High Efficiency Of Power Dissipation Research Articles

Intermediate temperature tensile behavior and processing map of a spray formed 7075 aluminum alloy

The intermediate temperature deformation behavior and microstructural evolution of a spray formed 7075 Al alloy were performed at temperatures 60–120 °C with strain rates 0.00001–0.1 s−1. The results reveal that the softening mechanism of the intermediate temperature deformation is dynamic recovery (DRV), which can be quantitated by Zener-Hollomon (Z) parameter. The constitutive equation can reasonably predict the stress-strain behavior of the alloy at intermediate temperatures. The activation energy is related to the deformation process and the interactions of the substructure, the average value is 140.1 kJ/mol. The higher efficiency of power dissipation in the processing map is related to the DRV at lower deformation temperatures. The optimum processing domain is located at the temperature of 90–120 °C and strain rate of 0.006–0.1 s−1 with a power dissipation efficiency range of 20%–40%. The processing parameters of the intermediate temperature deformation should be strictly controlled according to the strain. The uniform microstructure of 7075 alloys obtained by spray forming is crucial to overcome the disadvantage of poor deformability. The inferior coordinated deformation facilitates crack propagation at low strain rates. The high-density dislocation provides adequate nucleation sites for dynamic precipitation. The level of dynamic restoration facilitates the transformation from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs). The dislocations move to the grain/sub-grain boundary to form dislocation walls at low temperatures. The contribution to the stress from grain boundary (13.2–17.7 MPa), nanoscale precipitates (65.7–191.5 MPa), and dislocation (5.9–23.4 MPa) increases the difficulty of deformation. The deformation process at higher temperatures (105–120 °C) can be facilitated by the dissolution and coarsening of the nanoscale precipitates, and dislocation motion at the grain boundary.

Hot deformation behavior and dynamic recrystallization mechanism of Ti-48Al-2Nb-2Cr alloy with near-γ microstructure

Hot processing is extremely effective in optimizing the microstructure of γ-TiAl alloy, and hot deformation mechanism is the decisive factor in the microstructure evolution. In this paper, hot compression tests under different conditions were carried out to investigate the characteristics of hot deformation behavior and deformation mechanism of Ti-48Al-2 Nb-2Cr alloy with near-γ microstructure. The Arrhenius constitutive model was established, and the predicted flow stress agreed well with the experimental value. Hot processing maps at different strains were constructed. High power dissipation efficiency (η) region which was suitable for hot working appeared in the temperature range of 1180–1210 ℃ and the strain rate range of 0.001–0.01 s−1. At the strain rates from 0.001 to 0.1 s−1, dynamic recrystallization (DRX) served as the primary softening mechanism of the alloy, which was closely related to the disordered transformation of α2→α. At the temperature above Tα2→α and the strain rate of 1 s−1, flow softening of the alloy was mainly controlled by dynamic recovery (DRV). The occurrence of DRX in the lamellar structure can be promoted by the elevated temperatures and reduced strain rates. Discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) appeared in the γ and α/α2 phases of the alloy deformed at the conditions corresponding to high η region. With the decrease of η value, DRX nucleation of the alloy under the relevant conditions was chiefly dominated by DDRX.

Microstructure analysis, constitutive relationship, and processing map of novel pre-aged Mg-Zn-Gd-Er alloy with different deformation ranges

Abstract Pre-aged Mg-6Zn-1Gd-1Er alloy is a novel rapid aging hardening Mg alloy, and studying its hot deformation behavior has an important role in promoting the development of lightweight alloy materials. To study this, the flow stress curves of pre-aged Mg-6Zn-1Gd-1Er alloy at 180–380 °C and 10−3−10 s−1 were obtained by isothermal compression tests. The constitutive equations of the medium-high temperature deformation (MHTD) and the low-temperature deformation (LTD) were established, and their activation energies were 155.78 kJ mol−1 and 178.00 kJ mol−1, respectively. Based on the constitutive equation analysis, the glide and climb of dislocations and the cross-slip of dislocations was the deformation mechanism during MHTD and LTD, respectively. In order to determine the appropriate hot processing parameters, the hot processing map of the pre-aged Mg-6Zn-1Gd-1Er alloy under 0.2–0.8 strain was constructed based on the dynamic material model. The hot processing maps indicate that this pre-aged alloy at low temperature (180–230 °C) and high strain rates (1–10 s−1) mainly occurs flow instability, and the optimal hot processing window appears at a 330–380 °C and 10−3 to 10−2 s−1 range. Furthermore, the deformation mechanism of the stable domain with high power dissipation efficiency in the hot processing map was continuous dynamic recrystallization, discontinuous dynamic recrystallization, and particle-stimulated nucleation mechanisms.

