High Strain Rate Region Research Articles

Hot Workability and Microstructure Evolution of Homogenized 2050 Al-Cu-Li Alloy during Hot Deformation.

For this article, hot compression tests were carried out on homogenized 2050 Al-Cu-Li alloys under different deformation temperatures and strain rates, and an Arrhenius-type constitutive model with strain compensation was established to accurately describe the alloy flow behavior. Furthermore, thermal processing maps were created and the deformation mechanisms in different working regions were revealed by microstructural characterization. The results showed that most of the deformed grains orientated toward <101>//CD (CD: compression direction) during the hot compression process, and, together with some dynamic recovery (DRV), dynamic recrystallization (DRX) occurred. The appearance of large-scale DRX grains at low temperatures rather than in high-temperature conditions is related to the particle-stimulated nucleation mechanism, due to the dynamic precipitation that occurs during the deformation process. The hot-working diagrams with a true strain of 0.8 indicated that the high strain-rate regions C (300 °C-400 °C, 0.1-1 s-1) and D (440 °C-500 °C, 0.1-1 s-1) are unfavorable for the processing of 2050 Al-Li alloys, owing to the flow instability caused by local deformation banding, microcracks, and micro-voids. The optimum processing region was considered to be 430 °C-500 °C and 0.1 s-1-0.001 s-1, with a dissipation efficiency of more than 30%, dominated by DRV and DRX; the DRX mechanisms are DDRX and CDRX.

Study on the hot deformation behavior and microstructure evolution of as-forged GH3625 alloy

GH3625 alloy is widely used in aviation, nuclear power and other fields of hot section components. However, the high alloying level, significant deformation resistance, and narrow hot working window of the alloy bring great challenge to the plastic deformation of the alloy. The hot deformation behavior and microstructure evolution of as-forged GH3625 alloy were studied by hot compression tests with deformation temperatures of 930–1180 °C, strain rates of 0.001–1 s−1 and true strain of 0.92. The results show that the flow stress of the alloy exhibits noticeable characteristics of temperature-negative sensitivity and rate-positive sensitivity. The true stress-strain curves are of two types: dynamic recovery (DRV) and dynamic recrystallization (DRX). The strain-compensated Arrhenius constitutive model was used to predict the alloy's flow behavior, with a linear fitting correlation coefficient (R) of 0.9872 and an average relative error (AARE) of 8.92%. The hot processing map of the alloy based on Prasad was constructed and superimposed. It was found that there were two instability regions, which were located in the low temperature and high strain rate region and the high temperature and low strain rate region respectively. The optimal processing region was 1154∼1180 °C/0.75–1 s−1 combined with the true stress-strain curves and the microstructure. Continuous dynamic recrystallization (CDRX) at subgrains rotation and discontinuous dynamic recrystallization (DDRX) at grain boundaries were identified during thermal deformation. As the η value decreases, the dynamic recrystallization grain size decreases under the deformation condition of 930–1180 °C/1 s−1, and the microstructure evolution mechanism changes from DDRX→ DDRX + CDRX→ DDRX + CDRX + DRV → CDRX + DRV, and ∑3 TBs also reduces.

Hot processing map and high temperature deformation behaviour of TB17 Ti alloy

The thermal compression experiments of TB17 titanium alloy under different thermal deformation process parameters were carried out using a thermal simulation compressor. The high-temperature plastic flow behaviour of the alloy was studied. It was found that with the decrease of the deforming temperature and the increase of the strain rate, the flow stress increased, and the discontinuous yield phenomenon occurred in hot deformation. The larger the strain rate, the more obvious the discontinuous yield phenomenon. The thermal activation energy Q decreased with the increase of strain, and the average value of activation energy Q is 209.54 KJ / mol. The constitutive equation of high-temperature plastic flow of TB17 titanium alloy was established. The predicted values of this equation are in good agreement with the experimental values. The average error is 3.987 %, and the correlation coefficient is 0.9972, which has high accuracy. Based on the Prasad criterion, the hot processing map of TB17 titanium alloy was constructed. It was found that the flow instability zone was mainly concentrated in the high strain rate region. The flow instability zone was determined to be 795 °C ~ 895 °C, 0.046s-1 ~ 1s-1, and the stable deformation zone was mainly located in the region with high temperature and low strain rate. The optimum processing parameter range is 860 °C ~ 895 °C, 0.001 s-1 ~ 0.025 s-1.

