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The use of Raman spectroscopy in probing the deformation mechanisms of cellulose fibres (regenerated and natural), and two natural cellulose composite systems (wood and paper) is described. It is shown that during tensile deformation the 1095 cm−1 Raman band, corresponding to the stretching of the cellulose ring structure, shifts towards a lower wavenumber due to molecular deformation. By analysing a number of fibres with different microstructures this shift is shown to be invaluable in understanding the micromechanisms of deformation in these materials. Moreover, the rate of Raman band shift is shown to be invariant with stress for all fibre types, consistent with a fibre microstructure based on a modified series aggregate model. In the composite systems, such as wood and paper, it is shown that the stress-induced Raman band shift in the cellulose gives an important insight into their local deformation micromechanics. [ABSTRACT FROM AUTHOR]

Al–Zn–Mg–Cu alloys can be fabricated by a series of thermo-mechanical processing methods (e.g., hot rolling, forging and extrusion), which is able to serve in aeronautic, automobile, and marine industries because of its excellent physical properties. However, reaching the balance between high strength and favorable ductility to present its high performance is still in progress, during which temperature and strain rate are two very important external variables. More importantly, the core lies in sophisticated microstructure evolution paths involved in hot deformation, which consists of different microstructure mechanisms and behaviors and can be expressed as various mechanical responses. Therefore, a fundamental review of microstructure mechanisms and behaviors, microstructure evolution and relevant mechanical responses of Al–Zn–Mg–Cu alloys during high-temperature deformation is of great significance. In present paper, first, various experimental methods have been introduced. Second, general trends of mechanical properties changing with temperature and strain rate have been summarized. Third, major microstructure mechanisms and behaviors have been discussed. Then, a schematic illustration originating from dislocations' movement has been depicted, which succeeding microstructure evolution and mechanical responses (including superplasticity) have been reviewed accordingly. Finally, further suggestions of hot deformation of Al–Zn–Mg–Cu alloys have been given. [ABSTRACT FROM AUTHOR]

Oxide Dispersed Strengthened (ODS) ferritic stainless steels present well-known fine grains microstructures where dislocation movement is hindered by a dense precipitation of nano-oxides particles. Previous research, on the thermomechanical behavior at high temperature and strain rates, was focused on torsion tests (Karch in J Nucl Mater 459:53-61, 2014). Considering texture evolution and grain shape as indicators of the intragranular dislocation glide activity, it was shown that, for high temperature and strain rate, intragranular deformation was in competition with intergranular accommodation. The latter phenomenon was related to early damaging at grain boundaries. The occurrence of a transition phenomenon from an intragranular to an intergranular deformation mechanism, with increasing temperature, was recently confirmed by neutron diffraction spectroscopy (Stoica in Nature Commun 5:5178, 2014). In the present paper, hot extrusion (HE) tests are performed, avoiding damage due to the high stress triaxiality, and allowing further investigation of intragranular and intergranular plasticity at large strains. Three ferritic steels exhibiting various precipitation size and density were hot extruded. Microstructure evolution at different stages of deformation is investigated using the Electron Back-Scattered Diffraction (EBSD) technique. After extrusion at 1373 K (1100 °C), the microstructure of ODS steels consists of a mixture of small round shape grains and larger elongated grains containing low-angle grain boundaries. Texture measurements show the appearance of the α-fiber (<110>//extrusion direction) and an increase in its intensity during the extrusion process in the larger grains. The fragmentation of the large elongated grains by Continuous Dynamic Recrystallization (CDRX) partially occurs in ODS materials depending on precipitation reinforcement. For smaller grains, plastic deformation has no effect on crystallographic orientation and grain shape, indicating a grain boundary accommodation phenomenon as the major deformation mechanism. Precipitation density not only impacts the intragranular dislocation glide activity, but also reduces CDRX kinetics in coarse grains. [ABSTRACT FROM AUTHOR]

Auxetic materials are those which exhibit negative Poisson’s ratio, i.e. these solids expand transversely when stretched longitudinally. In recent years the concept of semi-auxetics has been examined for cellular solids based on combination of re-entrant and hexagonal microstructures. In this paper we identify a type of rotating unit that gives positive Poisson’s ratio so that a study can be made on rotating sub-structures that exhibit both positive and negative Poisson’s ratio characteristics. A second type of rotating geometry, whose Poisson’s ratio shifts from negative to positive as stretching increases, has also been identified. Based on kinematical studies we explore the relationship between the on-axis Poisson’s ratios in terms of novel lattice geometry and the magnitude of deformation. [ABSTRACT FROM AUTHOR]

This paper presents research work on the characteristics and micro mechanism of strain whitening of a thermoplastic olefin material. Systematic tensile tests have been carried out to investigate the relation between strain whitening extent and external factors, including the deformation employed and the environmental temperature. A new optical method has been developed for the measurement of strain on polymer tensile samples. Applying this method relation between whitening level (grey level change) and strain has been studied. A new concept of ‘strain whitening sensitivity’ has been proposed and defined as the strain whitening induced by unit deformation or strain. Non-monotonic relation between whitening level and strain has been found. Strained and fractured samples were observed with A JEOL 5800 LV SEM for the micro mechanism investigation. The change of microstructure on the sample surface has been extensively observed and the combined effects of small ridges and micro-voids on the scattering efficiency of the strained surface were regarded as reasons for the non-monotonic relation between whitening level and strain. [ABSTRACT FROM AUTHOR]

In this paper, rapid solidified MgZnY (at.%) alloy powders produced by an inert gas atomizer were consolidated using a severe plastic deformation technique of high pressure torsion (HPT) at room temperature and 373 K. The behavior of powder consolidation, matrix microstructural evolution, and mechanical properties of the powders and compacts were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, microhardness, and tensile testing. As the HPT processing temperature increases, the powders are more plastically deformed due to decreased deformation resistance, grain boundaries are more in equilibrium, powder bonding is enhanced due to increased interparticle diffusion, hence, tensile ductility and strength increases. On the other hand, hardness decreases with the increased processing temperature, due to less dislocation density. [ABSTRACT FROM AUTHOR]

