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It is vital to reveal the effect of microstructure features on the corrosion behavior of pure aluminum anode in alkaline electrolyte for Al-air batteries. In this paper, we extensively studied the influence of mechanical deformation on the corrosion microstructure and then corrosion features of pure aluminum anode. The results demonstrate that the cold-rolling deformation could facilitate the grain size refinement of pure aluminum. Surprisingly, the aluminum anodes with smaller grain sizes and larger grain boundary areas could effectively improve the corrosion resistance. The further characterization of the microstructure indicates that the deformation is capable of causing the fracture of the cathodic secondary phase precipitate clusters thus weakening the galvanic corrosion effects. The results of this paper could gain insights into the design and processing of pure aluminum for Al-air battery. [ABSTRACT FROM AUTHOR]

In this paper, the deformation mechanisms of a Fe–2.25%Cr–1%Mo (P22) steel are studied after tensile tests at room temperature (RT) and 550 °C (HT), creep-fatigue tests at 550 °C and stress relaxation test at 550 °C (HTSR). The RT, HT and HTSR tests produced permanent strain of about 2.5% by different processes. Deformation features such as the orientation of the grains, local misorientation, grain boundary type and distribution, etc., were characterized using electron backscatter diffraction. Transmission electron microscopy was done subsequently to obtain greater insight into the dislocation substructures. The as-received sample had a ferritic–bainitic microstructure, and a large amount of local misorientation was found in the bainite, indicating plastic strain due to phase transformation. After tensile strain to 2.5% at room temperature, the dislocations formed very small substructures (~100–200 nm) in the ferrite grains, and most of the retained plastic strain seemed to be concentrated in the bainite after deformation. Both the ferrite and bainite showed much lower local misorientation and dislocation wall content after a tensile test to 2.5% strain at 550 °C. Compared to the RT tensile sample, after creep-fatigue at 550 °C, the substructures in ferrite opened up considerably and formed small-angle grain boundaries, with clean areas as large as 20–25 μm. After stress relaxation at 550 °C, the ferrite displayed even less substructure, while the bainite seemed to have greater amounts of local misorientation than in the creep-fatigue case. However, the degree of misorientation was less pronounced than in the room temperature tensile case. These results have been discussed with respect to the causes behind the phenomena observed herein and their possible effects on mechanical behaviour. [ABSTRACT FROM AUTHOR]

Different mechanisms have been suggested by many authors as controlling the rate of superplastic flow in different materials. From the viewpoint of computational effort and aesthetics, it is highly desirable to explain the phenomenon, independent of the material/system considered, on a common basis. With this aim, a mesoscopic grain boundary sliding-controlled deformation model was proposed sometime ago as being responsible for superplastic flow in materials of different kinds. In this paper, a rigorous numerical computational procedure for the experimental validation of the model, which takes into account all the physical requirements of the model, is presented. The soundness of the new procedure is established by analysing the experimental data pertaining to many systems belonging to different classes of materials, and matching the results of the analysis with the experimental findings. [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]

This paper describes fabrication of Si nanograins through allotropic phase transformation by concurrent application of high pressure and intense straining using high-pressure torsion (HPT). Single-crystalline Si(100) wafers were processed by HPT under a pressure of 24 GPa at room temperature. X-ray diffraction and Raman analysis revealed that the HPT-processed samples were composed of metastable Si-III and Si-XII phases and amorphous phases in addition to the original diamond-cubic Si-I phase. It was found that nanograins formed because the Si-I diamond phase had transformed to high-pressure phases (Si-II, Si-XI, and Si-V) having metallic nature, and it then became easier to generate a high density of dislocations to form grain boundaries. The high-pressure phases were further transformed to the Si-XII and Si-III phases via the Si-II phase upon unloading and they existed as metastable phases at ambient pressure. Subsequent annealing at 873 K gave rise to reverse transformation to Si-I but with nanograin sizes. Although no appreciable photoluminescence (PL) peak was observed from the HPT-processed sample, a broad PL peak centered around 600 nm was detected from the annealed sample due to quantum confinement in the Si-I nanograins. [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]

