Effect Of Pre-deformation Research Articles

Effect of Pre-Deformation on the Cyclic Behavior and Fatigue of 304L SS

This study deals with the effect of the loading history on the cyclic behavior and the fatigue life of a 304L stainless steel at room temperature. The experiments have been performed using two specimens’ categories. The first one (virgin) has been submitted to only classical fatigue tests while in the second category, prior to the fatigue test; the specimen was subjected to a pre-hardening process under either monotonic or cyclic strain control. Cyclic softening followed by cyclic hardening are observed for the virgin specimens while only cyclic softening is exhibited by the pre-hardened specimens. The obtained results show that fatigue life is strongly influenced by the pre-hardening: the latter seems beneficial under stress control but detrimental under strain control, even in the presence of a compressive mean stress. The results are discussed regarding the cyclic evolution of the elastic modulus as well as the isotropic and kinematic parts of the strain hardening in different configurations: with or without pre-hardening, stress or strain control.

The effect of pre-deformation on corrosion resistance of the passive film formed on 2205 duplex stainless steel

Effect of pre-deformation on the corrosion resistance of 2205 duplex stainless steel was investigated by microstructure observations, electronic work function measurement and electrochemical experiments. Transmission electron microscope observations showed that the dislocation density in ferritic and austenitic phases increased with the increasing of strain. Moreover, the strain induced α′-martensite was observed in sample with large strain based on XRD analysis and Transmission electron microscope observations. The electron work function of ferrite was higher than that of austenite. In addition, the surface electron work function of ferritic and austenitic phases decreased with the increasing of strain. More dislocations and chloride ions promoted to form more oxygen vacancies and cation vacancies in the passive film based on point defect model and autocatalytic reaction. Therefore, the corrosion resistance of the passive film formed on 2205 duplex stainless steel decreased with the increasing of strain in borate buffer solution with chloride ions. These results were proven by further immersion test.

Effect of pre-deformation on microstructures and mechanical properties of high purity Al–Cu–Mg alloy

The effects of pre-deformation following solution treatment on the microstructure and mechanical properties of aged high purity Al–Cu–Mg alloy were studied by tensile test, micro-hardness measurements, transmission electron microscopy and scanning electron microscopy. The micro-hardness measurements indicate that compared with un-deformed samples, the peak hardness is increased and the time to reach peak hardness is reduced with increasing pre-strain. Additionally, a double-peak hardness evolution behavior of cold-rolled (CR) samples was observed during aging. The results of TEM observation show that the number density of S′(Al2CuMg) phase is increased and the size is decreased in CR alloy with increase of pre-strain. The peak hardness and peak strength of the CR alloy are increased because of quantity increasing and refinement of S′ phase and high density dislocation.

Influence of prior cold deformation on microstructure evolution of AISI D2 tool steel after hardening heat treatment

4mm thick plates of AISI D2 steel were subjected to two different percentage of cold rolling prior to quench hardening. Prior austenite grain size and volume fraction of carbides were reduced after hardening heat treatment for both 10% and 20% cold-rolled samples in comparison with non-deformed one. Hardness measurements revealed that pre-deformation resulted in a 3 to 4 HRC decrease. Scanning electron microscopy images revealed more uniform mean plate size of martensite for the cold rolled samples. The obtained results are analyzed in the framework of the existing theories on martensitic transformation and the influence of strain on second phase dissolution kinetics. The drop in hardness is related to the effect of pre-deformation on the dissolution rate of carbides. The volume fraction of martensite compared to non-deformed condition didn’t show dominant reduction.

Twinning-Induced Elasticity in NiTi Shape Memory Alloys

Pseudoelasticity (PE) in shape memory alloys relies on the formation of stress-induced martensite during loading and on the reverse transformation during unloading. PE yields reversible strains of up to 8 % and is applied in applications such as medical implants, flexible eye glass frames, damping elements, and others. Unfortunately, PE shows a strong temperature dependence and thus can only be exploited within a relatively narrow temperature window. The present work focuses on a related process, which we refer to as twinning-induced elasticity (TIE). It involves the growth and shrinkage of martensite variants which are stabilized by dislocations, which are introduced by appropriate cold work. TIE yields reversible strains of the order of 3 %. The TIE effect does not suffer from the strong temperature dependence of PE. The weak temperature dependence of mechanical TIE properties makes TIE attractive for applications where temperature fluctuations are large. In the present work, we study the TIE effect focusing on Ni50Ti50 shape memory alloy wires. The degree of plastic pre-deformation of the initial material represents a key parameter of the ingot metallurgy processing route. It governs the exploitable recoverable strain, the apparent Young’s modulus, and the widths of the mechanical hysteresis. Dynamic mechanical analysis is used to study the effects of pre-deformation on elementary microstructural processes which govern TIE.