Magnesium alloy (AZ31) based metal matrix composite reinforced with carbon nanotubes (CNTs) was fabricated using the technique of disintegrated melt deposition followed by hot extrusion. In this research paper, the microstructure, hardness, tensile properties, tensile fracture, high cycle fatigue characteristics, and final fracture behavior of CNTs-reinforced magnesium alloy composite (denoted as AZ31/1.0 vol.% CNT or AZ31/CNT) is presented, discussed, and compared with the unreinforced counterpart (AZ31). The elastic modulus, yield strength, tensile strength of the reinforced magnesium alloy was noticeably higher compared to the unreinforced counterpart. The ductility, quantified both by elongation-to-failure and reduction in cross-section area of the composite was higher than the monolithic counterpart. A comparison of the CNT-reinforced magnesium alloy with the unreinforced counterpart revealed a noticeable improvement in cyclic fatigue life at the load ratios tested. At all values of maximum stress, both the reinforced and unreinforced magnesium alloy was found to degrade the cyclic fatigue life at a lower ratio, i.e., under conditions of fully reversed loading. The viable mechanisms responsible for the enhanced cyclic fatigue life and tensile behavior of the composite are rationalized in light of macroscopic fracture mode and intrinsic microscopic mechanisms governing fracture. [ABSTRACT FROM AUTHOR]

This paper presents a study of microscale plastic deformation at the crack tip and the effect of microstructure feature on the local deformation of aluminum specimen during fracture test. Three-point bending test of aluminum specimen was conducted inside a scanning electron microscopy (SEM) imaging system. The crack tip deformation was measured in situ utilizing SEM imaging capabilities and the digital image correlation (DIC) full-field deformation measurement technique. The microstructure feature at the crack tip was examined to understand its effect on the local deformation fields. Microscale pattern that was suitable for the DIC technique was generated on the specimen surface using sputter coating through a copper mesh before the fracture test. A series of SEM images of the specimen surface were acquired using in situ backscattered electronic imaging (BEI) mode during the test. The DIC technique was then applied to these SEM images to calculate the full-field deformation around the crack tip. The grain orientation map at the same location was obtained from electron backscattered diffraction (EBSD), which was superimposed on a DIC strain map to study the relationship between the microstructure feature and the evolution of plastic deformation at the crack tip. This approach enables to track the initiation and evolution of plastic deformation in grains adjacent to the crack tip. Furthermore, bifurcation of the crack due to intragranular and intergranular crack growth was observed. There was also localization of strain along a grain boundary ahead of and parallel to the crack after the maximum load was reached, which was a characteristic of Dugdale-Barenblatt strip-yield zone. Thus, it appears that there is a mixture of effects in the fracture process zone at the crack tip where the weaker aspects of the grain boundary controls the growth of the crack and the more ductile aspects of the grains themselves dissipate the energy and the corresponding strain level available for these processes through plastic work. [ABSTRACT FROM AUTHOR]

The aim of this paper is to establish the correlation among sintering process, porosity, and important thermo-mechanical property of refractory concrete, i.e., creep. Creep deformation was investigated according to the standard laboratory procedure applied at three temperatures: 1200, 1300, and 1400 °C. Corundum and bauxite-based refractory concretes were investigated. The concretes are varying in chemical and mineralogical composition. Both loss of strength and degradation of material occur when refractory concrete is subjected to increased temperature and compressive static load. Measuring of thermo-mechanical properties can indicate and monitor the changes within microstructure. Variation of refractory concrete microstructure, as a consequence of sintering process, during exposure to constant compressive load and constant elevated temperature during certain time-intervals was investigated using scanning electron microscope and Image Pro Plus program for image analysis. Obtained results of the investigation proved that creep can be useful method when type of refractory concrete is to be chosen for an application. [ABSTRACT FROM AUTHOR]

This paper discusses the laser-irradiated microjoints between glass and polyimide for applications in neural implants. To facilitate bonding between them, a thin titanium film with a thickness of approximately 0.2 μm was deposited on glass wafers using the physical vapor deposition (PVD) process. Two sets of samples were fabricated where the bonds were created using diode and fiber lasers. The samples were subjected to tension using a microtester for bond strength measurements. The failure strengths of the bonds generated using fiber laser are quite consistent, while a wide variation of failure strengths are observed for the bonds generated with diode laser. Few untested samples were sectioned and the microstructures near the bond areas were studied using an optical microscope. The images revealed the presence of a sharp crack in the glass substrate near the bond generated with the diode laser. However, no such crack was observed in the samples made using fiber laser. To investigate the reasons behind such discrepancy in bond quality further, uncoupled three-dimensional finite element analyses (FEA) were conducted only for the samples created using diode laser. First, the transient heat diffusion-based FEA was conducted by using the laser power intensity distribution as a time dependent heat source. This model calculates the temperature distribution within the substrates as a function of time. Next, the structural model predicts the amount of residual stresses developed in the joint system as it is cooled down to room temperature. The out-of-plane normal component of residual stresses was within the failure strength range of glass that may have caused fracture initiation in the substrate. [ABSTRACT FROM AUTHOR]

A high fidelity assessment of accumulative damage of woven fabric composite structures subjected to aggressive loadings is strongly reliant on the accurate characterization of the inherent multi-scale microstructures and the underlying deformation phenomena. Damage in composite sandwich and joint structures is characterized by the coexistence of discrete (delamination) and continuum damage (matrix cracking and intralaminar damage). A purely fracture mechanics-based or a purely continuum damage mechanics-based tool alone cannot effectively characterize the interaction between the discrete and continuum damage and their compounding effect that leads to the final rupture. In this paper, a hybrid discrete and continuum damage model is developed and numerically implemented within the LS-DYNA environment via a user-defined material model. The continuum damage progression and its associated stiffness degradation are predicted based on the constituent stress/strain and their associated failure criteria while the discrete delamination damage is captured via a cohesive interface model. A multi-scale computational framework is established to bridge the response and failure predictions at constituent, ply, and laminated composite level. The calculated constituent stress and strain are used in a mechanism-driven failure criterion to predict the failure mode, failure sequence, and the synergistic interaction that leads to global stiffness degradation and the final rupture. The use of the cohesive interface model can capture the complicated delamination zone without posing the self-similar crack growth condition. The unified depiction of the continuum and discrete damage via the damage mechanics theory provides a rational way to study the coupling effects between the in-plane and the out-of-plane failure modes. The applicability and accuracy of the damage models used in the hybrid dynamic failure prediction tool are demonstrated via its application to a circular plate and a composite hat stiffener subjected to shock and low velocity impact loading. The synergistic interaction between the continuum and discrete damage is explored via its application to a sandwich beam subjected to a low velocity impact. [ABSTRACT FROM AUTHOR]