Characterization of Hot Workability in AISI 4340 Based on a 3D Processing Map

This study performed high-temperature compression tests at the temperature 900 to 1200 °C and strain rate 0.01 to 10 s−1 to characterize the high-temperature deformation behavior of AISI 4340. The constitutive equation of AISI 4340 was expressed using the Arrhenius model and the Zener–Hollomon (Z) parameter. Dynamic Recrystallization (DRX) behavior was evaluated by observing the compressed specimen with Electron Backscatter Diffraction (EBSD). The processing map is based on the dissipation efficiency of the dynamic material model (DMM) and the plastic instability criterion of Ziegler. At strain 0.4, the power dissipation efficiency value is 0.5 or more, and the instable zones are immediately identified through the processing map. The strain, strain rate and temperature data obtained from the FEM simulation of the hot forging process are displayed on the proposed 3D processing map to avoid the flow instability zones and ensure high power dissipation efficiency zones, allowing the operator to control the process’s temperature and speed.

Hot Compression Deformation Behavior and Microstructure of As-Cast and Homogenized AA2195 Al-Li Alloy

To understand the effect of the initial state of AA2195 Al-Li alloy on the forming process, as-cast and homogenized ingots were compressed by using a Gleeble-3150 thermo-mechanical simulator at different temperatures (360–480 °C) and strain rates (0.01–10 s−1). The hot compression deformation behaviors and microstructural characteristics of the two types of ingots were systematically investigated. The as-cast alloy possessed a better hot compressibility with higher power dissipation efficiency and lower rheological stress than the homogenized alloy under the same deformation conditions. When the temperature was increased above 450 °C, all the alloys showed similar rheological curves. Based on the rheological stress curves, processing maps for the as-cast (AC) and homogenized (HG) alloys were established, and optimal processing domains were identified. In addition, the homogenized alloys were dominated by a fibrous microstructure during deformation, whereas the as-cast alloy produced fine crystals at low temperature (360 °C) and equiaxed crystals at high temperature (480 °C). Our results show that it is possible to use the as-cast 2195 Al-Li alloy as the initial billet to get complicated components. This is attributed to the dispersed eutectic phases, which can provide more nucleation sites for Dynamic Recrystallization (DRX) and Dynamic Recovery (DRV) during hot deformation.

Characterization of Hot Deformation of near Alpha Titanium Alloy Prepared by TiH2-Based Powder Metallurgy.

