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To suppress the edge crack of the magnesium alloy sheet during the ordinary rolling process, a new rolling process named width-limited rolling was proposed in this paper. Width-limited rolling is a rolling method in which the width of the alloy sheet is limited by modifying the shape of the rollers, allowing a compressive stress field to form at the edge portion of the alloy sheet during rolling, resulting in the reduction of edge cracks. At present work, magnesium alloy sheets were separately subjected to ordinary rolling and width-limited rolling. The microstructure evolution and mechanical properties of the rolled sheets were investigated by EBSD, TEM, and XRD. The results exhibited that under the same rolling conditions, the sheet after ordinary rolling exhibited obvious edge cracks while no crack was found at the edge of the sheet after width-limited rolling. The edge crack suppressing effect was attributed to the reduction of the tensile stress along rolling direction during WLR, promoting the synchronous extension of the edge and center regions to suppress edge crack tendency. Microstructure observation showed that the compressive twins formed in the sheet after ordinary rolling usually exhibited as thin plates and cannot continue to fully develop due to the premature generation of the edge cracks. However, the compressive twins developed maturely in some of which double twins formed and various slip systems with different dislocation Burgers vectors occurred in the rolled sheet after WLR. More twin intersections and shear bands, providing more potential recrystallization nucleation sites, which are beneficial to weaken basal texture. With the cooperation of twinning and dislocation slip, the texture of the sheet after the width-limited rolling is weakened and the mechanical properties are improved. [ABSTRACT FROM AUTHOR]

Thermal deformation behavior of a Ni-Cr-Fe superalloy billet were investigated by hot compression experiments under temperatures of 900–1200 °C and strain rates of 0.001–1 s−1, and the corrosion properties of the superalloy after thermal deformation were also evaluated by electrochemical tests. Compression experiments determined that lower strain rates and higher temperatures reduce the superalloy's stress levels. The Arrhenius-type model accurately described the thermal deformation behavior of the superalloy. Furthermore, the optimal hot working domain was identified between 1120 and 1170 °C and strain rates of 0.001–0.01 s−1. Microstructure observations showed that the dynamic recrystallization (DRX), characterized by grain boundary bending nucleation and consumption of numerous dislocations is the main mechanism leading to grain refinement during thermal deformation. The results of the electrochemical corrosion tests proved that the corrosion predominantly occurred near the grain boundaries (GBs) of deformed grains, worsening with increased deformation temperatures. • Thermal deformation of a Ni-Cr-Fe superalloy over a wide range of temperatures and strain rates. • The Arrhenius-type model and hot processing maps were established. • The microstructure and DRX mechanisms depend on compression process parameters. • The difference in corrosion resistance was closely associated with the evolution of microstructure. [ABSTRACT FROM AUTHOR]

FeCrAl alloys have the opportunity to replace current Zr-based cladding materials in light water reactors, and dynamic recrystallization (DRX) plays an important role on microstructural controlling of FeCrAl alloys during hot or warm deformation, such as forging, hot rolling, extrusion. In this research, dynamic recrystallization mechanism of FeCrAl alloy has been systematically investigated by microstructure characterization after isothermal compression. Results show that deformation strain rate and temperature could significantly influence microstructure and DRX mechanism of FeCrAl alloy. When deformed at 0.1s−1, prior grains become long strip with serrated boundaries and are refined by geometric dynamic recrystallization (GDRX). Prior grains are not separated by high angle grain boundaries (HAGB) even deformed at 1200 °C, because strain is too small to impingement of HAGB. Whereas, when deformed at 10s−1 strain rate, there are lots of sub-boundaries with about 2° misorientation within grains, and several strain-free grains are found located at boundaries when deformed at 900 °C or 1000 °C, while the prior grains are divided by HAGB and equiaxed grains are formed at 1100 °C. It was found that mechanism of DRX changes from discontinuous dynamic recrystallization (DDRX) to continuous dynamic recrystallization (CDRX) with increasing temperature from 900 °C to 1100 °C. The phenomenon results from the dislocation movement behaviors changes with increasing temperature. This research will provide meaningful guidance for industrial application of FeCrAl alloys. [ABSTRACT FROM AUTHOR]

• The effect of deposition time on the structural properties NiO thin films. • Calculating taille the crystallite and strain based on x-rays using several methods. • Comparison of experimental results with theoretical results based on DFT calculations. • Calculation of elastic constants and mechanical properties based on DFT. A comparison between the experimental investigation and theoretical calculations is the goal of this research. This research is divided into two sections. The first one deals with a structural analysis, using X-rays, of thin layers of nickel oxide obtained through a simple chemical process. Utilizing DFT computations, the second section examines the elastic and structural properties. In the experimental part, we prepared thin layers of nickel oxide using the chemical spray pyrolysis (CSP) method for a solution of nickel chloride dehydrate (NiCl 2.6H 2 O) dissolved in distilled water on glass substrates heated to a temperature of 400C°. The concentration of the solution used is 0.1 mol/L. We changed the deposition time as follows: 5 min, 10 min, 15 min and 20 min. After preparing the nickel oxide layers, we conducted an analytical study of the various crystalline and lattice properties using X-ray diffraction. The analytical study using X-rays confirmed all the films (NiO) were crystallized in the cubic structure; the lattice parameter a is estimated to be 4.17 Å. The film is oriented along the (1 1 1) and (2 0 0) plane. Theoretical calculations confirmed the crystalline properties of NiO compound. The obtained values ​​of elastic constants proved that the studied material is mechanically stable. The value of the B/G ratio is 3.99, the material studied presents ductile behavior. The value of anisotropy coefficient A obtained at 0 GPa for our material is different to 1, thus indicating that it is elastically anisotropic. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of Mg-Ga-Sn alloys at 360–450 °C and 0.001–1 s−1 was systematically studied by using a thermal simulator. The flow stress is affected by temperature and strain rate, which basically accords with hyperbolic sine constitutive equations. Based on the experimental data, the prediction accuracy of the stress correction model and the artificial neural network (ANN) model was comprehensively compared for the alloy system. The ANN model has good prediction accuracy and a certain degree of extrapolation and generalization ability. By observing the microstructures, the hot processing maps of the ANN modified model were ultimately determined to be closer to the real situation, and the hot processing maps were partially expanded (450–480 °C, 1-2 s−1). Based on the hot processing maps, the suitable processing range (360–450 °C, 0.001–0.01 s−1; 390–420 °C, 0.4–1 s−1) was determined, and a possible processing range (450–480 °C, 0.001–2 s−1; 390–450 °C, 1-2 s−1) was predicted. The EBSD results revealed two typical dynamic recrystallization mechanisms (CDRX and DDRX) in the alloy, corresponding to a strong <0001>//CD texture. In the region of higher temperature and lower strain rate, an obvious bimodal texture is found in the alloy, which is related to the promotion of nonbasal slip by Ga. [Display omitted] • The ANN model exhibits higher prediction accuracy than the stress correction model. • The processing map modified by ANN more closely reflects to the actual situation. • The formation of LAGBs is promoted at high strain rates. • The bimodal texture is related to the addition of Ga. [ABSTRACT FROM AUTHOR]

Hot deformation plays a crucial role in strengthening and toughening of aluminum matrix composites, but the high hot deformation resistance and the microstructure defects generated after deformation need to be solved urgently. In this paper, a new material, B 4 C@B 2 O 3 /Al composites, with the low melting point B 2 O 3 phase at the interface, has been successfully prepared and the hot deformation behavior was studied in detail. By comparison, the hot deformation resistance and activation energy of the B 4 C@B 2 O 3 /Al composites is significantly lower than that of the B 4 C/Al composites. The softening mechanism of the B 4 C@B 2 O 3 /Al composites is mainly dynamic recrystallization (DRX) and the critical stress of DRX is much lower for the B 4 C@B 2 O 3 /Al composites than for the B 4 C/Al composites, while the volume fraction of DRX is higher than for the B 4 C/Al composites. Compared with the B 4 C/Al composites with similar particle content, the hot deformation temperature of the B 4 C@B 2 O 3 /Al composites decreases, but with high strength-plasticity compatibility (with tensile strength of 560 MPa and elongation of 4.2 %). This work provides an effective method to reduce the hot deformation resistance of the B 4 C/Al composites and explains the micro mechanism, guiding low-stress forming of the B 4 C/Al composites with high volume fraction and good mechanical properties. [ABSTRACT FROM AUTHOR]

