The anisotropic grain size effect on the mechanical response of polycrystals:The role of columnar grain morphology in additively manufactured metals

Additively manufactured(AM)metals exhibit highly complex microstructures,particularly in terms of grain morphology which typically features heterogeneous grain size distribution,irregular and anisotropic grain shapes,and the so-called columnar grains.The conventional morphological descriptors based on grain shape idealization are generally inadequate for representing complex and anisotropic grain mor-phology of AM microstructures.The primary aspect of microstructural grain morphology is the state of grain boundary spacing or grain size whose effect on the mechanical response is known to be cru-cial.In this paper,we formally introduce the notion of axial grain size from which we derive mean axial grain size,effective grain size,and grain size anisotropy as robust morphological descriptors ca-pable of effectively representing highly complex grain morphologies.We instantiated a discrete sample of polycrystalline aggregate as a representative volume element(RVE)featuring random crystallographic orientation and misorientation distributions.However,the instantiated RVE incorporates the typical mor-phological features of AM microstructures including distinctive grain size heterogeneity and anisotropic grain size owing to its pronounced columnar grain morphology.We ensured that any anisotropy ob-served in the macroscopic mechanical response of the instantiated sample primarily originates from its underlying anisotropic grain size.The RVE was then employed for mesoscale full-field crystal plasticity simulations corresponding to uniaxial tensile deformation along various axes via a spectral solver and a physics-based crystal plasticity constitutive model which was developed,calibrated,and validated in ear-lier studies.Through the numerical analyses,we isolated the contribution of anisotropic grain size to the anisotropy in the mechanical response of polycrystalline aggregates,particularly those with the charac-teristic complex grain morphology of AM metals.This contribution can be described by an inverse square relation.

Rice Grains from Slightly Saline Field Exhibited Unchanged Starch Physicochemical Properties but Enhanced Nutritional Values

This study aims to investigate grain quality and nutritional values of rice(Pokkali,a salt-tolerant cultivar;RD73,a new cultivar improved from KDML105 introgressed with Saltol QTL from Pokkali,and KDML105,a moderately salt-susceptible cultivar)grown under non-saline(0.04–0.87 dS/m)and slightly saline(1.08–4.83 dS/m)field conditions.The results revealed that salinity caused significant reduction in grain size but significant increments in reducing sugar and total protein contents in the grains.Nevertheless,the amounts of starch in the grains of KDML105 and Pokkali rice genotypes were unaffected by the stress.The starch granule size distribution was also unaffected by salinity.Interestingly,only starch from Pokkali was significantly diminished in amylose content,from 19.18%to 16.99%.Accordingly,parameters relating to starch gelatinization,retrogradation,and pasting properties of KDML105 and RD73 were unaffected by salinity;only Pokkali showed a significant increase in percentage of retrogradation along with a significant reduction in gelatinization enthalpy.In the saline field,total phenolic content and antioxidant capacity in the grains of all rice cultivars tended to increase,particularly in Pokkali.On average,essential element contents in grains from the saline-treated plants showed a 33%,32%,32%,22%,20%,11%,and 10%increase in total P,N,K,Mg,Zn,Fe,and Ca content,respectively.Interestingly,total Fe content exhibited the greatest percentage of increments in KDML105(187%).Taken together,cultivation of rice in the slightly saline field did not alter its eating and cooking qualities,while enhanced some nutritional properties such as proteins,minerals,and secondary metabolites like phenolic compounds.

Tailoring grain morphology in Ti-6Al-3Mo through heterogeneous nucleation in directed energy deposition

