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学者姓名：陈凯
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Abstract ：
Ni-based superalloys are widely used in harsh environments due to their exceptional high-temperature mechanical properties, and their microstructures are inevitably subjected to degradation, including accumulation of strain/stress, generation of high density of dislocations, and rafting of gamma'-particles, under creep damage. To prolong their service life, rejuvenation heat treatment is proposed to restore their microstructure. In this study, a Ni-based superalloy single crystal specimen with 0.15% creep strain is taken as a surrogate of partially served components. The microstructure, including the dislocation density and distribution as well as the size and morphology of gamma'-particles, is investigated. Then two comparative heat treatment protocols are applied to the crept superalloy single crystal. Because super-solvus homogenization treatment triggers recrystallization, a recovery pre-annealing step at sub-solvus temperature is designed to relieve the stored deformation energy. After homogenization and aging heat treatment, the single crystalline structure is preserved, and in the meanwhile the gamma'-particles are restored to uniform cuboidal morphology and the dislocations are fully eliminated Our findings provide a route to rejuvenate crept superalloy single crystals.
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| GB/T 7714 | Lin, Sicong , Shen, Hao , Zhou, Guangni et al. A new rejuvenation heat treatment of crept Ni-based superalloy single crystals [J]. | 42ND RISO INTERNATIONAL SYMPOSIUM ON MATERIALS SCIENCE: MICROSTRUCTURAL VARIABILITY: PROCESSING, ANALYSIS, MECHANISMS AND PROPERTIES , 2022 , 1249 . |
| MLA | Lin, Sicong et al. "A new rejuvenation heat treatment of crept Ni-based superalloy single crystals" . | 42ND RISO INTERNATIONAL SYMPOSIUM ON MATERIALS SCIENCE: MICROSTRUCTURAL VARIABILITY: PROCESSING, ANALYSIS, MECHANISMS AND PROPERTIES 1249 (2022) . |
| APA | Lin, Sicong , Shen, Hao , Zhou, Guangni , He, Weifeng , Chen, Kai . A new rejuvenation heat treatment of crept Ni-based superalloy single crystals . | 42ND RISO INTERNATIONAL SYMPOSIUM ON MATERIALS SCIENCE: MICROSTRUCTURAL VARIABILITY: PROCESSING, ANALYSIS, MECHANISMS AND PROPERTIES , 2022 , 1249 . |
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Abstract ：
A significantly refined microstructure with high twin and dislocation densities is a common feature in the Ti surface layers subjected to laser shock peening (LSP). In this study, in order to develop a detailed understanding of the different twin variants and accurate estimation of twin and dislocation densities that result from LSP, electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were performed at different depths below the peened surfaces of single and triple LSP impacted Ti. To overcome challenges associated with characterization of the nano-sized LSP-induced twins during the conventional EBSD analysis, a novel data mining strategy is developed to identify the characteristic straight twin boundary traces from the band contrast maps. Results show five types of twins, whose total density initially increases and then monotonically decreases with increasing distance from the LSP treated surface. The intersection of the primary and secondary type twins subdivides the grains and leads to grain refinement. In contrast, the dislocation density is highest at the LSP treated surface but decreases monotonically with the increasing depth. A similar trend in the variation of microhardness as a function of the depth indicates that LSP-induced strengthening is dominated by the dislocations and grain refinement. Further analysis reveals that the former's contribution is more pronounced than that of the latter. The understanding developed in this work can be useful for the design of the alloys and the LSP process for improved mechanical performance. © 2022 Elsevier Ltd.
