Twinning

Strain-controlled cyclic deformation behavior of a high-strength low-alloy (HSLA) Mg-1.2Zn-0.1Ca alloy fabricated via low-temperature extrusion at 150 °C was investigated at different strain amplitudes. Due to the partial dynamic recrystallization (DRX) during extrusion, the extruded HSLA magnesium alloy consisted of a unique heterostructure containing coarse unDRX grains and ultra-fine DRX grains of 0.8 μm, leading to a high tensile yield strength of 374 MPa and an elongation of 14%. The HSLA magnesium alloy exhibited cyclic stabilization at strain amplitudes of ≤0.4%, while cyclic hardening occurred at strain amplitudes of ≥0.6%. In contrast, the homogenized alloy with a uniform coarse-grained microstructure showed a strong cyclic hardening characteristic. Compared with the homogenized alloy, the HSLA magnesium alloy had a significantly higher cyclic stress level at all strain amplitudes, along with a longer fatigue life at lower and intermediate strain amplitudes owing to its higher monotonic strength. However, the homogenized alloy showed a longer fatigue life at a high strain amplitude of 0.8 % due to its better ductility and stronger capacity of storing deformation. While {10-12} < 10−11 > extension twinning occurred in both the homogenized and HSLA samples at high strain amplitudes, twins were primarily formed in the coarse unDRX grains in the compressive phase during cyclic deformation due to the c-axes of unDRX grains perpendicular to the loading direction, with twinning in the ultra-fine DRX grains being suppressed. The low-cycle fatigue life of both the homogenized and HSLA samples can be well predicted through an accumulative damage model based on the strain-energy density calculation and intrinsic fatigue toughness concept.

A complimentary set of experiments, in situ neutron diffraction and ex situ synchrotron X-ray diffraction, were used to study the phase-transformation and subgrain-deformation characteristics of a cobalt-based superalloy. The neutron diffraction indicated a strain-induced phase transformation in the cobalt-based superalloy under uniaxial tension and compression. The synchrotron X-ray diffraction revealed stackingfault accumulation and twinning under the same loading conditions. The extent of transformation was found to be greater under tension than under compression. Tensile plastic strains below 2% were accommodated by the stacking-fault creation, while those greater than 2% were accommodated by the phase transformation. Twinning was found to be more active under compressive loading than under tensile loading.

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Samples of quartz-bearing rocks were heated above the a (trigonal)-b (hexagonal) phase transformation of quartz (625-950°C) to explore changes in preferred orientation patterns. Textures were measured both in situ and ex situ with neutron, synchrotron X-ray and electron backscatter diffraction. The trigonal-hexagonal phase transformation does not change the orientation of c-and a-axes, but positive and negative rhombs become equal in the hexagonal b-phase. In naturally deformed quartzites measured by neutron diffraction a perfect texture memory was observed, i.e. crystals returned to the same trigonal orientation they started from, with no evidence of twin boundaries. Samples measured by electron back-scattered diffraction on surfaces show considerable twinning and memory loss after the phase transformation. In experimentally deformed quartz rocks, where twinning was induced mechanically before heating, the orientation memory is lost. A mechanical model can explain the memory loss but so far it does not account for the persistence of the memory in quartzites. Stresses imposed by neighboring grains remain a likely cause of texture memory in this mineral with a very high elastic anisotropy. If stresses are imposed experimentally the internal stresses are released during the phase transformation and the material returns to its original state prior to deformation. Similarly, on surfaces there are no tractions and thus texture memory is partially lost.

The paper examines how the Russian northern subnational units use paradiplomacy as a resource for problem-solving and ensuring their sustainable development. Particularly, this study focuses on three specific questions: First, the basic motives laying behind the subnational actors" international activities are examined. Second, the main paradiplomatic strategies, instruments and institutions are identified. Third, the negative and positive implications of paradiplomacy for the centerperiphery relations and Russia"s foreign policy are explored. Particularly, the paper focuses on the following paradiplomatic strategies: making direct agreements with international partners; attracting foreign investment; creating regions' positive image; cooperation with international organizations; establishing representative offices in foreign countries; city-twinning; participation in Euroregions and other sub-regional arrangements; capitalizing on national diplomacy and federal infrastructures, etc. The institutional framework available for the sub-state actors in the Arctic region is examined. The authors believe that paradiplomacy will remain an important resource for the Russian northern subnational actors in terms of capacity-building and positioning domestically and internationally.