TiH2-basd powder metallurgy (PM) is one of the effective ways to prepared high temperature titanium alloy. To study the thermomechanical behavior of near-α titanium alloy and proper design of hot forming, isothermal compression test of TiH2-based PM near-α type Ti-5.05Al-3.69Zr-1.96Sn-0.32Mo-0.29Si (Ti-1100) alloy was performed at temperatures of 1123–1323 K, strain rates of 0.01-1 s−1, and maximum deformation degree of 60%. The hot deformation characteristics of alloy were analyzed by strain hardening exponent (n), strain rate sensitivity (m), and processing map, along with microstructure observation. The flow stress revealed that the difference in softening/hardening behavior at temperature of 1273–1323 K and the strain rate of 1 s−1 compared to the lower deformation temperature and strain rate. The strain hardening exponents at temperatures of 1123 K are all negative under all strain rates, and the most severe flow softening with minimum value of n was observed at 1123 K and 1 s−1. The strain rate sensitives showed that the peak region with m value greater than 0.5 generally appeared in the high temperature range of 1273–1323 K, while strain rate sensitivity at low temperature behaved differently with strain rates. The processing map developed for strain of 0.6 exhibited high power dissipation efficiency at high temperatures of 1273–1323 K and a low strain rate of 0.01 s−1, due to microstructure evolution of β phase. The decrease of strain rate at 1323 K resulted in the formation of globularization of α lamellae. The instability domain of flow behavior was identified in the temperature range of 1123–1173 K and at the strain rate higher than 0.01 s−1 reflecting the localized plastic flow and adiabatic shear banding, and inhomogenous microstructure. The variation of power dissipation energy (η) slope with strain demonstrated that the power dissipation mechanism during hot deformation has been changed from temperature-dependent to microstructure-dependent with the increase of temperature for the alloy deformed at 0.1 s−1. Eventually, the optimum processing range to deform the material is at 1273–1323 K and a strain rate range of 0.01–0.165 s−1 (ln = −4.6–−1.8).

Hot deformation behaviour of Ti alloys: A review on physical simulation and deformation mechanisms

Titanium and its alloys, owing to their properties like high strength, toughness, corrosion resistance and thermal stability, are employable in various engineering and medical applications. The properties of titanium alloys depend upon the processing routes and their final microstructure. Therefore, the present review paper compiles the deformation behaviour of various alloys during hot deformation using a physical simulation. Subsequently, the flow stresses are analysed and utilized to develop the processing maps and the constitutive equations that are advantageous for predicting deformation mechanisms during the hot deformation. Specific features reported in the flow stress curves include work hardening, flow softening and steady-state behaviour. In certain cases, the yield point drop and oscillatory behaviour or serrations are also observed. Softening and oscillatory behaviour is an indicator of either dynamic recrystallization or flow-instability, whereas yield discontinuity signifies locking and unlocking of dislocations. In the processing maps, high power dissipation efficiency, η, reveals safe processing conditions, and the η value higher than 40% demonstrates dynamic recrystallization or globularization in the deformed microstructure, whereas the instability domain expresses shear band, flow localization, void formation and wedge cracks in the deformed microstructure. Amongst all the constitutive equations, the Arrhenius-type hyperbolic sine equation is the most suitable for Ti alloys for calculating flow stress and predicting dominant deformation mechanism using activation energy Q and stress exponent n.

Microstructure, Hot Deformation Behavior, and Textural Evolution of Mg-3Sn-2Al-1Zn-0.6Nd Alloy

To prepare wrought magnesium alloys with excellent plastic deformation properties, Mg-3Sn-2Al-1Zn-0.6Nd alloys were prepared. A hot compression test of Mg-3Sn-2Al-1Zn-0.6Nd alloy was carried out on a thermo-mechanical simulator. The hot deformation behavior of the alloys was studied, and the constitutive equations and the processing map at the strain of 0.8 were established. The processing map exhibited the stable domain (temperature range of 320–350 °C and strain rate range of 0.001–0.04 s−1) with the high power dissipation efficiency (>30%). A large number of fine dynamic recrystallization (DRX) grains and deformed twinning existed in the alloy after the hot deformation. The dominant texture of the Mg-3Sn-2Al-1Zn-0.6Nd alloy is <0001>//CD texture after the hot deformation. The continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) were the dominant recrystallization mechanisms, and {101¯2} extension twinning also occurred in the alloy during the hot deformation.

Hot Deformation Behavior and Microstructural Evolution Based on the Processing Map of Dual-Phase Mg-Li Based Alloy.