Study on thermal deformation behavior and microstructure evolution of P550 high nitrogen austenitic stainless steel

The high nitrogen austenitic stainless steel is widely used as power generation and geological exploration equipment materials because of its excellent strength, corrosion resistance and non-magnetic. In this paper, the mechanical behavior and microstructure evolution of P550 steel in the range of 900 °C–1200 °C and 0.001–10 s−1 deformation conditions were studied by physical and heat treatment simulations, metallographic observations and thermal processing maps. The results showed that the flow curves quickly reach the peak and then soften to a steady state, which indicates dynamic recrystallization (DRX) behavior. DRX is easy to occur when the deformation temperature is above 1080 °C. The activation energy of the forged P550 stainless steel was calculated as 519 kJ mol−1. There is a positive correlation between the peak stress, DRX critical stress, strain and Z value of the tested steel. The instability of the tested steel is easy to produce in the high strain rate region and low temperature region during hot working. Crack germinates and expands preferentially at the ‘necklace structure’ of inadequate dynamic recrystallization. Under the deformation state of 0.001 s−1, coarse crystals and mixed crystals are easily emerged during subsequent heat treatment. Combining the hot working map, the maximum deformation resistance and the grain evolution behavior during hot working and heat treatment, the suggested working window is T = 1020 °C–1200 °C and έ = 0.01–1 s−1.

Temporal evolution of the magmatic system at Nevado del Ruiz Volcano (Colombia) inferred from long-period seismic events in 2003–2020

Long-period (LP) seismic events have been broadly assumed to be generated by oscillations of crack fluid-filled resonators. We investigated the waveforms and spectral characteristics of LP seismic events recorded by five stations at Nevado del Ruiz Volcano, Colombia. The observed event types of LP events exhibited decaying harmonic oscillations with either monochromatic or polychromatic spectral features (NLP events) or events characterized by non-decaying harmonic oscillations (BLP events). The NLP events occurred over four periods: September 2003 (period I), January 2004–October 2004 (period II), October 2010–March 2012 (period III), and October 2019–April 2020 (period IV). Their source locations were determined to be within the first kilometer of the conduit placed below the Arenas crater. Their locations involved a distinct resonator for each of the four periods but a single resonator for all the events during a single period. Assuming a crack geometry at their sources and based on their locations, we considered a dusty gas (mixture of ash and water vapor) filling a crack resonator. We estimated the crack model parameters to investigate the temporal processes generating variations in frequency and quality factor Q. Then, the estimated parameters indicate that NLP events were triggered by magma fragmentation. We found that events from period III preceded phreatomagmatic eruptions, increased ash and gas emissions and SO2 flux, and increased overall seismic activity. Three years after this period III, a dome was emplaced at the base of the Arenas crater. Besides, events from period IV also preceded by ~3 years a significant increase in the overall seismic activity, which led to a change in alert activity at the volcano. We argue that BLP events were driven by resonances provoked by the unstable degassing through the uppermost magma plug's open cracks (tuffisite veins).In contrast, NLP events occurred by overpressure released through fractures along the conduit's walls (shear fractures). The shear fractures at the conduit wall were in a region of high strain rate where a decrease in confining pressure triggered fragmentation, resulting in dusty gas and, subsequently, a resonance of the crack. NLP and BLP events were in a narrow relationship with the ascent of vesiculated magma to the surface. Our results show that the LP events help diagnose the state of magmatic fluids and understand the eruption processes of Nevado del Ruiz Volcano. LP events are not always followed by explosive eruptions, but they do indicate significant overpressure developing in the shallow conduit.

Damage prediction in thermoplastics under impact loading using a strain rate-dependent GISSMO

With the increasing use of polymers in structural parts in areas ranging from automotive and aviation to electronic and common household goods a clear understanding of their mechanical behavior under dynamic conditions has become important. While the study of damage and fracture in metals has a long history, the prediction of damage in polymers is still in its fledging stages, not least due to the very complex microstructure. Owing to similarities in their behavior from a continuum mechanics perspective, applying models originally developed for metals is expedient but needs justification and validation. Further, rate-dependence must be accounted for. In this study, the damage and fracture behavior of two thermoplastic is investigated. The focus lies on the high strain and high strain rate regions. The GISSMO (generalized incremental stress-strain damage model) is applied to model the damage-induced softening of the material. Rate-dependence is accounted for by expanding the triaxiality failure diagram (TFD) to the strain rate dimension. Elastoplastic and damage parameters are obtained from tensile tests with different specimen geometries. Viscoelastic and viscoplastic behavior is neglected. The material model is validated by comparing the responses from FE simulation with experimental data from 3-point bending and ball drop tests with notched specimens and actual parts. It is found that this relatively simple model with straightforward parameter evaluation is capable of predicting damage and fracture under various conditions to some good accuracy.