Keyword ：
EBSD data mining; Grain subdivision; Laser shock peening; Microstructural gradient; Twin-twin intersections
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| GB/T 7714 | Huang, X. , Zhu, W. , Chen, K. et al. Twin and dislocation induced grain subdivision and strengthening in laser shock peened Ti [J]. | International Journal of Plasticity , 2022 , 159 . |
| MLA | Huang, X. et al. "Twin and dislocation induced grain subdivision and strengthening in laser shock peened Ti" . | International Journal of Plasticity 159 (2022) . |
| APA | Huang, X. , Zhu, W. , Chen, K. , Narayan, R.L. , Ramamurty, U. , Zhou, L. et al. Twin and dislocation induced grain subdivision and strengthening in laser shock peened Ti . | International Journal of Plasticity , 2022 , 159 . |
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Abstract ：
Strengthened by the L12 precipitates as such Ni3Al, the CuNi14Al3 alloyis utilized to manufacture the shroud rings which areone of the key components of power generators. However, after the sequent processing procedures including vacuum melting casting, forging and stress relief annealing heat treatment, the poor surface quality, scrap removal induced materials waste, forging cracks and cavities were detected from time to time in the final products. To uncover the mechanism of the formation of these macroscopic defects, the microstructural features and mechanical properties of the CuNi14Al3 alloy after each crucial processing stage were studied by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive X-ray spectroscope (EDS), and micro-hardness tester. Owing to the solidification characteristics of the CuNi14Al3 alloy, including the solidification sequence, rate and shrinkage, the microstructure of the ingots featured of coarse dendritic structures, which was over 10 mm in length, with severe elemental segregation and micro-pores. Since nickel had higher melting point than copper, the precipitationinduced elements like nickel and aluminum to segregate in the dendritic cores with a segregation ratio up to 0.3 and 0.4, respectively. From the dendritic cores to the interdendritic regions, the shape of the precipitate particles changed gradually from large regular-shaped cuboids (with the edge length around 200 nm) to fine irregular spherical shapes, with an average diameter of around 20 nm. The hardness values, obtained using the Vickers indenter, at the dendrite cores were higher than those in the interdendritic regions by approximately 13.1%. To investigate the tensile facture behavior of the ingot, the 45 ocone-shaped fractures revealed the brittleness characteristics of the alloy. However, at micro scale, the facture surface was dimple-shaped morphology with mass of pores, and the precipitate particles could be commonly observed at the bottom of the dimples, indicating that the stress concentration around the casting pores and shrinkage led to the fracture. After the sequent forging, the coarse dendrites and the micro-pores were inherited. Moreover, at the first step of the forging, the plastic deformation could not activate sufficient dynamic recrystallization, leading to the bimodal grain size distribution, in which the continuous small crystal grains distributed among the giant grains inherited from the casting organization. The bimodal microstructure led to the heterogeneity of the deformation partitions at further forging steps, which, in turn, induced the cracks to occur at the interfacial areas between the giant grains and the micro-pores. There was still no necking observed at the tensile facture of the forged specimens. Compared with those of the casting ingots, the dimples became shallower, which was an evidence of even more brittleness. A number of pores initiating from the casting cavities and shrinkage could still be found, and the pores were stretched by the large plastic deformation. All the defects, including dendritic structure, bimodal distributed grain size, pores and cracks, were left to the last processing step, stress relief annealing heat treatment. Unfortunately none of them could be eliminated by the annealing. The low temperature stress relief annealing treatment could not activate the recrystallization sufficiently and many giant grains were left over. Due to the high forging temperature, which was higher than the solutionizingheat treatment temperature of the CuNi14Al3 alloy, the cracks were oxidized as Al2O3, and the oxide particles along the cracks impeded the closure during forging. The densities of the alloys were measured to be 8.188 g•cm-3 after casting, 8.245 g•cm-3 after forging, and 8.284 g•cm-3 