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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]

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]

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]