Pre-deformation Conditions Research Articles

Effect of Pre-Deformation on Precipitation in Al–Zn–Mg–Cu Alloy

AbstractIn this work, strengthening effects and evolution of precipitates in a pre-deformed Al–Zn–Mg–Cu alloy during ageing were investigated using Vickers hardness measurements, tensile tests, and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). It was found that all cold rolled conditions had higher mechanical strength than the non-deformed condition for all ageing times and that this effect increases at higher deformation ratios. It was also found that the non-deformed condition has a higher age hardening response than that of the cold rolled conditions. A homogeneous precipitate distribution was observed in the non-deformed condition, while the cold rolled conditions contained non-uniformly distributed precipitates due to the introduced dislocations. This led to larger precipitate sizes and a reduction in the precipitate number densities in the pre-deformed conditions. HAADF-STEM analysis revealed differences in the fraction of different precipitate types between the non-deformed and the cold rolled conditions. η', η2, and disordered η phase were observed in the non-deformed condition, while η', η2 and the newly identified Y phase were observed in the cold rolled conditions. The disordered η phase contained structural units of the η1 phase and was associated with reducing the lattice misfit between this phase and the Al matrix. Formation of the Y phase was related to an accelerated nucleation rate in the regions of high dislocation density. Graphical abstract

Mechanical properties of cryo-rolled aluminium alloy AA2219 at 300, 77 and 20 K

In the present work, AA2219-T87 plates (40 mm thickness) in two different pre-deformation conditions: without solution treatment (WST) and solution treatment (ST) are cryo rolled (at 77 K) into sheets (imparting reduction ratio of ∼97.2%) and rods (reduction ratios of 30, 50 and 70%). The mechanical performance and ageing kinetics of the cryo rolled sheets are compared with cold rolled sheets, to assess any beneficial effect. The as-rolled sheets and rods were subjected to duplex ageing at 175 °C/3 min + 125 °C/8 h, which reduces the effective ageing time by several hours compared to industrially practiced ageing time for peak aged tempers. The microstructures of the ST sheets and rods in as-rolled and peak aged conditions consist of very fine structure with high dislocation density in the form of tangles. Peak ageing treatment generated uniform distribution of semi-coherent θ′ precipitates with slight decrease in dislocation density due to partial recovery of the structure. Tensile properties are evaluated for the sheets and rods in as-rolled and peak aged conditions at ambient (300 K) and cryogenic (77 and 20 K) temperatures. Significant improvement in the strength and ductility values were observed in as-rolled and peak aged conditions for ST sheets and rods, whereas tensile properties in WST condition were significantly lower. The combined effect of suppression of dynamic recovery (DRV), grain size refinement, dislocation strengthening and precipitation hardening from the θ′ precipitates are responsible for achieving optimum strength and ductility balance at temperatures up to 20 K. Based on the outcomes of the present work, severe deformation through cold/cryo/caliber rolling of the ST sheets and rods followed by peak ageing is very effective in improving the cryogenic strength and ductility over conventional processed routes for AA2219 alloy.

The effect of loading direction and pre-deformation on the low-cycle fatigue behavior of high-manganese twinning-induced plasticity steels

The low-cycle fatigue performance of high-manganese twinning-induced plasticity (TWIP) steels with the specimen axial direction of 0°, 22.5°, 45°, 67.5°, and 90° to the rolling direction is investigated in the range of the total strain amplitudes (Δε/2) of 0.6 % ∼ 4.4 % and two types of pre-deformed conditions (i.e., tension and tension-unloading). Experimental results show that the dependence of the fatigue life on the specimen orientation is obvious for lower strain amplitudes, and it gradually reduces with the increase of the applied strain level. The 0° orientations show the highest sensitivity to the pre-deformation process, and the tension-unloading pre-deformation exhibits the most severe change of the texture at fracture.

