Effect Of Pre-deformation Research Articles

YIELD STRESS BASED ON NATURAL STRAIN THEORY UNDER CYCLIC SHEAR LOAD AFTER LARGE SIMPLE SHEAR

This paper describes the variation of yield stress under cyclic loads after applying large pre-deformation. In this research, the Natural Strain is used as a strain representation for describing an elastoplastic behavior under large deformation. Using test pieces which is already given a pre-deformation of large simple shear, the yield stress under cyclic shear loads in the forward direction and the reverse direction is examined. As for the method for estimating yield stress in each cycle, the slope of a tangent in the principal deviatoric stress and the principal deviatoric strain curve is adopted. The experiments are conducted with the different sizes of pre-deformation and strain amplitude in order to reveal the effect of pre-deformation on the yield phenomenon. Then, these experimental results are compared with the results of yield stress in the previous study, which is obtained under cyclic load for tension and compression after applying the large uniaxial tension.

Effect of Pre-deformation on Grain Ultrafining by Intercritical Deformation in Low-Carbon Microalloyed Steels

In this study, the effect of pre-deformation at recrystallization and non-recrystallization zone on the grain ultrafining by the subsequent intercritical deformation (ID) was investigated on low-carbon microalloyed steel. The results showed that ultrafine grain microstructure with an average size of ~ 1.0 μm was fabricated through pre-deformation in the recrystallization zone followed by ID. When pre-deformed at the non-recrystallization zone prior to ID, the grain size increased to 1.6 μm with a heterogeneous distribution along with the well-developed dynamic recovery of ferrite. The grain ultrafining mechanism was attributed to the combined action of the deformation-induced ferrite transformation and the continuous dynamic recrystallization. In particular, the continuous dynamic recrystallization process during ID occurred on the pro-eutectoid ferrite as a result of the subgrain rotation mechanism and the absorbing dislocations mechanism.

Combined Effects of Pre-deformation and Pre-aging on the Mechanical Properties of Al-Cu-Mg Alloy with Sc and Zr Addition

The combined effects of pre-deformation and pre-aging on the mechanical properties of Al-Cu-Mg alloy with Sc and Zr addition were investigated. It is revealed that the introduction of pre-deformation can enhance the peak-aging strength, as well as tensile and yield strength, effectively due to the formation of finer and more dispersive precipitation. Pre-aging process before pre-deformation can increase the elongation while maintaining higher strength with a discontinuous distribution of precipitates at grain boundary. The precipitates of bean-like Al3(Sc, Zr) particles further strengthen the alloy via pinning the dislocations which are formed during pre-deformation process and hindering the dislocation motion. Furthermore, pre-deformation and pre-aging accelerate the kinetics of precipitation due to preferential sites provided by the dislocation and the increase of GPB zones’ size and distribution. The synergism of pre-deformation and pre-aging achieves a combination of better mechanical properties and shorter peak-aging time.

Effect of predeformation on globularization of Ti–5Al–2Sn–2Zr–4Mo–4Cr during annealing

Abstract The microstructure evolution during annealing of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s−1 deformation amount (height reduction) 20% and 50% and annealed at 810 °C, thermal grooving by penetration of β phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 °C, 0.01 s−1 and then annealed at 810 °C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries (HABs) remain. With long time annealing, the chain-like α grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti–5Al–2Sn–2Zr–4Mo–4Cr.

Effects of pre-deformation on the microstructures and corrosion behavior of 2219 aluminum alloys

In this work, effects of different pre-deformation on the microstructures and corrosion behavior of 2219 aluminum alloys were investigated. The results showed that the size of grains decreased gradually and the distributions of the precipitated phases was improved effectively during the aging processes, leading to an obvious increase in tensile strength and corrosion resistance. It demonstrated that the large amount of dislocations induced by the pre-deformation processes providing the preferential conditions for the θ′ precipitated phases. The fined and dispersed θ′ phases for this alloy subjected to 20% pre-deformation effectively hindered the movement of dislocations which enhanced the tensile strength. The tensile strength decreased slightly because of the uneven distributions of θ′ phase if the pre-deformation reaches to 30%. The rank of corrosion resistance of different pre-deformation after aging process from the highest to the lowest can be drawn as: 20%＞30%＞10%＞5%, which was attributed to the change of population of θ′ precipitates and the width of precipitation free zone (PFZ).