A common challenge in direct energy deposition(DED)is eliminating the anisotropy in mechanical performance associated with microstructure and the formation of coarse columnar grains.In this work,a heterogeneous nucleation mechanism was introduced into the melt pool,and,from this mechanism,an almost fully equiaxed grain morphology was obtained in the DED of Ti-6 Al-3 Mo.Three types of grain morphologies in DED Ti-6 Al-3 Mo,including full columnar grains,near-equiaxed grains and almost fully equiaxed grains were obtained from premixed and satellite powder blends from Ti,6 wt.%Al and 3 wt.%Mo,respectively.Combined with the analysis of the interactions between powder particles and the melt pool in DED,the formation mechanism of the equiaxed grains caused by the incomplete melting of high melting point Mo particles was revealed.As the prior-βgrains transformed from coarse columnar grains to fine-equiaxed grains,the strong<100>fiber texture along the deposition direction was weakened,while the size of theα-laths in the prior-βgrains slightly decreased,and the selection ofα-variants was weakened.Due to the transformation of the prior-βgrains from coarse columnar grains to fine-equiaxed grains,the tensile strength of the deposited samples increased from 982 MPa to 1082 MPa,while the yield strength increased from 840 MPa to 922 MPa,and the elongation of the as-deposited alloy also increased from 9.0%to 9.8%,which confirmed that the presence of fine-equiaxed grains is beneficial to the strength and plasticity of the DED alloy.This work further demonstrates the role that satelliting powders can play in terms of enhancing the columnar to equiaxed transition(CET)behavior associated with DED.

Morphological and physiological traits of large-panicle rice varieties with high filled-grain percentage

financed by the Special Program of Super Rice of Ministry of Agriculture, China （02318802013231）;the National Public Services Sectors （Agricultural） Research Projects, Ministry of Agriculture, China （201303102）;the Great Technology Project of Ningbo, China （2013C11001）

Mechanism of Ag_3Sn grain growth in Ag/Sn transient liquid phase soldering

Transient liquid phase(TLP)bonding is a potential high-temperature(HT)electron packaging technology that is used inthe interconnection of wide band-gap semiconductors.This study focused on the mechanism of intermetallic compounds(IMCs)evolution in Ag/Sn TLP soldering at different temperatures.Experimental results indicated that morphologies of Ag3Sn grains mainlywere scallop-type,and some other shapes such as prism,needle,hollow column,sheet and wire of Ag3Sn grains were also observed,which was resulted from their anisotropic growths.However,the scallop-type Ag3Sn layer turned into more planar with prolongingsoldering time,due to grain coarsening and anisotropic mass flow of Ag atoms from substrate.Furthermore,a great amount ofnano-Ag3Sn particles were found on the surfaces of Ag3Sn grains,which were formed in Ag-rich areas of the molten Sn and adsorbedby the Ag3Sn grains during solidification process.Growth kinetics of the Ag3Sn IMCs in TLP soldering followed a parabolicrelationship with soldering time,and the growth rate constants of250,280and320°C were calculated as5.83×10-15m2/s,7.83×10-15m2/s and2.83×10-14m2/s,respectively.Accordingly,the activation energy of the reaction was estimated about58.89kJ/mol.

Anisotropy of mechanical properties of 2297-T87 Al–Li alloy thick plates

The tensile properties of 2297-T87 Al–Li alloy thick plates at different thickness position and in different direction were analyzed via tensile testing,optical microscopy(OM),X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),and transmission electron microscopy(TEM).Results indicated that the ultimate tensile strength(UTS)and yield strength(YS)of the alloy decreased firstly and then increased from the 1/8T position to the 1/2T position,whereas elongation to failure(Ef)decreased gradually such that its value along the rolling direction(RD)was higher than those along the transverse direction(TD)at the same thickness position.From the 1/8T position to the 3/8T position of the alloy,the UTS and YS along the TD were higher than those along the RD.At the 1/2T position of the alloy,the UTS,YS,and Ef along the RD were the highest,whereas those along the normal direction(ND)were the lowest.Microstructural observations further revealed that the anisotropy of tensile properties was related to grain morphology,crystal texture,second-phase particles,and Li atom segregation.

Mechanical and corrosion properties of biodegradable magnesium mini-tubes with different grain morphologies:Size and distribution