Sheared Peridotites from Kimberley (Kaapvaal Craton, RSA): Record of Multiple Metasomatic Events Accompanied with Deformation

Abstract Sheared peridotites from the Kaapvaal craton may be broadly divided into two types: (1) high T and refertilized and (2) low T and highly depleted, which equilibrated at conditions lying either above or along the Kaapvaal craton conductive geotherm, respectively. Here, we have studied 14 low-T sheared peridotites from Kimberley entrained by several Late Cretaceous (90 Ma) kimberlites in order to constrain the nature and timing of the deformation. The sample suite comprises nine garnet peridotites (GPs) with various amounts of clinopyroxene ± isolated spinel, three garnet-free phlogopite peridotites (PPs) with minor amounts of spinel, one garnet–spinel peridotite (GSP) and one dunite. The peridotites have intense deformation textures, ranging from porphyroclastic to fluidal mosaic. Olivine and orthopyroxene compositions (Mg# = 91–94) indicate varying degrees of depletion, similar to coarse-grained peridotites from the same localities. Pre-deformation conditions of the GPs are preserved in the cores of large (>100 μm–mm diameter) porphyroclasts and give a range in temperature of 930–1000°C at pressures of 4.0 ± 0.4 GPa. The GSP was equilibrated at 840°C and 3.1 GPa. Projected onto a 40-mW/m2 geothermal gradient, the PP samples yield temperatures of 850–870°C at 3.3–3.4 GPa. Trace element measurements by laser ablation inductively coupled plasma mass spectrometry and electron microprobe indicate that the ‘cold’ sheared peridotites were influenced by several metasomatic events, ranging from ‘old’ pre-deformation metasomatism to interactions shortly before or during deformation. The old pre-deformation metasomatism is recorded in garnet, clinopyroxene and orthopyroxene porphyroclasts and implies interactions with phlogopite–ilmenite–clinopyroxene- or muscovite–amphibole–rutile–ilmenite–diopside-related metasomatic agents, which also led to crystallization of phlogopite in the garnet-free peridotites. A ‘young’ metasomatic event caused an enrichment in Fe, Ti, Ca and Y (+heavy rare earth elements) and is evident in zoned orthopyroxene and clinopyroxene and phlogopite, the crystallization of new clinopyroxene porphyroclasts and compositional heterogeneities in garnet. This young event marks the beginning of extensive kimberlite-related metasomatism in the late Cretaceous beneath Kimberley. The metasomatism caused the deformation (triggered by a kimberlite pulse?), resulting in the recrystallization of fine-grained, mainly olivine, neoblasts (down to <10 μm). These record the metasomatic conditions at the time of deformation, revealing an increase in temperature up to 1200°C accompanied by an increase in Ti content up to 300 μg/g. Crystal preferred orientations of olivine neoblasts suggest the presence of elevated concentrations of water (B, C, E type) or the presence of a melt during the deformation (AG type). We suggest that these high water contents led to hydrolytic weakening of the cratonic lithosphere and prepared the pathways for subsequent kimberlite magmas to reach the surface. We propose that the deformation is a byproduct of extensive metasomatism, resulting in a metasomatism–deformation cycle. In times of extensive magmatism and metasomatism, fluids and melts flow along the pathways established by previous metasomatic agents, leading to further hydrolytic weakening of these mantle segments. Later, deformation was initiated by a new pulse of melt/fluid, with one of the later pulses eventually reaching the surface and transporting fragments of sheared and undeformed peridotites with it. The remaining peridotite anneals after the period of extensive metasomatism and recrystallizes to become coarse-grained peridotite again.

Load partitioning behavior in a metastable austenitic stainless steel subjected to pre-deformation below and above Md temperature: Experimental and modeling studies

A physics-based model coupling the evolution of dislocation density in the austenite and strain-induced martensite phases with composite flow strength and kinetics of martensite transformation was developed to describe ambient temperature uniaxial tensile deformation behavior of mill annealed and pre-deformed 304 SS. The applicability of the model was evaluated by fitting the experimental stress-strain data and validated with the experimentally estimated dislocation density in the austenite phase of the steel. The modeling results revealed that the initial microstructure of the steel significantly influences the dislocation accumulation and annihilation rates as well as the load partitioning between austenite and martensite phases. Despite a lower initial dislocation density than the pre-deformed conditions, the mill annealed condition revealed a higher capacity (approximately two orders of magnitude) for dislocation accumulation in the austenite phase. The initial volume fraction of strain-induced martensite phase and the initial dislocation density of pre-deformed 304 SS are governed by the degree of pre-deformation and pre-deformation temperature, either below or above Md temperature (where Md is defined as the temperature above which plastic deformation does not result in austenite to martensite transformation). It is observed that storage, as well as annihilation rates in the austenite phase, are higher for the steel having a higher initial volume fraction of martensite and dislocation density. Though the pre-deformation altered the evolution of martensite volume fraction, the steel exhibited a minor variation in dislocation accumulation capability in the martensite phase for different conditions.

