Experimental study on tensile deformation behaviors under room and elevated temperatures induced by microstructure inhomogeneity of ZK60 Mg with a longitudinal weld

The tensile tests of the extruded ZK60 Mg containing a longitudinal weld seam were carried out at room and elevated temperatures, and the effects of induced microstructure inhomogeneity on tensile deformation behavior was clarified. The results show that the deformation mode, dynamic recrystallization(DRX), texture evolution and mechanical properties are strongly affected by the longitudinal weld seam,temperature, and loading direction. The room temperature(RT) deformation of welding zone is controlled by the dislocation slips with the association of some twins, while twinning plays significant roles in the accommodation of c-axis strain of the coarse grains on matrix zone.The deformation at RT stretched along extrusion direction(ED) and transverse direction(TD) are controlled by basal slip/twinning and basal slip/prismatic slip/twinning, respectively. During high temperature tension, the dislocation cross slip of pyramidal slip is activated, and grain boundary sliding occurred in welding zone, leading to the superplastic behavior. With the increase of tensile temperature, the predominant DRX mode is transformed from continuous DRX to discontinuous DRX. Moreover, the basal poles of the grains spread from TD towards ED with the decrease of maximum pole intensity when stretched along ED, while non-basal textures are transformed to (10-10) fiber texture when stretched along TD. The slip-dominated flow is seen during RT tension along ED, while twinning becomes predominant during RT tension along TD. The fine grain structure causes the superior RT tensile properties along ED of welding zone with ultimate tensile strength of 315 MPa and elongation to failure of 13.8%. With the increase of tensile temperature, the slipping-dominated deformation is transformed into twinning-dominated, causing the decrease of strength and increase of elongation.

Modeling uniaxial tensile deformation of polycrystalline Al using CPFEM

The crystal plasticity finite element modeling （CPFEM） is realized in commercial finite element code ABAQUS with UMAT subroutine on the basis of the crystal plasticity theory of rate dependent polycrystal constitutive relations in the mesoscopic scale. The initial orientations obtained by electron backscatter diffraction （EBSD） are directly input into the CPFEM to simulate the mechanical response of polycrystalline 1050 pure Al in uniaxial tensile deformation. Two polycrystal models and two tensile strain rates were used in the simulations. The stress-strain curves of tensile deformation were analyzed. The predictions and the corresponding experiment result show reasonable agreement and slight deviation with experiments. The flow true stress of strain rate 0.01 s^-1 is higher than that of strain rate 0.001 s^-1. At the strain less than 0.05, the stress saturated rate of the experiment is higher than the simulated results. However, the stress saturated rate of the experiment becomes gentler than the corresponding simulated predictions at the strain over 0.05. Also, necking was simulated by the two models, but the necking strain is not well predicted. Tensile textures at strain 0.25 were predicted at the low strain rate of 0.001 s^-1. The predictions are in good accord with the experimental results. 2008 University of Science and Technology Beijing. All rights reserved.

Fracture Behavior and Processing Deformation of C71500 Cupronickel Alloy during Hot Tensile Deformation

The hot tensile deformation properties and microstructure evolution of high purity C71500 cupronickel alloy at 1023-1273 K and 0.0001-0.1 s^(-1)strain rates were studied by uniaxial hot tensile deformation method.Based on the experimental data,the flow behavior,microstructure and fracture characteristics of the alloy were analyzed after considering the influence of different deformation parameters.The relationship between microstructure and high temperature(T≥1023 K)plasticity is discussed,and the fracture mechanism is revealed.The relationship between strain rate sensitivity coefficient and stress index and plastic deformation is discussed.The constitutive equation of the alloy is established by Johnson-Cook model.Based on the dynamic material model,the energy dissipation model is established,and Prasad’s instability criterion based on Ziegler’s expected rheological theory is used to predict the unstable region in the processing map.Processing map in hot tensile is analyzed to provide theoretical basis for different processing technology.

HIGH VISCOUS STRESS OF ORIENTED POLYOLEFINS UNDER UNIAXIAL TENSILE DEFORMATION

In this communication, by means of stress relaxation experiments, the viscous stress at various strains during tensile deformation of oriented polyolefin samples including high density polyethylene （HDPE）, linear low density polyethylene （LLDPE） and isotactic polypropylene （iPP）, has been determined. The viscous stress in the oriented samples takes up to 50%-70% of the total stress, which is unusually high compared with their isotropic counterparts. The unusual high viscous stress was discussed based on mainly the existence of shish structure in oriented polyolefins, which could enhance the inter-lamella coupling significantly.