This paper provides evidences on the feasibility of using an in-situ deformation process to produce elongated structures of a polyaniline complex (PANI CX), embedded in the bulk of filament-like polymer composites, and longitudinally oriented along the composites' main axial direction. The polyaniline complex was thermally blended with polystyrene- polybutadiene-polystyrene (SBS) at different weight compositions, and the resultant blends were capillary extruded into filaments. The extrudates' microstructure was analysed by scanning electron microscopy (SEM). The results of the analysis revealed a phase- separated morphology in the extrudates, which consisted of elongated domains of PANI CX embedded in the bulk of the SBS. The elongated structures displayed a considerable degree of uniformity and continuity, and were preferentially oriented in the extrusion direction. The formation of these structures was ascribed to a combination of factors, the main ones including elongational and shearing flows occurring in the molten/softened blends during the processing, and the stresses transferred from the highly viscous matrix to the particles of the PANI complex filler. [ABSTRACT FROM AUTHOR]

The high-temperature deformation behavior and fracture mechanism of Fe–Ni-Cr superalloy under high strain rates from 1 to 100 s−1 were studied by hot tensile experiments at a temperature range of 900–1150 °C. The results manifest that the high strain rate has significant influence on the microstructure evolution and local instability fracture behavior of the superalloy. At high strain rates, the flow behavior of the alloy shows obvious dependence on the strain rate and temperature. With the increase of strain rate, a higher ratio of low-angle and low-energy grain boundaries can be obtained while keeping fine and uniform equiaxed grain microstructure, yet the control window of hot deformation microstructure of the alloy is obviously narrowed. After deforming at temperatures of 950–1000 °C and strain rates of 10–50 s−1, the fine equiaxed grains with average grain size less than 10 μm can be controlled at high deformation rates. Under high strain rates and higher deformation temperature, it has been found that the plastic strain induced by recrystallization nucleation and growth at the original high angle grain boundary (HAGB) of the alloy is not enough to coordinate the rotation of the original grain and the sliding of the original HAGB during deformation, resulting in intergranular cracking. This is the fundamental reason for the abnormal change of thermal deformation power dissipation behavior, higher strain rate sensitivity, flow instability and fracture when the alloy is hot deformed at high strain rates. [ABSTRACT FROM AUTHOR]

The hot compression test, with a true strain of 0.9, was carried out at a temperature of 1100–1250 °C and a strain rate of 0.001–1 s−1 by a Gleeble3800 thermal simulation testing machine for the as-cast TNM alloy. The stress–strain curves were recorded to measure the deformation resistance and deformation uniformity of the whole specimens, and the microstructure was analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) from the perspectives of the extent of recrystallization and the orientation and size of the grains. At lower strain rates, the strain is more uniform within the specimen. At higher temperatures, a complete recrystallization microstructure showing an equiaxed nearly lamellar (NL) structure with a weak texture can be obtained at a low strain rate, and a microstructure showing an elongated fine-grained NL structure without texture can be obtained at a high strain rate. The deformation mechanisms were analyzed, and the processing parameters were optimized by constructing empirical hot processing maps. The parameters 1200–1250 °C and 0.1–0.01 s−1 are recommended for deformation to obtain a uniform fine grain structure economically without cracking of the specimen. [ABSTRACT FROM AUTHOR]

The microstructure evolution of GH4698 nickel-based superalloy was studied over a temperature range of 1000–1200 °C, a strain rate range of 0.01–1 s−1 and a strain range of 0.1–0.9 by uniaxial thermal compression. The dynamic recrystallization (DRX) behaviour and nucleation mechanism were characterized by electron backscattering diffraction (EBSD). Compared with the strain rate, the deformation temperature had a significantly different effect on the DRX volume fraction, DRX average grain size and grain boundary misorientation. Three types of DRX mechanisms may operate during thermal deformation. Discontinuous dynamic recrystallization (DDRX) characterized by serrated and bulging grain boundaries was the dominant DRX mechanism. Continuous dynamic recrystallization (CDRX) primarily occurred within the deformed grains, as well as at the interface between the dynamically recrystallized grains and the deformed matrix due to the difference in deformation compatibility in the original grains under various conditions. The pre-existing Σ3 twins can promote DRX nucleation through DDRX and twin dynamic recrystallization (TDRX) mechanisms. The verification of different DRX mechanisms is helpful to comprehensively understand the microstructure evolution of GH4698 nickel-based superalloys during thermal deformation. [ABSTRACT FROM AUTHOR]

In 2003 Nature Materials article, Keckes et al. presented deformation properties of a variety of woods in relation to deformation of their individual wood cells. Their point is “The remarkable mechanical properties of biological materials reside in their complex hierarchical structure...”. This holds for mineral-based biological materials such as bone as well as for wood. Indeed, one of us (J.L.K.) introduced the concept that to explain the material properties of cortical bone, it was necessary to treat it as a complex material/structural hierarchical composite. Calculations to determine anisotropic properties of bone measured using ultrasonic wave propagation techniques, were extended to similar measurements on both soft and hard woods. These anisotropic properties calculations have been extended to include data based on mechanical measurements of orthotropic elastic constants of both soft and hard woods for comparison with both earlier ultrasonic measurements and mechanical testing on other woods. This work illustrates the fact that understanding and modeling the properties of wood is a complex task as the symmetry changes with scale. For example, lignin is isotropic, hemicellulose and cellulose are transversely isotropic, while the cells and microstructure have orthotropic symmetry. [ABSTRACT FROM AUTHOR]

