increase in the hardness, together in the early stages (100 h). Continued aging to 500 h leads to increased precipitation of the Cr-rich α’, which provides significant strengthening, reaching maximum hardening, despite the continued loss of hardening by weakening by the Ostwald ripening of the Cu-rich precipitates. Extending the aging time to 1000 h leads to substantial reversed austenite transformation and a large number of ripening -copper precipitates that causes softening. The results of the impact tests showed that the major fracture mode was cleavage and/or quasi-cleavage.
