Study of the processing map and hot deformation behavior of a Cu-bearing 317LN austenitic stainless steel

The hot-working behavior of a Cu-bearing 317LN austenitic stainless steel (317LN–Cu) was investigated in the 950–1150 °C temperature and 0.01–10 s^− 1strain rate range, respectively. The effects of different deformation parameters and optimum hot-working window were respectively characterized through analyzing flow stress curves, constitutive equations, processing maps and microstructures. The critical strain for dynamic recrystallization (DRX) was determined by the inflection point on θ-σ and −∂θ/∂σ-σ curves. The peak stress was found to increase with decrease in temperature and increase in strain rate. Typical signs of DRX over a wide range of temperatures and strain rates were observed on the flow stress curves. The power dissipation maps in the strain range of 0.1–0.4 were basically similar, indicating the insignificant effect of strain on the power dissipation maps of 317LN–Cu. However, the instability maps showed strong strain sensitivity with increasing strain, which was attributed to the flow localization. The optimum hot-working window for 317LN–Cu was obtained in the temperature range 1100–1120 °C and strain rate range 0.01–0.018 s^− 1, with a peak efficiency of 38%. Microstructural analysis revealed fine and homogenized recrystallized grains in this domain.     

Quantitative Analysis of Work Hardening and Dynamic Softening Behavior of low carbon alloy Steel Based on the Flow Stress

In this study, the constitutive equation and DRX(Dynamic recrystallization) model of Nuclear Pressure Vessel Material 20MnNiMo steel were established to study the work hardening and dynamic softening behavior based on the flow behavior, which was investigated by hot compression experiment at temperature of 950 °C, 1050 °C, 1150 °C and 1250 °C with strain rate of 0.01 s⁻¹, 0.1 s⁻¹ and 10 s⁻¹ on a thermo-mechanical simulator THE RMECMASTOR-Z. The critical conditions for the occurence of dynamic recrystallization were determined based on the strain hardening rate curves of 20MnNiMo steel. Then the model of volume fraction of DRX was established to analyze the DRX behavior based on flow curves. At last, the strain rate sensitivity and activation volume V^* of 20MnNiMo steel were calculated to discuss the mechanisms of work hardening and dynamic softening during the hot forming process. The results show that the volume fraction of DRX is lower with the higher value of Z (Zener–Hollomon parameter), which indicated that the DRX fraction curves can accurately predicte the DRX behavior of 20MnNiMo steel. The storage and annihilation of dislocation at off-equilibrium saturation situation is the main reason that the strain has significant effects on SRS(Strain rate sensitivity) at the low strain rate of 0.01 s⁻¹ and 0.1 s⁻¹. While, the effects of temperature on the SRS are caused by the uniformity of microstructure distribution. And the cross-slip caused by dislocation piled up which beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions. Otherwise, the coarsening of DRX grains is the main reason for the high activation volume at low Z under the same strain conditions.     

Study of hot forging behavior of as-cast Mg–3Al–1Zn–2Ca alloy towards optimization of its hot workability

Mg–3Al–1Zn–2Ca (AZX312) alloy has been forged in the temperature range of 350–500 °C and at speeds in the range of 0.01–10 mm s⁻¹ to produce a rib-web shape with a view to validate the processing map and study the microstructural development. The process was simulated through finite-element method to estimate the local and average strain rate ranges in the forging envelope. The processing map exhibited two domains in the following ranges: (1) 350–450 °C/0.0003–0.05 s⁻¹ and (2) 450–500 °C/0.03–0.7 s⁻¹ and these represent dynamic recrystallization (DRX) and intercrystalline cracking, respectively. The optimal workability condition according to the processing map is 425–450 °C/0.001–0.01 s⁻¹. A wide flow instability regime occurred at higher strain rates diagonally across the map, which caused flow localization that should be avoided in forming this alloy. The experimental load–stroke curves correlated well with the simulated ones and the observed microstructural features in the forged components matched with the ones predicted by the processing map.     

