Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation s...Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation synchrotron radiation X-ray computed microtomo- graphy can be used to detect the inner damage evolution of a large-density material or component. This paper provides a brief review of studying the crack initiation and propagation inside lightweight materials with advanced synchrotron three-dimensional （3D） X-ray imaging, such as aluminum materials. Various damage modes under both static and dynamic loading are elucidated for pure aluminum, aluminum alloy matrix, aluminum alloy metal matrix composite, and aluminum alloy welded joint. For aluminum alloy matrix, metallurgical defects （porosity, void, inclusion, precipitate, etc.） or artificial defects （notch, scratch, pit, etc.） strongly affect the crack initiation and propagation. For aluminum alloy metal matrix composites, the fracture occurs either from the particle debonding or voids at the particle/matrix interface, and the void evolution is closely related with fatigued cycles. For the hybrid laser welded aluminum alloy, fatigue cracks usually initiate from gas pores located at the surface or sub-surface and gradually propagate to a quarter ellipse or a typical semi-ellipse profile.展开更多
We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy(HEA)with the body-centered cubic(bcc)structure.Different from the widely-investigated face-centered cubic(fcc)HEAs,th...We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy(HEA)with the body-centered cubic(bcc)structure.Different from the widely-investigated face-centered cubic(fcc)HEAs,the local lattice distortion is more pronounced in bcc ones,which has a strong influence on the defect properties and defect evolution under irradiation.Due to the large size of Ta,the exchange between vacancies and Ta exhibits lower energy barriers.On the other hand,interstitial dumbbells containing V and Cr possess lower formation energies.These defect energetics predicts an enrichment of V and Cr and a depletion of Ta andWin the vicinity of defect sinks.Besides,we find that interstitial dumbbells favor the[110]orientation in the HEA,instead of[111]direction in most nonmagnetic bcc metals,which helps to slow down interstitial diffusion significantly.Consequently,the distribution of migration energies for vacancies and interstitials exhibit much larger overlap regions in the bcc HEA compared to fcc HEAs,leading to the good irradiation resistance by enhancing defect recombination.Our results suggest that HEAs with the bcc structure may bear excellent irradiation tolerance due to the particular defect properties.展开更多
The grain surfaces(film surface and grain boundary)of polycrystalline perovskite films are vulnerable sites in solar cells since they pose a high defect density and initiate the degradation of perovskite absorber.Achi...The grain surfaces(film surface and grain boundary)of polycrystalline perovskite films are vulnerable sites in solar cells since they pose a high defect density and initiate the degradation of perovskite absorber.Achieving simultaneously defect passivation and grain protection from moisture is crucial for the viability of perovskite solar cells.Here,an in situ cross-linked grain encapsulation(CLGE)strategy that improves both device stability and defect passivation is reported.Cross-linkable semiconducting small molecules are mixed into the antisolvent to uniformly form a compact and conducting cross-linked layer over the grain surfaces.This cross-linked coating layer not only passivates trap states and facilitates hole extraction,but also enhances the device stability by preventing moisture diffusion.Using the CLGE strategy,a high power conversion efficiency(PCE)of 22.7%is obtained in 1.55-eV bandgap planar perovskite solar cells.The unencapsulated devices with CLGE exhibit significantly enhanced device stability again moisture and maintain>90%of their initial PCE after shelf storage under ambient condition for over10,000 h.展开更多
Emerging nano-devices with the corresponding nano-architectures are expected to supplement or even replace conventional lithography-based CMOS integrated circuits, while, they are also facing the serious challenge of ...Emerging nano-devices with the corresponding nano-architectures are expected to supplement or even replace conventional lithography-based CMOS integrated circuits, while, they are also facing the serious challenge of high defect rates. In this paper, a new weighted coverage is defined as one of the most important evaluation criteria of various defecttolerance logic mapping algorithms for nanoelectronic crossbar architectures functional design. This new criterion is proved by experiments that it can calculate the number of crossbar modules required by the given logic function more accurately than the previous one presented by Yellambalase et al. Based on the new criterion, a new effective mapping algorithm based on genetic algorithm （GA） is proposed. Compared with the state-of-the-art greedy mapping algorithm, the proposed algorithm shows pretty good effectiveness and robustness in experiments on testing problems of various scales and defect rates, and superior performances are observed on problems of large scales and high defect rates.展开更多