Biodegradable magnesium(Mg)alloys have received much attention due to their biocompatibility and biodegradation.In this study,to uncover the effects of grain morphologies,including grain size and distribution on mechanical and corrosion properties,biodegradable Mg-2.1Nd-0.2Zn-0.5Zr(wt.%)(denoted as JDBM)alloy mini-tubes for stent application with three typical microstructures were achieved success-fully by adjusting drawing parameters.Samples with the bimodal structure exhibit the highest strengthductility balance attributed to the combined effects of fine grains and coarse grains,but show the fastest corrosion rate of about 1.00±0.136 mm/year mainly due to the formation of micro galvanic couples between coarse and fined grains.Samples with fine equiaxed grains show the lowest corrosion rate of about 0.17±0.059 mm/year,as well as uniform corrosion mode and mechanical properties of yield strength(YS)256±5.7 MPa,ultimate tensile strength(UTS)266±3.8 MPa,and elongation to failure(EL)13.5%±1.8%,attributed to the high-density grain boundaries.Samples with coarse equiaxed grains exhibit medium corrosion resistance and mechanical properties of about 175±4.8 MPa,221±4.0 MPa,and 21.53%±4.1%.Considering the mechanical and in vitro corrosion properties,biodegradable JDBM alloy implants are recommended to be composed of fine equiaxed grains,which can be used as microstructural targets for fabrication and processing.

Microstructure and mechanical properties of TA15/TC11 graded structural material by wire arc additive manufacturing process

A graded structural material(GSM)with a material transition from TA15 to TC11 was fabricated by wire arc additive manufacturing(WAAM)method.The grain morphology,chemical composition,microstructure and mechanical properties of the as-deposited GSM were all characterized to investigate their variations along the deposition direction.The results indicate that from TA15 to TC11,the grain size decreases and a transition from columnar grains to equiaxed grains occurs.The content of alloy element alters greatly within a short distance,and the width of the mutation zone is 800μm.Both TA15 and TC11 regions exhibit basketweave microstructure withα-phase andβ-phase.However,during the transition from TA15 to TC11,theα-lath becomes fine,which leads to an increase in microhardness.The tensile test shows that the bonding strength at the interface is higher than the longitudinal strength of TA15,and the lateral elongation at the interface is higher than that of TA15 and TC11.

Numerical simulation and experimental validation on fabrication of nickel-based superalloy Kagome lattice sandwich structures

Nickel-based superalloy lattice sandwich structures present higher stiffness,higher strength and higher temperature resistance in comparison with other metals.In this study,the Kagome unit was adopted to design the lattice sandwich structure and ProCAST software was used to simulate the filling and solidification processes of the nickel-based superalloy.Grain morphology and sizes of the nickel-based superalloy lattice sandwich structures were simulated by using of cellular automaton coupled with finite element model(CAFE),and indirect additive manufacture combining with investment casting were carried out to fabricate the nickel-based superalloy lattice sandwich structures.The calculated grain morphology and sizes are in good agreement with the experimental results.The grains are mainly equiaxed with an average size of about 500µm.The simulated results also show that the superheat of melting and the mold preheated temperature have significant influence on the grain size of the Kagome lattice sandwich structures,lower superheat of melting and mold preheated temperatures are encouraged to obtain the fine grains while assuring the integrity of the Kagome lattice sandwich structures for industrial application.

Quantitative Simulation Study of Metal Additive Manufacturing by Kinetic Monte Carlo

Metal additive manufacturing (AM) is a disruptive manufacturing technology that takes into account the needs of complex structural forming and high-performance component forming. At present, the understanding of metal additive manufacturing simulation methods is not thorough enough, which restricts the development of metal additive manufacturing. Present work discusses the evolution of KMC method simulation results for simulating metal additive manufacturing at different length ratios and different scanning speeds. The results reveal that as the scanning speed increases, the main grains in the simulation results are transformed from coarse columnar grains to crescent-shaped grains, which are in good agreement with the existing experimental results. Besides, as the ratio of unit physical length to unit simulation length increases, the ratio of unit physical time to unit simulation time gradually decreases.

Influence of synthesis temperatures on the crystalline grain growth and morphology of lanthanum magnesium hexaaluminate

Lanthanum magnesium hexaaluminate（LaMgAl（11）O（19）, LMA） was prepared at different temperatures by solid-state reaction. Phase compositions and crystal morphologies of specimens synthesized at different temperatures were investigated using X-ray diffraction（XRD）, scanning electron microscopy（SEM）. It was observed that the crystalline grain size of LMA was not only dependent on the preparation temperature but also on its powder morphology. In the temperature range of 1300 e1550℃, LMA showed platelet grain and the average crystalline grain size increases with the increase in temperature. At1600℃, if the powder was sintered for two times, the equiaxed grain could be found with the decrease in grain space, resulting in the reduction of the crystalline grain size. Styles of specimens（powder or disk） might have no obvious influence on morphologies and sizes of LMA crystalline grains which were synthesized with the well-dispersed raw material mixtures. The synthesis temperature played a key role in influencing the free space for the formation and growth of crystalline grains.