after stress relief annealing, respectively. All values were significantly lower than the theoretical value (8.500 g•cm-3), revealing that the shrinkage cavities always existed and the defects could not be eliminated completely by the subsequent hot processing. Although the cracks emerging during the forging led to the failure of the product, the hardness and yield strength of the crack-free parts still met the requirements, mainly resulting from the dispersed precipitation hardening. From the dendritic cores to the interdendritic regions of the casting ingots, the size of the Ni3Al precipitate particles varied from 200 to 20 nm. The crystal structure of the precipitation was similar to the copper matrix and had the same orientation. After the forging and the annealing, the size of the precipitation became uniform at around 20-50 nm, which guaranteed the higher tensile strength at 855 MPa. The evolution of the precipitate particles proved that the forging and annealing processing was effective to achieve the required microstructure and mechanical properties, although it could not eliminate the casting defects.It could be concluded that, the formation of all the defects was attributed to the solidification characteristics of the alloy, including solidification rate, sequence and thermal shrinkage. Thus, the approach to improve the processing could be raised. Firstly, to improve the alloy composition by adding the grain refiner to promote the heteromorphy nucleation and/or the modifier to hinder the grain growth and the precipitating. Secondly, to optimize the casting processing by the sloping plate casting and the pressure casting to refine the grain size and restrain the shrinkage. The last but not the least, to add another homogenization annealing to eliminate the dendritic segregation and achieve better homogenization. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
Keyword ：
Age hardening Alumina Aluminum alloys Aluminum metallography Aluminum oxide Annealing Binary alloys Brittleness Casting Copper Copper alloys Copper metallography Cracks Crystal orientation Dendrites (metallography) Dynamic recrystallization Forging Fracture mechanics Grain growth Grain size and shape Ingots Metallic matrix composites Microhardness Morphology Nickel Nickel compounds Nickel metallography Plastic deformation Plasticity Precipitation (chemical) Scanning electron microscopy Segregation (metallography) Shrinkage Solidification Stress relief Temperature Tensile strength Ternary alloys Transmission electron microscopy Vacuum applications Waste treatment
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| GB/T 7714 | Feng, Rui , Chen, Kai , Qin, Yuanbin et al. Mechanism Study of Defect for Mation in CuNi14Al3 Shroud Rings [J]. | Chinese Journal of Rare Metals , 2021 , 45 (2) : 137-146 . |
| MLA | Feng, Rui et al. "Mechanism Study of Defect for Mation in CuNi14Al3 Shroud Rings" . | Chinese Journal of Rare Metals 45 . 2 (2021) : 137-146 . |
| APA | Feng, Rui , Chen, Kai , Qin, Yuanbin , Guo, Chuangli , Sun, Junpeng , Wang, Qun . Mechanism Study of Defect for Mation in CuNi14Al3 Shroud Rings . | Chinese Journal of Rare Metals , 2021 , 45 (2) , 137-146 . |
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Abstract ：
Synchrotron radiation-based micro-Laue technique has showcased great application potentials in materials science study for its unprecedented crystal orientation and lattice strain/stress resolution. Here we report the updated progress in the development of the micro-Laue technique on the X-ray test beamline at Shanghai Synchrotron Radiation Facility. So far, 40 mu m (h) x 50 mu m (v) X-ray beam spot is routinely obtained, with the convergent angle of 0.2 mrad (h) x 0.12 mrad (v). Area scans are conducted on a GH3535 Ni-based superalloy base metal and weld joint with the same chemical composition. By analyzing the tremendous amount of Laue diffraction patterns using in-house developed software packages, the crystal orientation, elastic strain, and defect distributions are mapped and investigated. Such a successful proof-of-principle study offers first-hand experience on the further optimization of the design and construction of the scanning micro-Laue facility on the superbend beamline with improved spatial resolution and multiple functions for simultaneous chemical fluorescence mapping and in-situ microstructural evolution studies. The micro-Laue diffraction beamline at Shanghai Synchrotron Radiation Facility will provide a versatile and powerful tool for the orientation and strain/stress mapping combined with phase identification with micron-sized spatial resolution.
