查看更多>>摘要：X-ray computed tomography (XCT), field emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDS) were evaluated for imaging and element identification of woody plant roots. Lateral roots of Japanese zelkova (Zelkova serrata) were severed in spring and maintained in soil for six months. The lateral roots were observed using XCT without maceration and sectioning. The general wood characteristics were discernible to reveal the bark and xylem structures in contrast-inverted tomograms. Virtual sections showed a newly formed ring of woundwood encircling the severed lateral roots. FESEM exhibited secondary xylem structures in which tyloses, fungal hyphae, and aggregates were present. While silicon was dispersed in and around the fungal hyphae, calcium was localized as distinct aggregates using EDS. These results suggest that the combined use of XCT, FESEM, and EDS has merit into the morphological assessment of tree health care, providing virtual sections, high-resolution images, and element composition from an entire woodblock.
查看更多>>摘要：Energy deposition in dielectric materials by electron irradiation is important in evaluating irradiation effects in various applications. Herein, we developed a novel Monte Carlo model to calculate the actual distribution of energy deposition in polymethyl methacrylate (PMMA) by simulating low-energy electron transport, including secondary electron cascades. We compared the energy deposition calculated using this model with the distri-bution of energy loss based on the continuous slowing down approximation (CSDA). The difference in depth distribution between energy deposition and energy loss near the surface is attributed to the secondary electron emission. The characteristics of energy deposition distributions at various incident angles and primary energy were analysed. Energy depositions based on different energy loss mechanisms were classified. Approximately half of the total energy deposition was formed in paths of the secondary cascade at keV-electron irradiation. The temporal properties of energy deposition show that the fast process of energy deposition occurs first near the surface of the dielectric material, then deep inside and 1-keV electrons deposit their energy in 10(-14) s.
查看更多>>摘要：To identify different types of precipitates and their composition, analytical electron tomography analysis on a needle-shaped sample was performed. Three-dimensional chemical maps from each element in a high alloyed steel are acquired and the resulting elemental maps are jointly reconstructed. Since analytical electron tomography data suffers from noise, total generalized variation regularization is used to improve the reconstruction quality compared to conventional reconstruction techniques. We analyse the influence of regularization parameters on these reconstructions in terms of elemental quantification, and compare these results to atom probe tomography measurements done on another sample of the same material.
Nohl, James F.Farr, Nicholas T. H.Sun, YigeHughes, Gareth M....
22页
查看更多>>摘要：Powder materials are used in all corners of materials science, from additive manufacturing to energy storage. Scanning electron microscopy (SEM) has developed to meet morphological, microstructural and bulk chemical powder characterization requirements. These include nanoscale elemental analysis and high-throughput morphological assays. However, spatially localized powder surface chemical information with similar resolution to secondary electron (SE) imaging is not currently available in the SEM. Recently, energy filtered (EF-) SEM has been used for surface chemical characterization by secondary electron hyperspectral imaging (SEHI). This review provides a background to existing powder characterization capabilities in the low voltage SEM provided by SE imaging, EDX analysis and BSE imaging and sets out how these capabilities could be extended for surface chemical analysis by applying SEHI to powders, with particular emphasis on air and beam sensitive powder surfaces. Information accessible by SEHI, its advantages and limitations, is set into the context of other chemical characterization methods that are commonly used for assessing powder surface chemistry such as by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The applicability of existing powder preparation methods for SEM to SEHI is also reviewed. An alternative preparation method is presented alongside first examples of SEHI characterization of powder surfaces. The commercial powder materials used as examples were carbon-fiber/polyamide composite powder feedstock (CarbonMide (R)) used in additive manufacturing and powders consisting of lithium nickel cobalt oxide (NMC). SEHI is shown to differentiate bonding present at carbonaceous material surfaces and extract information about the work function of metal oxide surfaces. The surface sensitivity of SEHI is indicated by comparison of pristine powders to those with surface material added in preparation. A minimum spatial localization of chemical information of 55 nm was achieved in differentiating regions of NMC surface chemistry by distinct SE spectra.
Mohammadi, M.Haghshenas, M.Shakil, S. I.Zoeram, A. S....
17页
查看更多>>摘要：A dual-stage indentation test at ambient temperature including a constant indentation load rate followed by a constant indentation load-hold segment was employed to assess the time-dependent plastic deformation of cast and additive manufactured Al-Cu-Mg-Ag-TiB2 alloys in as-fabricated and T7 conditions at room temperature. Optical microscopy, scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy techniques were used to study the microstructure of the samples and to correlate the microstructure with the creep properties. That is, the indentation load/displacement/time data from depth-sensing indentation creep were combined with the advanced microstructural assessments to analyze the controlling mechanisms of creep in as-cast, as-built, and T7 samples. Expectedly, the microstructure of samples manufactured by different methods was substantially different in terms of the grain size and the distribution of TiB2 particles. The theta'', theta' and omega phase were formed in all heat-treated samples; however, the density of omega phase was higher in the cast-T7 samples. Distinct microstructure and precipitation density resulted in different indentation-derived properties, both cast and AM samples at T7 condition showed enhanced creep resistance compared to their as-manufactured counterparts. The main controlling mechanism of creep deformation was found to be dislocation creep based on the indentation-derived creep stress exponent values.
NSTL
Elsevier