Open celled metal foams fabricated through metal sintering are a new class of material that offers novel mechanical and acoustic properties. Previously, polymer foams have been widely used as a means of absorbing acou...Open celled metal foams fabricated through metal sintering are a new class of material that offers novel mechanical and acoustic properties. Previously, polymer foams have been widely used as a means of absorbing acoustic energy. However, the structural applications of these foams are limited. The metal sintering approach offers a costeffective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. In this first part of two-paper series, the mechanical properties of open-celled steel alloy （FeCrA1Y） foams were characterized under uniaxial compression and shear loading. Compared to predictions from established models, a significant knockdown in material properties was observed. This knockdown was attributed to the presence of defects throu- ghout the microstructure that result from the unique fabrication process. Further in situ tests were carried out in a SEM （scanning electronic microscope） in order to investigate the effects of defects on the properties of the foams. Typically, the onset of plastic yielding was observed to occur at defect locations within the microstructure. At lower relative densities, ligament bending dominates, with the deformation initializing at defects. At higher relative densities, an additional deformation mechanism associated with membrane elements was observed. In the follow-up of this paper, a finite element model will be constructed to quantify the effects of defects on the mechanical performance of the opencell foam.展开更多
Additive manufacturing (AM) technology such as selective laser melting (SLM) often produces a high refection phenomenon that makes defect detection and information extraction challenging. Meanwhile, it is essential to...Additive manufacturing (AM) technology such as selective laser melting (SLM) often produces a high refection phenomenon that makes defect detection and information extraction challenging. Meanwhile, it is essential to establish a characterization method for defect analysis to provide sufcient information for process diagnosis and optimization. However, there is still a lack of universal standards for the characterization of defects in SLM parts. In this study, a polarization-based imaging system was proposed, and a set of characterization parameters for SLM defects was established. The contrast, defect contour information, and high refection suppression efect of the SLM part defects were analyzed. Comparative analysis was conducted on defect characterization parameters, including geometric and texture parameters. The experimental results demonstrated the efects of the polarization imaging system and verifed the feasibility of the defect feature extraction and characterization method. The research work provides an efective solution for defect detection and helps to establish a universal standard for defect characterization in additive manufacturing.展开更多
Narrow-gap Hg_(1-x)Cd_x Te material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x ≈ 0.3 are re...Narrow-gap Hg_(1-x)Cd_x Te material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x ≈ 0.3 are reviewed, including the defects and defect levels of intrinsic V_(Hg) and the extrinsic amphoteric arsenic(As) dopants, which can act as shallow/deep donors and acceptors. The influence of the defects on the determination of band-edge electronic structure is discussed when absorption or photoluminescence spectra are considered. The inconsistency between these two optical techniques is demonstrated and analyzed by taking into account the Fermi level position as a function of composition, doping level,conductivity type, and temperature. The defect level and its evolution, especially in As-doped HgCdTe, are presented. Our results provide a systematic understanding of the mechanisms and help for optimizing annealing conditions towards p-type As-activation, and eventually for fabricating high performance mid-infrared detectors.展开更多
Inline characterization for fabrication of silicon wafer PV （photovoltaic） devices may be used to optimize device efficiencies, reduce their performance variance, and their cost of production. In this article, the f...Inline characterization for fabrication of silicon wafer PV （photovoltaic） devices may be used to optimize device efficiencies, reduce their performance variance, and their cost of production. In this article, the frozen in strain from a variety of extended defects in silicon is shown to effect the polarization of light transmitted through a silicon substrate due to the photo-elastic effect. Transmission polarimetry on pre-fabricated silicon substrates may be used for identification of extended defects in the materials using a polarization analysis instrument. Instrumentation is proposed for detection of defects in raw silicon wafers for applications like raw silicon wafer sorting, scanning silicon bricks, and inline inspection prior to solar cell metallization. Such analysis may assist with gettering of silicon solar cells, may be implemented in the sorting and rejection procedures in PV device fabrication, and in general shows advantages for detection of defects in silicon wafer solar cell materials and devices.展开更多
基金The project supported by the US 0ffice of Naval Research （N000140210117） the National Basic Research Program of China （2006CB601202）+1 种基金 the National Natural Science Foundation of China （10328203, 10572111, 10632060） the National 111 Project of China.（B06024）.