In this work, a canning compression process was developed to perform hot compression deformation of high chromium cast iron (HCCI) on a Gleeble 3800 thermomechanical simulator at temperature of 950–1150 °C and strain rate of 0.01 s–1. The hot deformation behavior and microstructure evolution of HCCI were investigated. The mechanisms of carbide dissolution and refinement were analyzed. Results show that HCCI in the steel canning can achieve large plastic deformation without incurring macro-cracks. Static pressure exerted by carbon steel cans on HCCI helps inhibit the initiation and growth of cracks when HCCI deforms under triaxial stress. After HCCI was deformed at 1150 °C, fine carbide and low-volume fraction of carbide cavity were achieved. HCCI carbide dissolves and deforms during hot compression and will undergo tensile fracture when the maximum tensile stress is greater than its tensile strength. [ABSTRACT FROM AUTHOR]

Non-dendritic microstructures are generally obtained in metals after semi-solid deformation (deformation during solidification); however, dendritic growth is preferred without deformation. The fragmentation of dendrites is recognized as an essential contributing factor to non-dendritic microstructures. However, the underlying mechanism of fragmentation needs to be clarified in depth. It is infamously hard for researchers to carry out a direct observation of this process. Moreover, a comprehensive numerical survey of this process is not trivial. The present research reported a new method to model dendritic growth during semi-solid deformation. The motion and deformation of the solid coupled with liquid flow in the melt were treated as the two-phase flow because plastic materials could be formulated as non-Newtonian fluids. The vector-valued phase-field formulation and the self-constructed Navier–Stokes solver made it possible to simulate the growth, motion, deformation, fragmentation and agglomeration of two dendrites coupled with liquid flow in the melt. Computational results suggest that fragmentation can occur when the grain boundary is wet and penetrated by the melt, giving new supporting evidence to a previously proposed mechanism for the fragmentation of dendrites. [ABSTRACT FROM AUTHOR]

Titanium in situ reinforced with titanium boride (TiBw) has garnered significant attention as one of the most promising titanium composites today. A significant number of processing approaches have been reported on the fabrication of these unique composites. This brief review provides an update on recent activities within the area focusing largely on research conducted over the past 5 years. Approaches discussed include bulk deformation processes such as rolling, 2D forging, equal channel angular pressing, (laser and non-laser-based) additive manufacturing, and new microstructural designs implemented for this composite system. Moreover, the potential of this composite as a biomaterial is also discussed. [ABSTRACT FROM AUTHOR]

A systematic investigation on the mechanical response of the interior grain and grain boundary of yttrium aluminum garnet is carried out using nanoindentation and microstructure characterization. The nano-hardness is calculated, while the residual indent is analyzed in terms of surface profiles, plastic deformation and elastic recovery. The results show that the nano-hardness at the center of grain is higher than that in the grain boundary region. All indents display an anisotropic elastic recovery, mainly occurring in the loading direction. The grain boundary has a better plasticity than the center of grain, which is probably due to a weaker inter-atomic bonding force at the grain boundary rather than the formation of glassy phase at intergranular region. In addition, indentation size effect in the center of grain and at grain boundary region are determined by the analysis of nano-hardness using Meyer’s law. A weaker indentation size effect in the grain boundary region is observed due to a smaller elastic recovery. [ABSTRACT FROM AUTHOR]

High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing. [ABSTRACT FROM AUTHOR]

An MgZnY fine-grained solidified alloy with a grain size of 16 μm was prepared by high-pressure solidification. The microstructure characteristics and hot compressive deformation behavior of the alloy solidified under high pressure were compared with the atmospheric-pressure solidified alloy by carrying out the unilateral compression tests under a strain rate in the range of 0.001-1.0 s and at a deformation temperature in the range of 523-573 K. The true stress-true strain curve of the high-pressure solidified alloy shows the typical dynamic recrystallization rheological curve. EBSD results show that when the deformation was carried out at 573 K, nearly 90% dynamic recrystallization occurred in the high-pressure solidified alloy, and the newly formed grains were distortionless and had low dislocation density. The high-pressure solidified alloy showed a double-peak basal texture at a strain rate of 1.0 s. The two peak points showed a maximum pole density of 9.88 and 7.91, less than that in atmospheric-pressure alloy. When the deformation was carried out at the following conditions: deformation temperature = 573 K, strain rate = 0.001, and true strain = 0.9, the average Schmid factor (SF) for basal slip of the grains in the high-pressure solidified alloy was 0.419, and SF value for basal slip in 91% grains was greater than 0.3. [ABSTRACT FROM AUTHOR]

The development of annealing twins was studied in chromium-nickel austenitic stainless steels subjected to cold or warm working. The annealing behavior can be characterized by an austenite reversal, recrystallization, and grain growth, depending on the deformation microstructures. The grain coarsening during recrystallization followed by a grain growth was accompanied by the development of twin-related Σ3 CSL boundaries. The fraction of Σ3 CSL boundaries and their density are defined by a unique parameter that is a relative change in the grain size, i.e., a ratio of the annealed grain size to that one evolved by preceding plastic working ( D/ D ). The fraction of Σ3 CSL boundaries rapidly increased at early stage of recrystallization and grain growth while the ratio of D/ D attained 5. Then, the rate of increase in the fraction of Σ3 CSL boundaries slowed down significantly during further grain coarsening. On the other hand, the density of Σ3 CSL boundaries increased to its maximum at a ratio of D/ D about 2.5 followed by a gradual decrease during subsequent grain growth. [ABSTRACT FROM AUTHOR]

In this study, effects of dynamically formed precipitates on the microstructure and texture evolution were investigated during the post-deformation annealing. Two ternary alloys of Mg, Al, and Sn were produced and deformed at 250 and 300 °C to form different amounts of strain-induced precipitates during deformation and different levels of dynamic recrystallization. Subsequent annealing at deformation temperatures was performed at various times for up to 4 h and recrystallization, grain coarsening, and precipitation behaviors were characterized. The deformed structures were all partially dynamically recrystallized exhibiting necklacing. Static recrystallization (SRX) progressed by the transformation of the coarse grained un-necklaced regions to fine grains. It was found that increasing levels of pre-existing precipitates on dynamic recrystallized grain boundaries inhibited SRX as well as grain coarsening, by precipitation pinning. Texture was weakened after a short time annealing compared to the as-deformed condition and high amount of precipitates at the grain boundary restricted the grain coarsening and kept the texture weaken associated with grain coarsening. [ABSTRACT FROM AUTHOR]

