Hot Working Characteristics Research Articles

Hot-working characteristics and microstructure analysis of Zr-Sn alloy at different temperatures and strain rates

In this work, the hot-working characteristics and microstructure evolution of Zr-Sn alloy at 600–900 °C/0.01–10 s−1 were investigated. The results indicate that the flow stress of Zr-Sn alloy decreases with the increase of compression temperature and increases with the increase of strain rate. An Arrhenius constitutive equation for the Zr-Sn alloy was established, the average deformation activation energy was calculated to be 278630.1 J/mol. The processing map of Zr-Sn alloy was obtained based on the flow stress curve, revealing that the instability zone was mainly concentrated in the low temperature zone and the medium-high strain rate zone in the high temperature zone. As the temperature increases, the proportion of dynamic recrystallization (DRX) grains increases gradually. With the increase of strain rate, the proportion of DRX grains gradually decreases. Three DRX mechanisms were observed: continuous DRX (CDRX), discontinuous DRX (DDRX), and twin induced DRX (TDRX). The secondary phase of the initial grains is mainly FeCr phase, which is not completely dissolved at 650–750°C/0.01–1 s−1.

Primary hot working characteristics and microstructural evolution of as-cast and homogenized Ti-4Al-2.5V-1.5Fe alloy

Hot deformation characteristics of Ti-4Al-2.5V-1.5Fe-0.25O alloy in as-cast and homogenized condition was studied using isothermal hot compression tests in both β and α + β fields at strain rates ranging from 3 × 10−4 s−1 to 1 s−1. To understand the hot deformation behaviour and to identify the optimum regime for the primary breakdown of titanium alloy ingot, processing map based on strain rate sensitivity (m), kinetic analysis, and microstructural characterization were used. Micro-mechanisms of deformation in the β-field were analyzed with the help of reconstruction of parent β grain orientations using electron backscatter diffraction data. Kinetic analysis and microstructural characterization of samples deformed at low strain rates (ε̇<10−2 s−1) in β-field confirmed dynamic recovery assisted by dislocation glide/climb. In comparison, the samples deformed at higher strain rates (ε̇>10‐2s−1) in β-field exhibited deformation bands and recrystallized grains formed through static recrystallization. In the α + β field, kinetic parameters at low strain rates (ε̇<10−2 s−1) indicated dynamic globurization, which were corroborated by microstructural analysis. Samples deformed at high strain rates (ε̇>10−2 s−1) in the α + β field exhibited adiabatic shear bands, strain-induced porosity and lamellar α-kinking. The optimum regime for thermomechanical processing (900°C to 1150°C and 3ⅹ10−4 s−1 to 3ⅹ10−2 s−1) is arrived at by combining the strain rate sensitivity map and microstructural analysis. Further, constitutive equations have been developed to predict the steady-state flow stress values in β and α + β fields.

Hot-Working Characteristics and Dynamic Recrystallization Behavior of Hot Isostatically Pressed FGH4096 Superalloy

Hot-Working Characteristics and Dynamic Recrystallization Behavior of Hot Isostatically Pressed FGH4096 Superalloy

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

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

Temperature Effects on the Deformation Mechanisms in a Ni-Co-Based Superalloys

The tensile properties of a Ni-Co-based superalloy were investigated from room temperature to 900 °C. From 25 to 650 °C, the yield strength and tensile strength of the alloy decreased slightly, while the elongation decreased sharply. From 760 °C to 900 °C, the yield strength and tensile strength were greatly reduced, while the elongation also had a low value. With the increase in temperature, the deformation mechanism transformed from anti-phase boundary shearing to stacking fault shearing, and then from deformation twinning to Orowan bypassing, respectively. Deformation twins were generated in the deformed alloy with high-density stacking faults and they can contribute to the high strength. The alloy in this study has good mechanical properties and hot working characteristics below 760 °C and can be used as a turbine disk, turbine blade, combustion chamber, and other aircraft structural parts.

Optimized hot working parameters of Fe2.5Ni2.5CrAl multi-principal element alloys

The hot compressive deformation behavior of Co-free Fe2.5Ni2.5CrAl multi-principal element alloys (MPEAs) was investigated in the temperature and strain rate ranges of 800–1100∘C and 0.001 s−1 and 1 s−1, respectively. Microstructural observations were carried out by optical microscopy (OM) and electron backscatter diffraction (EBSD). A constitutive model based flow-stress analysis was carried out, the activation energy (Q) was obtained as 315.9 kJ/mol at steady state. The strain rate sensitivity (m), the power dissipation (η), and instability parameter (ξ) were utilized to construct the processing maps. Power-law breakdown and unstable flow occurred at the high strain rates at which strain hardening was pronounced. The optimal condition for successful hot working was determined to be at strain rates in the range of 10−2–10−3 s−1 and a temperature range of 850 ~ 1020∘C. FEM simulations revealed the strain and stress distribution during hot deformation and predicted instabilities during hot forming. The main deformation mechanism was dislocation climb with a stress exponent n > 5. The Q value for plastic flow in the power-law creep regime was calculated considering the effect of lattice diffusion of atoms and was in accordance with the measured Q value. Thus, our study revealed the hot working characteristics and the optimum processing parameters for successful hot working of Fe2.5Ni2.5CrAl MPEAs.

