•Hot deformation behavior and constitutive description of flow stress for HEAs are summarized.•Effects of deformation conditions, phases, and dynamic precipitation are discussed.•Necklace DRX and the ...effects of processing parameters on the DRX grain size are discussed.•Constitutive modeling techniques for the prediction of flow stress of HEAs are critically discussed.•Future prospects in the field of hot deformation and constitutive modeling of HEAs are listed.
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This review article summarizes the hot deformation behavior of high entropy alloys (HEAs) and the corresponding constitutive description of flow stress. The potential of hot working for grain refinement via dynamic recrystallization (DRX), reduction of casting defects, and enhancement of mechanical properties of HEAs is explained. The necklace formation, work hardening analysis for identification of the occurrence and initiation of DRX, and the effects of processing parameters on dynamically recrystallized grain size are discussed. The effects of deformation conditions (represented by the Zener-Hollomon parameter), alloying elements, dynamic precipitation, and the presence of phases on the hot deformation behavior and restoration processes of DRX and dynamic recovery (DRV) are overviewed. The application of processing maps for the characterization of the onset of flow instability, cracking, flow softening, and DRX during hot forming of HEAs is presented. Regarding the constitutive modeling of flow stress for characterization of material flow (at different deformation temperatures, strain rates, and strain), the utilization of the threshold stress (due to the presence of phases or their precipitation during high-temperature deformation), and temperature-dependent Young’s modulus, as well as correlating the obtained values of deformation activation energy and stress exponent with the expected ones from the creep theories are taken into account. Afterward, the available methods and equations for modeling and prediction of flow curves during thermomechanical processing are assessed, where the strain-compensated Arrhenius model, artificial neural network (ANN) model, Zerilli-Armstrong model, Johnson-Cook model, Hensel-Spittel model, and dislocation density-based multiscale constitutive model are presented. Finally, some suggestions for future research works are proposed.
Additive manufactured magnesium (Mg) alloys have widespread applications in the medical industry as orthopedic implants and biomedical stents, and in the transportation/automotive industry due to ...their status as the lightest structural metallic alloys. The printability of Mg alloys is challenging due to the high oxidization rate, rapid evaporation, and susceptibility to gas trapping. Accordingly, there might be many defects in the as-built parts such as cracking and delamination, porosity and lack of fusion, residual/thermal stresses and distortion, inhomogeneous/columnar microstructure, anisotropy in mechanical/physical properties, inclusions, and non-equilibrium phases formed during solidification. The removal of these defects has a great practical significance, where the post-processing heat treatments without altering the geometry of the parts are often sought in this regard. Accordingly, the present overview article focuses on and critically discusses the recent progress/advances in the application of hot isostatic pressing (HIP), solution annealing (solutionizing), and aging/precipitation heat treatment for the modification/homogenization of the microstructure and improvement of mechanical/functional properties of Mg alloys for the first time. The main fabrication methods are selective laser melting (SLM) from the category of powder bed fusion (PBF) processes, as well as wire and arc additive manufacturing (WAAM) from the category of directed energy deposition (DED) processes. Moreover, the adaptation of the friction stir processing (FSP) technology into additive manufacturing for grain refinement via dynamic recrystallization (DRX) and defect/pore closure (due to the elevated-temperature thermomechanical processing effects), combined severe plastic deformation (SPD) and thermal post-processing, hybridization of additive manufacturing for Mg alloys, and future prospects have been summarized.
In addition to grain size, the mechanical properties and corrosion resistance of magnesium alloys depend on other factors such as texture, distribution of alloying elements, and homogeneity of the ...microstructure. These attributes might change during grain refining processes, making the situation more complex and masking the real effect of grain size. Accordingly, in the present work, the grain size of commercially pure (CP) Mg was adjusted by grain growth annealing after casting and hot rolling (for grain refinement via dynamic recrystallization during thermomechanical processing) to investigate the effect of grain size on tensile properties, hardness, and bio-corrosion resistance in simulated body fluid (SBF). The grain growth kinetics of commercially pure Mg was studied, where the grain growth activation energy (Q) was found to be consistent with that of the grain boundary diffusion in Mg. Based on the Hall-Petch plots, it was revealed that the yield stress (YS), ultimate tensile strength (UTS), and hardness of pure Mg are highly sensitive to average grain size in comparison to common Mg alloys. Moreover, based on the polarization curves and Nyquist plots obtained from electrochemical impedance spectrometry (EIS) analysis, grain coarsening led to the enhanced corrosion resistance due to the decreased grain boundary regions, where a simple linear formula was obtained for correlating corrosion current density to average grain size.
