Entire Grain Research Articles

Dissociation Behavior of Dislocations in Ice

Dislocations in ice behave very differently from those in other materials due to the very low energies of stacking faults in the ice basal plane. As a result, the dislocations dissociate on the basal plane, from a perfect dislocation into two partial dislocations with equilibrium width we ranging from 20 to 500 nm, but what is the timescale to reach this dissociated state? Using physical models, we estimate this timescale by calculating two time-constants: the dissociation-completing time td and the dissociation-beginning time tb. These time constants are calculated for two Burgers vectors as a function of temperature. For perfect dislocations with Burgers vector <c + a>, td is more than one month even at the melting temperature TM, and it exceeds 103 years below −50 ℃, meaning that the dissociation cannot be completed during deformation over laboratory timescales. However, in this case the beginning time tb is less than one second at TM, and it is within several tens of minutes above −50 ℃. These dislocations can glide on non-basal planes until they turn to the dissociated state during deformation, finally resulting in sessile extended dislocations of various widths approaching to the equilibrium value we. In contrast, for perfect dislocations with Burgers vector <a>, td is less than one second above −50 ℃, resulting in glissile extended dislocations with the equilibrium width we on the basal plane. This width is sensitive to the shear stress τ exerted normal to the dislocation line, leading to extension of the intervening stacking fault across the entire crystal grain under commonly accessible stresses. Also, due to the widely dissociated state, dislocations <a> cannot cross-slip to non-basal planes. Such behavior of extended dislocations in ice are notable when compared to those of other materials.

In sink-limited spring barley crops, light interception by green canopy does not need protection against foliar disease for the entire duration of grain filling

Disease management in cereals is heavily reliant on the use of fungicides, but development of anti-microbial resistance, effects on non-target organisms and persistence of active ingredients in the environment and food chain challenge the sustainability of this approach. Better targeting of fungicides according to crop need within an integrated pest management (IPM) programme could improve the sustainability of disease management. The objectives of the present study were to determine 1) the duration of protection of post-anthesis canopy light interception required to maximise the yield of spring barley and 2) to relate this to the response of crops to timing of fungicide applications. As the yield of spring barley is considered to be sink-limited (limited by the number and storage capacity of grains) rather than source-limited (limited by the amount of carbon assimilates available for grain filling) in many environments, we hypothesised that the canopy would not need to be protected for the entire grain filling period. Field experiments were conducted at two sites in the UK (Edinburgh and Herefordshire) over four years, providing contrasting climates and soil types. Shading was used to determine the response of grain filling to reductions in light interception over defined intervals, thereby mimicking effects of foliar disease on light interception, as shading is easier to control than the onset and duration of disease epidemics. Shades giving ˜67% reduction in photosynthetically active radiation (PAR) were erected over plots of disease-free crops at weekly intervals commencing at flowering and leaving them in place until harvest. The required duration of protection of light interception was estimated as the period from flowering to the time at which the onset of shading had no effect on yield. In a separate experiment the response to five fungicide timing treatments was determined on three relatively disease-susceptible varieties. Timings were the start of stem extension (referred to here as T1 only) and T1 followed by a second application at either flag leaf emergence (early T2), flowering (mid T2) or the start of rapid grain growth (late T2); untreated plots served as controls. Results showed that canopy PAR interception does not need to be protected for the entire grain filling period in order to maximise yield. The critical period determined from shading was 3–5 weeks after 50% ear emergence depending on the site year, or the first 72–90% of grain filling. There was a significant yield response to fungicide treatment in all site-years of 0.33−0.74 t ha−1 irrespective of the disease severity and yield potential of the site. Where disease severity was low to moderate a T1 application on its own gave sufficient protection during grain filling to maximise yield. Later applications increased healthy area PAR interception further, but effects occurred late during grain filling and did not increase yield. When disease was severe a T1 plus mid T2 application was required to protect PAR interception during the critical early to mid- grain filling period. These results provide the necessary physiological understanding to help target fungicide applications according to crop need.

