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The hot deformation behaviors of an aged Inconel 718 superalloy are investigated by isothermal compression experiments at four strain rates and five deformation temperatures on a Gleeble-3500 thermo-mechanical simulator. The experimental results show that the true stresses are obviously affected by strain rate and deformation temperature. The true stress increases rapidly at the beginning of hot compressive deformation, which ascribes to the intense work hardening. The true stresses at high deformation temperatures are lower than those at lower deformation temperatures. The dynamic softening induced by DRX is weak at a relatively low deformation temperature. A strain-compensated Arrhenius-type constitutive equation linked with true stress, strain rate and deformation temperature is developed for the studied superalloy. The material constants ( α \alpha , n, Q and A) in the developed model are expressed as the functions of true strain. The flow stresses calculated by the developed constitutive equation are nicely consistent with the experimental ones, which confirms that the developed constitutive equation can accurately describe the hot deformation behaviors of the studied superalloy. [ABSTRACT FROM AUTHOR]

Generally, the obvious work hardening, dynamic recrystallization (DRX), and dynamic recovery behaviors can be found during hot deformation of Ni-based superalloys. In the present study, the classical dislocation density theory is improved by introducing a new dislocation annihilation item to represent the influences of DRX on dislocation density evolution for a Ni-based superalloy. Based on the improved dislocation density theory, the peak strain corresponding to peak stress and the critical strain for initiating DRX can be determined, and the improved DRX kinetics equations and grain size evolution models are developed. The physical framework and algorithmic idea of the improved dislocation density theory are clarified. Moreover, the deformed microstructures are characterized and quantitatively correlated to validate the improved dislocation density theory. It is found that the improved dislocation density-based models can precisely characterize hot deformation and DRX behaviors for the studied superalloy under the tested conditions. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Low-cycle fatigue failure behaviors of hot-rolled AZ91 magnesium alloy are investigated. [•] The fatigue life increases with the increase of the strain ratio and decrease of the peak stress. [•] Increasing stress ratio and decreasing peak stress can decrease the amount of residual twins. [•] The residual twins kink with each other and deteriorate the grain boundary. [•] A modified stress-based fatigue life model is developed for hot-rolled AZ91 magnesium alloy. [ABSTRACT FROM AUTHOR]

Abstract: In industrial forming processes, the metals and alloys are subject to complex strain, strain-rate, and temperature histories. Understanding the flow behaviors of metals and alloys in hot working has a great importance for designers of metal forming processes. In order to study the workability and establish the optimum hot formation processing parameters for some metals and alloys, a number of research groups have made efforts to carry out the thermo-mechanical experiments (compressive, tensile and torsion tests) over wide forming temperatures and strain-rates, and some constitutive equations were developed to describe the hot deformation behaviors. This paper presents a critical review on some experimental results and constitutive descriptions for metals and alloys in hot working, which were reported in international publications in recent years. In this review paper, the constitutive models are divided into three categories, including the phenomenological, physical-based and artificial neural network models, to introduce their developments, prediction capabilities, and application scopes, respectively. Additionally, some limitations and objective suggestions for the further development of constitutive descriptions for metals and alloys in hot working are proposed. [Copyright &y& Elsevier]

Abstract: Polymer-based conductive adhesive materials have become widely used in many electronic packaging interconnect applications. Uniaxial ratchetting behavior of anisotropic conductive adhesive film (ACF) was studied by uniaxial cyclic tension experiments. The effects of mean stress, stress amplitude and loading history on the ratchetting response of ACF material were analyzed. Results show that (1) the ratchetting strain amplitude and ratchetting strain rate of the ACF material increase with increasing stress amplitude or mean stress; (2) the ACF material has a strong memory of loading history. Prior stress cycling with higher mean stress or stress amplitude restrains the ratchetting strain in subsequent cycling with lower mean stress or stress amplitude. Prior stress cycling with higher stress rate will accelerate the plastic deformation of subsequent cycling with lower stress rate for the ACF material. [ABSTRACT FROM AUTHOR]