Hot shear deformation constitutive analysis and processing map of extruded Mg–12Li–1Zn bcc alloy

The hot shear deformation behavior of an extruded Mg–12Li–1Zn alloy was studied by shear punch test (SPT) in the temperature range 200–300 °C, and in the shear strain rate range 1.2 × 10⁻³–6.0 × 10⁻² s⁻¹. Based on the constitutive analysis of the SPT data, it was found that a sine hyperbolic function could properly describe the hot shear deformation behavior of the material. The activation energy of 108 kJ mol⁻¹ calculated from sine hyperbolic function together with the power-law stress exponents of 3.6–4.7 is indicative of lattice-diffusion-controlled dislocation climb mechanism as an operative deformation mechanism. As a new approach, the shear processing map was developed in order to determine the optimum processing condition, which was found to be 300 °C and 1.2 × 10⁻³ s⁻¹. Domains of the processing map are also interpreted on the basis of the associated microstructural observations. It was found that the post-deformation microstructure is sensitive to the Zener–Hollomon parameter, so that DRX was encouraged with decreasing Z-value.     

Effect of processing parameters on the hot deformation behavior of as-cast TC21 titanium alloy

Isothermal compression tests of as-cast Ti–6A1–2Zr–2Sn–3Mo–1Cr–2Nb (TC21) titanium alloy are conducted in the deformation temperature ranging from 1000 to 1150 °C with an interval of 50 °C, strain rate ranging from 0.01 to 10.0 s⁻¹ and height reductions of 30%, 45%, 60% and 75% on a computer controlled Gleeble 3500 simulator. The true stress–strain curves under different deformation conditions are obtained. Based on the experimental data, the effects of deformation parameters on the hot deformation behavior of as-cast TC21 alloy were studied. The deformation mechanisms of the alloy in the whole regimes are predicted by the power dissipation efficiency and instability parameter and further investigated through the microstructure observation. It is found that at the height reductions of 30%, 45% and 60%, the softening of stress–strain curves at high strain rate (>1.0 s⁻¹) is mainly associated with flow localization, which is caused by local temperature rise, whereas at low strain rate, the softening is associated with dynamic recrystallization (DRX). However, the instability showed in flow localization occurs at low strain rate of 0.01 s⁻¹ when the height reduction reaches 75%. In addition, the effects of strain rate, deformation temperature and height reduction on microstructure evolution are discussed in detail, respectively.     

Microstructure characteristic for high temperature deformation of powder metallurgy Ti–47Al–2Cr–0.2Mo alloy

Hot compression tests of a powder metallurgy (P/M) Ti–47Al–2Cr–0.2Mo (at. pct) alloy were carried out on a Gleeble-3500 simulator at the temperatures ranging from 1000 °C to 1150 °C with low strain rates ranging from 1 × 10⁻³ s⁻¹ to 1 s⁻¹. Electron back scattered diffraction (EBSD), scanning electron microscope (SEM) and transmission electron microscope (TEM) were employed to investigate the microstructure characteristic and nucleation mechanisms of dynamic recrystallization. The stress–strain curves show the typical characteristic of working hardening and flow softening. The working hardening is attributed to the dislocation movement. The flow softening is attributed to the dynamic recrystallization (DRX). The number of β phase decreases with increasing of deformation temperature and decreasing of strain rate. The ratio of dynamic recrystallization grain increases with the increasing of temperature and decreasing of strain rate. High temperature deformation mechanism of powder metallurgy Ti–47Al–2Cr–0.2Mo alloy mainly refers to twinning, dislocations motion, bending and reorientation of lamellae.     

Combined effect of strain-rate and mode-ratio on the fracture of lead-free solder joints

The critical strain energy release rate for the solder joint fracture was measured as a function of the strain rate and the mode ratio of loading. These data are useful in predicting the fracture of solder joints loaded under arbitrary combinations of tension and shear during the impact conditions typical of falling portable electronic devices. In this study, strain rates from quasi-static (close to 0 s^− 1) to 61 s^− 1 were investigated at phase angles from 0 to 60°, typical of the range found in microelectronic devices. Copper–solder–copper double cantilever beam (DCB) model specimens were prepared using SAC305 solder at cooling rates and times above liquidus typical of actual ball grid arrays (BGAs). A drop tester was designed and built to achieve different strain rates at various mode ratios. The critical initiation strain energy release rate, J_ci, increased about 70% from quasi-static to intermediate strain rates, before decreasing by more than 67% from intermediate strain rates to 42 s^− 1.     