Aero-thermo-elastic stability analysis of sandwich viscoelastic cylindrical shells in supersonic airflow

The aero-thermo-elastic stability of layered cylindrical shells with viscoelstic cores is investigated. The Donnell’s shell theory for the outer layers and the first order shear deformation theory for the viscoelastic layer are employed in conjunction with the von Karman–Donnell kinematic nonlinearity to construct the model. The pre-stresses and pre-deformations arisen from the temperature rise and static aerodynamic pressure are first determined by solving the nonlinear thermo-elastic equilibrium equations using by an exact analytical method. The results are then used in the linear aeroelastic stability equations and analyzed with the Galerkin’s procedure to determine the supersonic flutter boundaries of the structure. Numerical studies are performed to illustrate the effects of viscoelastic damping, geometrical parameters and temperature rise on the flutter stability margins. Special attention is put on the effect of pre-deformation on the aeroelastic stability of the shell. It is found that the pre-deformation could significantly alter the flutter boundaries for sufficiently high temperatures.

Peridynamic simulations of brittle structures with thermal residual deformation: strengthening and structural reactivity of glasses under impacts

In glass research, the effect and influence of pre-deformation by thermal or chemical treatment is of great importance when configuring different mechanical properties or scratch resistance on the surface of glasses. In particular, such pre-deformation affects dynamic fracture or damage evolution when glass structures are under impact or collision conditions. Peridynamics provides a seamless approach for the simulation of dynamic damage evolution of the system under aggressive environments. Revising the pair interaction of each material point, the effect of pre-deformation is implemented, and the corresponding damage evolution can be simulated conveniently. Our approach is composed of two steps: first, a static solution is found via energy minimization with thermal boundary conditions in the peridynamic platform. Second, comparing the initial and the pre-deformed structures from the energy minimization, the effect of residual deformation, strengthening and reactive behaviour of brittle structures are seamlessly simulated. The developed methods are applied to the Prince Rupert’s drop and Bologna vial, which are classic examples of strengthened glasses. This study reports the first complete and successful simulation of dynamic behaviour of strengthened glasses, and a significant contribution in simulating residual stress behaviour in any material.

Effect of pre-deformation on creep age forming of AA2219 plate: Springback, microstructures and mechanical properties

Applying pre-deformation to high strength aluminum alloy between solution treatment and artificial aging is one of the effective ways to relieve quench-induced internal stress and achieve improved mechanical properties. This paper studies the effects of pre-deformation on springback, microstructures and mechanical properties of creep-age formed 2219 aluminum alloy plate. The results show that the introduction of pre-deformation can remarkably reduce the amount of springback, enabling the radius of deformed plate gets closer to the target value (1160mm). The radius and springback of pre-stretched plate after creep age forming are 1370.1mm and 15.3%; while for non-stretched plate, the values are 1635.6mm and 29.1%, respectively. Furthermore, the mechanical performances of pre-deformation plate are better than those of non-deformation plate and more evenly distributed. As compared with non-stretched plate, the pre-stretched plate has higher tensile strength by 7.3%, higher yield strength by 20.8% and much lower in-plane anisotropy (IPA) of properties. These differences are attributed to the combined effects of heterogeneous nucleation and growth of precipitates at dislocations, discontinuous precipitates and narrower precipitation free zone (PFZ) along grain boundaries together with unobvious stress orientation effect in the pre-stretched plate.

An Investigation on the Effects of Pre-deformation and Temperature on Thixotropic Microstructure of AA2014 Aluminum Alloy

With copper as the main alloying addition, alloy from the 2XXX family offers high strength at low specific weight and are widely employed for aircraft, wheels and major structural components. However, they suffer from low forming speeds and require high forming pressures. Hence, it is very attractive to form these alloys in semisolid state for technical and economical reasons. In this study, one of the most important wrought alloys for aerospace applications, AA2014 was used. In order to form the best semi-solid forming products, thixotropic character must be known. For this purpose, AA2014 alloy as-cast and warm extruded samples were heated to 600, 610 and 620 °C in semi-solid region and held for 0, 5 and 10 min in the induction coil. All samples were cooled with water at room temperature. Microstructure analysis was conducted with metallographic methods and shape factor values were calculated. With increasing predeformation rate and heating temperature, the shape factor increases. Experimental results show that spherical shaped thixotropic microstructures which is required for semi-solid forming can be created in AA2014 alloy.