Investigating the effects of pre-deformation and aging conditions on localised corrosion behaviour of aluminium alloy 6061 via electrochemical polarisation

ABSTRACT Corrosion behaviour and intergranular corrosion (IGC) sensitivity of 6061 aluminium alloy were investigated using electrochemical polarisation. A 10% tensile stretching was carried out on as-quenched 6061 alloys to understand the effect of pre-deformation on precipitation during subsequent aging treatments. Grain boundary (GB) TEM micrographs were taken to correlate the relationship between the changes in microstructure and corrosion resistance. For artificially aged 6061 alloys, the introduction of the 10% pre-deformation reduces the corrosion rate, but is unable to change their IGC susceptible nature. Conversely, pre-deformation dramatically reduces the pitting depth and pit distribution of naturally aged 6061 alloys. Needle-like β″ precipitates were found homogeneously distributed in the matrix and the GB areas in the pre-deformed and naturally aged 6061-T3. It is suggested that strain-induced dislocations and misorientation sites cover the lack of vacancies around the as-quenched GBs, therefore promote homogeneous precipitation across the GBs which improves resistance against localised corrosion.

Ferrite phase transformation in dual-phase steel under shock loading

Microstructural changes and ferrite phase transformation under shock loading, between 8.5 GPa and 17.5 GPa, in a hot-rolled Lean Duplex Stainless Steel (commercially known as LDX 2101) were investigated in as-received and pre-deformed conditions. The latter condition was considered to distinguish classical deformation twins at high strain rates from those associated to the reversible ferrite phase transformation. Plate impact experiments were used to introduce compressive shock loading at peak stresses below and above the stress threshold of the ferrite phase transformation, 13 GPa. Effects of shock loading were also examined by compressing shocked samples quasi-statically and comparing their response with those tested in the as-received condition. The microstructural examinations revealed that the ferrite in LDX 2101 experienced a reversible phase transformation at a peak stress of ~17 GPa. The fingerprints for this transformation were {112}<111> primary twins and {332}<113> primary and secondary twins. In addition, the yield stress of the sample pre-shocked at ~17 GPa showed a considerable increase (⁓150 MPa) compared to the flow stress in as-received conditions.

Precisely Controlling the Output Force of Hydrogel Actuator Based on Thermodynamic Nonequilibrium Temporary Deformation.

Self-shaping hydrogel actuators have promising applications in various fields. However, one hydrogel actuator can generally access only one specifically predefined deformation and output force, which are determined by its thermodynamic equilibrium swelling state under external stimuli. Here, we present a simple yet versatile strategy for precisely programming the output force/energy of dual-gradient hydrogel actuators. The strategy is based on thermodynamic nonequilibrium snapping deformations occurring during the recovery process of predeformed dual-gradient hydrogel actuators in low-temperature water. The output force/energy of such thermodynamic nonequilibrium snapping deformation is highly associated with predeformation conditions of the hydrogel actuators, which increases with the increase of the predeformation temperature or time. In consequence, just by adjusting the predeformation conditions of the dual-gradient hydrogel actuators, their output force, energy, and power can be modulated precisely and continuously during the snapping deformation. The as-prepared hydrogel actuators can not only be used as smart lifters and grippers with ultrahigh accuracy of weight identification but also act as smart switches in the timing circuits with precisely adjustable operating time, paving the way for the design of a new generation of actuation materials.

