Effects of stress loading mode on microstructures and properties of Mg-9Gd-2Nd-0.5Zr alloy treated by creep aging

Creep aging forming(CAF) is a potential process used to manufacture large integral components of magnesium(Mg) alloys. The selected stress plays a crucial role in creep aging processes but the mechanism by which stress loading method affects creep aging of Mg alloys is still unclear. In this paper, the microstructural evolution of precipitated phases and precipitation-free zones(PFZ) at grain boundaries with different stress loading modes(unstressed, unidirectional tensile stress, and cyclic stress) at 250 ℃ were investigated along with changes in mechanical properties. The results showed that the addition of stress during aging effectively promoted the precipitation of precipitated phases, while unaffecting grain size. Unidirectional tensile stress caused directional growth of β phase([1010]), as well as rotation of weave towards the basal plane texture, resulting in namely stress orientation effect. Solute atoms diffused in the direction of tensile stress while vacancies moved perpendicular to the direction of tensile stress, resulting in PFZ at grain boundaries(157.06 nm). By contrast, cyclic stresses led to the growth of β phase in three directions([1010], [1100] and [0110]). The solute atoms and vacancies were uniformly distributed in the Mg matrix instead of directional diffusion, effectively reducing the width of PFZ(112.39 nm) at the grain boundary. These features significantly improved the mechanical properties of alloy specimens after cyclic stress creep aging when compared to unidirectional stress creep aging, with yield strength(YS), ultimate tensile strength(UTS), and elongation(EL) enhanced from 171.6 MPa, 305.5 MPa, and 4.4%to 174.8 MPa, 326.3 MPa, and 6.9%, respectively.

Precipitation orientation effect of 2124 aluminum alloy in creep aging

The precipitation behaviors of 2124 aluminum alloy under the conditions of artificial aging （AA）, creep aging （CA） and creep aging with pre-deformation （PCA） were investigated by means of mechanical property and microstructure. The results show that the mechanical properties of CA treated sample decrease significantly compared with AA treated sample. The yield strength of the CA treated sample falls by 14%, the tensile strength falls by 6.2%, and the elongation falls by 21%. Nevertheless, the mechanical properties of PCA sample are improved obviously, close to the AA treated sample. Moreover, the generation and control mechanisms of the precipitation orientation effect in 2124 aluminum alloy were studied. It is deduced that the key mechanism lies in the effect of dislocation.

Effect of stress on microstructures of creep-aged 2524 alloy

Microstructures of creep-aged 2524 （A1-4.3Cu-1.5Mg） aged at 170 ℃ with various stresses （0, 173 and 250 MPa） were studied on a creep machine. Ageing hardness curves under various stresses were plotted and the corresponding microstructures were characterized by transmission electron microscopy （TEM）. The results show that the value of peak hardness is increased, while the time to reach the peak hardness is reduced under an external stress. Meanwhile, the length of S（Al2CuMg） phase is shorter and the number density of S phases is larger in the creep-aged alloy. The predominant contribution to the peak hardness can be ascribed to the GPB zones with an elastic stress.

Micropillar compression using discrete dislocation dynamics and machine learning

Discrete dislocation dynamics(DDD)simulations reveal the evolution of dislocation structures and the interaction of dislocations.This study investigated the compression behavior of single-crystal copper micropillars using fewshot machine learning with data provided by DDD simulations.Two types of features are considered:external features comprising specimen size and loading orientation and internal features involving dislocation source length,Schmid factor,the orientation of the most easily activated dislocations and their distance from the free boundary.The yielding stress and stress-strain curves of single-crystal copper micropillar are predicted well by incorporating both external and internal features of the sample as separate or combined inputs.It is found that the machine learning accuracy predictions for single-crystal micropillar compression can be improved by incorporating easily activated dislocation features with external features.However,the effect of easily activated dislocation on yielding is less important compared to the effects of specimen size and Schmid factor which includes information of orientation but becomes more evident in small-sized micropillars.Overall,incorporating internal features,especially the information of most easily activated dislocations,improves predictive capabilities across diverse sample sizes and orientations.

