Increasing Deformation Temperature Research Articles

Ti6554 titanium alloy electrically assisted compression: modelling and simulation based on dislocation density theory

Electrically assisted compression experiments were conducted on Ti6554 titanium alloy to investigate the electroplasticity behavior under different process parameters (current density, duty cycle) and to analyze the effect of pulsed current on flow stress and temperature. An electroplasticity constitutive model based on dislocation density theory was developed and using ABAQUS subroutine secondary development for electrically assisted compression simulation. The results show that the established electroplasticity constitutive model can better predict the true stress-strain curves under different process parameters, and the average error is controlled at 6%. The evolution law of dislocation density reveals that α, which characterizes the dislocation strength, is smaller with the increase of current density, n and K2, which characterize the dynamic recovery mechanism of the material, increase with the increase of current density, and the dislocation density ρ decreases with the increase of deformation temperature.

Hot workability and microstructure evolution of wire arc additive manufactured 300M steel

Wire arc additive manufacturing (WAAM) technology offers a material-saving and efficient method of manufacturing the 300M steel components, but the obtained microstructure and properties hardly reach the level of wrought materials. By combining WAAM technology with forging process, a novel forming process is proposed. The preferred shape pre-forgings are easily prepared, and the number of forging steps significantly decreases. The WAAMed as-cast microstructure also can be transformed into the wrought state by the proposed forming process. The aim of this study is to investigate the hot deformation behavior and microstructure evolution of WAAMed 300M steel under various deformation temperatures and strain rates. The results show that the WAAMed 300M steel exhibits a higher plastic deformation resistance than the wrought 300M steel. With the increase of deformation temperature and strain rate, the difference of flow stress between the WAAMed and wrought 300M steel decreases. The hot deformation activation energy of WAAMed 300M steel is calculated as 374.1 kJ/mol, which is much higher than that of wrought 300M steel (332.3 kJ/mol). The possible processing windows obtained from the hot deformation activation energy maps are 1040-1120 °C/0.01-10 s−1 for the WAAMed 300M steel and 1010-1130 °C/ 0.1-10 s−1 for the wrought 300M steel. The constitutive model considering strain compensation is established to describe the hot deformation behaviors of WAAMed and wrought 300M steel. The high correlation coefficient and low average absolute relative error confirm the suitability of the developed constitutive models for predicting the flow stresses of WAAMed and wrought 300M steel.

Research on hot deformation behavior and constitutive model to predict flow stress of an annealed FeCrCuNi2Mn2 high-entropy alloy

In the present study, the hot deformation and dynamic recrystallization behaviors of an annealed FeCrCuNi2Mn2 high-entropy alloy were investigated through the hot compression tests. Flow curves were evaluated within a certain temperature range (700–1000 °C) and initial strain rate range (0.001–0.1 s−1), and the corresponding microstructures were assessed. Constitutive equations with strain-dependent material constants were established for the calculation of material constants and for modeling of flow stress behavior through the analysis of true stress-strain curves. The critical and peak stress and strain (dynamic recrystallization parameters) were extracted from the work hardening rate against stress curves. These parameters were then used to determine the recrystallized volume fraction under different conditions. The results indicated that with the increase in deformation temperature and decrease in strain rate, dynamic recrystallization parameters decreased. This trend was followed by an increase in recrystallized volume fraction and grain growth, resulting in a decrease in the hardness value of the alloy. Findings further revealed that the flow stress in the annealed alloy was higher compared with that in the as-cast alloy under the same deformation conditions. Microstructural observations and the evaluation of work hardening rate against stress curves showed the typical dynamic recrystallization characteristics as the dominant softening mechanism under different deformation conditions. The activation energy of hot deformation was determined to be 437 kJ/mol. In the present study, a power equation was established between critical stress and strain and the Zener–Hollomon parameter with the exponents of 0.089 and 0.086, respectively. Moreover, the dynamic recrystallization grain size was found to be proportionate to Z−0.11.

