High-temperature Rheological Behavior Research Articles

Research on the Hot Deformation Process of A100 Steel Based on High-Temperature Rheological Behavior and Microstructure.

To obtain the optimal hot deformation process, the rheological and dynamic recrystallization behaviors of A100 steel were researched through isothermal compression tests. Firstly, a Hensel-Spittel constitutive model was established based on the stress-strain curves. Secondly, dynamic recrystallization percentage and grain size models were established to identify the necessary conditions for complete dynamic recrystallization. Finally, microstructural analysis was employed to validate the accuracy of the recrystallization model. The results indicate that the flow stress is highly sensitive to both the strain rate and the temperature, and the HS model demonstrates a high predictive accuracy, with a correlation coefficient of 0.9914. There exists a contradictory relationship between decreasing the average grain size and increasing the recrystallization percentage. The higher the percentage of dynamic recrystallization, the larger the average grain size tends to be. This situation should be avoided when devising the actual processing procedures. The optimal hot working processes for achieving complete dynamic recrystallization and a smaller average grain size are as follows: a strain equal to or greater than 0.6, a temperature between 1193 and 1353 K, and a strain rate between 0.1 and 1 s-1.

Exploring the interplay between thermo-oxidative degradation and asphalt aging in thermoplastic polyurethane-modified asphalt: Mechanisms, properties, and performance evolution

The aging behavior of thermoplastic polyurethane-modified asphalt (TPUMA) is intricate and the mechanisms of its thermal degradation are not well understood. This study examines the viscoelastic, chemical and morphological characteristics of thermoplastic polyurethane modified asphalt (TPUMA) under different aging conditions (RTFOT/PAV). The rheological master curve model of the S parameter was used to analyze the fitting effect on TPUMA, with SBS (styrene–butadiene–styrene) modified asphalt serving as the control group. The relationship between the phase angle plateau area and polymer aging degradation was elucidated. This study investigates the impact of polymer degradation on the high-temperature rheological behavior and medium-temperature fatigue properties of asphalt through temperature sweep, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. Fourier transform infrared spectrometer (FTIR) and confocal laser scanning microscopy (CLSM) are used to qualitatively and quantitatively analyze the chemical composition and morphological evolution of TPUMA during thermal-oxidative degradation. The findings suggest that TPUMA's performance changes in the aging environment is result from the dual coupling effect of polymer degradation and asphalt oxidative hardening. The closely arranged isocyanate (-NCO) and polar component molecular chains in asphalt slow down its oxidation speed, which enhances the aging and deformation resistance of TPUMA. The successful blending of TPU and asphalt was confirmed, and the degradation degree of the polymer was quantitatively characterized by the percentage of the degraded area. The results provide insights to better understand the interplay between TPU degradation and asphalt oxidation.

Probing microstructural heterogeneity of La-based amorphous alloy under versatile mechanical stimuli

The intrinsic structural heterogeneity of amorphous alloy is closely related to the thermodynamics and dynamical behavior, such as relaxation/crystallization, glass transition and plastic deformation. However, the structural information is submerged into the meta-stable disordered long-range structure, which makes it very difficult to explore the structural heterogeneity of amorphous alloy. A mechanical excitation factor is insufficient to effectively describe the heterogeneity of the microstructure in amorphous alloy, particularly the correlation between structure and dynamics. To explore the essence of the structure in amorphous alloy, it is necessary to consider the different mechanical stimuli. La<sub>62</sub>Cu<sub>12</sub>Ni<sub>12</sub>Al<sub>14</sub> amorphous alloy is selected as the model system, dynamic mechanical process is probed by dynamic mechanical analyzer (DMA). The contributions of <i>α</i> relaxation process and <i>β</i> relaxation process are described in the framework of the quasi-point defect theory. Based on the quasi-point defect theory, the <i>α</i>-relaxation and <i>β</i>-relaxation in the La-based amorphous alloy are separated. Tensile strain rate jump measurements are conducted to study the high temperature rheological behavior of amorphous alloy. The contributions of elasticity, anelasticity, and plastic deformation during the homogeneous flow of amorphous alloy are determined within the framework of quasi-point defect theory. The present work aims to reveal the structural heterogeneities of amorphous alloys under the action of dynamics on various temporal scales. The physical background of the activation, propagation and coalescence of defects in amorphous alloy under different mechanical stimuli are reviewed.