An experimental method and a theoretical analysis based on continuum damage mechan- ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which is considered a ...An experimental method and a theoretical analysis based on continuum damage mechan- ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which is considered a typical defect on fixed plate according to the engineering practice. The general approach to the defects tolerance analysis of scratched fixed plate is presented. The method of fatigue life prediction for standard notched specimens has been established on the basis of continuum damage mechanics. For the purpose of obtaining the influence law of fatigue life in consequence of scratches, fatigue experiments of standard notched specimens and scratched specimens have been done. Evalu- ation of the fatigue life of scratched fixed plate has been carried out. And the value of scratch defects permissible to the condition of safety service life has been worked out. According to the results of the- oretical calculations, the fatigue experiment of scratched fixed plate has been performed. The outcome shows that the theoretical prediction tallies with the experimental results.展开更多
Carbon and boron have been considered to strengthen grain boundaries that might form during single crystal casting.In this study the effect of boron on solidification behavior and creep properties of the carbon doped ...Carbon and boron have been considered to strengthen grain boundaries that might form during single crystal casting.In this study the effect of boron on solidification behavior and creep properties of the carbon doped single crystal RR 2072 has been investigated.In order to understand solidification behavior with boron addition,the solid/liquid interface morphology and solidification microstructure were examined with solidification rate.The relationship between mi-crostructural evolution and creep properties of the carbon and boron modified single crystal has been also investigated.展开更多
Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applicati...Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers(dubbed defect tolerance) is a highly desirable property. Here,using density functional theory(DFT) calculations, we study the intrinsic defects in BaZrS_(3), a representative CP material.We compare Hubbard-U and hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the U value to obtain experimental bulk band gap and then using the obtained U value for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS_(3)can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium.BaZrS_(3)is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.展开更多
基金Acknowledgements The authors thank the National Natural Science Foundation of China （Grant No. 11572267）, the Open Foundation of the State Key Laboratory for Strength and Vibration of Mechanical Structures of Xi＇an Jiaotong University （Grant No. SV2016-KF-21）, the Science and Technology Project of Sichuan Province （Grant No. 2017JY0216）, and the Self-Developed Research Project of the State Key Laboratory of Traction Power of Southwest Jiaotong University （Grant No. 2015TPL_T07）.
文摘Damage accumulation and failure behaviors are crucial concerns during the design and service of a critical component, leading researchers and engineers to thoroughly identifying the crack evolution. Third-generation synchrotron radiation X-ray computed microtomo- graphy can be used to detect the inner damage evolution of a large-density material or component. This paper provides a brief review of studying the crack initiation and propagation inside lightweight materials with advanced synchrotron three-dimensional （3D） X-ray imaging, such as aluminum materials. Various damage modes under both static and dynamic loading are elucidated for pure aluminum, aluminum alloy matrix, aluminum alloy metal matrix composite, and aluminum alloy welded joint. For aluminum alloy matrix, metallurgical defects （porosity, void, inclusion, precipitate, etc.） or artificial defects （notch, scratch, pit, etc.） strongly affect the crack initiation and propagation. For aluminum alloy metal matrix composites, the fracture occurs either from the particle debonding or voids at the particle/matrix interface, and the void evolution is closely related with fatigued cycles. For the hybrid laser welded aluminum alloy, fatigue cracks usually initiate from gas pores located at the surface or sub-surface and gradually propagate to a quarter ellipse or a typical semi-ellipse profile.
基金This work was supported financially by the Project of the City University of Hong Kong(No.9610425)the Research Grants Council of Hong Kong(No.21200919).
文摘We report first-principles results of the point defect properties in a V-Ta-Cr-W high-entropy alloy(HEA)with the body-centered cubic(bcc)structure.Different from the widely-investigated face-centered cubic(fcc)HEAs,the local lattice distortion is more pronounced in bcc ones,which has a strong influence on the defect properties and defect evolution under irradiation.Due to the large size of Ta,the exchange between vacancies and Ta exhibits lower energy barriers.On the other hand,interstitial dumbbells containing V and Cr possess lower formation energies.These defect energetics predicts an enrichment of V and Cr and a depletion of Ta andWin the vicinity of defect sinks.Besides,we find that interstitial dumbbells favor the[110]orientation in the HEA,instead of[111]direction in most nonmagnetic bcc metals,which helps to slow down interstitial diffusion significantly.Consequently,the distribution of migration energies for vacancies and interstitials exhibit much larger overlap regions in the bcc HEA compared to fcc HEAs,leading to the good irradiation resistance by enhancing defect recombination.Our results suggest that HEAs with the bcc structure may bear excellent irradiation tolerance due to the particular defect properties.