Effect of pre-deformation in the β phase field on the microstructure and texture of the α phase in a boron-added β-solidifying TiAl alloy

In this work, the effect of pre-deformation in the β phase field on the microstructural characteristics of α phase in a Ti-40Al-8Nb-0.5B alloy (at. %) was investigated. The results showed that the morphology and crystallography of α phase were strongly influenced by the deformation. It was observed that if there was no deformation, α laths which formed strict Burgers orientation relationship with β matrix are predominant (∼81% in number fraction). In contrast, the Burgers α laths are significantly reduced after compression in the β phase field. Meanwhile, an abnormal double-fiber texture, <11–20> and <10–10>, is produced. After systematic analysis, we believe that the reduction of Burgers α is attributed to the heterogeneous nucleation of α phase at borides and the breakdown of the boride ribbons during deformation. Moreover, the formation of α texture is a synergetic consequence of β texture and boride texture.

Influence of pre-deformation on the precipitation of Cu-rich clusters in RPV model steel

The effect of pre-deformation on the precipitation process of Cu-rich clusters in reactor pressure vessels (RPV) model steel is studied. In this research, Fe-1.16wt%Cu binary alloy is selected as RPV model steel to simulate the precipitation process of Cu-rich clusters. The solid-solution Fe-Cu alloys were cold rolled with pre-deformation of 0, 10%, 25%, 40%, 60%, followed by aging at 450°C for a series time. The dislocation density, Vickers hardness and microstructure evolution of Fe-Cu alloys after aging were determined. It is revealed that the Vickers hardness of un-deformed specimens reaches to peak hardness after aging at 450°C for 100 h, while the specimens with larger dislocation density reach to peak hardness faster from the Vickers hardness test result. The result of transmission electron microscopy (TEM) indicates that pre-deformation promotes the process of precipitation of Cu-rich clusters and inhibits the growth of the Cu-rich clusters.

Investigation on the creep-age forming of an integrally-stiffened AA2219 alloy plate: experiment and modeling

Creep-age forming (CAF) is a relatively new sheet metal forming method for manufacturing large-scale components with accurate shape and desired performance. This paper fully investigates the strain distribution, springback characteristic, mechanical property, and shape quality of an integrally-stiffened AA2219 alloy plate during CAF process. A new set of unified creep-ageing constitutive equations incorporating the effect of pre-deformation is developed, and its effectiveness in FE solver MSC.Marc is validated by tension creep-ageing simulation. CAF simulation of the stiffened plate is conducted. The results indicate that the final shape of the plate is simultaneously determined by plastic and creep deformations, while the creep deformation plays a major role, with corresponding contribution percentage of 33 and 67%. Comparisons between experiment and modelling show that the deviations are approximately 11% for springback and 3.2% for yield strength, which confirms the validity of CAF modelling. Furthermore, yield strengths on the skin of the plate are more evenly distributed as compared with those on the stiffeners. In addition, the values of generatrix linearity of the formed plate are very small, which demonstrates that the CAF-formed integrally-stiffened plate has high-precision shape quality.

Effect of pre-deformation on the pre-corrosion multiaxial fatigue behaviors of 2024-T4 aluminum alloy

Pre-damages which contain pre-deformation and pre-corrosion have influences on multiaxial fatigue properties. In this paper, the effect of pre-tension of 1%, 2%, 3% and 4% as well as pre-torsion of 10°, 20°, 30° and 40° on fatigue life of 2024-T4 aluminum alloy under corrosion conditions is evaluated. Multiaxial fatigue tests are performed under constant amplitude sinusoidal wave loading with tension-torsion ratio of 3 in air at room temperature. The results indicate a reduction tendency of pre-corrosion multiaxial fatigue life with the pre-deformation level in the same pre-corrosion time. With the same pre-deformation level, the pre-corrosion multiaxial fatigue life decreases as pre-corrosion time increases. Pitting caused by corrosion is observed on the surface of specimens. The observed mechanical behavior and associated phenomena are directly linked to microstructure characteristics such as surface defects, corrosion pits and micro-cracks. The analysis of mechanism reveals that the synergistic combination of pre-deformation and pre-corrosion is more detrimental than that of either one acting separately. The alternate cyclic hardening and softening appear in the axial direction. The cyclic softening in the tangential direction becomes more serious with the increase of pre-deformation. The typical morphology of corrosion fatigue can be observed on the fracture. Involving the damage factors of single pre-damage conditions, which include pre-deformation and pre-corrosion effects, the damage factor for pre-corroded multiaxial fatigue after pre-deformation is deduced. Fine results are achieved according to the above methods with most predicted life in 2× scatter band.

Effects of Pre-deformation Annealing on Mechanical Properties of Ti-Based Amorphous Alloys

Ti 40 Ni 40 Cu 20 amorphous matrix composite plate specimens were fabricated by the levitation suspend melting-water cooled Cu mold process. The specimens were pre-compressed at different degrees with a universal testing machine and then annealed at 150 °C for 30 min. The effects of pre-deformation annealing processes on the microstructure and mechanical properties of Ti 40 Ni 40 Cu 20 alloy system were studied by a metallographic microscope, X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show the martensitic phase transformation that of the austenite phase under external force occurs. The phase transition induced by the deformation coupled with the annealing release of residual thermal stress plays a role in enhancing both strength and toughness of the amorphous matrix composite. Both martensite phases and austenite phases are increased with the increase with the degrees of pre-deformation increasing, and martensite phases are increased faster. Thus, the yield strength of the composite increases, while the ductility declines. Therefore the controllable yield strength in the pre-compression stage for shaping can be realized.

