Occurrence Of Dynamic Strain Aging Research Articles

The Effects of Strain Rate and Anisotropy on the Formability and Mechanical Behaviour of Aluminium Alloy 2024-T3

The present study focuses on the mechanical behaviour and formability of the aluminium alloy 2024-T3 in sheet form with a thickness of 0.8 mm. For this purpose, tensile tests at quasi-static and intermediate strain rates were performed using a universal testing machine, and high strain rate experiments were performed using a split Hopkinson tension bar (SHTB) facility. The material’s anisotropy was investigated by considering seven different specimen orientations relative to the rolling direction. Digital image correlation (DIC) was used to measure specimen deformation. Based on the true stress–strain curves, the alloy exhibited negative strain rate sensitivity (NSRS). Dynamic strain aging (DSA) was investigated as a possible cause. However, neither the strain distribution nor the stress–strain curves gave further indications of the occurrence of DSA. A higher deformation capacity was observed in the high strain rate experiments. The alloy displayed anisotropic mechanical properties. Values of the Lankford coefficient lower than 1, more specifically, varying between 0.45 and 0.87 depending on specimen orientations and strain rate, were found. The hardening exponent was not significantly dependent on specimen orientation and only moderately affected by strain rate. An average value of 0.183 was observed for specimens tested at a quasi-static strain rate. Scanning electron microscopy (SEM) revealed a typical ductile fracture morphology with fine dimples. Dimple sizes were hardly affected by specimen orientation and strain rate.

Absence of dynamic strain aging induced by precipitation in 316 austenitic stainless steel during thermal aging at 750 °C

Dynamic strain aging (DSA) has long been seen in the solution-treated austenitic stainless steels, but DSA effect is affected after long-term exposure to high temperature in the fourth-generation nuclear reactors. This study investigated the effect of precipitates on the DSA effect of 316 austenitic stainless steel after accelerated aging at 750 °C for 10, 100 and 1000 h, which is used to simulate the long-term microstructural evolution at service temperature. A gradual reduction in the DSA effect is found with an increase in the grain boundary precipitates after aging for 10 and 100 h. The frequency of the interactions between dislocations and grain boundaries decreases because moving dislocations are blocked by the precipitates formed at the grain boundaries. Meanwhile, the grain boundary precipitates occupy part of the grain boundaries, reducing the probability of dislocation emission from grain boundary. As the aging time prolongs to 1000 h, the newly-formed intragranular σ phase acts as an obstacle to the dislocation movement, resulting in an increase in waiting time (tw-AG1000). Also, Cr atoms can be drained from mobile dislocation into σ phase, leading to an increase in the aging time (ta-AG1000) required for pinning the arrested dislocations. As a result, the critical strain for the occurrence of DSA significantly increases, leading to the absence of DSA phenomenon.

Low‐Cycle‐Fatigue Performance of Stress‐Aged EN AW‐7075 Alloy

The effect of a novel heat treatment, that is, aging under superimposed external stress, on the fatigue performance and microstructural evolution of a high‐strength aluminum alloy (EN AW‐7075) is presented. Stress aging, a combination of heat treatment and superimposed external stress, can enhance the mechanical properties of EN AW‐7075 under monotonic loading due to the acceleration of precipitation kinetics. Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) reveal that a longer aging time and the presence of superimposed stress both promote the formation and growth of precipitates, that is, the precipitation of strengthening η´ precipitates. This is confirmed by differential scanning calorimetry (DSC) heating experiments of stressless and stress‐aged states. Furthermore, stress aging leads to a reduction of dimensions of precipitate‐free zones near grain boundaries. Cyclic deformation responses (CDRs) and half‐life hysteresis loops are evaluated focusing on the low‐cycle fatigue (LCF) performance of different conditions. A noticeable cyclic hardening seen in case of the specimens aged for a short time indicates the occurrence of dynamic strain aging (DSA). Eventually, stress aging allows for an enhancement of the monotonic mechanical properties of EN AW‐7075 without degrading the cyclic performance in the LCF regime.