Al-Cu-Li alloys exhibit enhanced performance when possessing a high substructure proportion and a low recrystallization proportion. To achieve this, it necessitates a thorough understanding of recrystallization behavior during its hot working and heat treatment. To this end, isothermal compression tests were conducted on an Al-Cu-Li alloy in the temperature range of 350–500 °C and strain rate range of 0.01–10 s−1. The deformed specimens underwent solution treatment at 530 °C/2 h followed by water quenching, and aging treatment at 155 °C/27 h. The microstructures of the deformed and heat-treated specimens were characterized using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). During hot deformation, continuous dynamic recrystallization (CDRX) dominates when the natural logarithm of the Zener-Hollomon parameter (lnZ) >26 and discontinuous dynamic recrystallization (DDRX) predominates when lnZ ≤ 26. A low proportion kinetic model associated with lnZ was constructed to describe the DRX behavior, and the model parameters were optimized using genetic algorithm (GA) to improve accuracy. During heat treatment, substantial static recrystallization (SRX) occurs following deformation at lnZ > 30, while it is limited when lnZ < 27. The comparison of average geometrically necessary dislocations (GNDs) before and after heat treatment reveals that the consumption of dislocations increases with increasing lnZ. Statistical analysis indicates that the density of low/medium angle grain boundaries (L/MAGBs) can be increased and the recrystallization fraction can be decreased within the lnZ range of 24 to 27. Therefore, these specific hot deformation conditions are recommended as the optimal hot working window for the Al-Cu-Li alloy. • The effect of secondary phases on the DRX behavior of the Al-Cu-Li alloy was analyzed. • A GA-optimized low proportion kinetic model for DRX of the Al-Cu-Li alloy was constructed. • The effect of hot deformation on SRX behavior during heat treatment was revealed. • A specific lnZ range that resulted in high substructure volume fraction and low recrystallization volume fraction was determined. [ABSTRACT FROM AUTHOR]

• Nano-sized W particle dynamically precipitate during deformation. • Nano-sized W particle promote DRX nucleation by PSN mechanism. • Nano-sized W particle inhibit DRX growth by pinning grain boundary migration. • Ductile-brittle fracture mechanism is dominant in non-DRX region. • Hole-joining fracture mechanism is dominant in DRX region. Understanding the relationship between nano-sized precipitates and dynamic recrystallization (DRX) during thermo-mechanical processing is vital for developing high-performance Mg-based alloys. This work uses experiment and phase field model to investigate the dynamic precipitation of W particles and DRX grains in the hot-extruded Mg 98.5 Y 1 Zn 0.5 alloys at 360, 380 and 400 °C and clarifies the fracture mechanisms in detail. The results reveal that under all temperatures, the hot-extruded Mg 98.5 Y 1 Zn 0.5 alloys are composed of block 18R long-period stacking order (LPSO) phase, lamellar 14H-LPSO phase, W particles and a typical bimodal structure containing fine DRX grains and coarse non-DRX grains. Noted that the W particles not only promote the DRX nucleation by hindering dislocation motion to increase elastic energy, but also inhibit the growth of DRX grains by pinning grain boundaries during deformation. In addition, the strength decreases while the plasticity increases with increasing temperature for the hot-extruded Mg 98.5 Y 1 Zn 0.5 alloys, but an excellent strength-plasticity balance is achieved at 400 °C. More importantly, analyzing the crack extension in non-DRX, DRX and non-DRX/DRX coexistence regions shows that a ductile-brittle fracture mechanism dominates in the non-DRX regions due to the difficulty of basal slip and low fracture toughness. But a hole-joining fracture mechanism dominates in the DRX regions. The fracture mechanism in the non-DRX/DRX coexistence region is mainly determined by the DRX volume fraction. These results can provide insights and valuable references for developing high-performance Mg-based alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

The effects of twinning on the dynamic recrystallization (DRX) of the Mg-6.58Gd-5.7Y-0.55Zr alloy were investigated through uniaxial compression tests at 400 °C and 450 °C with an initial strain rate of 0.001–0.1 s−1 and were characterized through optical microscopy (OM), scanning electron microscopy (SEM), electron back-scattering diffraction (EBSD) and transmission electron microscopy (TEM). At a relatively high strain rate, extension twins can mainly be activated during the initial stage of hot compression, and the subsequent DRX is closely related to the twin-twin and twin-dislocation interactions. The intersected twin boundaries of the extension twins from multiple twin variants may provide effective DRX sites and promote microstructure refinement. However, extension twins from a single twin variant pair may quickly grow, soon swallowing the matrix and decreasing the DRX efficiency. • DRX is closely related to the twin-twin and twin-dislocation interaction. • Non-basal slip dislocations may contribute much to DRX in the twinned grains. • Interaction between extension twin and non-basal slip promote DRX in twinned grain. • Quick growth extension twins leave a little probability of interaction with dislocations. [ABSTRACT FROM AUTHOR]

A lean Mg–Zn–Al alloy has been developed through melting-casting and subsequently thermomechanically processed within the temperature range of 523 K–723 K, by employing a novel 'hard plate hot forging' method. The elevated temperature deformation not only instigates dynamic recrystallization (DRX) and dissolution of second phase particles, but also transforms the solidification texture into basal fiber texture in the forged alloy. The DRX fraction increases as the forging temperature is raised from 523 K to 623 K, which increases the fraction of fine grains and weakens the strong basal fiber of the deformed alloy. However, further raising the forging temperature to 723 K promotes growth of the recrystallized grains along with nucleation of new ones, which eventually increases the average DRX grain size and re-strengthens the basal fibers. The specimen forged at 523 K exhibits considerably high strength (∼306 MPa) due to the larger size and higher area fraction of nano-sized τ-Mg 32 (Al,Zn) 49 particles that contribute to stage IV hardening through Orowan mechanism. Conversely, the weakened basal texture resulting from a high DRX fraction lead to an improved ductility (∼10.7%) in the specimen forged at 623 K. Image 1 • Hard plate hot forging method improves mechanical properties of Mg–Zn–Al alloy. • Finer deformed grains and lower DRX fraction improve YS in 523K-forged specimen. • Work hardening is dictated by distribution of nano-sized Mg 32 (Al,Zn) 49 particles. • Weaker basal fiber and bimodal grain size improve ductility in 623K-forged specimen. • Forging at 723K reduces ductility due to re-strengthening of basal fiber. [ABSTRACT FROM AUTHOR]

Deformation behavior of a new kind of high-strength low-alloy steel was investigated by isothermal compression tests at temperatures of 800–1200 °C and strain rates of 0.01–10 s−1. The flow behavior of the steel was characterized through the analysis of true stress-strain curves. A relevant constitutive equation was established, and proved to be suitable by comparing experimental and calculated data under various deformation conditions. Processing maps based on the dynamic material model were constructed with strains of 0.3, 0.5 and 0.7. The maps showed that the optimal hot-working temperature range of the new steel was 1050–1200 °C, while the optimal strain rate range was 0.018–0.562 s−1, which was consistent with the microstructure of the deformed specimens. Dislocations and substructures under different deformation conditions were observed and analyzed by TEM. The results indicated that there were two kinds of DRX nucleation mechanisms during hot deformation. • The flow behavior of HSLA steel was studied. • The constitutive equation of the peak stress for HSLA steel was established. • The processing maps of HSLA steel at different strains were constructed. • Two DRX mechanisms were observed in this studied steel. [ABSTRACT FROM AUTHOR]

