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The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy (LAZ1011) with a grain size of 3.2 µm, primarily composed of the BCC β phase and a small amount of the HCP α phase, were examined in a temperature range of 473 K to 623 K. The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling. The best superplasticity was achieved at 523 K and at strain rates of 10−4 -5 × 10−4 s−1, where tensile elongations of 550–600% were obtained. During the heating and holding stage of the tensile samples prior to tensile loading, a significant increase in grain size was observed at temperatures above 573 K. Therefore, it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms. In the investigated strain rate range, the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding, while at high strain rates, lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism. It was concluded that solute drag creep is unlikely to occur. During the late stages of deformation at 523 K, it was observed that grain boundary sliding led to the agglomeration of the α phase, resulting in significant strain hardening. Deformation mechanism maps were constructed for β-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate, stress, temperature, and grain size, using the constitutive equations for various deformation mechanisms derived based on the data of the current tests.

There is a growing interest in field‐assisted fast ceramic processing and long‐term service of electrochemical devices under harsh operation conditions. These extreme redox conditions can make some conventionally thought slow ions highly mobile in electrochemical materials and devices and greatly accelerate the microstructural evolution. Experimental observations for enhanced slow ion diffusion that controls mass transport include accelerated grain growth in zirconia and ceria under atmospheric and electrochemical reduction above 1000°C and lattice cavitation of high‐voltage Li‐rich layered cathodes of lithium‐ion batteries at room temperature. These observations cannot be explained by altered defect concentrations under defect chemistry arguments. Instead, they support hugely enhanced slow ion mobility. My colleagues and I recently proposed a new mechanism resulted from strong electron–phonon interactions and dynamic electronic relaxations at the saddle point of an ion hopping event, which significantly lowers the ion migration barrier. In this perspective article, the theory and its experimental and computational supports shall be discussed. Such an electronic effect holds even in nominally ionic ceramic materials with wide bandgaps and is expected to be general in many transition metal oxides. It rationalizes a variety of intriguing experimental observations and offers an electronic perspective on the redox enhancement of slow ion kinetics in structural, functional, and energy ceramics. [ABSTRACT FROM AUTHOR]

The role of anisotropic grain boundary energy in grain growth is investigated using textured microstructures that contain a high proportion of special grain boundaries. Textured and untextured Ca‐doped alumina was prepared by slip casting inside and outside a high magnetic field, respectively. At 1600°C, the textured microstructure exhibits faster growth than the untextured microstructure and its population of low‐angle boundaries increases. Atomic force microscopy (AFM) is employed to measure the geometry of thermal grooves to assess the relative grain boundary energy of these systems before and after growth. In the textured microstructure, the grain boundary energy distribution narrows and shifts to a lower average energy. Conversely, the energy distribution broadens for the untextured microstructure as it grows and exhibits abnormal grain growth. Further analysis of the boundary networks neighboring abnormal grains reveals an energy incentive that facilitates their growth. These results suggest that coarsening is not the only dominant grain growth mechanism and that the system can lower its energy effectively by replacing high energy boundaries with those of low energy. The faster growth of lower energy boundaries suggests that isotropic simulations do not adequately account for anisotropic grain growth mechanisms or anisotropic mobility. [ABSTRACT FROM AUTHOR]

Ferrite materials are urgently demanded in high-frequency miniaturized power electronics for their high electromagnetic properties and high electrical resistivity. However, traditional NiZn ferrites are faced with low resistivity and high loss at low-temperature sintering, which severely restrict their applications. In this study, CdO was substituted into Ni 0.22 Cu 0.2 Zn 0.58 Fe 2 O 4 ferrites at a presintered stage to refine the grain size and to achieve superior performance at low-temperature sintering. Interestingly, the electrical, magnetic and gyromagnetic properties of the NiCuZn ferrites exhibited a strong dependence on the concentration of Cd2+ ions. The Cd2+ ions entered into the lattice and substituted for Fe3+ at the octahedral site. SEM image results showed that CdO-substituted NiCuZn ferrites for the first sintering stage possess inhibition of abnormal grain growth, which can effectively solve the problem of shrinkage and grain compaction of ferrite materials in LTCC technology. Furthermore, to promote the grain growth at low sintering temperature, the optimized Bi 2 O 3 additives were added at final sintering stage. The resistivity of the optimized Cd2+ ions is significantly enhanced from 2.41 × 108 Ω cm to 8.51 × 108 Ω cm. Finally, the NiCuZnCd (x = 0.15)-1.2 wt % Bi 2 O 3 ferrites with the highest densification possess ρ = 8.51 × 108 Ω cm, ε′ = 18, tan δ ε = 6.0 × 10−3, μ′ = 81, f r = 117 MHz, tan δ μ = 4.8 × 10−2 and ΔH = 281 Oe. This work provides a new doping method for the design of the high frequency LTCC device. [ABSTRACT FROM AUTHOR]

