Computer Simulating Calculation on the Microstructure Evolutions during Hot Strip Rolling of C-Mn Steels

The program to predict the microstructure evolutions during hot strip rolling of C-M n steels has been developed in this paper, BV using this program, the microstructure changes with the processing parameters were analysed in detail. showing not only a good agreement of prediction with the measured values, but also entirely possibility to optimize hot strip rolling precess by computer simulation

Effects of Strain Rate,Temperature and Grain Size on the Mechanical Properties and Microstructure Evolutions of Polycrystalline Nickel Nanowires:A Molecular Dynamics Simulation

Through molecular dynamics（MD） simulation, the dependencies of temperature, grain size and strain rate on the mechanical properties were studied. The simulation results demonstrated that the strain rate from 0.05 to 2 ns–1 affected the Young＇s modulus of nickel nanowires slightly, whereas the yield stress increased. The Young＇s modulus decreased approximately linearly; however, the yield stress firstly increased and subsequently dropped as the temperature increased. The Young＇s modulus and yield stress increased as the mean grain size increased from 2.66 to 6.72 nm. Moreover, certain efforts have been made in the microstructure evolution with mechanical properties association under uniaxial tension. Certain phenomena such as the formation of twin structures, which were found in nanowires with larger grain size at higher strain rate and lower temperature, as well as the movement of grain boundaries and dislocation, were detected and discussed in detail. The results demonstrated that the plastic deformation was mainly accommodated by the motion of grain boundaries for smaller grain size. However, for larger grain size, the formations of stacking faults and twins were the main mechanisms of plastic deformation in the polycrystalline nickel nanowire.

Cross-sectional structure, microstructure and mechanical property evolutions of brass cladding pure copper stranded wire composite during drawing

A solid/liquid continuous casting and composite technology was used to produce d8.5 mm brass cladding pure copper stranded wire composite billet and the composite billet was then drawn. The results showed that the composite billet had good surface quality, metallurgical bonding interface between brass and pure copper as well as elongation of 53.1%. Synergistic deformation degree between pure copper wire and brass cladding layer was high during drawing. With an increase of the total deformation amount, the plastic deformation of the pure copper wire reduced triangular arc gaps between the pure copper wires and the triangular arc gaps were fully filled at 50%. When the total deformation amount was increased to 63%, dislocation cells and microbands successively formed in the pure copper wire. In the brass cladding layer, planar dislocation networks, twins and shear bands formed successively, and the main deformation mechanisms were dislocation sliding, twinning and shear deformation. The tensile strength increased from 240 MPa of the composite billet to 519 MPa of the one with the deformation amount of 63%, but the elongation decreased from 53.1% to 3.2%. A process of solid/liquid continuous casting and composite forming→drawing can work as a new compact method to produce brass cladding pure copper stranded wire composite as railway through grounding wire.

Frost deformation and microstructure evolution of porous rock under uniform and unidirectional freeze-thaw conditions

The frost deterioration and deformation of porous rock are commonly investigated under uniform freeze-thaw(FT)conditions.However,the unidirectional FT condition,which is also prevalent in engineering practice,has received limited attention.Therefore,a comparative study on frost deformation and microstructure evolution of porous rock under both uniform and unidirectional FT conditions was performed.Firstly,frost deformation experiments of rock were conducted under cyclic uniform and unidirectional FT action,respectively.Results illustrate that frost deformation of saturated rock exhibits isotropic characteristics under uniform FT cycles,while it shows anisotropic characteristics under unidirectional FT condition with both the frost heaving strain and residual strain along FT direction much higher than those perpendicular to FT direction.Moreover,the peak value and residual value of cumulative frost strain vary as logarithmic functions with cycle number under both uniform and unidirectional FT conditions.Subsequently,the microstructure evolution of rock suffered cyclic uniform and unidirectional FT action were measured.Under uniform FT cycles,newly generated pores uniformly distribute in rock and pore structure of rock remains isotropic in micro scale,and thus the frost deformation shows isotropic characteristics in macro scale.Under unidirectional FT cycles,micro-cracks or pore belts generate with their orientation nearly perpendicular to the FT direction,and rock structure gradually becomes anisotropic in micro scale,resulting in the anisotropic characteristics of frost deformation in macro scale.