During the past decade, fabrication of bulk nanostructured metals and alloys using severe plastic deformation (SPD) has been evolving as a rapidly advancing direction of nanomaterials science and technology aimed at developing materials with new mechanical and functional properties for advanced applications. The principle of these developments is based on grain refinement down to the nanoscale level via various SPD techniques. This paper is focused on investigation and development of new SPD processing routes enabling fabrication of fully dense bulk nanostructured metals and alloys with a grain size of 40–50 nm and smaller, namely, SPD-consolidation of powders, including nanostructured ones, as well as SPD-induced nanocrystallization of amorphous alloys. We also consider microstructural features of SPD-processed materials that are responsible for enhancement of their properties. [ABSTRACT FROM AUTHOR]

It is now recognized that grain boundary sliding (GBS) is often an important mode of deformation in polycrystalline materials. This paper reviews the developments in GBS over the last four decades including the procedures available for estimating the strain contributed by sliding to the total strain, ξ, and the division into Rachinger GBS in conventional creep and Lifshitz GBS in diffusion creep. It is shown that Rachinger GBS occurs under two distinct conditions in conventional creep depending upon whether the grain size, d, is larger or smaller than the equilibrium subgrain size, λ. A unified model is presented leading to separate rate equations for Rachinger GBS in power-law creep and superplasticity. It is demonstrated that these two equations are in excellent agreement with experimental observations. There are additional recent predictions, not fully resolved at the present time, concerning the role of GBS in nanostructured materials. [ABSTRACT FROM AUTHOR]

Severe plastic deformation through high-pressure torsion is used to refine the grain structure of the Mg–Al–Zn alloy down to ~ 140 nm and low temperature annealing is used to produce samples with different grain sizes, within the ultrafine range. The mechanical behavior is investigated using different testing techniques including microhardness, indentation creep, plane-strain compression, creep, and miniaturized tensile testing. The results allow a comprehensive analysis of the deformation mechanism. It is shown that the relationship between the flow stress and the inverse of the square root of the grain size is not linear in the ultrafine grained range and depends on temperature and strain rate. Grain refinement hardening and grain refinement softening can be observed at different temperatures and strain rates. There is an increase in strain-rate sensitivity and a decrease in apparent activation volume with decreasing the grain size. These experimental observations agree with the deformation mechanism of grain boundary sliding provided the thermal contribution for the threshold stress is taken into account. [ABSTRACT FROM AUTHOR]

An Al-6 %Cu-0.4 %Zr alloy was processed by high-pressure torsion to produce an ultrafine-grained structure with a grain size of ~200 nm at the steady-state level where the hardness remains constant with straining. Tensile testing showed that a maximum elongation of ~530 % was attained at 673 K with an initial strain rate of 1 × 10 s. Evaluation of the strain-rate sensitivity and the activation energy for the deformation confirmed that grain boundary sliding through grain boundary diffusion is the rate-controlling process for the superplastic deformation. [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]

Understanding the interaction between heterogeneous precipitates and grain boundaries (GBs) is of great significance for tailoring the stability and mechanical properties of nanograined materials. In this work, the nanoscale interaction between the cylindrical precipitate and the migrating GB is investigated by atomic simulation. The results show that the resistance for GB migration can be increased by decreasing the direction angle α (the angle between the axis of the precipitate and the tilt axis of GB). For the larger precipitate, the influence of direction angle is more pronounced. With the increase in shear strain, the interaction between the specific precipitate and GB changes the material deformation mechanism from "GB migration" to "GB migration accompanied with activated dislocations or GB deformation," which contributes to the softening of the material. By simultaneously tuning the direction angle and size of heterogeneous precipitates, the GB deformation can be strongly inhibited and the stability of GBs can be significantly improved. [ABSTRACT FROM AUTHOR]