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Preparation of high-entropy ceramics (HECs) requires long duration at high temperatures, which limits their wide application. In this study, high-entropy (La 0.2 Ce 0.2 Nd 0.2 Sm 0.2 Eu 0.2) 2 Zr 2 O 7 ceramics was prepared at low temperatures of 762–885 °C in very short time of 60 s using the flash sintering. The effects of electric field strength and current limit on the densification and grain growth, as well as the phase transformation were systematically investigated. Both density and grain size were increased with the increase of the electric field strength and current limit. The phase transformation from defective fluorite to pyrochlore occurred at large current limit. The flash-sintered bulks exhibited good mechanical properties. This study demonstrates that flash sintering is an effective method for rapid preparation of HECs at low temperatures. Moreover, the microstructure of HECs can be controlled by adjusting the electric field strength and current limit. [ABSTRACT FROM AUTHOR]

β‐silicon nitride (β‐Si3N4) ceramics with an additive oxide system of 1 wt% MgO and 3 wt% Re2O3 (Re = Gd, La, Y, and Yb) were fabricated by liquid phase sintering at 1950°C under nitrogen pressure of 748 kPa. Starting α‐Si3N4 powder with 10 vol% rod‐like β‐Si3N4 seed crystallites and an extended sintering time from 5 to 40 h resulted in the formation of bimodal microstructure composed of fine matrix grains and large grains. The 40 h‐sintered specimens of pseudo ternary β‐Si3N4‐MgO‐Gd2O3 system exhibited enhanced thermal conductivity of 127.2 ± 2.5 W m−1 K−1 associated with a degradation of the fracture strength from 1008.0 ± 38.0 to 491.7 ± 32.0 MPa, which was due to the formation of coarse‐grained aggregates that acted as both fracture origin as well as a thermal conductive pathway. The theoretical thermal conductivity was predicted for the sintered specimens by using equations based on a mean‐field micromechanics model to estimate the effective thermal conductivity of each component of binary composites. The calculation results suggested that the thermal conductivity of the large β‐Si3N4 grains (≥ 2 μm in diameter) was relatively high and estimated to be in the range of 175 to 191 Wm−1 K−1. The improved thermal conductivity of the 40 h‐sintered specimens was further discussed for the series of β‐Si3N4‐MgO‐Re2O3 systems based on the nanostructure characterization results obtained by the high‐resolution transmission electron microscopy and scanning transmission electron microscopy‐energy dispersive X‐ray spectrometry analyses. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The equiatomic high entropy alloy (HEA) NiCoCrFePd crystalizes as a single face-centered cubic (FCC) phase with strong local lattice distortion due to large atomic size mismatch between Pd element and other constitute elements. To better understand this quinary alloy, a family of single FCC phase equiatomic alloys made from the constituent elements of the NiCoCrFePd HEA, including the binary NiPd alloy, medium entropy alloys (MEAs) of NiCoPd, NiCrPd, and NiFePd, and the quinary NiCoCrFePd HEA with fully-recrystallized microstructure was experimentally investigated to understand the chemical effects on grain growth kinetics and solid solution hardening. With the principal elements increasing from two to five, the grain growth was increasingly inhibited in the annealing temperature range of 800–900 °C, while at 1000 °C and above, the NiCrPd MEA showed the slowest grain growth, which may attribute to the higher melting temperature of Cr and negative mixing enthalpy between Cr and other constituent elements, increasing the activation energy of grain growth. Moreover, the hardness depending on the grain size complied with the Hall-Petch relationship, in which NiCoPd exhibited the lowest hardness, while NiPd had a comparable hardness with NiCrPd and NiFePd. The above results suggested that the number of alloying elements was not the sole factor determining the sluggish diffusion and hardness. Instead, the type of constituent elements in the Pd-containing multicomponent alloys played more critical role. Furthermore, it was concluded that the strength of MEAs and HEA should depend on the combination of atomic size and modulus mismatch and electronegativity difference. [ABSTRACT FROM AUTHOR]

