Effect of heat treatment on tensile deformation behavior of Ni-Co film/Fe substrate systems

The effects of heat treatment on microstructure and tension property of Ni-Co film/Fe substrate systems were investigated. The deformation and fracture morphologies of Ni-Co films/Fe substrate systems were studied by in-situ scanning electron microscopy（in-situ SEM）before and after heat treatment.The results show that a Ni-Co/Fe diffusion layer appears between the film and substrate after heat treatment;the elongation of film/substrate system increases with increasing the heat treatment temperature. Both the strength and ductility of the film/substrate system are preferable when heat treatment temperature is 650 o C,meanwhile the maximum elongation is up to 46%.During tensile deformation,the deformation behaviors of Ni-Co film/Fe substrate are quite different before and after heat treatment.The samples after heat treatment went through the progress of holes’emergence,growth and extension,whereas the samples without heat treatment accompanied with no holes,just cracked instead,showing that appropriate heat treatment is helpful to improve the toughness of material,and mechanical properties.

Relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation

The relationship among microstructure,mechanical properties and texture of TA32 titanium alloy sheets during hot tensile deformation at 800℃was investigated.In the test,the original sheet exhibited relatively low flow stress and sound plasticity,and increasing the heat treatment temperature resulted in an increased ultimate tensile strength(UTS)and a decreased elongation(EL).The deformation mechanism of TA32 alloy was dominated by high angle grain boundaries sliding and coordinated by dislocation motion.The coarsening of grains and the annihilation of dislocations in heat-treated specimens weakened the deformation ability of material,which led to the increase in flow stress.Based on the high-temperature creep equation,the quantitative relationship between microstructure and flow stress was established.The grain size exponent andαphase strength constant of TA32 alloy were calculated to be 1.57 and 549.58 MPa,respectively.The flow stress was accurately predicted by combining with the corresponding phase volume fraction and grain size.Besides,the deformation behavior of TA32 alloy was also dependent on the orientation of predominantαphase,and the main slip mode was the activation of prismaticslip system.The decrease of near prism-oriented texture in heat-treated specimens resulted in the enhancement of strength of the material.

Flow behavior modeling of IMI834 titanium alloy during hot tensile deformation

A proper constitutive model was developed to predict the hot tensile flow behavior of IMI834 titanium alloy in α+β region. Hot tensile tests were performed at 800–1025 °C and 0.001–0.1 s−1. The constitutive model was developed through an Arrhenius-type equation at strains of 0.08–0.22 to characterize the hot tension behavior. It was found that the activation energies for hot tensile deformation of IMI834 titanium alloy are in the range of 519–557 kJ/mol at different strain values. The accuracy of predicted flow stress curves was evaluated using standard statistical parameters. These curves are appropriately found to be in good agreement with the experimental ones.

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.

Effect of small tensile deformation on damping capacities of Mg-1%Al alloy

Tensile tests with small deformation amounts of 0.5%,1%,3%and 5%were performed at room temperature on as cast Mg-1%Al alloy.Microstructures of the Mg-1%Al alloys before and after deformation were observed by optical microscopy(OM) and transmission electron microscopy(TEM).The strain amplitude dependent and temperature dependent damping capacities of the as-cast and deformed Mg-1%Al alloys were investigated by dynamic mechanical analysis(DMA).The mechanism of deformation on damping capacity of Mg-1%Al alloy was discussed.The results show that the as-cast Mg-1%Al alloy has high damping value at high strain.When the tensile elongation is higher than 3%,the damping values of this alloy in high strain region are significantly decreased at room temperature.But the large amount of dislocations produced by tensile deformation are activated by heat,and then increase the damping value at high temperature.

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.

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.

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.

Mechanical definition and standardized measurement of the strain hardening exponent in tensile deformation

It has been experimentally proved that strain hardening exponent has very strong sensitivity to structure. The measuring result of precise experiment indicated that the variational laws of nv(the strain hardening exponent under constant velocity), nε( under constant strain rate) and np( under constant load) with ε strain are entirely different. Considering the structure sensitivity in superplasticity and plasticity (which means that the strain hardening exponent is related to strain as well as strain rate), this paper deduces the analytical expressions for nv, nε and np from the state equation. Thus, the mechanical essence of nv, nε and np corresponding the change of e is revealed. And the experimental results on typical material Zn 5%AI are interpreted successfully which show reliability of the theory.

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.

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.

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.

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.

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.

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.

Molecular dynamics simulation of fracture behaviors of <110> tilt grain boundaries in γ-TiAl

Molecular dynamics(MD) simulations were carried out to study the fracture behaviors of several symmetric tilt grain boundaries in γ-Ti Al bicrystals with <110> misorientation axes. Tensile deformation along direction perpendicular to grain boundary was simulated under various strain rates and temperatures. The results indicate that the relative orientation of the grains and the presence of certain atom units are two critical factors of the interface structure affecting the stress required for dislocation nucleation. Dislocations nucleate and extend at or near the symmetric tilt grain boundaries during the tensile deformation of Σ3(111) 109.5°, Σ9(221) 141.1° and Σ27(552) 148.4° interfaces. For Σ27(115) 31.6° and Σ11(113) 50.5° interfaces, the interfaces fractured directly in a cleavage manner due to no dislocation emitted from the boundary. The tensile fracture mechanisms of the bicrystals are that micro-cracks nucleate at the grain boundary and propagate along the interface. The variance of crack propagation is whether there is accommodation of plastic region at the crack tips.

Quantitative analysis of orange peel during tension of 6063 alloy spun tubes

Severe surface roughening during plastic deforming of aluminum alloy parts can produce ＂orange peel＂ defects. To analyze ＂orange peel＂ of 6063 aluminum alloy tube quantificationally, the tensile tests of trapezoidal specimens were carried out. The tubes with different grain sizes were obtained by spinning and subsequent annealing heat treatment. The macroscopical behavior of surface roughening was characterized by surface roughness Ra using a laser scanning confocal microscope. The corresponding microscopic behavior was reflected by microstructures of specimens and in-situ observation using electron back-scattered diffraction（EBSD）. The obtained results show that the surface roughness increased firstly with increasing strain and then decreased slightly. There was a critical strain for aluminum alloy tube, below which ＂orange peel＂ defect would not occur. For the tube with a mean grain size of 80, 105, 130 and 175 μm, the critical strains were 10.17%, 5.74%, 3.15% and 1.62%, respectively. Meanwhile, the surface roughening behavior was produced by serious inhomogeneous deformation between grains as strain increased, and was aggravated as the grain size increased due to the larger local deformation in larger grains.

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.