Microstructure Modification and Ductility Improvement for TaMoNbZrTiAl Refractory High Entropy Alloys via Increasing Ti Content

Here, the composition of TaMoNbZrTiAl refractory high entropy alloy (RHEA) is optimized by increasing Ti content to improve its mechanical property especially the ductility, through comparing two RHEAs with different Ti content. The RHEAs contain two body-centered-cubic (BCC) phases. The BCC phase in the dendritic region is rich in Ta, Mo and Nb, and the BCC phase in the interdendritic region is enriched in Zr, Ti and Al. The as-cast RHEA with a higher Ti content remains dendritic microstructures, and Ti is mainly enriched in the interdendritic region. After annealing treatment at 1300 ℃ for 48 h, the dendritic microstructures change into equiaxed-grain morphology, accompanied by needle-like micron precipitates at grain boundaries in the RHEA with higher Ti content. For the as-cast RHEAs, the fracture strain increases by ~ 6.6% and the uniform plastic strain increases by ~ 5.9% at the compression test due to the increase of Ti content. Our work offers a reference for the composition design of RHEAs and makes a preliminary exploration of the optimization of the microstructures and mechanical properties.

Kernel position effects of grain morphological characteristics by X-ray micro-computed tomography (μCT)

Grain size and shape are important factors for yield and quality.The difference in grain phenotypic characteristics in the same maize hybrid is related to its position in the ear.This study aimed to clarify the distribution characteristics of grain morphological characteristics in the ear and to provide guidance for research of grain phenotype and kernel position effects.Three maize hybrids were used in the experiment,namely,Denghai 618(DH618),KX3564,and Xianyu 335(XY335),and the kernel number per row were 40,40,and 36,respectively.The X-rayμCT was applied to obtain five kernel morphological indicators,including grain length,width,thickness,volume,surface area.Grain sphericity,length-width ratio,specific surface area,and volume coefficient were further calculated.The results showed that there were three types of maize ear morphological indicators trends:grain length,width,volume,and surface area were parabolic;thickness and sphericity were inverted parabolic;length-to-width ratio and specific surface area were irregular.The volume coefficient of grain at different parts of the ear,namely the relation coefficient between grain volume and grain length,width,and thickness,was determined.The average value of the middle grains morphological indicators of the ear was taken to select kernels representing stable characteristics of the variety.Within the range of 5%deviation from the morphological mean value of the middle grains of the ear,the grains in the middle part accounted for 26.39%of the total ear,about 10 grains extending from the 14th grain at the base of the ear to the top.Within the range of 10%deviation,the middle accounted for 47.22%,about 18 grains extending from the 12th grain at the base of the ear to the top.This study found that grain morphological indicators were greatly different at different positions of the maize ear,and showed different change rules as extend from the base to the top of the ear.Therefore,there were different grain volume coefficients at different positions of maize ear.And the representative sampling range on maize ear was determined based on the comprehensive analysis of different morphological indexes variation of grain.

Comparison of irradiation-induced void formations in tungsten with equiaxed and columnar structures

Tungsten(W)has been received much attention,since it is regarded as one of the most promising plasma facing materials for fusion reactors.There are two typical morphologies of unirradiated polycrystalline W,which have the equiaxed and columnar grains,respectively.However,the role of arrangement of grain boundary(GB)in absorbing irradiation-generated point defects is still waiting to be identified.In current investigation,irradiation-induced void formations in W with equiaxed and columnar microstructures are predicted,respectively,using the developed phase-field model.The significant kinetic behavior,such as the generation and annihilation of point defects and the interaction between point defects and GB,is reasonably considered.The density,size and porosity of void formed in these two microstructures are examined and analyzed according to the effects of GB ratio,temperature and damage rate.Our analytical results show that higher GB ratio can effectively reduce void porosity,and the columnar-grained structure has better irradiation resistance than that of the equiaxed one in the case of small grain size.Most importantly,the predicted void sizes changed with temperature and damage rate agree well with the experimentally measured ones.Our work has a more beneficial contribution to the microstructural improvement of International Thermonuclear Experimental Reactor-grade W.