Constitutive Analysis and Microstructure Characteristics of As-Homogenized 2198 Al–Li Alloy under Different Hot Compression Deformation Conditions

The 2198 Al-Li alloy has unique superiority in mechanical performance and has been extensively used in the aerospace field. In this study, the hot deformation behavior of the 2198 Al-Li alloy was investigated on a Gleeble-1500 thermomechanical simulator with a strain rate of 0.01-10 s-1 in the temperature range of 330-510 °C. The Arrhenius constitutive equation of the alloy was established based on the true stress-strain curves to describe the rheology behaviors during the deformation of the alloy. The processing maps under the strain of 0.2-0.8 were constructed, which indicates the efficiency of power dissipation and instability of the deformed alloy. It was found that the instability domains are more likely to occur in the regions of low deformation temperature and high strain rate, corresponding to the high Zener-Hollomon (Z) parameter. The microstructure evolution of the studied alloy with different Z parameters was characterized. Then, the dynamic recrystallization (DRX) behavior was studied by electron backscatter diffraction, and the misorientation angle of deformed specimens was analyzed. The effect of different deformation temperatures and strain rates on the microstructure of the alloy and the behavior of dislocations and precipitations were investigated by transmission electron microscopy. The results demonstrate that continuous dynamic recrystallization (CDRX) and geomatic dynamic recrystallization (GDRX) mainly occur at the deformation conditions of a low Z value, and discontinuous dynamic recrystallization (DDRX) is likely to occur with increasing Z values.

Dynamics of inertial spheroids in a decaying Taylor–Green vortex flow

Inertial spheroids, prolates and oblates, are studied in a decaying Taylor–Green vortex (TGV) flow, wherein the flow gradually evolves from laminar anisotropic large-scale structures to turbulence-like isotropic Kolmogorov-type vortices. Along with particle clustering and its mechanisms, preferential rotation and alignment of the spheroids with the local fluid vorticity are examined. Particle inertia is classified by a nominal Stokes number St, which to first-order aims to eliminate the shape effect. The clustering varies with time and peaks when the physically relevant flow and particle time scales are of the same order. Low inertial (St&amp;lt;1) spheroids are subjected to the centrifuging mechanism, thereby residing in stronger strain-rate regions, while high inertial (St≫1) spheroids lag the flow evolution and modestly sample strain-rate regions. Contrary to the expectations, however, spheroids reside in high strain-rate regions when the particle and flow time scales are comparable due to the dynamic interactions between the particles and the evolving flow scales. Moderately inertial (St≤1) prolates preferentially spin and oblates tumble throughout the qualitatively different stages of the TGV flow. These preferential modes of rotation correlate with parallel and perpendicular alignments of prolate and oblate spheroids, respectively, with the local fluid vorticity. However, for high inertial spheroids preferential rotation and alignment are decorrelated due to a memory effect, i.e., inertial particles require longer time to adjust to the local fluid flow. This memory effect is not only due to high particle inertia, as in statistically steady turbulence, but also caused by the continuously evolving TGV flow scales.

The Unsteady Topology of Corner Separations

Abstract As a compressor is throttled three-dimensional separations develop in the corners between the blades and annulus endwall. Surprisingly, little is understood about the unsteady topology of these separations. One of the problems in studying corner separations is that it is often difficult to understand whether a particular flow structure in the separation is inherent to the separation itself or due to the response of the separation to changes in the inlet flow. In this paper, a novel experimental approach is taken to isolate the corner separation from external influences. A cascade is designed with the specific aim of precisely controlling the inlet flow. Contrary to earlier work, it is shown that the key saddle and focus pair, which describes the time-mean topology of the corner separation on the endwall, moves smoothly and continuously as the incidence of the flow is raised. This behavior is shown to be the result of the time-resolved topology of the flow field, which comprises numerous saddle and focus pairs that are produced stochastically in regions of high shear strain rate. Most importantly, the separation is shown to exhibit an extremely low-frequency behavior, changing in topology over timescales that are approximately 80 times the convection time through the blade passage. The behavior is shown to be intrinsic to the separation and causes the separation, for periods, to completely disappear from the endwall. This underlying unsteady structure of the separation is shown to have implications for the ability of RANS-based design codes to be able to accurately predict corner separations.