The effect of the fibre orientation of electrospun scaffolds on the matrix production of rabbit annulus fibrosus-derived stem cells

Annulus fibrosus （AF） tissue engineering has recently received increasing attention as a treatment for intervertebral disc 0VD） degeneration; however, such engineering remains challenging because of the remarkable complexity of AF tissue. In order to engineer a functional AF replacement, the fabrication of cell-scaffold constructs that mimic the cellular, biochemical and structural features of native AF tissue is critical. In this study, we fabricated aligned fibroua polyurethane scaffolds using an electrospinning technique and used them for culturing AF-derived-stem/progenitor cells （AFSCs）. Random fibrous scaffolds, also prepared via electrospinningy were used as a control. We compared the morphology, proliferation, gene expression and matrix production of AFSCs on aligned scaffolds and random scaffolds. There was no apparent difference in the attachment or proliferation of cells cultured on aligned scaffolds and random scaffolds. However, compared to cells on random scaffolds, the AFSCs on aligned scaffolds were more elongated and better aligned, and they exhibited higher gene expression and matrix production of coUagen-I and aggrecan. The gene expression and protein production of coUagen-II did not appear to differ between the two groups. Together, these findings indicate that aligned fibrous scaffolds may provide a favourable microenvironment for the differentiation of AFSCs into cells similar to outer AF cells, which predominantly produce collagen-I matrix.

Analysis of College English Teaching in Application Oriented Colleges and Universities Based on the Effect Oriented Concept

In order to cultivate more and more applied talents,promote the employment rate of college students,and improve the National English level,this paper,through theoretical analysis,reading and understanding the relevant literature,combined with practical work experience,through the design of teaching objectives,improving the curriculum evaluation system,and Innovating Curriculum teaching methods,achieves the effect-based teaching purpose.

Effects of cyclic uniaxial stress on mitosis orientation

Background:Cell division is one of the key roles in the cell development,cell differentiation,embryogenesis and recovery of tissues.Independent studies have shown that spindle alignment during not only asymmetric but also symmetric cell divisions is essential

Microstructure and mechanical properties of 2A12 aluminum alloy after age forming

The comparative experiments of age forming and artificial aging of 2A12 aluminum alloy were carried out. The effect of the age forming on the microstructure and mechanical properties was investigated. The results demonstrate that the grains are further squashed and elongated compared with artificial aging due to the existence of the applied stress during the age forming. Meanwhile, the precipitated phases change from circle shape with random orientation of age forming to long strip shape with uniform orientation of artificial aging. The dislocation configuration in samples changes from ring dislocation or helical dislocation of the artificial aging to long and straight dislocation of the age forming. Otherwise, age forming slightly reduces the tensile properties and fracture toughness of the alloy and enhances its fatigue crack growth rate.

Dependence of flow strength and deformation mechanisms in common wrought and die cast magnesium alloys on orientation,strain rate and temperature

The controlling plastic deformation mechanisms(i.e.slip or twinning)and the structural crash performance of Mg alloys are strongly influenced by loading mode,texture and microstructure.This paper summarizes the main results from an experimental program to assess these effects for commercial Mg alloy extrusions(AM30 and AZ31),sheet(AZ31),and high pressure die castings(HPDC,AM50 and AM60).Uniaxial tensile and compressive tests were performed over a wide range of strain rate and temperature(i.e.0.00075–2800 s^(−1) and 100℃ to−150℃)using conventional servo-hydraulic and high-strain-rate universal test machines and a split-Hopkinson-bar(SHB)apparatus.In primarily-slip-dominant deformation,the true stress–strain curves showed approximate power-law behavior,and the effects of strain rate and temperature on yield strength could be approximately described by constitutive equations linearly dependent on the rate parameter,Tln(5.3×10^(7)/ɛ˙)where T is test temperature in Kelvin andɛ˙is strain rate in s^(−1).In primarily-twin-dominant deformation,the effects of strain rate and temperature on yield and initial flow stress were negligible or small from quasi-static to 2800 s^(−1) owing to the athermal characteristics of mechanical twinning;the effects may become more pronounced with exhaustion of twinning and increasing proportion of slip.

A note on the surface motion of a semi-cylindrical canyon for incident cylindrical SH waves radiated by a finite fault

The plane-wave assumption for incident SH waves can be a good approximation for cylindrical and spherical waves radiated from finite sources, even when the source is as close as twice the size of the inhomogeneity, and when the source and the inhomogeneity are described within the same coordinate system. However, in a more general setting, and when the fault＇s radiation pattern must be considered, the plane-wave approximation may not yield satisfactory answers for arbitrary orientation of the fault. Jalali et al. （2015） demonstrated this for a semi-cylindrical, sedimentary valley, and in this study we extend their results to a case in which the semi-circular, sedimentary valley is replaced by a canyon. We describe the effects of incident cylindrical waves on the amplitudes of surface motion in and near the semi-cylindrical canyon when the causative faults are at different distances and have different curvatures and orientations.

