Wide Range Of Deformation Temperatures Research Articles

ОСОБЛИВОСТІ НЕОДНОРІДНОСТІ ПЛАСТИЧНОЇ ДЕФОРМАЦІЇ ГЕТЕРОФАЗНИХ НЕМЕТАЛЕВИХ ВКЛЮЧЕНЬ В СТАЛЯХ

The nature and level of plasticity of microcomposite heterophase inclusions in steels under pressure treatment condition was investigated. Plastic phases in heterophase inclusions of various types under the conditions of hot and cold deformation of steels were investigated. It is shown that each type of inclusions, which are microcomposite formations in steels, is characterized by its own laws of the development of deformation processes, which are determined by their chemical and phase composition, structure, deformation capacity of inclusion phases. The generalized of the plastic behavior of heterophase inclusions of various types with a complex structure have been established and inhibitory effect of non-deformable inclusion phases on the behavior of plastic phases in a wide range of deformation temperatures of steels has been established. The peculiarities of the nature of plasticity of heterophase inclusions with different compositions and structures are discussed. The use of the obtained results will make it possible to develop technologies for obtaining steels with a regulated content and types of heterophase non-metallic inclusions, which will significantly increase their technological plasticity, as well as prevent the formation of various types of defects during pressure treatment of steels.

FORMABILITY OF INVAR 36 ALLOY AT HIGH TEMPERATURES

By using of hot tensile tests, which were performed on simulator HDS-20, the formability of Invar 36 alloy was investigated. By a special type of a tensile test, involving a continuous control heating of the tested specimens and their simultaneous load by a constant tensile force of 80 N, a nil-strength temperature of investigated alloy 1419 °C was determined. By continuous uniaxial tensile tests to rupture the strength and plastic properties of the Invar 36 alloy were determined in the wide range of deformation temperatures (from 800 °C to 1390 °C) and mean strain rates (from 0.09 s-1 to 75 s-1). On the basis of obtained results the 3D maps were constructed, expressing the dependence of the contractual hot ultimate tensile strength, hot ductility and hot reduction of area of the Invar 36 alloy on the deformation temperature and on the mean strain rate. Based on the determined plastic properties, the nil-ductility temperature of the investigated alloy of 1390 °C was also determined.

Understanding processing map and microstructural evolution of powder metallurgy Ti-6Al-4V within a wide range of deformation temperatures

The hot deformation behavior and microstructural evolution of powder metallurgy (PM) Ti-6Al-4V are investigated using the Arrhenius constitutive model, hot processing map, microstructure observation, and hot deformation mechanism analysis. The optimal processing parameters obtained from the hot processing map are 1323–1423 K at 0.1–1 s−1, and 1423–1523 K at 1–10 s−1. Hot deformation in β region is attractive for PM Ti-6Al-4V. The dominant hot deformation mechanism of PM Ti-6Al-4V is dynamic recrystallization (DRX) in the (α + β) and β regions. Continuous dynamic recrystallization (CDRX) is the dominant mechanism in the (α + β) region. The combination of CDRX and discontinuous dynamic recrystallization (DDRX) is the preferred mechanism in the β region. The power-dissipation efficiency is affected by DRX, which consumes dislocations and refines the microstructure. Specific hot working parameters for thermomechanical processing (TMP) of PM Ti-6Al-4V are identified.

Determination and analysis of the constitutive parameters of temperature-dependent dislocation-density-based crystal plasticity models