Hot compression deformation behavior and processing maps of Al–0.5Mg–0.4Si–0.1Cu alloy

To improve the hot working stability of Al–0.5Mg–0.4Si–0.1Cu alloy, isothermal compression tests were performed at the temperature range of 350–500 °C and strain rate of 0.001–10 s−1. Strain-compensated Arrhenius constitutive equation containing Zener–Hollomon parameters was established to describe the hot deformation behavior. Its accuracy was evaluated within the whole strain range and the established constitutive equation can well predict the flow behavior. In addition, intrinsic machinability was further analyzed by constructing processing maps under different true strains based on dynamic material models. Microstructures are in fine agreement with processing maps and flow instability occurred mainly in high strain rate regions due to the presence of adiabatic shear bands and flow localization. Dynamic softening mechanism of the alloy mainly stems from dynamic recovery and partial dynamic recrystallization. Based on processing maps and microstructure observations, optimal process parameters of alloy were obtained, which are beneficial to optimize its hot working parameters.

Transport modes of inertial particles and their effects on flow structures and heat transfer in Rayleigh–Bénard convection

We investigate the flow characteristics and kinetic behaviors of particles in turbulent Rayleigh–Bénard convection particulate flows. Direct numerical simulations combined with a Lagrangian point-particle strategy were carried out in the range of Stokes numbers 2×10−4≤StL≤7.3×10−2 for Rayleigh numbers from 2×106 to 108 at the Prandtl number Pr=0.678. A two-way coupling model is employed in which the momentum exchange between the dispersed particles and the carrier fluid is taken fully into account. Based on various patterns of particle motion, we find three transport modes of inertial particles which are labeled as the circling transport (CCT) mode, the channel transport (CNT) mode, and the downpour transport (DPT) mode, respectively. These modes can switch to each other when Stokes numbers and Rayleigh numbers vary and exhibit different effects of particle motions on the flow field and heat transfer. For the CCT and DPT modes, compared with the CNT, a weakening alteration of flow structures and thermal plumes leads to no significant effect on the transport of momentum and heat. For the CNT mode, a pronounced effect of particles on enhancements of the turbulent momentum transport and heat transfer relates to the strong interaction between the particle clusters and the chaotic structures of eddies. What is more, the particles tend to homogeneously distribute for the CCT and DPT modes, although the particles exhibit different transport states. As for the CNT mode, under both preferential sweeping and centrifugal effects, particles accumulate into clusters that hover toward the region of high strain rate and the edges of eddies. We found that the averaged particle settling speeds are almost proportional to the Stokes number. The particle settling speeds are larger than the terminal velocity of Stokesian particles for the CCT and CNT modes as particles tend to settle in the downward fluid. In contrast, it becomes smaller than the terminal velocity for the DPT mode due to the drag of the upward fluid.

Investigation of the Flow Behavior of Air-Cooling Ti-6Al-4V Alloy after Superplastic Forming

The flow behavior of Ti-6Al-4V alloy during the air-cooling process after superplastic forming (SPF) has been discussed. In high-temperature constant strain rate tensile tests, the selected temperatures were 930, 900, 800, 700, and 600 °C, and the initial strain rates were 10−2, 10−3, and 10−4/s. The optimized deformation temperatures were 800~900 °C and the strain rates were 10−4~10−3/s. Then, the evolutions of activation energy and deformation strain are also discussed, and the effects of dislocation density and deformation activation energy on flow behavior were consistent. In addition, unstable flow is mainly concentrated in the low-temperature and high strain-rate regions, and this is mainly caused by dynamic recrystallization (DRX). After the SPF process, the possibility of material damage gradually increases during the air-cooling process.

Subdivision of Dynamic Recrystallization Mechanism in the Transition Zone and Microstructure Evolution of Incoloy825 Alloy

The hot deformation behavior of Incoloy825 alloy is investigated by isothermal compression test at the temperature range of 950–1150 °C with strain rates of 0.001–10 s−1. The dynamic recrystallization (DRX) mechanism in the transition zone is subdivided and clearly revealed. The results show that the instability domain is mainly located in the low temperature with high strain rate region (950–1050 °C, 1–10 s−1). The feasible domain can be divided into two parts: the first is located in the temperature range of 1000–1150 °C with a strain rate of 0.001 s−1, the second is located in strain rate of 0.01–1 s−1 at 1150 °C, and the optimum processing parameters is the temperature of 1150 °C with a strain rate of 1 s−1. A transition zone of the DRX mechanism appears during hot deformation, in which three DRX mechanisms occur, discontinuous dynamic recrystallization (DDRX) mechanism, continuous dynamic recrystallization mechanism (CDRX), and twin dynamic recrystallization (TDRX) mechanism. The formation of a DRX grain is the comprehensive effect of multiple mechanisms, which can promote and transform each other. Each mechanism contributes a different role.