Abstract In this work, we are interested in the new compounds Li 1.5 Rb 0.5 MoO 4 preparation by the solid state method. Also, we present a comparative study with LiRbMoO 4 and Li 2 MoO 4. The X-ray powder diffraction indicates that these compounds crystallize at room temperature in the monoclinic, orthorhombic and trigonal systems with the P2 1 , Pcab and R-3 space groups, respectively. The shapes of the grains for these ceramics were observed by means of scanning electron microscopy (SEM) images. The Tauc model was used to determine the optical gap energy (4, 4.3 and 3.9 ev) and the urbach energies (1.51, 0.35 and 1.14 ev) of our compounds. The electric and dielectric proprieties of Li 1.5 Rb 0.5 MoO 4 have been studied. We carried out complex impedance spectroscopy in the frequency range 200 Hz-5 MHz at different temperatures (575–723 K). The complex impedance diagram showed a single semicircle, implying that the response originates corresponding to the grains. As a result, an electrical equivalent circuit has been proposed. The spectra follow the Arrhenius law with two energies of activation 1.58 eV for impedance measurements and 1.25 eV for that of modulus. The alternative current (AC) electrical conduction of the three compounds is governed by the overlapping large polaron tunneling (OLPT). Highlights • The three compounds Li 2x Rb x MoO 4 (x = 0,0.5,1) are of the same order of gap energy 4 eV. • The three compounds are characterized by the same mechanism of conduction (OLPT). • The Conductivity in these materials depends on radius plolaron r 0. [ABSTRACT FROM AUTHOR]

Abstract AZ31 Mg alloy plates were pre-compressed at room temperature along the transverse direction (TD) to introduce { 10 1 ¯ 2 } extension twinning. Mechanical properties, microstructure evolution and dynamic recrystallization (DRX) mechanisms of twinned samples containing pre-existing twins during uniaxial compression were investigated and compared to those of as-received samples. The results indicated that compared to that of as-received sample compressed along the rolling direction (RD), the yield stress of twinned sample was dramatically increased at from room temperature to 200 °C. In contrast, when compressing along the normal direction (ND), the yield stress of twinned sample was greatly decreased at from room temperature to 200 °C. With the further increase of temperature, the as-received and twinned samples exhibited similar compression flow curves and obvious DRX had taken place. Continuous dynamic recrystallization (CDRX) was the main DRX mechanism in the as-received sample compressed along ND at 200 °C. Twin assisted DRX besides CDRX was also initiated in the as-received sample compressed along RD and in the twinned sample compressed along ND or RD at 200 °C. DRX mechanism was changed to discontinuous dynamic recrystallization (DDRX) in the as-received and twinned samples with the further increase of temperature. [ABSTRACT FROM AUTHOR]

Abstract In the present work the commonly stated but not explicitly demonstrated association between the chemical composition of a material, its stacking fault energy (SFE) and dynamic recrystallization (DRX) behaviour, is established using thermo-mechanical testing, microstructural characterization and thermodynamic calculations on a Fe-Cr-Ni-Mo model alloy with varying interstitial content (0.1 < (N + C) < 0.25 wt%). The thermodynamic calculation shows that SFE decreases from 27 mJ/m2 to 17 mJ/m2 with increase in interstitial content at room temperature. The values of SFE rise upto 205 mJ/m2 to 200 mJ/m2 at 1323 K. The alloy with minimum interstitial content and maximum SFE exhibits a sluggish DRX behaviour in the strain rate domain 0.1–1 s−1. The sluggishness gradually diminishes as the interstitial content is increased and SFE is decreased. The rate-dependency of nucleation is explained on the basis of interstitial content, which changes the SFE. The present investigation also elucidates the rate- dependent grain growth for the model alloy. [ABSTRACT FROM AUTHOR]

Flaring forming has been widely utilized in connecting tubes, fluid pipe circuit components and flight fairings. Surface quality of the flared inner wall significantly affects the connection properties and service reliability. However, the surface microstructure, hardness and roughness of flared thin-walled tubes have long lacked corresponding characterization and correlation analysis. In the present study, wear mechanism of a 5052 Al alloy flared tube is analyzed based on multi-scale characterization. Furthermore, the impact of flaring process parameters including spindle speed, feed rate and holding time on the surface roughness is investigated by considering the evolution of microstructure and microhardness. The results reveal that adhesive wear is the main wear mechanism in the flared tube, accompanied by a small amount of abrasive wear. The effect of process parameters on dynamic recrystallization (DRX) and grain orientation are also analyzed in detail. Based on ANOVA analysis, the spindle speed is found as the most crucial controllable parameter affecting the surface roughness. The feed rate is the second important parameter, while the holding time is found to be insignificant. Simulation and experimental results indicate that with the increase of strain, surface roughness first increases and then decreases. This non-monotonic trend is associated with the evolution of strain (strain rate, strain path, etc.) and microstructure (DRX, texture, hardening, etc.). ● The surface wear mechanism of a thin-walled tube during flaring process is studied in multi-scale. ● The effects of DRX, hardening and soft-hard orientation on the surface roughness during flaring are analyzed in detail. ● The influence of flaring process parameters on surface roughness is quantitatively analyzed. ● A non-monotonic evolution of surface roughness during flaring process is obtained. [ABSTRACT FROM AUTHOR]

Abstract A new near-β titanium alloy, Ti-5Al-5Mo-5V-3Cr-1Zr (Ti55531), has been widely used in industry due to its relatively wide processing window, high hardenability and strength. This study investigated the deformation and microstructural evolution of the Ti55531 alloy in the β single phase region. Hot compression tests were carried out at temperatures of 860–900 °C and strain rates of 0.001–10 s−1 on a Gleeble-3800D simulator. The metallographic and electron backscatter diffraction (EBSD) techniques were used to analyze the microstructural evolution. The results demonstrate that the stress curves exhibit discontinuous yield and flow softening phenomena, which are very sensitive to temperature and strain. A processing map was developed for this alloy, which shows that the instability increases with the strain. Dynamic recrystallization (DRX) is a typical characteristic in the beta region, which can take place at high temperatures and low strain rates. Based on this analysis, a physically-based deformation constitutive equation and DRX kinetics, critical condition and grain size models were developed. These models were implemented in a DEFORM subroutine to predict the deformation and microstructural evolution of the Ti55531 workpiece during nonisothermal forging. The comparison between the experimental and predicted results shows good agreement, which indicates that the model is reliable and that the subroutine provides an effective tool to predict the deformation and microstructures for industrial production. Highlights • The hot deformation behavior and microstructural evolution of a near beta titanium alloy Ti55531 was investigated by experiments and numerical modeling. • The discontinuous yielding, flow softening and DRX are typical characteristics for the Ti55531 alloy in beta region. • A physically-based constitutive model was proposed to model the hot deformation and microstructural evolution of the Ti55531 alloy. • The constitutive model is efficient to predict the flow stress, DRX grain size and volume fraction of a Ti55531 workpiece during forging. [ABSTRACT FROM AUTHOR]

The objective of the study is to understand the dynamic flow behavior of Ti–22Al–25Nb alloy at high temperatures using a modified Zerilli–Armstrong (Z-A) model. To investigate the dynamic mechanical behavior of titanium alloy, the material was subjected to quasi static and dynamic compression testing. It is found out that the modified Z-A models possess better predictability in evaluating the flow behavior of the Ti–22Al–25Nb alloy at elevated strain rates and temperatures. The model well established the quasi-static and dynamic behavior of the titanium alloy, mainly the effects of strain hardening and thermal softening. The regimes of high strain rate deformation behavior represented by dynamic recrystallization (DRX), lamellar globularization and the instability flow have been discussed. Using transmission electron microscopy (TEM) studies, it is found that the dislocation density is directly associated with strain rate. [ABSTRACT FROM AUTHOR]