Microstructure Evolution Behavior of Spray-Deposited 7055 Aluminum Alloy during Hot Deformation

The evolution behaviors of the second phase, substructure and grain of the spray-deposited 7055 aluminum alloy during hot compression at 300~470 °C were studied by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results show that the AlZnMgCu phase resulting from the deposition process dissolves gradually with the increase in deformation temperature, but the Al7Cu2Fe phase remains unchanged. The plastic instability of the spray-deposited 7055 aluminum alloy occurs at 470 °C with a 1~5 s−1 strain rate range. Partial dynamic recrystallization (PDRX) adjacent to the original high angle grain boundaries (HAGBs) not only occurs at 300~400 °C with the low strain rates ranging from 0.001 to 0.1 s−1 but also at 450 °C with a high strain rate of 5 s−1. Continuous dynamic recrystallization (CDRX) appears at 450 °C with a low strain rate of 0.001 s−1. The primary nucleation mechanism of PDRX includes the rotation of the subgrain adjacent to the original HAGBs and the subgrain boundary migration. The homogeneous misorientation increase in subgrains is the crucial nucleation mechanism of CDRX. At 300~400 °C, the residual coarse particle stimulated (PSN) nucleation can also be observed.

Hot workability and microstructural evolution of a nickel-based superalloy fabricated by laser-based directed energy deposition

Recently, an innovative process chain has been investigated and proposed, using laser-based directed energy deposition technology to produce pre-forms for forging. The advantage of this technology is to get high-performance near-formed parts at a low cost, compared traditional processing. Clarifying the hot workability and the microstructural evolution of as-deposited samples is the key to obtaining high performance parts. In present work, the plastic behaviors and dynamic recrystallization mechanisms of as-deposited nickel-based superalloy are studied. The compression curves are corrected by eliminating adiabatic heating and friction effect. And then the hot deformation activation energy and the constitutive equation of as-deposited sample are obtained. Compared to the wrought Inconel 625, as-deposited Inconel 625 has lower hot deformation activation energy (466.511 kJ/mol). The peak stress gradually decreases, while the recrystallized grain volume fraction gradually increases when deformation temperature increases and strain rate decreases. The characterization results of TEM and EBSD show that the discontinuous dynamic recrystallization mechanism nucleating by the bowing of grain boundaries occupies an absolute dominant position. In addition, combined with the microstructural evolution and hot processing map, the best hot working conditions of as-deposited Inconel 625 are obtained (deformation temperature: 1050–1150 ℃, strain rate: 0.001–0.01 s−1).

Dynamic Deformation Behavior and Fracture Characteristics of a near α TA31 Titanium Alloy at High Strain Rates.

The quasi-static and dynamic impact compression tests of the TA31 titanium alloy were conducted at the strain rates from 0.001 s-1 to 4000 s-1 and deformation temperatures from 293 K to 773 K, and the TA31 titanium alloy showed typical elastic-plastic characteristics. In the initial stage of compression (elastic deformation), the stress and strain are proportional, and the stress-strain curve is a straight line. In the plastic deformation stage, the flow stress decreases significantly with the increase of deformation temperature, while the strain rate has no significant effect on the flow stress during dynamic compression. A constitutive model has been established to predict the flow stress, and the relative error is 2.32%. It is shown by observing the microstructure that when the deformation temperature is 293 °C, and the strain rate reaches 1600 s-1, a shear band with an angle of about 45° to the axial direction of the specimen appears, and the severe shear deformation makes the α phase in the shear band fibrous and contains high-density dislocations. The formation process of the shear band and its influence on fracture are analyzed and discussed.

High temperature flow behavior and deformation mechanism of Nb-22.5Cr-2.5Mo alloy

The high temperature compression is performed by isothermal compression tests using Gleeble 3500 thermo-mechanical simulator at a constant strain rate for the hot-pressed Nb-22.5Cr-2.5Mo alloy. The deformation temperature ranges from 800 to 1200 °C and the strain rate ranges from 0.001 to 0.1 s−1. The high temperature flow behavior and deformation mechanism of the alloy are investigated based on the compression test data and TEM observation of the deformed microstructure. The results show that the ductile–brittle transition temperature of the alloy is about 800 °C, and the flow stress is sensitive to the deformation temperature and strain rate, in which the plastic deformation ability increases obviously with the increase of deformation temperature and the decrease of strain rate. Besides, the hyperbolic sine Arrhenius model with stress exponent of 3.131 and apparent activation energy of 402 kJ/mol is established for the peak flow stress. The value of apparent activation energy is higher than that of Nb metal (246 kJ/mol), which implies the existence of Laves phase NbCr2 makes the deformation of the alloy more difficult. Moreover, it is found that the deformation mechanisms in the Nbss matrix are mainly DRV controlled by the glide and climb of the dislocations and DRX formed by bulging nucleation mechanism, while the deformation mechanisms in the Laves phase NbCr2 particles are mainly twinning and synchroshear of the Shockley partial dislocation.

