Optimum Deformation Condition Research Articles

Hot Deformation Behavior and Processing Maps of a 9Ni590B Steel

To increase the hot workability and provide proper hot forming parameters of a 9Ni590B steel for the simulation and production, the hot deformation behavior of the 9Ni590B steel is investigated through isothermal compression tests using a Gleeble-3180 thermal–mechanical simulator over a temperature range of 850-1200 °C with strain rates of 0.001-5 s−1. The results indicate that as the deformation temperature increases and the strain rate decreases, the flow stress of the 9Ni590B steel decreases. The deformation–activation energy was calculated to be 364.99 kJ/mol based on the flow stress curve data. The dynamic material model (DMM) was used to establish the process map of the thermal deformation for the 9Ni590B steel. The results show that the optimal deformation conditions for the 9Ni590B steel hot working are with a temperature range of 1100-1200 °C and a strain rate range of 0.001-0.01 s−1. The validity of the calculations was confirmed by observing the microstructure of the 9Ni590B steel sample under the optimal thermal process parameters.

Hot Deformation Behavior and Microstructure Evolution of Cu-Ni-Co-Si Alloys.

The Cu-1.7Ni-1.4Co-0.65Si (wt%) alloy is hot compressed by a Gleeble-1500D machine under a temperature range of 760 to 970 °C and a strain rate range of 0.01 to 10 s−1. The flow stress increases with the extension of strain rate and decreases with the rising of deformation temperature. The dynamic recrystallization behavior happens during the hot compression deformation process. The hot deformation activation energy of the alloy can be calculated as 468.5 kJ/mol, and the high temperature deformation constitutive equation is confirmed. The hot processing map of the alloy is established on the basis of hot deformation behavior and hot working characteristics. With the optimal thermal deformation conditions of 940 to 970 °C and 0.01 to 10 s−1, the fine equiaxed grain and no holes are found in the matrix, which can provide significant guidance for hot deformation processing technology of Cu–Ni–Co–Si alloy.

Comparative Hot Workability Characteristics of an Al–Si/SiCp Aluminium Matrix Composite Hybrid Reinforced with Various TiB2 Additions

Hot compression tests were conducted on Al–Si/SiCp + TiB2 hybrid aluminium matrix composites with various TiB2 contents at temperatures from 350 to 500 °C and strain rates from 0.001 to 1 s−1. The hot workability characteristics and deformation mechanisms were investigated by combining constitutive equations, processing maps and microstructural observations through scanning electron microscopy and transmission electron microscopy measurements. The results showed that there were small differences in the peak stresses when the contents of TiB2 were 3% and 5%, while the peak stress increased when the content of TiB2 reached 8%. The contents of TiB2 had little influence on the activation energy but affected the processing maps to a certain extent. The areas of the instability zones were observed to gradually increase with increased TiB2 additions. The optimal deformation conditions of the studied materials migrated from a low temperature and high strain rate to a high temperature and low strain rate with increasing TiB2 content. In addition, the flow softening mechanism transformed from dynamic recrystallization + dynamic recovery to dynamic recovery with increasing TiB2 content.

Hot Deformation Characteristics and Processing Map Analysis of Pre-Forged AZ80 Magnesium Alloy

The hot deformation behavior of pre-forged AZ80 magnesium alloy is investigated by the isothermal compression tests at temperatures of 523–683 K and strain rates of 0.0001–0.1 s−1, and analyzed by the processing maps for guiding isothermal die forging. Flow localization and even cracking occurs at low temperatures and high strain rates, where shear deformation degree shows a positive correlation with the $$\xi \left( {\dot{\varepsilon }} \right)$$ value. Two stability regions with high efficiency is found out by the processing maps. At common stability region with high temperatures and low strain rates, peak power dissipation efficiency does not represent optimum deformation condition as reported in other materials. A Z parameter criterion is introduced for parameters optimization. javascript:void(0); a new stability domain of 523–590 K and 0.0001–0.01 s−1 is observed, which is typical for fine microstructure composed of equiaxed clean α-Mg grains and big particles both about 1 µm (573 K/0.01 s−1). Super plasticity is speculated to occur at that condition.