Physics-based crystal plasticity models rely on certain statistical assumptions about the collective behavior of dislocation populations on one slip system and their interactions with the dislocations on the other slip systems. One main advantage of using such physics-based constitutive dislocation models in crystal plasticity kinematic frameworks is their suitability for predicting the mechanical behavior of polycrystals over a wide range of deformation temperatures and strain rates with the same physics-based parameter set. In this study, the ability of a widely used temperature-dependent dislocation-density-based crystal plasticity formulation to reproduce experimental results, with a main focus on the yield stress behavior, is investigated. First, the material parameters are identified from experimental macroscopic stress–strain curves using a computationally efficient optimization methodology that uses a genetic algorithm along with the response surface methodology. For this purpose, a systematic set of compression tests on interstitial free (IF) steel samples is performed at various temperatures and strain rates. Next, the influence of the individual parameters on the observed behavior is analyzed. Based on mutual interactions between various parameters, the ability to find a unique parameter set is discussed. This allows identifying shortcomings of the constitutive law and sketch ideas for possible improvements. Particular attention is directed toward identifying possibly redundant material parameters, narrowing the acceptable range of material parameters based on physical criteria, and modifying the crystal plasticity formulation numerically for high-temperature use.

Deformation Behavior, Structure, and Properties of an Aging Ti-Ni Shape Memory Alloy after Compression Deformation in a Wide Temperature Range

The deformation behavior, microstructure, phase composition, and mechanical and functional properties of Ti-50.9 at.%Ni shape memory alloy during uniaxial compression in the temperature range from 25°C to 1000°C have been analyzed and are discussed herein. It was found that the deformation temperature of 300°C marked a boundary for the transition from the low- to high-temperature type of flow curves; achievement of the steady-state deformation stage was observed across a wide range of deformation temperatures. Following comprehensive analysis of the obtained data, the temperature ranges of the dynamic processes of recovery, polygonization, and recrystallization of the Ti-50.9 at.%Ni alloy were determined. Deformation in the range of dynamic polygonization is accompanied by not only the formation of B2-austenite and R-phase, but also the precipitation of fine Ti3Ni4 particles during deformational aging. The highest shape recovery characteristics were obtained after deformation of the Ti-50.9 at.%Ni alloy in the temperature range from 300°C to 600°C.

Evaluation of Hot Workability of Nickel-Based Superalloy Using Activation Energy Map and Processing Maps.

The stress-strain curves for nickel-based superalloy were obtained from isothermal hot compression tests at a wide range of deformation temperatures and strain rates. The material constants and deformation activation energy of the investigated superalloy were calculated. The accuracy of the constitutive equation describing the hot deformation behavior of this material was confirmed by the correlation coefficient for the linear regression. The distribution of deformation activation energy Q as a function of strain rate and temperature for nickel-based superalloy was presented. The processing maps were generated upon the basis of Prasad stability criterion for true strains ranging from 0.2 to 1 at the deformation temperatures range of 900–1150 °C, and strain rates range of 0.01–100 s−1. Based on the flow stress curves analysis, deformation activation energy map, and processing maps for different true strains, the undesirable and potentially favorable hot deformation parameters were determined. The microstructural observations confirmed the above optimization results for the hot workability of the investigated superalloy. Besides, the numerical simulation and industrial forging tests were performed in order to verify the obtained results.

Superelasticity of (TiZrHf)50Ni25Co10Cu15 high entropy shape memory alloy

The paper elucidates the superelastic characteristics of high entropy shape memory alloy (HESMA) (TiZrHf)50Ni25Co10Cu15 over a wide range of deformation temperatures. Axial compression experiments are presented for different heat treatments and local recoverable strains up to 5% are noted. Superelasticity is observed over a large temperature range up to 175°C. Depending on heat treatment, the critical stress exhibits a Clausius-Clapeyron (CC) slope between 1.4 and 6 MPa/°C up to 80 °C deformation temperature. Obvious deviations from linearity however and significantly higher transformation stresses reaching 1200 MPa are reported at higher temperatures. The temperature change during transformation is reported at 9 °C.

