Deformation Flow Stress Research Articles

Mechanical properties and flow stress constitutive relationship of Ti–6Al–4V alloy with equiaxed microstructure at cryogenic temperatures

This paper investigates the uniaxial tensile mechanical properties and flow behavior of Ti-6Al-4V alloys with equiaxed microstructure at cryogenic temperatures ranging from 77 K to 298 K and strain rates from 10−4/s to 10−2/s. Scanning electron microscopy is utilized to analyze the fracture morphology, aiming to reveal the fracture behavior at various temperatures. The applicability of the Zener-Hollomon parameter and the Johnson-Cook model in describing the flow stress of Ti-6Al-4V at cryogenic temperatures is analyzed. Moreover, a constitutive relationship modeling method based on the variational recurrent networks is proposed. Mechanical test results show a significant increase in the strength of equiaxed Ti-6Al-4V alloy under cryogenic conditions while the plastic deformation process is shortened. However, the fracture analysis indicates that even at 77 K, the fracture process is still dominated by ductile fracture, and brittle fracture does not occur within the range of 77 K to 298 K. The fitting results validate the performance of the Zener-Hollomon parameter and the Johnson-Cook model in describing the deformation flow stress of Ti-6Al-4V alloy at cryogenic temperatures. The results also indicate that the proposed constitutive relationship modeling method based on the variational recurrent network performs better, making it a potential method for widespread applications.

Delineating the role of dynamic and static recrystallization during hot working of nickel-based superalloy (IN600)

In the presented research, the dynamic working of nickel-based (IN600) superalloy was performed and the micro-mechanisms affecting the deformation behaviour were closely monitored, particularly the role of static and dynamic recrystallization. Hot deformation flow stress response indicated an increase in the true stress value with an increase in strain rate and decrease in temperature. The constitutive calculations indicated that deformation progressed mainly due to dislocation climb motion. The hot workability map indicated a peak power dissipation efficiency (PDE) of 0.39 in two working domains. The microstructural evolution in the hot deformed specimens depicted a consistent increase in dynamic softening at temperature ≥ 1000 °C, whereas, a steady decline in the extent of dynamic softening is observed with increase in strain rate from 0.01 s−1 to 1 s−1. The mechanism for microstructural evolution in this range (0.01–1 s−1) was identified as discontinuous dynamic recrystallization (DDRX). Moreover, at the highest strain rate of 10 s−1, a sudden surge in the recrystallization fraction was observed, which was attributed to the combined effect of DDRX and static recrystallization (SRX). Additionally, this study shows that the presence of twin boundaries (TBs) contributes to dynamic softening by serving as sites for nucleation of strain-free grains.

Insights into hot deformation of medium entropy alloys: Softening mechanisms, microstructural evolution, and constitutive modelling—a comprehensive review

The recent discovery of multicomponent principal alloys and the enhanced comprehension of their physical metallurgy have significantly advanced the understanding of microstructure engineering and material selection for high-tech applications. The exceptional combination of characteristics found in MEAs can be attributed to their distinctive phase constitution, which is aided by their multi-principal constituents. These properties are seldom encountered in ordinary alloys. Nevertheless, the use of these materials in their as-cast state is challenging due to issues such as the presence of heterogeneity in their chemical makeup, shrinkage porosity, unrefined dendritic structure, and the presence of a quasi-stable eutectic at grain boundaries. Consequently, the utilization of hot deformation methods for the purpose of achieving uniform and refined microstructures in as-cast MEAs has garnered significant interest as a viable approach to address these limitations. This review provides a comprehensive summary of the hot deformation characteristics of MEAs. Factors such as the alloy composition, the phase constituent, deformation parameters and recrystallization mechanisms were observed to influence the microstructural development and phase transition, flow curve characteristics, and mechanical characteristics of MEAs. Additionally, the use of processing map analysis for the determination of optimal processing zones for the hot deformation of MEAs was appraised. The discussion also encompassed the constitutive model description, molecular dynamics modeling, and machine learning algorithm for the prediction of the governing deformation mechanism and the deformation flow stress. Finally, future research directions are suggested.

Study on the Constitutive Modeling of (2.5 vol%TiB + 2.5 vol%TiC)/TC4 Composites under Hot Compression Conditions.