Detrital zircon U-Pb geochronology and geochemistry of the Riachuelos and Palma Sola beach sediments,Veracruz State,Gulf of Mexico:a new insight on palaeoenvironment

Zircons are abundant in the beach sediments.In this study,surface microtexture,mineralogy,bulk sediment geochemistry,trace element composition and U−Pb isotopic geochronology of detrital zircons collected from the Riachuelos and Palma Sola beach areas,southwestern Gulf of Mexico were performed to infer the sediment provenance and palaeoenvironment.The zircon microtexture was categorized as mechanically-and/or chemically-induced features.The weathering index values for the Riachuelos(~72−77)and Palma Sola(~71−74)beach sediments indicated moderate weathering of both of the two source areas.The major and trace element data of bulk sediments suggested passive margin settings for the two areas.The trace elemental ratios and chondrite-normalized rare earth element(REE)patterns of bulk sediments revealed that the sediments were likely sourced by felsic and intermediate igneous rocks.And the zircon Th/U ratios(mostly more than 0.2)and zircon REE patterns(with negative Eu and positive Ce anomalies)suggested a magmatic origin for both of the beach sediments from these two areas.Two distinct zircon age peaks respectively belonging to the Paleozoic and the Cenozoic were identified both in the Riachuelos and Palma Sola beach sediments.Zircon geochronology comparison research between the Riachuelos−Palma Sola beach sediments and potential source areas in SW Gulf of Mexico revealed that the source terrane supplied the Paleozoic zircons of this study was identified as the Mesa Central Province(MCP),and the Cenozoic zircons were transported from the nearby Eastern Alkaline Province(EAP).Moreover,although the Precambrian zircons were very few in the studied sediments,their geochronology and geochemistry results still could infer that they were contributed by the source terranes of Grenvillian igneous suites in the Oaxaca and the Chiapas Massif Complexes.

Microstructure of polycrystalline Fe_(82)Ga_(18) sample with solidification texture

Main attention of this paper was devoted to studying the effect of solidification texture on microstructure（phase constituents,grain morphology,and magnetic domain structure） of polycrystalline Fe_（82）Ga_（18） sample.The alloy was melted using button arc melting and solidified in water-cooled copper mold.Optical microscope（OM） results confirm the development of large columnar grains in the solidification microstructure.Phase constitution and magnetic domain structures of the sample were studied by X-ray diffraction（XRD） and magnetic force microscopy（MFM）.Results show a single-phase solid solution with an A2 structure for the sample which consists of regularly aligned magnetic domains.Although some maze-like subdomains are found in few regions,well-aligned stripe-like domains are predominant patterns in the sample.It demonstrates the high dependence of grain morphology and magnetic domain structure upon a preferred crystallographic direction during solidification.

Effects of Annealing Temperature on the Structural,Optical,and Electrical Properties of ZnO Thin Films Grown on n-Si<100>Substrates by the Sol–Gel Spin Coating Method

The effects of annealing temperature on the sol–gel-derived ZnO thin films deposited on n-Sh100 i substrates by sol–gel spin coating method have been studied in this paper.The structural,optical,and electrical properties of ZnO thin films annealed at 450,550,and 650 °C in the Ar gas atmosphere have been investigated in a systematic way.The XRD analysis shows a polycrystalline nature of the films at all three annealing temperatures.Further,the crystallite size is observed to be increased with the annealing temperature,whereas the positions of various peaks in the XRD spectra are found to be red-shifted with the temperature.The surface morphology studied through the scanning electron microscopy measurements shows a uniform distribution of ZnO nanoparticles over the entire Si substrates of enhanced grain sizes with the annealing temperature.Optical properties investigated by photoluminescence spectroscopy shows an optical band gap varying in the range of 3.28–3.15 eV as annealing temperature is increased from 450 to 650 °C,respectively.The fourpoint probe measurement shows a decrease in resistivity from 2：1 10 2to 8：1 10 4X cm with the increased temperature from 450 to 650 °C.The study could be useful for studying the sol–gel-derived ZnO thin film-based devices for various electronic,optoelectronic,and gas sensing applications.