Keyword ：
micro-Laue diffraction Ni-based superalloy orientation/strain mapping peak profile analysis synchrotron light source
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| GB/T 7714 | Ren, Chenyu , Jiang, Li , Kou, Jiawei et al. Development of micro-Laue technique at Shanghai Synchrotron Radiation Facility for materials sciences [J]. | SCIENCE CHINA-MATERIALS , 2021 , 64 (9) : 2348-2358 . |
| MLA | Ren, Chenyu et al. "Development of micro-Laue technique at Shanghai Synchrotron Radiation Facility for materials sciences" . | SCIENCE CHINA-MATERIALS 64 . 9 (2021) : 2348-2358 . |
| APA | Ren, Chenyu , Jiang, Li , Kou, Jiawei , Yan, Shuai , Li, Li , Liu, Mengting et al. Development of micro-Laue technique at Shanghai Synchrotron Radiation Facility for materials sciences . | SCIENCE CHINA-MATERIALS , 2021 , 64 (9) , 2348-2358 . |
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Abstract ：
A novel approach evolved from the classical Wilkens' method has been developed to quantify the local dislocation density based on X-ray radial profiles obtained by 3D synchrotron monochromatic X-ray microdiffraction. A deformed Ni-based superalloy consisting of gamma matrix and gamma ' precipitates has been employed as model material. The quantitative results show that the local dislocation densities vary with the depths along the incident X-ray beam in both phases and are consistently higher in the gamma matrix than in the gamma ' precipitates. The results from X-ray microdiffraction are in general agreement with the transmission electron microscopic observations. IMPACT STATEMENT A new approach based on 3D synchrotron microdiffraction showing broad application potential in heterogeneous materials was developed and applied to quantify local dislocation densities in a fatigued two-phase Ni-based superalloy.
Keyword ：
3D synchrotron microdiffraction dislocation density Ni-based superalloy transmission electron microscopy
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| GB/T 7714 | Zhou, Guangni , Pantleon, Wolfgang , Xu, Ruqing et al. Quantification of local dislocation density using 3D synchrotron monochromatic X-ray microdiffraction [J]. | MATERIALS RESEARCH LETTERS , 2021 , 9 (4) : 183-189 . |
| MLA | Zhou, Guangni et al. "Quantification of local dislocation density using 3D synchrotron monochromatic X-ray microdiffraction" . | MATERIALS RESEARCH LETTERS 9 . 4 (2021) : 183-189 . |
| APA | Zhou, Guangni , Pantleon, Wolfgang , Xu, Ruqing , Liu, Wenjun , Chen, Kai , Zhang, Yubin . Quantification of local dislocation density using 3D synchrotron monochromatic X-ray microdiffraction . | MATERIALS RESEARCH LETTERS , 2021 , 9 (4) , 183-189 . |
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Abstract ：
XtalCAMP is a software package based on the MATLAB platform, which is suitable for, but not limited to, the analysis and visualization of scanning Laue X-ray micro-/nanodiffraction data. The main objective of the software is to provide complementary functionalities to the Laue indexing software packages used at several synchrotron beamlines. The graphical user interfaces allow the easy analysis of characteristic microstructure features, including real-time intensity mapping for a quick examination of phase, grain and defect distribution, 2D color-coded mapping of microstructural properties from the output of other Laue indexing software, crystal orientation visualization, grain boundary characterization based on orientation/misorientation calculation, principal strain/stress analysis, and strain ellipsoid representation, as well as a series of additional toolkits. As an example, XtalCAMP is applied to the microstructural investigation of a solution-heat-treated Ni-based superalloy manufactured using a laser 3D-printing technique, and a deformed natural quartzite from Val Bregaglia in the Central Alps.