Hot deformation behaviors of a typical nickel-based superalloy are investigated by isothermal compression tests under the deformation temperature range of 920–1040 °C and strain rate range of 0.001–1 s −1 . Scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) technique and transmission electron microscopy (TEM) are employed to study the evolution of hot deformed microstructures. It is found that the fraction of low angle grain boundaries decreases with the increase of deformation temperature or the decrease of strain rate. This is related to the decrease of dynamic recrystallization degree under the low deformation temperature or high strain rate. The fraction of low angle grain boundaries shows a rapid increase at the relatively small deformation degree, and then a significant decrease due to the progress of dynamic recrystallization (DRX). The microstructural changes indicate that both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) take place during hot deformation. However, the small fraction of low angle boundaries with 10–15° misorientation indicates that the CDRX plays a minor role on the nucleation of dynamic recrystallization. Discontinuous dynamic recrystallization (DDRX) characterized by grain boundary bulging is the dominant nucleation mechanism for the studied superalloy. [ABSTRACT FROM AUTHOR]

Abstract: Uniaxial ratcheting and low-cycle fatigue failure behaviors of the hot-rolled AZ31B magnesium alloy are studied by uniaxial asymmetrical cyclic stress-controlled experiments at room temperature. The effects of mean stress, stress amplitude and stress rate on the uniaxial ratcheting response and ratcheting life of the studied magnesium alloy are analyzed. The microscopic observations near fracture surface are carried out. In addition, a fatigue parameter is introduced to describe the ratcheting damage and fatigue damage processes, and a new model is established to describe the relationship between the linear density of twins and the fatigue parameter. Results show that (1) the mean stress and stress amplitude has a great influence on the ratcheting strain and fatigue failure life. When the mean stress or stress amplitude is increased, the ratcheting strain and its rate rapidly increase. So, the fatigue failure life is reduced. (2) The increase of mean stress and stress amplitude can accelerate the generation of twins, which decreases the fatigue resistance and increases the ratcheting strain. However, the stress rate has little effect on the twinning. So, the effects of stress rate on ratcheting and low-cycle fatigue failure behaviors are not obvious under the tested conditions. This is because the studied magnesium alloy shows highly rate-independent property at room temperature within the tested strain rate range. (3) The established model can accurately describe the relationship between the linear density of twins and the fatigue parameter. Furthermore, the threshold fatigue parameter for twinning is found. [Copyright &y& Elsevier]

Abstract: The compressive deformation behaviors of 2124-T851 aluminum alloy were investigated over a wide range of temperature and strain rate on Gleeble-1500 thermo-simulation machine. The results show that the true stress–true strain curves exhibit a peak stress at a very small strain, after which the flow stresses decrease until high strains, showing a dynamic flow softening. The measured flow stress was modified by friction correction, and the corrected flow stresses are lower than the measured ones, which nicely reflect negative effects of the interfacial friction on the flow stress. A revised model is proposed to describe the relationships of the flow stress, strain rate and temperature of 2124-T851 aluminum alloy at elevated temperatures. The stress–strain values of 2124-T851 aluminum alloy predicted by the proposed model well agree with experimental results, which confirmed that the revised deformation constitutive equation gives an accurate and precise estimate for the flow stress of 2124-T851 aluminum alloy. [ABSTRACT FROM AUTHOR]

Highlights: [•] Corrosion resistance of Al–Zn–Mg–Cu alloy is sensitive to creep-aging processing. [•] The increase of applied stress can enhance the corrosion resistance. [•] The increased temperature first increases and then decreases corrosion resistance. [•] Discontinuous GB precipitate and narrow PFZ improve can corrosion resistance. [Copyright &y& Elsevier]

The hot compressive deformation behaviors of a typical Ni-based superalloy are investigated over wide ranges of forming temperature and strain rate. Based on the experimental data, the efficiencies of power dissipation and instability parameters are evaluated and processing maps are developed to optimize the hot working processing. The microstructures of the studied Ni-based superalloy are analyzed to correlate with the processing maps. It can be found that the flow stress is sensitive to the forming temperature and strain rate. With the increase of forming temperature or the decrease of strain rate, the flow stress significantly decreases. The changes of instability domains may be related to the adiabatic shear bands and the evolution of δ phase(Ni3Nb) during the hot formation. Three optimum hot deformation domains for different forming processes (ingot cogging, conventional die forging and isothermal die forging) are identified, which are validated by the microstructural features and adiabatic shear bands. The optimum window for the ingot cogging processing is identified as the temperature range of 1010–1040°C and strain rate range of 0.1–1s−1. The temperature range of 980–1040°C and strain rate range of 0.01–0.1s−1can be selected for the conventional die forging. Additionally, the optimum hot working domain for the isothermal die forging is 1010–1040°C and near/below 0.001s−1. [ABSTRACT FROM AUTHOR]