Various self-consistent polycrystal plasticity models for hexagonal close packed (HCP) polycrystals are evaluated by studying the deformation behavior of magnesium alloy AZ31B sheet under different uniaxial strain paths. In all employed polycrystal plasticity models both slip and twinning contribute to plastic deformation. The material parameters for the various models are fitted to experimental uniaxial tension and compression along the rolling direction (RD) and then used to predict uniaxial tension and compression along the traverse direction (TD) and uniaxial compression in the normal direction (ND). An assessment of the predictive capability of the polycrystal plasticity models is made based on comparisons of the predicted and experimental stress responses and R values. It is found that, among the models examined, the self-consistent models with grain interaction stiffness halfway between those of the limiting Secant (stiff) and Tangent (compliant) approximations give the best results. Among the available options, the Affine self-consistent scheme results in the best overall performance. Furthermore, it is demonstrated that the R values under uniaxial tension and compression within the sheet plane show a strong dependence on imposed strain. This suggests that developing anisotropic yield functions using measured R values must account for the strain dependence.

ÐStress±strain responses of single and polycrystals of Had®eld steel were modeled using a viscoplastic self-consistent approach. A unique hardening formulation was proposed in the constitutive model incorporating length scales associated with spacing between twin lamellae and grain boundaries. TEM observations lend further support to the length scales incorporated into the constitutive model. Many of the experimental ®ndings were made on " 111 and " 144 crystal orientations deformed in tension, displaying ®ne twin lamellae at small strains in addition to slip in intra-twin regions. A natural outcome of the model was the small deformation activity inside the twinned regions and higher deformations between the twins. The model utilized dislocation density as a state variable and predicted the stress±strain responses and texture evolution in single crystals accurately over a broad range of strains. The responses of polycrystals with three grain sizes (100, 300, and 1000 mm) were also captured closely with the model in addition to the twin volume fraction evolution with increasing deformation. Based on the simulations, it was possible to explain unequivocally the upward curvature in stress±strain curves in the single crystals and in coarse grained polycrystals of Had®eld steel. Overall, the combined experimental and modeling eorts provide a reliable tool to characterize slip±twin interaction in low stacking fault energy f.c.c. materials.

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A series of nickel layers was electrodeposited at different current densities from a Watts type electrolyte containing the additive 2-butyne-1,4-diol in various concentrations. The internal structure of the nickel electrodeposits was systematically investigated applying complementary microscopic and diffraction based characterization methods involving both surface and cross section investigations with different resolution and statistics. The complementary information gathered from combining the various techniques of microstructure characterization, in particular, supported the investigation of twins and the preferred crystallographic orientations of grains in the electrodeposits. Additive-free deposition results in relatively large columnar grains with numerous growth twins of nanoscale dimensions. The presence of the additive in the electrolyte yields considerable grain refinement already at low additive concentration, but the preferred crystallographic orientation of grains changes gradually with increasing additive concentration and twins with nanoscale dimensions are detected also in these samples.

The structure of deca-dodecasil 3R (DD-3R), Si120O240, a very well suited material for the synthesis of inorganic/organic composites structured on a nanometer level, has been investigated in detail. So far, a highly complicated twinning has hampered its structure description at a desirable level of accuracy. This twinning has now been resolved and a new structure determination is presented. Structure refinement in the R\bar 3 space group revealed a large, unusually shaped atomic displacement ellipsoid for oxygen-bridging units (tetrahedra), bridging Si—O bonds shorter than expected and the linear Si—O—Si′ bond angle dictated by special positions at a threefold axis. A structure model based on a statistically disordered bridging O atom improved the accuracy of the Si—O bonds of interest, but provided unacceptable O—O contacts. To solve this dilemma, ab initio NVT molecular dynamics calculations were performed to study the possible configurations. Wavelet analysis of the time variatio...

It is generally accepted that growth of eutectic silicon in aluminium-silicon alloys occurs by a twin plane re-entrant edge (TPRE) mechanism. It has been proposed that modification of eutectic silicon by trace additions occurs due to a massive increase in the twin density caused by atomic effects at the growth interface. In this study, eutectic microstructures and silicon twin densities in samples modified by elemental additions of barium (Ba), calcium (Ca), yttrium (Y) and ytterbium (Yb) (elements chosen due to a near-ideal atomic radii for twinning) in an A356.0 alloy have been determined by optical microscopy, thermal analysis, X-ray diffractometry (XRD) and transmission electron microscopy (TEM). Addition of barium or calcium caused the silicon structure to transform to a fine fibrous morphology, while the addition of yttrium or ytterbium resulted in a refined plate-like eutectic structure. Twin densities in all modified samples are higher than in unmodified alloys, and there are no significant differences between fine fibrous modification (by Ba and Ca) and refined plate-like modification (by Y and Yb). The twin density in all modified samples is less than expected based on the predictions by the impurity induced twining model. Based on these results it is difficult to explain the modification with Ba, Ca, Y and Yb by altered twin densities alone.