Mechanical properties of a 7075-T6 aluminum alloy at elevated temperatures

Abstract In this study, the mechanical properties of a 7075-T6 aluminum alloy were investigated experimentally and numerically. Tensile tests were carried out at various temperatures (25–400 °C) and cross-head speeds (1–200 mm min−1). The results showed that the tensile strength of the aluminum alloy decreased with increasing deformation temperature. Also, the temperature had more effect on the mechanical properties than on the strain rate. The fracture morphology of test specimens was investigated using a scanning electron microscope. The bending behavior of aluminum alloy at elevated temperatures was investigated with finite element simulations. It obtained a good correlation with the validation study, and it can be predicted as the high-temperature behavior of aluminum alloy with finite element simulations. The analysis results show that the temperature dramatically affects the load-carrying capacity of aluminum. The load-carrying capacity and the absorbed energy values of aluminum alloy decreased with the increasing temperature on bending behavior.

Microstructure evolution and dynamic recrystallisation behaviour in hot deformation of Haynes 214 superalloy

The microstructure evolution and dynamic recrystallisation (DRX) behaviour of Haynes 214 superalloy were investigated in the deformation temperature range of 900 ~ 1180 ℃ and strain rate range of 0.1 ~ 10 s−1 during isothermal compression tests. According to the true stress-strain curves that were obtained from the tests, it was found that temperature and strain rate significantly influence the hot deformation behaviour of Haynes 214 alloy. The fraction and grain size of the dynamic recrystallisation both increase as deformation temperature increases. Fine and uniform DRX grains are obtained at low and high strain rates, whereas at 1 s−1, DRX grain size and fraction decrease. In addition, both continuous dynamic recrystallisation (CDRX) and discontinuous dynamic recrystallisation (DDRX) occur during hot deformation, both being affected by strain rate and deformation temperature. At the same time, the fraction of ∑3 n (n = 1, 2, 3) twin boundary increases as temperature increases and is higher at a lower strain rate (0.1 s−1) and higher strain rate (5, 10 s−1), but lower at the intermediate strain rate of 1 s−1.

Hot Deformation Behavior and Microstructure Evolution of a Novel Al-Zn-Mg-Li-Cu Alloy.

Lightweight structural alloys have broad application prospects in aerospace, energy, and transportation fields, and it is crucial to understand the hot deformation behavior of novel alloys for subsequent applications. The deformation behavior and microstructure evolution of a new Al-Zn-Mg-Li-Cu alloy was studied by hot compression experiments at temperatures ranging from 300 °C to 420 °C and strain rates ranging from 0.01 s−1 to 10 s−1. The as-cast Al-Zn-Mg-Li-Cu alloy is composed of an α-Al phase, an Al2Cu phase, a T phase, an η phase, and an η′ phase. The constitutive relationship between flow stress, temperature, and strain rate, represented by Zener–Hollomon parameters including Arrhenius terms, was established. Microstructure observations show that the grain size and the fraction of DRX increases with increasing deformation temperature. The grain size of DRX decreases with increasing strain rates, while the fraction of DRX first increases and then decreases. A certain amount of medium-angle grain boundaries (MAGBs) was present at both lower and higher deformation temperatures, suggesting the existence of continuous dynamic recrystallization (CDRX). The cumulative misorientation from intragranular to grain boundary proves that the CDRX mechanism of the alloy occurs through progressive subgrain rotation. This paper provides a basis for the deformation process of a new Al-Zn-Mg-Li-Cu alloy.