Correlation of stacking fault energy with deformation mechanism in Cu–(2, 20)Zn alloys

Copper–zinc alloys with different zinc contents contain different stacking fault energies (SFE). The influence of SFE on the deformation mechanism during surface mechanical attrition treatment was studied in this work. Research results indicate that the deformation mechanism directly correlated with the SFE in Cu–Zn alloys. Deformation twinning plays a paramount role during original deformation in Cu–20Zn (19 mJ/m2). However, for Cu–2Zn alloy with low-medium SFE (38 mJ/m2), the deformation mechanism is dominated by the dislocation slipping. Microbands are the predominant microstructural features in large strain and high strain rate regions for both Cu–Zn alloys in the present study. They are likely to be formed by the splitting of the high-density dislocation walls.

The kinetics of dynamic recrystallization and construction of constitutive modeling of RAFM steel in the hot deformation process

The dynamic recrystallization (DRX) behavior of austenite in reduced activation ferritic/martensitic steel was investigated by isothermal compression tests and constitutive modelling. The flow stress decreases with deformation temperature increasing and strain rate decreasing. The constitutive equations were constructed based on the analysis by Arrhenius equations. Based on the dynamic material model, the hot processing map was constructed. In the stability region, the power dissipation efficiency (η) increases with increasing strain, and the softening is dominated by DRX when η grows to a specific value. However, η decreases as strain increases further after the complete evolution of DRX, indicating coarsening of DRXed grains. As the strain increases, the processing stability region shifts to the low temperature and high strain rate region. A novel recrystallization kinetics model was developed by considering the characteristics of the recrystallization velocity with strain increasing. It can reflect the "slow-rapid-slow" growth trend of recrystallization volume fraction (XDRX). The relationship between XDRX and D¯ (average grain size of austenite) was constructed, which indicates that D¯ decreases with strain increasing after the onset of DRX. When XDRX is greater than 50%, the decrease rate of D¯ slows down until the steady-state is reached. Although strain increase further, the grain size remains constant. This suggests that the expected D¯ can be obtained by controlling XDRX during hot deformation.

Statistical Correlation of Seismicity and Geodetic Strain Rate in the Chinese Mainland

AbstractThe correlation between seismicity and crustal deformation is investigated by introducing the earthquake catalogs from 1900 to 2019 and the Global Positioning System (GPS) strain rate during 1999–2007 in the Chinese mainland. The primary results show that (1) about 76.9% of earthquakes with M&amp;gt;6.5 since 1900 and 74.7% of events with M&amp;gt;5.5 between 1970 and 2019, occur in 30% of the region with high-strain rate; (2) the statistics of earthquakes greater than M 5.0 since 1990 show when temporally approaching to the time period of GPS observation, more earthquakes concentrated in the region with high-strain rate. In details, in a 9 yr statistics window, the ratio of cumulative seismicity that occurred in 30% of the high-strain rate regions from 2008 to 2017 is about 16.1%–20.7% lower than those in the previous two periods. Meanwhile, in a 4 yr statistics window, the ratios of cumulative seismicity that occurred in 30% of the high-strain rate regions in the periods of 2011–2015 and 2015–2019 are lower than other five periods by about 9.6%–31.2%. These periodic statistics show that high-strain rate matches well with the historical earthquakes (M≥5.0) than the future earthquake events. In general, the 9 yr GPS observations correspond well to the historical seismicity in the Chinese mainland, but the predicted effect for the future moderate earthquakes is not as good as that of the retrospective test.

An Experimental and Numerical Study of Quenching-Induced Residual Stresses Under the Effect of Dynamic Strain Aging in an IN718 Superalloy Disc

Abstract The effects of dynamic strain aging (DSA) on residual stresses generated in Ni-base superalloys during heat treatments are not well understood. In this study, the residual stress field induced by water quenching an IN718 disc while undergoing DSA is studied using coupled thermo-mechanical finite element (FE) analyses in conjunction with neutron diffraction (ND) measurements. A visco-plastic constitutive model that incorporates the effect of DSA is proposed to describe the experimentally observed negative strain rate sensitivity and abnormal temperature dependence phenomena in the stress–strain response of solid solution treated IN718. The predicted quenching residual stresses in the disc agree well with the ND measurements. Due to the DSA, a propagating high plastic strain rate region can be identified in the disc during the early stages of the quenching process. Due to the negative strain rate sensitivity and abnormal temperature dependence effects caused by DSA, the predicted residual stresses are approximately 10% greater than when those two effects are not accounted for. The effects of different convection heat transfer conditions in the FE model are examined and discussed. It is found that the convection heat transfer coefficients have a great influence both on the disc residual stresses and DSA-related plastic strain rate field predictions.