Insertal Orientation Has No Influence on the Expression of gfp Gene and the Growth of the Host Synechococcus sp.PCC7942

In transgenic process, a foreign gene can be integrated in the host genome in two directions, which may influence its expression. In order to study the effects of insertal orientation, the gfp reporter gene was inserted in the isiAB locus of Synechococcus sp. PCC7942 in different directions, and the GFP expression levels and the growth of the transgenic algae were compared. It was showed that the gfp gene could express in each direction, and no significant difference was detected on algal growth and GFP expression levels between the two recombinant algae.

Seismic assessment of RC frames infilled with innovative CFS walls considering seismic orientation effect

The metal tailings porous concrete cold-formed steel(MCFS)wall is an innovative cold-formed steel(CFS)wall with good thermal and mechanical properties,which has the potential to be widely utilized as the infilled wall(IW).In this paper,the MCFS walls are adopted in the reinforced concrete(RC)frame,and the seismic performance of the building subjected to ground motions with various incidence angles are investigated.Three-dimensional finite element model of the studied building is developed with full consideration of the in-plain(IP)and out-of-plane(OP)behavior of MCFS walls.Incremental dynamic analysis is conducted to obtain the deformation responses of frames and damage ratios of MCFS walls under the combined effect of seismic intensity and orientation.Fragility curves are generated to assess the seismic performance of the building and investigate the effect of ground motion orientation.The results validate the superior performance of infilled MCFS walls,and reveal that the seismic orientation has a considerable impact on the response along each reference axis of the structure.Furthermore,different incidence angles induce up to 10.2%and 14.4%variations in the median Sa(T1)of fragilities for the frames in X and Y axes,and the corresponding change rates in the median Sa(T1)for the walls are 13.5%and 15.1%,respectively.However,for the overall performance of the building,the seismic orientation effect is less significant.The rates of changes in median Sa(T1)are less than 4%for both frames and MCFS walls.

Large piezoelectric anisotropy and high hydrostatic piezoelectric activity due to an appreciable orientation effect and porosity in novel 2-2-0 composites

The polarization orientation effect and porosity effect on the piezoelectric properties and related parameters are studied in 2-2-type composites based on domain-engineered relaxor-ferroelectric[011]-poled single crystals.The parameters,which are of great interest,are an anisotropy of the piezoelectric coefficients d_(3j)^(*),an anisotropy of the energy-harvesting figures of merit d_(3j)^(*)g_(3j)^(*) and the hydrostatic piezoelectric coefficient d_(h)^(*).An orientation of the main crystallographic axes in each polydomain single-crystal layer is described by anglesβandγ.Diagrams built for the first time show the(β,γ)regions,where a large anisot­ropy of d_(3j)^(*)(or d_(3j)^(*)g_(3j)^(*))is achieved,and where inequality d_(h)^(*)>1000 pC/N holds.A large local max d_(h)^(*)=1930 pC/N is achieved in a 2-2-0 PZN-0.065PT-based composite at the longitudinal piezoelectric coefficient d33*=2290 pC/N and figure of merit d*33g*33=1.02.10−9 Pa−1.The aforementioned large parameters are to be of value in piezoelectric sensing,energy harvesting and hydroacoustics.

Substrate orientation effect in covalent organic frameworks/2D materials heterostructure by high-resolution atomic force microscopy

Heterostructures based on covalent organic frameworks(COFs)and other two-dimensional(2D)materials attract considerable attention due to their extraordinary properties and tremendous application potential.Substrate effects play a crucial role in the integration of ultrathin COF films onto 2D materials through direct polymerization.In this study,highly ordered monolayer COFs were successfully constructed on the surfaces of highly oriented pyrolytic graphite(HOPG),hexagonal boron nitride(hBN),and molybdenum disulfide(MoS_(2)).High-resolution atomic force microscopy(HR-AFM)imaging clearly reveals the substrate orientation effect in COFs/2D materials heterostructure.Honeycomb networks formed via Schiff-base reaction and boronic acid condensation reaction can epitaxially grow in specific orientations relative to the underlying substrate lattices.This work provides direct evidence for substrate effects in the on-surface synthesis of COFs and paves the way for further investigation into the intrinsic electronic properties of monolayer COFs and the development of multifunctional hybrid devices.