Tensile deformation behavior of high strength anti-seismic steel with multi-phase microstructure

To investigate the tensile deformation behavior of high strength anti-seismic steel with multi-phase microstructure,tensile tests with strains of 0.05,0.12 and 0.22 were performed at room temperature.Microstructure of tested steels was observed by means of optical microscopy（OM）,transmission electron microscopy（TEM）and scanning electron microscopy（SEM）.Tensile mechanical properties of tested steels were obtained,and the influence of bainite content on deformation behavior was also discussed.Meanwhile,the deformation mechanism of steel with three kinds of microstructures of bainite,pearlite and ferrite was analyzed.Results show that tested steel with high volume fraction of bainite exhibits a continuous deformation behavior,and this may be attributed to a higher bainite volume fraction and a lower mobile dislocation density.The morphology of microstructure will influence the mechanical properties of tested steels.An increasing content of bainite can improve the tensile strength,but reduce the plasticity and toughness of the tested steels.In the deformation process of 0.039 Nb steel,the ferrite and bainite have priorities to deform,and the deformation exhibits co-deformation of all microstructures in the later stage of deformation.In the deformation process of 0.024Nb-0.032 Vsteel,the ferrite and pearlite have priorities to deform,and the deformation exhibits co-deformation of all microstructures in the later stage of deformation.

Polymorphic Transition of Pre-oriented Polybutene-1 under Tensile Deformation:In Situ FTIR Study

Deformation-induced phase transition of FormⅡto FormⅠin polybutene-1(PB-1)has been investigated by time-resolved Fourier transform infrared(FTIR)spectroscopy over a wide temperature range from 25℃to 105℃.The initial film sample containing orientated lamellae is prepared by pre-stretching of PB-1 melt followed by solidification.This is to realize a homogeneity of subsequent deformation at the mesoscale of lamellar stacks by avoiding large-scale spherulites.The deformation induced phase transition is recognized to occur with two stages:first,FormⅡundergoes the lamellar fragmentation,slipping or local melting after yielding to activate its transition to FormⅠ,which may be realized by releasing the restrictions on chains translational movements in crystalline phase;second,the phase transition proceeds with a continuous dissipation of external work and determines the tensile mechanical response of film.To quantify the relationship between crystalline transition of FormⅡto FormⅠand external tensile field,a simple kinetic equation is well established based on FTIR measurement.The equation can describe not only the dependence of crystal transitional degree on applied specific work,but also the retardation effect of elevating temperature on phase transition.

Hot tensile deformation behavior and constitutive model of ZK61M high-strength magnesium alloy sheet

Hot deformation behavior of the annealed ZK61 M magnesium alloy sheet was explored using tensile tests with strain rates varying from 0.001 to 0.030 s^(-1) in temperatures range of 423-513 K.The obtained results indicate that the flow stress increased with deformation temperature decreasing and strain rate increasing.Dynamic recrystallization(DRX)occurs when the temperature is higher than 423 K,and the recrystallization volume fraction increases with temperature rising.At a given temperature,the measured DRX volume fraction at a higher strain rate is smaller than that at a lower strain rate.Dimples are observed throughout the tested temperature range.Moreover,they grow larger as temperature increases.An average absolute relative error(AARE)of 2.65%proves that the peak stress predicted by the constitutive model is in good agreement with the experimental results.The correlation coefficient(R’)obtained for the predicted stress and the experimental value considering the strain on the material constant are between 0.9831 and 0.9977.In addition,AARE and root mean square error(RMSE)are less than 6.5%and 8.5 MPa,respectively.This indicates that the deviation of the predicted value from the experimental value is small and the predictions of the proposed model are reliable.