The deformation behavior of the as-extruded Mg-Li-Al-Zn-Si alloy was studied by conducting a hot compression test, with a temperature range of 180–330 °C and a strain rate range of 0.01–10 s−1. The constitutive relationship of flow stress, temperature, and strain rate was expressed by the Zener–Hollomon parameter and included the Arrhenius term. By considering the effect of strain on the material constants, the flow stress at 240–330 °C could be precisely predicted with the constitutive equation (incorporating the influence of strain). A processing map was established at the strain of 0.7. The unsafe domains that are characterized by uneven microstructures were detected at low temperatures (<230 °C) or high temperatures (>280 °C), with high strain rates (>1 s−1). The optimum hot deformation region was obtained at a medium temperature (270–300 °C), with a peak power dissipation efficiency of 0.44. The microstructural evolution in different domains is investigated. The unstable domains are characterized by a non-uniform flow behavior and uneven microstructure. The observation showed that the dynamic recrystallization (DRX) process could easily occur at the safe domain with high power dissipation efficiency. For the α-phase, some features of continuous dynamic recrystallization can be found. The triple points serve as prominent nucleation sites for the β-phase DRX grains and the growth in the grains was carried out by subgrain boundary migration. The microstructure exhibits characteristics of discontinuous dynamic recrystallization.

Hot deformation behavior and 3D processing map of super austenitic stainless steel containing 7Mo–0.46N–0.02Ce: Effect of the solidification direction orientation of columnar crystal to loading direction

In the present paper, hot compression tests on a super austenitic stainless steel (SASS) containing 7Mo–0.46N–0.02Ce were performed at temperatures of 900 °C-1200 °C and strain rates of 0.01–10 s−1. The effect of angle between solidification direction of columnar crystal and loading direction (0°, 30°, 60°, and 90°) on the flow behavior and microstructure evolution of SASS was studied. Results showed that, samples with different columnar crystal characteristics and test conditions displayed various flow behaviors due to the difference in dynamic restoration softening mechanism, flow localization, and shear band formation. With the decrease of the angle between the solidification direction of columnar crystal and loading direction, the deformation activation energy (Q) and the ln Z value of SASS decreased at the true strain of 0.7. It indicates that dynamic recovery (DRV) and dynamic recrystallization (DRX) are more likely to happen in the samples with low angles. The location and range of high efficiency of power dissipation (η) region and instability region of the samples differed much with different columnar crystal characteristics. This means obviously different hot workability and microstructure evolution behaviors. At the true strain of 0.7, no negative η-value region was observed in the 0° sample, and the range of instability region was relatively small. On the whole, SASS presented the optimum hot workability when the angle between the solidification direction of columnar crystal and loading direction was 0°.

Dynamic Recrystallization Behavior and Processing Map of the 6082 Aluminum Alloy.

Multiple hot-compression tests were carried out on the 6082 aluminum (Al) alloy using a Gleeble-1500 thermal simulation testing machine. Data on flow stresses of the 6082 Al alloy at deformation temperatures of 623 to 773 K and strain rates from 0.01 to 5 s−1 were attained. Utilizing electron backscatter diffraction (EBSD) and a transmission electron microscope (TEM), the dynamic recrystallization behaviors of the 6082 Al alloy during hot compression in isothermal conditions were explored. With the test data, a hot-working processing map for the 6082 Al alloy (based on dynamic material modeling (DMM)) was drawn. Using the work-hardening rate, the initial critical strain causing dynamic recrystallization was determined, and an equation for the critical strain was constructed. A dynamic model for the dynamic recrystallization of the 6082 Al alloy was established using analyses and test results from the EBSD. The results showed that the safe processing zone (with a high efficiency of power dissipation) mainly corresponded to a zone with deformation temperatures of 703 to 763 K and strain rates of 0.1 to 0.3 s−1. The alloy was mainly subjected to continuous dynamic recrystallization in the formation of the zone. According to the hot-working processing map and an analysis of the microstructures, it is advised that the following technological parameters be selected for the 6082 Al alloy during hot-forming: a range of temperatures between 713 and 753 K and strain rates between 0.1 and 0.2 s−1.