Investigation on the hot deformation behaviors and globularization mechanisms of lamellar Ti–6Al–4V alloy within a wide range of deformation temperatures

In this study, the hot deformation behavior and microstructural evolution of Ti–6Al–4 V alloy having a lamellar initial microstructure were systematically investigated within a wide range of deformation temperatures (700–950 °C). Flow softening was commonly observed in the true stress–strain curves and the amount of flow softening gradually decreased with increasing deformation temperature. Based on the microstructure characterization and quantitative analysis of the deformed microstructures, the deformation temperatures were roughly divided into two regions, namely region I (900–950 °C) and region II (700–900 °C). By a detailed transmission electron microscopy (TEM) analysis, different globularization mechanisms of α phase were found for the two regions. At relatively higher deformation temperatures (region I), α lamellae sub-division and grain growth was determined to be the main globularization mechanism. At relatively lower deformation temperatures (region II), on the other hand, dynamic recrystallization (DRX) of α lamellae was confirmed to be the dominant globularization mechanism. In addition, nano-twinning also acted as a secondary globularization mechanism of α lamellae in region II. Finally, it was found that the presence of α lamellae enhanced the DRX of β phase, by providing a strain partitioning between soft β phase and hard α phase as well as reducing the size of β phase.

Investigation on the Hot Deformation Behaviors and Globularization Mechanisms of Lamellar Ti-6Al-4V Alloy within a Wide Range of Deformation Temperatures

In this study, the hot deformation behavior and microstructural evolution of Ti-6Al-4V alloy having a lamellar initial microstructure were systematically investigated within a wide range of deformation temperatures (700~950°C). Flow softening was commonly observed in the true stress-strain curves and the amount of flow softening gradually decreased with increasing deformation temperature. Based on the microstructure characterization and quantitative analysis of the deformed microstructures, the deformation temperatures were roughly divided into two regions, namely region I (900~950°C) and region II (700~900°C). By a detailed transmission electron microscopy (TEM) analysis, different globularization mechanisms of α phase were found for the two regions. At relatively higher deformation temperatures (region I), α lamellae sub-division and grain growth was determined to be the main globularization mechanism. At relatively lower deformation temperatures (region II), on the other hand, dynamic recrystallization (DRX) of α lamellae was confirmed to be the dominant globularization mechanism. The DRX of α lamellae firstly occurred either along the colony boundaries or at the lamellae kinking areas, and then expanded to the interiors of α lamellae. In addition, nano-twinning also acted as a secondary globularization mechanism of α lamellae in region II. Finally, it was found that the presence of α lamellae enhanced the DRX of β phase, by providing a strain partitioning between soft β phase and hard α phase as well as reducing the size of β phase.

Dynamic Precipitation and Substructure Stablility of Cu Alloy during High Temperature Deformation

Structural and mechanical effects of the dynamical precipitation in two copper-base alloys have been investigated over a wide range of deformation temperatures. Basing upon the information gained during the experiment, also some general conclusion may be formulated. A one concerns the nature of dynamic precipitation(DP). Under this term it is commonly understood decomposition of a supersaturated solid solution during plastic straining. The process may, however, proceed in two different ways. It may be a homogeneous one from the point of view of distribution and morphological aspect of particles or it may lead to substantial difference in shape, size and particles distribution. The effect is controlled by the mode of deformation. Hence it seems to be reasonable to distinguish DP during homogeneous deformation from that which takes place in heterogeneously deformed alloy. In the first case the process can be analyzed solely in terms of particle-dislocation-particle interrelation. Much more complex problem we are facing in heterogeneously deforming alloy. Deformation bands and specific arrangement of dislocations in form of pile-ups at grain boundaries generate additional driving force and additional nucleation sites for precipitation. Along with heterogeneous precipitation, there is a homogeneous precipitation in areas between bands of coarse slip which also deform but at much smaller rate. This form of decomposition is responsible for a specially high hardening rate during high temperature straining and for thermally stable product of the decomposition of alloy.

Hot Deformation Behaviour and Microstructural Evaluation of Zr-1Nb Alloy

In nuclear water reactors, zirconium alloys are extensively used as fuel cladding material and in other structural applications. Uniaxial hot compression tests were performed to understand the deformation behavior of Zr-1Nb alloy. Therefore, hot compression tests were performed in the temperature range of 700-1050°C, which envelopes α-phase, (α+β) phase, and β-phase. True stress-strain curves, processing maps, microstructural observation and kinetic analysis were used to discuss the deformation behavior of Zr-1Nb alloy. Deformation at a strain rate of 10-2 s-1 reveals softening at lower temperatures and steady state behavior at higher temperatures. Processing map also reveals domain of high efficiency at 10-2 s-1 strain rate for a wide range of deformation temperatures. The flow softening and high power dissipation efficiency predicts dynamic recrystallization or dynamic recovery during the hot deformation of studied alloy.

