Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《材料研究学报》
Abstract： Effect of the leaching process of SiO2- and Al2O3-based ceramic core on the microstructure and mechanical property of the investment cast Co-based superalloy DZ40M is investigated. It is shown that after immersion in the leaching medium for SiO2-based ceramic core for 24 h, the microstructure and mechanical property of the alloy does not vary evidently; although after immersion in the leaching medium for Al2O3-based ceramic core for above 300 h, the microstructure variation of DZ40M alloy is not evident, but its mechanical property decreased remarkably, which may be due to the occurrence of an embrittled layer of about 1 mm in thickness on the alloy surface. The embrittled layer is caused by hydrogen embrittlement resulted from charging hydrogen during immersion in the leaching medium for Al2O3-based ceramic core.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： HR3C steel is a new type of austenitic heat-resistant steel which has been widely used for superheater and re-heater tubes in the ultra-supercritical (USC) boiler. The mechanical properties of HR3C steel were dependent on the stability of the microstructure, particularly the large amount of precipitates formed during service. The precipitation of s phase in HR3C steel during long-term aging for 2000 h at temperature of 700 and 750 ℃ was investigated by OM, SEM and TEM. The phase calculation method was applied to understand the factors influencing the precipitation. After 1000 h of the aging duration, irregular mass second phase was found to precipitate at the grain boundary, followed by the subsequent increasing and coarsening with time. The constituent elements of the phases were determined as Fe and Cr through SEM equipped with EDS. Further SAED analysis results led to the confirmation that these phases were basically s- FeCr compound. Combined with the prediction made through New PHACOMP method, the microstructure or phase structure in initial state may affect the subsequent precipitation behavior.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： As one of the most promising next generation reactors, the molten salt breeder reactor (MSBR) with excellent inherence security has attracted more and more attentions in recent years due to energy shortage and the security problem of traditional nuclear reactor. The most significant service characteristic of the structural material used in MSBR is the existence of FLiNaK molten salt compared with other nuclear reactors. FLiNaK molten salt is very corrosive to the structural material in the reactor, and affects the safety operation of nuclear power plants. A polycrystalline Ni-Mo-Cr-Fe superalloy was developed and used as an important structural material in MSBR at Oak Ridge National Laboratory (ORNL), but the corrosion mechanism of the alloy in FLiNaK molten salt has not been determined since the study terminated in 1970' s as some politic reasons. Alloy served in harsh environments, often using protective coating to improve the corrosion properties. While few works about the coating corrosion resistance in FLiNaK molten salt were reported at present. Al2O3 and Cr2O3 coatings usually have excellent corrosion resistance in molten salt, such as sulphate, nitrate and halide molten salt. But, whether the oxide film has corrosion resistance in FLiNaK molten salt has not been determined. In this work, the corrosion mechanism of alloy in FLiNaK molten salt was studied by using immersion corrosion experiment through the method of SEM, EDS and XRD. The influence of Al2O3 coating on corrosion resistance in FLiNaK molten salt was also investigated. The results show that the Al2O3 coating does not affect the exsolution corrosion characteristics of Cr and Mo elements in FLiNaK molten salt at 700 ℃ for 400 h. The different is that naked alloy exhibits intergranular corrosion characteristic, and the alloy with Al2O3 coating exhibits spot corrosion characteristic. The Al2O3 coating cannot improve the corrosion resistance of the alloy in FLiNaK molten salt. The Al2O3 film dissolved in molten salt and resulted in the exposure of the alloy surface. The corrosion rate was increased since the formation of corrosion cell between oxide film and the exposed alloy surface.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： Tungsten is a candidate material for the first wall and divertor in a tokamak fusion reactor, in which it is required to withstand a high neutron irradiation. The defects created in cascade form the primary state of damage and their subsequent evolution gives rise to important changes in their microstructures and engineering properties. However, the evolution and aggregation of radiation- induced defects in atomic level can not be observed by experiments up till now. In this work, molecular dynamics (MD) method was used to explore the microstructural processes and atomic mechanism of the formation and evolution of defects in the initial stage of radiation in bcc-W. The range of primary knock-on atom (PKA) energies is 1.0~25.0 keV, and simulation temperature range from 100 to 900 K. The number and