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Abstract Zirconia-based shape memory ceramics (SMCs) exhibit anisotropic mechanical response when undergoing elastic deformations as well as during austenite–martensite phase transformation. This behavior results in different types of strain incompatibility at grain boundaries, which we study here using a micromechanical model. A single-crystal model is implemented to provide a full mechanistic three-dimensional description of the anisotropic elastic as well as martensitic transformation stress–strain response, including non-Schmid behavior caused by the significant volume change during martensitic transformation. This model was calibrated to and validated against compression tests of single-crystal zirconia micro-pillars conducted previously, and then used to model bi-crystals. Upon the introduction of a grain boundary, the simulation provides detailed information on the nucleation and evolution of martensite variants and stress distribution at grain boundaries. We identify bi-crystal configurations which result in very large stress concentrations at very low deformations due to elastic incompatibility, as well as others where the elastic incompatibility is relatively low and stress concentrations only occur at large transformation strains. We also show how this approach can be used to explore the misorientation space for quantifying the level of elastic and transformation incompatibility at SMCs grain boundaries. Graphical abstract Micromechanics models provide insights on grain boundary elastic and phase transformation strain incompatibility in shape memory zirconia

ZnO nanorod-based UV photosensing devices are synthesized using one-pot synthesis method, and their sensing properties are studied with the variation of nanorod growth area. With the variation of electrode position for the maximum growth area, the UV photosensing properties are thoroughly examined. Structural, morphological and optical properties are studied using XRD, FEG-SEM, FEG-TEM and UV–VIS spectroscopy. AC electrical conductivity, dielectric measurements and modulus spectroscopy at room temperature in a frequency range from5 Hz to 5 MHz are performed. During the electrical conduction processes in the sample, the physical parameters of ZnO nanostructures such as dielectric constant, relaxation frequency and electrical conductivity are examined at dark and UV-illuminated condition. The dependence of conductivity, dielectric constants and modulus with frequency and UV on–off conditions are discussed. The correlation between response and recovery time with growth surface area of ZnO nanostructure is established with the help of complex impedance spectroscopy. The imaginary part of electrical modulus versus angular frequency is drawn, and the value of stretch exponent (β) is calculated for maximum and minimum surface area under dark and UV-illuminated condition from where the type of relaxation process is studied.

The influence of cold rolling deformation on the electrochemical and corrosion behavior of 654SMO super-stainless steel in a high-temperature 3.5% NaCl solution was investigated by potentiodynamic curves, EIS, Mott–Schottky plots and XPS. Results of the electrochemical experiments and surface analyses showed that 654SMO under 33.3% reduction had a maximum deterioration in corrosion properties. After heavy deformation (55.6% and 66.7%), the corrosion resistance of 654SMO improved. XRD and EBSD were performed to illustrate the potential mechanism for the improvement in corrosion resistance. Results showed that there was no strain-induced martensite transformation for steels even under 66.7% deformation, and the dislocation density increased monotonically with an increasing deformation. The cold rolling texture of steels could be described by high Goss, S, brass and copper textures with a low brass-R component. Misorientation analysis and grain boundary characterization obtained from EBSD showed that a large number of mechanical twins formed in steels under 55.6% and 66.7% reductions. A hypothesis was proposed that the combined effect of the strong rolling texture and ∑3 twin boundaries ameliorated the corrosion resistance of 654SMO under large deformations.

Nowadays, electromagnetic pollution originated from artificial intelligence devices, fifth-generation (5G) cellular networks, as well as ever-increasing electronic devices applying and/or producing electromagnetic waves has excited the global concern. Evidently, the novel threats are springing up as a sleeping giant awaiting to irrupt; thus, the immediate counteraction is inescapable against the augmenting harmful electromagnetic waves. Till date, based on the permeability and permittivity of the materials in the microwave region, diverse microwave absorbing structures have been fabricated to overcome the aforementioned problem. It is worth noting that nanostructures are under the spotlight as a hot spot generated from their incomparable surface area-to-volume ratio tuning polarizability, magnetic features, electrical conductivity, eddy current loss, and other absorbing mechanisms. It should be noted that the secondary pollution produced at the threshold of the absorbing structures is tunable by the impedance matching. Hitherto, the size, shape, and morphology of nanostructures have been manipulated to improve microwave attenuation. The more surface area-to-volume ratio brings the more defect, dipole, and interfacial polarization as well as enhances the interfacial interactions at heterogeneous interfaces providing more multiple reflections and scattering. On the other hand, the intrinsic properties of the absorbing media and their unique interactions at grain boundaries can promote microwave attenuation which have recently attracted a great deal of attention. The obtained results manifest that the morphology and medium influence on microwave absorbing characteristics are the tip of the iceberg investigated by diverse approaches. In this study, a comprehensive prospect is presented using recent researches related to the size, shape, defect, morphology, and medium effect on the microwave absorbing mechanisms paving the way for microwave attenuation. The achieved works have attested that the mentioned parameters are the vital factors influencing the microwave absorbing properties.

The present study was designed to investigate the role of $$\left\{ {11\overline{2}1} \right\}$$ extension twinning on deformation and subsequent recrystallization behavior of binary Mg-Y alloys (Mg-5wt.%Y and Mg-10wt.%Y). The selected alloys in solution-treated condition were uniaxially deformed at room temperature and then annealed. Increasing the Y content switches the dominant twinning mode from $$\left\{ {10\overline{1}2} \right\}$$ extension twins and $$\left\{ {10\overline{1}1} \right\} - \left\{ {10\overline{1}2} \right\}$$ double twins, to less commonly observed $$\left\{ {11\overline{2}1} \right\}$$ extension twins. The former was found to assist recrystallization, while the contribution of latter in the formation of new grains was minimal. Moreover, the concurrent precipitation in the Mg-10Y alloy pins the grain boundaries and twin boundaries and thereby suppresses the recrystallization of the alloy despite holding for a longer duration. Finally, the weakening of the annealing texture was only observed in the Mg-5Y alloy as compared to the Mg-10Y alloy. This was attributed to the grain boundary bulging as the prominent mechanism of recrystallization in the Mg-10Y alloy.

The effect of deformation temperature on tensile behavior of Inconel 718 alloy has been studied by a self-developed in-situ high-temperature tensile stage inside a scanning electron microscopy at a temperature range from room temperature (RT) to 750 °C. The dynamic microstructure evolution and mechanical properties at different temperatures were performed and compared by the uniaxial tensile tests. The in-situ test results showed that the mechanical properties and fracture mechanisms of Inconel 718 alloy were sensitive to deformation temperatures. From RT to 650 °C, the yield stress and ultimate tensile strength decrease slightly and the tensile ductility is comparable. While up to 750 °C, the yield stress and ultimate tensile strength decrease significantly, the elongation and reduction of cross section also showed a significant decrease from RT to 750 °C. It was found that at RT and 650 °C, tensile cracks tended to initiate around the carbide particles and the triple junctions of grain boundaries, also propagated transgranularly; at 750 °C, the cracks initiated at grain boundaries and propagated intergranularly. In fact, with the increase in deformation temperature, the fracture mechanism transformed from the ductile transgranular fracture to the brittle intergranular fracture.