Study on hot workability and optimization of process parameters of a modified 310 austenitic stainless steel using processing maps

To investigate the optimized hot deformation parameters of a modified 310 austenitic stainless steel, the hot compression tests were performed using a Gleeble 3500 thermal simulator. The hot deformation behavior and hot workability characteristics were investigated in a temperature range of 800–1100 °C and a strain rate range of 0.1–10 s⁻¹. The hot processing maps of the tested steel were developed based on the dynamic material model (DMM), from which the safe deformation regions and instable deformation regions were determined. The corresponding microstructural and hardness evolutions during deformation were analyzed in detail. It was found that the deformation in the safe regions was beneficial to dynamic recovery (DRY) and dynamic recrystallization (DRX), while the deformation in unstable region would lead to flow instability, kink boundaries and grain growth. Near 950 °C, the energy dissipation rates were unusually lower, and the hardness of the deformed sample exhibited a significant increase, as a result of strain-induced precipitation. Coupled with the microstructure analysis and processing map technology, the workability map was schematically plotted and the optimal working conditions were determined. Such conditions were: temperatures in the range of 1075–1100 °C and strain rates in the range of 0.5–1.7 s⁻¹. These conditions are critical to attain an excellent homogeneous microstructure with fine grains after deformation for the modified 310 austenitic stainless steel.     

Characterization of hot compression behavior of a new HIPed nickel-based P/M superalloy using processing maps

Isothermal forging was a critical step process to fabricate the high-performance nickel-based superalloy. The temperature and strain rate served the most critical role in determining its microstructure and mechanical properties. In this article, we employed the hot compression to simulate the isothermal forging process upon the temperature ranging from 1000 °C to 1100 °C in combination with a strain rate of 0.001–1.0 s^− 1 for a new P/M nickel-based alloy. The activation energy was determined as 903.58 kJ/mol and the processing maps at a strain range of 0.4–0.7 were developed. The instability domains were more inclined to occur at strain rates higher than 0.1 s^− 1 and manifested in the form of adiabatic shear bands. The map further demonstrated that the regions with peak efficiency of 55% were located at 1080 °C/0.0015 s^− 1 and 1095 °C/0.014 s^− 1, respectively. Obvious dynamic recrystallization could be detected at the strain rate 0.01 s^− 1 leading to a significant flow stress drop and the grain growth was remarkably triggered under 1100 °C. The findings can shed light on the forging processing optimization of the new nickel-based superalloy.     

Development of processing maps for a Ni-based superalloy

The hot deformation characteristics of a Ni-based superalloy were studied in the temperature range 1050–1180 °C and strain rate range 0.01–10 s^− 1 using hot compression tests. Processing maps for hot working were developed on the basis of the variations of efficiency of power dissipation with temperature and strain rate, interpreted using a dynamic materials model. A hot deformation equation is given to characterize the dependence of peak stress on the temperature and strain rate. A hot deformation apparent activation energy of the Ni-based superalloy is about 496 kJ/mol. The processing maps of the Ni-based superalloy obtained in a strain range of 0.1–0.7 are essentially similar, which indicates that strain does not have a significant influence. The maps exhibit a clear domain with its peak efficiency at about 1140 °C and 0.01 s^− 1; the domain has its peak efficiency of about 36–41% for different strains. On the basis of hot deformation microstructural observations, the full recrystallization region can be identified in the processing map at a strain of 0.7.     

Hot deformation behavior of an austenitic Fe–20Mn–3Si–3Al transformation induced plasticity steel

Hot deformation behavior of an austenitic Fe–20Mn–3Si–3Al transformation induced plasticity (TRIP) steel was investigated by hot compression tests on Gleeble 3500D thermo-mechanical simulator in the temperature ranges of 900–1100 °C and the strain rate ranges of 0.01–10 s⁻¹. The results show that the flow stress is sensitively dependent on deformation temperature and strain rate, and the flow stress increases with strain rate and decreases with deformation temperature. The peak stress during hot deformation can be predicted by the Zener–Hollomon (Z) parameter in the hyperbolic sine equation with the hot deformation activation energy Q of 387.84 kJ/mol. The dynamic recrystallization (DRX) is the most important softening mechanism for the experimental steel during hot compression. Furthermore, DRX procedure is strongly affected by Z parameter, and decreasing of Z value lead to more adequate proceeding of DRX.     