High-Temperature Rheological Behavior and Microstructure Evolution of Mo-12Si-8.5B Alloy Reinforced by Layered Mo2TiAlC2 Phase

High-Temperature Rheological Behavior and Microstructure Evolution of Mo-12Si-8.5B Alloy Reinforced by Layered Mo2TiAlC2 Phase

A new constitutive model and hot processing map of 5A06 aluminum alloy based on high-temperature rheological behavior and higher-order gradients

To develop a high-precision constitutive model and hot processing map for 5A06 aluminum alloy, the hot deformation behavior of the alloy was investigated through isothermal compression experiments and microstructure analysis experiments, which were conducted at temperatures ranging from 573 K to 773 K and at strain rates ranging from 0.01 to 10 s−1. Firstly, a new constitutive model, which is based on the partial derivatives of the experimental flow data and does not significantly increase the material parameters, was proposed. Secondly, a comparison and analysis of the predictive accuracies of both the new model and the classic model were conducted. Finally, the new constitutive model was used to construct the hot processing maps of the 5A06 aluminum alloy, and the optimal hot processing parameters were validated through metallographic experiments. The results show that a high-precision constitutive model can be constructed with a small number of material parameters by considering the second-order approximation between logarithmic stress and temperature, as well as the third-order approximation between logarithmic stress and logarithmic strain rate. The mean square errors of the new model were significantly lower than those of the Arrhenius model and Hense-Spittle model for all strain rates and temperatures. There were significant differences in the prediction accuracy of the AH and HS models at different temperatures and strain rates, indicating their accuracy was dependent on temperature and strain rate. The coefficients of the new model were significantly higher than those of the AH and HS models. Moreover, the proximity of predicted values to experimental values was ranked in descending order as follows: new model, AH model, and HS model. The energy dissipation rate is relatively high when the strain rate is lower than 10 s-1 and the temperature is higher than 623 K. The instability factor is larger than zero for all conditions except when the strain rate is equal to 10 s−1. The optimal hot working temperature range for 5A06 aluminum alloy is 623–700 K, and the strain rate should be in the range of 0.01 s−1 to 1 s−1. The microstructure analysis matches the predicted results from hot processing maps, which can guide the hot working process of 5A06 aluminum alloy.

High-temperature rheological behavior and non-isothermal pyrolysis mechanism of macerals separated from different coals

It is a challenge to accurately characterize the caking behavior of coal after thermal softening and its reaction mechanism. In this work, the formation behavior of metaplast during coal macerals coking was investigated using high-temperature confocal laser scanning microscopy and high-temperature small-amplitude oscillatory shear rheometer, the source of diversities in thermal fluidity of coal was revealed by thermogravimetric-mass spectrometry analysis and kinetic-thermodynamic theory calculations. The results showed that although vitrinite was the generator of metaplast in the thermoplastic stage, the expansion rate of vitrinite from coking coal is more than 70% greater than that from gas coal for two consecutive times. Moreover, the total weight loss of vitrinite from gas coal was about 1.262 times higher than that from coking coal, but the latter exhibited more generous aliphatic groups in pyrolysis products. In the thermal flow interval, the reaction activation energy of vitrinite and inertinite from coking coal and gas coal was 271.0 ± 0.7, 302.0 ± 1.5, 241.0 ± 0.1 and 300.25 ± 1.55 kJ/mol, respectively. Eventually, the kinetic and thermodynamic mechanism parameters of raw coal and macerals had favorable correspondence regularity, and macerals with the most prominent parameters would be dominant in the overall thermal properties of raw coal.