The magnetic and compressive properties of the ternary Ni40.6Fe36.4Ti23 eutectic alloys solidified under electromagnetic levitation condition were investigated. An undercooling range from 32 to 141 K was achieved, and a ternary eutectic consisting of a fibrous Fe2Ti phase and lamellar γ-Fe(Ni) + Ni3Ti phases formed. In the ternary eutectic, the γ-Fe(Ni) and Ni3Ti phases kept cooperative growth, while the Fe2Ti phase grew either cooperatively with these two phases or sometimes independently. Theoretical calculations showed that there existed a vertical flow field and temperature gradient in the center of the levitated alloy droplet, contributing to the directional growth behavior of eutectic grain. The growth velocity of primary Ni3Ti dendrite increased by 2.4 times, while that of ternary eutectic increased by 77% as undercooling rose, and consequently, the microstructures were significantly refined. The temperature stability of coercivity and residual magnetization below ambient temperature was improved once alloy undercooling reached 128 K, ascribed to the enhancement of the exchange coupling effect between the magnetic domains inside refined grains. The fracture strain of the ternary eutectic alloy increased with undercooling because microcrack propagation was further hindered and the plastic deformation was more homogeneous. Meanwhile, the fracture was dominated by transgranular (TG) mode at an undercooling of 132 K because the bonding force of grain boundaries became stronger.

Nanocrystalline metals are generally unstable due to a large volume fraction of high-energy grain boundaries associated with a small grain size. Preferential dopant segregation to the high-energy grain boundaries is observed to enhance the stability of the material’s microstructure by minimizing its energy. Nanocrystalline aluminum-dopant systems were evaluated for thermodynamic stability against grain growth and phase precipitation via the mechanism of grain boundary segregation according to a modified regular nanocrystalline solution model. Fifty-one potential dopant elements have been evaluated for their efficacy in stabilizing nanostructures with three potential candidates, magnesium, lanthanum, and silicon, identified possessing the characteristics to promote grain boundary segregation and a state of thermodynamic stability in aluminum’s nanocrystalline regime. The minimum dopant content required to achieve nanocrystalline microstructure stability is identified for each of the three candidate elements. Beyond this minimum content, further addition of the dopant elements decreased the final microstructure’s stability with no effects on the existence of a stable nanocrystalline state.

Ti-6Al-4 V is a popular alloy in additive manufacturing (AM) due to its applications in the biomedical implants and aerospace industries where the complex part geometries allowed by AM provide cost and performance benefits. Ti-6Al-4 V goes through a β → α’ transformation after solidification which is known to experience variant selection, e.g., through the formation of clusters of variants which, when situated together, partially accommodate the strain of the phase transformation. During electron beam powder bed fusion AM, an in situ decomposition of α’ martensite occurs during the cyclic reheating caused by melting successive layers, resulting in α + β microstructures. How variant selection influences the evolution beyond the initial rapid cooling remains an open question. Using 3D electron backscatter diffraction, we provide a clearer understanding without ambiguity from sectioning effects of how α’ decomposes into microstructures with distinct morphologies and variant/intervariant distributions. We extract quantitative 3D information on the various intervariant boundaries networks formed in samples printed using three different electron beam scanning strategies. This shows that differing mechanisms during the decomposition result in a shift from self-accommodating clusters in an acicular microstructure, to either the preferred growth of six variants in a basketweave microstructure, or to a colony microstructure where variant selection is determined by prior-β grain boundaries. We propose a new representation of the misorientations arising from the Burgers orientation relationship, which we refer to as intervariant network diagram, to reveal how variant selection during the martensitic transformation and subsequent decomposition leads to the intervariant boundary networks observed. This holistic understanding of the microstructural evolution has the potential to allow tailoring of microstructures and properties for specific applications.

Recently, α-MgAgSb-based materials have proved to be a kind of potential thermoelectric materials around room temperature. Here, a series of Zn-doped α-MgAgSb have been successfully synthesized by high-temperature milting and spark plasma sintering combined with annealing. Effect of Zn-doping on the microstructure and thermoelectric performance of α-MgAgSb has been investigated. Results show that Zn-doping can enhance the crystallization and carrier concentration, resulting in an increased electrical performance. Simultaneously, multiscales of nanodots, defects, grain boundaries and impurities have been introduced to reduce the lattice thermal performance. Finally, both the optimized electrical and thermal properties significantly promote the thermoelectric performance. A peak ZT of 1.29 has achieved for Mg0.985Zn0.015Ag0.97Sb0.99 at 550 K, about 18% higher than MgAg0.97Sb0.99, which indicates that Zn-doping into Mg-site is beneficial to optimize the performance of α-MgAgSb-based thermoelectric materials.

In order to clarify the relationships among austenite transformation degree, microstructure and fracture toughness, the simulated inter-critical heat-affected zones (ICHAZ) of high-strain pipeline steel were prepared with five different austenitizing degrees (0%, 20%, 50%, 80% and 100%). The microstructure and the fracture toughness of simulated ICHAZ specimens were investigated. It was found that the microstructure evolution and fracture toughness of ICHAZ were closely related to the austenite transformation degree. In partially austenitized ICHAZ, the fresh bainite and ferrite could break the original structure and decreased effective grain size. The fine grains with disorderly arranged M–A constituents could improve fracture toughness of partially austenitized ICHAZ. In contrast, the linearly aligned M–A constituents in 0%-austenitized region and the chain-distributed ones in 100%-austenitized region could lead to deterioration of fracture toughness. Furthermore, the excellent fracture toughness of partially austenitized ICHAZ was related to the high density of high-angle grain boundaries (HAGBs), homogeneous distribution of local strain as well as the high percentage of small-deformed grains (SDGs).

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.

Varistors are technologically important for their large energy handling capabilities and highly nonlinear electrical behavior when voltages above a characteristic switch field are applied. It is generally accepted that the prototypical ZnO–Bi2O3 varistor system forms electrostatic Schottky barriers at grain boundaries in response to residual Bi and other dopants left at grain surfaces during Bi2O3 segregation. While barrier heights can be modulated with formulation and defect chemistry, mechanisms by which dopant locations, defect compensation, and local phases determine varistor behavior are not completely understood. Bulk studies are challenging due to random grain boundary formation and difficulties studying individual boundaries. To circumvent these challenges in the ZnO–Bi2O3 varistor system, we use as-deposited and post-heat-treated thin film ZnO–Bi2O3 prototypes to simulate bulk varistor grain boundary phase formation and investigate resulting defect chemistry. Characterizing interactions between Bi2O3 films deposited on thin film and single-crystal ZnO by XRD and TEM-EDS revealed primarily Zn-out diffusion, resulting in two (Bi2O3)1−x(ZnO)x, or BZO, phases. Using these results, we present a saturated front model correlating changes in Bi2O3 thickness to phase evolution. We subsequently explore the influence of MnO doping leading to substantial changes in phase evolution for post-heat-treated (Mn:ZnO)–Bi2O3 stacks. Dopant-controlled Bi2O3 phase formations yield a 12 × difference, on average, between nonlinear coefficients for γ*- and β*-BZO.