Effect of quenching cooling rate on residual stress and microstructure evolution of 6061 aluminum alloy

In this study,the cooling rate was manipulated by quenching with water of different temperatures(30,60 and 100℃).Surface and internal residual stresses in the quenched 6061 aluminum alloy samples were measured using hole-drilling and crack compliance methods,respectively.Then,the processability of the quenched samples was evaluated at cryogenic temperatures.The mechanical properties of the as-aged samples were assessed,and microstructure evolution was analyzed.The surface residual stresses of samples W30℃,W60℃and W100℃is−178.7,−161.7 and−117.2 MPa,respectively along x-direction,respectively;and−191.2,−172.1 and−126.2 MPa,respectively along y-direction.The sample quenched in boiling water displaying the lowest residual stress(~34%and~60%reduction in the surface and core).The generation and distribution of quenching residual stress could be attributed to the lattice distortion gradient.Desirable plasticity was also exhibited in the samples with relatively low quenching cooling rates at cryogenic temperatures.The strengthes of the as-aged samples are 291.2 to 270.1 MPa as the quenching water temperature increase from 30℃to 100℃.Fine and homogeneous β"phases were observed in the as-aged sample quenched with boiling water due to the clusters and Guinier-Preston zones(GP zones)premature precipitated during quenching process.

Exploring the mechanical behavior and microstructure of compacted loess subjected to dry-wet cycles and chemical contamination

Due to climatic factors and rapid urbanization,the soil in the Loess Plateau,China,experiences the coupled effects of dry-wet cycles and chemical contamination.Understanding the mechanical behavior and corresponding microstructural evolution of contaminated loess subjected to dry-wet cycles is essential to elucidate the soil degradation mechanism.Therefore,direct shear and consolidation tests were performed to investigate the variations in mechanical properties of compacted loess contaminated with acetic acid,sodium hydroxide,and sodium sulfate during dry-wet cycles.The mechanical response mechanisms were investigated using zeta potential,mineral chemical composition,and scanning electron microscopy(SEM)tests.The results indicate that the mechanical deterioration of sodium hydroxidecontaminated loess during dry-wet cycles decreases with increasing contaminant concentration,which is mainly attributed to the thickening of the electrical double layer(EDL)by Nat and the precipitation of calcite,as well as the formation of colloidal flocs induced by OH,thus inhibiting the development of large pores during the dry-wet process.In contrast,the attenuation of mechanical properties of both acetic acid-and sodium sulfate-contaminated loess becomes more severe with increasing contaminant concentration,with the latter being more particularly significant.This is primarily due to the reduction of the EDL thickness and the erosion of cement in the acidic environment,which facilitates the connectivity of pores during dry-wet cycles.Furthermore,the salt expansion generated by the drying process of saline loess further intensifies the structural disturbance.Consequently,the mechanical performance of compacted loess is sensitive to both pollutant type and concentration,exhibiting different response patterns in the dry-wet cycling condition.

Effect of Ni on microstructure and mechanical properties of Al−Mg−Si alloy for laser powder bed fusion

The microstructures and mechanical properties were systematically studied for the high-strength Al−5Mg_(2)Si−1.5Ni alloy fabricated by laser powder bed fusion(L-PBF).It is found that the introduction of Ni(1.5 wt.%)into an Al−5Mg_(2)Si alloy can significantly improve the L-PBF processibility and provide remarkable improvement in mechanical properties.The solidification range of just 85.5 K and the typical Al−Al3Ni eutectics could be obtained in the Ni-modified Al−5Mg_(2)Si samples with a high relative density of 99.8%at the volumetric energy density of 107.4 J/mm^(3).Additionally,the refined hierarchical microstructure was mainly characterized by heterogeneousα-Al matrix grains(14.6μm)that contain the interaction between dislocations and Al−Al3Ni eutectics as well as Mg_(2)Si particles.Through synergetic effects of grain refinement,dislocation strengthening and precipitation strengthening induced by Ni addition,the L-PBFed Al−5Mg_(2)Si−1.5Ni alloy achieved superior mechanical properties,which included the yield strength of(425±15)MPa,the ultimate tensile strength of(541±11)MPa and the elongation of(6.2±0.2)%.