Hot working characteristics of HEXed PM nickel-based superalloy during hot compression

Abstract To study the hot deformation behavior of a new powder metallurgy nickel-based superalloy, hot compression tests were conducted in the temperature range of 1020–1110 °C with the strain rates of 0.001–1 s−1. It is found that the flow stress of the superalloy decreases with increasing temperature and decreasing strain rate. An accurate constitutive equation is established using a hyperbolic-sine type expression. Moreover, processing map of the alloy is constructed to optimize its hot forging parameters. Three domains of dynamic recrystallization stability and instability regions are identified from the processing map at a strain of 0.7, respectively. The adiabatic shear band, intergranular crack and a combination of intergranular crack and wedge crack are demonstrated to be responsible for the instabilities. Comprehensively analyzing the processing map and microstructure, the optimal isothermal forging conditions for the superalloy is determined to be t=1075–1105 °C and =10−3–10−2.8 s−1.

Hot workability characteristics of low-density Fe–4Al–1Ni ferritic steel

The hot-working behavior of a low-density Fe–4Al–1Ni ferritic steel at the deformation temperature in the range of 700–950 °C and the strain rate in the range of 0.01–10 s-1 was studied on a Gleeble-3800 thermomechanical simulator by means of a compression test. The hot-working behavior of the experimental steel was in accord with a material with intermediate stacking fault energy. The deformation mechanism is controlled by the glide and climb of dislocations. The constitutive equations were established to predict peak stress. The apparent deformation activation energy of experimental steel was about 347.5 kJ/mol. Electron backscatter diffraction was applied to study the microstructure after deformation. The experimental results showed that both continuous dynamic recrystallization and discontinuous dynamic recrystallization could occur, and increasing deformation temperature and strain rate is conducive to the occurrence of discontinuous dynamic recrystallization behavior. According the dynamic materials model, the processing maps of the experimental steel were established. Combined with the microstructure results, the power consumption efficiency of continuous dynamic recrystallization, discontinuous dynamic recrystallization and dynamic recovery decreases gradually. There are two flow instability domains, which are related to mischcrystal microstructure caused by partial dynamic recrystallization. The optimum deformation parameters for industrial processing are as follows: deformation temperature 750–900 °C, strain rate 10 s-1.

On the prediction of hot deformation mechanisms and workability in Al6063/Nip and Al6063/steelp composites using hyperbolic-sine constitutive equation

The present study investigates the hot deformation mechanisms and workability in novel AA6063-Nip and AA6063-Steelp composites using hyperbolic-sine constitutive equation. The AA6063-Nip and AA6063-Steelp composites were produced with AA 6063 as matrix, and 6 wt% Ni or 6 wt% steel particles as reinforcement for each of the composite, with the adoption of double stir casting method for the composite production. Axisymmetric compression testing was performed using Gleeble 3500 thermomechanical simulator at temperature and strain rate of 200–400 °C and 0.01–10 s−1 respectively to a global strain of 0.5, while constitutive model was used to study the hot working characteristics of AA6063-Nip and AA6063-Steelp composites. The results showed that anomalous flow stress oscillations and partial insensitivity to strain rate, characterised the flow stress patterns displayed by both composites. The activation energies (QHW) values derived at incremental strain, were within the range of 83.8 to 218.4 kJ/mol for AA 6063/Nip and 14.2 to 271.9 kJ/mol for AA 6063/Steelp composites. The highest values of the QHW, for AA 6063/Nip was 53% and for AA 6063/Steelp was 91% higher than that for self-diffusion of Aluminium (QSD ∼142 kJ/mol), which suggest that the deformation controlling mechanism was work hardening facilitated by dispersion strengthening. This was supported by the stress exponent values which exceeded 5 for both composites – affirming dispersion strengthening to dominate the deformation process. Also, the QHW of the composites was intermediate in comparison with the range of 111 – 509 kJ/mol reported for AMCs of similar reinforcement composition in literature, indicating that both composites have intermediate workability.

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.

