PLC Effect Research Articles

Electric pulse-induced suppression of the Portevin – Le Chatelier behavior of 5086 aluminum alloy under uniaxial tension

The electrical-assisted tensile tests of 5086 Al alloy sheets with different current parameters were carried out at room temperature with a frequency of 150 Hz and voltages of 50 V, 60 V and 70 V. It was found that the serrated plastic instability (named PLC effect) was eliminated as the pulse current increased to 150 Hz/60 V, but the PLC effect was observed with 150 Hz/50 V. To distinguish the thermal effect and athermal effects of pulse current on PLC effect, the comparative heating tensile (HT) test in furnace with a temperature rising trend of 150 Hz/60 V was conducted. The obtained curves still showed serrated flow behavior, indicating that the thermal effect was insufficient to suppress the PLC effect. The influence of pulse current on the microstructure and texture evolution was investigated through TEM and EBSD. According to the microscopic analysis, the pulse current accelerated the solute atoms' diffusion and dislocation movement. S orientation {123}<634> of 150 Hz/60 V presented more obvious transformation compared with that of HT specimen. It was illustrated that the athermal effect of pulse current plays an important role in the crystal orientation and suppressing the PLC effect.

On the normal and inverse Portevin–Le Chatelier behavior in hot rolled Inconel 617 superalloy

In the present study the effect of hot rolling process on the normal and inverse Portevin-Le Chatelier behavior was investigated. The hot rolling process was carried out at 950 °C, 1050 °C, and 1150 °C to capture the effect of thermomechanical process on elimination or postponing of dynamic strain aging phenomenon in Inconel 617 during subsequent deformation process. The tensile test was performed within the temperature range between 350 °C and 750 °C at a constant strain rate. The microstructure evaluations were carried out by optical microscope and scanning electron microscope. The serrated flow was observed in the stress-strain curves at specific temperatures. The type of serrations changed from type B to type C at the strain rate of 5 × 10−4 s−1 as the tensile test temperature was enhanced. The change of normal PLC effect to the inverse PLC effect was intensified when the hot rolling temperature was increased; Hence, the inverse PLC effect was observed at 750 °C in the sample which had rolled at 1150 °C. Whilst the serrated flow was not seen at 750 °C in the samples which had rolled at 950 °C and 1050 °C. The critical strain, for the initiation of the serrated flow was found to reduce with the increasing temperature of hot rolling from 950 °C to 1150 °C. After tensile test, the microstructural evaluations revealed the proven substantial role of precipitation of γ′ and the Cr-rich M23C6 carbides in pinning of the mobile dislocations, which led to the inverse PLC effect.

PLC Effect at Different Types of Loading During Static Tensile Testing of Aluminium Alloys

PLC Effect at Different Types of Loading During Static Tensile Testing of Aluminium Alloys

Competing deformation mechanisms in an austenite-ferrite medium-Mn steel at different strain rates

The study of strain rate is of particular significance in automotive applications. Thus, we describe here the mechanical behavior and deformation mechanisms in Fe-0.2C–11Mn–2Al medium-Mn steel in the strain rate range of 2 × 10−4–200s−1. The ultimate tensile strength decreased from 1456 MPa to 1086 MPa with increase in strain rate, the strain rate sensitivity index m of flow stress decreased generally from −0.00154 to −0.0146 with the increase of strain, and the uniform elongation decreased from 39.4% to 33.0% with the increase of strain rate (2 × 10−4-2s−1). However, the elongation increased to 37.5% when the strain rate is further increased to 200s−1. Transformation-induced plasticity (TRIP) effect and PLC effect was dominant at low strain rates (2 × 10−4–2 × 10−3s−1), but at medium strain rates (2 × 10−2-2s−1), TRIP effect was significantly suppressed, twining-induced plasticity (TWIP) effect and softening effect increased gradually with strain rate, which compensated for the loss of TRIP effect. At high strain rates (20–200s−1), TRIP effect, TWIP effect and softening effect enhanced simultaneously, but PLC effect was suppressed with increase in strain rate, contributing to increase in ductility with increasing strain rate. According to the fracture microstructure, it was indicated that normal stress was dominant at low strain rates, while shear stress played an increasingly prominent role at medium and especially high strain rates.