We investigated the magnetic, morphological, and structural properties of FeCuNi. The powder alloy is elaborated by mechanical alloying process for 10 h with varying the Cu content. The aims of this work are to study the effect of Ni/Cu ratio on the magnetic and microstructure properties. The crystallite size decreases with the increase of Ni. The reduction of crystallite size proceeds slowly until 17 nm for 30% of Ni. Coercivity and saturation magnetization increases from 105.4 Oe, 122.568 emu/g to 156.77 Oe, 140.679 emu/g respectively caused by the increase of the concentration of Cu and dislocation density as well as the decrease of the crystallite size. [ABSTRACT FROM AUTHOR]

Mg-10Zn-6Y-0.5Zr (wt%) alloy and Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy with medium RE content have been fabricated by conventional casting and indirect extrusion. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy shows a bimodal microstructure containing dynamic recrystallized (DRXed) grains with average grain size of 2 μm and deformed regions. In addition to the fragmented W phase particle bands distributing along the extrusion direction, large amount of nano W phase and small amount of nano β 2 ′ phase are precipitated in the matrix. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy exhibits completely dynamic recrystallized microstructure with average grain size of 3 μm. The broken W phase particles are distributed homogeneously in the matrix. Icosahedral quasicrystal phase layer is observed at the surface of some W phase particles in the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. The as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy exhibits yield strength of 341 MPa, ultimate tensile strength of 368 MPa and elongation to failure of 6.8%. While the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr (wt%) alloy shows lower yield strength of 247 MPa, ultimate tensile strength of 330 MPa and higher elongation to failure of 19.8%. The higher strength in the as-extruded Mg-10Zn-6Y-0.5Zr (wt%) alloy is mainly attributed to higher area fraction of unDRXed regions with strong texture and the precipitation of nano W and β 2 ′ phase. The fully recrystallized microstructure with weak texture and the formation of icosahedral quasicrystal phases with good coherent bond with α-Mg contribute to the good ductility of the as-extruded Mg-10Zn-3Y-3Gd-0.5Zr alloy. [ABSTRACT FROM AUTHOR]

The emerging and exponential growth of telecommunication networks have developed a variety of smart and powerful devices to handle a wide range of multimedia applications such as Voice over IP (VoIP), video streaming, etc . 3GPP introduced Long Term Evolution (LTE) in release 8 and LTE-Advanced (A) in release 10 to support multimedia traffic as these technologies offers high data rate, high bandwidth, and low latency. It also created new challenges to handle resource allocation and power optimization of User Equipment (UE). The paper explores radio resource allocation and power consumption problem of UE in LTE environment. An intelligent scheduling scheme developed is based on Cooperative Game Theory (CGT) method and AHP-TOPSIS method. It distributes resources in a fair way among a number of applications and UE are prioritized based on certain criteria like delay, throughput history, UE buffer space and channel conditions and preferences. In LTE, Discontinuous Reception (DRX) has been adopted to conserve the battery life of UE. DRX periodically switches off the radio interfaces to conserve the battery life but it may breach Quality of Service (QoS). Therefore, the DRX parameters need to be further optimized to satisfy QoS and minimize power consumption of UE. DRX parameters are dynamically adjusted on the basis of current load and channel condition of the network. Power saving operations are numerically analyzed. Simulation results show that the expert and an intelligent system can distribute resources in a fair way among UE, improves the battery consumption of UE up to 85% and packets transmission delay by 10% as compared to existing scheme for real-time applications. [ABSTRACT FROM AUTHOR]

In this paper, the role of trace Ag in the dynamic recrystallization (DRX) behaviors and mechanical properties of Mg-7.5Gd-1.5Y-0.4Zr (wt.%) alloy are illustrated, aided by hot deformation with advanced characterization techniques. Results show that dynamic precipitates cannot occur at temperatures of 420 °C and 470 °C. Adding 0.5 wt% Ag causes sluggish DRX in Mg-Gd-Y-Zr alloys, and grain boundaries are more stable due to Gd and Ag co-segregation, which improves the flow stress during hot compression. To better illustrate the relationship between Ag micro-alloying and mechanical properties, based on the hot compression test, Mg-Gd-Y-Zr extrusion bars with and without Ag are fabricated at 470 °C and at an extrusion ratio of 9. The Mg-7.5Gd-1.5Y-0.4Zr-0.5Ag (wt.%) extrusion bar exhibits excellent strength in the synergistic strengthening effects of the strong texture, high density dislocation, and segregation of Gd and Ag at grain boundaries. Therefore, this work lays the foundation for the subsequent fabrication of large-scale components in Ag-free and Ag-containing Mg-Gd-based alloys. • No dynamic precipitates occur at temperatures of 420 °C and 470 °C. • The Ag addition improves the flow stress and restricts DRX during hot compression. • The extrusion bar containing Ag shows excellent strength. [ABSTRACT FROM AUTHOR]

Résumé Des marbres prélevés dans les carrières de Sidi-Lamine et Tiskram dans la région de Khénifra, d’Oued Yquem dans la région de Skhirate à Rabat et dans les carrières Rossini et Sahara dans la région de Tiflet ont été caractérisés par diffraction des rayons X, spectroscopie Raman, et spectrométrie de résonance paramagnétique électronique (RPE). La calcite a été identifiée dans tous les échantillons comme phase cristalline principale avec de faibles taux de dolomite et de quartz. Les caractéristiques des spectres de RPE des ions Mn 2+ et Fe 3+ (impuretés) et des défauts ponctuels (induits par l’irradiation des éléments radioactifs naturels) dépendent de la carrière de prélèvement et sont susceptibles d’utilisation comme indicateurs de provenances dans les études archéométriques. Marbles sampled from the quarries of Sidi-Lamine and Tiskram in the region of Khenifra, Oued Yquem in the region of Skhirate/Rabat and from the quarries of Rossini and Sahara in the region of Tiflet have been characterized by mean of X-ray diffraction (XRD), Raman scattering and EPR spectrometry techniques. In all samples, calcite has been identified as the main crystal phase with low levels of dolomite and quartz. The characteristics of Mn 2+ and Fe 3+ ions (impurities), and those of punctual defects (induced by natural radioelements irradiation) depend on the sampling quarry; they are likely to be used as provenance indicators in archaeometric studies. [ABSTRACT FROM AUTHOR]

A novel method referred as electric-associated corrugated wide limit alignment (E-CWLA) was proposed to address the contradiction between strength and plasticity of hot-rolled Mg sheets. The counterpart without electricity was known as CWLA. A huge number of tensile twins (TTs) was induced in CWLAed sample R300, and dynamic recrystallization (DRX) occurs. Strong transverse direction (TD)-titled texture accounts for the huge difference in yielding strength between different loading directions, which are closely related to Schmid factors of prismatic and pyramidal slips, resulting in different ultimate tensile strength (UTS) and ductility of R300 along different directions. E-CWLAed sample E300 presents good in-plane mechanical isotropy with the maximum UTS of 272.1 MPa, yielding strength of 213.6 MPa and elongation of 22.7%, increasing by 32%, 53% and 83% compared with the as-received sheets, respectively. Regardless loading direction, basal and non-basal slips possess similar SFs and greatly facilitates uniform plastic deformation and mechanical isotropy of E300. The special microstructure including lots of fine grains, some large grains and TTs results in a bimodal basal texture with very weak TD-titled component promotes its good deformation compatibility. Electricity contributes little to TTs formation of E300, and its thermal effect promoting dislocation mobility and DRX and the athermal effect increasing DRX nucleation rate are responsible for final grain size distribution. [ABSTRACT FROM AUTHOR]