The corrosion mechanism of as-cast, heat-treated (H400) and extruded (E30, E60, E90) Mg-3Zn-1Mn-1Y alloys with different microstructure is investigated by scan electron microscope (SEM), scan Kelvin probe force microscope (SKPFM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance analysis and immersion experiments equipped with a dynamic corrosion device. The relevant results are as follows: continuously strip-like I-phase (Mg3Zn6Y) in as-cast alloy distributed along the grain boundary played a significant obstacle impact during corrosion, whereas this capability is weakened after heat treatment and large plastic extrusion deformation. However, extrusion deformation significantly improved alloy corrosion performance, the extruded E30 alloy performed superior anti-corrosion behavior among the three extruded alloys owing to the smaller potential difference between I-phase (2.59 V) and DRXed (2.51 V) or un-DRXed (2.54 V) grains. In addition, the corrosion obstacle effect of grains boundaries (the grain boundary has higher potential than the Mg substrate), dense corrosion products film protection (isolate the substrate from contact with SBF) and typical basal texture (lower reactivity of base atoms) have great influence on corrosion behavior.

The improvement of recrystallization texture and magnetic properties in grain-oriented electrical steel with trace Bi addition processed by strip casting process was studied in this study. Low casting temperature and sufficient liquid steel flow during strip casting process enabled relatively homogeneous distribution of Bi in the as-cast strip, which accelerated the precipitation during solidification and cooling process. As a result, relatively high density of duplex MnS + AlN, MnS and AlN was formed at grain boundaries and inside grain. Due to the synergistic effect of continuous precipitation and fragmentation of coarse precipitates during cold rolling, the number density of precipitates was increased and mean size was decreased along the processing route. High density of precipitates is attributed to severe inhomogeneous plastic deformation, which promoted the formation of high density in-grain shear bands during cold rolling and recrystallization Goss texture during annealing. Homogeneous microstructure with average grain size of ~ 11.6 μm, strong Goss texture with intensity of 2.5 multiples of random distribution, fine precipitates with number density of ~ 1.9 × 109 /cm2 and mean size of ~ 49 nm were formed after primary recrystallization annealing. Furthermore, grain-oriented electrical steel with Bi addition experienced complete secondary recrystallization of exact Goss grains during high-temperature annealing, which is attributed to beneficial optimization of Goss texture and strong inhibition effect, and superior magnetic induction B8 of 1.91 T was obtained. It is expected that this study paves a new way for fabrication of high-performance grain-oriented electrical steel.

The aim of this work was to braze molybdenum and graphite with Ti–40Zr–8.5Nb–1.5Be filler metal in order to demonstrate the possibility of its application for X-ray tube target brazing, further to investigate the joint microstructure using energy-dispersive X-ray spectroscopy (EDS), electron backscattered diffraction (EBSD), X-ray diffraction (XRD), and electron microscopy as well as to conduct shear and unbrazing tests. It is shown that the brazed joint consists of matrix from β-(Ti, Mo) solid solution, mixed ZrC and TiC carbide layers at the braze/graphite interface, and beryllides TiBe2 and MoBe2 located at the grain boundaries of β-(Ti, Mo). The presented data made it possible to propose a brazed joint formation mechanism and explain the concentration of beryllides at the grain boundaries during brazing, as well as the mixed carbide layer formation from the side of the graphite. The mechanical tests showed that Mo/graphite brazed joints have a shear strength of at least 28.0 ± 0.9 MPa. However, sample failure occurred through the graphite due to the graphite surface mechanical treatment and the presence of a ductile β-Ti phase in the joint. The evaluation of joint thermal properties was performed using unbrazing tests. The unbrazing temperature was 1882 °C, which was caused by formation of refractory phases during brazing. The microstructure study shows that unbrazing occurs through the β-(Ti, Mo) phase with grain boundaries and beryllides eutectic melting.

The grain boundary (GB) excess volume is an important structural factor that is strongly correlated with various thermodynamic and kinetic properties of GBs such as GB energy, GB mobility, GB diffusivity, and GB segregation energy, etc. However, the excess volume is usually reported as an average value of the entire GB. Such simplification does not consider the spectral nature of the excess volume in a GB, which cannot be used to describe the atomic mechanisms of some kinetic process, such as GB migration, that involves only a few atoms at a time. Here, we explore the spectrum of atomic excess volume in representative nanocrystalline Ni and Al samples as well as 388 Ni bicrystals based on the Olmsted dataset by using atomistic simulations. It is found that the nanocrystalline Ni and Al models show a skew-normal distribution in the spectrum of both the atomic excess volume and the atomic excess energy in the GBs, which show a weak inverse correlation between them. This is in stark contrast to the widely reported positive correlation between GB energy and excess volume based on the average value. We further show based on the statistical analysis that the correlation between the atomic excess volume and excess energy strongly depends on the GB type and a universal trend between them does not exist. While low ∑ Ni GBs generally shows a strong inverse linear correlation between these two properties, such correlation is weak for high ∑ Ni GBs. Moreover, we find that the spectrum of the excess volume shows characteristics distribution in some special Ni GBs. For example, twist GBs generally show a symmetrical unimodal distribution while most surveyed ∑3 Ni GBs with anti-thermal behavior show an apparent bimodal distribution. Nevertheless, a strong correlation is found between the atomic excess volume and the segregation energy based on the nanocrystalline Al model with Mg impurity, which implies a possible universal trend between the two properties. The current study thus shows that the excess volume provides useful insights in revealing the elemental structure–property correlations in GBs, which may be used as a structural variable in future thermodynamic modeling of GBs.

In this work, experimental methods, such as electrochemical measurements, hydrogen collection technique, battery performance tests, and microstructure analysis, are used to investigate the electrochemical properties and discharge behaviors of Al–4.5Zn–0.05In and Al–4.5Zn–0.05In–0.05Ga/Sn/Bi anodes in 4 M NaOH solutions. Results suggest that the discharge performance of Al–Zn–In anodes can be further enhanced by adding Ga, Sn, or Bi elements. These elements show a dissolution-deposition behavior on the anode surface, which reduces the resistance of the passive film and increases the activity of active sites on the electrode surface. Also, adding Sn or Bi works better than adding Ga. Because Ga element is likely to cause severe local corrosion at the grain boundaries. Furthermore, the peak energy densities of Al–4.5Zn–0.05In–0.05Sn and Al–4.5Zn–0.05In–0.05Bi anodes at 40 mA cm−2 are approximately 3628.64 Wh kg−1 and 3456.12 Wh kg−1, respectively, which are 29.6% and 23.5% higher than that of Al–4.5Zn–0.05In anodes.