On the Strain-Hardening Behavior and Twin-Induced Grain Refinement of CP-Ti Under Ambient Temperature Compression

In this paper, a systematic investigation on the twin-induced grain fragmentation of commercially pure Titanium was carried out under quasi-static uniaxial compression test at ambient temperature. The compression tests were interrupted at various strain levels in order to examine the progressive evolution of the microstructure and texture. The detailed microstructural analysis was performed using the electron backscattered diffraction technique. The microstructural features indicated the presence of $$ \{ 10\bar{1}2\} $$ extension twins (ET), $$ \{ 11\bar{2}2\} $$ contraction twins (CT) and their interactions. The strain-hardening behavior of the material corroborates with the microstructural evidences. The strain-hardening rate and its derivative clearly distinguish the regions of slip- and twin-dominating zones with the increasing strain. The deformation texture substantiates that along with the twins, dislocation slips were active. The slip-based deformation finally deviates the twin boundaries from its special character at medium-to-high strains. At low strains, ET originate in texturally soft grains. These twin domains are comparatively texturally harder. They interact to form ET–ET with ~ 56.8 deg about $$ \langle 10\bar{1}0 \rangle $$ , with twin lamellar structure and consumes the entire parent grain with further deformation by twin expansion. CT develop on texturally hard grains with subsequent strains and were texturally softer. CT–CT, ET–CT-type twin interactions, and CT–ET double twins with ~ 77, ~ 87, and ~ 44.5 deg about $$\langle 10\bar{1}0 \rangle $$ , $$\langle 4\bar{2}\bar{2}1 \rangle $$ and $$\langle 5\bar{1}\bar{4}0 \rangle $$ axes, respectively, were observed. The microstructural changes corresponding to twin-boundary migration, interaction, and grain refinement are discussed on the basis of grain orientation spread and grain reference orientation deviation.

Charged grain boundary transitions in ionic ceramics for energy applications

Surfaces and interfaces in ionic ceramics play a pivotal role in defining the transport limitations in many of the existing and emerging applications in energy-related systems such as fuel cells, rechargeable batteries, as well as advanced electronics such as those found in semiconducting, ferroelectric, and piezotronic applications. Here, a variational framework has been developed to understand the effects of the intrinsic and extrinsic ionic species and point defects on the structural and electrochemical stability of grain boundaries in polycrystalline ceramics. The theory predicts the conditions for the interfacial electrochemical and structural stability and phase transitions of charged interfaces and quantifies the properties induced by the broad region of electrochemical influence in front of a grain boundary capable of spanning anywhere from a few angtroms to entire grains. We demonstrate the validity of this theory for YxZr1−xO2−x/2, cubic yttria stabilized zirconia. For small crystallographic misorientations, sharp Debye-type interfaces, D(1):{mathrm{C}}^{VY}{mathrm{S}}^{underline {VY} }, are favored and promote high ionic conductivity in materials in polycrystalline form. For large grain boundary misorientations and large amounts of [Y2O3] substitutions, three Mott–Schottky interfaces, MS(2):{mathrm{C}}^{VY,underline h e}{mathrm{S}}^{underline {VYh} e}, MS(2):{mathrm{C}}^{VYunderline h e}{mathrm{S}}^{eunderline {hVY} }, and MS(2):{mathrm{C}}^{VY}{mathrm{S}}^{underline h e} are responsible for controlling grain boundary segregation and the observed poor macroscopic ionic transport, in great agreement with the scientific literature.

Cesium-Incorporated Triple Cation Perovskites Deliver Fully Reversible and Stable Nanoscale Voltage Response.

Perovskite solar cells that incorporate small concentrations of Cs in their A-site have shown increased lifetime and improved device performance. Yet, the development of fully stable devices operating near the theoretical limit requires understanding how Cs influences perovskites' electrical properties at the nanoscale. Here, we determine how the chemical composition of three perovskites (MAPbBr3, MAPbI3, and Cs-mixed) affects their short- and long-term voltage stabilities, with <50 nm spatial resolution. We map an anomalous irreversible electrical signature on MAPbBr3 at the mesoscale, resulting in local V oc variations of ∼400 mV, and in entire grains with negative contribution to the V oc. These measurements prove the necessity of high spatial resolution mapping to elucidate the fundamental limitations of this emerging material. Conversely, we capture the fully reversible voltage response of Cs-mixed perovskites, composed by Cs0.06(MA0.17FA0.83)0.94Pb(I0.83Br0.17)3, demonstrating that the desired electrical output persists even at the nanoscale. The Cs-mixed material presents no spatial variation in V oc, as ion motion is restricted. Our results show that the nanoscale electrical behavior of the perovskites is intimately connected to their chemical composition and macroscopic response.