Effect of pre-deformation on aging creep of Al–Li–S4 alloy and its constitutive modeling

A set of uniaxial tensile creep tests at different pre-deformations, aging temperatures and stress levels were carried out for Al–Li–S4 alloy, and the creep behavior and the effects of pre-deformation on mechanical properties and microstructures were determined under basic thermodynamics conditions of aging forming. The results show that pre-deformation shortens the time of primary creep and raises the second steady-state creep rate. Then, the total creep strain is greater, but in the range of test parameters it is still smaller than that without pre-deformation. In addition, transmission electron microscopy (TEM) observation shows that pre-deformation promotes the formation of T1 phase and θ' phase and makes them distribute more dispersively, while inhibits the generation of δ' phase, which leads to the improvement of mechanical properties of the alloy. A unified constitutive model reflecting the effects of aging mechanism, stress levels and different pre-deformations was established. The fitting results agree with the experimental data well.

预变形对汽车用Al-Mg-Si-Cu合金析出行为的影响

To reduce the weight of car body, Al- Mg- Si- Cu alloys have been widely used to produce outer body panels of automobiles due to their favorable high strength- to- weight ratio, corrosion resistance, weldability and good formability. Al- Mg- Si- Cu alloys belong to age- hardenable aluminium alloys, whose strength derives mainly from the matrix precipitation during aging treatments. However, their bake hardening response still need to be further improved to enhance their dent resistance. A novel thermo- mechanical treatment consisting of conventional pre-aging, pre-deformation and re-aging was developed to enhance the tensile properties and bake hardening increment of Al-Mg-Si-Cu alloys. In this work, the effect of pre-deformation on the precipitation behaviors of AlMg-Si-Cu alloy was studied by DSC, mechanical property measurement and TEM. The results show that, the GPzone dissolution rate decreases with increasing pre-deformation during the slow heating up process for the pre-aged alloy, the corresponding activation energies of 0, 5% and 15% pre-deformed alloy calculated by Avrami-JohnsonMehl method are 137.1, 189.5 and 141.3 k J/mol, respectively. If the pre- deformed alloys are directly bake hardened at 185 ℃ for 20 min, precipitation and bake hardening increment can be greatly improved by pre-deformation(the highest bake hardening increment is 160 MPa), but the bake hardening increment rate gradually decreases if the pre- deformation is above 10%. In addition, the GP zone dissolution rates of pre- deformed alloys after bake hardening treatment are much lower when the heat treatment temperatures are below one certain value, but if the treatment temperatures above it, the corresponding GP zone dissolution rates are higher than that of alloy without pre-deformation, finally, the activation energy changes from high value to low value even can be observed in the ln[(d Y/d T)f/f(Y)]-1/T curve. For the β″ precipitation in the alloys, with increasing pre-deformation, its activation energy gradually decreases, corresponding gradually increase of precipitation rate.

Investigation on fast and energy-efficient heat treatments of AA6082 in HFQ processes for automotive applications

For HFQ volume production in automotive applications, short heat treatment time is an important factor for efficient and cost effective manufacturing. In this study, fast, efficient and energy saving solution heat treatment (SHT) and ageing processes have been identified based on precipitation nucleation and growth mechanisms and a series of experiments. Material chosen was AA6082, which is an alloy favoured for automotive body structures. The effects of heating rate, soaking temperature and time on SHT processes, and the influence on post mechanical properties, have been characterised. A duplex ageing process integrated paint bake process has been developed, with an optimum ageing condition determined. In addition, the effect of pre-deformation has been analysed.

The interaction of precipitation and deformation in a binary Mg–Ca alloy at elevated temperatures

The effect of pre-deformation on precipitation hardening response as well as the work-hardening behavior of a binary Mg–Ca alloy are investigated. Our results show that application of 5% pre-deformation increases the precipitation hardening response of the material and decreases the annealing time by 50%. The dislocations introduced during the pre-deformation process act as predominant nucleation sites and result in a higher number of precipitates of smaller size. During the thermomechanical treatments, the work hardening behavior is altered by the state of the precipitates, namely, under-aged, peak-aged and over-aged. After the elastic–plastic transition, under-aged and peak-aged materials show a continuously decreasing work-hardening rate, while the over-aged material has an initial constant work-hardening rate. The absolute values of the work hardening rate are far less sensitive to the precipitation stage compared to aluminum alloys; a fact that explains the low work hardening capacity of magnesium compared to aluminum.

Effect of predeformation on the transition from hexagonal phase to square phase near the melting point using phase field crystal method

The two-mode phase field crystal (PFC) method is used to calculate the phase diagram. And in this paper it is used to simulate the effects of predeformation degree and isothermal temperature on the hexagonal grain boundary evolution and on the hexagonal/square phase transition. Results show that when there is no predeformation in the initial phase, the grain boundary defect causes the pre-melting around the melting point; predeformation increases and the interaction between deformation and defects induces the pre-melting around the melting point; and the predeformation further increases, deformation induces liquid phase and square phase simultaneously at the distortion place. The bigger the predeformation and the closer to melting point the maintained temperature, the more obvious the growth of liquid phase is; on the contrary, the square phase grows obviously. The distortion energy is released with time and the phase of grain finally becomes square phase. It can be concluded that keeping the hexagonal phase isothermal near the melting temperature, the liquid phase appears at the grain boundary or at the other defects because the predeformation leads to the increase of atom activity, thus increasing atom disorder degree. Then with the release of distortion energy, the grain phase finally transforms into an equilibrium square phase. In this way the hexagonal/square transition time is extended.