Keyword ：
computer programs crystal orientation maps scanning Laue X-ray micro-/nanodiffraction strain/stress analysis texture analysis
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| GB/T 7714 | Li, Yao , Chen, Kai , Dang, Xiaofeng et al. XtalCAMP: a comprehensive program for the analysis and visualization of scanning Laue X-ray micro-/nanodiffraction data [J]. | JOURNAL OF APPLIED CRYSTALLOGRAPHY , 2020 , 53 : 1392-1403 . |
| MLA | Li, Yao et al. "XtalCAMP: a comprehensive program for the analysis and visualization of scanning Laue X-ray micro-/nanodiffraction data" . | JOURNAL OF APPLIED CRYSTALLOGRAPHY 53 (2020) : 1392-1403 . |
| APA | Li, Yao , Chen, Kai , Dang, Xiaofeng , Zhang, Fengying , Tamura, Nobumichi , Ku, Ching-Shun et al. XtalCAMP: a comprehensive program for the analysis and visualization of scanning Laue X-ray micro-/nanodiffraction data . | JOURNAL OF APPLIED CRYSTALLOGRAPHY , 2020 , 53 , 1392-1403 . |
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Abstract ：
Manganese oxide (Mn3O4) is of great potential for lithium storage based on conversion reactions, but its application in rechargeable lithium batteries is severely hindered by the low electric conductivity and large volume variation during lithiation/delithiation. Herein, a biomimetic ear-of-wheat-like nanocomposite of ultrafine Mn(3)O(4)nanoparticles (MONPs) and multi-walled carbon nanotubes (MWCNTs) is prepared using a facile solvothermal method. The tightly packed MONP "cereal-grains" are directly grown and uniformly interspersed on the outer surface of skeleton MWCNT "central stems." The ultrafine MONPs are favorable to lithium incorporation/extraction while the interconnected MWCNT skeletons provide a highly conducting network for electron transportation. Consequently, a high reversible capacity of 810 mA h g(-1)is obtained at the current density of 40 mA g(-1). After 50 cycles at 160 mA g(-1), the nanocomposite still delivers a capacity up to 796 mA h g(-1), which is higher than twice of that of pure Mn(3)O(4)nanopowders. The unique nanostructure and the facile biomimetic method can be widely extended to design and explore various high-performance energy materials for lithium/sodium ion batteries and fuel cells.
Keyword ：
anode energy storage lithium battery nanocomposite nanostructure
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| GB/T 7714 | Sun, Xiaofei , Li, Meijuan , Ndahimana, Anastase et al. Biomimetic Synthesis of Ear-of-wheat-shaped Manganese Oxide Nanoparticles on Carbon Nanotubes for High-capacity Lithium Storage [J]. | ENERGY & ENVIRONMENTAL MATERIALS , 2020 , 4 (3) : 399-406 . |
| MLA | Sun, Xiaofei et al. "Biomimetic Synthesis of Ear-of-wheat-shaped Manganese Oxide Nanoparticles on Carbon Nanotubes for High-capacity Lithium Storage" . | ENERGY & ENVIRONMENTAL MATERIALS 4 . 3 (2020) : 399-406 . |
| APA | Sun, Xiaofei , Li, Meijuan , Ndahimana, Anastase , Ding, Peng , Xu, Youlong , Hu, Qiongdan et al. Biomimetic Synthesis of Ear-of-wheat-shaped Manganese Oxide Nanoparticles on Carbon Nanotubes for High-capacity Lithium Storage . | ENERGY & ENVIRONMENTAL MATERIALS , 2020 , 4 (3) , 399-406 . |
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Abstract ：
Ni-based superalloys are widely used in challenging environments due to their exceptional mechanical properties. To enhance their resistance to damage, surface modification by laser shock pinning (LSP) is an approach to improve performance of superalloys. Considering that superalloys are typically used at high temperatures, the thermal stability of the LSP-processed material should be studied. In this article, the hardness and microstructure of a LSP-processed Ni superalloy, DZ17G, are characterized after annealing at various temperatures (up to 1000 degrees C) for different time periods. The results show that the majority of the strength increase achieved at the sample surface from LSP processing is lost after annealing at 800 degrees C for 10 h. Detailed microstructural characterization by synchrotron mu XRD and metallography shows that the hardness decrease is due primarily to the annihilation of dislocations, and no recrystallization occurs in the temperature range studied.