Background: The average gestational age at onset of labour which could be spontaneous or
induced differs among pregnant women. The gestational age correlates with the maturity of the
foetus which in turn plays an important role in the initiation of labour.
Objective: To determine the average gestational age at onset of labour, induction of labour and
Caesarean section at the Federal Medical Centre, Yenagoa, Bayelsa State, Nigeria.
Materials and Methods: This was a five-year retrospective review amongst patients who presented to the labour ward of Federal Medical Centre, Yenagoa in labour between 1st January,
2016 and 31st December, 2020. Data was entered into a pre-designed proforma and analysed
using IBM SPSS version 23.0.
Results: There were 4,571 deliveries in the 5-year period under review. More than half (55.3%) of
the women were in the fourth decade of life, with median age of 31 years (15 – 52 years), about
half (52.3%), of the women were multiparous, while almost a quarter (23.5%) were primiparous.
The modal gestational age for spontaneous onset of labour for all pregnant women was 38 weeks.
Two-third (66.0%) of the women were delivered per vaginam, while the other one-third (34.0%) had
Caesarean section.
Conclusion: The gestational age at onset of labour and delivery is associated with foetal and
maternal outcomes. It is therefore necessary for women to have antennal care and interventions in
pregnancy under qualified healthcare providers, as this will in turn reduce the public health burdens
of large number of preterm deliveries.

A general theoretical and computational procedure for dealing with an exponential-logarithmic kinematic model for transformation stretch tensor in a multiphase phase field approach to stress- and temperature-induced martensitic transformations with N martensitic variants is developed for transformations between all possible crystal lattices. This kinematic model, where the natural logarithm of transformation stretch tensor is a linear combination of natural logarithm of the Bain tensors, yields isochoric variant–variant transformations for the entire transformation path. Such a condition is plausible and cannot be satisfied by the widely used kinematic model where the transformation stretch tensor is linear in Bain tensors. Earlier general multiphase phase field studies can handle commutative Bain tensors only. In the present treatment, the exact expressions for the first and second derivatives of the transformation stretch tensor with respect to the order parameters are obtained. U...

A thermodynamically consistent, novel multiphase phase field approach for stress-and temperature-induced martensitic phase transformations at finite strains and with interfacial stresses has been developed. The model considers a single order parameter to describe the austenite↔martensitic transformations, and another N order parameters describing N variants and constrained to a plane in an N-dimensional order parameter space. In the free energy model coexistence of three or more phases at a single material point (multiphase junction), and deviation of each variant-variant transformation path from a straight line have been penalized. Some shortcomings of the existing models are resolved. Three different kinematic models (KMs) for the transformation deformation gradient tensors are assumed: (i) In KM-I the transformation deformation gradient tensor is a linear function of the Bain tensors for the variants. (ii) In KM-II the natural logarithms of the transformation deformation gradient is taken as a linear combination of the natural logarithm of the Bain tensors multiplied with the interpolation functions. (iii) In KM-III it is derived using the twinning equation from the crystallographic theory. The instability criteria for all the phase transformations have been derived for all the kinematic models, and their comparative study is presented. A large strain finite element procedure has been developed and used for studying the evolution of some complex microstructures in nanoscale samples under various loading conditions. Also, the stresses within variant-variant boundaries, the sample size effect, effect of penalizing the triple junctions, and twinned microstructures have been studied. The present approach can be extended for studying grain growth, solidifications, para↔ferro electric transformations, and diffusive phase transformations.

We report a new zirconium titanate compound (Zr,Ti)O 2 with 27.5-35 mol% titania (TiO 2) formed from the oxides at 35-38 kbar, 1400-1500 1C. Crystal structure investigations at atmospheric conditions with powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) revealed a monoclinic structure related to that of M-fergusonite (beta). Unit-cell dimensions (from 27.5 to 35 mol% TiO 2

Epitaxial CGS films were gram on (100) GaAs as a function of CulGa ratio with and without Na dosing. All asgrown films showed good crystalline quality as evidenced by the FWHM value of the *rocking curve for the (008) reflection being less than 300 arcsec for all films. In particular, the lowest value ever reported for CGS (80 arcsec) was measured for a Nadoped, Cu-rich CGS film. TEM analysis revealed pseudomorphic growth for all films with the strain believed to be released by the formation of twins in localized regions in the sample. From PL spectra at 10 K, donor-acceptor transitions were associated with Vm-Vs, and CUG-VS~ defects as confirmed from their activation energies. A new defect level related to Na, which was tentatively assigned to Naa, was observed for Cu-rich, Nadosed CGS film and its activation energy was proposed as 20 meV above the valence band edge.

