Search

We investigate grain growth at 1000 °C, a critical temperature for abnormal grain growth in copper foils. By ex-situ annealing experiments at 1000 °C, it is found that abnormal grains grow through the entire sample thickness, forming a polycrystalline structure with a single layer of grains. The migration of the boundaries surrounding the abnormally large grains are characterized by optical microscopy and electron backscatter diffraction. The migration rates are found to vary significantly from place to place, which is analysed based on boundary characteristics, i.e., misorientation and boundary curvature, and the size distribution of the neighbouring grains.

Adding alloying elements has long been known to improve the thermal stability of nanostructured metals via atoms segregation or/and precipitated particles. Despite this, questions regarding the effect of particles on microstructure and their synergic impacts on structural coarsening remain nebulous. Here, we demonstrate the interactions between nanoparticles and microstructural coarsening by Y-junction motion during recovery of lamellar-nanostructured Al–1.0%Si that exhibit good thermal stability. In-situ annealing experiments in a transmission electron microscope reveal three ways for particles to pin moving Y-junctions: (1) direct pinning from particles precipitated at lamellar boundaries or/and inside lamella; (2) synergic pinning from a neighbouring interconnecting dislocation boundary and the particles located at the junction of interconnecting and lamellar boundaries; (3) indirect pinning caused by the particles located at interconnecting dislocation boundaries inside neighbouring lamellae. These pinning mechanisms originating from Si nanoparticles enable high thermal stability in the lamellarnanostructured Al–1.0%Si alloy. The findings enrich the current understanding on the specific role of particles related to structural coarsening resistance in lamellar-nanostructured Al alloys.

Soil erosion control and water resource protection can closely interact during restoration of terrestrial ecosystems. In semi‐arid ecosystems, an urgent issue is how vegetation restoration can achieve the goal of soil erosion mitigation and water conservation, which in turn, feeds back to ecosystem functioning.We reviewed 78 articles from 22 countries in semi‐arid areas to evaluate the effects of vegetation type (i.e., forest, grassland, and scrubland) on run‐off and sediment yields across different environmental conditions (i.e., vegetation coverage, rainfall intensity, slope gradient, and soil texture).Our meta‐analysis shows that run‐off and sediment reduction both increased as the vegetation coverage increased, and tended to be stable when vegetation coverage exceeded 60%. Vegetation provided a greater benefit for sediment reduction than for run‐off control under intense rainfall. Grasslands were generally more effective in reducing sediment than other vegetation types. Forests, grasslands, and scrublands were most efficient in soil erosion control on 20‐30°, 0‐25°, and 10‐25° slopes, respectively. Grasslands and scrublands generally performed better with respect to soil erosion control on moderately coarse soils, whereas forests were most effective on medium‐textured and moderately fine soils.Synthesis and applications. Effective restoration and soil erosion control in semi‐arid ecosystems strongly depends on the selection of vegetation type. Our study further indicates that, for land managers, it is critical to consider local slope, and soil texture, and maintain appropriate vegetation coverage to achieve ecosystem sustainability. Grasslands might be particularly suitable to optimize the trade‐off between soil erosion control and surface water resource in semi‐arid regions.

Climate change and land use intensification are the two most common global change drivers of biodiversity loss. Like other organisms, the soil meso-fauna are expected to modify their functional diversity and composition in response to climate and land use changes. Here, we investigated the functional responses of Collembola, one of the most abundant and ecologically important groups of soil invertebrates. This study was conducted at the Global Change Experimental Facility (GCEF) in central Germany, where we tested the effects of climate (ambient vs. ‘future’ as projected for this region for the years between 2070 and 2100), land use (conventional farming, organic farming, intensively-used meadow, extensively-used meadow, and extensively-used pasture), and their interactions on the functional diversity (FD), community-weighted mean (CWM) traits (life-history, morphology), and functional composition of Collembola, as well as the Soil Biological Quality-Collembola (QBS-c) index. We found that land use was overwhelmingly the dominant driver of shifts in functional diversity, functional traits, and functional composition of Collembola, and of shifts in soil biological quality. These significant land use effects were mainly due to the differences between the two main land use types, i.e. cropland vs. grasslands. Specifically, Collembola functional biodiversity and soil biological quality were significantly lower in croplands than grasslands. However, no interactive effect of climate × land use was found in this study, suggesting that land use effects on Collembola were independent of the climate change scenario. Overall, our study shows that functional responses of Collembola are highly vulnerable to land use intensification under both climate scenarios. We conclude that land use changes reduce functional biodiversity and biological quality of soil.

Desertification has become an important issue for the sustainable development of human society at global scale and has led to the changes in soil properties and vegetation cover. Biocrusts and litter crusts play roles in improving the soil microhabitat of sandy ecosystems. Soil microbial communities mediate ecosystem functions in various ecosystems, e.g., soil biogeochemical processes. However, limited information is available about how the underlying processes of bio-crusts/litter crusts restoration are driven by soil bacterial communities in sandy land. Here, we investigated the changes in soil bacteria from three groups (sandy land, bio-crusts, and litter crusts) and three soil layers (0–2 cm, 2–5 cm, 5–10 cm) with nine replicates each collected in July 2019 utilized high-throughput pyrosequencing of the V4-V5 rRNA gene region. Most soil nutrients (SOM, AP, AK, and TN) and enzyme activities (BG and DHA) had differences among the three groups and three soil layers. OTU richness and diversity of bacteria were positively correlated with most soil variables. The constructed co-occurrence networks between soil variables and bacterial communities, and within bacterial communities showed that bacterial taxa had closer relationships with all soil variables in crusts than sandy land and varied among the three sand groups (sandy land, bio-crusts, and litter crusts). The result showed that the composition of bacterial community was regulated mainly by soil variables and crust types. Compared with sandy land, more predictors in nutrient cycling were found in crust types. They played major roles in nutrient cycling in desert ecosystem restoration on the basis of random forest modeling. Our findings indicate some bacterial taxa may played the predominant roles in connecting with soil variables and other bacterial taxa across crusts types, and litter crusts and bio-crusts drive the nutrient cycling by mediating the restoration of bacterial taxa in san