High-Temperature Rheological Behavior and Composition Design of Hf-Be-Ti-Zr-Cu-Ni High-Entropy Amorphous Alloy

High-Temperature Rheological Behavior and Composition Design of Hf-Be-Ti-Zr-Cu-Ni High-Entropy Amorphous Alloy

Application of Four Different Models for Predicting the High-Temperature Flow Behavior of 1420 Al–Li Alloy

In this paper, the high-temperature rheological behavior of 1420 aluminum–lithium alloy under experimental conditions (temperatures of 350–475 °C and strain rates of 0.01–10 s−1) was systematically investigated using a Gleeble-3500 thermal simulation tester (temperature 350~475 °C, strain rate of 0.01~10 s−1). Based on the flow stress curves of this alloy, four different types of high-temperature constitutive models of the alloy were constructed: the Arrhenius (AR) model, the Modified Johnson–Cook (MJC) model, the Modified Zerilli–Armstrong (MZA) model, and the VOCE model. The prediction accuracy of the four constitutive models was compared, and the response of the accuracy of the four constitutive models to the deformation parameters (temperature, deformation rate, and strain) was analyzed. The results showed that the VOCE, AR, and MZA models had high overall prediction accuracy with average absolute relative error (AARE) of 1.8933%, 3.9912%, and 7.8422%, respectively. The VOCE model could achieve the prediction of large strain deformation resistance under small strain with small batch experimental conditions for the corresponding conditions. The AR model had optimal prediction accuracy for the high-rate deformation process. The MJC model had the optimal prediction accuracy for the low-temperature low-rate deformation process. The MZA model had better prediction accuracy for the low-rate high-temperature deformation process. The 1420 aluminum–lithium alloy process parameters selection area constitutive model matching diagram was constructed.

Modelling and physical analysis of the high-temperature rheological behavior of a metallic glass

The high-temperature rheological behavior, around the glass transition temperature, of a Zr48Cu34Ag8Al8Pd2 metallic glass was investigated by strain rate jump experiments. The results show that the plastic deformation behavior and apparent viscosity strongly depend on temperature and strain rate. The high temperature rheology can be interpreted within the framework of the free volume model. The relative defect concentration deduced from the free volume model depends on temperature and strain rate and it explains the evolution of apparent viscosity within testing conditions, which is inversely correlated with the defect concentration. The stress overshoot is found to be a characteristic feature of the high-temperature rheological behavior. The origin of the stress overshoot is analyzed based on the physical meaning of the parameters in the free volume model. The results demonstrate that the strength of the stress overshoot is determined by the time of change from non-equilibrium to equilibrium defect concentrations. This study highlights the link between the stress overshoot phenomenon and the initial structural state, examining the influence of physical aging and stress relaxation on the high-temperature deformation process of metallic glasses.

Study on Constitutive Relation of Nickel-Base Superalloy Inconel 718 Based on Long Short Term Memory Recurrent Neural Network

The high temperature tensile test of Inconel 718 under the conditions of deformation temperature of 950 °C–1100 °C and strain rate of 0.0005 s−1–0.1 s−1 was carried out, and its true stress–true strain curve was drawn. Through the analysis of the flow stress of Inconel 718 under different conditions, it can be seen that the high-temperature rheological behavior of Inconel 718 is affected by the coupling of strain hardening effect and dynamic softening effect, and has significant loading history correlation. By applying the stretched data, a long short term memory (LSTM) recurrent neural network was trained to characterize the constitutive relationship of Inconel 718. The experimental results show that the prediction results of the LSTM constitutive model are extremely consistent with the experimental data, which is significantly better than the modified Johnson–Cook (M-JC) model. Finally, high temperature tensile experiments under variable strain rates were carried out to verify the feasibility of the LSTM constitutive model in the complex loading and unloading stages.

Microscopic hardness and dynamic mechanical analysis of rapidly solidified Fe-based amorphous alloys

A systematic work was conducted to investigate the nanoindentation, dynamic relaxation, high-temperature rheological behavior, and structural relaxation after high-temperature deformation of Fe52-xCo20NixB19Si5Nb4 (x = 7,12,17, labeled as S1, S2 and S3) metallic glass. The results of nanoindentation indicate that the hardness of amorphous alloy reduces first and then enhances with the increase of Ni content. S1 alloy exhibits the highest hardness of 13–16 GPa, while relatively excellent compression plasticity is reached in S2 alloy. Besides, the glass transition temperature (Tg), initial crystallization temperature (Tx), α relaxation temperature (Tα) and internal friction change at different temperatures were determined and compared. The critical temperature, strain rate during non-Newton to Newtonian rheology and Newtonian viscosity at Tg temperature were discussed. Moreover, it was found that the activation volume improved and then decreased due to structural relaxation. At last, combined with the width of the supercooled liquid region, relaxation behavior and rheological viscosity at high temperature, the microstructure evolution of the three kinds of metallic glass under Tg temperature deformation was explained.