Effect of Temperature, Strain and Strain Rate on Efficiency of Power Dissipation during Hot Deformation of Fe-28Ni-17Co-11.5Al-2.5Ta-0.05B (at. %) Shape Memory Alloy Using Taguchi Method

Recently a ferrous-based Fe-28Ni-17Co-11.5Al-2.5Ta-0.05B (at.%) shape memory alloy (abbreviated NCATB) has attracted attention because of its huge superelasticity (～13%). In order to manufacture this alloy on a large scale, a deeper knowledge of the plastic deformation behaviour of the alloy is required. During hot deformation, temperature and strain rate exert significant effect on the mechanical properties. The main objective of the work, therefore, is to investigate the influence of deformation parameters, such as temperature, strain rate and strain, on flow behaviour of an NCATB shape memory alloy. Flow behaviour tests on an NCATB alloy were performed on a Gleeble-3800 thermomechanical simulator at deformation temperatures of 1100, 1150 and 1200°C and strain rates of 0.1, 1.0 and 10s-1 with the strains maintained at 0.2, 0.4 and 0.6, respectively. The workpiece is considered asa dissipater of power, and the features of power dissipation will,therfore, be seen as changes in the microstructure. These features of power dissipation are measured by a parameter called efficiency of power dissipation (η). It is directly related to the strain rate sensitivity parameter(m). Taguchi method is used to evaluate the influence of deformation temperature, strain rate and strain on efficiency of power dissipation. Based on the results, optimum parameters for higher efficiency of power dissipation are: 1150°C (temperature), 0.1 s-1 (strain rate) and 0.2 (strain). An analysis of experimental results in terms of percentage contribution reveals that strain rate plays a more predominant role (39.73%) compared to temperature (24.03%) and strain (32.73%) on NCATB alloy.

The effect of addition of Sn to copper on hot compressive deformation mechanisms, microstructural evolution and processing maps

The high-temperature compressive deformation behavior of a Cu-10wt.% Sn solid solution alloy was studied in the temperature range of 843–993K and in the strain rate range of 10−3 – 10s−1 and the relationships among the flow stress, strain rate and temperature were determined. Based on the data obtained from the compression tests, the deformation mechanism was identified, and the processing maps were constructed. The Cu-10Sn alloy exhibited solute drag creep at low strain rates and high temperatures and power law breakdown (PLB) at high strain rates and low temperatures. In the processing maps, above the temperature of 933K, the alloy did not show flow instability up to a high strain rate of 10s−1 and showed high power dissipation efficiencies (31–35%) even at the very high strain rate of 10s−1. Furthermore, at 993K, the fraction of dynamically recrystallized grains after compressive deformation was as high as 0.83 at 10s−1. These results indicate that the Cu-10Sn alloy exhibits a significantly better hot workability and a higher quality of post-deformation microstructures compared to the pure Cu where dislocation climb creep is the main deformation mechanism. Continuous dynamic recrystallization occurred at 843K, while discontinuous dynamic recrystallization occurred at 993K. Comparison of the current results with the previous work on the Cu-4.9Sn alloy indicates that the increase of Sn concentration in Cu matrix extends the regime of solute drag creep and delays the onset of PLB to a lower temperature and a higher strain rate.

Comparison of Hot Deformation Behavior Characteristics Between As-Cast and Extruded Al-Zn-Mg-Cu (7075) Aluminum Alloys with a Similar Grain Size.

The hot compressive behavior and processing maps of as-cast and extruded 7075 aluminum alloys with a similar grain size (320–350 μm) were studied and compared, which allows us to directly observe the effect of segregated phases in the as-cast microstructure on the deformation behavior and hot workability of 7075 alloys. In the as-cast alloy, the compound phases segregated along the interdendritic interfaces within the interiors of original grains provided the additional sites for continuous dynamic recrystallization via the particle stimulation nucleation mechanism. As a result, the as-cast alloy exhibited higher fractions of recrystallized grains and smaller grain sizes than the extruded alloy after compression. The stress exponent values of the as-cast alloy were smaller than those of the extruded alloy. In the processing maps, the domain associated with high power dissipation efficiencies (≥35%) occurred in a wider temperature range in the as-cast alloy compared to the extruded alloy. The segregated phases that remained undissolved in the as-cast alloy after compressive deformation could be effectively eliminated during the solid solution treatment (753 K for 2 h) for T6 aging applied after hot compression. The current results suggest the possibility and advantage of omitting the extrusion step when preparing 7xxx aluminum forging or extrusion feedstocks for hot working. The proposed method can be applied to other precipitation hardenable aluminum alloys.