Effect of Thermo-Mechanically Activated Precipitation on the Hot Deformation Behavior of High Strength Aluminum Alloy AA7075

The present study investigates the effect of two different microstructural conditions on the hot deformation behavior of precipitation-hardenable AA7075 by compression tests ranging from 200 °C to 350 °C and strain rates from 0.1 s−1 to 10 s−1. The first condition is solution heat-treated and quenched in water, whereas the second condition is achieved by subsequent artificial aging and stabilization for 24 h at the respective intended deformation temperature. Both conditions indicate an increase in flow stress with increasing strain rate and decreasing deformation temperature. Moreover, with increasing deformation temperature and decreasing strain rate, the flow behavior gradually changes as dynamic recrystallization becomes the dominant factor for the flow curve appearance. At the same deformation temperature, higher flow stresses are obtained for the as-quenched condition due to the dynamic precipitation and growth of very small precipitates (r < 20 nm) during hot deformation. For the deformation temperature of 200 °C and the strain rate of 10 s−1, higher peak stresses of 110 MPa are obtained for the as-quenched condition. This is confirmed by the transmission electron microscopy investigations, which show the formation of very fine precipitates for the as-quenched condition, while coarse precipitates can be found in the stabilized microstructure. Despite this observation, the work hardening analysis reveals lower strain-hardening rates for the as-quenched condition and higher critical stresses for the onset of dynamic recrystallization compared to the thermally stabilized microstructure.

Investigation of High-Temperature Constitutive Behavior of Ti555211 Titanium Alloy Subjected to Plastic Deformation in the Different Phase Regions

Ti555211 titanium alloy is subjected to plastic deformation in the dual-phase (α + β phase) zone and single-phase (β phase) zone at various deformation temperatures and strain rates. High-temperature constitutive equations of the alloy in the dual-phase zone and single-phase zone are established in order to describe deformation behavior of the alloy in the different phase zones. By comparing the constitutive equation of the alloy in the dual-phase zone with that of the alloy in the single-phase zone, the deformation activation energy of the former was found to be higher than that of the latter. It is obvious that the deformation activation energy of α phase is obviously greater than that of β phase. Furthermore, the microstructural evolution of the alloy is different in the dual-phase zone and single-phase zone. When the alloy was subjected to plastic deformation in the dual-phase zone, the size of the grains in the β phase increased with the decreasing strain rate. When the alloy was subjected to plastic deformation in the single-phase zone, the size of the grains in the β phase considerably increased with the increasing deformation temperature. In particular, in the microstructures of the alloy subjected to plastic deformation in the single-phase region, the elongated grains can be observed at higher strain rates. Furthermore, it is more difficult for the alloy to induce plastic deformation in the dual-phase region than in the single-phase region.

Investigation of isothermal continuous hot deformation behavior of the new as-cast alumina-forming austenitic alloy

Multi-pass isothermal continuous hot deformation experiments were designed for homogenization and recrystallization in the as-cast alumina-forming austenite (AFA) heat-resistant alloy. Flow curves and microstructure characterization were used to study the grain evolution with different deformation parameters in each pass. In particular, attention was paid to the dendrites and segregated phase. Under different hot deformation conditions, the alloys show significant work-hardening characteristics, which result from the strengthening effect of the primary segregated MC-type carbide. The increase in deformation temperature contributes significantly to dynamic recrystallization (DRX), and the main mechanism of DRX is discontinuous DRX (DDRX). The continuous DRX (CDRX) is less occurring. Static recrystallization (SRX) occurs during the isothermal holding time between deformation passes. SRX becomes more and more apparent with temperature and the holding time. The increase in the deformation passes leads to a gradual disappearance of the alloy dendrites and an increase in the recrystallization volume fraction. Meanwhile, the segregated phase gradually decomposes into particles and partially dissolves. However, the segregated phase particles eventually show band-like distribution. SRX grains around the segregated phase will exhibit similar orientations due to particle-stimulated nucleation (PSN) mechanisms. Until the grain size increases to the point that it can escape from particle restraint, it will transform to random orientation. The above study confirms that multi-pass isothermal continuous hot deformation can improve the as-cast microstructure and guide practical industrial production.