High-temperature rheological behavior and fatigue performance of lignin modified asphalt binder

The objective of this study was to introduce lignin as a bio-additive to modify the base asphalt and investigate the high-temperature rheological performances of lignin modified asphalts and virgin asphalt. In this study, asphalt PG 58-28 was selected as the virgin asphalt, and four contents, 2%, 4%, 6% and 8%, of the total binder by weight of lignin were incorporated in the base binder. Rotational viscosity (RV), dynamic shear rheometer (DSR), and multiple stress creep recovery (MSCR) tests were conducted to characterize the rheological performances of different types of asphalts. Linear amplitude sweep (LAS) test was employed to evaluate the fatigue performance. The results showed that the incorporation of lignin increased the viscosity of virgin asphalt at different rotational speeds. The activation energy showed an increasing trend as the lignin increased compared with the virgin asphalt. Meanwhile, the lignin incorporated into the asphalt binder increased the elastic components, and improved the resistance of asphalt binder to the permanent deformation regardless of the lignin contents. The addition of lignin in the asphalt binder could retard oxidation reactions that occurred in the asphalt during the rolling thin film oven aging. In addition, the incorporation of lignin may degrade the fatigue life of asphalt. However, when the content of lignin was less than 8%, the reduction was small. This study could provide a prospective foundation for the utilization of lignin extracted from waste biomass as an exceptional and renewable bio-additive in the field of asphalt pavement engineering.

Effect of organic reagents on high temperature rheological characteristics of organic rectorite modified asphalt

The molecular structure of organic reagents has a great effect on properties of organic rectorite (OREC) modified asphalt binder. This paper aims at comparing the influence of molecular chain length and benzyl group on the high temperature rheological characteristics of OREC modified binder. Here, three organic quaternary ammonium salts, including dodecyl trimethyl ammonium chloride (DTAC), dodecyl dimethyl benzyl ammonium chloride (DBAC) and octadecyl trimethyl ammonium chloride (OTAC), were selected as REC modifiers to prepare ORECs. These ORECs were then employed to modify base binder, respectively. The X-ray diffraction (XRD) test and thermogravimetric (TG) test were conducted to study the structure characteristics and thermal behavior of ORECs and corresponding modified binders. The high temperature rheological behavior, rutting and stress susceptibilities of OREC modified binders were evaluated by the temperature and frequency sweep tests, multiple stress creep recovery (MSCR) test. Results indicate that, the organic reagent affects the rheological behavior of OREC modified binder not only by enlarging the basal spacing of REC (specific surface area), but also directly by specific functional groups (e.g. benzyl group). Moreover, the organic reagent with longer molecular chains (18 carbon atoms) or containing benzyl groups is conductive to the improvement in elastic property and stiffness, and reduction in rutting and stress susceptibilities of OREC modified binder. The comparison demonstrates that DBAC containing benzyl groups exhibits better effect. Therefore, organic reagents containing benzyl groups are preferred to obtain OREC modified binder with excellent high temperature property.

High-temperature Rheological Behavior and Numerical Simulation Technology for 6061 Aluminum Alloy Connecting Rods

High-temperature Rheological Behavior and Numerical Simulation Technology for 6061 Aluminum Alloy Connecting Rods

High-temperature Rheological Behavior and Numerical Simulation Technology for 6061 Aluminum Alloy Connecting Rods

High-temperature Rheological Behavior and Numerical Simulation Technology for 6061 Aluminum Alloy Connecting Rods

High temperature rheological behavior and sintering kinetics of CF/PEEK composites during selective laser sintering