A J Parker Cooperative Research Centre for Hydrometallurgy 1 Department of Applied Chemistry, Curtin University of Technology, Australia; E-Mail: [email protected], [email protected] 2 Nanochemistry Research Institute, Curtin University of Technology, Australia; E-Mail: [email protected], [email protected] 3 Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia; E-Mail: [email protected]

The paper reports a substantial improvement of the static and cyclic strength of a Cr-Ni-Ti austenitic stainless steel nanostructured by equal channel angular pressing (ECAP). After ECAP at room temperature or 673 K, the mean grain size decreased from 14 µm to 430 nm or 940 nm, respectively; corresponding ultimate tensile strength increased from 610 MPa to 1230 MPa or 940 MPa, and the fatigue limit increased from 275 MPa to 375 MPa or 475 MPa. These enhanced strength properties result from the grain refinement assisted by the intensive twinning in the austenite during ECAP at room temperature and 673 K as well as partial martensitic transformation during ECAP at room temperature. Moreover, the partial martensitic transformation and an increase in the fraction of high angle grain boundaries during subsequent high-cycle fatigue tests were particularly favorable for the improvement of fatigue properties.

An anisotropic viscoplastic constitutive model was developed for the description of the high-strain rate behaviour of zirconium, a HCP metal that exhibits strength differential effects and strong anisotropic strain hardening. The evolution laws for the strength differential parameter and the anisotropy coefficients involved in the expression of the yield criterion were obtained based on numerical tests performed with a crystal plasticity model. The strain rate dependent parameters involved in the formulation were determined from results of dynamic in-plane tests performed on a high purity zirconium plate [9, 10] on a Split Hopkinson Pressure Bar (SHPB). Simulations of the Taylor impact test were conducted using the finite element code ABAQUS with the anisotropic viscoplastic model. The very good agreement between the simulated and experimental post-test geometries of the Taylor specimens in terms of major and minor side profiles and impact interface footprints shows the ability of the phenomenological model to capture the influence of twinning on texture evolution.

This contribution reports on the Raman spectra and polarised light images obtained for hexagonal six-fold twinned and diamond shaped single crystals of synthetic and industrial gibbsite. The results are interpreted in terms of a possible growth mechanism for gibbsite.

Deformation-induced nanoscale twinning is one of the mechanisms responsible for the excellent combination of strength and fracture toughness of the single-phase, face-centered cubic CrMnFeCoNi (Cantor) alloy, especially at cryogenic temperatures. Here, we use a novel, modified dogbone geometry that permits the sampling of varying stress and strain regions within a single tensile specimen to characterize the onset of twinning in CrMnFeCoNi at 293 K, 198 K and 77 K. Electron backscatter diffraction (EBSD) and backscattered electron (BSE) imaging revealed the presence of deformation nano-twins in regions of the samples that had experienced plastic strains of ∼25% at 293 K, ∼16% at 198 K, and ∼8% at 77 K, which are similar to the threshold strains described by Laplanche et al. (Acta Mater. 118, 2016, 152-163). From these strains we estimate that the critical tensile stress for the onset of twinning in this alloy is on the order of 750 MPa.

The study was conducted on Saanen goats raised in Croatia. The object of the study was to determine the average litter size (LS), birth weight (BW) and total litter weight (TLW). The study included a total of 2 500 goats among which 1 786 were phenotyped. A total of 6 349 records for BW and 4 256 records for LS and TLW were used in descriptive and inferential statistical analysis. Determined averages for LS, BW and TLW were 1.74 lambs, 3.27 kg and 5.65 kg, respectively. Twinning and tripling rates were 36.9% and 6.2%. Single-trait analysis under repeatability animal model was used in estimation of variance components and prediction of breeding values. Season (as year-month interaction), age at lambing (as quadratic regression) nested within parity and type of birth were treated as fixed, while herd-year, additive genetic, permanent environmental and residual were treated as random effects, respectively. Investigated environmental effects significantly affected all reproductive traits (p<0.001). The largest phenotype variability among investigated traits was determined for TLW. Additive genetic effect accounted for 7%, 5% and 4% in total variability for LS, BW and TLW, respectively. Genetic trends of reproductive traits were estimated for the period from year 2000 to 2010. A positive genetic trend was determined for LS, a negative genetic trend for BW and genetic stagnation for TLW.