The hot deformation behavior of titanium matrix composites plays a crucial role in determining the performance of the formed components. Therefore, it is significant to establish an accurate constitutive relationship between material deformation parameters and flow stress. In this study, hot compression experiments were conducted on a (2.5 vol%TiB + 2.5 vol%TiC)/TC4. The experiments were performed under temperatures ranging from 1013.15 to 1133.15 K and strain rates ranging from 0.001 to 0.1 s-1. Based on the stress-strain data obtained from the experiment, the constitutive models were established by using the Arrhenius model and the BP neural network algorithm, respectively. Considering the relationship between strain rate, hot working temperature, and flow stress, a comparative analysis was conducted to evaluate the prediction accuracy of two different constitutive models. The research results indicate that the flow stress of (2.5 vol%TiB + 2.5 vol%TiC)/TC4 increases with decreasing temperature and increasing strain rate, and the stress-strain curve shows obvious work hardening and softening behaviors. Both the Arrhenius model and the BP neural network algorithm are effective in predicting the hot compression flow stress of (2.5 vol%TiB + 2.5 vol%TiC)/TC4, but the average relative error and root mean square error of the BP neural network algorithm are smaller and the correlation coefficient is higher, thus possessing higher accuracy and reliability.

Hot Deformation Behavior and Processing Maps of 26CrMo7S Steel Used in Oil Exploration.

The hot deformation behavior and flow stress characteristics of experimental 26CrMo7S steel were analyzed using a thermal simulator under a range of conditions, including a strain rate range of 0.01~10 s-1, a temperature range of 850~1250 °C, and a maximum deformation amount of 70%. The Arrhenius constitutive model was built for the corresponding conditions, and the model's accuracy was verified through error analysis. Additionally, hot processing maps were constructed to analyze the processing zone of the steel under different hot deformation conditions. Finally, the microstructure of the processing zones was observed and verified using the electron backscattered diffraction (EBSD). The results indicate that the interaction of work hardening and dynamic softening influences the hot deformation behavior of 26CrMo7S steel. The Arrhenius constitutive equation with a value of the correlation coefficient (r = 0.99523) accurately predicts the flow behavior of 26CrMo7S steel under different strains. The optimal processing zone obtained with the hot processing maps is within a deformation range of 1010~1190 °C and a strain rate range of 0.01~10-1.5 s-1, and the obtained microstructure is in good agreement with the analysis results.

Arrhenius constitutive equation and artificial neural network model of flow stress in hot deformation of offshore steel with high strength and toughness

ABSTRACT In this study, the thermal deformation behaviour of a high strength offshore steel at different temperatures and rates was investigated through thermal compression experiments.An Arrhenius constitutive model and a back propagation artificial neural network (BP-ANN) were established to address more complex deformation characteristics. The performances of both models were was evaluated using standard statistical parameters such as the correlation coefficient (R) and average absolute relative error (AARE). The results showed that both models can accurately predict the rheological stresses generated during deformation.The BP-ANN outperforms the Arrhenius equation model with correlation coefficients of fit greater than 99.9% and less than 0.8% relative error. At a strain rate of 0.01 s−1 and 10 s−1, the accuracy of the ANN decreases slightly due to the fact that it exceeds the strain rate range of the training set, as compared to the Arrhenius constitutive equations as these are more accurately predicted.

Hot deformation behavior and flow stress modeling of coarse-grain nickel-base GH4151 superalloy ingot materials in cogging

Due to the high deformation resistance and poor thermal ductility of the new cast GH4151 alloy ingots, cracks are easy to occur during cogging process. For clarifying the effects of deformation parameters on microstructural evolution and dynamic recrystallization (DRX) nucleation mechanisms. In this work, the causes of crack formation and extension were first investigated using SEM and EBSD. The study revealed that the reasons for crack formation and propagation are the MC carbides at the original grain boundaries, large-size γ′ phase, residual eutectic phases, and tiny pores near the grain boundaries. Subsequently, a series of hot compression tests were performed using a Thermecamastor-Z thermo-mechanical simulator at temperatures ranging from 1080 °C to 1160 °C and a strain rate range of 0.01–10 s−1. The constitutive equation of the Arrhenius model and the hot working map was established, determining activation energy(Q) of 1086.58 kJ·mol−1. Large-size γ′ is coherent with the matrix. For the γ+γ′ dual-phase region, heterogeneous strain-induced dynamic recrystallization (HDRX) occurs, and discontinuous dynamic recrystallization (DDRX) is the main nucleation mechanism for DRX. However, for γ single-phase region, DDRX plays a more significant role. Furthermore, the MC phase (>1 μm) has different crystal orientations with the γ matrix and acts as sites for recrystallization through particle-stimulated nucleation (PSN). Finally, a fine and uniform grain structure can be obtained in the temperature range of 1120–1135 °C and the strain rate range of 0.1 s−1 to 1 s−1.