As a kind of high performance polymer with excellent mechanical strength, high temperature property and chemical resistance, the polyether-ether-ketone (PEEK) and its composites are the promising candidates that can satisfy the demands for high stiff and lightweight in aerospace industry. So it is very attractive to fabricate PEEK and its composites parts with additive manufacturing technology, especially the selective laser sintering (SLS), due to its advantage on the fabrication of the parts with complex geometries. However, the strengths of the PEEK and its composites prepared by SLS are obviously lower than their injection molded parts and the laser sintering kinetics of the PEEK composites is seldom studied. In this paper, to fabricate the carbon fibers (CF) reinforced PEEK composites with high strength by SLS, the sintering kinetics of CF/PEEK composites was thoroughly studied based on the high temperature rheological behavior. A novel effective melting zone was defined by combining the simulated temperature distribution with the viscosity-temperature relationship and used to predict the process planning. Finally, the calculation results were validated by employing the simulation parameters in experiments and the tensile strength of CF/PEEK composites reached 109 ± 1 MPa with an elasticity modulus of 7365 ± 468 MPa, which is 85% higher than injection molded pure PEEK. Therefore, methods in this work could be considered as a complement to the numerical analysis of SLS process and the reinforced CF/PEEK composites may be used in aerospace industry for the structure optimization and lightweight design with complex geometries.

A Comparative Study on Modeling of High Temperature Rheological Behavior of AZ80 Magnesium Alloy Using Artificial Neural Network and Inverse Method

Artificial neural network (ANN) and inverse method were employed in modeling the rheological behavior of the AZ80 magnesium. The hot deformation behavior of extruded AZ80 magnesium was investigated by compression tests in the temperature 350-450 and strain rate range 0.01-50 s-1. Investigation of flow stress curves and microstructure of the compression specimen illustrate occurrence of dynamic recrystallization. The inverse method of non-liner regression was used to determine the parameters of the suggested constitutive equation. The maximum relative errors at different temperatures and different strain rates between experimental and predicted flow stresses by ANN and inverse method were compared. The results show the ANN derives statistical models have better similar prediction ability to those of inverse method, especially at high strain rate. This indicates that ANN can be used as an alternative modeling tool for high temperature rheological behavior studies.

Modeling of High Temperature Flow Stress of AZ80 Magnesium Alloy with Support Vector Machines and Artificial Neural Network

Support vector machines (SVM) and artificial neural network (ANN) were employed in modeling the flow stress of the AZ80 magnesium. The hot deformation behavior of extruded AZ80 magnesium was investigated by compression tests in the temperature 350-450 and strain rate range 0.01-50 s-1. The maximum relative errors at different temperatures and different strain rates between experimental and predicted flow stresses by SVM and ANN were compared. The results show the SVM derives statistical models have better similar prediction ability to those of ANN, especially at high strain rate. This indicates that SVM can be used as an alternative modeling tool for high temperature rheological behavior studies.

Experimental investigation of the creep behavior of MgO at high pressures

The high-temperature rheological behavior of polycrystalline periclase, MgO, has been investigated using the deformation-DIA on a synchrotron beamline at pressures up to 10 GPa. Significant experimental scatter in stress measurement illustrates current limitations of this technique. Although temperature and stress sensitivities are not well constrained, there is a clear dependence of creep rate on pressure. Based on our results, the creep rate of MgO depends on confining pressure with an activation volume of V* ≈ 2.4 × 10 −6 m 3/mol. The grain-scale view of deformation processes reveals, as other D-DIA studies have, that subpopulations of grains, grouped by orientation, obey slightly different flow laws. The measurements also reveal that stress heterogeneity in the sample, whether caused by external conditions or processes internal to the sample itself, contribute a significant portion of the overall uncertainty in stress measurement.

Modeling of high temperature rheological behavior of AZ61 Mg-alloy using inverse method and ANN

Inverse method and artificial neural network were employed in modeling the rheological behavior of the AZ61 Mg alloy. The hot deformation behavior of these alloys was investigated by compression tests in the temperature range 250–350 °C and strain rate range 0.0005–0.1 s −1. Investigation of stress–strain curves and microstructure of the compression specimen illustrate occurrence of dynamic recrystallization. To determining parameters of two suggested constitutive equations global optimization technique, genetic algorithm, was used. The predicted results by inverse method and ANN depicted a good agreement with the experimental data even if the ANN results has shown the best predicted capability.