基金financially supported by the National Key R&D Program of China(2018YFB1500102,2018YFB2200101)the National Natural Science Foundation of China(61974063,61921005)+3 种基金Natural Science Foundation of Jiangsu Province(BK20190315)the Fundamental Research Funds for the Central Universities(14380168)the Thousand Talent Program for Young Outstanding Scientists in ChinaProgram for Innovative Talents and Entrepreneur in Jiangsu。
文摘The grain surfaces(film surface and grain boundary)of polycrystalline perovskite films are vulnerable sites in solar cells since they pose a high defect density and initiate the degradation of perovskite absorber.Achieving simultaneously defect passivation and grain protection from moisture is crucial for the viability of perovskite solar cells.Here,an in situ cross-linked grain encapsulation(CLGE)strategy that improves both device stability and defect passivation is reported.Cross-linkable semiconducting small molecules are mixed into the antisolvent to uniformly form a compact and conducting cross-linked layer over the grain surfaces.This cross-linked coating layer not only passivates trap states and facilitates hole extraction,but also enhances the device stability by preventing moisture diffusion.Using the CLGE strategy,a high power conversion efficiency(PCE)of 22.7%is obtained in 1.55-eV bandgap planar perovskite solar cells.The unencapsulated devices with CLGE exhibit significantly enhanced device stability again moisture and maintain>90%of their initial PCE after shelf storage under ambient condition for over10,000 h.
基金the National Natural Science Foundation of China under Grant Nos. 61071024, U0835002the Innovation Fund for Young Researchers of University of Science and Technology of Chinathe EU’s 7th Framework Programmefor Research (FP7) under Grant No. 247619
文摘Emerging nano-devices with the corresponding nano-architectures are expected to supplement or even replace conventional lithography-based CMOS integrated circuits, while, they are also facing the serious challenge of high defect rates. In this paper, a new weighted coverage is defined as one of the most important evaluation criteria of various defecttolerance logic mapping algorithms for nanoelectronic crossbar architectures functional design. This new criterion is proved by experiments that it can calculate the number of crossbar modules required by the given logic function more accurately than the previous one presented by Yellambalase et al. Based on the new criterion, a new effective mapping algorithm based on genetic algorithm （GA） is proposed. Compared with the state-of-the-art greedy mapping algorithm, the proposed algorithm shows pretty good effectiveness and robustness in experiments on testing problems of various scales and defect rates, and superior performances are observed on problems of large scales and high defect rates.
文摘An experimental method and a theoretical analysis based on continuum damage mechan- ics are applied for the defects tolerance of fixed plate. The defects type studied in this article is scratch, which is considered a typical defect on fixed plate according to the engineering practice. The general approach to the defects tolerance analysis of scratched fixed plate is presented. The method of fatigue life prediction for standard notched specimens has been established on the basis of continuum damage mechanics. For the purpose of obtaining the influence law of fatigue life in consequence of scratches, fatigue experiments of standard notched specimens and scratched specimens have been done. Evalu- ation of the fatigue life of scratched fixed plate has been carried out. And the value of scratch defects permissible to the condition of safety service life has been worked out. According to the results of the- oretical calculations, the fatigue experiment of scratched fixed plate has been performed. The outcome shows that the theoretical prediction tallies with the experimental results.
文摘Carbon and boron have been considered to strengthen grain boundaries that might form during single crystal casting.In this study the effect of boron on solidification behavior and creep properties of the carbon doped single crystal RR 2072 has been investigated.In order to understand solidification behavior with boron addition,the solid/liquid interface morphology and solidification microstructure were examined with solidification rate.The relationship between mi-crostructural evolution and creep properties of the carbon and boron modified single crystal has been also investigated.
基金supported by the National Natural Science Foundation of China (11774365)the Natural Science Foundation of Shanghai (19ZR1421800)+4 种基金Shanghai International Cooperation Project (20520760900)the Opening Project and Science Foundation for Youth Scholar of State Key Laboratory of High Performance Ceramics and Superfine Microstructures (SKL201804 and SKL201803SIC) support by US National Science Foundation (NSF) (CBET1510121)US Department of Energy (DOE) (DEEE0007364)support by US NSF (CBET-1510948).support by US NSF (DMR-1506669)support by the Fundamental Research Funds for the Central Universities (DUT21RC(3) 033)。
文摘Chalcogenide perovskites(CPs) exhibiting lower band gaps than oxide perovskites and higher stability than halide perovskites are promising materials for photovoltaic and optoelectronic applications. For such applications, the absence of deep defect levels serving as recombination centers(dubbed defect tolerance) is a highly desirable property. Here,using density functional theory(DFT) calculations, we study the intrinsic defects in BaZrS_(3), a representative CP material.We compare Hubbard-U and hybrid functional methods, both of which have been widely used in addressing the band gap problem of semi-local functionals in DFT. We find that tuning the U value to obtain experimental bulk band gap and then using the obtained U value for defect calculations may result in over-localization of defect states. In the hybrid functional calculation, the band gap of BaZrS_(3)can be accurately obtained. We observe the formation of small S-atom clusters in both methods, which tend to self-passivate the defects from forming mid-gap levels. Even though in the hybrid functional calculations several relatively deep defects are observed, all of them exhibit too high formation energy to play a significant role if the materials are prepared under thermal equilibrium.BaZrS_(3)is thus expected to exhibit sufficient defect tolerance promising for photovoltaic and optoelectronic applications.