Tensile deformation behavior of nickel-free high-manganese austenitic cryogenic-temperature steel

Nickel-free high-manganese austenitic Fe–24.4Mn–4.04Al–0.057C steel was produced by smelting,and the homogenized forged billet was hot-rolled.The plastic deformation mechanism was investigated through tensile testing of the hot-rolled sample.Different characterization techniques such as scanning electron microscopy,transmission electron microscopy,electron backscattered diffraction,and X-ray diffraction were used to analyze the microstructural evolution of steel under different strain levels.The steel had a single austenite phase,which was stable during deformation.After hot rolling,annealing twins were observed in the microstructure of the steel.The steel showed an excellent combination of mechanical properties,like a tensile strength of 527 MPa,impact energy of 203 J at−196℃,and an elongation of 67%till fracture.At the initial deformation stage,the dislocations were generated within the austenite grains,entangled and accumulated at the grain boundaries and annealing twin boundaries.Annealing twins participated in plastic deformation and hindered the dislocation movement.As the deformation progressed,the dislocation slip was hindered and produced stress concentration,and the stacking faults evolved into mechanical twins,which released the stress concentration and delayed the necking.

Static Tensile Deformation Behaviors of an Fe-30Mn-3Al-3Si TWIP Steel Studied by In-Situ Neutron Diffraction

TWIP (TWinning Induced Plasticity) steel is one of the advanced steels with attractive mechanical properties.The typical composition of TWIP steel includes a large amount of manganese with some aluminum and silicon.Previous study has shown that TWIP steel exhibits high strength with adequate elongation at high strain rates,so that TWIP steel is desired to be applied for automotive use.However,there are few studies concerning the deformation behaviors aimed to make clear the TWIP effect in TWIP steel.In this study,static tensile deformation behaviors of an Fe-30Mn-3Al-3Si TWIP steel and a SUS310S one were studied by in situ neutron diffraction during tensile deformation.In terms of mechanical properties obtained by the static tensile tests,the TWIP steel showed better balance of tensile strength and uniform elongation than the 310S steel.The angular dispersion neutron diffraction with a wavelength of 0.16 nm was performed during stepwise tensile testing by using a neutron diffractometer for residual stress analysis (RESA) at the Japan Atomic Energy Agency.A specimen was extended in a step by step manner and neutron diffraction profiles of (111),(200) and (311) for austenite were obtained at each step.The diffraction peak,lattice plane spacing,lattice plane strain and so on were determined by the profile analysis as a function of applied stress.The changes of lattice plane strain for austenite in the TWIP and 310S steels indicated several deformation stages in the tensile deformation and can be discussed the difference of intergranular stress between the two samples.

Uniaxial tensile deformation behavior of a sandwich-like structural TiNb-NiTi composite for biomedical applications

The uniaxial tensile deformation behavior of a sandwich-like structural TiNb-NiTi composite was investigated by uniaxial tensile test and in situ high-energy synchrotron X-ray diffraction(SXRD).It is found that below 1.2%macroscopic strains,the elastic deformations of the B2,β,B19'andα"phases take place in the TiNbNiTi composite.During the subsequent loading,theβ→α"and B2→B19'stress-induced martensitic transformations(SIMTs)occur within the macroscopic strains of 0.5%-4.2%and the macroscopic strains of 0.7%-6.2%,respectively.At the macroscopic strain of about 4.2%,the outer TiNb layer of the TiNb-NiTi composite experiences a partial fracture,as proved by the disappearance of(040)_(α")and a sudden jump in the(110)_(B19')d-spacing caused by load transfer.With further uniaxial tensile deformation,the TiNbNiTi composite finally fractures at a strain of~6.2%.Our results might provide some valuable information for understanding the deformation behavior of novel sandwich-like structural shape memory composites in more depth.

Tensile properties of functionalized carbon nanothreads

Low dimensional sp~3 carbon nanostructures have attracted increasing attention recently, due to their unique properties and appealing applications. Based on in silico studies, this work exploits the impacts from functional groups on the tensile properties of carbon nanothreads(NTH)– a new sp~3 carbon nanostructure. It is found that functional groups will alter the local bond configuration and induce initial stress concentration, which significantly reduces the fracture strain/strength of NTH. Different functional types lead to different local bond reconfigurations, and introduce different impacts on NTH. Further studies reveal that the tensile properties decreases generally when the content of functional groups increases. However, some NTHs with higher content of functional groups exhibit higher fracture strain/strength than their counterparts with lower percentage. Such observations are attributed to the synergetic effects from the sample length, self-oscillation, and distribution of functional groups. Simulations show that the tensile behaviour of NTH with the same functional percentage differs when the distribution pattern varies. Overall, ethyl groups are found to induce larger degradation on the tensile properties of NTH than methyl and phenyl groups. This study provides a comprehensive understanding of the influence from functional groups, which should be beneficial to the engineering applications of NTH.