Effect of rolling temperature on the occurrence of dynamic strain aging of Inconel 617 superalloy

Inconel 617 specimens were hot rolled at 950 °C, 1050 °C, and 1150 °C to examine the effect of thermomechanical processing on the occurrence of dynamic strain aging (DSA), followed by performing the tensile tests at temperature range of 350 °C–750 °C with the strain rates of 5 × 10−4 s−1, 5 × 10−3 s−1, and 1 × 10−2 s−1. The microstructural evolution was studied by an optical microscope, a scanning electron microscope (SEM), and differential scanning calorimetry (DSC). The stress-strain curves were analyzed in terms of serration intensity and types. The serrated flow at temperature range of 450 °C–750 °C underwent changes by the strain rate and the temperature, and the serration type changed from types A + B and B to type C. The transformation of Portevin-Le Chatelier (PLC) effect from normal to the inverse PLC effect was observed at a temperature higher than 550 °C. The activation energy was calculated and it was found that the diffusion of Cr and Mo substitutional atoms are mainly responsible for the DSA effect in hot rolled Inconel 617 superalloy. The hot rolling temperature was also found to have a significant impact on the occurrence of DSA. Moreover, it was indicated that as the hot rolling temperature increases from 950 °C to 1150 °C, the occurrence of dynamic strain aging is intensified.

Cyclic deformation and dynamically induced short-range ordering in small particles reinforced Al composite

Cyclic deformation of an Al-Cu-Mg composite strengthened by small non-shareable particles was firstly investigated through strain controlled low-cycle fatigue (LCF) tests. In comparison with the reported Al-Cu-Mg composites, the in-situ TiB2/Al-Cu-Mg composite presented higher fatigue life at all the tested strain amplitudes. The composite exhibited cyclic hardening response, which was contributed by non-shareable particles, dislocations and dynamically deformation-induced short-range orderings in the Al matrix. Considering plastic strain evolution, the cyclic hardening model was established and well fitted with experimental results. When cyclic loading was controlled at higher strain amplitudes, the serrated flow occurred on stress-strain hysteresis loops and then it disappeared after the first few cycles related to the occurrence of dynamic strain aging. Onset of the stress serration on stress-strain hysteresis loop was greatly dependent on the strain amplitude rather than cumulative plastic strain. Finally, the correlative cyclic hardening model of small particles reinforced Al composite was analytically discussed based on microstructure evolution and cyclic stress-strain responses.

Comprehensive analysis of evolution of serrated hysteresis loops of Alloy 617 M during low cycle fatigue

Dynamic strain aging (DSA) has a pronounced effect on low cycle fatigue (LCF) behavior of materials. One of the manifestations of occurrence of DSA under LCF is serrated hysteresis loops (HLs). Analysis of the evolving serrated HLs under LCF loading has a large potential to provide information on the underlying principles of the occurrence of DSA. However, as manual analysis of serrated HLs is cumbersome, it has not been studied so well. A methodology for automated analysis of the serrated flow behavior under LCF loading is developed and used in the present paper for comprehensive analysis of evolution of DSA behaviour in Alloy 617 during low cycle fatigue. For the first time, the magnitude of the evolving serrations both within a cycle and through the entire fatigue life has been represented as 2D stress drop maps to visualize the scale of DSA occurrence at any moment within the entire fatigue event for a given strain amplitude-temperature combination. Quantitative characterization of serrated behaviour is reported as a function of fatigue cycle for different total strain amplitude and temperature combinations. Critical parameters for the initiation of DSA determined by stress drop and strain jump methods indicate a progressive nature, typical of fatigue deformation. Pronounced DSA activity at 773 K as compared to that at 573 K and 973 K is also reflected in terms of micro-strain in deformed specimens as observed by electron back-scatter diffraction (EBSD) analysis. • Methodology is proposed for comprehensive study of evolution of DSA during LCF • Visualization of scale of DSA at any moment within entire fatigue event as 2D maps • Dynamic nature of DSA with strain cycling under LCF is observed • Optimum plastic strain-temperature-cycle number combination only initiates DSA • Most conducive temperature for DSA occurrence in Alloy 617 M during LCF is 773 K

Occurrence of dynamic strain aging in intercritically annealed low carbon high aluminum medium manganese steels