The effects of pre-deformation on the creep aging behavior and mechanical properties of Al-Li-S4 alloys

In the present work, the effects of pre-deformation on the creep ageing and associated mechanical properties were investigated regarding Al-Li-S4 alloys. It was found that pre-deformation caused significant reduction in the creep strain, but enhancement in the tensile strength. Meanwhile, a “multi-step stage” feature of the creep strain response was observed during creep ageing. The microstructural evolution at different stages were examined accordingly using transmission electron microscope (TEM). Two strengthening precipitates were identified, including the tetragonal θ′ (Al2Cu) and T1 (Al2CuLi) phases. Both were further analyzed with respect to their sizes (length and thickness) and volume fractions during creep ageing. Additionally, pre-deformation initiated some lath-shaped s’(Al2CuMg) precipitates, as confirmed using high-angle annular dark filed (HAADF) imaging and energy dispersive spectroscope (EDS). This work indicates that novel Al-Li-S4 alloys, with improved mechanical properties, can be obtained through manipulating and introducing pre-deformation to the creep ageing.

Effect of residual stresses on notch toughness of the tempered martensitic steel F82H-MOD

The effect on notch toughness of residual stresses introduced by pre-deforming double edge notched tensile specimens of the high-chromium reduced activation tempered martensitic steel F82H-mod was investigated. Residual elastic strains/stresses were introduced by pre-deformation in tension at room temperature up to different levels. Measurements of residual strains/stresses were performed by neutron diffraction using POLDI Materials Science Diffractometer at Paul Scherrer Institute in Switzerland. A good agreement between the calculated residual stresses by finite element modeling and the measured ones was found. The pre-deformed specimens were then tested up to fracture at −150°C and compared with specimens tested without pre-deformation. The local fracture stress in the notch vicinity was determined from finite element simulations and compared with previously calibrated fracture stress on pre-cracked fracture specimens tested in the brittle to ductile transition region. The fracture stress of the double edge notched specimens was consistent with that of pre-cracked specimens. The effect of pre-deformation on ultimate fracture load was not found to be beneficial for the specimen geometry considered. This behavior was attributed to the broad stress distribution characteristic of notch with a peak location that does not lie in the compressive residual stress region near the notch root.

Effects of pre-deformation on microstructure and properties of Al–Cu–Mg–Ag heat-resistant alloy

The effects of the pre-deformation on the microstructure, mechanical properties and corrosion resistance of Al–Cu–Mg–Ag alloys were investigated by means of hardness tests, tensile tests, intergranullar corrosion (IGC) tests and transmission electron microscopy (TEM), respectively. The results show that with the increase of deformation amount, the aging hardening rate increases while the strength of the alloy decreases and then increases. The sample with a pre-deformation of 6% possesses the highest tensile strength due to the refinedly and homogeneously distributed precipitations. The pre-deformation aging accelerates the heterogeneous nucleation of Ω and θ′ phases at dislocations, and also refines the precipitations both in the grains and along the grain boundaries. The precipitation of Ω phase is restrained while that of θ′ phase is accelerated in pre-deformed Al–Cu–Mg–Ag alloy compared with the sample without pre-deformation. In addition, the width of the precipitate free zone decreases with increasing the pre-deformation amount, leading to a narrower IGC passageway. This results in an enhanced IGC resistance of Al–Cu–Mg–Ag alloy treated by pre-deformation aging.

Effect of pre-deformation on microstructure and mechanical properties of WE43 magnesium alloy

The effect of cold plastic deformation by multi-directional forging prior to artificial aging treatment on the microstructure and mechanical properties of WE43 alloy was investigated. The results show that the pre-deformation produced high density of dislocations and deformation twins. After peak-aging treatment at 200°C, the pre-deformation reduced the average size of fine β″ and β′ precipitates and promoted the formation of β1 phase. Additionally, spheroid–shaped precipitates formed at twin boundaries and the deformation twins were thermally stable during the aging treatment. Mechanical properties reveal that the tensile yield and ultimate strength is significantly enhanced from 191±3MPa to 270±15MPa and 278±5MPa to 320±18MPa, respectively.