The deformation behavior and grain size models of hot extruded (HEXed) FGH4096 superalloy at the temperature of 1040–1130 ℃ and the strain rate of 0.001–1 s−1 were investigated by hot compression. On the basis of the corrected flow stress curves, the constitutive equation considering the strain variable and hot working maps were established. The dynamic recrystallization (DRX) behaviors and microstructure evolution in different regions in hot working map superimposing the hot working instability maps were also analyzed. Discontinuous dynamic recrystallization (DDRX) occurs simultaneously with continuous dynamic recrystallization (CDRX) in the HEXed FGH4096 superalloy at low temperature, while only DDRX is activated at high deformation temperature. The wedge cracks, voids, and intergranular cracks are the main causes of flow instability. An optimal hot working window of deformation temperature = 1102–1130 ℃ and strain rate = 10−1.26–10−0 s−1 was obtained by combining the hot working maps and microstructure evolution. An established new grain size model by extending the Z parameter can predict the average grain size more accurately. • Constitutive equation and hot working maps are gained by friction-temperature corrected stresses. • An optimal working window is gained by combining hot working maps and microstructure. • Different DRX mechanisms dominate in different hot working regions. • A new grain size model is established by extending the Z parameter. [ABSTRACT FROM AUTHOR]

Mg–6.0 Zn–2.0 Yb–0.5 Zr (wt%) alloy exhibits excellent strength and ductility synergy after thermomechanical and heat treatment. Unfortunately, the hot workability and microstructure evolution under specific deformation regimes remain uncertain to date. In this work, the constitutive model and hot processing maps were established based on a series of isothermal compression tests. A detailed examination of deformation microstructures at different processing regimes revealed that the hot workability and correlated microstructure development were deformation condition dependent. When compressed at lower strain rates and higher deformation temperatures, the softening was promoted by dynamic recrystallization (DRX) and the prevalence of discontinuous dynamic recrystallization (DDRX) generally resulted in a complete DRX process with coarse grains and much-intensified texture. On the contrary, work hardening was improved with increasing dislocation density, and the continuous DRX (CDRX) may control the partial DRX progress, often presenting a much-refined microstructure with a more dispersed texture. Interestingly, a low strain rate of 0.001 s−1 and a moderate deformation temperature of 300 °C effectively balanced the nucleation rate and grain growth to finally achieve a much refined and relatively homogeneous grain structure. Further investigation concerning the activation energy suggested that the workability improved with increasing strain rate and temperature. Enhanced hot workability at most deformation regimes was achieved due to a lower average activation energy Q value in comparison with that of 1.0 wt% Yb alloyed ZK60 counterpart, which was likely due to a higher activity of non-basal slips achieved in this alloy. [Display omitted] • Constitutive model and hot processing maps are established for the ZYbK620 alloy. • Optimum hot processing window and unstable region are predicted and confirmed. • Orientation features are used to identify the dominant DRX nucleation in stable regions. • Operative deformation mechanisms at different deformation regimes are determined. • Mechanism underlying activation energy Q varies with Yb addition was clarified. [ABSTRACT FROM AUTHOR]

Aluminum and titanium alloy joints were fabricated by ultrasonic welding (USW). The interface microstructure and mechanical properties of the Al/Ti joint were investigated. A relatively sufficient metallurgical bonding was achieved at the welding time of 0.3 s, after which the fracture pattern of the joint transformed from interfacial failure to nugget pull-out failure, and the shear load reached a stable level, with a maximum lap shear load of 3650 N. Electron backscatter diffraction (EBSD) was performed to analyze crystallographic characteristics in the faying interface. It revealed that dynamic recrystallization (DRX) mainly occurred at the interface of the Al side owing to severe plastic deformation and heat generation. • A mechanical interlocking structure appeared at the welding time of 0.4 s. • No IMCs were detected. • A maximum lap shear load of 3650 N reached. • Dynamic recrystallization mainly occurred at the interface of the Al side. [ABSTRACT FROM AUTHOR]

Surface integrity determines, among other factors such as tool material and wear, the chemical composition and microstructure of the workpiece material as well as selected cutting parameters, the performance of machined parts. The aggressive nature of the cutting process influences the surface integrity and causes altered microstructure on the workpiece surface. Most popular example is the White Layer formation, which reduces the fatigue resistance of components. To study the influence of cutting parameters on White Layer thickness for a steel of grade AISI 4140, in this paper, a physics-based dislocation density-based model is implemented to predict the White Layer formation under the assumption of dynamic recrystallization. As a material model, a modified coupled damage mechanics model based on Johnson–Cook is implemented, which considers in comparison to the original one, damage induced softening using damage initiation and fracture indicators as well as strengthening mechanisms through grain refinement and dislocation damping at high strain rates. Dry orthogonal cutting is modeled via Coupled-Eulerian–Lagrangian method in Abaqus/Explicit. The developed model is validated based on experimental data regarding grain size and White Layer thickness. The model overestimated the grain size on the machined workpiece rim zone by a factor of 2–4, while the White Layer thickness was predicted with an error of max. 0.36 μ m. [ABSTRACT FROM AUTHOR]

The quenching expansion tests in the temperature range 350–500 ℃ and isothermal compression tests in the range 350–500 ℃ & 0.01–10 s−1 of a homogenized Al-Cu-Li alloy were conducted to investigate the flow behavior and thermal expansion behavior. The corresponding microstructures of the tested specimens were characterized by back-scattered electron-scanning electron microscope (BSE-SEM), electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM). Coarse secondary phases including Al 2 CuLi (T 1), Al 2 (Cu-Ag)(Li-Mg) (Ω), Al 2 Cu (θ), Al 2 CuMg (S) dissolve with increasing temperature, which is likely to increase the coefficient of thermal expansion. The temperature rising induced by deformation heat varies from 2.29 ℃ to 38.32 ℃ with increasing strain rate and decreasing temperature. Three different constitutive models were calculated, evaluated and optimized, based on which, the two-step optimized Johnson-Cook model showed the highest precision. At the temperature ≤ 400 ℃, the existences of undeformable coarse phases (especially T 1 or Ω phase) promote particle stimulated nucleation (PSN), which pronouncedly increases the volume fraction of dynamic recrystallization (DRX) and decreases the flow stress. At temperature of 450 ℃, most of undeformable coarse phases dissolved, cutting-off mechanism of S and θ phase was observed, which is no longer beneficial to PSN, and CDRX becomes the main DRX mechanism. • Flow behavior and hot expansion behavior of the homogenized Al-Cu-Li alloy were analyzed. • Microstructures before and after compression at high temperature of the homogenized Al-Cu-Li alloy were compared. • A novel two-step optimized Johnson-Cook model with high prediction precision was proposed. • Cut-off mechanism of Al 2 CuMg phase during deformation were identified. • PSN and CDRX were characterized and the effects of precipitates on them were discussed. [ABSTRACT FROM AUTHOR]

Long Term Evolution (LTE) and LTE-Advanced (A) networks have been introduced to accommodate the User Equipment (UEs) that supports high complex technologies such as OFDM, SC-FDMA, MIMO. Recently, 3GPP presented 5G technology to meet the performance requirement of the International Mobile Telecommunication (IMT)-2020. It supports three specific services like Enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communication (URLLC), massive Machine Type Communication (mMTC). To increase the capacity of the network, 5G will deploy an ultra-dense network in the metro area. It fulfils the spectral efficiency requirement but at the same time increases handover rate. Due to handover, the power consumption of UEs may increase dramatically. To overcome this issue, LTE-A network adopts Discontinuous Reception (DRX) to conserve battery life of UE. 5G networks will also apply evolved variations of this scheme. In general, DRX is composed of some parameters and these need to be optimized during mobility. This paper presents a method for preservation of the battery life of UEs during mobility. The proposed mechanism comprises of three parts. In the first part, Part 1 , the operation of normal DRX during mobility is explored. The next parts, Part 2 and Part 3 , utilize the machine learning-based methods for the pre-prediction of Target eNB (TeNB) and provide ranks to the UEs during handover. Further, DRX parameters are adjusted according to the dynamic behaviour of the network. Handover latency, end-to-end delay is improved by 20% and 55%, respectively as compared to the conventional scheme. Further, machine learning based (Part 2) and dynamic adjustment of DRX parameters (Part 3) contribute to enhance the power saving factor by maximum up to 85%, and 33% as compared to state of art mechanism. • An Energy Efficient handover mechanism for next generation telecom networks. • First part of the scheme explores the static DRX operations during mobility. • Next parts pre-predict the future TeNB using machine learning classifiers. • DRX parameters are adjusted based on load and channel conditions. • Results shows the reduction in battery consumption of UEs during mobility. [ABSTRACT FROM AUTHOR]