The effect of Al (0.4 and 1 wt%) addition on the hot deformation behavior of the Mg-3Sn-2Ca (TX32) alloy has been studied with the help of processing maps generated in the temperature and strain rate ranges of 300-500 °C and 0.0003-10 s. The deformed specimens have been examined as regards changes in texture and microstructure using electron back scatter diffraction and transmission electron microscopy, respectively. The map for the TX32 base alloy exhibited two dynamic recrystallization (DRX) domains in the temperature and strain rate ranges: (1) 300-350 °C and 0.0003-0.001 s, and (2) 390-500 °C and 0.005-0.6 s. While 0.4 wt% Al addition to TX32 did not result in any significant change in the processing map, the map for the alloy with 1 wt% Al (TX32-1Al) exhibited four domains in the ranges: (1) 300-325 °C and 0.0003-0.001 s, (2) 325-430 °C and 0.001-0.04 s, (3) 430-500 °C and 0.01-0.5 s, and (4) 430-500 °C and 0.0003-0.002 s. In the first three domains, DRX has occurred, whereas in the fourth domain, grain boundary sliding takes place causing intercrystalline cracking in tension. In Domain 1 for all the alloys, DRX has occurred predominantly by basal slip and recovery by climb as confirmed by the resulting basal texture and tilt type sub-boundary structure. In Domain 2 of the base alloy and Domain 3 of the alloy with 1 wt% Al, second-order pyramidal slip dominates associated with cross-slip which randomizes the texture, and forms tangled dislocations and twist type sub-boundaries in the microstructure. The addition of 1 wt% Al causes solid solution strengthening and results in Domain 2 of the map of TX32-1Al alloy and in this domain basal+prismatic slip dominate. [ABSTRACT FROM AUTHOR]

Various static and (equilibrium and non-equilibrium) dynamic molecular-level computational methods and tools are utilized in order to investigate the basic shock-wave physics and shock-wave material interactions in polyurea (a nano-phase segregated elastomeric co-polymer). The main goal of this investigation was to establish relationships between the nano-segregated polyurea microstructure (consisting of rod-shaped, discrete, so-called 'hard domains' embedded into a highly compliant, so-called soft matrix) and the experimentally established superior capability of this material to disperse and attenuate resident shock waves (e.g., those generated as a result of blast-wave impact). By analyzing molecular-level interactions of the shock waves with polyurea, an attempt was made to identify and quantify main phenomena and viscous/inelastic deformation and microstructure-altering processes taking place at the shock front, which are most likely responsible for the superior shock-mitigation behavior of polyurea. Direct molecular-level simulations of shock-wave generation and propagation in the 'strong-shock' regime are utilized in order to construct the appropriate shock-Hugoniot relations (relations which are used in the construction of the associated continuum-level material models). Extension of these relations into the 'weak-shock' regime of interest from the traumatic brain injury prevention point of view is also discussed. [ABSTRACT FROM AUTHOR]

The influence of grain boundaries and fine precipitation on the corrosion behavior was investigated in two model aluminum-lithium alloys, namely (in wt%) Al-1.6Li (lithium in a solid solution) and Al-2.3Li (lithium in the form of AlLi precipitation), subjected to three different severe plastic deformation (SPD) treatments which refined the microstructure of the alloys to the ultrafine grain size. The SPD techniques used in the experiments were equal channel angular pressing (ECAP), hydrostatic extrusion (HE), and extrusion-torsion (ET). The corrosion behavior was examined using a potentiodynamic polarization test, electrochemical impedance spectroscopy, and an immersion test followed by a SEM surface analysis. The electrochemical tests were conducted in a 0.1 M NaSO solution added with 100 ppm of Cl. The immersion tests (48 h) were performed in a 3.5% NaCl solution at room temperature. The results indicate that the pitting potential, pit number, and stability of the passive layer formed on the surface of the substrates undergo changes depending on the average grain size and the presence of precipitation or its lack. The corrosion resistance, examined in the solution mentioned above, appears to increase with decreasing average grain size. The ET method gave the microstructure with the lowest corrosion resistance. [ABSTRACT FROM AUTHOR]

Models for the nano/micro-structural deformation and mechanical properties of auxetic materials (i.e. materials with a negative Poisson's ratio) have been previously developed. However, most of these models have been two-dimensional, were usually designed specifically to describe some particular class of auxetic materials, and generally only described the behaviour of one particular plane whilst completely ignoring the out-of-plane behaviour of the material. A three-dimensional model has been developed which can be applied to several classes of auxetic materials, including microporous expanded polymers such as e-PTFE, e-UHMWPE and e-PA, body-centered cubic metals and foams. It is generalised that its underlying structure is not specific to a lengthscale or material as the previous list shows. The new model offers a better insight into the underlying principles behind the observed auxetic behaviour and offers a significant improvement in the agreement of the models with existing experimental data. It is shown that there are geometric limitations to the number of planes that can simultanesously display auxetic behaviour. This has ramifications on the design of ordered auxetic materials. [ABSTRACT FROM AUTHOR]

One of the most important characteristic features of a low-density thermally bonded non-woven material is its discontinuous and non-uniform microstructure, resulting in a complicated and unstable deformation mechanism of the material. In order to estimate the effects of such microstructure on the overall mechanical properties of the non-woven material, tensile tests are carried out for specimens with different systems of marks for both two principle directions-machine direction and cross direction-with images being captured with high-speed camera. The non-uniform strain fields are analysed based on the obtained images. Discontinuous finite-element models are developed to study the deformation mechanism of non-woven specimens in both principle directions, and the effects of the discontinuous and non-uniform fibrous network and different arrangements of bond points are analysed numerically. [ABSTRACT FROM AUTHOR]

In order to compare plastic deformation and microstructural evolution behavior deformation between equal channel angular pressing (ECAP) and forward extrusion (FE) processes, finite element analyses in associated with the mechanism of dislocation glide and cell formation have been employed. It was found from the simulation results that the ECAP process is superior to the FE process, in terms of strength, grain refinement and deformation homogeneity as well as repeatability due to the equal channels of entry and exit. [ABSTRACT FROM AUTHOR]