Room temperature torsional deformation behaviour of bicrystal aluminium specimens (corresponding to Σ5 family) is studied by the application of constant twist rate using molecular dynamics simulations by employing the (embedded atom method) EAM potential. To simulate the torsional loading, periodic boundary condition is employed in x-direction, whereas shrink-wrapped boundary condition is applied in y- and z-directions. A constant twist rate of 1°/ps has been applied at either end of the samples in opposite directions. The variation of potential energy as a function of relative rotation between the ends of the specimen is recorded. The evolution of different types of dislocation and characteristics behaviour due to interactions among dislocations during deformation has been analysed. The populations of Shockley partial dislocations, dislocation loops, dislocation locks, and dislocation junctions increase as the torsional deformation progresses. The structural variations occurred in the specimen are explained with the aid of defect evolutions (such as vacancies population and amorphous atoms percentage as a function of torsion angle), and the grain boundary migration and grain rotation processes are described with atomic snapshots. Additionally, we have tried to correlate trends between grain boundary energy and various deformation mechanisms. [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]

The {332}<113> twin-twin and twin-dislocation pairs at various grain boundaries were systematically examined by using electron backscattered diffraction technique in a slightly deformed β-type Ti-15Mo-5Zr alloy. The effect of grain boundary angle on twinning transfer behavior in neighboring grain was quantitatively analyzed in terms of strain accommodation combined macroscopic Schmid law. The twinning transfer occurred readily at the low angle grain boundaries without significant local stress concentration and formed a twin-twin pair dominated by applied stress, i.e., macroscopic Schmid law. At the high angle grain boundaries, it often resulted in a twin-twin pair with non-Schmid factor twinning variant or a twin-dislocation pair with geometrically necessary dislocations at the boundary area dominated by the strain accommodation. The activation of non-Schmid factor twinning variant and slip system in neighboring grain was due to their high accommodative capacity while releasing the local internal stress concentration, which was caused by the twinning transfer at high angle grain boundaries. [ABSTRACT FROM AUTHOR]

In this study, experimental data have been obtained which reveal taking place of complex physical processes under conditions of the structural superplasticity not only in the grain boundary, as it is commonly believed, but also in the grain body. It was established for the first time that superplastic deformation of the eutectic alloys is accompanied by significant changes in their Young’s moduli. It was demonstrated that under superplastic deformation the observed changes of the elastic properties of the eutectic Sn-38wt%Pb alloy under study are caused mainly by the decomposition of supersaturated solid solutions on the basis of the alloy components and the relaxation of internal stresses. It was also found that the viscous dislocation-diffusion non-conservative flow is actively developing in the eutectic alloys under conditions of superplasticity, in contrast to the existing ideas about grain boundary sliding as the main mechanism of the matter transport. The experimental results obtained are important for the deeper understanding of the physical nature of the structural superplasticity effect. [ABSTRACT FROM AUTHOR]

Due to forming processes of the upcoming manufacturing technology of sheet-bulk metal forming, where bulk forming operations are applied to sheet metal, ductile damage occurs due to high triaxial stress and strain states in the material. To consider this type of damage in models for an optimized process design, a description of the critical material state is required, taking the main damage mechanisms into account. In comparison to single-phase materials, where voids nucleate mainly at grain boundaries and triple junctions, in dual-phase materials also phase boundaries or the movement of different hard phases due to forming process contribute to ductile damage. In this study, the mechanisms of nucleation and growth of voids were analyzed in a dual-phase steel DP600 at different strain states and forming temperatures. By specimen preparation using ion-beam slope cutting and scanning electron microscopy, it was possible to observe at nano- and microscale voids, cracks, and elements of deformation reliefs. A correlation between the shape of voids and their location in the crystal lattice was found, whereby the mechanisms of their nucleation, growth, and coalescence could be described. [ABSTRACT FROM AUTHOR]