Effect of pre-deformation on the oxidation resistance of a high Si ferritic/martensitic steel in oxygen-saturated stagnant lead-bismuth eutectic at 550 °C

The oxidation resistance of a high Si ferritic/martensitic steel with and without pre-deformation in oxygen-saturated stagnant lead-bismuth eutectic at 550°C has been investigated. It is found that pre-deformation changes the morphology of the oxide scale locally. In some positions, the internal oxidation zone beneath the inner oxide layer disappears and/or the thickness of the inner oxide layer decreases. These changes are related to the formation of an enhanced Cr-rich belt locally in the inner oxide layer. Additionally, the local enhanced Cr-rich belt induces many voids at the inner/outer oxide layer interface, which deteriorates the oxidation resistance of the material.

Effect of Pre-deformation on Microstructure and Pitting Corrosion Behavior of UNS S32205

Effect of Pre-deformation on Microstructure and Pitting Corrosion Behavior of UNS S32205

Effect of pre-deformation on creep age forming of 2219 aluminum alloy: Experimental and constitutive modelling

Applying pre-deformation to high strength aluminum alloy has significant impacts on shape formation and mechanical properties of component in creep age forming process. The suitable degree of pre-deformation can not only improve forming efficiency, but also attain sound mechanical properties. This paper experimentally investigates the effects of pre-deformation on creep strain, mechanical properties and microstructures of AA2219. The results show that pre-deformation can prolong the duration of primary creep stage and considerably facilitate creep strain. Through mechanical property tests, it is found that pre-stretched AA2219 possesses a high-performance “peak ageing strengthening region” with little fluctuation during creep ageing of 7–13h. Further examinations by TEM tests indicate that this is due to the fact that the morphology of precipitates in this region remains unchanged without remarkable coarsening. Based on microstructural evolution and ageing strengthening theory, a set of physically-based creep ageing constitutive model is proposed. The developed model takes into account the effect mechanism of pre-deformation and incorporates the coupled interactions of microstructure, yield strength and creep strain. A good agreement between predicted and experimental values is achieved, which verifies the accuracy of the developed model. Hence, it provides the theoretical basis for the prediction of shape and properties in creep age forming of large-scale panel component.

Effect of pre-deformation on the microstructures and properties of 2219 aluminum alloy during aging treatment

The changing of the microstructure and properties with the pre-deformation degree of the 2219 aluminum alloys during aging treatment was investigated. The results reveal that the pre-deformation leads to the increasing of the dislocation density in the matrix that in turn gives rise to the formation of the dense and smaller precipitated θ′ phases with dispersive distribution in the α-matrix, which results in the enhancing of the strength of the pre-deformed samples. It is also observed that the strength of the 4.19% pre-deformed sample shows an abrupt slightly decline by comparing with the 2.88% pre-deformed sample, which caused by the formation of the non-uniformly distributed θ′ precipitates due to the large amount of the dislocation cells formed by the pre-deformation in the matrix.

Influence of pre-deformation, sensitization and oxidation in high temperature water on corrosion resistance of AISI 304 stainless steel

The effects of pre-deformation on sensitization of AISI 304 stainless steel were investigated by the double loop electrochemical potentiokinetic reactivation test. The effects of pre-deformation and sensitization on high temperature oxidized film formed in high temperature water were analyzed by a XRD and SEM. The electrochemical impedance spectroscopy at room temperature was used to study corrosion resistance of oxidized film. The point defect density of oxidized film was calculated by Mott–Schottky plots. The results showed that the value of the degree of sensitization first decreased and then slight increased with the increasing of engineering strain. Moreover, low temperature promoted to form sensitization induced “secondary” α′-martensite. The sample with 20% engineering strain had higher impedance value than other samples. The result was supported by further Mott–Schottky experiments. Considering increased α′-martensite with the increasing of strain, the results of the impedance were more consistent with values of the degree of sensitization.

Effects of pre-deformation on microstructure and tensile properties of Al—Zn—Mg—Cu alloy produced by modified strain induced melt activation

The effects of Al—8B grain refiner on microstructure and tensile properties of an Al—12Zn—3Mg—2.5Cu alloy produced by modified strain induced melt activation process were investigated. Pre-deformation of 60% was used by hot working at 300 °C. After pre-deformation, the samples were heated to a temperature above the solidus and below the liquidus point and maintained in the isothermal conditions at three different temperatures (500, 550 and 590 °C) for varying time (10, 20 and 40 min). It was observed that strain induced melt activation has caused the globular morphology of α(Al) grains. Microstructural study was carried out on the alloy by using optical microscope and scanning electron microscope in both unrefined and B-refined conditions. The results showed that for the desired microstructures of the alloy during SIMA process, the optimum temperature and time are 550 °C and 10 min, respectively. After the T6 heat treatment, the average tensile strengths increased from 278 to 585 MPa and 252 to 560 MPa for samples refined with 3.75% Al—8B before and after SIMA process, respectively. The ultimate strength of SIMA specimens is lower than that of B-refined specimens.