Effects of pre-deformation mode and strain on creep aging bend-forming process of Al−Cu−Li alloy

Abstract The bending deformation method was adopted to characterize the creep deformation behavior of Al−Cu−Li alloy in the creep aging forming (CAF) process based on a series of CAF tests, and the evolution laws of its mechanical properties and microstructures under different pre-deformation conditions were studied. The results show that the bending creep strain characterization method can intuitively describe the creep variation. With the increase of the pre-deformation strain, the creep strain of the specimen firstly increases and then decreases. The increase of the pre-deformation strain can promote the course of aging precipitation, and improve the formed alloy’s tensile properties at room temperature, the Kahn tearing properties, and the fatigue propagation properties. Pre-rolled specimens produce a slightly weaker work hardening than pre-stretched specimens, but they also create a stronger aging-strengthening effect; thus the strength, toughness and damage performance can be improved to some extent. Among all the types of specimens, the specimen with 3% rolling after CAF treatment has the best comprehensive mechanical properties.

Effects of pre-strain on the surface residual stress and corrosion behavior of an Al-Zn-Mg-Cu alloy plate

The surface residual stress as well as corrosion behavior of an Al-Zn-Mg-Cu alloy plate is investigated under various pre-deformation conditions via X-ray diffraction, transmission electron microscopy, laser scanning microscope, open circuit potentials and electrochemical impedance spectroscopy measurements. Results reveal that the major extent of residual stresses from quenching can be relieved by 2% pre-strain, while the surface residual stress condition transforms from compression to tension if pre-strain exceeds 4%. During aging, the dislocations introduced by pre-strain promote the nucleation of large η phase and accelerate the coarsening of η′ precipitates. With increasing the pre-strain level, the number density of coarse η phase both at grain boundary and within matrix increases, resulting in a decrease in the corrosion resistance. In addition, the immersion test reveals an acceleration of corrosion when tensile residual stress exists in the surface of plate.

The effect of heavy deformation on the precipitation in an Al-1.3Cu-1.0Mg-0.4Si wt.% alloy

This work has investigated the effect of the combination of natural ageing and 80% pre-deformation after solution heat treatment on precipitation during subsequent artificial ageing in an Al-1.3Cu-1.0Mg-0.4Si wt.% alloy. It was found that a combined use of atomic resolution aberration corrected high-angle annular dark-field scanning transmission electron microscopy and scanning precession electron diffraction enabled a detailed characterisation of precipitates in heavy pre-deformed materials. The dominant phase in the undeformed condition was the L phase. L was also found to be nucleated in the undistorted regions of the Al matrix in the pre-deformed conditions. Two phases with high aspect ratios were nucleated on dislocations: The C phase and a previously reported phase, which we named here the ‘E phase’. The crystal structure of E was solved experimentally as monoclinic with core composition Mg6Al2Si2Cu4, supported by density functional theory calculations. It was determined that the order of pre-deformation and natural ageing had an influence on the relative fractions of the aforementioned phases formed during artificial ageing. An increased fraction of C+E relative to L was found in the condition where the pre-deformation was applied after natural ageing as compared to the condition where the pre-deformation was applied before natural ageing.

Analysis of empirical relation between microstructure, texture evolution and fatigue properties of an Al-Cu-Li alloy during different pre-deformation processes

The microstructure and fatigue properties of Al-Cu-Li alloy sheets were investigated respectively under the conditions of without pre-deformation, 3% pre-stretching deformation and 8% pre-rolling deformation utilizing scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) in present work. Results show that the intensive Goss texture and relatively weaker Brass, Cube texture were formed in without pre-deformed alloy after aging treatment. The pole density level of Goss texture was decreased remarkably and the intensity of Brass, Cube texture was increased lightly after 3% pre-stretching deformation and 8% pre-rolling deformation. The magnitude order of fatigue crack propagation (FCP) rate of the alloy under different pre-deformation conditions was dadNpre−rolling > dadNpre−stretching > dadNnon−predeformation in stage II (Paris regime). The combined contribution of T1 phase with different size, amount and the intensity of Goss texture is the main factors affecting the FCP rate of Al-Cu-Li alloy.