Medium manganese steel grades heat treated with the quench and partition (Q&P) treatment have shown promising results of strength and formability, but the number of studies on high aluminum medium manganese Q&P steels still remains rather limited. Consequently, this study investigates the mechanical properties, behavior and microstructures of a low carbon-high aluminum medium manganese (3%) steel after intercritical annealing and subsequent Q&P heat treatments with varying heat treatment parameters. Samples that were intercritically annealed above 760 °C showed an ultimate tensile strength (UTS) of around 1500 MPa with uniform elongation values of approximately 10%. On the other hand, the samples annealed at 740 °C showed somewhat lower UTS values (in the range of 1000 … 1200 MPa) but much higher uniform and total elongations, i.e., considerably improved formability. However, the stress-strain curves of the samples annealed at 740 °C showed rather severe serrations that can be connected to the dynamic strain aging (DSA) phenomena, which limits the usability of the steel especially in applications where good surface quality of the deformed (sheet) is required. Therefore, the main focus of this article is on the samples annealed at temperatures close to A1, where DSA serrations tend to appear. The evidence gathered from these investigations leads to the conjecture that the DSA serrations are due to the free carbon and nitrogen originating from the dissolution of M(C,N) and M2(C,N) type carbides, which were formed during the intercritical annealing at temperatures producing less than 50% of the austenite phase. Other reasons for the occurrence of DSA in the current test materials can be the scarcity of martensite and the morphology of the retained austenite.

Deformation behaviour and strain rate sensitivity of 304L SS at elevated temperatures

ABSTRACT Tensile deformation behaviour of nuclear grade 304 L SS (PHWR calandria vessel material) was presented at temperatures 300 K to 1123 K and at three different strain rates. The deformation behaviour is influenced by the strain-induced martensitic transformation at 300 K, the occurrence of dynamic strain ageing (DSA) at intermediate temperatures (573–873 K) and the dominance of strain softening at high temperatures (973–1123 K). The occurrence of DSA caused anomalies in flow behaviour and ductility for the steel. At high temperatures, strain softening manifested in a rapid decrease in flow strength with increasing temperature and decreasing strain rate. Further, instantaneous (mi) and quasi-steady state strain rate sensitivity (ms) with strain were evaluated using strain rate jump tests. At low and DSA temperatures, the initial and quasi-steady transient response differs. Contrary to this, the value of mi is equal to ms at high temperatures.

Macro-micro behaviors of Ti–22Al–26Nb alloy during warm tension

In this paper, the plastic flow rules and fracture evolution mechanisms of the nearly O + B2 Ti–22Al–26Nb alloy during warm tension have been studied within a wide temperature range of 20–800 °C. The macro-micro deformation behaviors of the material have been investigated by means of SEM, EBSD and TEM. It is found that the stress-strain curve at 400 °C exhibits serrated patterns, indicating the occurrence of dynamic strain aging at mild temperature. The overall yield strength decreases and the uniform elongation increases with the temperature in general. However, an unexpected peak of yield strength and also an unexpected valley of uniform elongation are exhibited at 600 °C. Additionally, the uniform elongation shows a positive correlation with strain rate at 600 °C. With the comprehensive analyses of fracture surface characteristics, the morphological variation of the constituent phases and the dislocation structure evolution, the causations of the above phenomena are further explained as follows. The B2 phase is mainly responsible for deformation coordination between O laths with the original {110}B2∥(001)O orientation barely changed, and act as a media for propagating localized slip deformation to O grains. The abnormal mechanical responses at 600 °C are mainly attributed to the change of fracture mode caused by the precipitation of fine acicular O grains, while the softening mechanism at 800 °C is mainly dominated by the dynamic globularization of the O phase.

Cyclic deformation response of austenitic Ni-based alloy: Mechanical behavior, internal stress evolution and microstructural feature

Cyclic deformation response of an austenitic Ni-based alloy was investigated by symmetrical/asymmetrical strain cycling tests at room temperature (RT) and 350°C. The effects of strain amplitude/ratio and ambient temperature on the cyclic deformation behavior were discussed in terms of microstructural features and internal stresses. Results indicate that the cyclic hardening/softening at RT is mainly attributed to the increase/decrease in back stress. Whilst at 350°C, the contribution of effective stress to cyclic deformation response becomes important due to the planar slip promoted by the occurrence of dynamic strain aging (DSA) throughout the fatigue process. Accordingly, the continuous cyclic hardening at 350°C comes from the combined action of back stress and effective stress.