Mg-3Gd (wt. %) samples were prepared by accumulative roll-bonding (ARB) and subsequent annealing to produce samples with average grain sizes in a wide range from 3.3 μm to 45.1 μm. These samples were tensile tested at room temperature. Dislocation structures and deformation twins in the tested tensile samples were characterized by transmission electron microscopy. Dislocations with different types of Burgers vector were identified based on two-beam diffraction contrast experiments. The results revealed that deformation twins and dislocations are dominant in coarse-grained samples while and dislocations characterize the fine grain deformation structure. The transition of deformation mechanisms and its implications for microstructural design and property optimization are discussed.

Collembola are highly abundant and diverse soil animals and play key roles in litter decomposition and nutrient cycling. Given their functional significance, it is important to understand their responses to human-induced global changes, such as climate change and land-use intensification. Here, we utilized an experimental field study, to test the interactive effects of climate (ambient vs. future) and land use (five land-use regimes, from extensively-used meadow to conventional farming) on three eco-morphological life forms of Collembola: epedaphic, hemiedaphic, and euedaphic species. We found that the effects of climate change on Collembola density were modulated by land use, and that the responses of different life forms to climate × land use interaction differed in magnitude and/or direction. The densities of total and hemiedaphic Collembola significantly decreased under organic farming and marginally increased in grasslands under future climatic conditions, whereas epedaphic Collembola tended to decrease their density with climate change in grasslands. In contrast, the density of euedaphic Collembola significantly increased with climate change in intensively-used grasslands. Further, we found that grasslands (especially extensively-used meadow) support the most abundant Collembola communities, with high species richness but low evenness. Multivariate analyses revealed independent effects of climate change and land-use intensification on Collembola community composition. Together, our findings indicate that the effects of climate change on Collembola communities depend on their life forms and land-use types. Surface-dwelling Collembola are more vulnerable to land use and climate change than those living in deeper soil layers. This may slow down the process of soil-surface litter decomposition in a changing world.

The recovery kinetics of a nanoscale lamellar structure Al-0.3%Cu alloy, which was produced by 98% cold rolling, during annealing at temperatures from 100 to 200 °C have been analyzed in this study. Microstructural characterization using electron channelling contrast in the scanning electron microscope shows a uniform coarsening of the lamellar structure and gradual precipitation of second phase particles (Al2Cu) during annealing at these temperatures. Fitting of the microhardness values for samples annealed for between 4 and 4096 minutes at different temperatures with a recovery model reveals a change, in the apparent activation energy from 79 kJ/mol at the beginning to 105 kJ/mol at the end of recovery annealing, which leads to a discussion of the recovery mechanisms.

The evolution of the microstructure and texture during annealing has been studied in the center layer of 95% cold rolled Al–0.3%Cu with a large initial grain size. The cold-rolled condition is characterized by a strong Brass texture component and a deformed microstructure comprising lamellar structures intersected by a large number of shear bands. Recrystallization and precipitation take place during annealing at 200 °C, and a strong Goss texture develops. In the beginning of recrystallization, Goss oriented grains nucleate preferentially at the shear bands. At a later stage of recrystallization, new Goss nuclei can appear in regions where lamellae of the dominant Brass component are interspersed with Goss-oriented subgrains. When recrystallization is almost complete, recrystallized Goss-oriented grains grow into grains of other orientations, which results in a rapid increase in the average grain size of Goss-oriented grains and strengthening of the Goss texture. As a result, new low angle boundaries are formed between Goss-oriented grains in this strongly textured material.

Surface gradient nanostructured metals characterized by grain size and grain orientation variations from the surface to the interior can be produced by surface plastic deformation. Grain orientation mapping allows a quantitative characterization of both the microstructural and textural gradients that determine the properties and performance of such surface deformed metals. Two-dimensional (2D) orientation mapping techniques in a scanning electron microscope and a transmission electron microscope are typically used to generate grain orientation maps in surface gradient nanostructured metals. In this paper, examples of such grain orientation maps are given to show the advantages and limitations of 2D grain orientation mapping. The challenges associated with the indexing of superimposed electron diffraction patterns are discussed in particular, leading to the conclusion that solving this problem can ultimately only be achieved by 3D orientation mapping.

An Fe-23Cr-8.5Ni duplex stainless steel was used to prepare samples with different volume-fraction-weighted grain sizes (d(alpha gamma)), ranging from the nano-scale to the micrometer-scale by cold rolling and subsequent annealing. The cold rolled sample with d(alpha gamma) of 72 nm showed a high yield strength of about 1.3 GPa but only a small tensile elongation. An abrupt increase of ductility was observed as d(alpha gamma) increased to 375 nm, resulting in a good combination of yield strength of 738 MPa and tensile elongation of 29%. Further increase of d(alpha gamma) up to the micrometer-scale results in continued decreases in yield strength but with only a limited improvement in the ductility.