In this study, the effect of strontium addition on hot deformation of AZ61 alloy was investigated by hot compression tests. A reference alloy (AZ61) and an Sr-containing alloy (AZ61 + Sr) was cast while their average initial grain size were supposed to be about 140 and 40 µm, respectively. In AZ61 + Sr alloy, the Sr-containing precipitations were stable at homogenization temperature. Analysing the hot compression curves, it was revealed that dynamic recrystallization phenomenon had occurred and controlled the thermomechanical behaviour of the alloys. The derived constitutive equations showed that the hot deformation parameters (n and Q) in AZ61 + Sr alloy is smaller than those of AZ61 alloy; this can be related to the small initial grain size and the lower amounts of solute aluminium atoms. The analysis of DRX kinetics along with the micrographs of the deformed microstructures showed that at the same condition the development of DRXed microstructure in AZ61 + Sr alloy was faster than AZ61 alloy. The increased recrystallized microstructure was interpretated to be attributed to (1) the more grain boundaries present and (2) the existance of the Al-Mg-Sr precipitations assisted the PSN mechanism. Also, the attenuated intensity of the basal texture of AZ61 + Sr was related to the DRX fraction of microstructure. [ABSTRACT FROM AUTHOR]

ZnSe layers were grown on ZnO substrates by the metal organic chemical vapor deposition technique. A new structure appeared at lower thicknesses films. The structural properties of the thin films were studied by the X-ray diffraction (XRD) and Raman spectroscopy methods. First, Raman selection rules are explicitly put forward from a theoretical viewpoint. Second, experimentally-retrieved-intensities of the Raman signal as a function of polarization angle of incident light are fitted to the obtained theoretical dependencies in order to confirm the crystallographic planes of zinc blend ZnSe thin film, and correlate with DRX measurements. Raman spectroscopy has been used to characterize the interfacial disorder that affects energy transport phenomena at ZnSe/ZnO interfaces and the Photoluminescence (PL) near the band edge of ZnSe thin films. [ABSTRACT FROM AUTHOR]

Magnesium matrix nanocomposite (1 vol.% nano-SiCp/AZ31) sheets were successfully fabricated by hot rolling at 350 °C with per pass reduction of 15% and total reduction up to 84%. Microstructure and texture evolution of the nanocomposites during hot rolling were investigated. Twinning and associated dynamic recrystallization (TDRX) were the dominant features at the initial stage of hot rolling. With the increase of rolling passes, grains were refined gradually due to dynamic recrystallization (DRX) and distribution of nanoparticles was also well modified. Meanwhile, shear bands became denser and longer with proceeding of hot rolling. Basal texture splitting along transverse direction was observed during hot rolling and intensity of the basal texture first increased and then showed a sharp decrease, while the uniformity kept increasing. Mechanical properties of the nanocomposite sheets were substantially enhanced. Compared with that of the as-cast nanocomposite, yield strength of the 11 passes hot-rolled sheet was more than doubled. Mechanical properties of the nanocomposite sheets showed a distinct anisotropy along rolling direction and transverse direction. [ABSTRACT FROM AUTHOR]

The dual-phase Mg-9Li-3Al-2Sr-2Y alloy was extruded at 553 K using Double Change Channel Angular Pressing (DCCAP) with an extrusion ratio of 17. The commercial code DEFORM-3D was used to develop a numerical model for deformation of the investigated material and the strain distribution, damage and grain shape evolution were predicted. The accurate computation of the material flow and deformation was performed, of which the results showed good agreement with microscope observations and micro-hardness measurements on the deformed billet and extrudate. Results suggest that dynamic recrystallization (DRX) occurs during the deformation and leads to grain refinement during the DCCAP process. The tensile strength and elongation after fracture in middle part of the extrudate show optimum values of 246.6 MPa and 19.9%, respectively. [ABSTRACT FROM AUTHOR]

The dual-phase Mg–9Li–3Al–2Sr–2Y alloy was extruded at 553 K using Double Change Channel Angular Pressing (DCCAP) with an extrusion ratio of 17. The commercial code DEFORM-3D was used to develop a numerical model for deformation of the investigated material and the strain distribution, damage and grain shape evolution were predicted. The accurate computation of the material flow and deformation was performed, of which the results showed good agreement with microscope observations and micro-hardness measurements on the deformed billet and extrudate. Results suggest that dynamic recrystallization (DRX) occurs during the deformation and leads to grain refinement during the DCCAP process. The tensile strength and elongation after fracture in middle part of the extrudate show optimum values of 246.6 MPa and 19.9%, respectively. [ABSTRACT FROM AUTHOR]

Substructure and twin boundary evolution of alloy 617B during dynamic recrystallization (DRX) was investigated by optical microscope, electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) technique. Simulated compression tests were carried out at different true strains in the temperature range of 1120-1210 °C with a strain rate of 0.001 s-1. The results show that discontinuous dynamic recrystallization (DDRX) featured by original grain boundary bulging is the dominant nucleation mechanism for alloy 617B. The progressive subgrain rotation, which is a characterization of continuous dynamic recrystallization (CDRX) can be detected at the early stage of hot deformation at lower temperature, which can just be considered as an assistant mechanism. The evolution of substructure and twin boundaries have a significant effect on DRX process of alloy 617B. Twinning formation can active the DRX process by accelerating original grain boundary bulging and separation of bulging grain boundaries. The formation of twin steps resulting from twin slipping provide additional DRX nucleation locations. The effort of twins gets weaker with the increase of temperature as the DRX grain growth process associated with grain boundary area reduction gradually becomes a preferential mechanism for energy minimization. Different from previous study, the fraction of twin boundaries decrease with the increase of temperature, which can be attributed to the twin boundary accelerated prior grain growth process. Such process also results in the serious bulging of grain boundaries into adjacent grains. [ABSTRACT FROM AUTHOR]

The quaternary Cu 2 FeSnS 4 (CFTS) is regarded like the one of the semiconductors promoting as an effective photovoltaic absorber because of their earth-abundant and non-toxic elements. The thin films were elaborated by spray pyrolysis method deposited onto glass substrates at 370 °C for one hour with post-sulfurization treatment at 450 °C for 30 min. XRD spectra analysis showed that the CFTS thin films have tetragonal structure with a main peak corresponding to the direction (1 1 2). The Raman spectrum confirmed these results with an appearance of two main peaks corresponding to the CFTS situated at the positions 289 cm −1 and 318 cm −1 . The CFTS films exhibit a homogeneous, rough and dense topography with a thickness of about 0.8 μm. The films of CFTS present a high absorption coefficient (≥10 5  cm −1 ) and the direct band gap energy is found to be 1.55 eV, which confirms their use as an absorber for solar cells. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of Mg 97 Y 2 Zn 1 alloys during rolling at 450 °C and 500 °C have been investigated in this work. The microstructure of pre-rolled alloy mainly consisted of the α-Mg matrix, block 18R LPSO phase distributed at the grain boundary, and lamellar 14H LPSO phase distributed in grain interior. After rolling, the 18R LPSO phase and 14H LPSO phase were kinks obviously at both temperatures of alloys. The alloy rolled at 500 °C produced serious DRX, and the occurrence of DRX is related to the 14H LPSO phase: (i) the interface between 14H LPSO phase and α-Mg matrix could act as a nuclear site of DRX grain and further refine grain by discontinuous DRX mechanism. (ii) The kink boundary of 14H LPSO phase evolved into a grain boundary through the continuous DRX mechanism and promotes the generation of DRX. Tensile testing indicated that the alloy rolled at 450 °C possessed the higher yield strength, and the alloy rolled at 500 °C had the higher ultimate tensile strength. The dominant deformation mechanism of the 450 °C rolled alloy was a prismatic slip and prismatic kink, and the formation of a strong rolling basal texture resulted in the improvement of yield strength. For the alloy rolled at 500 °C, the formation of rolling texture is mainly related to twinning. In addition, the severe DRX degree with refined DRX grains contributed to the improvement of ultimate strength and ductility for the alloy rolled at 500 °C. [ABSTRACT FROM AUTHOR]