Crystallographic orientation effect on cutting-based single atomic layer removal

The ever-increasing requirements for the scalable manufacturing of atomic-scale devices emphasize the significance of developing atomic-scale manufacturing technology. The mechanism of a single atomic layer removal in cutting is the key basic theoretical foundation for atomic-scale mechanical cutting. Material anisotropy is among the key decisive factors that could not be neglected in cutting at such a scale. In the present study, the crystallographic orientation effect on the cutting-based single atomic layer removal of monocrystalline copper is investigated by molecular dynamics simulation. When undeformed chip thickness is in the atomic scale, two kinds of single atomic layer removal mechanisms exist in cutting-based single atomic layer removal, namely, dislocation motion and extrusion, due to the differing atomic structures on different crystallographic planes. On close-packed crystallographic plane, the material removal is dominated by the shear stress-driven dislocation motion, whereas on non-close packed crystallographic planes, extrusion-dominated material removal dominates. To obtain an atomic, defect-free processed surface, the cutting needs to be conducted on the close-packed crystallographic planes of monocrystalline copper.

A Physically Based Dynamic Recrystallization Model Considering Orientation Effects for a Nitrogen Alloyed Ultralow Carbon Stainless Steel during Hot Forging

The nitrogen alloyed ultralow carbon stainless steel is a good candidate material for primary loop pipes of AP1000 nuclear power plant. These pipes arc manufactured by hot forging, during which dynamic recrystallization acts as the most important microstructural evolution mechanism. A physically based model was proposed to describe and predict the microstructural evolution in the hot forging process of those pipes. In this model, the coupled effects of dislocation density change, dynamic recovery, dynamic recrystallization and grain orientation function were con sidered. Besides, physically based simulation experiments were conducted on a Gleeble 3500 thermo-mcchanical sire ulator, and the specimens after deformation were observed by optical metallography （OM） and clectron back scat toted diffraction （EBSD） method. The results confirm that dynamic recrystallization is easy to occur with increasing deformation temperature or strain rate. The grains become much finer after full dynamic recrystallization. The model shows a good agreement with experimental results obtained by OM and EBSD in terms of stress strain curves, grain size, and recrystallization kinetics. Besides, this model obtains an acceptable accuracy and a wide applying scope for engineering calculation.

Orientation effects on C2(5)-C2'(5')linked bioxazole isomers synthesized via regioselective and sequential C—H arylation

Bis(4-fluorophenyl) substituted oxazole(2,5-Oxz) and C2(5)-C2'(5') linked bioxazole isomers(C2-C2'_BOxz,C2-C5'_BOxz and C5-C5'_BOxz) were concisely synthesized via palladium-catalyzed regioselective and sequential C-H arylation in 1-3 reaction steps along with 20%-83% of total yields from oxazole and4-bromofluorobenzene.The linking orientation plays a key role in the packing geometry and photophysical properties of C2-C2'_BOxz,C2-C5'_BOxz and C5-C5'_BOxz.These bioxazole isomers in solid state showed significant differences in photoluminescence quantum yields(PLQY)(0.33,0.25 and 0.04,respectively),delayed fluorescence properties and powder X-ray diffraction(PXRD) patterns,suggesting the divergence in intermolecular interactions.The theoretically calculated gradient isosurfaces and complexation energies indicate the existence of intense π-π interactions between molecular layers,which are in good agreement with the variation trend of optical properties.

Hydrostatic piezoelectric parameters of lead-free 2-0-2 composites with two single-crystal components:Waterfall-like orientation dependences

A system of hydrostatic parameters is studied in novel 2-0-2 composites that contain two lead-free piezoelectric single-crystal components.The ferroelectric domain-engineered alkali niobate-tantalate-based single-crystal layer promotes large values of the piezoelectric coefficients g^(*)33 and g^(*)h,hydrostatic squared figure of merit d^(*)hg^(*)h,and hydrostatic electromechanical coupling factor k^(*)h of the composite wherein the 0-3 Li_(2)B_(4)O_(7)single crystal/polyethylene layers are adjacent to the aforementioned single-crystal layer.Hereby,the role of the elastic anisotropy of the 0-3 layer is emphasized.An orientation effect concerned with rotations of the crystallographic axes of the piezoelectric Li_(2)B_(4)O_(7)single crystal in the 0-3 layer is first studied.It is shown that the orientation of the crystallographic axis Z of the Li_(2)B_(4)O_(7)single crystal in the polymer matrix strongly influences the piezoelectric properties and hydrostatic parameters of the composite.Examples of the so-called waterfall-like orientation dependences of the hydrostatic parameters are analyzed.The composite based on the domain-engineered[Li_(x)(K_(1-y)Na_(y)_(1-x)](Nb_(1-z)Ta_(z)TO_(3):Mn single crystal is of interest due to g^(*)h~10^(2)mV·m/N,d^(*)hg^(*)h~10^(-10)Pa-1,and k^(*)h≈0.70-0.75 in the studied volume-fraction and orientation ranges,and these hydrostatic parameters are to be taken into account in the field of piezotechnical,hydroacoustic,and energy-harvesting applications.