Hot Deformation Behavior and Processing Map of a Fe-11Mn-10Al-0.9C Duplex Low-Density Steel Susceptible to κ-Carbides

The hot deformation behavior of a Fe-11Mn-10Al-0.9C duplex low-density steel has been investigated, based on a series of isothermal compression tests at temperatures of 800-1100 °C and strain rates of 0.001-10 s−1. At relatively lower temperatures, with austenite decomposing, continuous dynamic recrystallization of ferrite and the formation of inter-granular κ-carbide were responsible for significant softening. At high deformation temperature where austenite was a dominant phase, dynamic recrystallization (DRX) is the restoration mechanism. Processing maps were developed at different plastic strains employing dynamic materials model and further verified through microstructural characterization. The optimal hot deformation condition at a large strain (0.7) was identified as deformation temperature of 950-1100 °C and strain rate of 0.01-1.0 s−1. In this domain, the original coarse grains could be replaced by the fine and uniform recrystallized grains, indicating that the high efficiency was dissipated by DRX. Meanwhile, two instable regions resulted from the formation of inter-granular κ-carbides and necklace structure should be avoided during hot processing.

Hot Deformation Behavior and Microstructural Evolution of a Novel β-Solidifying Ti-43Al-3Mn-2Nb-0.1Y Alloy.

In this paper, the hot deformability and mechanical properties of a novel Mn- and Nb- containing TiAl alloy were studied systematically with the use of isothermal compression experiments. The results show that the alloy has low deformation resistance and a low activation energy (392 KJ/mol), suggesting that the alloy has good hot deformability. A processing map was established, which shows that the present alloy has a smaller instability region and wider hot working window compared with other TiAl alloys. Microstructural observation shows that the initial lamellae completely transformed into fine equiaxial γ grains when the alloy was compressed at 1200 °C/0.01 s−1, which corresponds to the optimum deformation condition. Based on the above results, an intact TiAl billet was successfully fabricated by one-step large deformation using a four-column hydraulic machine. The microstructure of the billet is almost completely composed of recrystallized γ grains with large angle boundaries. Tensile testing shows the billet exhibits high tensile strength (780 MPa) and high elongation (1.44%) simultaneously, which benefits from fine γ grains with an average size of 4.9 μm. The ductile–brittle transition temperature is between 750–800 °C.

Characterization of Hot Deformation Behavior of Nanosized Al₂O₃ Reinforced Al6061 Composites.

The hot deformation behavior of Al6061/Nano-Al₂O₃ composites were investigated at temperatures of 300 to 500 °C and strain rates of 0.001∼1/s using compression tests. The composite fabricated by the infiltration method consisted of an Al matrix and Al₂O₃ particles with a mean size of 200 nm. Interestingly, the true stress-true strain curves under all compressive conditions showed a peak stress at the initial stages of deformation, in which the peak stress increased with decreasing temperature and faster strain rate. The Z parameter, which is known as the temperature-compensated strain rate showed a linear relationship with the flow stress. The hot deformation mechanism is believed to occur through dynamic recrystallization, where fine equiaxed grains and dislocations were observed at the deformed specimens. A processing map was applied to evaluate the hot workability and flow instability region to determine the optimal deformation conditions of the composite.

Study on the Hot Deformation Behavior and Microstructure Evolution of Cu-Cr-In Alloy

Based on the hot compressive tests in the temperature range of 700-900 °C and strain rate range of 0.01-10 s−1, the hot deformation behavior of a Cu-Cr-In alloy was investigated. The true stress–strain curves of the alloy were obtained, and a constitutive equation for the alloy was established by the method of equivalent stress. The processing maps were constructed based on the constitutive equation, and the microstructural evolutions were analyzed and correlated with the processing maps. The results show that the true stress of the alloy increased with decreasing strain rate and decreased with increasing temperature. The microstructures of the alloy deformed under different conditions were in good accordance with the processing maps results. According to the processing maps and the microstructures of the alloy with true strains of 0.4 and 0.8, the optimal hot deformation conditions lie in the range of 850-900 °C and strain rate range of 0.01-0.1 s−1.

Investigation on the Thermal Deformation Behavior of the Nickel-Based Superalloy Strengthened by γ′ Phase