Elevated Temperature Compression Deformation Behavior of Commercial Pure Zr Combined with the Constitutive Equation and Processing Map

The compression deformation behavior of commercial pure zirconium at elevated temperature is systematically investigated at different conditions. The corresponding deformation mechanism of pure Zr is clarified for analyzed flow stress, work hardening rate, activation energy, and microstructure. A modified Arrhenius‐type equation is proposed for future numerical simulation, which shows a good relativity between the theoretical and experimental data. The apparent deformation activation energy is 209 kJ mol−1, indicating that a cross‐slip of dominant dislocation mechanism controls the deformation process. Established based on the dynamic material model (DDM), processing maps indicate that the optimum processing conditions are 700–900 °C at 0.1–0.14 s−1 and 905–950 °C at 3–20 s−1 with the high efficiency of power dissipation. Microstructure examination reveals that the main restoration mechanism in the safe domain is related to dynamic recrystallization and the unstable regional microstructure results in the flow localization and cracking behavior.

Modified constitutive model and workability of 7055 aluminium alloy in hot plastic compression

To obtain flow behavior and workability of 7055 aluminium alloy during hot deformation, hot compression tests at different temperatures and strain rates are conducted. True stress-strain curves of 7055 aluminium alloy under different conditions are obtained and the flow stress increases with ascending strain rate and descending temperature. For Arrhenius constitutive equation, each material parameter is set as a constant, which will bring forth large error for predicting flow behavior. In this work, material parameters are fitted as a function of temperature or strain rate based on experimental results and a modified constitutive equation is established for more accurate prediction of flow behavior of 7055 aluminium alloy. The effects of temperature and strain rate on power dissipation and instability are analyzed to establish a processing map of 7055 aluminium alloy. The dominant deformation mechanism for microstructure evolution at different deformation conditions can be determined and high efficiency of power dissipation may be achieved from power dissipation map. Meanwhile, proper processing parameters to avoid flow instability can be easily acquired in instability map. According to the processing map, optimized processing parameters of 7055 aluminium alloy are temperature of 673–723 K and strain rate of 0.01–0.4 s−1, during which its efficiency of power dissipation is over 30%. Finite element method (FEM) is used to obtain optimized parameter in hot rolling process on the basis of processing map.

Characterization of Hot Workability of 5052 Aluminum Alloy Based on Activation Energy-Processing Map

In the design of hot forming processes for aluminum alloys, hot processing maps are usually used as a powerful tool for processing parameters optimizations. Although the stability of deformation is considered in conventional hot processing (CHP) maps, the difficulty of deformation, i.e., whether deformation is easy to occur, is not taken into account. Therefore, it is difficult for CHP maps to efficiently and accurately obtain the optimal processing parameters and achieve satisfying hot workability. Hence, in this study, thermal compression tests were performed to investigate the hot forming behavior of 5052 aluminum alloy in the deformation temperature range of 553-733 K and strain rate range of 0.001-1 s−1. We proposed an activation energy-processing (AEP) map by coupling the CHP map and the activation energy value, and thereby applied it to evaluate the hot workability of 5052 aluminum alloy. In CHP maps, the region with the highest power dissipation efficiency is generally considered to be the best processing region. However, the AEP map shows that materials with satisfying hot workability not only depends on high power dissipation efficiency, but also on low activation energy values. At the strain of 0.7, the optimal hot processing region predicted by the CHP map lies in the temperature range of 583-673 K and strain rate range of 0.001-0.1 s−1, but that predicted by AEP map locates in the temperature range of 643-733 K and strain rate range of 0.001-0.1 s−1. Microstructure characterization implies that the optimal processing region predicted by the CHP map presents necklace-like structures, which are non-uniform and unbeneficial for deformation, while that predicted by the AEP map consists of fine, uniform and equiaxed grains. Thus, it is implied that the processing regions predicted by the AEP map are more suitable for forming, i.e., the reasonability of the AEP map is verified.