Mechanical Properties of DS NiAl/Cr(Mo) Alloys with Low Addition of Hf for High-temperature Applications

A multiphase NiAl-28Cr-5.85Mo-0.15Hf alloy, which was directionally solidified （DS） in an Al2O3-SiO2 mold by standard Bridgman method and then underwent prolonged solution and aging treatment was prepared. The microstructure, tensile properties as well as tensile creep of the heat-treated alloy at different temperatures were studied. The alloy was composed of NiAI, Cr（Mo） and Hf-rich phase and small amount of fine Heusler phase （Ni2AlHf）. Although the present alloy exhibited high tensile strength at low temperature, it was weaker than that of system with high content Hf but still stronger than that of many NiAl-based alloys at high temperatures. The fracture toughness is lower than that of DS NiAl-28Cr-6Mo alloy. Nevertheless, advantageous effects on the mechanical properties, i.e. the decrease in brittle-to-ductile transition temperature （BDTT） were obtained for the low content of Hf. The obtained creep curves exhibit conventional shape： a short primary creep and long accelerated creep stages. The rupture properties of the heat-treated alloy follow the Monkman-Grant relationship, which exhibits similar creep behavior to that of NiAl/Cr（Mo） system with high Hf content.

Deformation Temperature and Lamellar Thickness Dependency of FormⅠto Form Ⅲ Phase Transition in Syndiotactic Polypropylene during Tensile Stretching

Phase transition from form Ⅰ to form Ⅲ in syndiotactic polypropylene crystallized at different conditions during tensile deformation at different temperatures was investigated by using in situ synchrotron wide angle X-ray diffraction technique. In all cases, the occurrence of this phase transition was observed. The onset strain of this transition was found to be crystalline thickness decided by crystallization temperature and drawing temperature dependent. The effect of drawing temperature on this phase transition is understood by the changes in mechanical properties with temperature. Moreover, crystalline thickness dependency of the phase transition reveals that this form Ⅰ to from Ⅲ phase transition occurs first in those lamellae with their normal along the stretching direction which have not experienced stress induced melting and recrystallization.

Effects of γ-irradiation and Deformation Temperature on Tensile Properties of Pb-2 mass% Sb Alloy

Effects ofγ-irradiation and deformation temperature（T）on the tensile properties of Pb-2mass% Sb alloys were studied.The samples were annealed at 458 Kfor 2hin air,then water quenched after they wereγ-irradiated（the different doses were 0.5,1.0,1.5,and 2.0 MGy）.The tensile properties were performed using stress-strain measurements at a constant strain rate（1.2×10^（-3） s^（-1））and at different T（303-393K）.It was found that at constant dose,the fracture stress（σF）decreases while the fracture strain（εF）increases as Tincreases.At particular T,σFincreases whileεFdecreases with increasing dose.The strain-hardening exponent（n）,which is the slope of the relation between ln（σ）and ln（ε）of the parabolic part of the stress-strain curve,was determined and its values increase as Tincreases and decrease as the dose increases.The value of the activation energy increases as the dose increases from 0.07 eV for un-irradiated sample to 0.1eV for the 2 MGy-irradiated sample.These values are in accordance with that needed for dislocation movement and ordering process.An interpretation of the results was given,based on the creation of point and line defects due toγ-irradiation,and that results in a distribution of beta phase（Sb-phase）,leading to a difficulty in the movement of dislocations,so there is an increase in alloy hardness.