Microstructure and Mechanical Properties of Cryorolled Aluminum Alloy AA2219 in Different Thermomechanical Processing Conditions

In the present study, aluminum alloy AA2219-T87 bars were cryorolled to various amounts of deformation in two pre-deformation conditions: (1) without solution treatment i.e., as-received T87 (WST-CR) and (2) with solution treatment (ST + CR). The solution treated and cryorolled bars were further annealed leading to a third condition: (3) solution treated, cryorolled, and annealed (CR + Annealed). Room-temperature mechanical properties have been evaluated for all three cryorolled conditions. Significant improvement in the 0.2 pct YS and UTS values was obtained for bars cryorolled to cross-sectional area reduction of more than 50 pct in the solution-treated condition (ST + CR), whereas for bars cryorolled in the without solution-treated condition (WST-CR), only an improvement in the 0.2 pct YS was observed. Cryorolling did not enhance the precipitation kinetics nor did it increase the response of the alloy to aging. The mechanical properties were correlated to the microstructures obtained by optical and transmission electron microscopy. Microstructural evolution in the ST + CR condition indicated gradual progression of the principal restoration mechanism from dynamic recovery (DRV) to dynamic recrystallization with an increasing amount of plastic deformation. Transmission electron microscopy of WST-CR and ST + CR specimens showed an increase in dislocation density as a function of the amount of deformation indicating suppression of DRV at cryogenic temperatures. Cryorolling in the solution-treated condition to cross-sectional area reduction of more than 50 pct (ST + 70 pct CR) was found to impart an optimum combination of strength and percent elongation in the present study.

Static recrystallization simulations by coupling cellular automata and crystal plasticity finite element method using a physically based model for nucleation

This study presents a 2D cellular automata simulation of static recrystallization (SRX) arising from the subgrain growth in single-phase material following cold deformation by coupling with a crystal plasticity finite element (CPFE) method. The spatial distribution of the stored deformation energy was obtained by CPFE simulation, based on which the initial deformed microstructure consisting of nonuniformly distributed subgrains was predicted. To simulate grain/subgrain growth during annealing, a curvature-driven mechanism was used, in which the grain/subgrain boundary energy and mobility were misorientation-dependent. On the SRX nucleation, a physically based model using critical subgrain size as criterion was adopted, which could provide better insight into the recrystallization nucleation mechanism involving grain boundary bulging. Simulations under different pre-deformation conditions were performed, and the influence of strain rate and strain on the SRX microstructure evolution and the transformation kinetics were investigated. Results show that deformation at higher strain rate can accelerate the SRX kinetics, and the SRX behavior depends more on the deformation state of individual grain than the nominal strain due to the relatively small computational domain.

Influence of Ultrasonic Treatment on Shape Memory Effects in Ti-50,4at.%Ni Alloy

In the present study we investigate the effect of ultrasonic treatment on the functional properties of Ti 50,4at.%Ni alloy after the processing in free and pre-deformed conditions. It is shown that the shape memory effect and its realization peculiarities depend on the parameters and conditions of ultrasonic influence. Ultrasonic treatment of preliminary deformed TiNi alloy in pre-deforming conditions promotes the reduction of strain restoring at the subsequent heating through the temperature interval of reverse martensite transformation. I. e. some setting of induced strain occurs during the ultrasonic treatment of material in pre-deforming conditions. In the specimens after ultrasonic treatment, it is observed the extension of shape recovery temperature range in the first thermal cycle, as well as the dependence of strain recovery temperature dynamics on the power of ultrasonic influence. Also it is established that ultrasonic treatment helps to increase the shape memory effect.

On the low-cycle fatigue response of pre-strained austenitic Fe61Mn24Ni6.5Cr8.5 alloy showing TWIP effect

The low-cycle fatigue behavior of a high manganese austenitic alloy showing TWIP (Twinning-Induced Plasticity) in its homogenized as-received (AsRec) and in pre-strained conditions was determined. Pre-strains were applied both in tension and compression. The fatigue experiments, conducted in total strain control under fully reversed push–pull loading, were accompanied by thorough microstructural investigations utilizing electron backscatter diffraction and transmission electron microscopy. The results clearly lay out the different microstructural evolutions during cyclic loading of the AsRec and the pre-deformed conditions. Cyclic hardening prevails for the AsRec condition due to the increase in dislocation density and the subsequent rearrangement of dislocations into labyrinth and cell structures upon further cycling, whereas pronounced softening accompanied by a decrease in absolute value of mean stress dominated the cyclic deformation response of the pre-deformed conditions.