The role of grain boundary (GB) migration in producing stacking faults (SFs) in nanosized C15 structured ZrFe2 Laves phase precipitate was studied by transmission electron microscopy (TEM). Results revealed that the interaction between the studied second phase particle (SPP) and the GB was occured, which result in the curvature change of GB near the SPP. The movement of GB was hindered by the SPP which changed the normal migration of GB to that leaving behind a large number of faulted stacking in the SPP. In addition, the SPP was embedded in the α-Zr grain matrix; therefore, a dragging force of GB was applied on the SPP. Further deformation engendered the stacking faults in the centre of SPP by virtue of the maximum dragging force on the GB.

The evolution of heterogeneous microstructure and mechanical properties of a 12Cr–10Ni–Mo–Ti maraging steel was investigated at different aging temperatures. As the aging temperature increases, more reversed austenite forms with the recovery of martensite matrix. When aging temperature is up to 560 °C, more lath-like reversed austenite coalesces together and leads to the formation of martensite and austenite dual-phase microstructure. Fine η-Ni3(Ti, Al) particles initially precipitate at 440 °C and grow up with increased aging temperature. Notably, it was found that η-precipitates can be encompassed in reversed austenite at 500 °C. Thermodynamic calculations further verify the austenite reversion, and nanoprecipitation can occur independently of each other though there is competition of Ni element. However, it leads to the coarsening and dissolution of η-precipitates as the aging temperature further increases. The desirable heterogeneous microstructure of the aged martensite matrix, soft reversed austenite and stable η-precipitates at 500 °C contributes to a high yield strength (~ 1 GPa, 25 °C; ~ 1.4 GPa, -196 °C) and a reasonable cryogenic impact toughness (~ 60 J, − 196 °C), which is mainly ascribed to the precipitation strengthening of η-precipitates, transformation-induced plasticity (TRIP) toughening effect from the lath-like reversed austenite and the increased misorientation toward high-angle grain boundary.

The influence of crystallographic texture on the total amount of solute segregated at the grain boundaries (Xgb,tot) and consequently the weighted grain boundary energy (γw) of a nanocrystalline material is investigated. Toward this end, two different 3D nanostructures, one with random crystallographic texture and the other with {111} texture, were generated. The grain boundary misorientation distribution was obtained from both the 3D nanostructures and converted into an equivalent grain boundary energy distribution using the data from Olmstead et al. It was found that both Xgb,tot and γw are higher for the nanostructure bearing random texture vis-a-vis the {111} texture. This has implications in the development of thermally stable nanocrystalline materials. The effect of texture is also discussed through a case study on the Ni–W system by invoking the nanocrystalline stability criterion proposed by Kalidindi and Schuh.

Electromigration (EM) is considered as a serious issue that threatens the reliability of electronic packaging. For the long-term reliability of the application of pure silver thin films, it is important to investigate its EM effect; however, there are limited studies focused on this aspect. In this study, the EM of a silver thin film deposited on a glass substrate was examined at a current density of 8.89 × 105 A/cm2 and room temperature of 15 °C. During the EM test, the new phenomenon of the thin-thread silver structures with a unique direction was noted. To explain this, finite element analysis was applied to simulate the temperature and direction of the current flow. The effect of thermal and stress migration could be ignored in this experiment based on the temperature distribution results. The electron wind force played an important role in the formation of the thin-thread silver with nucleation structure following the direction and strength of the electron flow. By analyzing the failure location, melting was observed near the cathode since the generation of the thin-thread silver decreased the contact area for passing current. Finally, reducing the grain boundaries was proposed as an approach to improve the reliability of the pure silver sample, which is paramount for manufactures.

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 $$\alpha$$ (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.

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.

The phenomenon of entropy-dominated grain boundary segregation is introduced and discussed. Numerous examples of the grain boundaries and solutes exhibiting this phenomenon are compiled and predicted for example of α-iron-based alloys and other host materials. Consequences of entropy-dominated grain boundary segregation for grain size stabilization and intergranular embrittlement are shown.

Local curvatures have a profound influence on sintered microstructure. Here, using phase-field simulations, particle curvature effects were phenomenologically investigated by using geometrical configurations of two, three, and four particles, and by systematically varying particle curvatures. Some geometries, involving two, three and four particles, exhibited the expected smooth neck-length evolution, where the maximum neck length was determined by grain boundary (GB) energy ( $$\gamma _{GB}$$ ) rather than surface energy ( $$\gamma _{S}$$ ). In contrast, triangular arrangement of particles with unequal radii manifested a secondary necking event in form of a step during neck evolution. The secondary necking event coincided with internal pore collapse, and only specific range of particle radius ratios manifested such a mechanism. $$\gamma _{S}$$ played a dominant role in triggering the secondary necking event, while $$\gamma _{GB}$$ determined the remnant microstructure. Broadly, the geometries employed here allow us to computationally examine the sintering of particles that display wide variation in shapes and size distributions.

The samples of polycrystalline cobalt were strained in tension in the second stage of work hardening in order to activate twinning. The identification of twins and their orientation was analyzed using electron backscatter diffraction. The study of twin variant selection was carried out based on two parameters, namely the Schmid factor (SF) and the geometric compatibility factor (m'). The results indicate that the grains contained the $$\left\{ {10\overline{1}2} \right\}$$ extension twins in most cases while the $$\left\{ {11\overline{2}1} \right\}$$ extension twin mode was present in few cases, as well. In the grains containing only one twin variant, the SF analysis correctly predicted the activated twins in most cases. In the grains with variant pairs in para-position, nearly half of the studied twins had the highest SF of all possible variants, which means that they followed the Schmid law. On the other hand, for twin pairs in meta- or ortho-position, a different behavior was observed. Twins in these configurations were selected rather by the strain compatibility criterion than by the Schmid law, as SF values of the activated twins were significantly lower than those of the twins in para-position. Of these two configurations, the ortho-position one is highly preferred. The combined analysis using SF and m' parameter, predicted the occurrence of specific twin modes and variants only partially. A local analysis considering the effect of neighboring grains should be developed to account for the cases where the two parameters fail to explain the occurrence of particular twins, which seems to be related to the presence of a high fraction of high-angle grain boundaries.