Microstructure evolution in an as-cast Na modified Al–7%Si (wt. pct.) alloy was examined during redundant and monotonic straining by repetitive equi-channel angular pressing (ECAP) under ambient temperature conditions, and during friction stir processing (FSP). Redundant straining during repetitive ECAP was accomplished by processing following route BC while monotonic straining employed route A. Single- and multi-pass FSP was conducted on this same as-cast material using an FSP tool having a threaded pin. The as-cast microstructure comprises equiaxed primary α dendrite cells embedded in the Al–Si eutectic constituent. The evolution of this microstructure during repetitive ECAP can be described by idealized models of this process. The primary and eutectic constituents can still be discerned and the Si particle distribution is not homogenized even during ambient temperature processing involving von Mises strains >9.0. In contrast, the primary and eutectic constituents cannot be distinguished in the stir zone after even a single FSP pass. Strain estimates based on the shape change of the primary α constituent indicate that the Si particle distribution has become homogeneous at local von Mises strains of 2.5–3.0 during the FSP thermomechanical cycle. Mechanical property data are consistent with strain path during SPD processing by repetitive ECAP and FSP. [ABSTRACT FROM AUTHOR]

The microstructure evolution of extruded Cu–0.18 wt% Zr polycrystals processed by high-pressure torsion (HPT) at room temperature at the pressure of 4 GPa and the different number of the HPT revolutions (i.e. different strain) was investigated using the combination of the electron back-scatter diffraction, microhardness measurements and the X-ray diffraction. A significant transition from the inhomogeneous microstructure after few HPT revolutions into the homogeneous equiaxed microstructure with increasing number of HPT rotations was observed. HPT straining leads to the grain size refinement by a factor more than 100 after the 25 HPT revolutions. Moreover, the EBSD revealed an increase in the fraction of high-angle grain boundaries (HAGBs) with increasing HPT straining reaching the value of 70% after 25 revolutions. Additionally, a slight increase of the twin-related CSL Σ3 grain boundaries occurred during the microstructure refinement. The microhardness measurements confirmed the billet radial inhomogeneity at early stages of the HPT straining, whereas with increasing number of the HPT rotations, causing the specimen fragmentation and homogenization, the microhardness values increased. The average crystallite size and the average dislocation density in individual specimens determined by the XRD diffraction were in the range of approximately 100–200 nm and 2 × 1015 m−2, respectively. Moreover, XRD measurements confirmed the absence of residual stresses in all specimens. [ABSTRACT FROM AUTHOR]

Ultrafine grain of pure copper 99.98% was produced by severe plastic deformation using the equal-channel angular pressing (ECAP) method. Copper samples were ECAPed from 1 to 8 passes following route BC; fine grain sizes of 250 nm were developed after eight passes. Important enhancement in the mechanical strength properties was obtained. Subsequent heat treatments (HT) were carried out to evaluate the thermal stability of the grains of the ECAPed samples. Microstructure and mechanical properties were evaluated to determine the recovery and recrystallization temperatures. Differential scanning calorimetry (DSC) tests were conducted to all samples in order to determinate these temperatures. The activation energy of the recrystallization process was also determined by the DSC technique and good correlation was obtained with the microstructure and mechanical properties. An important decrease in the mechanical properties and an increasing heterogeneous grain size distribution were observed when heat treatments were performed. [ABSTRACT FROM AUTHOR]

AZ31 magnesium alloy sheets were processed by normal rolling (NR), one-pass equal channel angular rolling (1P-ECAR), and cross equal channel angular rolling (C-ECAR) at 400 °C on a die with 105 ° channel angle. The microstructure, texture, and tensile properties of sheets were measured. The results show that ECAR processing can weaken the basal plane texture, thus obviously improve the mechanical properties. The yield ratio σs/σb decreases and strain hardening exponent n increases along rolling direction (RD) during ECAR, which means that the uniform plastic formability is enhanced. After C-ECAR, the mechanical properties along both the RD and transverse direction (TD) are improved. Different twinning types, fine $$ \left\{ {10\overline{1} 1} \right\} $$ contraction twinning in the NRed sheets and coarse $$ \left\{ {10\overline{1} 2} \right\} $$ extension twinning in the ECARed sheets, were observed. The easier activation of $$ \left\{ {10\overline{1} 2} \right\} $$ twinning and basal 〈a〉 slip leads to the lower yield strength of the ECARed sheets. Dynamic recrystallization (DRX) during the rolling process has great effect on the microstructure of the as-deformed and annealed sheets. The annealed C-ECARed sheets have significant finer and homogenous grains than the annealed NRed sheets, which is attributed to the rarely DRX process during ECAR. The average grain sizes of the annealed C-ECARed samples and NRed samples are 14 and 24 μm, respectively. [ABSTRACT FROM AUTHOR]

Common to metals deformed to high strains is a very fine microstructure, high strength, and limited ductility. Structure and property optimization by annealing after deformation must, therefore, be explored. In the present study, commercial purity aluminum has been annealed after cold rolling to ultrahigh strains up to $$ \varepsilon _{{{\text{vM}}}} = 6.2 $$ and annealing processes have been studied in terms of recovery and conventional recrystallization. These processes have been analyzed by isochronal and isothermal annealing in the temperature range 140–420 °C. It has been found that the recrystallization temperature is a little affected by the rolling strain, whereas the rate of recovery and the temperature range over which recovery takes place increase significantly as the strain is increased. These observations are discussed as to how they can guide studies of nanostructured metals processed by plastic deformation. [ABSTRACT FROM AUTHOR]