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•Hot deformation behavior and constitutive description of flow stress for AM parts are summarized.•Effects of deformation conditions, phases, and additive manufacturing process are ...discussed.•Techniques with in situ hot working effect such as additive friction stir deposition are summarized.•Constitutive modeling techniques for the prediction of flow stress are critically discussed.•Future prospects in the field of hot deformation of additively manufactured components are proposed.
Hot working, as an important group of post-processing routes for additive manufacturing technology (3D printing), is used to reduce the solidification/processing defects and anisotropy of properties, grain refinement, improvement of mechanical properties, processing of pre-formed parts, and increasing the applicability domain. Accordingly, the present state of the art of the elevated temperature deformation behavior and constitutive description of flow stress during thermomechanical processing of additively manufactured parts is summarized in this monograph. Besides the effects of temperature and strain rate (represented by the Zener-Hollomon parameter), the significance of initial phases and the type of additive manufacturing process on the hot deformed microstructure, restoration processes of dynamic recovery (DRV) and dynamic recrystallization (DRX), flow stress, workability, and hot deformation activation energy is critically discussed. In this regard, the α'-martensite in Ti-6Al-4V titanium alloy produced by selective laser melting (SLM), the precipitates in aluminum alloys (such as 2219 Al alloy) produced by wire and arc additive manufacturing (WAAM), and the Laves phase in Inconel 718 superalloy produced by laser metal deposition (LMD) are remarkable examples. The utilization of innovative methods with in situ hot working effects such as additive friction stir deposition (AFSD) is also enlightened. Regarding the constitutive equations for modeling and prediction of hot flow stress, the reports on the strain-compensated Arrhenius model, artificial neural network (ANN) approach, DRX/DRV kinetics models, Johnson-Cook equation, and Fields-Backofen formula are presented, and the potentials of the modified, simplified, and physically-based approaches are discussed. Finally, the future prospects in this research field such as the hybridization of additive manufacturing with hot forming processes, work-hardening analysis for obtaining the onset of DRX, unraveling the effects of as-built microstructure, developing processing maps, proposing some physical-based unified constitutive models, and investigation of novel and/or widely-used alloys such as austenitic stainless steels, high-entropy alloys, and aluminum alloys (e.g. AlSi10Mg alloy) are proposed.
Superplasticity of a hot rolled Mg–3Zn–0.5RE–0.5Zr (ZEK300) alloy Savaedi, Zeinab; Mirzadeh, Hamed; Aghdam, Rouhollah Mehdinavaz ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
08/2023, Letnik:
881
Journal Article
Recenzirano
Superplasticity of a hot rolled fine-grained Mg–3Zn–0.5RE–0.5Zr (ZEK300) alloy was assessed via shear punch testing (SPT). The deformation behavior of the alloy having a grain size of 4.5 μm ...exhibited regions I, II and III, typical of superplastic materials. In region II, the strain rate sensitivity indices of ZEK300 alloy were obtained as 0.51, 0.48 and 0.41 at 350, 400 and 450 °C, respectively. The average activation energy of 87.6 kJ mol–1 implies that the principal mechanism of deformation is grain boundary sliding (GBS) facilitated by grain boundary diffusion.
