Deformation, Phase Transformation and Recrystallization in the Shear Bands Induced by High-Strain Rate Loading in Titanium and Its Alloys

α-titanium and its alloys with a dual-phase structure （α＋β） were deformed dynamically under strain rate of about 10^4 s^-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate （9×10^5 S^-1） deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations in the bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products （α2） had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10 μm in diameter observed within the bands are proposed to be the results of recrystallization.

Shifts in Carbon Stocks through Soil Profiles Following Management Change in Intensive Agricultural Systems

Soil carbon content is an important ecosystem property, especially under the ongoing climate change. The stability of soil organic matter (SOM) is controlled by environmental and biological factors including anthropogenic-induced agricultural management change. However, understanding the effects of anthropogenic activities (e.g., intensive agricultural practices) on carbon stability of soil profiles remains a challenge. The objective of this study was to determine the changes in carbon stocks through soil profiles following agricultural management change from grain fields to greenhouse vegetable fields. The sampling sites were located in an intensive vegetable production area in northernChina. A total of 20 pairs of grain fields (GF) and adjacent vegetable fields (VF) within a distance of50 mwere selected. The results showed that soil organic carbon (SOC) storage increased by 10.6 mg C ha-1 in upper soil layers but decreased by 5.3 mg C hm2 indeeper soil layers due to large input of organic manure and chemical fertilizer following the conversion from GF to VF. Conversion to VF also led to increased dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) concentrations. Extremely higher input of chemical N fertilizer in the VF led to the soil C:N ratio decreased by 2.02 times and the -N leached to deeper soils increased by 3.7 times compared to that in the GF. The pH value and microbial biomass carbon (MBC) content were lower in the VF than in the GF. These results indicate that excessive nitrogen application as fertilizers might lead to deeper soil carbon depletion. Reducing nitrogen addition in intensive agricultural systems is thus necessary to reduce soil carbon loss and to maintain a relatively sustainable soil system.

Microstructural Characterization of the Shear Bands in Fe-Cr-Ni Single Crystal by EBSD

An investigation has been made into the microstructural characterization of the shear bands generated under high-strain rate （≈10^4 s^-1） deformation in Fe-15%Cr-15%Ni single crystal by EBSD-SEM （electron backscatter diffraction-scanning electron microscopy）, TEM （transmission electron in microscopy） and HREM （high- resolution electron microscopy）. The results reveal that the propagation of the shear band exhibits an asymmetrical behavior arising from inhomogenous distribution in plasticity in the bands because of different resistance to the collapse in different crystallographic directions; The γ-ε-α′phase transformations may take place inside and outside the bands, and these martensitic phases currently nucleate at intersections either between the twins and deformation bands or between the twins and ε-sheet. Investigation by EBSD shows that recrystallization can occur in the bands with a grain size of an average of 0.2μm in diameter. These nano-grains are proposed to attribute to the results of either dynamic or static recrystallization, which can be described by the rotational recrystallization mechanism. Calculation and analysis indicate that the strain rate inside the shear band can reach 2.50×10^6 s^-1, which is higher, by two or three orders of magnitude, than that exerted dynamically on the specimen tested.

Deformation Localization and Shear Fracture of a Rapidly Solidified Al-Fe-V-Si Alloy at Elevated Temperature

The tensile and fatigue behavior of a dispersoid strengthened, powder metallurgy Al-Fe-V-Si alloy at ambient and elevated temperatures was investigated. The results show that the strength and ductility of the alloy decrease significantly with increasing temperature and decreasing strain rate. Micro-structural examinations reveal that this change in mechanical behavior with increasing temperature is related to the mode of deformation of the alloy. Further observations show that localized shear deformation is responsible for the losses in both strength and ductility of the alloy at elevated temperature.

Effects of Wheat-Faba Bean Intercropping on Soil Microbial Community Structure in the Rhizosphere

Phospholipid fatty acids (PLFA) analysis and real-time quantitative PCR were used to investigate the effect of wheat-faba bean intercropping on soil microbial community in the rhizosphere and ammonia monooxygenase (amoA) gene abundances of ammonia-oxidizing archaea (AOA) and bacteria (AOB) at harvest stage via field trials in the red soil. We found that the bacteria and fungi of faba bean and actinomycetes of wheat in the rhizosphere showed significant (p < 0.05) difference between intercrops and monocrops at harvest. In total, 37 PLFA were detected at harvest stage in the rhizosphere, including 31 bacterial PLFA, 3 fungal PLFA, and 3 actinomycete PLFA. Compared with the rhizosphere of monocropped faba bean, a lower AOB abundance was found in the intercropping at harvest stage, whereas no significant difference in the AOB abundance was found in the rhizosphere of monocropped and intercropped wheat. There was no significant difference in the AOA abundance between monocrops and intercrops rhizosphere, but a higher AOA abundance in the intercropping systems was found. After intercropping, the abundance of AOB in rhizosphere was significantly higher than that of AOA. Our findings suggest that wheat-faba bean intercropping may change the micro-environment and microbial community structure in the rhizosphere.

Guinier-Preston Zone,Quasicrystal and Long-period Stacking Ordered Structure in Mg-based Alloys,A Review

Both the solid solution and precipitation are mainly strengthening mechanism for the magnesium-based alloys. A great number of alloying elements can be dissolved into the Mg matrix to form the solutes and precipitates.Moreover, the type of precipitates varies with different alloying elements and heat treatments, which makes it quite difficult to understand the formation mechanism of the precipitates in Mg-based alloys in depth. Thus, it is very hard to give a systematical regularity in precipitation process for the Mg-based alloys. This review is mainly focused on the formation and microstructural evolution of the precipitates, as a hot topic for the past few years, including Guinier-Preston Zones, quasicrystals and long-period stacking ordered phases formed in a number of Mg-TM-RE alloy systems, where TM = Al, Zn, Zr and RE = Y,Gd, Hd, Ce and La.