Grain rotation is commonly observed during the evolution of microstructures in polycrystalline materials of different kinds, including metals, ceramics, and colloidal crystals. It is widely accepted that interface migration in these systems is mediated by the motion of line defects with step and dislocation character, i.e., disconnections. We propose a crystallography-respecting continuum model for arbitrarily curved grain boundaries or heterophase interfaces, accounting for the disconnections' role in grain rotation. Numerical simulations demonstrate that changes in grain orientations, as well as interface morphology and internal stress field, are associated with disconnection flow. Our predictions agree with molecular dynamics simulation results for pure capillarity-driven evolution of grain boundaries and are interpreted through an extended Cahn-Taylor model. [ABSTRACT FROM AUTHOR]

The abnormal grain growth of steel, which is occurs during carburization, adversely affects properties such as heat treatment deformation and fatigue strength. This study aimed to control abnormal grain growth by controlling the materials and processes. Thus, it was necessary to investigate the effects of microstructure, precipitation, and heat treatment conditions on abnormal grain growth. We simulated abnormal grain growth using the cellular automaton (CA) method. The simulations focused on the grain boundary anisotropy and dispersion of precipitates. We considered the effect of grain boundary misorientation on boundary energy and mobility. The dispersion state of the precipitates and its pinning effect were considered, and grain growth simulations were performed. The results showed that the CA simulation reproduced abnormal grain growth by emphasizing the grain boundary mobility and the influence of the dispersion state of the precipitate on the occurrence of abnormal grain growth. The study findings show that the CA method is a potential technique for the prediction of abnormal grain growth. [ABSTRACT FROM AUTHOR]

Ultrafast high‐temperature sintering (UHS) is a joule heating method with an extremely high heating rate (∼103–104°C/min). In this work, commercial ZrB2 powders were rapidly densified by UHS to >90% relative density within 60 s in vacuum without pressure. Bulk density improved from 75% to 93% of relative density by increasing the sintering duration from 10 to 60 s. The final grain size increases from 2.7 ± 1.1 to 19.0 ± 8.4 μm when the sintering time increased from 10 to 60 s. X‐ray diffraction and energy‐dispersive spectroscopy show crystalline phase and compositional uniformity in ZrB2 after UHS. [ABSTRACT FROM AUTHOR]

This study utilized high rotational speeds (5500, 8500, and 10,000 rpm) and various traverse speeds (300, 600, and 900 mm/min) to carry out micro-friction stir welding on 0.8 mm thick plates of 5052–0 and 5052-H32 aluminum alloys. The weld heterogeneity was assessed through microstructural analysis and tensile testing under various process parameters. It was found that high rotational speeds generate enough heat to provide grain growth within the stirring zone. Moreover, the stirring zone showed a sizeable population of equiaxed grains, measuring less than 5 μm, that resulted in an improved mechanical strength of the joint. The joint efficiencies in the 5052-O and 5052-H32 alloys were significantly improved. The joint efficiencies of yield strength for 5052-O and 5052-H32 ranged between 129 and 139%, and 118% and 124%, respectively. The joint efficiencies of tensile strength for 5052-O varied between 102 to 109%, while in 5052-H32 they ranged from 93 to 100%. A comparison of the micro friction stir welding parameter to conventional thick plate friction stir welding showed that the former provided superior properties. [ABSTRACT FROM AUTHOR]

Solid-state sintering of Y 2 O 3 is difficult and requires high-temperature heat treatment or the use of a sintering additive. In this study, liquid-phase sintering was utilized to produce dense Y 2 O 3 bodies with fine-grained microstructure. Al 2 O 3 and SiO 2 were added to a commercial nano-Y 2 O 3 powder using aluminum nitrate and tetraethylorthosilicate (TEOS) as the precursors; the samples were uniaxially pressed at 100 MPa and sintered at 1500 °C and 1650 °C. The addition of the sintering aids increased the relative density of the samples sintered at lower temperatures; also, the sintering aids suppressed grain growth. The dissolution of Y 2 O 3 into the liquid phase changes the solid-liquid interfacial energy resulting in the formation of isolated yttrium-silicate/yttrium-aluminate grains and accounts for the suppression of the growth of yttria grains. [Display omitted] [ABSTRACT FROM AUTHOR]