Primary hot working characteristics of an as-cast and homogenized nickel base superalloy DMR-742 in the sub and super-solvus temperature regime

Primary deformation behaviour of a medium alloyed nickel base superalloy DMR-742 in the as-cast and homogenized condition (furnace cooled) was evaluated in the sub-solvus and super-solvus temperature regimes. The flow stress in the sub-solvus regime was found to be highly sensitive to temperature. The contribution of back stress to the flow stress sensitivity was estimated using the microstructure dependent analytical equations and compared with the back stress estimated using experimental steady state flow stress. It was established that Orowan looping or by-passing mechanism contributes to the back stress resulting in high flow stress sensitivity in the sub-solvus regime. In the super-solvus regime, the material was relatively temperature insensitive and exhibited discontinuous dynamic recrystallization (DDRX) with a characteristic power dissipation value of 38–44% in three different temperature-strain rate regimes. Disregarding the industrially non-viable low strain rate regime, the recrystallization kinetics in the moderate and high strain rate regime was estimated using grain size factor compensated grain orientation spread maps. A higher rate of recrystallization observed in the material deformed at high temperature-strain rate was attributed to relatively strong dislocation interactions and weak recovery. The true stress exponent, activation volume and energy estimated using back stress and elastic modulus compensated flow stress revealed that diffusion controlled climb and cross-slip as the rate controlling deformation mechanism. Side-pressing under high secondary tensile stress conditions was used to evaluate the workability and validate the experimental findings.

Hot working characteristics of S32760 super duplex stainless steel

Hot deformation behavior of S32760 super austenitic stainless steel was studied in the temperature range of 950 ∼ 1250 °C and strain rate range of 0.1∼10 s-1 employing Gleeble 3800 equipment. The flow stress was modeled using Arrhenius equation and Zener-Hollomon parameter(Z). The microstructures of the specimens under various conditions were investigated, and dynamic recrystallization of austenite, dynamic recovery of ferrite and phase contents varied with temperature and strain rate. The difference of flow stress between experiment and constitutive equation was explained by the phase contents. Finite element analysis was performed to calculate forging load under the same conditions of compression test using modeled flow stress. It was validated that forging load can be predicted precisely with Arrhenius equation.

Dynamic Recrystallization and Hot-Working Characteristics of Ni-Based Alloy with Different Tungsten Content

The hot deformation behavior of the GY200 Ni-based alloys with different tungsten (W) content were investigated by means of hot compression tests, microscopic observations, and processing maps at temperatures between 950 °C and 1200 °C, strain rate between 0.01 s−1 and 10 s−1 with strain of 0.9. The hyperbolic-sine type constitutive equations were established between peaks tress and deformation conditions through Z parameters, and for alloys with higher W content results in higher activation energy and complete recrystallization temperature. The hot-working maps were exploited based on the experimental data. The hot-working maps showed that the instability zone extended with increasing W content. The stable domain of alloys are located in the temperature range between 1025 °C and 1200 °C and strain rate range between 0.01 s−1 and 1 s−1, dominated by the dynamic recrystallization (DRX) microstructural evolution, suited for hot deformation. The cracking on the surface of the sample compressed at 950 °C was resulted from the tensile stress, while the fracture of the sample compressed at 1200 °C was triggered by the melting of grain boundaries.

Optimization of Hot Workability and Control of Microstructure in 18Ni (M250 Grade) Maraging Steel Using Processing Maps

This article examines the hot working characteristics of M250 grade maraging steel by performing isothermal compression tests varying the temperatures and strain rates. A processing map has been developed, indicating microstructurally “stable” and “unstable” regions during hot working. At strain rates (ϵ, ˙, , , , , ) above 0.1 s−1 and temperatures (T) below 1,000°C, stress–strain curves show strain hardening behavior, whereas steady-state behavior is shown at strain rates below 0.01 s−1 and temperatures above 1,050°C. Above 1,150°C, flow softening is observed at 0.001 and 0.01 s−1. In the processing map, two distinct microstructurally stable domains are observed: one is at T = 1,150–1,200°C and ϵ, ˙, , , , , = 0.001–0.01 s−1, and another is at T = 1,000–1,150°C and ϵ, ˙, , , , , = 0.001–0.1 s−1. Based on microstructural observations, electron backscattered diffraction results, and the high efficiency of power dissipation, dynamic recrystallization is the softening mechanism. A constitutive relation useful in computer modeling is developed, using the generated flow stress data.