文摘Open celled metal foams fabricated through metal sintering are a new class of material that offers novel mechanical and acoustic properties. Previously, polymer foams have been widely used as a means of absorbing acoustic energy. However, the structural applications of these foams are limited. The metal sintering approach offers a costeffective means for the mass-production of open-cell foams from a range of materials, including high-temperature steel alloys. In this first part of two-paper series, the mechanical properties of open-celled steel alloy （FeCrA1Y） foams were characterized under uniaxial compression and shear loading. Compared to predictions from established models, a significant knockdown in material properties was observed. This knockdown was attributed to the presence of defects throu- ghout the microstructure that result from the unique fabrication process. Further in situ tests were carried out in a SEM （scanning electronic microscope） in order to investigate the effects of defects on the properties of the foams. Typically, the onset of plastic yielding was observed to occur at defect locations within the microstructure. At lower relative densities, ligament bending dominates, with the deformation initializing at defects. At higher relative densities, an additional deformation mechanism associated with membrane elements was observed. In the follow-up of this paper, a finite element model will be constructed to quantify the effects of defects on the mechanical performance of the opencell foam.
基金Supported by National Natural Science Foundation of China(Grant No.52075100)Shanghai Municipal Science and Technology Committee Innovation Program(Grant No.23ZR1404200).
文摘Additive manufacturing (AM) technology such as selective laser melting (SLM) often produces a high refection phenomenon that makes defect detection and information extraction challenging. Meanwhile, it is essential to establish a characterization method for defect analysis to provide sufcient information for process diagnosis and optimization. However, there is still a lack of universal standards for the characterization of defects in SLM parts. In this study, a polarization-based imaging system was proposed, and a set of characterization parameters for SLM defects was established. The contrast, defect contour information, and high refection suppression efect of the SLM part defects were analyzed. Comparative analysis was conducted on defect characterization parameters, including geometric and texture parameters. The experimental results demonstrated the efects of the polarization imaging system and verifed the feasibility of the defect feature extraction and characterization method. The research work provides an efective solution for defect detection and helps to establish a universal standard for defect characterization in additive manufacturing.
基金Project supported by the Major Program of the National Natural Science Foundation of China(Grant Nos.61790583,61874043,61874045,and 61775060)the National Key Research and Development Program,China(Grant No.2016YFB0501604)
文摘Narrow-gap Hg_(1-x)Cd_x Te material with a composition x of about 0.3 plays an extremely important role in mid-infrared detection applications. In this work, the optical properties of doped HgCdTe with x ≈ 0.3 are reviewed, including the defects and defect levels of intrinsic V_(Hg) and the extrinsic amphoteric arsenic(As) dopants, which can act as shallow/deep donors and acceptors. The influence of the defects on the determination of band-edge electronic structure is discussed when absorption or photoluminescence spectra are considered. The inconsistency between these two optical techniques is demonstrated and analyzed by taking into account the Fermi level position as a function of composition, doping level,conductivity type, and temperature. The defect level and its evolution, especially in As-doped HgCdTe, are presented. Our results provide a systematic understanding of the mechanisms and help for optimizing annealing conditions towards p-type As-activation, and eventually for fabricating high performance mid-infrared detectors.
文摘Inline characterization for fabrication of silicon wafer PV （photovoltaic） devices may be used to optimize device efficiencies, reduce their performance variance, and their cost of production. In this article, the frozen in strain from a variety of extended defects in silicon is shown to effect the polarization of light transmitted through a silicon substrate due to the photo-elastic effect. Transmission polarimetry on pre-fabricated silicon substrates may be used for identification of extended defects in the materials using a polarization analysis instrument. Instrumentation is proposed for detection of defects in raw silicon wafers for applications like raw silicon wafer sorting, scanning silicon bricks, and inline inspection prior to solar cell metallization. Such analysis may assist with gettering of silicon solar cells, may be implemented in the sorting and rejection procedures in PV device fabrication, and in general shows advantages for detection of defects in silicon wafer solar cell materials and devices.
基金supported by the National Natural Science Foundation of China (No.12202190)Outstanding Postdoctoral Program in Jiangsu Province (No.2022ZB233)Research Start-up Funding from Nanjing University of Aeronautics and Astronautics (No.90YAH21131)。