• Superplasticity of fine-grained Mg-10Li alloy was studied. • Severe plastic deformation was used to achieve the fine grains. • Its deformation mechanisms for superplastic flow were analyzed. • Deformation mechanism maps were constructed in 2D and 3D. The superplastic behavior and associated deformation mechanisms of a fine-grained Mg-10.1 Li-0.8Al-0.6Zn alloy (LAZ1011) with a grain size of 3.2 µm, primarily composed of the BCC β phase and a small amount of the HCP α phase, were examined in a temperature range of 473 K to 623 K. The microstructural refinement of this alloy was achieved by employing high-ratio differential speed rolling. The best superplasticity was achieved at 523 K and at strain rates of 10−4 -5 × 10−4 s−1, where tensile elongations of 550–600% were obtained. During the heating and holding stage of the tensile samples prior to tensile loading, a significant increase in grain size was observed at temperatures above 573 K. Therefore, it was important to consider this effect when analyzing and understanding the superplastic deformation behavior and mechanisms. In the investigated strain rate range, the superplastic flow at low strain rates was governed by lattice diffusion-controlled grain boundary sliding, while at high strain rates, lattice diffusion-controlled dislocation climb creep was the rate-controlling deformation mechanism. It was concluded that solute drag creep is unlikely to occur. During the late stages of deformation at 523 K, it was observed that grain boundary sliding led to the agglomeration of the α phase, resulting in significant strain hardening. Deformation mechanism maps were constructed for β-Mg-Li alloys in the form of 2D and 3D formats as a function of strain rate, stress, temperature, and grain size, using the constitutive equations for various deformation mechanisms derived based on the data of the current tests. [ABSTRACT FROM AUTHOR]

Ultrafast high‐temperature sintering (UHS) is a joule heating method with an extremely high heating rate (∼103–104°C/min). In this work, commercial ZrB2 powders were rapidly densified by UHS to >90% relative density within 60 s in vacuum without pressure. Bulk density improved from 75% to 93% of relative density by increasing the sintering duration from 10 to 60 s. The final grain size increases from 2.7 ± 1.1 to 19.0 ± 8.4 μm when the sintering time increased from 10 to 60 s. X‐ray diffraction and energy‐dispersive spectroscopy show crystalline phase and compositional uniformity in ZrB2 after UHS. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is widely used for forming metals due to its complexity in geometrical design. Defects are unavoidably introduced in the manufacturing process, which requires post-processing. But it leads to grain growth. In this work, a series of post-heat treatments were used to study the effect of δ phase precipitation on grain growth and mechanical properties in SLM Inconel 718. Optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to study the microstructure of the specimens. The results showed that the precipitation of the δ phase increased with increasing aging time and that the growth of grains was inhibited by the δ phase. After 750◦C pre-aging for 48 h, the solution-treated specimen had the optimum strength and plasticity. [ABSTRACT FROM AUTHOR]

The restoration of an yttria dispersion strengthened tungsten plate and the corresponding microstructural evolution are investigated through in situ annealing using high-temperature confocal laser scanning microscopy. The geometrically necessary dislocation density and subgrain/grain evolution at each annealing stage are confirmed using the electron backscatter diffraction technique. The microstructure's evolution is divided into distinct stages of recovery, recrystallization, and grain growth based on their characteristic features. During the recovery process, the fomation of subgrains occurs. The primary mechanism of recrystallization nucleation is dominated by the strain-induced boundary migration mechanism, and the subgrains preexisting at grain boundaries are the main nucleation sites.