The hot deformation behavior and processing map of Ti–47.5Al–Cr–V alloy

The high temperature flow behavior of as-extruded Ti–47.5Al–Cr–V alloy has been investigated at the temperature between 1100 °C and 1250 °C and the strain rate range from 0.001 s^− 1 to 1 s^− 1 by hot compression tests. The results showed that the flow stress of this alloy had a positive dependence on strain rate and a negative dependence on deformation temperature. The activation energy Q was calculated to be 409 kJ/mol and the constitutive model of this material was established. By combining the power dissipation map with instability map, the processing map was established to optimize the deformation parameters. The optimum deformation parameter was at 1150 °C–1200 °C and 0.001 s^− 1–0.03 s^− 1 for this alloy. The microstructure of specimens deformed at different conditions was analyzed and connected with the processing map. The material underwent instability deformation at the strain rate of 1 s^− 1, which was predicted by the instability map. The surface fracture was observed to be the identification of the instability.     

Hot workability and deformation mechanisms in Mg/nano–Al2O3 composite

The response of extruded Mg/nano–Al₂O₃ (1 vol.%) composite to hot working in the temperature range 300–500 °C and strain rate range 0.0003–10 s^?1 has been characterized using processing map and kinetic analysis. The hot working window for the composite occurs at strain rates >0.1 s^?1 and the optimum range of temperature is 400–450 °C. In this window, the behavior of the composite is similar to that of the matrix and is controlled by the grain boundary self-diffusion. At lower strain rates, however, the composite exhibits much higher apparent activation energy than that for lattice self-diffusion unlike the matrix material. The deformed microstructures revealed that the prior particle boundaries decorated by the nano-Al₂O₃ particles, are stable and do not slide, rotate or migrate but kink after compressive deformation and as such contribute to the high temperature strength of the composite.     

Experimental study on the dynamic tensile behavior of a poly-crystal pure titanium at elevated temperatures

A new technique for measuring dynamic tensile behavior of metallic materials at elevated temperatures was developed. This technique employs a rapid contact heating method to obtain a stable and nearly homogenous high temperature field in the testing gage of the specimen. As an application of this new technique, a commercially pure titanium (CP-Ti) was tested in the strain rate range of 300 s⁻¹–1400 s⁻¹ and in a temperature range of 298 K–973 K. Quasi-static experiments (10⁻³ s⁻¹, 10⁻² s⁻¹) were also performed in the same temperature range for comparison. The testing results indicated that both temperature and strain rate have pronounced influence on the mechanical behavior of CP-Ti.     

Hot tensile deformation behaviors and constitutive model of 42CrMo steel

The hot tensile deformation behaviors of 42CrMo steel are studied by uniaxial tensile tests with the temperature range of 850–1100 °C and strain rate range of 0.1–0.0001 s⁻¹. The effects of hot forming process parameters (strain rate and deformation temperature) on the elongation to fracture, strain rate sensitivity and fracture characteristics are analyzed. The constitutive equation is established to predict the peak stress under elevated temperatures. It is found that the flow stress firstly increases to a peak value and then decreases, showing a dynamic flow softening. This is mainly attributed to the dynamic recrystallization and material damage during the hot tensile deformation. The deformation temperature corresponding to the maximum elongation to fracture increases with the increase of strain rate within the studied strain rate range. Under the strain rate range of 0.1–0.001 s⁻¹, the localized necking causes the final fracture of specimens. While when the strain rate is 0.0001 s⁻¹, the gage segment of specimens maintains the uniform macroscopic deformation. The damage degree induced by cavities becomes more and more serious with the increase of the deformation temperature. Additionally, the peak stresses predicted by the proposed model well agree with the measured results.     

Hot deformation behavior of the new Al–Mg–Si–Cu aluminum alloy during compression at elevated temperatures

The hot deformation behavior of the new Al–Mg–Si–Cu aluminum alloy was investigated by compression tests in the temperature range 350 °C–550 °C and strain rate range 0.005 s^− 1–5 s^− 1 using Gleeble-1500 system, and the associated structural changes were studied by observations of metallographic and TEM. The results show that the true stress–true strain curves exhibit a peak stress at a small strain (< 0.15), after which the flow stresses decrease monotonically until high strains, showing a dynamic flow softening. The stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in an exponent-type equation with the hot deformation activation energy Q of 236 kJ/mol. The substructure in the deformed specimens consists of very small amount and fine precipitates with equaixed polygonized subgrains in the elongated grains and developed serrations in the grain boundaries, indicating that the dynamic flow softening is mainly as the result of dynamic recovery (DR) and recrystallization (RDX).     