A peek into the origin of creep in sand

This paper presents the results of an experimental study of the particle scale mechanisms that underpin creep, on-going deformations under constant external load, in dry non-cemented sand under 1D oedometric compression loading at 2500 kPa. Traditional observations on the boundary of the sample are complemented with simultaneous measurements of the 3D kinematics of both the entire grain assembly and details of grain-scale mechanisms using synchrotron based X-ray tomography at two different spatial resolutions. Both the continuum response and the local grain scale response are captured using two spatial resolutions, i.e. {6.5},{upmu }hbox {m} and {0.65},{upmu }hbox {m} respectively. The results, for the first time, illustrate that small displacements measured at the boundary can be the result of rather pronounced fracturing at the individual grain scale.

Cost optimization in agribusiness based on life cycle costing

In efforts to achieve and sustain competitiveness and contribute to the goal of sustainable development of society, entity management requires information that will enable the adoption of adequate decisions. The changed business environment and the growing importance of the issues that emerge from the domain of traditional business, both spatial and temporal, have necessitated the monitoring of costs not only during the production phase, but throughout the entire grain cycle of the product. Since conventional cost accounting systems do not have the capacity to generate the above information, in theory and practice, a life cycle costing system (LCC) has been developed. The aim of the paper is to point out the specificity and importance of perceiving and capturing the impacts and consequential costs that arise during the life cycle of the product, with particular reference to agribusiness, precisely because of the complexity of optimizing costs in that sector.

Precipitation of η-Ni3(Ti, Al) Phase at Grain Boundaries in an Austenitic Precipitation-Strengthened Stainless Steel

The precipitation of the η-Ni3(Ti, Al) phase at grain boundaries in austenitic stainless steels significantly affects grain-boundary-related properties of the bulk material. In this study, the precipitation behavior of the η-Ni3(Ti, Al) phase in a thermally aged austenitic precipitation-strengthened stainless steel was evaluated during aging at 750 °C for 0.5 to 64 hours using scanning electron microscopy, transmission electron microscopy, and atom probe tomography. A higher number of plate-like η-Ni3(Ti, Al) phase particles precipitated at the grain boundaries with increasing aging time, and grew into the grain interior until the entire grain was occupied by this phase. The η phase had a {0001}η//{111}γ, $$ \langle 11\bar{2}0\rangle_{{{\upeta }}} $$ //〈110〉γ semi-coherent orientation relationship with the matrix, and contained many stacking faults. Ni- and Ti-rich layers alternated periodically between adjacent stacking faults in the η phase. Al segregated at stacking faults and the interface between the η phase and matrix. The partition coefficients of Ni, Al, and Si between the η precipitates and matrix decreased with increased aging time; however, the partition coefficient of Ti did not change significantly. The partition coefficients of the other elements increased with increasing aging time. The Ti:Al ratio of the η phase significantly increased with increasing aging time. Based on the experimental results, the precipitation and growth behaviors of η-Ni3(Ti, Al) phase precipitated at grain boundaries were discussed, which are expected to contribute to the design of austenitic stainless steel compositions with improved mechanical properties.

Hermetic storage of dry soybean (Glycine max): creating an effective modified atmosphere using soaked grain as O 2 depletor: Poster

Hermetic storage of grains and oilseed has been proposed as a solution for reducing food losses in developing countries. However, to obtain full benefit of the hermetic storage it is required to achieve a low O2 concentration (below 2%) or high CO2 concentration (above 20%). The gas concentration inside the hermetic container is the result of the balance between the respiration and gas exchange rates with the outside (permeability and leakage). When the grain is dry, an insufficient modification in the internal atmosphere is achieved (exchange rate higher than respiration rate), allowing insect development and, hence, grain losses. This study focuses in creating an effective modified atmosphere during the hermetic storage of dry soybean using soaked grain as O2 depletor. Three big bags with internal polyethylene liners of 70 µm thickness were filled with 590 kg of soybean (Glycine max, with 12.5% m.c.) and sealed. Gas concentration evolution was measured during 15 days (basal condition). Later, four plastic perforated bottles filled with of 4.3 kg of soaked soybean (44% m.c.) were inserted in each bag. The bags were re-sealed and gas concentration was measured during 45 days. Results indicated that the soaked soybean acted as an O2 depletor, reducing the gas concentration to 1% in only 8 days, and maintained below 1% during 45 days. This research indicated that a small portion of soaked grain (0.4% dry matter (d.m.)) can be used to generate an effective modified atmosphere to prevent biological activity in the entire grain mass. This is a simple and inexpensive approach to reduce food losses under low cost hermetic storage.