Dynamic strain aging in DP1000: Effect of temperature and strain rate

The present study reports on an extensive experimental campaign performed to identify the occurrence of dynamic strain aging (DSA) in a fine-grained DP1000 steel. Tensile tests are performed covering 7 orders of strain rate, i.e., 0.0001 s-1 to 1080 s-1, and temperatures ranging from −40 °C to 400 °C. The test results are thoroughly analysed with particular attention to typical features of DSA, such as serrated flow, thermal hardening, negative strain rate sensitivity and blue brittleness. In addition to the plastic strain, DSA is sensitive to both temperature and strain rate. DSA effects are most dominant at higher temperatures and lower strain rates. However, even at the highest strain rate, traces of DSA are found in DP1000. At temperatures below 100 °C, no DSA is observed. The way and extent to which DSA manifests itself depend on the specific combination of temperature and strain rate. Analysis of the serrations stimulate the hypothesis that quasi-periodic dislocation cells might lie at their origin. In addition, scanning electron microscopy images of the fracture surfaces reveal finer and shallower dimples with flat features in the dynamic strain aging regime.

On the fatigue and dwell-fatigue behavior of a low-density steel and the correlated microstructure origin of damage mechanism

The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damage mechanisms of Fe–Mn–Al–C lightweight steel. Surprisingly, alteration in loading mode from monotonic to cyclic induces reversible dislocation movement and facilitates the occurrence of dynamic strain aging. Additionally, applying dwell time by an acceleration of strain aging intensified stress asymmetry during dwell fatigue. The occurrence of strain aging has a bilateral effect on the crack initiation and growth. On one hand, strain aging stimulates twin formation and retards fatigue crack initiation, however, on the other hand, reduces hardening capacity, restricts the plastic deformation and facilitates crack propagation.

Influence of C and N on Strain-Induced Martensite Formation in Fe-15Cr-7Mn-4Ni-0.5Si Austenitic Steel.

In this study, the effect of interstitial contents on the mechanical properties and strain-induced martensite formation in an austenitic stainless steel was investigated. The mechanical properties of solution annealed Fe-15Cr-7Mn-4Ni-0.5Si-(0.01-0.2)N-(0.01-0.2)C concentrations in weight percent stainless steels were studied using room temperature tensile tests. All three alloys used in the present study have a sum content of C + N of about 0.2 wt.%. To verify the influence of C and N on deformation behavior, microstructural investigations are performed using light optical microscopy, scanning electron microscopy, and magnetic and hardness measurements. Moreover, strain-induced α′-martensite nucleation was characterized by scanning electron microscope using EBSD. In the present alloy system, carbon provides a stronger austenite stabilizing effect than nitrogen. Hence, the smallest amount of strain-induced α′-martensite was formed in the steel alloyed with 0.2 wt.% C. It also exhibited the optimal mechanical properties, including the highest ultimate tensile strength (1114 MPa), uniform elongation (63%), and total elongation (68%). Moreover, the interstitial content influences the occurrence of dynamic strain aging (DSA), which was only observed in the steel alloyed with carbon. With increasing C content, the triggering strain for DSA decreases, which can be confirmed by in situ magnetic measurements during tensile testing.

Saturation stress based models and their applicability to tensile flow behaviour of superalloy 617M

Four different saturation stress based models were employed to investigate the uniaxial tensile deformation behaviour of boron added Alloy 617M. Voce relationship described the tensile flow behaviour of the alloy to a reasonable extent at high strain levels over the temperatures range of 300 K–1023 K. On the contrary, the employed macroscopic Estrin-Mecking model could not provide an adequate description to flow stress versus true plastic strain data at different temperatures. In addition to Estrin-Mecking and Voce relationships, two different saturation models (Model-I and Model-II) were empirically developed and used in the present investigation. The developed relationships provide a better description of Alloy 617M work hardening behaviour compared to the existing models. Relative applicability of the different relationships has been verified based on their predictive capability of the tensile properties such as true yield and ultimate tensile strength and true uniform plastic strain. It was found that the predicted tensile properties using Model-II are comparable with the experimental data than those prediction obtained from the other models. The predicted shear modulus compensated saturation stress exhibited a peak value at 923 K due to the occurrence of dynamic strain ageing as well as precipitation strengthening. In the temperatures ranging from 473 K to 973 K, the observed lower values in the temperature dependent rate constant associated with the Model-II suggested the reduced activity of dynamic recovery at intermediate temperatures compared to 300 K and 1023 K. The rapid decrease in saturation stress, true ultimate strength and uniform plastic strain is the clear indication of the dominance of dynamic recovery effects at 1023 K for the Alloy 617M.