Effect of cold rolling deformation on microstructure evolution and mechanical properties of spray formed Al−Zn−Mg−Cu−Cr alloys

The impact of cold rolling deformation,which was introduced after solid solution and before aging treatment,on microstructure evolution and mechanical properties of the as-extruded spray formed Al−9.8Zn−2.3Mg−1.73Cu−0.13Cr(wt.%)alloy,was investigated.SEM,TEM,and EBSD were used to analyze the microstructures,and tensile tests were conducted to assess mechanical properties.The results indicate that the D1-T6 sample,subjected to 25%cold rolling deformation,exhibits finer grains(3.35μm)compared to the D0-T6 sample(grain size of 4.23μm)without cold rolling.Cold rolling refines the grains that grow in solution treatment.Due to the combined effects of finer and more dispersed precipitates,higher dislocation density and smaller grains,the yield strength and ultimate tensile strength of the D1-T6 sample can reach 663 and 737 MPa,respectively.In comparison to the as-extruded and D0-T6 samples,the yield strength of the D1-T6 sample increases by 415 and 92 MPa,respectively.

Microstructure evolution and hot workability of in-situ synthesized Ti_(2)AlC/TiAl composite

The in-situ micro-nano Ti_(2)AlC particles reinforced TiAl(Ti_(2)AlC/TiAl)composite was fabricated using spark plasma sintering.The hot workability of Ti_(2)AlC/TiAl composite was studied,and the effect of micro-nano particles on flow stress and dynamic recrystallization of composite was discussed.The results showed that the micro-nano Ti_(2)AlC particles included strengthening and softening effects during hot deformation,resulting in the fact that the Ti_(2)AlC/TiAl composite exhibited a higher flow stress and more sufficient dynamic recrystallization.The strengthening effect was mainly attributed to the Ti_(2)AlC particles induced refinement strengthening and hindered dislocation motion at the initial stage.Moreover,the precipitation of nano-TiCr2 particles induced by stress concentration during hot deformation also contributed to higher flow stress via impeding dislocation motion.Meanwhile,the refined microstructure and dislocation pile-up caused by micro-nano particles during deformation provided more nucleation sites for dynamic recrystallization,which significantly promoted the dynamic recrystallization of the second stage.The present results reveal that the Ti_(2)AlC/TiAl composite exhibited excellent hot workability,which is important to promote the application of TiAl alloys.

Effect of Gd Addition on Hot Deformation Behavior and Microstructure Evolution of 7075 Aluminum Alloy

In order to clarify the effect of rare earth Gd on the microstructure evolution and deformation behavior of 7075 aluminum alloy during hot compression,uniaxial compression tests of Al-Zn-Mg-Cu-0.5%Gd were conducted at strain rates of 0.001,0.01,0.1,and 1 s^(-1)with the temperatures ranging from 350 to 450℃.The microstructural evolution during deformation was characterized using optical microscopy and electron backscatter diffraction(EBSD)techniques.The experimental results indicate that the addition of the rare earth element Gd significantly increases the peak flow stress and thermal activation energy of the alloy.Due to the pinning effect of rare earth phases,dislocation movement is hindered,leading to an increased level of work hardening in the alloy.However,the dynamic recrystallization of the alloy is complicated.At a high Z(Zener-Hollomon parameter)values,recrystallization occurs in the form of DDRX(Discontinuous Dynamic Recrystallization),making it easier to nucleate at grain boundaries.As the Z value decreases gradually,the recrystallization mechanism transitions from discontinuous dynamic recrystallization(DDRX)to continuous dynamic recrystallization(CDRX).At a low Z values with the strain rate of 0.001 s^(-1),the inhibitory effect of rare earths weakens,resulting in a comparable recrystallization ratio between Al-Zn-Mg-Cu-Gd alloy and 7075 aluminum alloy.Moreover,the average grain size of the aluminum alloy with Gd addition is only half that of 7075 aluminum.The addition of Gd provides Orowan and substructure strengthening for the alloy,which greatly improves the work-hardening of the alloy compared with 7075 aluminum alloy and improves the strength of the alloy.

