Simulated and experimental investigation on discontinuous dynamic recrystallization of a near-α TA15 titanium alloy during isothermal hot compression in βsingle-phase field

A cellular automaton（CA） modeling of discontinuous dynamic recrystallization（DDRX） of a near-α Ti-6Al-2Zr-1Mo-1V（TA15） isothermally compressed in the β single phase field was presented.In the CA model,nucleation of the β-DDRX and the growth of recrystallized grains（re-grains） were considered and visibly simulated by the CA model.The driving force of re-grain growth was provided by dislocation density accumulating around the grain boundaries.To verify the CA model,the predicted flow stress by the CA model was compared with the experimental data.The comparison showed that the average relative errors were10.2%,10.1%and 6%,respectively,at 1.0,0.1 and 0.01 s^-1 of 1020 ℃,and were 10.2%,11.35%and 7.5%,respectively,at 1.0,0.1and 0.01 s^-1 of 1050 ℃.The CA model was further applied to predicting the average growth rate,average re-grain size and recrystallization kinetics.The simulated results showed that the average growth rate increases with the increasing strain rate or temperature,while the re-grain size increases with the decreasing strain rate;the volume fraction of recrystallization decreases with the increasing strain rate or decreasing temperature.

A discontinuous dynamic recrystallization model incorporating characteristics of initial microstructure

In order to describe and predict the kinetic process of discontinuous dynamic recrystallization （DDRX） during hot workingfor metals with low to medium stacking fault energies quantitatively, a new physically-based model was proposed by considering thecharacteristics of grain size distribution, capillary effect of initial grain boundaries （GBs） and continuous consumption of GBs. UsingIncoloy 028 alloy as a model system, experiments aiming to provide kinetic data （e.g., the size and volume fraction of recrystallizedgrain） and the associated microstructure were performed. Good agreement is obtained between model predictions and experimentalresults, regarding flow stress, recrystallized fraction and grain size evolution. On this basis, a thermo-kinetic relationship upon thegrowth of recrystallized grain was elucidated, i.e., with increasing thermodynamic driving force, the activation energy barrierdecreases.

Microstructural evolution and dynamic recrystallization mechanisms of additively manufactured TiAl alloy with heterogeneous microstructure during hot compression

Microstructural evolution and dynamic recrystallization(DRX)mechanisms of a Ti-48Al-2Cr-2Nb(at.%)alloy prepared by selective electron beam melting(SEBM)during hot deformation at 1150℃and 0.1 s^(-1)were investigated by hot compression tests,optical microscope(OM),scanning electron microscope(SEM),electron back-scattered diffraction(EBSD)and transmission electron microscope(TEM).The results show that the initial microstructure of the as-SEBMed alloy exhibits layers of coarseγgrains and fineγ+α_(2)+(α_(2)/γ)lamellar mixture grains alternately along the building direction.During the early stage of hot deformation,deformation twins tend to form within the coarse grains,facilitating subsequent deformation,and a small number of DRX grains appear in the fine-grained regions.With the increase of strain,extensive DRX grains are formed through different DRX mechanisms in both coarse and fine-grained regions,involving discontinuous dynamic recrystallization mechanism(DDRX)in the fine-grained regions and a coexistence of DDRX and continuous dynamic recrystallization(CDRX)in the coarsegrained regions.

Investigating the effect of pyroptosis on the slow CD4+T cell depletion in HIV-1 infection,by dynamical analysis of its discontinuous mathematical model

HIV infection is one of the most serious causes of death throughout the world.CD4+T cells which play an important role in immune protection,are the primary targets for HIV infection.The hallmark of HIV infection is the progressive loss in population of CD4+T cells.However,the pathway causing this slow T cell decline is poorly understood[16].This paper studies a discontinuous mathematical model for HIV-1 infection,to investigate the effect of pyroptosis on the disease.For this purpose,we use the theory of discontinuous dynamical systems.In this way,we can better analyze the dynamical behavior of the HIV-1 system.Especially,considering the dynamics of the system on its discontinuity boundary enables us to obtain more comprehensive results rather than the previous researches.A stability region for the system,corresponding to its equilibria on the discontinuity boundary,will be determined.In such a parametric region,the trajectories of the system will be trapped on the discontinuity manifold forever.It is also shown that in the obtained stability region,the disease can lead to a steady state in which the population of uninfected T cells and viruses will preserve at a constant level of cytokines.This means that the pyroptosis will be restricted and the disease cannot progress for a long time.Some numerical simulations based on clinical and experimental data are given which are in good agreement with our theoretical results.

Generalized projective synchronization between two chaotic gyros with nonlinear damping

In this paper, the chaotic generalized projective synchronization of a controlled, noised gyro with an expected gyro is investigated by a simple control law. Based on the theory of discontinuous dynamical systems, the necessary and sufficient conditions for such a synchronization are achieved. From such conditions, non-synchronization, partial and full synchronizations between the two coupled gyros are discussed. The switching scenarios between desynchronized and synchronized states of the two dynamical systems are shown. Numerical simulations are illustrated to verify the effectiveness of this method.