Stainless-steel bipolar plates (BPPs) are of great significance in low-cost, easily processable, lightweight proton exchange membrane fuel cells (PEMFCs) despite the challenge presented by corrosion in protective coatings. Localized corrosion along the grain boundaries in a crystal film is common, but few preventive measures have been developed so far. Thus, we propose a novel strategy using a tantalum (Ta) and carbon (C) co-modification to improve the chemical stability of titanium carbide (TiC)-based coatings (Cr/Ta/TiC/C). During the film growth, the subjacent Ta atoms were thermally diffused throughout the columnar structure of TiC and reacted with the C layer. The reaction product, i.e., TaC, acted as a chemical passivator to the grain boundary. Combined with the C capping layer, these functional layers synergistically suppressed any localized corrosion. Therefore, corrosion current densities within the United States Department of Energy’s technical recommendations were achieved in both potentiostatic and potentiodynamic polarization. Meanwhile, by controlling the Ta metal dispersion, the interfacial contact resistance between the multilayer structure and the carbon paper can be reduced to 7.1 mΩ·cm−2 at a compaction force of 140 N·cm−2. The substantial improvement in the corrosion resistance and conductivity of BPP places our work among the most efficient anticorrosion systems in PEMFC applications reported so far.

The paper studies the wetting of grain boundary triple junctions (GB TJs) by the second solid phase (intermetallic) δ in the Cu–In alloys. In this system, the portion of grain boundaries in a copper-based solid solution (Cu), which are "wetted" by the second solid phase δ, changes non-monotonically with increasing temperature. At first, the portion of such completely wetted GBs increases from zero to almost 100% when the sample is heated, and then quickly falls back to zero. The condition of complete wetting for the GB TJs (σGB > 1.73 σSS) is less stringent than for the GBs (σGB > 2 σSS). Therefore, if the transition from incomplete to complete wetting occurs with an increase in temperature, then all GB TJs should become completely wetted at a temperature TWTJ, lower than the temperature TWGB, at which all GBs become completely wetted. In this work on the Cu–In system, it was found experimentally for the first time that the wetting of the GB TJs also behaves non-monotonously. The percentage of wetted GB TJs also increases to 100% at first and then falls with increasing temperature. In this case, the portion of wetted GB TJs exceeds the portion of wetted GBs not only when it increases with increasing temperature, but also then, with the subsequent disappearance of fully wetted GBs. Grain boundary triple junctions in (Cu-In) solid solution are “wetted” by the δ intermetallic in broader temperature interval than grain boundaries.

Abstract Alloy 718 samples were fabricated by electron beam melting (EBM) additive manufacturing process. The work focused on systematic investigation of response of the material to various thermal post-treatments, involving hot isostatic pressing (HIPing), solution treatment (ST) and two-step aging, to tailor post-treatment procedure for EBM-built Alloy 718. Results showed that HIPing at lowered temperature can be used for attaining desired defect closure while preserving grain size. Subjecting the material to ST, with or without prior HIPing, mainly caused precipitation of δ phase at the grain boundaries with prior HIPing decreasing the extent of δ phase precipitation. Moreover, results suggest that the utility of ST, with prior HIPing, could be dictated by the need to achieve a certain δ phase content, as the typically targeted homogenization after ST had already been achieved through HIPing. Detailed investigation of microstructural evolution during subsequent aging with and without prior HIPing showed that a significantly shortened aging treatment (‘4 + 1’ h), compared to the ‘standard’ long treatment (‘8 + 8’ h) traditionally developed for conventionally produced Alloy 718, might be realizable. These results can have significant techno-economic implications in designing tailored post-treatments for EBM-built Alloy 718. Graphical abstract

In this study, WC-Al2O3 composite was fabricated by vacuum hot-pressing sintering. The corrosion behavior of WC-Al2O3 composite in NaOH and H2SO4 solutions was investigated by electrochemical measurements. The corrosion mechanisms were analyzed and revealed in light of corrosion morphology observation and composition characterization. The results confirmed that WC-Al2O3 composite possessed higher corrosion resistance than WC-Co hard metal in H2SO4 solution. Conversely, WC-Al2O3 composite behaved similar corrosion resistance compared with WC-Co hard metal in NaOH solution. The key reason for higher corrosion resistance in H2SO4 solution is the stable WO3 passive film. The oxidation of WC phase leads to neck cracks along with grain boundaries, which is attributed to the preferential corrosion of grain boundary and the stress derived from the volume expansion during polarization and drying processes. In NaOH solution, the corrosion mechanism of WC-Al2O3 composite mainly attributed to the dissolution of WC phase, but Al2O3 phase is relatively stable.

Under irradiation conditions, excess point defects interact strongly with the solute atoms in fusion reactor materials. The solutes can bind with point defects and form clusters such as solute–vacancy complexes. The evolution of these complexes at long timescale significantly influences the mechanical properties of the irradiated materials. In this study, we mainly use climbing image nudged elastic band method to investigate the evolution and migration of titanium–vacancy complexes in a vanadium-based alloy. The transition pathways associated with atomic trajectories of complex evolution in bulk and in grain boundary vicinity are calculated. Results show that both basin energies and transition barriers are affected when a complex is in grain boundary vicinity. The evolution is revealed to be driven by multiple titanium–vacancy interactions synergistically. The migration is supposed to be induced by two mechanisms: the vacancy reorientation jumps and complex dissociation–reformation which are both based on titanium–vacancy interactions. This research contributes to the understanding of solute diffusion and early-stage radiation defects in vanadium-based alloys.

A simulated annealing (SA) method based on molecular dynamics is employed to reveal atomic structures of asymmetric tilt grain boundaries (ATGBs) in MgO. Σ5 and Σ13 ATGBs with the [001] tilt axis are systematically investigated. The ATGBs after SA simulations dissociate into saw-toothed nanofacets composed of multiple structural units. These nanofacets are lower in GB energy than those obtained from a γ-surface method with structural optimization, demonstrating the importance of SA-based methods for obtaining low-energy structures of ATGBs. For most of the Σ5 ATGBs, the nanofacets consist of only structural units of Σ5 symmetric tilt GBs (STGBs). For the Σ13 ATGBs studied, their nanofacets do not consist of only Σ13 STGBs but always contain non-Σ13 structural units, which probably results from a large difference between the excess volume of Σ13(510) and Σ13(320) STGBs. It is also found that ATGBs have a larger number of metastable structures whose GB energies are close to the lowest energy structure than STGBs, due to the fact that ATGB nanofacets are more tolerant of variation in facet junction, structural units and their arrangement. Consequently, the lowest energy structures have low probabilities of being formed than metastable structures.