This parper reports a simple extrusion pathway for fabricating Zn–1Mg alloy with a bimodal structure. The alloy was prepared by casting and extruding at 200 °C and an extrusion ratio of 25:1. Microstructure and mechanical properties of the Zn–1Mg alloys were systematically investigated using OM, XRD, SEM, EBSD, TEM, and tensile tests. The results show that the Zn–1Mg alloy consisted of primary α -Zn dendrites and a three-component eutectic structure of α -Zn + Mg 2 Zn 11 + MgZn 2. The yield strength, ultimate tensile strength and elongation of extruded alloy at room temperature reached ∼289 MPa, ∼320 MPa, and ∼32%; and the average size of fine grains and coarse grains were ∼1.65 and ∼6.84 μm, respectively. Besides, dynamic recrystallization occurred during hot deformation, and particles in the broken phase were effective sites for the nucleation of dynamic recrystallized grains nucleation via a particle-stimulated nucleation mechanism. [ABSTRACT FROM AUTHOR]

Lithium diphosphate glasses doped MgO was prepared via a melt quenching technique. The samples were characterized by X-ray diffraction (XRD), Raman and impedance spectroscopy. XRD spectra reflected the amorphous nature of the glasses Raman spectra show structural network modifications with the composition variations of the studied glasses. Raman spectra of the studied glasses contain also typical phosphate glasses bands. Thus the band at ∼698 cm −1 assigned to symmetric stretching vibrations of P O P groups and that from ∼1168 cm −1 is attributed to symmetric stretching motions of the non-bridging oxygen (NBO) atoms bonded to phosphorous atoms (PO 2 ) in phosphate tetrahedron. Electric properties were investigated using complex impedance spectroscopy in a frequency range from 40 Hz to 6 MHz at room temperature. The impedance spectra were analyzed in terms of equivalent circuits involving resistors, capacitors and constant phase elements (CPE). Constant-phase elements (CPE) are used in equivalent electrical circuits for the fitting of experimental impedance data. The AC conductivity exhibited a Jonscher’s universal power law according with the relation σ ( ω ) = σ (0) + Aω s and it is observed that as the MgO content increases, frequency exponent ( s ) decreases. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of a nickel-based superalloy was investigated by means of isothermal compression tests in the strain rate range of 0.001–10 s −1 at 1110 °C. Transmission electron microscope (TEM) and electron backscatter diffraction (EBSD) technique were used to study the effect of strain rate on the microstructure evolution of the alloy during hot deformation. The results revealed that the dynamic recrystallization (DRX) process was stimulated at high strain rates ( ε ̇ ⩾ 5 s - 1 ) due to the high dislocation density and adiabatic temperature rise. Meanwhile, high nucleation of DRX and low grain growth led to the fine DRX grains. In the strain rate rage of 0.001–1 s −1 , the volume fraction of DRX grains increased with the decreasing strain rate, and the grain growth gradually governed the DRX process. Moreover, the strain rate has an important effect on DDRX and CDRX during hot deformation. On the other hand, particular attention was also paid to the evolution of twin boundaries during hot deformation. It was found that there was a lower fraction of Σ 3 boundaries at the intermediate strain rate of 1 s −1 , while the fractions of Σ 3 boundaries were much higher at both the lower strain rates ( ε ̇ ⩽ 0.1 s - 1 ) and higher strain rates ( ε ̇ ⩾ 5 s - 1 ). [ABSTRACT FROM AUTHOR]

The microstructure and tensile properties of AZ80+X%Ca (X=0, 0.1, 0.5) magnesium alloy have investigated after applying extrusion process at 280 °C and 340 °C. Optical and scanning electron micrographs parallel to extrusion direction at 280 °C showed dynamically recrystallized grains. There were also initial grains elongated in extrusion direction in the AZ80+X%Ca alloy. Finer microstructures were observed by increasing calcium content due to the formation of some precipitates during grain growth. EDS analysis determined the newly formed precipitates as Al 2 Ca. The grain size was reduced from 90 μm to 9 μm by extrusion process in the sample with 0.5% Ca. At higher extrusion temperature (340 °C), similar microstructure was observed, except that the grain size was increased and there was no initial grains left in the structure anymore. From tensile testing, ultimate tensile strength (UTS) value was increased from 304 MPa to 329 MPa in extruded AZ80+0.5%Ca alloy at 280 °C. [ABSTRACT FROM AUTHOR]

A series of mixed oxides (ZrO 2 –La 2 O 3 ) was investigated to establish the effect of the source of the sulphate ion and the modification of sol–gel zirconia with La 2 O 3 . Supports were synthesized varying the content of La 2 O 3 (2, 3, 5 and 10 wt.%). Sample sulphation took place in situ, maintaining the amount at 20 wt.% using concentrated H 2 SO 4 and a 1 M (NH 4 ) 2 SO 4 solution as the sulphating agents. These catalytic materials were characterized by: X-ray diffraction, nitrogen adsorption (BET), FTIR pyridine, 2-propanol dehydration, Scanning Electron Microscopy (SEM) and isomerization of n-hexane. The modification of sol–gel zirconia with La 2 O 3 originated an increase in the surface area. When increasing the content of La 2 O 3 (3, 5 and 10 wt.%) a diminution of the surface area for samples sulphated with H 2 SO 4 (CASL n ) occurred. On the contrary, for samples sulphated with (NH 4 ) 2 SO 4 (CSAL n ) a not defined behavior was presented. In mixed oxides, the tetragonal phase was present which is characteristic of sulphated zirconia. By SEM, the morphology of the support can be perfectly observed showing the presence of clusters in each of them. It was observed that the crystallite size did not change when increasing the lanthanum content for the CASL n supports. According with the FTIR pyridine technique all the samples exhibited the presence of Brönsted and Lewis sites, and the support that achieved the highest acidity was the one containing 2 wt.% of La 2 O 3 (CASL2). It was determined that the effect of the sulphate agent generated more active catalysts in terms of conversion of n-hexane and it was also observed that La 2 O 3 provided a higher catalytic selectivity toward isomerization products. [ABSTRACT FROM AUTHOR]