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| GB/T 7714 | Zhou, Guangni , Shen, Hao , Zhu, Wenxin et al. Thermal stability of laser shock peening processed Ni-based superalloy DZ17G [C] . 2019 . |
| MLA | Zhou, Guangni et al. "Thermal stability of laser shock peening processed Ni-based superalloy DZ17G" . (2019) . |
| APA | Zhou, Guangni , Shen, Hao , Zhu, Wenxin , Tamura, Nobumichi , Chen, Kai , Zhang, Yubin . Thermal stability of laser shock peening processed Ni-based superalloy DZ17G . (2019) . |
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In situ tensile tests show atypical defect motions in the brittle Na2Ti3O7 (NTO) nanowire (NW) within the elastic deformation range. After brittle fracture, elastic recovery of the NTO NW is followed by reversible motion of the defects in a time-dependent manner. An in situ cyclic loading-unloading test shows that these mobile defects shift back and forth along the NW in accordance with the loading-unloading cycles and eventually restore their initial positions after the load is completely removed. The existence of the defects within the NTO NWs and their motions does not lead to plastic deformation of the NW. The atypical defect motion is speculated to be the result of the glidibility of the TiO6 layers, where weakly bonded cation layers are in between. Exploration of the above novel observation can establish new understandings of the deformation behavior of superlattice nanostructures.
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| GB/T 7714 | Bo Arixin , Chen Kai , Pickering Edmund et al. Atypical Defect Motions in Brittle Layered Sodium Titanate Nanowires. [J]. | The journal of physical chemistry letters , 2018 , 9 (20) : 6052-6059 . |
| MLA | Bo Arixin et al. "Atypical Defect Motions in Brittle Layered Sodium Titanate Nanowires." . | The journal of physical chemistry letters 9 . 20 (2018) : 6052-6059 . |
| APA | Bo Arixin , Chen Kai , Pickering Edmund , Zhan Haifei , Bell John , Du Aijun et al. Atypical Defect Motions in Brittle Layered Sodium Titanate Nanowires. . | The journal of physical chemistry letters , 2018 , 9 (20) , 6052-6059 . |
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Abstract ：
At elevated temperatures, heavy liquid metals and their alloys are known to create a highly corrosive environment that causes irreversible degradation of most iron-based materials. It has been found that an appropriate concentration of oxygen in the liquid alloy can significantly reduce this issue by creating a passivating oxide scale that controls diffusion, especially if Al is present in Fe-based materials (by Al-oxide formation). However, the increase of the temperature and of oxygen content in liquid phase leads to the increase of oxygen diffusion into bulk, and to promotion of the internal Al oxidation. This can cause a strain in bulk near the oxide layer, due either to mismatch between the thermal expansion coefficients of the oxides and bulk material, or to misfit of the crystal lattices (bulk vs. oxides). This work investigates the strain induced into proximal bulk of a Fe-Cr-Al alloy by oxide layers formation in liquid lead-bismuth eutectic utilizing synchrotron X-ray Laue microdiffraction. It is found that internal oxidation is the most likely cause for the strain in the metal rather than thermal expansion mismatch as a two-layer problem. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Keyword ：
FeCrAl alloy Laue X-ray microdiffraction Oxidation Strain Thermal constriction
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| GB/T 7714 | Popovic, M. P. , Chen, K. , Shen, H. et al. A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic [J]. | ACTA MATERIALIA , 2018 , 151 : 301-309 . |
| MLA | Popovic, M. P. et al. "A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic" . | ACTA MATERIALIA 151 (2018) : 301-309 . |
| APA | Popovic, M. P. , Chen, K. , Shen, H. , Stan, C. V. , Olmsted, D. L. , Tamura, N. et al. A study of deformation and strain induced in bulk by the oxide layers formation on a Fe-Cr-Al alloy in high-temperature liquid Pb-Bi eutectic . | ACTA MATERIALIA , 2018 , 151 , 301-309 . |
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