The relationship between microstructure evolution and mechanical performance of Al–Zn–Mg–Cu alloys with varying Cu/Mg ratios was discussed in detail under different two-step aging (T7X). The results showed that the undissolved second-phase particles including σ-Al7Cu2Fe and T-Al2Mg3Zn occurred in the quenched Al–Zn–Mg–Cu alloys. When the Cu/Mg ratio approaches 1.64, the S-Al2CuMg phase was also observed. Although the Cu/Mg ratio did not change the precipitation sequence of the Al–Zn–Mg–Cu alloys, it changed the coarsening rate and precipitate size distribution during aging process. The Al–Zn–Mg–Cu alloy with the lowest Cu/Mg ratio has the slowest coarsening rate and the highest strength (655 MPa). The fracture morphology of Al–Zn–Mg–Cu alloys changes from the typical brittle fracture to the intergranular-dominated mixed fracture mode or ductile fracture when the Cu/Mg ratios increases. Besides, the T79-aged alloys with varying Cu/Mg ratios have similar grain boundary precipitates (GBPs) and precipitate-free zones (PFZs). The T74-aged alloys with higher Cu/Mg ratio have more coarser GBPs and wider PFZs.

The growth of graphene on Ni magnetic films is of great significance for graphene spintronics, whereas the existence of grain boundaries and twin crystal structures in Ni films is an obstacle for obtaining the large-scale and uniform graphene. In this paper, an epitaxial wafer-scale single-crystalline Ni(111) film with the flat and clean surface was successfully prepared on the commercial α-Al2O3(0001) substrate by a two-step method, which was demonstrated with several characterization methods. According to the abnormal grain growth mechanism, the clean and uniform sapphire surface plays a key role for the single crystallization of Ni films as it induces a weak interface energy difference between two atomic stacking structures (ABC and ACB), thus stimulating the evolution of Ni films from (111) out-of-plane textures to single crystals. Furthermore, an ultra-flat and wrinkle-free graphene monolayer was synthesized on the prepared Ni film, which further verified its high quality and effectiveness.

Abstract In this work, we report that modification of the chemical composition of grain boundaries of La2/3-xLi3xTiO3 double perovskite, one of the most promising Li-ion conducting solid electrolytes, can be a convenient and versatile way of controlling the space charge potential, leading to a mitigated electrical resistance of the grain boundaries. Two groups of additives are investigated: lithium-enriching agents (Li3BO3, LiF) and 3d metal ions (Co2+, Cu2+), both expected to reduce the Schottky barrier. It is observed that Li-containing additives work effectively at a higher sintering temperature of 1250 °C. Regarding copper, it shows a much stronger positive impact at lower temperature, 1150 °C, while the addition of cobalt is always detrimental. Despite overall complex behavior, it is documented that the decreased space charge potential plays a more important role in the improvement of lithium conduction than the thickness of the grain boundaries. Among the proposed additives, modification of La2/3-xLi3xTiO3 by 2 mol.% Cu2+ results in the space charge potential reduction by 32 mV in relation to the reference sample, and the grain boundary specific conductivity increase by 80%, as measured at 30 °C. Introduced additive allows to obtain a similar effect on the conductivity as elevating the sintering temperature, which can facilitate manufacturing procedure. Graphic abstract

The mechanical properties of metallic systems at the nanoscale can be modified by varying their structure and composition. One example of a deformation-resistant structure is a core–shell nanostructure (CSN). In the present work, we use molecular dynamics simulations to perform nanoindentation and retractions to understand plastic deformation of core–shell nanostructures. The core consists of aluminum (Al), the shell is amorphous silicon (a-Si), and the substrate is either crystalline Al or a-Si. The unique aspect of this work is that we study the deformation behavior of CSNs that contain symmetric and asymmetric grain boundaries in the core with two different orientations; comparisons are made to deformation in a CSN with a single-crystal core. Nanoindentation on CSNs with 5 nm and 10 nm core radii shows that the elastic stiffness with and without a grain boundary is similar when the substrate material is the same. Five-nanometer-core-radius CSNs with a-Si and Al substrates and an asymmetric tilt grain boundary in the core show 100% recovery from dislocation plasticity, but damage within the core leads to reduction of ~ 50% of the atoms that no longer being identified as FCC crystal structure, which makes these CSNs non-deformation-resistant. CSNs with Al substrate (5 nm and 10 nm core radii) obtained 100% recovery from plasticity and retained its crystal structure after unloading when the core is single crystal or contains a symmetric tilt grain boundary. Moreover, a single-crystal core can withstand nanoindentation to 100% of the shell thickness, whereas a symmetric tilt grain boundary core can only withstand nanoindentation about 80% of the shell thickness and still have 100% recovery from plasticity. Therefore, CSNs with single-crystal core are more reliable for deformation-resistant behavior than those that contain grain boundaries.

A solid-solution treated Al–Cu binary alloy ingot containing 2.42 wt% copper was subjected to a multi-directional forging at ambient temperature followed by a recrystallization annealing at 400 °C and aging at 175 °C. Then, the dependence of precipitate morphology on grain boundary types was studied by field emission scanning electron microscopy, electron backscatter diffraction and grain boundary trace analysis. The results show that no precipitate is found at the coherent twin boundaries (singular boundaries). Discontinuous or necklace-like precipitates are observed at the near singular (vicinal) boundaries with grain boundary inter-connections of {1 1 1}/{1 1 1} (excluding coherent twin boundaries), but continuous precipitates are developed at the random boundaries. A surface etching result indicates that the coherent twin boundaries are immune to, while the near singular boundaries are more resistant to intergranular corrosion compared to random boundaries. O-lattice theory analysis indicates that the near singular boundaries usually have specific atomic structure of periodic good matching sites isolated by the periodic dislocations. This could be the origin of discontinuous precipitates and higher resistance to intergranular corrosion in comparison with random boundaries. Based on the fact that coherent twin boundaries are hard to be introduced due to the high stacking fault energy, it is suggested that to purse a grain boundary character distribution containing high frequency near singular boundaries would be a promised approach to higher the resistance to intergranular corrosion for aluminum and its alloys in view of grain boundary engineering.

The challenge of enhancing the high-temperature oxidation resistance of TiAl alloys is hereby addressed by Co addition. Isothermal oxidation tests were conducted on the newly designed TiAl-Co alloys in laboratory air at 900 °C up to 100 h. Sintered microstructure, oxidation kinetics, scale structure, spallation resistance and oxidation mechanisms were systematically investigated. Results show that the original sintered microstructure of TiAl alloys mainly consists of matrix phases α2-Ti3Al/γ-TiAl lamellae, while the Co addition leads to the formation of the two additional Co-rich phases of CoAl2Ti and Ti (Al, Co, Cr and Nb) at grain boundaries. The Co-doped TiAl alloys exhibit an improved high-temperature oxidation resistance compared with the Co-free alloy. The presence of the Co-rich phases network along the grain boundaries and Co-rich layer at the scale/substrate interface can hinder the inward diffusion of oxygen and the outward diffusion of Ti and Al, thereby suppressing the growth of oxide scale and improving the spallation resistance of TiAl alloys. As a result, the TiAl-3Co alloy possesses excellent oxidation resistance, with the minimum mass gain of 4.08 mg/cm2, thinnest scale thickness of 17.8 μm and without surface spallation or crack formation after isothermal oxidation for 100 h. This result would pave the way for designing high-temperature oxidation-resistant TiAl-based alloys.