Free surface effects on rotational deformation mediated by grain boundary dislocations in nanocrystalline materials are theoretically described. The critical stresses and characteristic geometric parameters for the rotational deformation occurring in nanocrystalline materials near their free surfaces are calculated and compared with those specifying the rotational deformation in bulk regions. The role of the free surface effects in the interpretation of electron microscopy data for plastically deformed nanocrystalline materials is discussed. [ABSTRACT FROM AUTHOR]

The formation of Mg segregations at and near deformation-distorted grain boundaries (GBs) in ultrafine-grained Al-Mg alloys is theoretically described as a process enhanced by stress fields of extrinsic dislocations existing at such GBs. The equilibrium Mg concentration profiles near low-angle and high-angle GBs containing extrinsic dislocations are calculated. The results of the calculations explain the experimental observations (reported in the scientific literature) of spatially inhomogeneous Mg segregations characterized by high Mg concentrations at and near GBs in ultrafine-grained Al-Mg alloys processed by severe plastic deformation. [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]

Structural features, microhardness, and mechanical properties of three binary Al-Mg alloys and a commercial AA5182 alloy subjected to high pressure torsion at room temperature were comparatively investigated using transmission electron microscopy, high-resolution transmission electron microscopy, and quantitative X-ray diffraction measurements. Average grain sizes measured by dark-field images are in the range 71-265 nm while the sizes of coherent domains decreased tremendously from 86 to 46 nm as the Mg content increased from 0.5 to 4.1 wt%. The average dislocation density in the deformed alloys is in the range 0.37 × 10-4.97 × 10 m. Both the microhardness and tensile strength of all the deformed alloys increased dramatically as compared to the undeformed counterparts. The yield strength with values ranging from 390 to 690 MPa in the deformed alloys is typically five to seven times higher than that of the same undeformed alloys. Calculations based on the Hall-Petch and Taylor equations suggest that the strengthening mechanisms contributing to the very high strength may depend not only on the conventional mechanisms of grain size strengthening and dislocation strengthening, but also on the additional mechanisms related to the contributions from stacking faults and nanotwins, and nonequilibrium GBs observed in the deformed alloys. [ABSTRACT FROM AUTHOR]

Experiments were conducted to evaluate the microstructures and mechanical properties of a Cu-0.1 % Zr alloy processed using two different techniques of severe plastic deformation: equal-channel angular pressing (ECAP) and high-pressure torsion (HPT). The samples were processed at room temperature through ECAP for eight passes or through HPT for 10 turns. The results show HPT is more effective both in refining the grains and in producing a large fraction of grain boundaries having high angles of misorientation. Both procedures produce reasonably homogeneous hardness distributions but the average hardness values were higher after HPT. In tensile testing at 673 K, the highest strength and ductility was achieved after processing by HPT. This is attributed to the grain stability and high fraction of high-angle grain boundaries produced in HPT. [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]

In this article, we report on the application of our spherical nanoindentation data analysis protocols to study the mechanical response of grain boundary regions in as-cast and 30% deformed polycrystalline Fe-3%Si steel. In particular, we demonstrate that it is possible to investigate the role of grain boundaries in the mechanical deformation of polycrystalline samples by systematically studying the changes in the indentation stress-strain curves as a function of the distance from the grain boundary. Such datasets, when combined with the local crystal lattice orientation information obtained using orientation imaging microscopy, open new avenues for characterizing the mechanical behavior of grain boundaries based on their misorientation angle, dislocation density content near the boundary, and their propensity for dislocation source/sink behavior. [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]

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 nanostructure and the carbon distribution in a pearlitic steel processed by torsion under high pressure was investigated by three-dimensional atom probe. In the early stage of deformation (shear strain of 62), off-stoichiometry cementite was analysed close to interphase boundaries and a strong segregation of carbon atoms along dislocation cell boundaries was observed in the ferrite. At a shear strain of 300, only few nanoscaled off-stoichiometry cementite particles remain and a nanoscaled equiaxed grain structure with a grain size of about 20 nm was revealed. 3D-AP data clearly point out a strong segregation of carbon atoms along grain boundaries. The influence of this carbon atom segregation on the nanostructure formation is discussed and a scenario accounting for the nanocrystallisation during severe plastic deformation is proposed. [ABSTRACT FROM AUTHOR]