The origin of cyclic hardening under low strain amplitude (with N ¼ 25284 cycles to failure) followed by pseudo-plateau response under high strain amplitude (with N ¼ 2671 cycles to failure) during fully reversal (R ¼ À1) strain-controlled pullepush fatigue of Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr (wt.%) at room temperature condition was explored. The (i) dislocations trapping between LPSO (long period stacking order) lamellas, (ii) substructure development, and (iii) deformation twinning and tangling/rearrangement of partials within twin band were known as the main factors contributing to the room temperature cyclic hardening response. The pseudo-plateau behavior and cyclic stabilization were also attributed to the co-formation of the veins structure in the vicinity of 18R LPSO and reversion of 14H LPSO at higher strain amplitudes.

An analytical model is presented that can successfully predict the strain hardening behaviour as well as the variations in twin volume fraction in polycrystalline Magnesium alloy Mg-3Al-0.3Mn that twins profoundly during deformation. The model is composed of three basic elements: (i) Twin fraction prediction, based on crystal plasticity elements, (ii) a two-phase composite model composed of the matrix and the twins by adopting the "Iso-work" hypothesis, (iii) a strain hardening approach inspired from a crystal plasticity model. The experiments include uniaxial compression tests for two different cases at ambient temperature. The microstructures were characterized at various strains up to fracture using the Electron Back-Scattered Diffraction technique in a FEG-SEM. The microstructural investigation revealed the formation of a lamellar structure of alternated layers of matrix and { } 1012 1011-extension twin domains. With progressive deformation, the twins broadened and consumed the entire microstructure prior to fracture. The model could accurately reproduce the experimental twin-induced sigmoidal shaped flow curve together with the twin volume fraction evolution.

We investigate the temperature and rate dependence of slip, twinning, and secondary twinning in high-purity hexagonal close packed α-Zr over a wide range of temperatures and strain rates (from 76 K to 673 K and 0.001 s-1 to 4500 s-1). To reliably identify the dominant deformation mechanisms for each condition, we employ electron-backscattered diffraction (EBSD), dislocation theory, multi-scale polycrystal constitutive modeling, and a thermally activated dislocation density evolution based hardening law. We demonstrate with direct comparison with measurement that the constitutive model, with a single set of intrinsic material parameters, can predict the underlying texture evolution, primary and secondary slip and twin activity, and twin volume fraction associated with the different loading orientations and applied temperatures and strain rates. We find that the ሼ101 ത 2ሽ〈101 ത 1 ത 〉 twin is the preferred tension twin, either as a primary or secondary twin depending on the sample orientation, over the broad temperature and strain rate range tested. In contrast, we show that the preferred contraction twin, whether ሼ112 ത 2ሽ〈112 ത 3 ത 〉 or ሼ101 ത 1ሽ〈101 ത 2 ത 〉, is sensitive to temperature but insensitive to strain rate and whether it is a primary or secondary twin. Based on the concomitant changes in the dominant slip mode predicted by the model and revealed by the texture development, we rationalize that the temperature-induced transition in contraction twinning is due to the increased predominance of basal <a> slip at high temperatures (> 673K). Last, our analysis implies that all twin modes studied are rate insensitive and so the strong influence of strain rate and temperature on twinning is due to the rate-sensitivity of slip.

"I weave Your Name on the loom of my mind,
To make my garment when You come to me.
My loom has ten thousand threads
To make my garment when You come to me.
The sun and moon watch while I weave Your Name;
The sun and moon hear while I count Your Name…"

- Kabir

The influence of the hot forming process of AZ31B wrought and twin roll cast (TRC) magnesium alloy sheets on the microstructure and corrosion behaviour have been evaluated. The corrosion behaviour was investigated by hydrogen evolution experiments in chloride-containing solution. Filiform-like corrosion was predominant attack to the AZ31 magnesium alloys, as observed by in-situ corrosion observation. The intermetallic particle existence and grain structure significantly influenced the corrosion rate. The dendritic structure of the as-cast TRC alloy was severely attacked, revealing that the as-cast alloy was highly susceptible to corrosion. The presence of twins in wrought alloy was found to act as a corrosion barrier, while the increase in grain size showed the high corrosion rate of the alloy.