Characteristics of the Hot Workability of an AZ91D Magnesium Alloy Using 3D Processing Maps

Hot compression tests were carried out on an a homogenized as-cast AZ91D magnesium alloy at temperatures ranging from 220 °C to 380 °C and strain rates ranging from 0.001 to 10 s−1 by means of a Gleeble-3500 thermo mechanical simulator. True stress-–true strain curves were given. A constitutive modeling of the homogenized alloy was proposed to describe the flow characteristic. The deformation activation energy was estimated to be 142.27 kJ mol−1. Continuous three-dimensional (3D) processing maps were developed based on the true stress–true strain data as a function of strain, temperature, and strain rate. A detailed interpretation of the established 3D processing maps was conducted. The results showed that the variation of the 3D processing maps was significantly strain dependent. Dynamic recrystallization domains with high-power dissipation efficiencies and instability domains with negative instability coefficient were identified from the 3D power dissipation maps and the 3D instability maps, respectively. It was also revealed that the instability domains distinctly became enlarged with the increasing strain. Optimized temperature and strain rate ranges at various strains were determined. Furthermore, hot workability characteristics were clarified through examining the microstructures obtained under conditions falling within stability and instability domains with various strains. The results proved that the developed 3D processing maps can provide an accurate prediction of the hot deformation behavior for the homogenized AZ91D alloy.

Thermal Deformation Behavior and Processing Map of Al-Mg-Er Alloy

To study the hot deformation behavior of Al-Mg-Er alloy, hot compression tests were conducted on a Gleeble-1500D thermal simulator at the temperature range of 200-500°C with the strain rates from 0.001 to 10s-1. With the increase in the deformation temperature and the decrease in strain rates, the flow stress of the Al-Mg-Er alloy decreased. Processing maps were constructed to study on hot workability characteristics. The results showed that the flow stress curves exhibited the typical dynamic recrystallization characteristics and the stress decreased with the increase of deformation temperature and the decrease of strain rate. Moreover, the processing maps were established on the basis of dynamic material model and Prasad’s instability criterion.

Hot Workability of 16Cr-5Ni Stainless Steel Using Constitutive Equation and Processing Map

The hot working characteristics of 16Cr-5Ni stainless steel are studied using the results of hot compression tests. Hot compression tests were performed to a total true strain of 0.69 in the strain rate range of 0.001-10 s−1 and temperature range of 900-1100°C. Average value for activation energy is obtained as 403 kJmol−1. The processing maps were constructed based on dynamic materials model at true strain of 0.5. Stable and unstable regimes for hot working are identified and these are verified from the microstructural observations. Optimum hot working conditions associated with dynamic recrystallization are found to be in the strain rate range of 0.01-0.1 s−1 and temperature range of 1000-1100°C, which correspond to a peak power dissipation efficiency of 31%.

The processing map and microstructure evolution of Ni-Cr-Mo-based C276 superalloy during hot compression

Isothermal hot compression tests have been performed to study the hot working characteristics of Ni-Cr-Mo-based C276 superalloy in the temperature range 1000–1200 °C and strain rate range 0.001–5.0s−1. The critical strain and stress for the initiation of dynamic recrystallization (DRX) were determined from the strain rate hardening curves. The processing map based on dynamic materials model was developed at the true strain of 1.0. Coupled analysis with the microstructure observation illustrates that the processing map give good representations of microstructure evolution. And in-grain shear bands were found to be formed when deformed in flow instability area. The grain boundary character and misorientation were analyzed using electron backscatter diffraction (EBSD). It is found DRX fraction increases with the increasing deformation temperature and deformation degree, associated with the increasing fraction of high angle grain boundary (HAGB) and Σ3 twin boundary. And the misorientation distribution approaches the microstructure with random distributed orientation with the increasing DRX, implying no obvious texture was formed after DRX.

Reactive mechanism and mechanical properties of in-situ hybrid nano-composites fabricated from an Al–Fe2O3 system by friction stir processing

In-situ Al/(Al13Fe4+Al2O3) hybrid nano-composite was fabricated using reactive friction stir processing (FSP) by introduction of Fe2O3 powder into the stir zone of rolled AA1050 aluminum alloy. Composite reinforcements were produced in-situ by exothermic reaction of Al and Fe2O3 that initiated by hot working characteristics of FSP. However, the existence of intermediate phase (Fe3O4) suggests that the reaction was not completed due to short time of FSP. EBSD results showed that the matrix mean grain size decreased to 8 and 3μm after FSP without and with introduction of powder, respectively; this was also associated with the marked increase in HAGB. The fabricated nano-composite exhibited superior hardness (45HV) and ultimate tensile strength (~171MPa) as compared to those of the base and FSPed alloy with no powder addition. Formation of in-situ reinforcements and grain refinement acted as major and minor contributors to enhancement of mechanical properties (hardness and ultimate tensile strength), respectively.