Influence of prestraining on the high-temperature fatigue behaviour of polycrystalline nickel-based superalloys in the VHCF range

The influence of a monotonic predeformation at room temperature on the very high cycle fatigue (VHCF) behaviour was studied on polycrystalline nickel-based superalloys (Nimonic 75 and Nimonic 80A) in three characteristic precipitation (precipitationfree, peak-aged and overaged) and different predeformation conditions. Isothermal fatigue tests were executed at temperatures up to 800 °C. With increasing intermediate temperature (400 °C–600 °C) the effect of predeformation becomes weaker which might partially be explained by the beginning of a recovery of the dislocation arrangement as well as attributed to effects not related to the strain hardened microstructure, such as the formation of oxide layers and the materials notch sensitivity for the testing conditions used given pronounced surface roughening due to the prestraining. Isothermal cyclic deformation at 800 °C revealed a pronounced decrease of cyclic lifetime for all precipitation conditions with or without a mechanical prehistory. Transmission electron microscopy was carried out in order to characterize the influence of the microstructure, the resulting dislocation slip behaviour and the relevant dislocation/particle interaction mechanism on the VHCF behaviour.

The role of monotonic pre-deformation on the fatigue performance of a high-manganese austenitic TWIP steel

The fatigue performance of a high-manganese austenitic steel featuring the twinning-induced plasticity (TWIP) effect was investigated in both thermomechanically treated rolled and pre-deformed conditions. A thorough set of mechanical experiments and microstructural analyses demonstrated that microstructural evolutions during high-strain monotonic and low-strain cyclic deformations differ significantly. Specifically, a high twin density is obtained as a result of monotonic deformation, and a low twin density, yet a noticeable increase in twin thickness, is observed in the fatigued samples. Furthermore, the fatigue performance of the pre-deformed TWIP steel samples is superior to that of the as-received steel, which is attributed to the enhanced interaction of glide dislocations with twins of increased density owing to the monotonic pre-deformation.

High Temperature Mechanical Spectroscopy in Ordered Ni3(Al, Ta)

Mechanical loss measurements were performed on polycrystalline and single crystalline samples (of three different orientations) of a Ni 3 (Al,1%Ta) alloy with the L12 ordered structure. Measurements were conducted in torsion pendula, on as-cast samples and samples predeformed either at 300 K or at 1300 K, and revealed the occurrence of two main phenomena: (a) The presence of a well-defined internal friction peak at a temperature of about 950 K for a frequency of 1 Hz. This relaxation peak has an activation energy of about 3 eV and its amplitude is strongly dependent on sample orientation and predeformation conditions. (b) An internal friction background, which amplitude at high temperatures (above 1100 K) mainly depends on strain amplitude and predeformation conditions. Both phenomena appear closely related to the presence of point defects, to the complex dissociation mode of superdislocations and to the change in dislocation mechanisms occurring at the peak temperature in flow stress (about 800 K) in relationship with a change in active slip systems.

Lattice Defects Affecting Moisture-Induced Embrittlement of Ni-based L12 Ordered Intermetallics

ABSTRACTMoisture-induced embrittlement of Ll2 alloys (such as Ni3(Si,Ti) and Ni3AI) is observed by tensile test and SEM fractography. A variety of microstructures were prepared by selecting pre-deformation and heat treatment conditions. It is shown that tensile ductility and the associated fractography depend on structure as well as test atmosphere. Well-annealed specimens are susceptible to moisture-induced embrittlement while pre-deformed specimens are resistive to moisture-induced embrittlement. Also, this embrittlement is generally sensitive to the heat treatment scheme preceded by the pre-deformation. Results indicate that the embrittlement occurs when hydrogen is enriched on grain boundaries. On the other hand, the embrittlement can be suppressed when hydrogen is trapped at lattice defects such as dislocations and vacancies. These results are discussed in association with the kinetics of hydrogen in the pre-deformed microstructure.