Epitaxial SnO 2 thin films were grown on (1 1 0) (a-cut) and (1 0 0) (m-cut) sapphire substrates using plasma enhanced atomic layer deposition (PEALD) with dibutyltindiacetate (DBTDA) as a precursor. X-ray diffraction, X-ray pole figure, and high resolution TEM analyses revealed that SnO 2 film deposited on a-cut sapphire was (1 0 1) oriented with a small component of (2 0 0) orientation, and the (1 0 1) planes were slightly tilted due to the presence of (2 0 0) plane and/or twinning. SnO 2 film on m-cut sapphire was strongly (0 0 1) oriented with a small amount of the (3 0 1) orientation. The determined in-plane orientation relationships were [0 1 0]SnO 2 //[0 0 1]Al 2 O 3 and [1 0 1 ]SnO 2 //[1 1 0]Al 2 O 3 (a-cut) and [0 1 0]SnO 2 //[0 0 1 ]Al 2 O 3 and [1 0 0]SnO 2 //[0 1 0]Al 2 O 3 (m-cut) consistent with the previous reports.

Deformation behavior of high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N stainless steel was investigated utilizing electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). During deformation, the &lt;110&gt; grains rotated and the trace of these grains moved towards into the dodecahedral plane (the line connecting (001) and (111) planes). Misorientation mapping in EBSD showed that the special boundaries (almost Σ3) gradually diminished whereas the low-angle boundaries were developed. TEM observation showed that (i) the low-angle boundaries developed corresponded to the deformation twinning with {111}&lt;112&gt; component, (ii) the deformation twinning showed the strong orientation dependence relative to tensile axis, and (iii) the deformed microstructure was characterized by extended stacking faults, planar dislocation array in low strain regime, and by well-developed deformation twinning in high strain region, respectively.

Magnesium alloys based composites were deformed at ambient temperature. The acoustic emission (AE) was detected in situ during deformation. The time dependence of the AE count rate was measured at two threshold levels. Two AE peaks were found. The peak observed at the onset of plastic deformation was ascribed to massive twinning and dislocation slip, and the second, broader maximum was caused mainly by fibre breakage and debonding at the fibre-matrix interfaces. The AE activity was significantly influenced by the load transfer from the matrix to the fibres.

A metastable b Tie10Ve3Fee3Ale0.27O (wt.%) alloy was subjected to thermo-mechanical processing to induce a and u phase formation, so that the alloy can exhibit the features responsible for both transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) behaviour during deformation. The alloy thereafter was deformed at different strain rates (10 À3 , 10 À1 , 10 1 , 10 2 s À1) at ambient temperature. At slow strain rate (10 À3 s À1), in addition to slip the alloy displayed a dominant deformation mechanism with a 00 martensite formation, where mechanical {332}〈113〉b twinning and deformation-induced u phase were also activated. At an intermediate strain rate, 10 À1 s À1 , there was a competition between stress-induced phase transformations and stress-induced twinning deformation mechanisms. With increasing strain rate to 10 1 s À1 or higher; it was found that the dominant deformation mode was twinning. These results have been correlated with the b phase stability of the samples.

Samples collected across the NW Grenville Front in Ontario, Canada, have been used to document the change in feldspar microstructures produced during shearing under metamorphic conditions that range from upper amphibolite to lower greenschist grade. The differential displacement across this 5 km thick section of the Grenville Front tectonic zone is at least 10 km. At upper to mid-amphibolite conditions both plagioclase and potassium feldspars behave plastically. Grainsize reduction occurs through grain boundary migration and/or subgrain rotation and produces a core-andmantle structure. At middle to lower amphibolite grade, grain-size reduction is accomplished through grain boundary migration. At lower amphibolite to upper greenschist grade, grain-size reduction occurs by the nucleation and growth of new grains with a different composition. The abundance of intracrystalline deformation at this grade is inversely proportional to the amount of fine-grained matrix. In ultramylonite with a high matrix to porphyroclast ratio few intracrystalline strain features occur other than ubiquitous undulatory extinction. Myrmekite is well developed on the high stress boundaries in K-feldspar. At upper to mid-greenshist conditions, feldspars deform mainly by slip on synthetic shear fractures. Deformation twins, undulatory extinction, deformation bands and kink bands occur in plagioclase, and perthite flames and myrmekite occur principally on high stress boundaries in K-feldspar. Grain-size reduction in feldspar is accomplished through cataclasis. At middle to lower greenschist facies, deformation in feldspars is dominated by antithetic fractures. The transition from the dominance of synthetic to antithetic fractures is gradational. Below lower greenschist grade, rocks deform by pervasive cataclasis of all minerals.