Dynamic strain aging behavior of accident tolerance fuel cladding FeCrAl-based alloy for advanced nuclear energy

The Fe-13Cr-4Al alloy has become a promising candidate material for accident tolerance fuel (ATF) cladding of light-water reactors (LWRs) due to its excellent oxidation resistance to high-temperature water vapor. However, the tensile deformation behavior of the Fe-13Cr-4Al alloy under different strain rates at different temperatures is still unclear. In the present study, the tensile behavior and deformed microstructure of the Fe-13Cr-4Al alloy were investigated at strain rates from 5 × 10–4 to 1 × 10–2 s−1 in the temperature range from RT to 600 °C. Serrations were observed in the tensile engineering stress–strain curves of the intermediate temperature ranging from 300 to 450 °C at all the three strain rates, indicating the occurrence of dynamic strain aging (DSA). As the strain rate increased, the temperature range where serrated plastic flow occurred shifted to the high temperature regime. Serrated plastic flow occurred after a certain critical plastic strain, and the critical plastic strain decreased with the increase in temperature and increased with the increase in strain rate. In the DSA regime of the Fe-13Cr-4Al alloy, the plateau in the yield strength, ductility minima, negative strain rate sensitivity, the peaks of strain hardening exponent and work hardening rate were observed, which were the typical manifestations of the DSA. The activation energies of serrated plastic flow evaluated by three different methods were 157 ± 35, 92 ± 10 and 93 ± 10 kJ/mol, respectively. According to the values of activation energy, the controlling mechanism responsible for the DSA of the Fe-13Cr-4Al alloy was found to be the interaction between substitutional aluminum atoms and dislocations. The fracture surfaces of the specimens tested at 400 °C under three strain rates showed the mixed fracture mode, which contained dimples and cleavage facets. The tensile samples at 600 °C showed a completely ductile fracture mode with large and deep dimples. A large number of dislocation tangles in the microstructure of the specimens tested at 400 °C under all the strain rates were observed, with a large amount of Fe2Nb Laves particles along the grain boundaries and in the matrix. Dislocation pile-up was also observed around the grain boundaries and second-phase particles. With the increase in the strain rate, the number of subgrains increased, and a clear dislocation cell structure was also observed.

Dynamic behavior and modified artificial neural network model for predicting flow stress during hot deformation of Alloy 925

In this work, the hot deformation behavior of Alloy 925 with intermediate strain rates of 0.01s−1-10s−1 ranging from 900 °C to 1150 °C has been investigated through the isothermal hot compression tests. Some features of the flow curves corresponding to negative strain rate sensitivity have been observed and discussed associated with the microstructural evolution, showing the nucleation mechanism of dynamic recrystallization and the occurrence of dynamic strain ageing. Besides, we have employed two typical constitutive models, namely, Arrhenius model and backpropagation artificial neural network (BP ANN) model to describe the flow behavior, and also developed a modified BP ANN model based on genetic algorithm (GA-BP ANN). The results show that the GA-BP ANN model has the highest accuracy and stability for predicting the flow stress. The correlation coefficient between the predicted and experimental values is 99.99 %, and the average absolute relative error is only 0.54 %. The comparative investigation on the predicted values of different ANN models reflects that GA can reduce the randomness of initial weights and thresholds of BP ANN and also can further increase the accuracy and stability of ANN model. Moreover, the increasing number of input training data can improve the prediction performance of neural network. For a single-layer neural network, 12 hidden layers can effectively ensure the reliability of the constitutive model.

Torsional thermomechanical fatigue behavior of 316LN stainless steel

Abstracts Torsional thermomechanical fatigue behaviors of 316LN stainless steel at various equivalent shear strain amplitudes (0.6%, 0.8%, 1.0%, 1.2%) were investigated. A prolonged secondary hardening occurring exclusively at the strain amplitude of 0.6% was ascribed to the dominance of a planar slip mode in plastic deformation. As a strengthening mechanism, the occurrence of dynamic strain aging at the strain amplitude of 1.0% offset the magnitude of cyclic softening partially. The fatigue-dominated failure behavior with the formation of representative shear-type cracks was assisted by oxidation damage. The preferential oxidation along surface dense slip bands accelerated the microcrack nucleation and crack growth, leading to a bilinearity decrease in fatigue life with increasing strain amplitudes.