Effect of Ti addition on microstructure and mechanical properties of Zn-22Al alloy after ECAP

The effect of Ti addition on microstructure and mechanical properties of Zn-22Al eutectoid alloy with 0.15 wt%Ti was investigated.It was observed that the presence of Ti changes the morphology of n phase in the alloy.Addition of Ti to Zn-Al alloy caused the formation of Ti(Zn,Al)_(3);phase.Before applying equal channel angular pressing(ECAP),two times of homogenization treatment were conducted on the alloy.After secondary homogenization,the microstructure consisted of a homogeneous and fine mixture ofαand n phases and the as-cast lamellar structure removed.After homogenization,ECAP was carried out on Ti-containing Zn-22Al alloy.The fraction of high angle grain boundaries increased with increasing the number of ECAP passes.The average grain size reduced from 930 nm after secondary homogenization to 380 nm after 8 passes of ECAP.The texture of the alloy also changed by applying ECAP.Maximum elongation to failure of the homogenized alloy was 135%at a strain rate of 10^(-5)s^(-1)which enhanced to a maximum of 405%at a strain rate of 10^(-3)s^(-1)after 8 passes of ECAP.It was also observed that by conducting ECAP and increasing the number of passes the hardness decreases,which indicates work-softening behavior due to dynamic recovery/recrystallization.

Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting

Microstructure evolution and solidification behaviour of ZrB_(2)-SiC composite ceramics fabricated by laser surface zone-melting were investigated.Microstructure coarsening at high scanning speed and mi-crostructure refining after turning off the laser was observed due to the changes in the solidification rate.The solidification behaviour from bottom to top of the molten pool was studied,where there are some coarsen eutectic bands caused by the secondary heating of the melting pool on the solidified eu-tectic zone in the molten pool.The deviation of melt composition from the eutectic ratio due to the volatilization of SiC can form a coarse primary ZrB_(2) phase among fine eutectic structure(single-phase instability),and the constitutional supercooling due to the accumulation of impurity elements can form coarse eutectic dendrites among fine eutectic structure(two-phase instability).Both single-phase insta-bility and two-phase instability are adverse to the mechanical properties,which should be prevented by adjusting the composition of raw materials and the solidification process.

Study of microstructure evolution of magnesium alloy cylindrical part with longitudinal inner ribs during hot flow forming by coupling ANN-modified CA and FEA

Hot flow forming(HFF)is a promising forming technology to manufacture thin-walled cylindrical part with longitudinal inner ribs(CPLIRs)made of magnesium(Mg)alloys,which has wide applications in the aerospace field.However,due to the thermo-mechanical coupling effect and the existence of stiffened structure,complex microstructure evolution and uneven microstructure occur easily at the cylindrical wall(CW)and inner rib(IR)of Mg alloy thin-walled CPLIRs during the HFF.In this paper,a modified cellular automaton(CA)model of Mg alloy considering the effects of deformation conditions on material parameters was developed using the artificial neural network(ANN)method.It is found that the ANN-modified CA model exhibits better predictability for the microstructure of hot deformation than the conventional CA model.Furthermore,the microstructure evolution of ZK61 alloy CPLIRs during the HFF was analyzed by coupling the modified CA model and finite element analysis(FEA).The results show that compared with the microstructure at the same layer of the IR,more refined grains and less sufficient DRX resulted from larger strain and strain rate occur at that of the CW;various differences of strain and strain rate in the wall-thickness exist between the CW and IR,which leads to the inhomogeneity of microstructure rising firstly and declining from the inside layer to outside layer;the obtained Hall-Petch relationship between the measured microhardness and predicted grain sizes at the CW and the IR indicates the reliability of the coupled FEA-CA simulation results.