Serrated flow behaviors in a Ni-based superalloy

Serrated flow behaviors in Ni-20Cr-18W alloy were studied under different deformation conditions. It was found that there are no serrations observed on the tensile curves of the alloy at the temperature of lower than 250 °C and the strain rate of 10−3 s−1. As the deformation temperature improves, the serrations first starts with the type A (250 °C) and transfers to the mixed type A + B (300 °C and 400 °C), then to the mixed type B + C (500 °C). Meanwhile, the serration behaviors are closely related with the strain rate. It showed that when the deformation temperature is fixed, the serration curves starts with the type A (10−3 s−1), then transfers to the mixed type A + B (10−2 s−1) and eventually to type D (10−1 s−1) with the increasing strain rates from 10−3 s−1 to 10−1 s−1. Results showed that the serration behaviors of the alloy are related to the normal PLC effect. Combined with the McCormick’s model, the activation energy for the serrated flow behavior in this alloy is calculated to be 103.386 kJ mol−1 and the value of m + β to be 2.514, which suggests that the serrated flow of Ni-20Cr-18W superalloy is related to the interplay between the substitutional solute atoms and the movable dislocations.

Experimental Characterization and Modelling of the PLC Effect in an AlMg-Alloy

In the present work, uniaxial tension tests have been conducted to study the mechanical response of a commercial Al4.5wt%Mg alloy (AA5182). The measurements range from the strain rate of 10-4 to 100 s-1 at room temperature. Digital image correlation (DIC) is also utilized to characterize the heterogeneous deformation of PLC localization. An extremely high camera frame rate (1000Hz) is applied to accurately measure the critical strain of instabilities, especially for tests at high strain rates (&gt;10-1 s-1). The objective of this work has been to evaluate currently existing constitutive and physically based models to see to which extent they can match the experimental findings related to dynamic strain aging, i.e. stress-strain curves, work hardening behavior and critical strain behavior.

Influence of the non-monotonic loading and short stops on the regularities of the jerky flow in the Al-Mg alloy

The aim of the paper is to investigate the influence of the non-monotonic loading and short stops on the spatial-time inhomogeneity due to the jerky flow in the Al-Mg alloy. Experimental study on the regularities of inhomogeneous deformation and the processes of macroscopic localization of the plastic flow due to the Portevin-Le Chatelier effect was carried out. Using the digital image correlation technique the data on the initiation and propagation of the strain bands were obtained. Experimental data were obtained that show the effect of short-term stops and non-monotonic loading on the regularities of inelastic deformation of the Al-Mg alloy when the PLC effect manifests itself. Short stops decrease the level of critical strain when the jerky flow starts. Non-monotonic tests led to a change in the type of the PLC effect and a change in the regularities of the spatial-time inhomogeneity of plastic flow.

Portevin-Le Chatelier effect in austenitic steel Fe-18%Cr-8%Ni

The study of the mechanical behavior of the austenitic Fe-18% Cr-8% Ni steel was carried out in the temperature range of 530°C - 680°C at a strain rate of 1×10−3 s−1, as well as at a temperature of 620°C and strain rates of 1×10−2 s−1 - 1×10−4 s−1. At these conditions, the PLC effect was observed. Type A serrations were observed in the temperature range 530 - 680°C. A decrease in the strain rate at a temperature of 620°C leads to a change in the type of serrations from type A to type B.

Change of Specimen Temperature during the Monotonic Tensile Test and Correlation between the Yield Strength and Thermoelasto-Plastic Limit Stress on the Example of Aluminum Alloys.

This paper presents an attempt to generalize the description of the course of specimen temperature changes during the tensile test and to connect the value of the thermoelasto-plastic limit stress with the value of a clear (physical) or proof strength (offset yield strength) on the example of tests of the following aluminum alloy sheets used in Poland for airplane structures: 2024-T3 and D16 in three grades: D16ATV, D16CzATV, and D16UTV. A thermographic camera was used for specimen surface temperature measurement during the tensile test. The Portevine–Le Chatelier effect (the so-called PLC effect) was observed for tests of specimens cut from sheet plates, which was strongly reflected in the temperature fluctuations. The course of temperature change during tensile tests was divided into four characteristic stages related to the occurrence of a clear or offset yield strength. It was found that if there is a clear yield strength, the value of the thermoelasto-plastic limit stress was greater than this yield strength. If there was an offset yield strength, the value of the thermoelasto-plastic limit stress was lower than this yield strength. The differences in the aforementioned values of individual yield strengths did not exceed several percent. Thus, it can be concluded that the thermoelasto-plastic limit stress determined on the basis of the course of specimen temperature changes during the tensile test is well correlated with the value of the yield strength of the material.