Behaviour of the Angoumois grain moth ( Sitotroga cerealella Oliv.) in different grain substrates and assessment of losses

The Angoumois grain moth, Sitotroga cerealella, is a primary stored grain pest, which development occurs within a single grain. The respond of the pest to various offered grain substrates was studied in no choice laboratory experiment (temperature 27±1oC; relative humidity 60-80%), by rearing moth populations on entire grains (corn, wheat, barley, sorghum, millet, tall fescue and Kentucky bluegrass) and mechanically damaged grains (corn in fractions with/without embryo, polished rice). The pest behaviour was determined by observation of the entrance and exit hole position on different grains. The food consumption was estimated after adult emergence, by measuring of mass losses of infested grains. Mass losses were correlated with quantitative and qualitative grain parameters. The development was successfully accomplished in all grain substrates, except in Kentucky bluegrass. Strategies of larval penetration and exit hole position depended on morphological properties of grains. As a rule, the development of an individual was completed in a single grain, but in polished rice the transfer from one to another grain was observed. The highest loss of infested grain was recorded in corn grains (55.48 mg), the lowest in tall fescue grains (2.40 mg). Positive correlations were detected between the mass losses and protein, lipid and sugar content, negative in relation to cellulose and ash content.

Протеолитические ферменты и их белковые ингибиторы из зерна тритикале

Протеолитические ферменты играют значительную роль в процессах, протекающих при хранении и переработке растительного сырья. На современном этапе приоритетами любой пищевой технологии является сохранение нативных свойств биологически ценных компонентов сырья, обладающих лечебно-профилактическими свойствами, и модификация пищевого сырья с целью получения компонентов с определенными технологическими и функциональными свойствами. В настоящее время наибольшее распространение получили методы ферментативной модификации зернового сырья с использованием микробных ферментных препаратов. В то же время исследование собственных протеолитических ферментов, их выделение и очистка, с целью применения для модификации эндогенных белков, к которым они проявляют наибольшее сродство, представляется весьма интересной задачей, в плане использования всего биопотенциала зерна и “экологичности” получаемых продуктов. Такое исследование неразрывно сопряжено с изучением белковых ингибиторов протеиназ, которые представляют исключительный интерес как фактор регуляции процесса протеолиза. В статье приведены экспериментальные данные по выделению, частичной очистке и характеристике протеолитических ферментов зерна тритикале, действующих в кислой, нейтральной и щелочной областях рН. Показано, что кислые и нейтральные протеиназы зерна тритикале являются ферментами тиолового типа, Щелочные протеиназы относятся к сериновым протеиназам. Методом гель-хроматографии определена их молекулярная масса: 75000, 250000 и 50000 Да соответственно. Предложена схема выделения и очистки белковых ингибиторов эндогенных протеиназ из зерна тритикале. Показана их способность подавлять активность собственных протеиназ и трипсина. Проведено разделение ингибиторов трипсина и щелочных протеиназ тритикале (с молекулярной массой 30000 ÷ 35000 Да) и ингибиторов кислых и нейтральных протеиназ тритикале (с молекулярной массой 15000 ÷ 20000 Да). Частично очищенных препараты протеиназ и их белковых ингибиторов, полученные по предложенным схемам могут быть использованы для ферментативной модификации растительных белков и регуляции процессов протеолиза в различных пищевых технологиях, использующих зерновое сырье.