An Mg–12Gd–3Y (wt%) alloy was prepared by conventional casting method using permanent steel mold. Then this alloy was subjected to hot processing, involving hot extrusion and free forging. Tensile strength at room temperature can be improved, with the highest ultimate tensile strength (UTS) value of 390.2 MPa achieved by hot extrusion in comparison to that of as-cast alloy. Temperature dependence of tensile strength is distinguishable for the as-extruded alloy, while the relative stability in UTS values of the alloy after being freely forged should be ascribed to the inter-crossing among deformation bands located at various orientations and the accommodation effect of twining lamellas resulting from forging process on plastic deformation during tensile test at elevated temperatures. Further annealing after hot processing can only have adequate influence on the tensile strength of as-forged alloy. For the alloy freely forged and annealed at 523 K for 4 h, the highest UTS (441.1 MPa) at room temperature is found, which should be mainly related to an evolution from the original as-forged microstructure with subgrains to a more stable combination of large and refined grains through dynamic recrystallization during free forging, and the stress at offset yield YS (384.3 MPa) is also comparable to that relatively high value of 396.9 MPa after solution treatment and isothermal aging of the as-cast alloy. [ABSTRACT FROM AUTHOR]

The mechanical properties of grain boundaries (GBs) and the development of grain-boundary sliding (GBS) were studied in the pure Zn using precision microindentation technique, optical, electron and atomic-force microscopy. Results have shown the different dependencies of the microhardness values on the indentation depth for GBs and individual grains. When the size of the plastic zone around the imprint was comparable to the grain size, GBs acted as barriers for dislocation sliding bands and twins. With applying the higher load, more grains were involved in the process of deformation, but microhardness did not increase. That was explained by the activation of GBS, leading to the relaxation processes. In its turn, the microhardness values measured at low loads in the vicinity to GBs and triple junctions (TJs) were higher than those measured in the grain interior. Thus, movement of the ensemble of defects to the GBs during microindentation is the activating factor for GBS in polycrystalline Zn. At the same time, during spreading of the deformation at low loads in the vicinity to GBs the activation of GBS was not observed. [ABSTRACT FROM AUTHOR]

A compressive split-Hopkinson pressure bar apparatus and transmission electron microscopy (TEM) are used to investigate the deformation behaviour and microstructural evolution of Ti–15Mo–5Zr–3Al alloy deformed at strain rates ranging from 8 × 102 s−1 to 8 × 103 s−1 and temperatures between 25 °C and 900 °C. In general, it is observed that the flow stress increases with increasing strain rate, but decreases with increasing temperature. The microstructural observations reveal that the strengthening effect evident in the deformed alloy is a result, primarily, of dislocations and the formation of α phase. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. Additionally, the square root of the dislocation density varies linearly with the flow stress. The amount of α phase increases with increasing temperature below the β transus temperature. The maximum amount of α phase is formed at a temperature of 700 °C and results in the minimum fracture strain under the current loading conditions. [ABSTRACT FROM AUTHOR]

Microstructure and fracture behavior of brazed joint between commercially pure titanium and low carbon steel using silver (Ag–34Cu–2Ti) and copper (Cu–12Mn–2Ni ) based alloys have been characterized to determine the effect of brazing parameters and chemical composition on the strength of brazed joints. It is found that the shear strength of brazed joints strongly depends on the lap width. Furthermore, the fracture path and the value of shear strength significantly changed with the type of filler alloy. The two filler metals showed metallurgical interaction with steel and titanium forming different kinds of intermetallic compounds such as CuTi, Cu2Ti, and FeTi with silver based filler and Ti2Cu, FeTi and TiCuFe with copper based filler. [ABSTRACT FROM AUTHOR]

The effects of strain and temperature on the microstructure and the detailed structure of dislocation walls in compressed pure polycrystalline copper were systematically studied. The microstructure observed consisted of dislocation cells and second generation microbands (MB2) and is presented in a microtructural map. The detailed structure of the cell’s boundaries evolves with increasing strain and/or temperature from tangled dislocations into arrays of parallel dislocations. Interplay between strain and temperature controls the microstructure and the detailed structure of the dislocation boundaries. Above 0.5 Tm only MB2 are observed; a different type of MB2 is also observed, one order of magnitude wider than the one observed at the lower temperature. With increasing strain and temperature the MB2 density increases. It seems that dislocation cells and MB2 are competitive dislocation patterns and at elevated temperatures the MB2 is the preferred dislocation pattern. [ABSTRACT FROM AUTHOR]

The shear strength of pure nickel (Ni), and its alloy, Ni–60Co (by wt%), has been determined during one-dimensional shock loading in the impact stress range 0–10 GPa. The influence of the reduced stacking fault energy (SFE) for the Ni–60Co has been investigated. The shear strength (τ) and the lateral stress (σ y ) both increase with the impact stress for each material. The shear stress has been found to be higher in the nickel than in the alloy. The progressive decrease of the lateral stress behind the shock front indicates an increase of the shear strength. A more complex mechanism of deformation has been found for the alloy since twin formation has been observed in the microstructure, while none has been seen in nickel. It is thought that mechanical twinning plays a predominant role in the deformation mechanism of the alloy resulting in the reduction of the material strength. [ABSTRACT FROM AUTHOR]

The microstructure and texture evolution of a commercially pure titanium sheet during cold-rolling is investigated in detail by X-ray diffraction and by orientation imaging in the FEG-SEM and in the TEM. The experimental data are compared with simulation results obtained by a viscoplastic self-consistent model. The aim of this work is to provide with a detailed description of the fine scale deformation structures obtained after 80% cold-rolling and to identify the mechanisms by which these structures form. Such a detailed investigation is nowadays possible thanks to high spatial resolution orientation imaging techniques. This work highlights the important role of mechanical twinning as one of the grain fragmentation mechanisms. The microstructure obtained after 80% thickness reduction can be separated into two distinct parts: 85 vol.% of the material is fine-subdivided with highly misoriented sub-micron features and the others 15 vol.% consist in lamellar structures formed in grains initially oriented in a particular region of orientation space, which have not undergone twinning. The influence of these structures on recrystallization mechanisms are also discussed. [ABSTRACT FROM AUTHOR]

There is an increasing interest in applying back pressure during equal channel angular pressing (ECAP) to improve the process for better control of microstructure and property. The effect of increasing back pressure on deformation characteristics during ECAP such as the plastic deformation zone (PDZ) size and strain rate distribution in the PDZ, size of the corner gap and strain distribution on the longitudinal section were analysed by finite element analysis for both the quasi-perfect plastic and strain hardening materials. This investigation revealed that the back pressure influence very differently the PDZ of the quasi-perfect plastic and strain hardening materials. Many beneficial effects of back pressure were observed in the strain hardening material, with reduced PDZ size, dramatically reduced corner gap, and more uniform strain distribution. For the quasi-perfect plastic material, however, the application of increasing back pressure leads to broadening of PDZ and a decrease in strain rate homogeneity. [ABSTRACT FROM AUTHOR]