The isothermal compression tests of the nickel-based superalloy Waspaloy were carried out under various temperatures from 1040 to 1120 °C and strain rates from 0.01 to 10 s−1 with the height reduction of 60% and the flow stress curves were obtained. The curves show that the flow stress is greatly affected by the temperature and strain rates. Regression analysis of the experimental results was carried out to learn about the deformation behavior through the Arrhenius equation and came to the conclusion that the activation energy of Waspaloy is 669.7 kJ/mol. The constitutive equation of the Waspaloy was constructed. Meanwhile, the processing maps of the Waspaloy for the power dissipation and the flow instability were constructed. The processing map of the power dissipation and the flow instability depicts that the strain plays a major role in the processing maps. The instability zone is prone to appear at higher strain rates with the increasing strains. According to the instability processing map, there are three unsafe regimes around 1040–1120 °C/1.5–10 s−1, 1040–1080 °C/0.02–0.1 s−1 and 1110–1120 °C/0.02–0.3 s−1 that should be avoided during deformation process. The power dissipation maps show that the maximum dissipation is prone to appear at low strain rates (0.01 s−1) when the strain is about 0.1~0.6 while at middle strain rates (0.1–1 s−1) when the strain is over 0.6, and when the true strain is 0.9, the optimum processing condition is around 1060–1120 °C/0.1–1 s−1. The dynamic microstructures under different temperatures and strain rates were also obtained. We concluded that lower strain rates and higher temperatures are more applicable to obtain fully-recrystallized microstructures. Based on the instability maps and the power dissipation maps and the dynamic microstructures, the optimum deformation conditions are determined to be around 1080–1100 °C/0.1–1 s−1 and 1040–1120 °C/0.01 s−1.

High temperature deformation and control of homogeneous microstructure during hot pack rolling of Ti-44Al-5Nb-(Mo, V, B) alloys: The impact on mechanical properties

Hot workability and deformation mechanism of β-solidifying γ-TiAl alloy with a nominal composition of Ti-44Al-5Nb-1Mo-2V-0.2B (in at%) were systematically studied under uniaxial hot compression. The strain rate sensitivity exponent (m) and processing maps at strains of 0.2 and 0.6 were developed. Based on an analysis of the processing maps and the corresponding microstructure, 1200 °C/0.1 s−1 was defined as the optimum deformation condition. At low temperatures and high strain rates, pileup of dislocations at lamellar colonies was found to be responsible for deformation, which provided the driving force for sub-grain boundary formation. As deformation progressed, twinning-induced dynamic recrystallization (DRX) and near complete breakdown of lamellae through the rearrangement of sub-boundaries were the main deformation mechanism. Moreover, nano-lamellar structure and stacking faults (SF) were generated. The hot isostatically pressed (as-HIPed) alloy had relatively good workability, and crack-free sheets were obtained from the as-HIPed alloy with different reductions. A multiple phase, homogeneous as-rolled microstructure without coarse residual lamellar colonies (RL) or shear bands was obtained when the total rolling reduction was 78.8%. The ultimate tensile stress (UTS) and ductility at 800 °C ranged from 523 to 553 MPa and from 21% to 32%, respectively, for different deformation reductions.

Hot workability of V-Ti microalloyed steel for forging

The hot compression and the hot tensile experiments were carried out on a Gleeble3800 thermal-mechanical simulator at different deformation conditions. The relationship between the flow stress and Zener-Hollomon parameter was established by the hyperbolic sine function. The hot deformation apparent activation energy is about 371 kJ/mol. There are two peak regions of m-value in the m maps with true strain of 0.2. One peak corresponds to the temperature of 1050 °C and the strain rate of 0.01 s−1, the other one corresponds to the temperature of 1200 °C and the strain rates within range of 0.1 s−1 ∼ 1 s−1. There is only one peak region (1150 °C ∼ 1200 °C, 0.1 s−1 ∼ 1 s−1) of m-value, when true strain is 0.4 or 0.9. The reduction of area increases from 65% to 98% with the temperature increases from 800 °C to 1200 °C. In temperature range of 1000 °C ∼ 1200 °C, the reduction of area is always over 90%, which means that the plasticity of the steel is fine. According to the results of the research, it can be proved that the optimal deformation conditions with different strain correspond to the peak regions of m-value. The optimum deformation conditions is the temperature of 1200 °C and the strain rates within range of 0.1 s−1 ∼ 1 s−1, which were suitable for the true strain with 0.2, 0.4 and 0.9 at the same time.

Hot deformation behavior of AA6005 modified with CaO-added Mg at high strains

Hot torsion tests were carried out on an AA6005 modified with CaO-added Mg to study its hot deformation behavior. The flow curves indicated that the failure strain of the modified alloy was greater than that of the conventional alloy at low temperature and all strain rates employed in this study. The constitutive analysis was conducted on the effective stress–effective strain data, and the derived activation energy for hot deformation of the modified alloy was lower than that of the conventional alloy. The processing maps were established at various strains, and the power dissipation efficiency increased as the strain increased. The gap between contour lines decreased as the strain increased, indicating that the power dissipation efficiency became more sensitive to the strain. The optimum deformation conditions were determined by comparing the power dissipation efficiency in the processing maps. However, the power dissipation efficiency of the modified alloy was greater than that of the conventional alloy. The observed microstructure demonstrated that the lower activation energy, greater failure strain, and higher power dissipation efficiency were primarily attributed to the different states in the distribution of second phase particles caused by the use of CaO-added Mg.