Crystallography of phase transformation during quenching from β phase field of a V-rich TiAl alloy

Well-developed $$ \alpha_{2}^{{\prime }} $$ -martensitic laths were formed in a Ti–40Al–10V (at.%) alloy after a homogenization treatment within the β phase field followed by brine quenching. The morphology and crystallography of martensite were examined by electron backscatter diffraction. It was found that the martensitic transformation was incomplete and about 35 vol% β phase was retained to room temperature. No diffusional or massive transformation has been detected in the β grain interior. All the 12 martensite variants were formed according to the Burgers orientation relationship (BOR) with the parent β grain. While global variant selection has not been detected, local variant selection occurred so that three self-accommodant variants which shared a common 〈11.0〉 axis were predominant in local regions. Based on the traces of the variants, the habit plane was determined to be close to {679}β by using a simply geometrical method. Besides, $$ \alpha_{2}^{{\prime }} $$ plates were frequently observed along the β grain boundaries, which accorded to a strict BOR with one of the adjacent β grains, but tended to grow into the other β grain and hence resulted in serrated interface. Such features were an indication of massive transformation. Moreover, an apparent variant selection criterion for the grain boundary $$ \alpha_{2}^{{\prime }} $$ plates was noted. That is, if a $$ \alpha_{2}^{{\prime }} $$ variant has, in addition to an exact BOR with one of the two adjacent β grains, a near BOR with the other β grain, this $$ \alpha_{2}^{{\prime }} $$ plate would be very large and even extends along the entire grain boundary.

Conventional and fractal analyses and nanoscale behavior studies of electrodeposited silver films

Silver films were electrodeposited onto gold substrates mounted on a rotating disc electrode. The effects of rotation speed and current density on the conventional and fractal analyses of the films were studied. Conventional processing indicates that grain size and the RMS roughness decrease as the rotation speed of substrate increases. The fractal analysis suggests that the fractal dimension can be used to explain the variation of the entire grain morphology along direction of the growth. Moreover, results show that the samples electrodeposited at higher current densities are much rougher (and have bigger grain sizes) than those grown at lower current densities. Also, the results show that the increasing substrate rotation speed has the same effect as decrease of deposition current density on the conventional parameters of the silver films.

Surface characterization of zirconia ceramics in ultrasonic vibration-assisted grinding

In order to clarify the surface features of zirconia ceramics fabricated by ultrasonic vibration-assisted grinding (UVAG), five geometric parameters (width dw, depth hd, length ld, spacing df and number N) of UVAG surface are selected to characterize UVAG surface topography. In this study, firstly, the mathematic modeling between five geometric parameters and grinding parameters (spindle speed, feed rate, cutting depth and power ratio) is revealed considering the overlapping of entire grains on the end face of tool. The expected value of center-to-center distance between two successive grooves, k0, k1, k2, k3 and k4 are introduced to consider the effect of overlapping. Besides, the experiments of UVAG on zirconia ceramics are carried out to verify the theoretical values of width dw, depth hd, length ld, spacing df and number N. Finally, it is found that the theoretical values and experimental values are well consistent with each other. Therefore, this mathematic modeling can be applied to characterize surface topography in UVAG of zirconia ceramics.

Three-dimensional grain growth in pure iron. Part I. statistics on the grain level

Grain evolution in pure iron is determined in three dimensions using diffraction contrast tomography at a synchrotron source. During annealing for 75 min at 800∘C, the evolution of initially 1327 grains is quantified as a function of 15 time-steps. A comprehensive statistical analysis is provided based on the equivalent radius, the number of faces and the mean width parameters of the grains. We introduce analytical relations between these parameters, validate them, and discuss their physical meaning. While the sample is fully recrystallized, the growth is found not to be self-similar, as evidenced in changes in the distributions of normalized grain size and number of faces per grain. More importantly, a strong decrease in the slope of the growth rate over the mean width of grain faces is observed, indicating a slowdown of grain growth. The data is used to determine the applicability of the isotropic MacPherson-Srolovitz theory to an anisotropic material such as iron. Geometrical properties that are averaged over the entire grain ensemble are well described by the model, but the properties and evolution of the individual grains exhibit substantial scatter.

Modelling the physical multiphase interactions of HNO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; between snow and air on the Antarctic Plateau (Dome C) and coast (Halley)