Cubic-phase garnet-type Li7La3Z2O12 is a promising candidate for an electrolyte of all-solid-state lithium-ion batteries; however, its poor sinterability due to Li sublimation during firing has impeded large scale development. This study demonstrates a solid-state reactive sintering (SSRS) process with added CuO as a sintering aid to enable enhanced materials processing at lower temperatures. Applying the SSRS process with the addition of 1 wt% CuO decreased the sintering temperature for 0.5 mol%Ta-doped LLZTO pellets having over 90% relative density from 1250 to 1100 °C to reduce Li loss. The 1 wt% CuO addition did not lead to secondary phase formation as detected by XRD, nor to appreciable electronic conduction below 100 °C as measured by four-point probe method. The 1 wt% CuO-mixed LLZTO pellet exhibited high conductivity of approximately 3.0 × 10−4 S·cm−1 (bulk) and 5.45x10−5 S·cm−1 (grain boundary). The mechanism of CuO function as a sintering aid is presumed to be enabling liquid-phase sintering along with enhancing the decomposition of LiOH. The combined SSRS process along with optimized CuO sintering aid addition is a one-step process that is a practical technique to enhance the preparation of LLZO-based electrolyte for all-solid-state lithium-ion batteries.

An ultrafine-grained (UFG) Al-4.8%Zn-1.2%Mg-0.14%Zr (wt%) alloy was processed by high pressure torsion (HPT) technique and then aged at 120 and 170 °C for 2 h. The changes in the microstructure due to this artificial aging were studied by X-ray diffraction and transmission electron microscopy. It was found that the HPT-processed alloy has a small grain size of about 200 nm and a high dislocation density of about 8 × 1014 m−2. The majority of precipitates after HPT are Guinier–Preston (GP) zones with a size of ~ 2 nm, and only a few large particles were formed at the grain boundaries. Annealing at 120 and 170 °C for 2 h resulted in the formation of stable MgZn2 precipitates from a part of the GP zones. It was found that for the higher temperature the fraction of the MgZn2 phase was larger and the dislocation density in the Al matrix was lower. The changes in the precipitates and the dislocation density due to aging were correlated to the hardness evolution. It was found that the majority of hardness reduction during aging was caused by the annihilation of dislocations and some grain growth at 170 °C. The aging effect on the microstructure and the hardness of the HPT-processed specimen was compared to that observed for the UFG sample processed by equal-channel angular pressing. It was revealed that in the HPT sample less secondary phase particles formed in the grain boundaries, and the higher amount of precipitates in the grain interiors resulted in a higher hardness even after aging.

The evolution of grain boundary character distribution (GBCD) in the CoCrMo alloys processed by SLM and post-heat treatments (aging and solid solution) has been investigated by the electron backscatter diffraction (EBSD) and transmission electron microscope techniques. A high fraction of Σ3n (n = 1, 2, 3) grain boundaries and the corresponding clusters occur in the solid solution-treated samples at 1150 °C, which indicates GBCD optimization is somewhat realized. The coherent and incoherent Σ3 boundaries were distinguished via the single-section trace analysis method based on EBSD measurements. Σ3 boundaries in the SLMed and aged samples were determined as incoherent, while those in the solid solution-treated sample are coherent. Regular e precipitation did not occur in the solid solution-treated samples as in the aged samples. Instead, stacking fault bands associated with coherent Σ3 twin boundaries are dominant. It suggests that post-heat treatment has a significant influence on the GBCD, especially the Σ3 grain boundary characteristics.

The characteristics of the intervariant boundary network that resulted from the $$\beta \to \alpha^{\prime}$$ martensitic phase transformation in a Ti–6Al–4V alloy were studied using the crystallographic theories of displacive transformations, five-parameter grain boundary analysis and triple junction analysis. The microstructure of Ti–6Al–4V martensite consisted of fine laths containing dislocations and fine twins. The misorientation angle distribution revealed four distinct peaks consistent with the intervariant boundaries expected from the Burgers orientation relationship. The phenomenological theory of martensite predicted four-variant clustering to have the lowest transformation strain among different variant clustering combinations. This configuration was consistent with the observed Ti–6Al–4V martensitic microstructure, where four-variant clusters consisted of two pairs of distinct V-shape variants. The $$63.26^\circ /[\overline{10}\, 5\, 5\, \overline{3}]_{{\alpha^{\prime}}}$$ and $$60^\circ /[1\, 1\, \overline{2}\, 0]_{{\alpha^{\prime}}}$$ intervariant boundaries accounted for ~ 38% and 33% of the total population, respectively. The five-parameter boundary analysis showed that the former had a twist character, being terminated on the $$(\overline{3}\, 2\, 1\, 0)_{{\alpha^{\prime}}}$$ plane, and the latter revealed a symmetric tilt $$(1\, 0\, \overline{1}\, 1)_{{\alpha^{\prime}}}$$ boundary plane. The $$63.26^\circ /[\overline{10}\, 5\, 5\, \overline{3}]_{{\alpha^{\prime}}}$$ and $$60^\circ /[1\, 1\, \overline{2}\, 0]_{{\alpha^{\prime}}}$$ had the highest connectivity at triple junctions among other intervariant boundaries. Interestingly, the boundary network in Ti–6Al–4V martensite was significantly different from the commercially pure Ti martensite, where only $$60^\circ /[1\, 1\, \overline{2}\, 0]_{{\alpha^{\prime}}}$$ intervariant boundaries largely were found at triple junctions due to the formation of three-variant clustering to minimize the transformation strain. This difference is thought to result from a change in the martensitic transformation mechanism (slip vs twinning) caused by the alloy composition.

Welding thermal cycles with different peak temperatures were reproduced by a Gleeble testing machine to simulate the heat-affected zone of a Ni-17Mo-7Cr superalloy-welded joint. The effects of the thermal cycle times and peak temperatures on the microstructure and tensile properties of the thermal simulation specimens were systematically studied. The results show that no eutectic carbides are observed below 1300 °C, even when the number of thermal cycles is increased to 5. However, the eutectic reaction occurs above 1300 °C and causes a significant change in the carbide morphology because it transforms from a granular to lamellar structure. Moreover, the carbide composition transforms from (Ni, Cr)3Mo3C for the primary carbides to Ni3(Mo, Cr)3C for the lamellar carbides after the eutectic reaction. Tensile tests show that the thermal cycle has a minor effect on the tensile properties, except when the specimen underwent 5 thermal cycles with a peak temperature of 1340 °C. This is mainly due to the severe liquation reaction caused by elevated temperatures from the welding heat source, which induces cracking along the grain boundaries and results in a degradation of the tensile properties.