Hot Deformation Behavior of Hot-Extruded AA7175 Through Hot Torsion Tests.

The hot deformation behavior of hot-extruded AA7175 was investigated with flow curves and processing maps through hot torsion tests. The flow curves and the deformed microstructures revealed that dynamic recrystallization (DRX) occurred in the hot-extruded AA7175 during hot working. The failure strain was highest at medium temperature. This was mainly influenced by the dynamic precipitation of fine rod-shaped MgZn2. The processing map determined the optimal deformation condition for the alloy during hot working.

The research on vacuum isothermal bloom for powder metallurgy V-5Cr-5Ti alloy guiding by the constitutive models and the error analysis

For studying the vacuum isothermal cogging technology for V-5Cr-5Ti alloy, the isothermal hot compression tests are conducted in the deformation temperature ranging from 1150 °C(1423 K) to 1400 °C(1673 K) with an interval of 50 °C, strain rate ranging from 0.001 to 1 s−1 and height reductions of 55% on a computer controlled thermal simulation machine. The three kinds of constitutive equations of V-5Cr-5Ti alloy are deduced based on the true stress–strain curves. The analysis is carried out for the error for constitutive models and the optimum deformation condition. Isothermal hot cogging in vacuum is carried out guiding by the constitutive models and the optimum deformation conditions. Warm rolling is adopted for sheet manufacture of the cogging billet. The test results show that strain-compensated Arrhenius constitutive model is the most accurate and modified Johnson Cook constitutive model is the most efficient among them; by the solution steps, microstructure with metallographic and EBSD technology and other factors, the error reasons generated at lower strain rate of 0.001 s−1 and 0.01 s−1 in the modified Johnson-Cook and Zerilli-Armstrong models are explicit to some extent; the optimum deformation condition is at the temperature of 1250–1400 °C and the strain rate is 0.001–0.02 s−1, which are determined through strain rate sensitivity coefficients(m), deformation activation energy(Q) and the processing map; the mechanical properties of the sheet by warm rolling are the yield of 400 MPa, the tensile strength of 535 MPa and the elongation rate of 35%. And the material utilization rate is high up to 90%.

Hot Deformation and Processing Maps of Al-15%B4C Composites Containing Sc and Zr

Hot deformation behavior and processing maps of three Al-15%B4C composites denoted as the base composite (Al-15vol.%B4C), S40 (Al-15vol.%B4C-0.4wt.%Sc) and SZ40 (Al-15 vol.%B4C-0.4wt.%Sc-0.24wt.%Zr) were studied by uniaxial compression tests performed at various deformation temperatures and strain rates. The constitutive equations of the three composites were established to describe the effect of the temperature and strain rate on hot deformation behavior. Using the established constitutive equations, the predicted flow stresses on various deformation conditions agreed well with the experimental data. The peak flow stress of the composites increased with the addition of Sc and Zr, attributing to the synthetic effect of solute atoms and dynamic precipitation. The addition of Sc and Zr increased the activation energy for hot deformation of Al-B4C composites. The processing maps of the three composites were constructed to evaluate the hot workability of the composites. The safe domains with optimal deformation conditions were identified for all three composites. In the safe domains, dynamic recovery and dynamic recrystallization were involved as softening mechanisms. The addition of Sc and Zr limited the dynamic softening process, especially for dynamic recrystallization. The microstructure analysis revealed that the flow instability was attributed to the void formation, cracking and flow localization during hot deformation of the composites.

Hot Deformation Characterization of Mg-Sm-Zn-Zr Alloy Using Artificial Neural Network and 3D Processing Map

The true stress-strain data from isothermal hot compression tests on Gleeble-1500D thermo mechanical simulator, in a wide range of temperatures (350-450°C) and strain rates (0.001-1s-1), was employed to establish the PSO-BP network prediction model and 3D processing map of Mg-Sm-Zn-Zr alloy. It was found that the PSO-BP model could be efficient and accurate in predicting flow stress, most of relative errors were in the range of -4% to 6%, and the average relative error was found to be 1.52%. Then considering the effect of strain, the 3D processing map was established to characterize the hot workability of the alloy. The 3D processing map exhibited the maximum efficiency domain and the instability domain, which could be used to determine the optimal deformation conditions. The optimum processing parameters of Mg-Sm-Zn-Zr alloy were deformation temperatures of 400-450°C and strain rates of 0.003-0.1s-1.