Effect of TiB_(2) Nanoparticles on Microstructure and Mechanical Properties of Ni_(60)Cr_(21)Fe_(19) Alloy in Rapid Directional Solidification Process:Molecular Dynamics Study

Molecular dynamics(MD)simulations are employed to delve into the multifaceted effects of TiB_(2) nanoparticles on the intricate grain refinement mechanism,microstructural evolution,and tensile performance of Inconel 718 superalloys during the rapid directional solidification.Specifically,the study focuses on elucidating the role of TiB2 nanoparticles in augmenting the nucleation rate during the rapid directional solidification process of Ni_(60)Cr_(21)Fe_(19) alloy system.Furthermore,subsequent tensile simulations are conducted to comprehensively evaluate the anisotropic behavior of tensile properties within the solidified microstructures.The MD results reveal that the incorporation of TiB₂nanoparticles during the rapid directional solidification of the Ni_(60)Cr_(21)Fe_(19) significantly enhances the average nucleation rate,escalating it from 1.27×10^(34)m^(-3)·s^(-1)to 2.55×10^(34)m^(-3)·s^(-1).Notably,within the face centered cube(FCC)structure,Ni atoms exhibit pronounced compositional segregation,and the solidified alloy maintains an exceptionally high dislocation density reaching up to 10^(16)m^(-2).Crucially,the rapid directional solidification process imparts a distinct microstructural anisotropy,leading to a notable disparity in tensile strength.Specifically,the tensile strength along the solidification direction is markedly superior to that perpendicular to it.This disparity arises from different deformation mechanisms under varying loading orientations.Tensile stress perpendicular to the solidification direction encourages the formation of smooth and organized mechanical twins.These twins act as slip planes,enhancing dislocation mobility and thereby improving stress relaxation and dispersion.Moreover,the results underscore the profound strengthening effect of TiB_(2) nanoparticles,particularly in enhancing the tensile strength along the rapid directional solidification direction.

Flow softening behavior and microstructure evolution of Al-5Zn-2Mg aluminum alloy during dynamic recovery

The flow stress behavior and microstructure development of Al-5Zn-2Mg （7005） aluminum alloy were studied by hot compression tests at deformation temperatures between 300-500 ＆#176;C and strain rates between 0.05-50 s-1. The deformed structures of the samples were observed by optical microscopy （OM）, transmission electron microscopy （TEM） and electron backscattering diffraction （EBSD） analysis. The calculated activation energy is 147 kJ/mol, which is very close to the activation energy for lattice self-diffusion in aluminum （142 kJ/mol）. Dynamic recovery is the dominant restoration mechanism during the deformation. At high strain rate of 50 s-1, temperature rise due to deformation heating leads to a significant flow softening. Microstructure observations indicated that the remaining softening after deformation heating correction at high strain rate and the softening observed at high temperature are associated with grain coarsening induced by grain boundary migration during dynamic recovery process.

Effect of heat treatment on microstructure and tensile properties of A356 alloys

Two heat treatments of A356 alloys with combined addition of rare earth and strontium were conducted.T6 treatment is a long time treatment（solution at 535 ℃ for 4 h ＋ aging at 150 ℃ for 15 h）.The other treatment is a short time treatment（solution at 550 ℃ for 2 h ＋ aging at 170 ℃ for 2 h）.The effects of heat treatment on microstructure and tensile properties of the Al-7%Si-0.3%Mg alloys were investigated by optical microscopy,scanning electronic microscopy and tension test.It is found that a 2 h solution at 550 ℃ is sufficient to make homogenization and saturation of magnesium and silicon in α（Al） phase,spheroid of eutectic Si phase.Followed by solution,a 2 h artificial aging at 170 ℃ is almost enough to produce hardening precipitates.Those samples treated with T6 achieve the maximum tensile strength and fracture elongation.With short time treatment（ST）,samples can reach 90% of the maximum yield strength,95% of the maximum strength,and 80% of the maximum elongation.

Effect of homogenization treatment on microstructure and mechanical properties of DC cast 7X50 aluminum alloy