Constitutive flow stress formulation for aeronautic aluminum alloy AA7075-T6 at elevated temperature and model validation using finite element simulation

A judicious material constitutive model used as input to the numerical codes to denote elastic, plastic, and thermomechanical behavior under elevated temperatures and strain rates is essential to analyze and design a process. This work describes the formulation of different constitutive models, such as Johnson–Cook, Zerilli–Armstrong, Arrhenius, and Norton–Hoff models for high-strength aeronautic aluminum alloy AA7075-T6 under a wide range of deformation temperatures and strain rates. The adeptness of the formulated models is evaluated statistically by comparing the value of the correlation coefficient and average absolute error between experimental and predicted flow stress results, and numerically when simulating AA7075-T6 machining process. Though all the models show a reasonable degree of accuracy of fit, based on the average absolute error of the data and finite element predictions when simulating the AA7075-T6 machining process, Zerilli–Armstrong model can offer an accurate and precise estimate and is very close to the experimental results over the other models.

Optimum Deformation Criteria and Flow Behavior Description of Boron-Alloyed Steel through Numerical Approach

The capability of a phenomenological, a physical-based, and a restoration-based model in flow behavior description has been evaluated comparatively to determine the optimum high-temperature deformation condition for a boron-alloyed steel. For this purpose, the hot compression tests are performed over wide ranges of strain rate and temperature. The modified Zerilli–Armstrong model is found to be simple and handy for flow modeling since it employs less material constants compared to the other models. The strain-compensated Arrhenius constitutive equation is accurate and can be used to predict the flow behavior of similar alloys over a wide range of deformation temperatures. The restoration-based constitutive analysis is the most accurate approach for flow modeling because it takes different stages of deformation into account separately. Finally yet importantly, the experimental data are used to develop the efficiency maps and the optimum processing domains are determined.

Constitutive Modeling of Hot Deformation Behavior of High-Strength Armor Steel

The hot isothermal compression tests of high-strength armor steel under a wide range of deformation temperatures (1100-1250 °C) and strain rates of (0.001-1/s) were performed. Based on the experimental data, constitutive models were established using the original Johnson-Cook (JC) model, modified JC model, and strain-compensated Arrhenius model, respectively. The modified JC model considers the coupled effects of strain hardening, strain rate hardening, and thermal softening. Moreover, the prediction accuracy of these developed models was determined by estimating the correlation coefficient (R) and average absolute relative error (AARE). The results demonstrate that the flow behavior of high-strength armor steel is considerably influenced by the strain rate and temperature. The original JC model is inadequate to provide good description on the flow stress at evaluated temperatures. The modified JC model and strain-compensated Arrhenius model significantly enhance the predictability. It is also observed from the microstructure study that at low strain rates (0.001-0.01/s) and high temperatures (1200-1250 °C), a typical dynamic recrystallization (DRX) occurs.

Hot Deformation Behaviors and Processing Maps of 2024 Aluminum Alloy in As-cast and Homogenized States

The isothermal hot compression tests of as-cast and homogenized 2024 aluminum alloy were carried out under wide range of deformation temperatures (623-773 K) and strain rates (0.001-10 s−1). The constitutive equations for both initial states were established based on Arrhenius model, and the processing maps were constructed based on the dynamic material model. The results show that the flow stress of samples is evidently affected by both the strain rate and deformation temperature, and the flow stress in homogenized state is always higher than that in as-cast state. Through calculating the correlation coefficient (R) and average absolute relative error of the established constitutive equations, it indicates that Arrhenius model can only provide a rough estimation on the flow stress. However, a much more precise value of the flow stress was obtained by introducing the strain compensation into Arrhenius model, since the effects of strain on the material constants were well considered. Furthermore, according to the processing maps, a suggested range of deformation temperature and strain rate for hot forming process were given then: temperature range 710-773 K and strain rate range 0.001-1 s−1 for as-cast state, and temperature range 680-773 K and strain rate range 0.003-0.22 s−1 for homogenized state.