Flow softening and dynamic recrystallization behavior of BT9 titanium alloy: A study using process map development

In the present study, uniaxial compression tests were employed between 1000 and 1100 °C under the strain rates of 10−3, 10−2 and 10−1 s−1 to investigate the hot deformation behavior of BT9 titanium alloy. Work hardening behavior interpretation and analytical investigations including calculation of deformation activation energy, and developing process maps were used to establish a numerical correlation between microstructural evolution and the flow behavior of the alloy. The results showed that dynamic recrystallization takes place at severe condition (T = 1000 °C and ε˙ = 0.1 s−1), while dynamic recovery is the major microstructural mechanism at other condition. According to dynamic material model and Prasad's instability criterion, the maximum power dissipation of 52% and 46% occur at 1000 °C/0.1s−1 and 1150 °C/0.001 s−1, respectively. Electron backscattered diffraction images and high resolution optical images also revealed that continuous dynamic recrystallization is the governing mechanism at these deformation conditions resulting in a significant grain refinement. Considering the calculated deformation activation energies, power efficiency domains and the microstructural observations, 1000 °C/0.1 s−1 was determined as the optimum deformation condition.

Dynamic Recrystallization Kinetics and Microstructural Evolution for LZ50 Steel During Hot Deformation

The dynamic recrystallization (DRX) behavior of LZ50 steel was investigated using hot compression tests at a deformation temperature of 870-1170 °C and a strain rate of 0.05-3 s−1. The effects of deformation temperature, strain, strain rate, and initial austenite grain size on the microstructural evolution during DRX were studied in detail. The austenite grain size of DRX was refined with increasing strain rate and decreasing temperature, whereas the initial grain size had no influence on DRX grain size. A model based on the Avrami equation was proposed to estimate the kinetics of the DRX under different deformation conditions. A DRX map, which was derived from the DRX kinetics, the recrystallized microstructure, and the flow stress analysis, can be used to identify optimal deformation conditions. The initiation of DRX was lower than Zc (critical Zener-Hollomon parameter) and higher than ec (critical strain). The relationship between the DRX microstructure and the Z parameter was analyzed. Fine DRX grain sizes can be achieved with a moderate Z value, which can be used to identify suitable deformation parameters.

The Superplastic Properties and Microstructures Evolution of High Nb Ti<sub>3</sub>Al Based Alloy

The superplasticity of high Nb Ti3Al based alloy - Ti-23Al-17Nb (at.%) alloy sheet under the conditions of 940~1000°C and 5.5×10-5s-1~1.7×10-3s-1are studied. The results show the elongation changes as a parabola with the deformation temperature increasing, and the maximum elongation obtained at 960°C and 5.5x10-5s-1 is 1447.5%. Work hardening stage increases much more than softening stage when strain rate is decreased due to the increasing of element Nb. Compared with primary microstructure, the lath-like α2 grains gradually disappeared, the α2 grains became more equiaxed, and the content and size of α2 grains are decreasing with increasing of deformation temperature. The volume fraction ratio of α2 and β phase at the optimum deformation condition is 50:50%. The cavities mechanism at the fracture tip was discussed; it can be defined that the cavities could be avoided when deformation temperature is higher than 940°C.

Deformation behavior and processing maps during isothermal compression of TC21 alloy

In this study, isothermal compression tests were conducted at a Gleeble-1500 simulator at deformation temperatures ranging from 1073 to 1283 K, strain rates ranging from 0.01 to 5.00 s−1, and height reductions ranging from 20 % to 60 %. The flow stress and apparent activation energy for deformation and constitutive equation were used to characterize the deformation behavior of TC21 alloy during the isothermal compression. The processing maps combined microstructure observations were established based on dynamic material model (DMM) over a range of strain rates and temperatures. The results show that an initial yield drop is observed above 1203 K or at higher strain rates ranging from 1.00 to 5.00 s−1, and oscillatory flow curves are presented particularly at a strain rate of 5.00 s−1. Strain has some influence on the apparent activation energy for deformation during the isothermal compression of TC21 alloy. The Q-values and microstructure observation confirm that dynamic recrystallization (DRX) occurs in the β single-phase region. The constitutive equation during the isothermal compression of TC21 alloy is developed using the Zener–Hollomon parameter in the exponent-type equation. The maximum and minimum relative errors between the calculated and the experimental flow stress are 14.1 % and 0.3 %, respectively. The peak efficiency of power dissipation at a strain of 0.7 is about 0.51 occurring at a deformation temperature of 1073 K and strain rate of 0.01 s−1, corresponding to an optimal deformation condition of TC21 alloy.