In most cases, the microstructure of implants is stable and changeless after implanted into the body. However, the metallic joint replacements would be worn during patients’ movements. Their subsurface microstructures were deformed and changed. That may affect the corrosion resistance of the joint. Due to the complex surface situation on the worn joints, it was difficult to distinguish and evaluate the influence of the subsurface microstructure from surface roughness, wear debris, etc. In this study, a CoCrMo alloy used for artificial joints was treated by high-energy shot peening method to obtain a similar deformed surface to the worn joints, but without introducing other influencing factors. The corrosion rate of the deformed alloy which was treated for 4 h was down by 93.3% in the phosphate-buffered saline (PBS) solution compared with the untreated alloy. However, with the addition of bovine serum albumin (BSA) into PBS, the treated alloy showed the poorer corrosion resistance when its concentration was equal to or greater than 0.1 μmol L−1. The defects (grain boundaries and stacking faults), which were introduced into the alloy surface during peening process, could accelerate anodic dissolution, improve element diffusion and increase the number of active sites. These were beneficial for forming a more compact and thicker passive film which enhanced the corrosion resistance of the alloy. However, the deformation of subsurface could promote the adsorption of protein on the alloy surface. The adsorbed protein molecules would chelate with metallic ions and weaken the passive film.

The Mg–Zn–Ca–Sr alloy has good application prospects as a bone implant material; however, the as-cast alloy has both poor plasticity and formability, and there are few studies on its deformation properties. In this study, the microstructure, deformation behavior, textural evolution, and processing map of an Mg–3wt%Zn–1wt%Ca–0.5wt%Sr alloy were studied via a compression test using a Gleeble 1500D thermo-mechanical simulator. The mean apparent activation energy of the hot compression deformation of the Mg–3wt%Zn–1wt%Ca–0.5wt%Sr alloy was 250.44 kJ/mol. With an increase in temperature, both the grain size and the degree of dynamic recrystallization increased. Dynamically recrystallized grains predominantly nucleated near the grain boundary and the secondary phases. After compression, the alloy had a strong basal texture, and its textural strength decreased at first and then increased slightly as the deformation temperature rose. The optimal process parameters of the as-cast Mg–Zn–Ca–Sr alloy involved deformation temperatures of 603–633 K and strain rates of 0.03–0.005 s–1.

The work develops the material science of advanced superionic conductors (AdSICs). The AdSICs have been distinguished by the authors as a new class of solid-state ionic conductors due to the best ion-transport properties and their special crystal structure that is close to optimum for fast ion transport (FIT). Structure descriptors, a new geometry of 3D close packing of FIT tunnels inside the unit cell, and the distinctive properties of grain boundaries (GBs) in AdSICs have been revealed. On this structural basis and a recently developed theory of ion transport on a nanoscale (“structure-dynamic approach of nanoionics,” SDA), the absence of Jonsher’s universal dynamic response (UDR) in polycrystalline AdSICs has been explained. In solid-state ionic conductors, UDR holds in a frequency (ω) range depending on heights (η) and heights difference (Δη) of potential barriers which mobile ions overcome in a non-uniform crystal potential landscape. In polycrystalline AdSICs, η is not above 0.2 eV and Δη ≤ ~ 0.1 eV; therefore, the SDA indicates the response to external electric excitations has an ohmic character, i.e., does not depend on ω. The important role of processes of structural self-organization and the formation of low-energy coherent GBs in AdSICs is emphasized. It is concluded that a deeper understanding of the structure and properties of AdSICs can serve as a guide for searching and designing new materials/devices with FIT.

Recent experiments demonstrated that hierarchical double contraction nanotwins (DCTWs), i.e., $$ \left\{ {10\bar{1}1} \right\} - \left\{ {10\bar{1}1} \right\} $$ nanotwinned structures, can simultaneously improve the strength and ductility of Mg–Li alloys. With Mg as model material using atomistic simulations and interface defect analysis, we characterize structural characteristics of boundaries associated with DCTWs and investigate plastic deformation mechanisms of double contraction nanotwinned structures. It is revealed that the boundaries associated with DCTWs are composed of $$ \left\{ {10\bar{1}1} \right\} $$ coherent twin boundaries (CTBs), symmetrical tilt grain boundaries (STGBs), and asymmetrical tilt grain boundaries (ASTGBs). Under mechanical loadings, the corresponding grain boundary defects along STGBs and ASTGBs act as sources for nucleating and emitting basal and pyramidal dislocations, enhancing the plasticity. Meanwhile, the densely distributed CTBs in DCTWs act as strong barriers for dislocation motion, strengthening the material.

The intergranular corrosion (IGC) behavior of an extruded 6005A alloy profile with the coexisting of peripheral coarse grain (PCG) structure and partial recrystallized grain (PRG) structure was investigated by using an accelerated corrosion test, electrochemical impedance spectroscopy and a quasi in situ examination of IGC process. PCG structure was found to have a unique IGC behavior that pitting corrosion and subsequent IGC are less severe and will not be transformed into intragranular corrosion as they were found in PRG structure. Microstructure characterization reveals that the microstructural differences in grain boundary precipitates, primary α-AlFeMnSi intermetallic particles and grain characteristic between PCG structure and PRG structure are the reason for these phenomena. Further analysis indicates that the grain boundaries decorated with more AlFeMnSi particles and Q phase precipitates are more sensitive to corrosion, where Q phase precipitates are the primary cathodes and the most important factor affecting IGC; AlFeMnSi particles are supposed to initiate pitting corrosion since they are dissolved as anodes in the early stage of corrosion. With the development of corrosion, they are transformed into cathodes and become the bridges of IGC propagation by connecting the Q phase precipitates at grain boundary. In addition, grain characteristic was also found to have great effects on IGC. With the decrease in grain size and the increase in the frequency of high-angle grain boundaries and the dislocation density, corrosion becomes more severe and more likely to be transformed into intragranular corrosion.

In this article, the coarse grained heat affected zone (CGHAZ) of a low carbon high strength steel was simulated at two heat inputs on a Gleeble-3800 thermo-mechanical simulator. A comparative study was conducted to reveal the role of Cu addition in toughness improvement by microstructure characterization and Charpy impact test. Microstructure observation suggested that there is no observable difference in the microstructure and prior austenite grain size between Cu-free steel and Cu-bearing steel, but a higher density of high-angle grain boundary (HAGB) was obtained in Cu-bearing steel with 50 kJ/cm. This was intrinsically associated with the configuration of three Bain groups from the aspect of crystallography. The optimum configuration can be achieved by adjusting transformation driving force, cooling rate and nucleation characteristics during martensite/bainite transformation. In this study, Cu addition played a determining role in increasing transformation driving force at high cooling rate, and altering the diffusion kinetics of alloying elements at low cooling rate. Accordingly, the density of HAGB can be optimized to be beneficial for high toughness in CGHAZ. Therefore, the optimum toughness was obtained in Cu-bearing steel with heat input of 50 kJ/cm, which was featured by the impact energy of ~ 198 J at − 40 °C.