Abstract. Emissions of nitrogen oxide (NOx = NO + NO2) from the photolysis of nitrate (NO3−) in snow affect the oxidising capacity of the lower troposphere especially in remote regions of high latitudes with little pollution. Current air–snow exchange models are limited by poor understanding of processes and often require unphysical tuning parameters. Here, two multiphase models were developed from physically based parameterisations to describe the interaction of nitrate between the surface layer of the snowpack and the overlying atmosphere. The first model is similar to previous approaches and assumes that below a threshold temperature, To, the air–snow grain interface is pure ice and above To a disordered interface (DI) emerges covering the entire grain surface. The second model assumes that air–ice interactions dominate over all temperatures below melting of ice and that any liquid present above the eutectic temperature is concentrated in micropockets. The models are used to predict the nitrate in surface snow constrained by year-round observations of mixing ratios of nitric acid in air at a cold site on the Antarctic Plateau (Dome C; 75°06′ S, 123°33′ E; 3233 m a.s.l.) and at a relatively warm site on the Antarctic coast (Halley; 75°35′ S, 26°39′ E; 35 m a.s.l). The first model agrees reasonably well with observations at Dome C (Cv(RMSE) = 1.34) but performs poorly at Halley (Cv(RMSE) = 89.28) while the second model reproduces with good agreement observations at both sites (Cv(RMSE) = 0.84 at both sites). It is therefore suggested that in winter air–snow interactions of nitrate are determined by non-equilibrium surface adsorption and co-condensation on ice coupled with solid-state diffusion inside the grain, similar to Bock et al. (2016). In summer, however, the air–snow exchange of nitrate is mainly driven by solvation into liquid micropockets following Henry's law with contributions to total surface snow NO3− concentrations of 75 and 80 % at Dome C and Halley, respectively. It is also found that the liquid volume of the snow grain and air–micropocket partitioning of HNO3 are sensitive to both the total solute concentration of mineral ions within the snow and pH of the snow. The second model provides an alternative method to predict nitrate concentration in the surface snow layer which is applicable over the entire range of environmental conditions typical for Antarctica and forms a basis for a future full 1-D snowpack model as well as parameterisations in regional or global atmospheric chemistry models.

NanoSIMS element mapping and sulfur isotope analysis of Au-bearing pyrite from Lannigou Carlin-type Au deposit in SW China: New insights into the origin and evolution of Au-bearing fluids

Sulfur isotope signatures of Au-bearing pyrite from Lannigou Au deposit, a typical Carlin-type Au deposit in SW China, provide valuable information about the origin of the ore-forming minerals. Analysis by NanoSIMS was used to determine S isotope compositions of Au-bearing pyrite and to map the grain-scale distributions of Au, Cu, As and S in pyrite from the deposit. Based on different textural pattern of pyrites revealed by back-scattered electron (BSE) images, they are divided into three types: Py-1 diagenetic pyrite without core-rim structure, Py-2 pyrite with an Au-free core and a rhythmically-zoned Au-bearing rim, Py-3 Au-bearing pyrite with rhythmic zoning across the entire grain. The element distributions and S isotope compositions of four paragenetic stages are recognized on the basis of textural observation. Py-1 grains and the Au-free homogeneous cores of zoned crystals were formed in Stage 1 while the Au-bearing rims of the zoned crystals with rhythmic zonation of As and Cu, and to a lesser degree Au, were formed in two superimposed stages: stage 2 formed the inner zone that is enriched in As alone; and stage 3 formed the outer zone that is enriched in both Au and As. Other sulfides such as realgar, cinnabar and stibnite are formed in the last stage. The relationship between Au and As distributions in pyrite rim is complicated, changing from coupled to decoupled at the nanoscale. Such complexity is interpreted to reflect fluctuation of fluid composition and temperature with time, which in turn affect the modes of occurrence of As and Au. It is inferred that As mainly occurs in the crystal lattice replacing S whereas Au is mainly present as nanoparticles that were trapped in pyrite during crystal growth. The Au-bearing rims of the zoned pyrite crystals are characterized by highly variable δ34S values from 1.1 to 18.1‰, which exceed the values of the Triassic calcareous host rocks (10–14‰). In contrast, the δ34S values of the Au-free cores of zoned pyrite crystals vary over a narrower interval and are mainly between 6 and 12‰, close to the values of pyrite crystals in the sedimentary country rocks. Our new analyses also reveals that the δ34S values of the Au-bearing fluids generally increase during the formation of the deposit. The observed S isotope variations are consistent with mixing between a magmatic-related fluid with mantle-like δ34S value (∼0‰) and a sedimentary or deep basin brine fluid with elevated δ34S value (>18‰), with an increasing contribution from the latter with time. The notably varied values of δ34S and the disseminations of Au and other trace elements such as As and Cu in pyrite crystals indicate that the process responsible for Au precipitation in this deposit occurred in an open hydrothermal system.