Bacterial Community Dynamics Distinguish Poultry Compost from Dairy Compost and Non-Amended Soils Planted with Spinach

The aim of this study was to determine whether and how poultry litter compost and dairy manure compost alter the microbial communities within field soils planted with spinach. In three successive years, separate experimental plots on two fields received randomly assigned compost treatments varying in animal origin: dairy manure (DMC), poultry litter (PLC), or neither (NoC). The composition and function of bacterial and fungal communities were characterized by the amplicon sequencing of marker genes and by the ecoenzyme activity, respectively. The temporal autocorrelation within and among years was adjusted by principal response curves (PRC) to analyze the effect of compost on community composition among treatments. Bacteria in the phylum Bacteriodetes, classes Flavobacteriia and Spingobacteriales (Fluviicola, Flavobacteriia, and Pedobacter), were two to four times more abundant in soils amended with PLC than DMC or NoC consistently among fields and years. Fungi in the phylum Ascomycota were relatively abundant, but their composition was field-specific and without treatment differences. The ecoenzyme data verify that the effects of PLC and DMC on soil communities are based on their microbial composition and not a response to the C source or nutrient content of the compost.

Modeling serrated flow of SS 316L under dynamic strain aging effect

The serrated behavior of the stress-strain curves also known as PLC effect due to dynamic strain aging of SS 316L is investigated here from room temperature to $$ 550^{\circ}{\text{C}} $$ . Tensile tests were conducted for strain rates $$ 10^{ - 5}{-}10^{ - 2} $$ /s. Serrations of type D, type A and type A+B were observed at different loading conditions. A material model was fitted to the experimental data to simulate the serrated flow in the stress strain diagrams. For this an approach similar to a previous study done with an Al-Mg alloy was followed. However, few changes in the analysis steps were performed to accommodate temperature dependency, a feature not addressed in the earlier work. In addition, the fitment technique was improvised so that the material model could be fit through a substantially smaller set of experimental data, thus improving the speed of the fitting process. Finally, comparisons were done between the experimental data and the results from the simulations. Critical strains from the simulations were found to be of the same order of magnitude of the experimental critical strains and the serrations could also be found in the simulated stress-strain diagrams similar in some aspects to the experimental serrations.

Multiple precipitates and weakened PLC effect in the electro-pulsing treated Al-Mg-Si alloy

In this work, electro-pulsing is executed on the Al-Mg-Si alloy to weaken the PLC effect. It is found that during only 260 ms of electro-pulsing treatment, more completely recrystallized α-Al grains are obtained. Besides, multiple distributed Mg2Si precipitates and Mg4(Si,Cu) clusters combined with regularly distributed dislocation networks are observed in the electro-pulsing treated Al-Mg-Si alloy. Compared with traditionally annealed sample, because of the weakened PLC effect and obviously different substructures, both of the strength and ductility of the Al-Mg-Si are improved via electro-pulsing treatment. This interesting finding laid the foundation of developing new Al-Mg-Si alloy with better properties more efficiently from the viewpoint of deformation behavior, not the microstructure-property relationship.

Microstructure and strain-stress analysis of the dynamic strain aging in inconel 625 at high temperature

Serrated flow is a result of unstable plastic flow, which occurs during tensile and compression tests on some dilute alloys. This phenomenon is referred as the Portevin Le-Chatelier effect (PLC effect). The aim of this research was to investigate and analyze this phenomenon in Inconel 625 solution strengthened superalloy. The tested material was subjected to tensile tests carried out within the temperature range 200-700 °C, with three different strain rates: 0.002 1/s, 0.01/s, and 0.05 1/s and additional compression tests with high deformation speeds of 0.1, 1, and 10 1/s. The tensile strain curves were analyzed in terms of intensity and the observed patterns of serrations Using a modified stress drop method proposed by the authors, the activation energy was calculated with the assumption that the stress drops’ distribution is a direct representation of an average solute atom’s interaction with dislocations. Subsequently, two models, the standard vacancy diffusion Bilby-Cottrell model and the realistic cross-core diffusion mechanism proposed by Zhang and Curtin, were compared. The results obtained show that the second one agrees with the experimental data. Additional microstructure analysis was performed to identify microstructure elements that may be responsible for the PLC effect. Based on the results, the relationship between the intensity of the phenomenon and the conditions of the tests were determined.

The Portevin-Le Chatelier effect with surface potential

Surface potential of AA 3204 undergoing a serrated plastic flow (PLC effect) was monitored in a dilute brine electrolyte under various strain rates at 30 °C. Significant potential bursts at the launch of the stress drop regimes of the flow were revealed. The serration counts and frequency of the PLC effect matched with that of the bursts precisely, and average burst magnitude (ΔV) was found to be directly proportional with that of the stress drops (Δσ). The bursts were attributed to the electrons in strain fields of the slip steps exposed to the electrolyte during the local banding events. The utility of the electrochemical set-up for investigation of the PLC effect and monitoring deformation and damage progress of materials were affirmed.