Effect of intercritical annealing on deformation behavior and flow stress predictive models of AISI 8620 steel

Effect of intercritical annealing on deformation behavior and flow stress predictive models of AISI 8620 steel

A study of mechanical characteristics and microstructural evolution of copper-nickel alloy sheet undergoing ultrasonic vibration assisted uniaxial tension

The phenomenon that the ultrasonic vibration (UV) can reduce the flow stress in the metal plastic deformation has been shown in many studies, however, the mechanism of the flow stress decline when the copper-nickel alloy sheet undergoes the UV is unclear yet. In this study, a series of tensile tests are conducted on the copper-nickel alloy sheet. The results indicate that the UV induces softening effect, i.e., the significant decline of the flow stress and the tensile strength. Nevertheless, the elongation of specimens decreases obviously in the tensile tests. To investigate the mechanisms, the microstructure evolution of the copper-nickel alloy sheet in the UV assisted tensile tests are explored by the scanning electron microscope (SEM), the electron backscattering diffraction (EBSD) and the transmission electron microscope (TEM). It is found that after the UV superimposition the high-angle grain boundaries (HAGB) retain more and the reduction of the twinning decreases in the copper-nickel alloy sheet, which impairs the plasticity and the elongation. The results also show that the average grain size under the UV conditions is bigger, which leads to the decrease of the flow stress and weaken the plasticity of the metal.

Thermal deformation behavior and constitutive model of 42CrMo4 steel

42CrMo4 steel is a widely used high-strength alloy steel in various large-bearing manufacturing fields. The rheological stress curve of 42CrMo4 steel with the best heat treatment scheme was obtained through the thermal compression experiment. A mathematical model was established using the hyperbolic sine function to relate deformation temperature, strain rate, and flow stress during thermoplastic deformation. The flow stress curves of 42CrMo4 alloy steel show typical dynamic recovery and recrystallization characteristics.

Hot workability characteristics of two A335 P92 steels for power plant application: A comparative study

The article reports on the workability of two P92 steels having a chromium content of 8.29 and 9.48 wt%. Constitutive equations were used to calculate material parameters describing the hot deformation flow stress. Hot deformation tests were conducted using the Gleeble® 3500 thermomechanical facility. Test conditions were: temperature of 850-1000°C and strain rate of 0.1-10s-1 to a strain of 0.5. The flow stress curve results show that dynamic recovery was the only softening mechanism. A comparative study of the two steels revealed that Cr content had a marginal significance on the flow stress behaviour. Constitutive analysis results of the material parameters were: a stress exponent of 9.0 (P92-A), and 11.0 (P92-B), while the activation energy was 369 kJmol-1 (P92-A), and 472 kJmol-1 (P92-B). A brief explanation of the material parameter results is in this article. A flow stress model was developed to predict the flow stress behaviour of the two P92 steels investigated. The results show that the model accurately predicts the flow stress at all the deformation conditions applied. The statistical parameters showed a good correlation between the predicted and the experimental data. Therefore, this model can be used to develop metal forming schedules for industrial applications.

Role of temperature and strain rate on evolution of microstructure, flow stress and constitutive equation in hot deformation of AZ80A Mg alloy

Role of temperature and strain rate on evolution of microstructure, flow stress and constitutive equation in hot deformation of AZ80A Mg alloy

Simulation study on the nano-crystalline Cu-Ag alloys with gradient segregation

Via equidistance scaling method, several parts of the segregated domains from granular interior to grain boundary are identified. Based on this method, the model of nano-crystalline (NC) Cu-Ag alloy with gradient segregation is constructed. The issue how the solute concentration (SC) distribution is more conducive to the strength enhancement is explored by molecular dynamic (MD) simulation. The simulation results reveal that sample with higher intra-granular SC possess more dislocation activities, thinner amorphous inter-granular films (AIFs), more homogeneous deformation and higher flow stress at plastic stage. The results turn the opposite way in sample with higher SC nearby grain boundary. Meanwhile, the observed phase transition is analyzed during the deformation progress.