Fatigue Damage Mechanism of AL6XN Austenitic Stainless Steel at High Temperatures

By the combination of transmission electron microscope, neutron diffraction and small-angle neutron scattering methods, mechanical fatigue behavior of AL6XN austenitic stainless steel was investigated in the temperature range of 400–600 °C. At 400 °C, in addition to the occurrence of dynamic strain aging, the formation of short-range order was evidenced from the forbidden electron diffraction spot of 1/3 {422} in face-centered cubic (fcc) structure viewed down [111] zone axis, which facilitate the planar slip mode of dislocation and result in the work hardening during the fatigue deformation. The fatigue damage is mainly dominated by the accumulation of planar slip band and the interaction among various slip systems. With increasing temperature, precipitates of chi phase, Laves phase and sigma phase were formed during the fatigue tests at 500 and 600 °C. An increase in precipitation content at 600 °C has also been confirmed by both scanning electron microscope and small-angle neutron scattering analysis. The dislocation pileup originating from the uncoordinated deformation between precipitate and austenitic matrix is an important fatigue damage leading to crack. The continuous cycle softening behavior was also observed on the fatigue curve at 600 °C, which is considered to be caused by dynamic recovery.

Cyclic deformation and cracking behavior of 316LN stainless steel under thermomechanical and isothermal fatigue loadings

Isothermal fatigue (IF) tests at 250 °C, 350 °C and 450 °C, and thermomechanical fatigue (TMF) tests of 316LN stainless steel within the temperature range of 250–450 °C under in-phase (IP) and out-of-phase (OP) mechanical strain-temperature phase angles were carried out. Comparison of the cyclic deformation behavior, microcrack nucleation mechanisms, crack growth and failure behavior were performed between the IF test at 450 °C (IF-450 °C) and TMF tests. Results showed that the cyclic deformation behavior was governed by the combination of thermally activated recovery process, dynamic strain aging (DSA) and nitride precipitations for IF-450 °C and TMF tests. The occurrence of DSA and nitride precipitations including Z-phase and MX phase were found to promote the planar slip of dislocations and enhance the cyclic stress response. The occurrence of recovery process, however, offset the strengthening effects caused by DSA and precipitations, accelerating the softening stage. The intergranular cracking was attributed to the strong impingement of slip bands on severely oxidized grain boundaries, which can be found only on the specimen surface or near-surface regions. The transgranular cracking, resulting from the cyclic slip localization which was characterized by the formation of persistent slip markings (PSMs) in the form of surface intrusions and extrusions was enhanced by the presence of brittle oxide. The ultimate failure was still dominated by the transgranular propagation.

Effects of Dynamic Strain Aging on Strain Hardening Behavior, Dislocation Substructure, and Fracture Morphology in a Ferritic Stainless Steel

Dynamic strain aging at different temperatures and its effects on the strain hardening behavior, dislocation substructure and fracture morphology in a stainless steel grade 430 was investigated. Sheet type specimens were subjected to tensile tests performed at a temperature range of 298 K to 873 K. Subsequently, the strain hardening behavior of the material was depicted via modified Crussard–Jaoul analysis, strain hardening rate, and instantaneous strain hardening exponent curves. Changes in the dislocation substructure during the tests were characterized by means of X-ray diffraction and transmission electron microscopy. Scanning electron microscopy was used to investigate the fracture morphology of the specimens. The results indicated the occurrence of dynamic strain aging from 523 K to 773 K by the presence of the Portevin–Le Chatelier effect. These results were reinforced by the strain hardening analysis that revealed a three staged behavior at most of the studied temperatures, except during the dynamic strain aging regime, which presented an extra stage. Different substructures were observed as a function of the test temperatures: cellular dislocation substructure in the samples deformed at 298 K and 673 K, an array of straight and parallel dislocations in conjunction with a cellular substructure at 673 K, and finally a subgrained substructure with fine precipitates was formed at 873 K. A ductile surface fracture presenting a network of dimples and voids was present at all investigated temperatures, with a dimple size refinement being observed during the dynamic strain aging regime.