Effect of Si and Ti on dynamic recrystallization of high-performance Cu-15Ni-8Sn alloy during hot deformation

Effect of Si and Ti on dynamic recrystallization(DRX)of Cu-15Ni-8 Sn alloy was studied using hot compression tests over deformation temperature range of 750-950℃and strain rate range of 0.001-10 s^-1.The results show that the dynamic recrystallization behavior during hot deformation is significantly affected by the trace elements of Si and Ti.The addition of Si and Ti promotes the formation of Ni16Si7Ti6 particles during hot deformation,which promotes the nucleation of dynamic recrystallization by accelerating the transition from low-angle boundaries(LABs)to high-angle boundaries(HABs).Ni16Si7Ti6 particles further inhibit the growth of recrystallized grains through the pinning effect.Based on the dynamic recrystallization behavior,a processing map of the alloy is built up to obtain the optimal processing parameters.Guided by the processing map,a hot-extruded Cu-15 Ni-8Sn alloy with a fine-grained microstructure is obtained,which shows excellent elongation of 30%and ultimate tensile strength of 910 MPa.

Grain refinement and weak-textured structures based on the dynamic recrystallization of Mg–9.80Gd–3.78Y–1.12Sm–0.48Zr alloy

We utilized electron backscatter diffraction to investigate the microstructure evolutions of a newly developed magnesium-rare earth alloy(Mg–9.80 Gd–3.78 Y–1.12 Sm–0.48 Zr)during instantaneous hot indirect extrusion.An equiaxed fine-grained(average grain size of 3.4±0.2μm)microstructure with a weak texture was obtained.The grain refinement was mainly attributed to the discontinuous dynamic recrystallization(DDRX)and continuous DRX(CDRX)processes during the hot indirect extrusion process.The twin boundaries formed during the initial deformation stage effectively increased the number of high angle grain boundaries(HAGBs),which provided sites for new grain nuclei,and hence,resulted in an improved DDRX process.Along with DDRX,CDRX processes characterized by low angle grain boundary(LAGB)networks were also observed in the grain interior due to effective dynamic recovery(DRV)at a relatively high temperature of 773 K and high strain rates.Thereafter,LAGB networks were transformed into HAGB networks by the progressive rotation of subgrains during the CDRX process.

Deformation Behavior of 6063 Aluminum Alloy During High-Speed Compression

The deformation behavior characteristics of 6063 aluminum alloy were studied experimentally by isothermal compression tests on a Gleeble- 1500 thermal-mechanical simulator. Cylindrical specimens of 14mm in height and 10mm in diameter were compressed dynamically at temperatures ranging from 473 to 723K and at higher strain rntes from 5 to 30s^-1. It is fouud that the flow curves not only depend on the strain rate and temperature but nlso on the dynamic recovery aud recrystallization behavior. The results show that the flow stress decreased with the increase of temperature, while increased with the increase of strain rate. The discontinuous dynamic recrystallization （DDRX） may take place at a high strain rate of 20s^-1 under the tested conditions. At 30s^-1 , the flow curve can exhibit,flow softening due to the effect of temperature rise that raised the temperature by aboat 32K in less than 0.05s.

From the new Austrian tunneling method to the geoengineering condition evaluation and dynamic controlling method

The new Austrian tunneling method （NATM） is widely applied in design and construction of underground engineering projects. When the type and distribution of unfavorable geological bodies （UGBs） associated with their influences on geoengineering are complicated or unfortunately are overlooked, we should pay more attentions to internal features of rocks grades IV and V （even in local but mostly controlling zones）. With increasing attentions to the characteristics, mechanism and influences of engineering construction-triggered geohazards, it is crucial to fully understand the disturbance of these geohazards on project construction. A reasonable determination method in construction procedure, i.e. the shape of working face, the type of engineering support and the choice of feasible procedure, should be considered in order to mitigate the construction-triggered geohazards. Due to their high sensitivity to groundwater and in-situ stress, various UGBs exhibit hysteretic nature and failure modes. To give a complete understanding on the internal causes, the emphasis on advanced comprehensive geological forecasting and overall reinforcement treatment is therefore of more practical significance. Compre- hensive evaluation of influential factors, identification of UGB, and measures of discontinuity dynamic controlling comprises the geoengineering condition evaluation and dynamic controlling method. In a case of a cut slope, the variations of UGBs and the impacts of key environmental factors are presented, where more severe construction-triggered geohazards emerged in construction stage than those predicted in design and field investigation stages. As a result, the weight ratios of different influential factors with respect to field investigation, design and construction are obtained.

Interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding

The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large number of dislocation pairs(DP),stacking faults(SF),and micro-twins(MT)in the primary γ′.These defects act as fast channels for elemental diffusion,leading to supersaturation of the primary γ′and promoting the growth of the γ-shell.On the one hand,the primary γ′with a γ-shell moves towards the bonding interface due to anomalous yielding phenomena of the primary γ′and plastic flow during HCB process.The increase in the number of defects leads to the growth of γ-γ′heterogeneous epitaxial recrystallization(HERX)grain with coherent structure at the bonding interface,which promotes the bulge of the interface grain boundaries(IGBs).On the other hand,the nucleation and growth of a necklace-like distribution of discontinuous dynamic recrystallization(DDRX)grain at the interface lead to the healing of IGBs.With the synergistic action of DDRX and HERX,the mechanical properties of Ni-Co-based superalloy joints through HCB achieve the same level as the base material.This finding further enriches the theory of interface healing in HCB.