Under specific deformation conditions, thermoforming in the supercooled liquid region (SLR) might lead to Newtonian flow characterized by high strain-rate-sensitivity-index (m) of ∼1 and achieving ...superplastic ductilities. Both incipient deformation-induced crystallization and rapid increase in the stress-assisted free volume lead to decreased m-values and transition to non-Newtonian flow. The maximum elongations can be achieved near the transition strain rate from Newtonian to non-Newtonian flow. The effects of heating rate to the thermoforming temperature, total processing time, and the extent of the SLR are significant for structural stability against the in-situ crystallization during elevated-temperature hot deformation. Increasing the deformation temperature normally accentuates the superplastic behavior, but high temperatures might promote crystallization and loss of superplastic ductility . Future prospects for research have been recognized as optimization of the volume fraction of the crystalline (reinforcement) phase in BMG composites, superplasticity of high-entropy BMGs, thermoplastic micro-formability, ultrasonic-assisted forming, improved thermoplastic formability by alloying method, and superplasticity of BMG parts fabricated by additive manufacturing processes.
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•Superplastic behavior of biomedical magnesium alloys is overviewed.•The influence of grain size, deformation temperature, and strain rate is assessed.•Grain refinement by ...thermomechanical processing and severe plastic deformation methods is reviewed.•Importance of thermal stability against the grain coarsening is emphasized.•High-strain-rate superplasticity and low-temperature superplasticity are summarized for Mg alloys.
The superplastic behavior of medical magnesium alloys is reviewed in this overview article. Firstly, the basics of superplasticity and superplastic forming via grain boundary sliding (GBS) as the main deformation mechanism are discussed. Subsequently, the biomedical Mg alloys and their properties are tabulated. Afterwards, the superplasticity of biocompatible Mg-Al, Mg-Zn, Mg-Li, and Mg-RE (rare earth) alloys is critically discussed, where the influence of grain size, hot deformation temperature, and strain rate on the tensile ductility (elongation to failure) is assessed. Moreover, the thermomechanical processing routes (e.g. by dynamic recrystallization (DRX)) and severe plastic deformation (SPD) methods for grain refinement and superplasticity in each alloying system are introduced. The importance of thermal stability (thermostability) of the microstructure against the grain coarsening (grain growth) is emphasized, where the addition of alloying elements for the formation of thermally stable pinning particles and segregation of solutes at grain boundaries are found to be major controlling factors. It is revealed that superplasticity at very high temperatures can be achieved in the presence of stable rare-earth intermetallics. On the other hand, the high-strain-rate superplasticity and low-temperature superplasticity in Mg alloys with great potential for industrial applications are summarized. In this regard, it is shown that the ultrafine-grained (UFG) duplex Mg-Li alloys might show remarkable superplasticity at low temperatures. Finally, the future prospects and distinct research suggestions are summarized. Accordingly, this paper presents the opportunities that superplastic Mg alloys can offer for the biomedical industries.
•Optimum temperature for germination of Charnushka was estimated as 19.2 ± 0.28.•The beta modified model performed best to quantify Charnushka germination response to temperature.•Hydropriming ...increased the base temperature compare to light and hormone priming treatments.•The thermal time required to reach 50 and 95% germination under light condition was 1300 and 2500 degree-hour, respectively.
The response of seed germination to environmental factors can be estimated by nonlinear regression. This study was performed to compare four nonlinear regression models (segmented, beta, beta-modified, and dent-like) for describing the germination rate and temperature relationships of Charnushka seeds under light and utilizing seed-priming treatments at six constant temperatures. Its aim was to identify the cardinal temperatures and thermal times required to reach different germination percentiles. Models and statistical indices were calibrated using an iterative optimization method, and their performance was compared by the root mean square error (RMSE), coefficient of determination (R2), and Akaike information criterion correction (AICc). The beta model under dark conditions was found to be the best model for predicting the required time to reach 50% germination (D50) (R2, 0.99; RMSE, 0.0004; AICc, 19.17). Based on the model outputs, the base, optimum, and maximum temperatures of seed germination under dark conditions were 0.10 ± 0.2, 19.2 ± 0.28, and 35.0 ± 0.19 °C, respectively. However, hydropriming resulted in a higher base temperature of approximately 5 °C. The thermal times required for 50% and 90% of seed germination under dark conditions were 1130.4 and 1543.5 degree days, respectively. Seed priming using GA3 exhibited lower thermal time requirements for the 50% fraction (923.0) and the 90% fraction (1384.5) of total seed germination.