Hot deformation behavior and mechanism of a new metastable β titanium alloy Ti–6Cr–5Mo–5V–4Al in single phase region

Abstract A new metastable β titanium alloy Ti–6Cr–5Mo–5V–4Al (Ti-6554) has shown good application potential in large parts. In order to study the hot deformation behavior and mechanism of the Ti-6554 alloy in the β single phase region, hot compression tests were carried out at temperatures of 800–950 °C and strain rates of 0.001–10 s−1 on the Gleeble-3500 thermal simulation machine. Strain-compensated Arrhenius constitutive model was used to predict the flow behavior of the alloy, and the correlation coefficient between the experimental and predicted values reached 0.982. Based on the hot processing map, it was found that the instability region was mainly concentrated in the high strain rate area, and the peak efficiency of power dissipation (η) region occurs in the temperature range of 913–928 °C and the strain rate of 0.001–0.0025 s-1. There was an obvious DRX phenomenon in the stability region, while the instability region was dominated by deformation band (DB) and flow localization (FL). The continuous dynamic recrystallization (CDRX) by progressive rotation of subgrains and discontinuous dynamic recrystallization (DDRX) by grain boundaries bulging could be observed. DDRX mainly occurred in high temperature and low strain rate regions, while the CDRX process occurred in the high strain rate region. As the η decreased, the deformation mechanism changed from DDRX to CDRX and further to dynamic recovery (DRV), DB, FL.

Molecular dynamics study of coupled layer thickness and strain rate effect on tensile behaviors of Ti/Ni multilayered nanowires* *Project supported by the National Natural Science Foundation of China (Grant No. 11572259), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2019JQ-827), and the Scientific Research Program Funded by Shaanxi Provincial Education Department, China (Grant No. 19JK0672).

Novel properties and applications of multilayered nanowires (MNWs) urge researchers to understand their mechanical behaviors comprehensively. Using the molecular dynamic simulation, tensile behaviors of Ti/Ni MNWs are investigated under a series of layer thickness values (1.31, 2.34, and 7.17 nm) and strain rates (). The results demonstrate that deformation mechanisms of isopachous Ti/Ni MNWs are determined by the layer thickness and strain rate. Four distinct strain rate regions in the tensile process can be discovered, which are small, intermediate, critical, and large strain rate regions. As the strain rate increases, the initial plastic behaviors transform from interface shear (the shortest sample) and grain reorientation (the longest sample) in small strain rate region to amorphization of crystalline structures (all samples) in large strain rate region. Microstructure evolutions reveal that the disparate tensile behaviors are ascribed to the atomic fractions of different structures in small strain rate region, and only related to collapse of crystalline atoms in high strain rate region. A layer thickness-strain rate-dependent mechanism diagram is given to illustrate the couple effect on the plastic deformation mechanisms of the isopachous nanowires. The results also indicate that the modulation ratio significantly affects the tensile properties of unequal Ti/Ni MNWs, but barely affect the plastic deformation mechanisms of the materials. The observations from this work will promote theoretical researches and practical applications of Ti/Ni MNWs.

Examination of Dynamic Strain Ageing Effects during Rapid Quenching of Inconel 718 Superalloy Disc

In this work, an experimental measurement, contour method, is implemented for an after quenching IN718 forging specimen to obtain the distribution of residual stress field. A sequentially coupled thermal mechanical finite element model is developed with the similar 3D geometry of the experimental specimen and implemented the same heat transfer boundary of the rapid quenching with the experimental condition. A thermal mechanical rate dependent continuum plasticity model for IN718 alloy, with the dynamic strain ageing (DSA) effect incorporated, is developed to study the impact of DAS effect on the evolution of residual stress during rapid quenching. The modelling predictions of residual stress are in good agreement with the contour method measurements. The impact of DSA effect is further quantified, indicating that an annular high plastic strain rate region in the core part of the disc is captured during the simulation of the quenching process.