Effect of Pre-Deformation on Fracture Behavior Transition due to Strain-Rate Change in Fe-5%Si Alloy

Effect of Pre-Deformation on Fracture Behavior Transition due to Strain-Rate Change in Fe-5%Si Alloy

Refinement of Cast Cr-V-Mo Steel by Using Recrystallization and Partial Melting Method and Post Heat Treatments

The conventional route for tool steel manufacturing consumes large amounts of energy and time and results in a long process chain for the manufacture of products. Environmental consciousness is fuelling the development of an improved route with a shorter process chain and lower energy consumption that can replace the conventional one. An energy-efficient process route for manufacturing products with high quality was proposed based on recrystallization and partial melting (RAP) technology. To verify the feasibility of the RAP-based route, the effects of predeformation, partial melting, and post heat treatments on the microstructure characteristics and mechanical properties of cast Cr-V-Mo steel were studied experimentally. During the RAP process, plastic deformation, recrystallization, austenization, grain growth, and partial melting occurred. When the RAP processed specimen was quenched from 1050 oC after isothermal holding for 480 s and then tempered twice at 560 oC for 2h, microstructural evolution occurred in both former solid-phase and liquid-phase regions and caused a good combination of mechanical properties.

Influence of pre-deformation on jerky flow in Ni–10Pd during high-temperature instrumented indentation

During instrumented microindentation at 450 °C, prominent and limited serrations were exhibited in the load–depth curves corresponding to an annealed Ni–10Pd and a deformed Ni–10Pd specimen, respectively. After fully recrystallizing the deformed Ni–10Pd sample and minimizing the stored strain energy, the characteristic jerky flow behaviour was restored in the Ni–10Pd sample during instrumented nanoindentation at 450 °C. The effect of pre-deformation on the serrated flow behaviour is rationalized using a modified cavity expansion model that accounts for the reconfiguration of dislocation substructures and solute–dislocation interactions.

Effect of pre-deformation enhanced thermal aging on precipitation and microhardness of a reactor pressure vessel steel

Microstructure evolution in neutron irradiated Reactor Pressure Vessel (RPV) steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150 °C and water quench, deformation 10% and 30% respectively, and then thermal aging at 500 °C for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy (TEM). The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates (CRPs) and carbides, deposition of martensite and work hardening.

Effect of predeformation on microstructural evolution of a Zr alloy during 550–700 °C aging after β quenching

In this paper, we report the effect of a 20% predeformation on the microstructural evolution of a Zr–0.85Sn–0.4Nb–0.4Fe–0.1Cr–0.05Cu alloy during aging between 550 and 700°C after β quenching. Transmission electron microscopy, electron backscatter diffraction, electron channeling contrast and secondary electron imaging techniques are jointly utilized to carry out detailed microstructural characterization. By comparing microstructures between directly aged specimens (group A) and specimens aged after a 20% predeformation (group B), it is revealed that the introduced predeformation could exert remarkable influences on the Zr alloy. As the aging temperature and/or time increase, initial plate structures finally recrystallize in both groups. In spite of the similarity of the general evolution profile, the predeformation introduced in group B evidently reduces the required aging temperature and time. Distinct recrystallization nucleation behaviors due to different recrystallization mechanisms are also found in both groups. Noticeable differences between the with- and without-predeformation groups also include grain size, distribution of second-phase particles and misorientation angle distribution features in recrystallized specimens. Reasons accounting for the accelerated recrystallization and distinct microstructural characteristics in group B are discussed and attributed to the defects introduced during the predeformation. In addition, grain size calculation by applying the Zener equation shows that, although equilibrium states are not attained in both groups, the case with the predeformation is closer to the ideal equilibrium.

Effect of pre-deformation on microstructure and mechanical properties of 2219 aluminum alloy sheet by thermomechanical treatment

Thermomechanical treatment is usually used to achieve good mechanical properties and microstructure of metal materials. The effect of pre-deformation on the microstructure and mechanical properties of 2219 aluminum alloy sheet by TMT process was investigated. The studies show that the yield strength and tensile strength increase firstly and decrease with the increase of pre-deformation under a certain heat treatment condition and total deformation. The tensile strength of 2219 aluminum alloy sheet reaches the maximum value when the pre-deformation is about 2%. It is also found that the very fine Al2Cu appears inside the grain, which is the precipitated phase for the strengthening of the 2219 aluminium alloy.