Influence of thermally activated processes on the deformation behavior during low temperature ECAP

High strength aluminum alloys are generally hard to deform. Therefore, the application of conventional severe plastic deformation methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low temperature deformation in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically deform a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially deformed from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low temperatures, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic deformation at low temperatures. We then discuss how the deformation temperature and velocity influence the occurrence of PLC effects and the homogeneity of the deformed ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low temperature deformed materials as a function of deformation temperature.

Vpliv hitrosti deformacije na pojav PLC in akustično emisijo monokristalov zlitine CuZn30, stiskane pri povišani temperaturi

Vpliv hitrosti deformacije na pojav PLC in akustično emisijo monokristalov zlitine CuZn30, stiskane pri povišani temperaturi

Effect of cryorolling on the mechanical properties of AA5083 alloy and the Portevin–Le Chatelier phenomenon

The effect of cryorolling on the mechanical properties of an AA5083 alloy was investigated. The effect of rolling strain and temperature on the Portevin–Le Chatelier effect experienced by aluminium alloys with magnesium as a major constituent was also studied. Microstructure evolution during room temperature (RT) and cryorolling (LNR) and their effect on the mechanical properties of the AA5083 alloy were studied in detail. The results showed that the hardness values increased as the rolling reduction was increased. Compared to RT rolling, LNR did not have a significant influence. Deformation-induced precipitation particles of Al6Mn during RTR resulted in enhanced mechanical properties compared to LNR conditions. A negligible amount of precipitation was observed due to suppressed adiabatic heating for samples under LNR conditions. The presence of manganese (more than its solid solubility limit) in the test material could have influenced the behaviour of the AA5083 alloy material upon rolling. The Portevin–Le Chatelier effect was clearly observed, and it was noted that with smaller grain size and an increasing dislocation density, the critical strain for the onset of the PLC effect was lowered.

Multiscale Characterization of the Work Hardening Mechanisms in Fe–Mn Based TWIP Steels

AbstractWhen strained in tension, high‐manganese austenitic twinning induced plasticity (TWIP) steels achieve very high strength and elongation before necking. The main hypotheses available in the literature about the origin of their excellent work hardening include deformation twinning and dynamic strain ageing. In order to provide some answers, various experiments at different scales were conducted on Fe–Mn–C steels and the Fe–28 wt%Mn–3.5 wt%Al–2.8 wt%Si alloy. At a macroscopic scale, tensile tests were performed on all the studied grades. It was shown that, though the Fe–Mn–Al–Si based alloy retains very high elongation, the Fe–Mn–C steels properties are even more extraordinary. Tensile tests at different strain rates with the help of digital image correlation were also performed on the Fe–20 wt%Mn–1.2 wt%C steel to study the PLC effect occurring in this type of steel. It is suggested that supplementary hardening could come from reorientation of Mn–C pairs in the cores of the dislocations. At a microscopic scale, the Fe–20 wt%Mn–1.2 wt%C TWIP steel and the Fe–Mn–Al–Si grade were thoroughly investigated by means of in situ TEM analysis. In the Fe–Mn–C steel, the formed twins could also lead to a composite effect, since they contain plenty of sessile dislocations. In the Fe–Mn–Al–Si alloy, mechanical twins are thicker and contain fewer defects, leading to a lower work hardening than the other grade.

Instable Plasticity and Precipitation in AZ91D Magnesium

Instable plasticity, which is normally a consequence of interactions between diffusing solute atoms and dislocations, is observed in AZ91D magnesium at room temperature. Experimental measurements of different heat treatment of AZ91D magnesium were taken to investigate different influence on PLC effect by the presence and structural state of second phase in this study. Tensile specimens were tested at room temperature at a crosshead speed of 0.6 mm/min. The results indicate that some number of large,coherent precipitates prevents serrated flow by way of trapping vacancies, but small precipitates content do not supress it.

Role of phospholipase C and protein kinase C in Aspergillus nidulans during growth on pectin or glucose: Effects on germination and duplication cycle

The effects of PLC and Pkc inhibitors on Aspergillus nidulans depend on the carbon source. PLC inhibitors Spm and C48/80 delayed the first nuclear division in cultures growing on glucose, but stimulated it in media supplemented with pectin. Less intense were these effects on the mutant transformed with PLC-A gene rupture (AP27). Neomycin also delayed the germination in cultures growing on glucose or pectin; however, on glucose, the nuclear division was inhibited whereas in pectin it was stimulated. These effects were minor in AP27. The effects of Ro-31-8425 and BIM (both Pkc inhibitors) were also opposite for cultures growing on glucose or pectin. On glucose cultures of both strains BIM delayed germination and the first nuclear division, whereas on pectin both parameters were stimulated. Opposite effects were also detected when the cultures were growing on glucose or pectin in the presence of Ro-31-8425.