The unique deformation behavior of nanocrystalline materials is considered to be caused by suppression of conventional lattice dislocation slip (which dominates in coarse-grained materials) and effective action of alternative deformation mechanisms occurring through motion of grain boundary defects. A significant role of grain boundary sliding in deformation processes in nanocrystalline materials was shown in models and was revealed experimentally. [ABSTRACT FROM AUTHOR]

High-temperature tensile deformation behavior of high-purity HIPed silicon nitride material was investigated in the temperature range between 1600°C and 1750°C. Recoverable anelastic and non-recoverable deformation was observed in high-purity HIPed silicon nitride. A power-law deformation model analogous to rheological models was used to distinguish the different deformation components. A stress exponent n = 1.64 and an activation energy Q1 = 708 kJ/mol was determined for the non-recoverable deformation. For the anelastic deformation a stress exponent p = 4 and an activation energy Q3 = 619 kJ/mol was observed. Diffusional creep and grain boundary sliding with the accomodation process responsible for the anelastic component are discussed as deformation mechanisms. [ABSTRACT FROM AUTHOR]

A new technique for Scanning Electron Microscopy (SEM), which provides a mesoscopic coordinate system inscribed on the surface of the center of a tension test specimen has been proposed. Such technique allows to establish in a repeatable way any angle relative to any axis of any coordinate system, or distances between grains, or to measure local or global true deformation in parallel or perpendicular directions relatives to the tension axis. The application of such technique for a Zn-20.2%Al - 1.8% Cu alloy tension test specimen with a total length between shoulders of 412 μm length and a gage length of 371 μm, deformed at room temperature, allows to obtain: The mapping of the granular flow during superplastic deformation; this result is in qualitative agreement with similar flow-diagrams obtained previously by Ashby and Verral ( Acta Metall. 21, 1973, p. 149) from their oil-emulsion model. [ABSTRACT FROM AUTHOR]

The γ ↔ α2 phase transformation in fractured high temperature stress rupture Ti-48Al-2Nb(at.%) alloy has been studied by analytical electron microscopy. α2 and γ phases were found at grain boundaries. α2 layers that suspended in γ layers and interfacial ledge higher than 2 d(111)γ at γ/α2 interfaces were observed in the lamellar grains. These facts indicated that γ ↔ α2 phase transformation and dynamic recrystallization have occurred during high temperature stress rupture deformation. It can be concluded that deformation induced γ ↔ α2 phase transformation and dynamic recrystallization resulted in the presence of γ particles at grain boundaries. A structural and compositional transition area between deformation-induced α2(or γ) and its adjacently original γ(or α2) phases was found by HREM and EDS and is suggested as a way to transform between γ and α2 phase during high temperature stress rupture deformation. The transition area was formed by slide of partial dislocations on close-packed planes and diffusion of atoms. [ABSTRACT FROM AUTHOR]

The low-cycle fatigue (LCF) behaviour of a Ni–Fe base superalloy Inconel 718 was studied at room temperature. Deformation mechanisms operating at different strain amplitudes were established by detailed transmission electron microscopy at various fractions of fatigue life. It was observed that there was an increase in the number of microtwins present in the microstructure with increase in number of cycles, N, at low strains, where very little slip activity was identified. The undeformed specimens contain a number of annealing twins in the microstructure which increased in number with increase in cyclic deformation. Electron microscopy also revealed the existence of grain-boundary ledges in the undeformed specimens. A typical region of the grain-boundary area of the deformed samples showed a front of microtwins in their “nascent” state, advancing from one grain into the other. It was concluded that in the low-strain regime, cyclic deformation was accommodated by forming new microtwin interfaces emerging from grain-boundary ledges present in the undeformed specimens. [ABSTRACT FROM AUTHOR]