Most traditional powder melting-based additive manufacturing (AM) technologies generally yield high-performance parts at the expense of additional cost and energy consumption. As an economical and efficient alternative method, material extrusion (ME) that deploys polymer-based filaments with highly filled metal particles offers the possibility of scalable, low-cost fabrication of metal components. As a critical step, sintering governs the mechanical strength and geometry of the final parts. The grain growth behavior induced during sintering should be well controlled to achieve the parts with the desired mechanical performance. Due to the nature of AM, grain growth kinetics could also involve extremely complex grain boundary migration and atomic diffusion mechanisms caused by the heterogeneous pore distribution. In this work, an analytical model was developed to predict and understand the grain growth behavior of stainless steel (SS) 316L built by ME-based sintering-assisted AM. Such a model accounts for anisotropic viscosity parameters calibrated through a three-dimensional dilatometry test, enabling the prediction of grain size evolution during sintering. Grain growth kinetic parameters were further identified by the grain size data at the heating and holding stages. To validate and generalize the model, we also conducted the grain size evolution prediction under different sintering temperature profiles for as-built SS 316L specimens. This work will provide scientific insights into the grain growth behavior of metal parts built by this AM technique and its understanding can be readily transferred to other sintering-assisted AM processes like binder jetting and ink writing for metal structure creation.

A Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr (wt.%) alloy is processed by solution treatment and high pressure torsion (HPT) at room temperature to produce a nanostructured light material with high hardness. The stability of this alloy is subsequently tested through isochronal annealing for 0.5 h at 373 K to 673 K. The results reveal a thermal stability that is vastly superior to that of conventional Mg-based alloys processed by severe plastic deformation: the grain size remains at around 50 nm on heating to 573 K, and as the temperature is increased to 673 K, grain growth is restricted to within 500 nm. The stability of grain refinement of the present alloy/processing combination allowing grain size to be limited to 55 nm after exposure at 573 K, appears to be nearly one order of magnitude better than for the other SPD processed Mg-RE type alloys, and 2 orders of magnitude better than those of SPD processed RE-free Mg alloys. This superior thermal stability is attributed to formation of co-clusters near and segregation at grain boundaries, which cause a thermodynamic stabilization of grain size, as well as formation of β-Mg5RE equilibrium phase at grain boundaries, which impede grain growth by the Zener pinning effect. The hardness of the nanostructured Mg-Gd-Y-Zn-Zr alloy increases with increasing annealing temperature up to 573 K, which is quite different from the other SPD-processed Mg-based alloys. The high hardness of 136 HV after annealing at 573 K is mainly due to solute segregation and solute clustering at or near grain boundaries.

This study investigated the effects of KCl treatment on microstructure and thermoelectric properties of n-type Bi2Te2.7Se0.3 (BTS) thermoelectric materials. The innovative KCl treatment was originally intended to introduce nanopores through selective dissolution of KCl from a mixture of thermoelectric materials and KCl. However, it unexpectedly induced substantial variations in material composition and microstructure during the subsequent spark plasma sintering (SPS) process. Hydroxyl groups adsorbed on the powder surface during the dissolution resulted in the emergence of a Bi2TeO5 secondary phase within the BTS matrix after the SPS process at 450 ℃. The concentration of Bi2TeO5 increased with an increase in the KCl content. Furthermore, a remarkable grain growth occurred at low KCl concentrations, likely due to the liquid-phase formation in a Te-rich composition during SPS. However, excessive Bi2TeO5 at higher KCl concentrations hindered grain growth. These variations in the microstructure had complex effects on electrical properties: The TeBi antisite defects increased the electron concentration, and Bi2TeO5 reduced electron mobility. Additionally, the lattice thermal conductivity decreased due to the presence of Bi2TeO5, from 0.8 W∙m−1∙K−1 at 298 K for the pristine BTS to 0.6 W∙m−1∙K−1 at 298 K for BTS treated with 1 wt% KCl. These insights allowed precise adjustments of the electrical and thermal conductivities, leading to an enhancement in the maximum value of figure-of-merit (ZT) from 0.76 to 0.96 through the selective dissolution of KCl approach. We believe that our observations potentially enable advances in thermoelectric materials by engineering microstructures.

Ultrafine/nano WC–Co cemented carbide is widely used because of its high hardness, strength, toughness, and other comprehensive properties. However, WC grain growth during preparation is a persistent issue that hinders the development of this type of cemented carbide. In this context, we review current research on the preparation of ultrafine/nano WC–Co composite powder and sintering methods of ultrafine/nano cemented carbide. The correlation between grain growth and densification during sintering is analyzed. The key technologies inhibiting WC grain growth are explored and discussed, and the synergism between transition metal carbides and rare-earth element mixtures is found to effectively inhibit the growth of WC grains and improve the general performance of ultrafine/nano WC–Co cemented carbide. Finally, future research directions and development trends of ultrafine/nano WC–Co cemented carbides are presented.