The paper presents a correlation between microstructure and crystallographic texture in hot-rolled AZ31 magnesium alloy. The microstructure and texture evolution are investigated using optical microscopy, field emission scanning electron microscopy, X-ray diffraction, respectively. The results indicated discontinuous dynamic recrystallization, twinning dynamic recrystallization, and particle stimulated nucleation as the main mechanisms during hot deformation. The average size of grains decreased from 19 to 1 lm as the rolling reduction increased from 0 to 60%. A large area fraction of new grains was observed at 40% thickness reduction. At the beginning of plastic deformation, basal slip and extension twinning increased the intensity of {0001} basal fiber texture. Dynamic recrystallization had a considerable effect on weakening the basal texture. Interestingly, some unusual highly stable components including ð01 13Þ½7 813; ð01 13Þ½ 2110; and ð01 13Þ½14 5 3 existed at all deformation conditions and their intensity remained nearly unchanged.

Background Trauma is the leading cause of death in the young (ages 1-44) and the current life situation is responsible for producing emergency injuries from motor vehicle accidents, violence and from acute life threatening illnesses. The training of emergency nurses is therefore of priority based on the increasing demands on the entire emergency health care system. The study evaluates the education and training of emergency nursing programme that has been offered for the past seven (7) years at a Nursing Education Institution (NEI) in the Limpopo province. The programme has not has not been formally evaluated. Aim The overall aim of the study is to explore and describe the views of students pertaining to the emergency nursing programme offered at the NEI in the Limpopo province and to make recommendations for the refinement of the emergency nursing programme, based on the views of the nursing students. Methods A qualitative design working from an Appreciative Inquiry approach was employed. Purposive sampling was used and focus group interviews were conducted with 20 Professional nurses who are trained as emergency nurses at the NEI from 2007 to 2013. Two main themes emerged: theoretical aspects and clinical aspects, which included both positive and negative views. The findings were used to make recommendations to refine the programme.

The microstructure and texture evolution during cold rolling with total thickness reductions of 20-80% (nominal strains of 0.22-1.61) and their effect on the tensile behavior of an Fe-17Mn-1.5Al-0.3C steel were studied. The cold rolling to total strains of 0.5 was accompanied by multiple deformation twinning, resulting in the formation of twin/matrix lamellae with the boundary spacing of 35 nm. Correspondingly, the textural changes were characterized by the rapid evolution of rather strong Brass and S texture components. An increase in the rolling strain led to further reduction in the boundary spacing down to about 20 nm and the development of shear banding, which promoted the formation of γ-fiber (〈111〉||ND) at large strains. Before cold rolling, the investigated steel exhibited a large total elongation above 90% because of the TWIP (twinning-induced plasticity) effect and a relatively low yield strength of 245 MPa. The cold rolling resulted in significant increase in the yield strength up to 1440 MPa after rolling to a total strain of 1.61, whereas the total elongation decreased to 5%. The strengthening of the present steel during cold rolling was attributed to increased dislocation density and reduced twin/grain boundary spacing.

Background and context: The Royal College of Midwives is engaged in a long-term twinning partnership with the Uganda Private Midwives Association. Uganda is one of the poorest countries in the world and only 27% of women and newborns have their needs met (UNFPA, 2014). A well-skilled, competent midwifery workforce is required to meet these needs yet Ugandan student midwives often receive poor-quality clinical education. The Ugandan Nurses and Midwives Council approached the Royal College of Midwives for assistance in designing a system of mentorship for Ugandan midwifery to address this gap. The project was funded by UK-Aid through the Tropical Health and Education Trust. Aims of the project: MOMENTUM was a 20-month action research project that aimed to develop and pilot a model of mentorship for student midwives in Uganda. This article focuses on one workstream relating to practice development, a twinning project that used workbased learning and appreciative inquiry, embedded in an action research approach, to facilitate practice development. Conclusions: This project added to the body of knowledge about midwifery twinning for building capacity in mentorship, research, and cross-cultural competence. MOMENTUM created a powerful community of practice that was enabling, fulfilling and transformative. Replication of this would require funding, management capacity and sufficient lead time for participatory planning and piloting. MOMENTUM's audit tool was a bespoke design for this pilot project and so may not be transferable to other settings without further development, testing and validation. Implications for practice: • Twinning, action research, appreciative enquiry and workbased learning can be effective in enabling practice development • The impact of midwifery twinning on leadership development requires further investigation, together with greater evidence on the reciprocal impact of twinning on the sending country