Mounting evidence is pointing to some emerging novel behaviors of metals with ultrafine-grain (UFG) and/or nanocrystalline (NC) microstructures. One such novel behavior is related to the thermodynamic and kinetic aspects of plastic response in the UFG/NC regime. Two inter-related parameters, viz., the strain rate sensitivity (SRS) and the activation volumes of plastic deformation, are used as fingerprints for the thermodynamics and kinetics of plastic deformation. Changes of these parameters with grain size may indicate transition of plastic deformation mechanisms. Therefore, investigations of these phenomena may bring out new strategies for ingenious design and synthesis of UFG/NC materials with desirable properties. In this article, we present a critical review on the experimental results and theories associated with the SRS of UFG/NC metals with different lattice structures, and the influences on some constitutive responses. [ABSTRACT FROM AUTHOR]

A review is provided of the use of analytical models and two dimensional (2D) and three dimensional (3D) microstructure based FEM models to accurately predict the properties of particle reinforced composite materials. It is shown that analytical models do not account for the microstructural factors that influence the mechanical behavior of the material. 2D models do capture the anisotropy in deformation behavior induced by anisotropy in particle orientation. The experimentally-observed dependence of Young's modulus and tensile strength is confirmed by the 2D microstructure-based numerical model. However, because of the 2D stress state, a realistic comparison to actual experimental values is not possible. A serial sectioning process can be used to reproduce and visualize the 3D microstructure of particle reinforced metal matrix composites. The 3D microstructure-based FEM accurately represents the alignment, aspect ratio, and distribution of the particles. Comparison with single particle and multiparticle models of simple shape (spherical and ellipsoidal) shows that the 3D microstructure-based approach is more accurate in simulating and understanding material behavior. [ABSTRACT FROM AUTHOR]

Effect of orientation on microstructure and mechanical properties of thermoplastic starches with different amylose/amylopectin ratios was studied to understand the relationship between structure and properties in starch-based materials. Hydrogen bonds and the highly branched microstructure in amylopectin resist the orientation of the polymer chains. The unique microstructures of amylopectin form gel-balls and super-globes after gelatinization. A gel-ball contains mainly the chains from same sub-main chain in amylopectin, and remains in regular pattern and keeps a certain “memory”. The gel-balls and super-globes can be deformed under shear stress. However, the deformation does not alter the orientation ofthe polymer chains inside the gel-balls significantly. Orientation increases both modulus and yield stress but decreases the elongation, which is mainly contributed to by the orientation of amorphous phase. The oriented super-globe has large interior stress after retrogradation (crystallization) that results in micro-cracks and poor mechanical properties. [ABSTRACT FROM AUTHOR]

Microstructure, high-temperature compressive and tensile deformation, and corrosion property of multi-phase alloys based on Ni3Al-Ni3T1-Ni3Nb pseudo-ternary alloy system were investigated. The microstructures of these alloys were largely dependent on alloy composition but independent of annealing temperature. Alloys composed of multi-phase microstructures of L12, D024 and D0a showed substantially enhanced compressive yield stress as well as a certain amount of compressive plasticity at whole temperature, while they did not show reasonable tensile elongation at whole temperature. Also, alloys composed of lamellar-like multi-phase microstructures are effective in enhancing compressive yield stress particularly at high temperature. Multi-phase alloys with low Nb contents have good corrosion resistance, especially in high concentration of sulfuric acid. [ABSTRACT FROM AUTHOR]

The deformation mechanism in high-strain-rate superplastic P/M7475 before and after continuous dynamic recrystallization (CDRX) was investigated. The recrystallization process in P/M7475 differed from that in conventional superplastic material, I/M7475. In I/M7475, the fine-grained microstructure was obtained by static recrystallization before deformation. On the other hand, the substructure in P/M7475 evolved into fine grains during deformation by CDRX. The percentage of high-angle and random boundaries was low at an initial stage of deformation. However, it increased with strain in P/M7475. The microstructural change in P/M7475 influenced a deformation mechanism and affected grain boundary sliding (GBS). The ratio of contribution of GBS to total elongation was low at an early stage of deformation in P/M7475. However, it increased with deformation progressed. It is suggested that the deformation behavior in P/M7475 changed from dislocation creep to superplasticity as the dominant deformation mechanism changed to GBS. The activation energy for superplastic flow in P/M7475 was close to that for lattice self-diffusion in pure aluminum. It is therefore concluded that the dominant deformation mechanism after CDRX in P/M7475 is GBS accommodated by dislocation movement controlled by lattice self-diffusion, similar to that in I/M7475. [ABSTRACT FROM AUTHOR]

Chromium tanned bovine leather has been dried under uniaxial strain and its collagen fibre distribution examined using high-angle X-ray diffraction. Microstructural modelling of the fibre kinematics showed that under large-strain deformation (30%) the fibres behave in a psuedo-affine manner. At decreasingly lower strains the fibre re-orientation is seen to progressively deviate from the pseudo-affine prediction; an observation which can be understood in terms of a combination of fibre-fibre adhesion and changes in fibre substructure. The material was also subjected to mechanical testing and tensile data is presented here which indicates how fibre orientation affects tensile modulus. This work represents the first quantitative microstructural model for collagen fibre distribution in strained leather. [ABSTRACT FROM AUTHOR]

The accommodation of severe plastic deformation in impact crater formation, ballistic rod flow and penetration in thick targets, shaped charge formation, and a variety of friction-stir welding and processing is shown to occur by microstructure refinement, particularly dynamic recrystallization in the development of localized or overlapping adiabatic shear bands. Optical metallography and transmission electron microscopy observations of solid-state flow in adiabatic shear zones are compared to illustrate these mechanisms which can often involve intermixed microstructural regimes composed of recovery, recrystallization, and grain growth phenomena. [ABSTRACT FROM AUTHOR]