distribution of defects produced by displacement cascades have been studied; the influence of PKA direction and temperature on the number of steady Frenkel pairs has also been researched; defect clusters and the threshold energy have been simulated. The results showed that for morphology distribution of defects induced in the peak time of cascade, the more intensive the defects are, the less the steady Frenkel pairs numbers are, on the contrary, the more decentralized the defects are, the more the steady Frenkel pairs numbers are; the number of steady Frenkel pairs is insensitive to PKA direction, but has a trend to decline with the temperature elevating; the percentage of interstitial clusters is higher than that of the vacancy clusters, while vacancies tend to form larger clusters; the average threshold energy of W is less affected by temperature and has certain anisotropy. The results of this work can provide data for analyzing the behavior of W material under nuclear environment.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract： The structural and compositional features of amorphous alloys can be described by cluster- plusglue atom model, which is an effective method for the composition design of amorphous alloys. In the Fe-B binary system, Fe2B phase is an intermetallic phase related to Fe83B17 eutectic point. Under the framework of the highest radial number density and isolation principle, the local structure of Fe2B phase is characterized by a B-centered Archimedean octahedral antiprism [B-B2Fe8] atomic cluster. Combined with the electron consistence criterion, the [B-B2Fe8]Fe (here the center and shell atoms are separated by a hyphen, a cluster is enclosed in square brackets, the glue atom is out square brackets) is then determined as an ideal cluster formula for Fe-B binary amorphous. To further enhance the glass-forming ability (GFA) of the alloy, the center B and shell Fe atoms in [B-B2Fe8]Fe are replaced with Si and Ta, respectively, due to their large negative enthalpy of mixing between Si-Fe and (B, Si)-Ta atomic pairs, and Fe-B-Si-Ta quaternary composition series, namely [Si-B2Fe8- xTax]Fe, are thus derived. The experimental results reveal that the bulk amorphous alloys with a diameter of 1.0 mm can be achieved for [Si-B2Fe8- xTax]Fe (x=0.4~0.7) compositions. Among them, [Si-B2Fe7.4Ta0.6]Fe (i.e. Fe70B16.67Si8.33Ta5, atomic fraction, %) is the best glass former, its glass transition temperature Tg, supercooled liquid region ΔTx and the reduced glass transition temperatures Trg are 856 K, 33 K and 0.584, respectively. The Vickers hardness, saturation magnetization and coercivity of the [Si-B2Fe7.6Ta0.4]Fe (i.e. Fe71.67B16.67Si8.33Ta3.33) amorphous alloy are measured to be 1117 HV, 1.37 T, and 3.0 A/m, respectively.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-19 Cooperative journals: 《金属学报》
Abstract：研究了230 ℃, 5×103 A/cm2条件下液-固电迁移对Ni/Sn-9Zn/Ni 线性焊点界面反应的影响. 在液-固电迁移过程中,Ni/Sn-9Zn/Ni 焊点表现出明显的反极性效应, 即阴极界面金属间化合物(IMC)持续生长变厚, 并且一直厚于阳极界面IMC.由于排除背应力的影响, Sn-9Zn 液态钎料中Zn 原子的反常迁移行为归因于其有效电荷数在高温下为正值, 即在电子风力作用下Zn原子向阴极界面定向迁移, 从而导致焊点在液-固电迁移过程中发生反极性效应. 回流焊后, Ni/Sn-9Zn/Ni 焊点两侧界面上均生成了较薄的Ni5Zn21层. 液-固界面反应过程中(无电流)焊点两侧界面IMC均随时间延长而生长变厚, 从而消耗钎料中的Zn原子并使界面处的相平衡发生变化, 导致界面IMC由Ni5Zn21转变为[Ni5Zn21+(Ni, Zn)3Sn4]. 与之相较, 液-固电迁移过程中阴阳两极界面IMC的类型一直为Ni5Zn21, 并未发生IMC类型的转变. 这是由于, 在电子风力作用下, 阴极界面附近钎料中Zn原子的含量充足, Zn与Ni 反应生成Ni5Zn21型IMC; 同时, 电子风力也阻碍了Zn原子向阳极界面的扩散, 从而抑制了阳极界面IMC的生长, 导致界面IMC较薄, 因此阳极界面也未发生IMC类型的转变. 此外, 运用反证法进一步验证了Zn的有效电荷数在高温下是正值.
Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-18 Cooperative journals: 《材料研究学报》
Abstract： Crystallization behavior and soft magnetic properties of amorphous alloys Fex(SiB)96-xP3Cu1 (x=75, 78, 80, 83 and 85, atomic fraction, %) were investigated. It was found that the apparent activation energy for crystallization decreased with the increasing Fe content of the Fex(SiB)96- xP3Cu1 alloys. The phases precipitated after properly complete crystallization treatment were the same for all the alloys with varying Fe content. The annealed Fex(SiB)96- xP3Cu1 (x=80, 83 and 85) alloys exhibited a uniform nanostructure with grain size smaller than 20 nm, while the grain sizes of the alloys with x=75 and 78 ranged from 5 nm to 50 nm. The saturation magnetization enhanced nonlinearly as the Fe content increased from 75 to 85. The nanocrystalline alloy Fe85Si3B8P3Cu1 exhibited excellent soft magnetic properties with a coercivity of 12 A穖-1 and a saturation magnetization of 1.87 T. The core loss values of nanocrystalline alloys Fe85Si3B8P3Cu1 and Fe83Si4B9P3Cu1 were still less than 1.0 W穔g- 1 even if the saturation magnetic induction intensity was up to 1.7 T, which were superior to that of the commercial Fe78Si9B13 alloy and nonorientated silicon steel.
Subjects: Materials Science >> Materials Science (General) submitted time 2016-11-04 Cooperative journals: 《金属学报》
Abstract：采用应力松弛方法研究了2种HR3C耐热钢的初始态试样和时效态试样的高温蠕变变形行为，并分析了其微观组织特点。结果表明，尽管2种HR3C耐热钢的化学成分相近，但其蠕变行为有明显差异。相同条件下，晶粒较粗的HR3C耐热钢初始态与时效态的蠕变速率均低于晶粒较细的HR3C耐热钢，具有较高的蠕变抗力。2种HR3C耐热钢经过高温时效处理后，蠕变抗力均明显降低。晶粒较细小的HR3C钢在高温时效后其应力指数(n)与蠕变表观激活能(Q)的降低幅度更加显著，表明晶粒较细的HR3C耐热钢的蠕变抗力的稳定性低于晶粒较粗的HR3C耐热钢。
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