Constitutive modeling of hot deformation behavior of AlCrFeNi multi-component alloy

In present paper, the hot deformation behavior of an equiatomic AlCrFeNi medium entropy alloy (MEAs) was investigated. Hot compression tests were carried out at various temperatures ranging from 800 °C to 1100 °C at different strain rates from 0.001 s−1 to 1 s−1. The flow stress analysis was performed on AlCrFeNi MEAs by using Arrhenius type relationship, and a linear dependence of flow stress on Zener–Hollomon parameter (Z) can be determined. Moreover, a comparative study was carried out to further evaluate the predictability of the Arrhenius-type constitutive equation and artificial neural network (ANN), support vector machine (SVM) model. The results show that the constitutive model developed by SVM performs better to describe the interdependency between deformation temperature, strain rate and flow stress. The activation energy (Q) for high-temperature deformation was calculated as 376.6 kJ/mol, and the related strain rate sensitivity (m), the power dissipation (η), and instability parameter (ξ) were also derived. The processing maps suggest that the flow instability tends to occur at high strain rate and the optimum processing parameters can be determined to direct the hot working process.

Hot deformation behavior and flow stress modeling of a novel CoNi-based wrought superalloy

The thermal deformation behavior and flow stress modeling of a novel CoNi-based wrought superalloy after forging was investigated at γ' sub-solvus temperature (1050 °C and 1075 °C) and γ' super-solvus temperature (1100 °C and 1125 °C) with strain rate range from 0.001 s−1 to 0.1 s−1 under a 50% strain. Scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques were used to characterize the microstructures and explain the flow behavior. The results show that the flow stress increases with decreasing temperature and increasing strain rate. Dynamic recrystallization (DRX) occurs under all deformation conditions. When the alloy was deformed sub-solvusly at 1075 °C/0.01 s−1 and 0.001 s−1 conditions, the γ' phase dissolved resulting in substantial grain growth. The constitutive equations were established via the flow stress data with the respect to the γ' phase dissolution. The activation energies for the γ + γ' dual-phase region and the γ single-phase region of the studied alloy are about 650 and 390 kJ/mol, respectively, which is comparable with traditional Ni-based superalloys.

Evolution of strain-induced precipitates in Inconel 617B alloy and their effect on flow behavior

Strain-induced precipitation was systematically investigated in austenitic Inconel 617B superalloy (IN617B) after deformation of 0.2 true strain in its service temperature range (700–850 °C). The precipitation-time-temperature (PTT) curves obtained by stress relaxation experiments showed a classic C-shape with the nose temperature of 800 °C, and a minimum incubation period of 30 s, and the main strain-induced precipitate was M23C6 carbide. After specimens deformed at 800 °C to a strain of 0.2 were held between 10 and 1000 s, they underwent a second-pass strain test, during which the M23C6 precipitates evolved and influenced the flow stress; this behavior was investigated. During the nucleation, growth, and coarsening of the strain-induced precipitates, the morphology of the M23C6 particles gradually changed from spherical to polygonal with increasing size, but the precipitates always maintained their cube-on-cube orientational relationship with the austenitic matrix. During the nucleation stage before 30 s, many pre-precipitation clusters and weak static recovery softening led to low second-deformation flow stress, which persisted at approximately 630 MPa. In the precipitation growth phase before 360 s, recovery softening balanced precipitation hardening. The strain-induced precipitates grew larger, and they were able to pin dislocations. In addition, some complex microstructures resulting from particle collisions were observed. This resulted in the maximum rate of increase of the second deformation flow stress, which quickly reached almost 700 MPa. When the holding time was extended to 1000 s, the recovery softening effect further increased, while the M23C6 particles gradually coarsened; this weakened the increasing trend of the second deformation flow stress, which increased to only 715 MPa at 1000 s

Hot Deformation Behavior and Processing Maps of a New Ti-6Al-2Nb-2Zr-0.4B Titanium Alloy.