The evolution of the eutectic structures in the as-cast and homogenized 7X50 aluminum alloys was studied by scanning electron microscopy(SEM), transmission electron microscopy(TEM), energy dispersive spectrometer(EDS), differential scanning calorimetry(DSC), X-ray diffraction(XRD) and tensile test. The results show that the main phases are S(Al2CuMg), T(Al2Mg3Zn3) and Mg Zn2, with a small amount of Al7Cu2 Fe and Al3 Zr in the as-cast 7X50 alloy. The volume fraction of the dendritic-network structure and residual phase decreases gradually during the homogenization. After homogenization at 470 °C for 24 h and then 482 °C for 12 h, the T(Al2Mg3Zn3) phase disappears and minimal S(Al2CuMg) phase remains, while almost no change has happened for Al7Cu2 Fe. There is a strong endothermic peak at 477.8 °C in the DSC curve of as-cast alloy. A new endothermic peak appears at 487.5 °C for the sample homogenized at 470 °C for 1 h. However, this endothermic peak disappears after being homogenized at 482 °C for 24 h. The T(Al2Mg3Zn3) phase cannot be observed by XRD, which is consistent with that T phase is the associated one of S(Al2CuMg) phase and Mg Zn2 phase. The volume fraction of recrystallized grains is substantially less in the plate with pre-homogenization treatment. The strength and fracture toughness of the plate with pre-homogenization treatment are about 15 MPa and 3.3 MPa·m1/2 higher than those of the material with conventional homogenization treatment.

Microstructure evolution of Mg-9Gd-2Er-0.4Zr alloy during solid solution treatment

Microstructure evolution of the cast Mg-9Gd-2Er-0.4Zr alloy during solid solution treatment at temperature of 460-520 ℃ for 3-12 h was investigated by using optical microscope（OM）,scanning electron microscope（SEM） and transmission electron microscope（TEM）.The results indicated that the grain size and the shape of second phase were obviously changed with time and/or temperature going on.At 460 ℃ for 3 h,the morphology of the Mg5（GdEr） phase was changed into fragmentized island morphology and the volume faction of the phase decreased.After solution solid treatment at 460 ℃ for 6 h,the Mg5（GdEr） phase was already completely dissolved,but some cuboid-shaped RE-rich phase precipitated.As the temperature increased,the morphology of the Mg5（GdEr） phase was transformed into the same morphology as that at 460 ℃ for 6 h.It was suggested that the microstructure evolution of the alloy during the solid solution treatment was concluded as follows：Mg5（GdEr） eutectic phase→Gd/Er atom diffusing into matrix→spheroidic Mg5（GdEr） phase→cuboid-shaped RE-rich phase→grain boundary immigration.

Creep properties and microstructure evolution of nickel-based single crystal superalloy at different conditions

The creep properties of nickel-based single crystal superalloy with [001] orientation was investigated at different test conditions. The microstructure evolution of γ′ phase, TCP phase and dislocation characteristic after creep rupture was studied by SEM and TEM. The results show that the alloy has excellent creep properties. Two different types of creep behavior can be shown in the creep curves. The primary creep is characterized by the high amplitude at test conditions of (760 °C, 600 MPa) and (850 °C, 550 MPa) and the primary creep strain is limited at (980 °C, 250 MPa), (1100 °C, 140 MPa) and (1120 °C, 120 MPa). A little change ofγ′precipitate morphology occurs at (760 °C, 600 MPa). The lateral merging of the γ′ precipitate has already begun at (850 °C, 550 MPa). Theγphase is surrounded by theγ′phase at (980 °C, 250 MPa). Theγphase is no longer continuous tested at (1070 °C, 140 MPa). At (1100 °C, 120 MPa), the thickness ofγphase continues to increase. No TCP phase precipitates in the specimens at (760 °C, 600 MPa), (850 °C, 550 MPa) and (980 °C, 250 MPa). Needle shaped TCP phase precipitates in the specimens tested at (1070 °C, 140 MPa) and (1100 °C, 120 MPa). The dislocation shear mechanism including stacking fault formation is operative at lower temperature and high stress. The dislocation by-passing mechanism occurs to form networks atγ/γ′interface under the condition of high temperature and lower stress.

Solidification process and microstructure evolution of bulk undercooled Co-Sn alloys

A series of Co-Sn alloys with Sn content ranging from 12% to 32%（mole fraction） were undercooled to different degrees below the equilibrium liquidus temperature and the solidification behaviors were investigated by monitoring the temperature recalescence and examing the solidification microstructures.A boundary clearly exists,which separates the coupled growth zone from the decoupled growth zone of eutectic phases for the alloys with Sn content ranging from 14% to 31%（mole fraction）.The other Co-Sn alloys out of this content range are hard to be undercooled into the coupled growth zone in the experiment.It is found that the so-called non-reciprocal nucleation phenomenon does not happen in the solidification of undercooled Co-Sn off-eutectic alloys.