During dynamic tensile extrusion (DTE) the material is subjected to a complex deformation history, including high strain rates, large strains and elevated temperatures. This technique provides unique means to explore material performance under extreme conditions. In this work, the microstructural evolution of 99.98% commercially pure copper during the DTE test was investigated by means of electron backscatter diffraction (EBSD). The investigation was focused on the segment of the extruded jet that remained in the die, since numerical simulation showed that material points along the longitudinal axis of such segment correspond to different stages of a common temperature compensated deformation history. Therefore, post mortem microstructure information extracted at different locations along the center line is equivalent to in situ real-time measurement during the deformation process. EBSD investigations along the center line showed a progressive elongation of the grains, and an accompanying development of a strong 〈0 0 1〉 + 〈1 1 1〉 dual fiber texture. Meta-dynamic discontinuous dynamic recrystallization (DRX) occurred at larger strains, and it was demonstrated that nucleation occurred during straining, while subsequent grain growth took place during post-deformation cooling in the die. According to strain energy minimization arguments, the recrystallization resulted in an increased 〈0 0 1〉 texture component. The critical strain for recrystallization was well predicted from a power-law dependence on the Zener–Hollomon parameter, including grain size dependence and a temperature dependent activation energy. In addition, it was shown that 〈0 0 1〉 and 〈1 1 1〉oriented grains develop different dislocation substructures during straining, exhibiting elongated cells/micro-bands and typical cell structures, respectively. The present results also confirm that dynamic tensile ductility increases with decreasing initial grain size as a result of grain refinement and lowering of dislocation and twin densities during DRX. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites represent a new class of material alternative to conventionally filled polymers. This new class of material is synthesized from a mixed polymeric matrix at a weak percentage with montmorillonites as inorganic charges. Their dispersion is facilitated by the organophilization of their structure by the exchange of inside foliar cations with compatilization possessed at once hydrophiles and hydrophobes ends, respectively, to be compatible with clay and polymer. The objective of this study is to use organophilized montmorillonites in the presence of monomer tetrahydrofuran to obtain polytétrahydrofuran montmorillonites (PTHF–Mmt) of composites by polymerization in situ. The organophilisation of the Mmt is formed by active cationic surface. The obtained results show an increase in the distance inside the reticular in the diffractograms of X-rays (DRX) and the appearance of absorption bands of the characteristics of polytétrahydrofuran on the spectra of infrared spectroscopy (IR), which indicate pre-polymerization of tetrahydrofuran in the galleries of clay and, therefore, the obtaining of a nanocomposite. We have also studied the thermal stability of the samples by differential analysis calorimetric (DSC) analysis, and we can conclude that the nanocomposites are stabilized thermally by the presence of clay in the matrix. [ABSTRACT FROM AUTHOR]

Three known dislocation density based models are compared to each other, and to available experimental results. All three models were embedded into ANSYS finite element (FE) software and firstly utilised to predict aluminium and copper transformations (dislocation density evolution and the resulting grain size) in a result of a single pass of equal channel angular pressing (ECAP). It is demonstrated that for the studied problem dislocation density evolution under severe plastic deformation (SPD) can be precisely predicted utilizing simple classical model. One of the models was utilized to predict defect structure evolution for the series of ECAP passes. Simulations have revealed that within the framework of the proposed model the increase of the dislocation density on ECAP pass is proportional to yield strength increment on the previous pass for both studied materials. This fact gives grounds to a proposal of a semi-analytical approach, predicting dislocation density evolution in a result of consequent ECAP passes on the basis of a numerical simulation of the two first passes. The utilized kinetic model for dislocation density evolution separates between densities of mobile and immobile dislocations. Employing the idea of separation of dislocations into mobile and immobile, a new approach for dynamic recrystallization coupling dislocation density and the size of grain formed in metal is proposed. The proposed approach for dynamic recrystallization appeared to be applicable for the whole range of grain sizes. [ABSTRACT FROM AUTHOR]

The hot deformation behavior of a γ′-hardened nickel-based superalloy was investigated by means of isothermal compression tests in the temperature range of 1010–1210 °C with a strain rate of 0.1 s −1 . The electron backscatter diffraction (EBSD) technique and transmission electron microscope (TEM) were employed to investigate the effect of deformation temperature and strain on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). Microstructure observations revealed that the size and volume fraction of DRX grains increased with the increasing temperature. A power exponent relationship was obtained between the stable DRX grain size and the peak stress. Additionally, it was found that the effect of CDRX characterized by progressive subgrain rotation became weaker with the increasing deformation temperature, and DDRX was the operating nucleation mechanism of DRX at higher deformation temperature. On the other hand, the effect of DDRX became stronger with the increasing strain, and CDRX can only be considered as an assistant nucleation mechanism of DRX at the later stage of deformation for the alloy deformed at 1160 °C. Nucleation of DRX can also be activated by the twinning formation. Hence, particular attention was also paid to the evolution of twin boundaries during hot deformation. [ABSTRACT FROM AUTHOR]

In this study, the Mg–7Gd–5Y–1Nd–0.5Zr alloy can reach a high ductility by the process of multi-directional forging, and the evolution of the microstructure, texture and the mechanical properties were discussed systematically. The results show that after the solutionized sample was multi-forged at 500 °C, its grain size can be refined from 292 um to 58 um. As the forging temperature decreased, fine particles precipitated in the matrix. The volume fraction of the particles increased with the forging temperature decreasing, so the nucleation and growth of crystallization were strongly restricted. There was no recrystallization as the forging temperature fell to 410 °C, and the severe deformed grains distributed as streamlines perpendicular to the final compression axis. The texture intensity decreased with increasing forging passes. The sample with best ductility was obtained after compressed at 470 °C, with an elongation to failure of 21% at room temperature, which is increased by 200%, in comparison with that of the samples in solutionized condition. EBSD results revealed that the mean grain size was 15 um. Refined grains as well as the weakened texture were the key factors to its high ductility. [ABSTRACT FROM AUTHOR]

In this study, texture c-axis//ND of ZK61-T6 Mg alloy was reoriented towards c-axis//ED, TD and tilted in between ED and TD in a ZK61-PC Mg alloy through cross pre-compression. Subsequently, quasi-static and dynamic mechanical behaviour was examined. The results showed that compressive yield strength, ultimate compressive strength and elongation to fracture were considerably increased from 140 to 220 MPa, 374–437 MPa and 0.15–0.16, respectively. This increase was the synergistic effect of texture, grain refinement through twin boundaries and pre-induced dislocation hardening effect. In addition, an exceptional increase of ultimate compressive strength (531 MPa) was obtained under dynamic loading. The microstructure evolution of deformed specimens revealed that the propensity and width of the adiabatic shear band were increased with an increase in strain rate in ZK61-PC Mg alloy. In addition, twinning, de-twinning, and dislocation inside the twin and the matrix absorbed the high-stress energy and provided a higher mechanical response in ZK61-PC Mg alloy. The twinning induce rotational dynamic recrystallization mechanism was responsible for the development of fine grains. Based on the results, it is recommended that pre-compression is a practical way to increase the efficiency of the ZK61 Mg alloy. • Cross pre-compression redistributed the texture through numerous twinning activity. • The CYS, UCS and FE were increased significantly in ZK61-PC Mg alloy. • Width and propensity of ASB increased with increase in strain rate in ZK61-PC Mg alloy. • Twin induce rotational dynamic recrystallization mechanism was responsible for development of FGs. • and type of dislocations were witnessed inside the twin and in the matrix. [ABSTRACT FROM AUTHOR]

The flow behavior of 2099 alloy was investigated by means of hot compression tests in the temperature range of 300-500 °C and strain rate range of 0.001-10 s-1. Processing maps were developed on the basis of the dynamic materials model (DMM). The results show that the flow stress increases with increasing strain rate and decreasing temperature. At a given deformation condition, the flow stress composed three stages: work hardening stage, softening stage and steady stage. Microstructure observation indicates that in the deformation temperature range of 300-420 °C and strain rate of 0.001-10 s-1 shows a dynamic recovery (DRV) character; while that deformed in the deformation temperature range of 420-500 °C and strain rate of 0.001-10 s-1 shows a dynamic recrystallization (DRX) character. According to the processing map and microstructure observation, DRV and DRX are the main deformation mechanisms in the safe regions, while flow instability is manifested as adiabatic shear bands and flow localization at the strain of 0.7. The optimum processing parameters for 2099 alloy at different strains conditions are given with the efficiency dissipation more than 0.3. [ABSTRACT FROM AUTHOR]