Hot deformation behavior and constitutive modeling of homogenized 6026 aluminum alloy

Abstract The isothermal hot compression tests of homogenized 6026 aluminum alloy under wide range of deformation temperatures (673–823 K) and strain rates (0.001–10 s−1) were conducted using Gleeble-1500 thermo-simulation machine. According to the experimental obtained true stress–strain data, the constitutive equations were derived based on the original Johnson–Cook (JC) model, modified JC model, Arrhenius model and strain compensated Arrhenius model, respectively. Moreover, the prediction accuracy of these established models was evaluated by calculating the correlation coefficient (R) and average absolute relative error (AARE). The results show that the flow behavior of homogenized 6026 aluminum alloy is significantly affected by the strain rate and temperature. The original JC model is inadequate to provide good description on the flow stress at evaluated temperatures. The modified JC model and Arrhenius model greatly improve the predictability, since both of these models consider the coupled effects of deformation temperature and strain rate. However, to give more precise description, the influence of strain on the material constants should be introduced into Arrhenius model.

Determining the Conditions for Dynamic Recrystallization in Hot Deformation of C–Mn–V Steels and the Effects of Cr and Mo Additions

The refinement of microstructure and its homogeneity during controlled hot strip rolling is primarily achieved by controlling the austenite recrystallization before its transformation during accelerated cooling. The paper describes the methodology to determine the deformation conditions favorable for dynamic recrystallization (DRX). Using this methodology it becomes possible to delineate the conditions for postdeformation static and metadynamic recrystallization as well. The work is based on viscoplastic power law formalism applied to steady state flow within wide range of deformation temperatures and strain rates. Two equations of the same form but with different coefficients can be used depending on whether the steady state flow is controlled by dynamic recovery (DRV) or DRX. The transition from DRV- to DRX at the corresponding value of Zener-Hollomon parameter Zt can be viewed as the demarcation between static and metadynamic recrystallization occurring after deformation. The approach is illustrated using low carbon Mn–V steel. Alloying with Cr and especially with Mo suppresses DRX and MDRX as manifested by increasing Zt.

Constitutive behavior of as-cast A356

The constitutive behavior of aluminum alloy A356 in the as-cast condition has been characterized using compression tests performed over a wide range of deformation temperatures (30-500{\deg}C) and strain rates (\approx0.1-10 /s). This work is intended to support the development of process models for a wide range of conditions including those relevant to casting, forging and machining. The flow stress behavior as a function of temperature and strain rate has been fit to a modified Johnson-Cook and extended Ludwik-Hollomon expression. The data has also been assessed with both the strain-independent Kocks-Mecking and Zener-Hollomon frameworks. The predicted plastic flow stress for each expression are compared. The results indicate that the extended Ludwik-Hollomon is best suited to describe small strain conditions (stage III hardening), while the Kocks-Mecking is best employed for large strain (stage IV). At elevated temperatures, it was found that the Zener-Hollomon model provides the best prediction of flow stress.

Superplastic Behavior of Fine‐Grained β‐Silicon Nitride Material under Compression

The deformation behavior of a hot‐pressed, fine‐grained β‐Si3N4 ceramic was investigated in the temperature range 1450°—1650°C, under compression, and the results for strain rate and temperature dependence of the flow stress are presented here. The present results show that the material is capable of high rates of deformation (∼10−4—10−3 s−1) within a wide range of deformation temperatures and under a pressure of 5—100 MPa; no strain hardening occurs in the material, even at slow deformation rates, because of its stable microstructure; Newtonian flow occurs, with a stress exponent of approximately unity; and the material has activation energy values for flow in the range 344—410 kJ·mol−1. Grain‐boundary sliding and grain rotation, accommodated by viscous flow, might be the mechanisms of superplasticity for the present material.