A Comparative Study of Three Constitutive Models concerning Thermo-Mechanical Behavior of Q345 Steel during Hot Deformation

The Gleeble-3800 thermal simulator was used to perform hot compression experiments on Q345 steel at a temperature of 1123~1373 K, a strain rate of 0.01~10 s−1, and 60% deformation. Analysis of the flow curves of Q345 steel revealed that flow stress decreases with the increase of deformation temperature and decrease of strain rate. According to the stress–strain curve of Q345 steel, three constitutive models of Johnson–Cook, Modified Johnson–Cook and strain-compensated Arrhenius were established. By comparison, it was found that the strain-compensated Arrhenius model has higher accuracy, and its correlation coefficient and average relative error are 0.995 and 4.93%, respectively. In addition, the thermal processing map of Q345 steel was established, and the optimal processing range was temperature 1253–1373 K, strain rate 0.5–10 s−1.

Dynamic recrystallization behavior and numerical simulation of S280 ultra-high strength stainless steel

The S280 ultra-high strength stainless steel was subjected to isothermal constant strain rate compression experiments under the conditions of deformation temperature 1000–1150 °C and strain rate 0.001–10 s−1 by Thermecmaster-Z thermal simulation testing machine. The flow behavior of S280 ultra-high strength stainless steel was analyzed; the dynamic recrystallization critical strain model, dynamic recrystallization volume fraction model, dynamic recrystallization grain size and average grain size model of the steel were established, and its dynamic recrystallization behavior was numerically simulated. The results show that the flow stress of S280 ultra-high strength stainless steel increases with the increase of strain rate and the decrease of deformation temperature. The distribution of dynamic recrystallization volume fraction and average grain size in each deformation region after thermal compression is not uniform, and the dynamic recrystallization volume fraction increases with the increase of deformation temperature and decrease of strain rate; the average grain size increases with the increase of deformation temperature and strain rate. The numerical simulation results are in good agreement with the experimental results, which can provide a theoretical basis for the microstructure control of the steel during thermal deformation.

Deformation Behavior and Constitutive Model of 34CrNi3Mo during Thermo-Mechanical Deformation Process.

With higher creep strength and heat resistance, 34CrNi3Mo has been widely used in the production of engine rotors, steam turbine impellers, and turbine blades. To investigate the hot deformation behaviors of 34CrNi3Mo steel, hot compressive tests were conducted on a Gleeble-3500 thermomechanical simulator, under the temperature range of 1073 K–1373 K and strain rate ranges of 0.1 s−1–20 s−1. The results show that the flow stress of 34CrNi3Mo steel under high temperatures is greatly influenced by the deformation temperature and strain rate, and it is the result of the interaction between strain hardening, dynamic recovery, and recrystallization. Under the same deformation rate, as the deformation temperature increases, the softening effect of dynamic recrystallization and dynamic recovery gradually increases, and the flow stress gradually decreases. Under the same deformation temperature, with the increase of strain rate, the influence of strain hardening on 34CrNi3Mo steel is gradually in power, and the flow stress gradually increases. To predict the flow stress of 34CrNi3Mo steel accurately, a modified Arrhenius-type constitutive model considering the effects of strain, temperature, and strain rate at the same time was made based on the experiment data. On this basis, the evolution law of deformation activation and instability characteristics of 34CrNi3Mo steel were investigated, and the processing map of 34CrNi3Mo steel was established. The formability of 34CrNi3Mo steel under high temperature deformation was revealed, which provided a theoretical foundation of the equation of reasonable hot working process.