Deformation-induced nanoscale twinning is one of the mechanisms responsible for the excellent combination of strength and fracture toughness of the single-phase, face-centered cubic CrMnFeCoNi (Cantor) alloy, especially at cryogenic temperatures. Here, we use a novel, modified dogbone geometry that permits the sampling of varying stress and strain regions within a single tensile specimen to characterize the onset of twinning in CrMnFeCoNi at 293 K, 198 K and 77 K. Electron backscatter diffraction (EBSD) and backscattered electron (BSE) imaging revealed the presence of deformation nano-twins in regions of the samples that had experienced plastic strains of ∼25% at 293 K, ∼16% at 198 K, and ∼8% at 77 K, which are similar to the threshold strains described by Laplanche et al. (Acta Mater. 118, 2016, 152-163). From these strains we estimate that the critical tensile stress for the onset of twinning in this alloy is on the order of 750 MPa.

A constitutive model based on the dislocation glide and deformation twinning is adapted to facecentered cubic high-entropy alloys (HEAs) as exemplified by the CrMnFeCoNi system. In this model, the total dislocation density is considered as the only internal variable, while the evolution equation describing its variation during plastic deformation is governed by the volume fraction of twinned material. The suitability of the model for describing the strain hardening behavior of HEAs was verified experimentally through compression tests on alloy CrMnFeCoNi and its microstructure characterization by electron backscatter diffraction and X-ray diffraction using synchrotron radiation. IMPACT STATEMENT We adopted a constitutive model based on dislocation density and twin volume fraction evolution, to analyze the deformation behavior of the high-entropy alloy CrMnFeCoNi theoretically.

The viscoplastic intermediate /-model was applied in this work to predict the deformation behavior and texture evolution in a magnesium alloy, an HCP material. We simulated the deformation behavior with different intergranular interaction strengths and compared the predicted results with available experimental results. In this approach, elasticity is neglected and the plastic deformation mechanisms are assumed as a combination of crystallographic slip and twinning systems. Tests are performed for rolling (plane strain compression) of random textured Mg polycrystal as well as for tensile and compressive tests on rolled Mg sheets. Simulated texture evolutions agree well with experimental data. Activities of twinning and slip, predicted by the intermediate /-model, reveal the strong anisotropic behavior during tension and compression of rolled sheets.

Formation of annealing twins has been studied from the beginning of 20 th century. The related mechanisms as growth accident, nucleation of twins and nucleation of partial Shockley loops were suggested. The simulation was also realized by molecular dynamics simulations at the atomic scale. In this paper, a microscopic scale simulation of primary recrystallization and twinning by Monte Carlo approach was realized for a nickel alloy. Different twin morphologies were simulated. It showed a possibility of dependence of grain growth direction on twin formation during annealing. The incoherent Σ3 and Σ9 boundaries formation is verified as the indirect outcome after coherent Σ3 formation.

High strength steels are susceptible to H-induced failure, which is typically caused by the presence of diffusible H in the microstructure. The diffusivity of H in austenitic steels with fcc crystal structure is slow. The austenitic steels are hence preferred for applications in the hydrogen-containing atmospheres. However, the fcc structure of austenitic steels is often stabilized by the addition of Ni, Mn or N, which are relatively expensive alloying elements to use. Austenite can kinetically also be stabilized by using C. Here, we present an approach applied to a commercial cold work tool steel, where we use C to fully stabilize the fcc phase. This results in a microstructure consisting of only austenite and an M7C3 carbide. An exposure to H by cathodic hydrogen charging exhibited no significant influence on the strength and ductility of the C stabilized austenitic steel. While this material is only a prototype based on an existing alloy of different purpose, it shows the potential for low-cost H-resistant steels based on C stabilized austenite.

This work is concerned with the effects of A1 on the deformation mode and tensile properties of Fe-19Mn-5Cr (0-5.5)A1 0.25C alloys. The deformation mode at room temperature shifted from (s + ~') martensites to deformation twinning to slip with increasing A1 content. A1 increased the stacking fault energy at a rate of 10 mJ mm-2 wt.%-1, which is sufficiently high to give birth to the large variation of the deformation mode. On the other hand, bct ~' martensites were induced during deformation at low temperatures, together with deformation twins. The formation of bct ~' martensites was preceded by the prior formation of deformation twins. Fe-19Mn 5Cr-3.5A1-0.25C alloy composition exhibited excellent elongations exceeding 65% at both room temperature and 77 K. It was found in this work that the sequential formation of strain-induced deformation twins and ~' martensites was responsible for exhibiting excellent elongations at both room temperature and 77 K.