The hot deformation behaviors of a new Ti-6Al-2Nb-2Zr-0.4B titanium alloy in the strain rate range 0.01–10.0 s−1 and temperature range 850–1060 °C were evaluated using hot compressing testing on a Gleeble-3800 simulator at 60% of deformation degree. The flow stress characteristics of the alloy were analyzed according to the true stress–strain curve. The constitutive equation was established to describe the change of deformation temperature and flow stress with strain rate. The thermal deformation activation energy Q was equal to 551.7 kJ/mol. The constitutive equation was On the basis of the dynamic material model and the instability criterion, the processing maps were established at the strain of 0.5. The experimental results revealed that in the (α + β) region deformation, the power dissipation rate reached 53% in the range of 0.01–0.05 s−1 and temperature range of 920–980 °C, and the deformation mechanism was dynamic recovery. In the β region deformation, the power dissipation rate reached 48% in the range of 0.01–0.1 s−1 and temperature range of 1010–1040 °C, and the deformation mechanism involved dynamic recovery and dynamic recrystallization.

Analysis on the hot deformation flow stress curves of novel 6082 aluminium alloys with Mn addition

Two types of 6082 alloy, base alloy free of Mn and novel 0.75Mn alloy with an addition of 0.75% Mn, were prepared. A heat treatment of 450 °C for 6 h was performed, during which large numbers of α-Al (Fe, Mn) Si dispersoids precipitated in 0.75Mn alloy. Uniaxial compression tests were carried out and a series of flow stress curves were obtained at temperature range of 400-550 °C and at strain rate range of 0.001s-1-1s-1. The results revealed an impressive difference between the flow stress curves of base and 0.75Mn alloy that after the yield plateau, the flow stresses of base alloy remained fairly steady at certain levels while the flow stress in 0.75Mn alloy decreased along with strain until the end of deformation. The reason for the decrease of flow stress in 0.75Mn alloy was neither the dissolution of dispersoids nor the dynamic recrystallization. The decrease of flow stress was attributed to the loss of Mn solid solution strengthening effect based on the Mn diffusion rate-controlling mechanism and “pipe diffusion”.

Predicting Workability of a Low-Cost Powder Metallurgical Ti-5Al-2Fe-3Mo Alloy Using Constitutive Modeling and Processing Map.

A low-cost titanium alloy (Ti–5Al–2Fe–3Mo wt.%) was designed and fabricated by blended elemental powder metallurgy (BEPM) process. The high-temperature deformation behavior of the powder metallurgical Ti–5Al–2Fe–3Mo wt.% (PM-TiAlFeMo) alloy was investigated by hot compression tests at temperatures ranging from 700 to 1000 °C and strain rates ranging from 0.001 to 10 s−1. The flow curves were employed to develop the Arrhenius-type constitutive model in consideration of effects of deformation temperature, strain rate, and flow stress. The value of activation energy (Q) was determined as 413.25 kJ/mol. In order to describe the workability and predict the optimum hot processing parameters of the PM-TiAlFeMo alloy, the processing map has been established based on the true stress–true strain curves and power dissipation efficiency map. Moreover, microstructure observations match well with the analyses about deformation mechanisms, revealing that dynamic recovery and dynamic recrystallization are dominant softening mechanisms at relatively high temperatures. However, the kinking and breaking of microstructure prefer to occur at relatively low temperatures.

Hot deformation behavior of hard-to-deform Ni-based Alloy

The very poor hot workability of hard-to-deform GH4742 alloy is represented in the aspects of very narrow available deformation temperature range, high deformation-resistant force and low thermoplasticity. In this paper, the hot deformation behavior of a Ni-based superalloy was studied in the temperature range of 1060-1160°C and strain rate range of 0.05-0.5 s−1 using hot compression tests. A hot deformation equation is given to characterize the dependence of peak stress on the temperature and strain rate. Results of hot compression test of the GH4742 alloy were indicated that the hot deformation is sensitive to temperature and strain rate. A special heat treatment to change the ingot microstructure is proposed to improve the hot workability of the GH4742 alloy. Modified microstructure induces that the hot deformation flow stress of GH4742 alloy was decreased effectively and hot deformation plasticity was increased obviously.