Role of pre-strain on the corrosion behaviour of Al-Zn-Mg P/M alloy

In the present study, Al-Zn-Mg alloy has been fabricated through the powder metallurgy route by keeping Zn content at 5.6% and varying Mg from 0% to 3%. The optimum composition of Mg was found to be 2% based on relative density, microhardness and microstructure. Al-5.6Zn-2Mg was subjected to deformation at various temperatures (300 °C, 400°C and 500°C) and strain rates (0.5, 0.05 and 0.005). Potentiodynamic polarization and electrochemical impedance spectroscopy were used to assess the electrochemical behaviour of deformed preforms. Scanning electron microscopy was utilized to study the microstructure and corrosion morphology of Al-5.6Zn-2Mg under different conditions. In the present study, deformation behaviour (axial strain (εz), formability stress index (βσ)) has been related to mechanical (hardness) and electrochemical properties (corrosion rate, pitting potential (Epit)). By increasing deformation, potentiodynamic polarization results showed a decrease in corrosion current density (icorr) and an increase in pitting potential, which increased the corrosion resistance of the alloy. The corrosion resistance of the alloy increased significantly by increasing deformation temperature and lowering strain rate. Corrosion rate also decreases with an increase in axial strain and formability stress index. The corrosion mechanisms found in deformed preforms were pitting and intergranular corrosion. The corrosion morphologies also revealed the closure of pores due to increase in temperature and a decrease in strain rate.

Comprehensive improvement of strength and ductility in CLAM steel subjected to TEU: The role of heterogeneous microstructure

To improve the comprehensive properties of CLAM steel and expecting good performance in service conditions, twist extrusion and upsetting (TEU) based thermo-mechanical treatment (TMT) was introduced into the steel at 600 °C, 670 °C, and 740 °C. Optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) was used to characterize the microstructural evolution during the deformation. Uniaxial tension test was used to evaluate the tensile mechanical property. The results show that the grain size and dislocation density of the processed samples decrease from the as-received condition, but are higher than that in the as-tempered conditions. The particle sizes of M23C6 and MX in the TEUed samples are lower than that in the as-tempered case, which contribute a lot to the yield strength. The yield strength of the TEUed CLAM steel decrease with the increase of deformation temperature and a good match in strength and ductility, relating to heterogeneous microstructure, has been achieved at the deformation temperature of 670 °C (yield stress: 853.59 MPa, ultimate tensile stress: 992.4 MPa, elongation: 15.7%). The K value and exponent in the Hall-Petch relationship should be modified owing to the volume fraction of martensite, which is harder than ferrite and causes interface elastic mismatch stress, is different at different temperatures.

Hot deformation and recrystallization behavior of a new nickel-base superalloy for ultra-supercritical applications

The hot deformation behavior of nickel-base superalloy at different temperatures (950–1150 °C) and strain rates (0.01–10 s−1) was investigated by using Gleeble-3800 thermal simulation machine. And the strain compensation Arrhenius model was established according to the obtained stress and strain with the calculated values of the correlation coefficient and the average absolute relative error of 0.986 and 7.17953%, respectively. Meanwhile, the recrystallization fraction model was also established. EBSD was utilized to characterize the microstructure of the experimental materials, and it is found that with the increase of deformation temperature, the recrystallization fraction shows a gradual increasing trend, and the grain grows gradually, while with the increase of strain rate, the recrystallization fraction first decreases and then increases. In addition, the recrystallization mechanism of the test materials is dominated by discontinuous dynamic recrystallization and supplemented by continuous dynamic recrystallization. Recrystallization is initially formed at the original grain boundary, and then gradually develop from the grain boundary to the interior of the grain. The twins inside the grain hinder the dislocation movement, which is conducive to DRX nucleation at the twin boundary. As the recrystallization fraction increases, Σ3 twin boundary fraction increases first and then decreases, and the reason for this change is further discussed.

Microstructural evolution and silicide precipitation behavior of TiCp/near-α titanium matrix composite during hot compression

In this study, TiCp/near-α titanium matrix composite underwent hot compression deformation to investigate the microstructure evolution and silicide precipitation behavior in the α + β phase region. The results show that the peak stress decreases with the increase of temperature or the decrease of strain rate, and the stress-strain curves show a similar trend with the increase of strain under the same other parameters. The silicides with larger size are mainly distributed at the α/β phase boundaries, and a small number of silicides with smaller size can be observed in α phases. In addition, with the increase of deformation temperature, the number and size of silicides first increase and then decrease. With the increase of strain rate, the number of silicides increases while the size first decreases and then increases. Moreover, with the increase of strain, the number of silicides first increases and then decreases while the size decreases. Meanwhile, 925 °C is more conducive to dynamic recrystallization than 885 °C during hot compression.