Effect of Deformation Temperature on Deformation Mechanism of Fe-6.5Si Alloys with Different Initial Microstructures

Deformation behaviors and mechanisms under different temperatures for columnar-grained Fe 6.5Si （mass%） alloys fabricated by directional solidification and equiaxed grained Fe-6.5Si alloy fabricated by forging were comparatively investigated. The results showed that, with increasing the deformation temperature from 300℃ to 500℃, the elongation increased from 2.9% to 30.1% for the equiaxed-grained Fe-6.5Si alloy, while from 6.6% to about 51% for the columnar-grained Fe-6.5Si alloy. The deformation mode of equiaxed-grained Fe 6.5Si alloy trans ferred from nearly negligible plastic deformation to large plastic deformation dominated by dislocation slipping. Comparatively, the deformation mode of the columnar grained alloy transferred from nearly negligible plastic deformation to plastic deformation dominated by the twining, and finally to plastic deformation dominated by dislocation slipping. Meanwhile, compared with the alloy with equiaxed grains, it was found that ultimate tensile strength and elongation could be increased simultaneously, which was ascribed for the twinning deformation in columnar-grained Fe-6.5Si al loy. This work would assist us to further understand the plastic deformation mechanism of Fe-6.5Si alloy and pro vide more clues for high-efficiency production of the alloy.

Dislocation glide and mechanical twinning in a ductile VNbTi medium entropy alloy

An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%.The{112}<111>twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission.Dislocations dominate subsequent tensile deformation,and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations(e.g.,debris,dipoles,and loops)and dense dislocation networks.The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration.The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium-and high-entropy alloys.

Microstructure evolution and mechanical property characterization of a nickel-based superalloy at the mesoscopic scale

Nickel-based superalloys have become the critical materials of micro-parts depending on outstanding mechanical properties.The effects of the grain size and precipitates on the mechanical properties at the mesoscopic scale are difficult to be revealed using conventional macroscopic material constitutive models.In the present study,the microstructure evolution of the γ" phase and the tensile mechanical properties of a nickel-based superalloy at the mesoscopic scale were investigated systematically.Three variants of γ" phases precipitated corresponding to [00],[00] and [001] orientations of the matrix y phase.The quantitative statistics results showed that as the aging time increases,the particle size and volume fraction of the γ~" phase increase.As the grain size increases,the flow stress decreases due to the dwindling of grain boundary strengthening.Furthermore,the precipitation strengthening of γ" and γ" phases induces the increase of flow stress.An important conclusion is drawn that the size effect at the mesoscopic scale depends not only on the sample size and grain size but also on the particle size and volume fraction of the precipitates.The established constitutive model which considers grain boundary strengthening,precipitation strengthening and solid solution strengthening can accurately describe the flow stress characteristics of nickel-based superalloys at the mesoscopic scale.

Evaluation of Microstructure and Magnetic Properties in Non-oriented Electrical Steel Strained by Tension

The effects of deformation on the microstructure and magnetic properties of non oriented electrical steels were investigated. Box annealed electrical steel sheets were deformed by tension at four different strains： 3%, 8%, 12 % and 25 % The internal grain misorientation caused by tensile deformation was measured by electron backscat- tering diffraction （EBSD） with grain orientation spread （GOS） as an indicator of the lattice distortion. The experi- mental results showed that the average GOS value increases with the strain. The microstructure and crystallographic texture of deformed samples did not show a significant change in samples strained below 25 %. However, the mag- netic properties were strongly affected： coercivity was directly proportional to the square root of the GOS value and energy losses increased as the strain level was increased.

Hot Ductility of Severe Plastic Deformed AA6061 Aluminum Alloy

The hot ductility of 6061 aluminum alloy,which was subjected to two different severe plastic deformations（SPD）,was studied at different temperatures and strain rates.The tensile tests were carried out at the temperature range of 300-500 ℃ and at the strain rates of 0.0005-0.01 s^（-1）.The microstructure evolution was characterized using optical microscopy,transmission electron microscopy and X-ray diffraction technique.The influences of the microstructure after SPD,thermomechanical parameters（temperature and strain rate） and specimen size on the hot formability of this alloy were then analyzed.The results show that a decrease in grains/subgrains exhibited significant effect on the hot ductility of SPDed samples.The constitutive equations were then developed to model the hot formability of the studied alloy.The developed model can be represented by Zener-Hollomon parameter in a hyperbolic sinusoidal equation form.Both the changes of elongation to failure and Zener-Hollomon parameter indicate that the hot ductility of the alloy is more sensitive to the temperature rather than to the strain rate.The uniform elongation is independent of the specimen size,but the postnecking elongation increases dramatically as the ratio of l/A^（1/2） decreases.