Hot deformation behavior and workability characteristics of bimodal size SiCp/AZ91 magnesium matrix composite with processing map

The hot deformation behavior of (0.2 um 1.5 vol.% + 10 um8.5 vol.%) bimodal size SiCp/AZ91 magnesium matrix composite fabricated by stir casting was investigated at the temperature of 270–420 °C and strain rate of 0.001–1 S⁻¹. The flow stress at the strain of 0.5 was used for kinetic analysis. Results indicate that dislocation climb is likely to be the main deformation mechanism responsible for the present composite. By evaluating the efficiencies of power dissipation and instability parameters, the processing maps are developed to optimize the hot working processing. Two domains of dynamic recrystallization are found in the processing map. One exists at the temperature of 270–370 °C and strain rate of 0.001–0.01 s⁻¹ with maximum dissipation efficiency of 38%; the other exists at 420 °C and 0.01 s⁻¹ with peak dissipation efficiency of 24%. The instability region of flow behavior can also be recognized at the temperature of 270–320 °C and the strain rate of 0.1–1 s⁻¹. The characteristic microstructures predicted from the processing map agree well with the result of microstructure observations.     

Hot deformation and processing map of an as-extruded Mg–Zn–Mn–Y alloy containing I and W phases

The hot deformation characteristics of an as-extruded ZM31 (Mg–Zn–Mn) magnesium alloy with an addition of 3.2 wt.% Y, namely ZM31 + 3.2Y, have been studied via isothermal compression testing in a temperature range of 300–400 °C and a strain rate range of 0.001–1 s^− 1. A constitutive model based on hyperbolic-sine equation along with processing maps was used to describe the dependence of flow stress on the strain, strain rate, and deformation temperature. The flow stress was observed to decrease with increasing deformation temperature and decreasing strain rate. The deformation activation energy of this alloy was obtained to be 241 kJ/mol. The processing maps at true strains of 0.1, 0.2, 0.3 and 0.4 were generated to determine the region of hot workability of the alloy, with the optimum hot working parameters being identified as deformation temperatures of 340–500 °C and strain rates of 0.001–0.03 s^− 1. EBSD examinations revealed that the dynamic recrystallization occurred more extensively and the volume fraction of dynamic recrystallization increased with increasing deformation temperature. The role of element Y and second-phase particles (I- and W-phases) during hot compressive deformation was discussed.     

Hot deformation and processing maps of X-750 nickel-based superalloy

The deformation behavior of X-750 superalloy was investigated using the hot compression test in the temperature range of 850–1050 °C, and strain rate of 0.1–50 s⁻¹. The experimental results show that the flow stress of superalloy is significantly sensitive to the strain, the strain rate and the deformation temperature. Using dynamic materials model the processing maps of X-750 superalloy at strain of 0.1, 0.3 and 0.5 were established respectively. Microstructure observations reveal that the grain size as well as the volume fraction of the recrystallized grains increased at higher deformation temperature or lower strain rate. At strain of 0.5, the flow instability domain mainly located at lower temperature which is associated with shear band formation and flow localization. The optimum parameters for hot working of the alloy are deformation temperature of 1000–1050 °C and strain rate of 0.1–1 s⁻¹ according to the processing map and microstructure at true strain of 0.5.     

Temperature dependent work hardening in Ti–6Al–4V alloy over large temperature and strain rate ranges: Experiments and constitutive modeling

The plastic deformation behaviors of Ti–6Al–4V alloy over wide ranges of strain rate (from 10⁻⁴ to 10⁴ s⁻¹) and temperature (from 20 to 900 °C) are investigated by the quasi-static and dynamic uniaxial compression tests. The microstructure evolution of Ti–6Al–4V alloy at different temperatures is discussed. Material generates higher ductility and formability when temperature is higher than 500 °C, which leads to the decrease of work hardening rate. The true stress–strain responses are modeled with the JC, modified JC, KHL and modified KHL models. In detail, a temperature dependent work hardening function is introduced into the original JC and KHL models. The parameters of the four models for Ti–6Al–4V alloy are calculated by GA optimization method. The average standard deviations between the experimental and calculated flow stresses range from 4% to 13%, which validates the accuracy of the models. In addition, comparison of flow stresses at dynamic (10,000 s⁻¹), the work hardening rates at dynamic (7500 s⁻¹), as well as the quasi-static jump experiments were proposed to further validate the models. The modified JC and modified KHL models could characterize the temperature dependent work hardening effect for Ti–6Al–4V alloy over large strain rate and temperature ranges.