The Investigation on Flow Behavior of Powder Metallurgy Ti-10V-2Fe-3Al Alloy Using the Prasad Stability Criterion

The hot deformation behavior of Ti-10V-2Fe-3Al alloy obtained by the powder metallurgy (PM) method was investigated. Material for the research was produced by blending of elemental powders followed by uniaxial hot pressing. Thermomechanical tests of Ti-10V-2Fe-3Al compacts were carried out to determinate the stress-strain relationships at the temperature range of 800 °C to 1000 °C and strain rate between 0.01 and 10 s−1. Based on the dynamic material model (DMM) theory, processing maps at constant strain value were developed using data obtained from hot compression tests. The processing maps were elaborated for the final strain value, which was 0.9, and with flow instability criterion domains applied to it. Two critical regions associated with the flow behavior of the investigated material were revealed. Microstructural changes during hot deformation at various temperatures and strain rates were discussed. The correlation between calculated efficiency of power dissipation, flow instability criterion, and microstructure evolution was determined. The presence of defects was confirmed in regions predicted by the instability maps. The microstructure of the investigated alloy, corresponding to the high efficiency of power dissipation characterized by the occurrence of dynamic recrystallization (DRX) phenomena, was also shown. Additionally, average hardness values in relation to variable process parameters were designated. Based on the conducted studies and analysis, processing windows for Ti-10V-2Fe-3Al alloy compacts were proposed.

Hot compression deformation behavior of Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu alloy

The hot deformation behavior of Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu alloy containing coarse second phase particles is studied. The flow stress increases with decreasing temperature and increasing strain rate. The stress-strain result is fitted to the hyperbolic sine equation to obtain the constitutive equation of the alloy. The processing map is constructed and it shows that low temperature and high strain rate lead to both low efficiency of power dissipation and instability and two domains with high efficiency of power dissipation out of the instability area is suitable for hot processing of the alloy: 580 K–670 K, 0.001 s−1–0.01 s−1 and 630 K–670 K, 0.01 s−1–1 s−1, the latter one is recommended for hot deformation for the higher strain rate. It was revealed that the effect of coarse particles on the restoration mechanism is dependent on the deformation condition. Under low Zener-Hollomon value, particles hinder discontinuous dynamic recrystallization through grain boundary pinning making dynamic recovery and continuous dynamic recrystallization the main restoration mechanism. Under high Zener-Hollomon value, the misorientation gradient near particles increases and the efficiency of particle stimulated nucleation increases. The enhanced particle stimulated nucleation accompanied by more active twinning and twin related recrystallization make the fraction of dynamic recrystallized grain to be higher under high Zener-Hollomon value.

Constitutive modeling and processing map for hot deformation of Ti–15Mo–3Al-2.7Nb-0.2Si

Hot tensile tests of a metastable β alloy, Ti–15Mo–3Al-2.7Nb-0.2Si, were conducted in the wide temperature range of 750–950 °C with strain rates from 0.01 to 0.00005s−1. The flow behavior, constitutive modeling, strain rate sensitivity exponent (m), processing map and microstructural evolution were investigated. The results showed that the flow stress decreases with increasing temperature and decreasing strain rate. Discontinuous yielding was observed in the flow stress curves at high strain rates. The apparent activation energy under different discrete true strains was much higher than the self-diffusion activation energy of pure α or β-Ti. A constitutive model considering the strain effect is proposed with an average relative error of 8%. The m-value distribution and processing maps show that the stability region corresponds to a higher m value (>0.2) or higher power dissipation efficiency (η > 0.33), and the deformation mechanism relates to dynamic recrystallization (DRX), grain boundary sliding (GBS) and dynamic recovery (DRV). An instability region appeared at temperatures of 800–825 °C and high strain rates of 0.01–0.001s−1. The microstructural observations demonstrate that DRV with the formation of subgrains is the main deformation mechanism in the β field, accompanied by DRX and rotation of the β grains. When the testing temperatures were lower than Tβ, DRV was the main deformation mechanism of the deformed region. Static recovery was the primary mechanism for the grip regions.