Fatigue behavior of an ultrafine-grained metastable CrMnNi steel tested under total strain control

An ultrafine-grained (UFG) microstructure in a metastable austenitic CrMnNi steel was achieved using a thermo-mechanically controlled process by rotary swaging and subsequent reversion annealing. The material with an average grain size of 0.7μm was cyclically deformed in total strain controlled tests at strain amplitudes in the range of 0.3%≤Δεt/2≤1.2%. This treatment increased the cyclic stress amplitudes as well as the fatigue life in comparison with the conventionally grained counterpart. For strain amplitudes Δεt/2≥0.4% a martensitic phase transformation occurred, which was observed in situ by a ferrite sensor as an increase of the α′-martensite fraction. The microstructure changes, and the deformation mechanisms in particular, were investigated by means of electron backscatter diffraction, scanning electron microscopy in transmission mode and transmission electron microscopy that revealed the formation of small α′-nuclei which rapidly grew until the entire austenitic grain was transformed.

Effect of dislocation density-twin interactions on twin growth in AZ31 as revealed by explicit crystal plasticity finite element modeling

In this work, we employ the recently developed framework for the explicit modeling of discrete twin lamellae within a three-dimensional (3D) crystal plasticity finite element (CPFE) model to examine the effects of dislocation densities in the twin domain on twin thickening. Simulations are carried out for 1¯012101¯1 extension twins in a magnesium AZ31 alloy. The model for the twin lamellae accounts for the crystallographic twin-matrix orientation relationship and characteristic twin shear transformation strain. The calculations for the mechanical fields as a result of twinning consider that one of three types of twin-dislocation density interactions have occurred. One case assumes that the expanding twin retains in its domain the same dislocation density as the parent. The second one considers that twin expansion has lowered the dislocation density as the twin thickens, and the last one, the Basinski effect, assumes that when twin sweeps the region, the dislocation density incorporated in the twin domain is amplified. In the modeling approach, the twin is thickened according to a criterion that maintains the stress state in the vicinity of the grain at a pre-defined characteristic twin resistance. The calculations show that most of the averaged properties, such as the rate of dislocation storage in the entire twin grain, the twin growth rate, the stress field in the twinned grain and neighboring grains, and the slip activity in the parent matrix are not significantly altered by dislocation storage in the twin. The results indicate that, however, the slip activity in the twinned domain is affected. In particular, in the increased dislocation density case, the rate of dislocation density in the twin domain increases at low strains when the twin is first growing from 2% to 5% volume fraction. This initial boost in the dislocation density storage rate causes the newly expanded dislocation twin to contain more stored dislocations than the other cases for all strain levels. Another interesting difference concerns the preference for one or two twins for the same total twin volume fraction; for the increased dislocation twin or twin that retains the dislocation density as it grows, formation of two twins is favored. For a twin that removes dislocation density, only one twin is preferred. The results imply that in the case with reduced dislocation density leads to lower stored dislocations and dislocation storage rates, and lower pyramidal slip activity.

Microstructural evolution of extruded AZ31 alloy with bimodal structure during compression

The twinning behavior and microstructural variations of extruded Mg alloy with a bimodal structure during compression along the extrusion direction are investigated using AZ31 alloy partially recrystallized during hot extrusion; this alloy consists of fine dynamically recrystallized (DRXed) grains (22µm) and coarse unDRXed grains (305µm). It is found that the stronger <10−10> texture and larger grain size of the unDRXed grains in comparison to those of the DRXed grains result in an increase in the Schmid factor for {10−12} twinning and a reduction in the twinning stress, respectively; this consequently leads to a much higher activation of {10−12} twinning during compression in the unDRXed grains. The size of the unDRXed grains decreases considerably to 84µm by the formation of a number of narrow twin bands at a compressive strain of 5%, and it then increases to 112µm by the growth and coalescence of the twin bands at a strain of 10%. However, despite the formation of twins, the size of the DRXed grains does not change during deformation, because twinning occurs throughout the entire grain owing to the low internal strain in these grains. These results indicate that the relative activity of {10−12} twinning and the microstructural and textural evolutions in the DRXed and unDRXed grains are considerably different, which is attributed mainly to the differences in their size, texture, and internal accumulated strain.