BaCe0.65Zr0.2Y0.15O3-δ (BCZ20Y15) has raised great interest due to its good protonic conductivity and chemical stability. However, the sintering of the material is considerably challenged by its refractory nature. In the current work, almost fully densified single-phase BCZ20Y15 with grain sizes exceeding 10 μm was successfully fabricated by sintering at 1500 °C by using calcined powders consisting of naturally separated perovskite phases and 0.5 wt% NiO. The role of NiO as sintering aid was elucidated by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Atom Probe Tomography (APT) methods, concerning global and local material composition. Furthermore, the mechanism leading to the promoted densification and grain growth is elucidated based on current experimental results and a comprehensive review of the literature.

Uranium silicide (U3Si2) is regarded as a viable fuel option for improving the safety of nuclear power plants. In the present work, phase-field simulations were employed to investigate grain growth phenomena, encompassing both isotropic and anisotropic grain growth. In simulations of isotropic grain growth, it is commonly assumed that the energy and mobility of the grain boundaries (GBs) remain constant, represented by average values. The calculated grain growth kinetic rate constant, K, exhibits a close correspondence with the experimental measurements, indicating a strong agreement between the two. In simulations of anisotropic grain growth, the values of GB energy and mobility are correlated with the angular disparity between GBs. The simulation results demonstrated that the growth rate of U3Si2 can be influenced by both the energy anisotropy and mobility anisotropy of GBs. Furthermore, the anisotropy in mobility results in a greater prevalence of low-angle GB distribution in comparison to high-angle GBs. However, the energy anisotropy of GBs does not impact the frequency distribution of the angle difference between GBs.

Cu–Cu joints have been adopted for ultra-high density of packaging for high-end devices. However, the processing temperature must be kept relatively low, preferably below 300 °C. In this study, a novel surface modification technique, quenching treatment, was applied to achieve Cu-to-Cu direct bonding using (111)-oriented nanotwinned Cu. The quenching treatment enabled grain growth across the Cu–Cu bonding interface at 275 °C. During quenching treatment, strain energy was induced in the Cu film, resulting in a wrinkled surface morphology. To analyze the strain energy, we utilized an electron backscattered diffraction system to obtain crystallographic information and confirmed it using kernel average misorientation analysis.

Dual-phase (DP) steel has been widely used in automotive steel plates with a balance of excellent strength and ductility. Grain refinement in DP steel is important to improve the properties further; however, the factors affecting grain growth need to be well understood. The remaining problem is that acquiring data through experiments is still time-consuming and difficult to evaluate quantitatively. With the development of materials informatics in recent years, material development time and costs are expected to be significantly reduced through experimentation, simulation, and machine learning. In this study, grain growth behavior in DP steel was studied using two-dimensional (2D) and three-dimensional (3D) Monte Carlo modeling and simulation to estimate the effect of some key parameters. Grain growth can be suppressed when the grain boundary energy is greater than the phase boundary energy. When the volume fractions of the matrix and the second phase were equal, the suppression of grain growth became obvious. The long-distance diffuse frequency can promote grain growth significantly. The simulation results allow us to better understand the factors affecting grain growth behavior in DP steel. Machine learning was performed to conduct a sensitivity analysis of the affecting parameters and estimate the magnitude of each parameter's effects on grain growth in the model. Combining MC simulation and machine learning will provide one promising research strategy to gain deeper insights into grain growth behaviors in metallic materials and accelerate the research process. [ABSTRACT FROM AUTHOR]

Li 2 TiO 3 ceramic pebbles with uniform structure, high density and good mechanical property were successfully fabricated by wet process. The Li 2 TiO 3 pebbles sintered at 1000 °C for 4 h had satisfactory density (91% T.D.) and crush load (a.v. 27.1 N). The apparent activation energy of Li 2 TiO 3 grain growth was 201 ± 7 kJ/mol. Accelerated densification was observed in a reducing atmosphere, this might be attributed to the oxygen vacancies generated by the reduction of Ti4+ to Ti3+ in 0.1%H 2 +He atmosphere, which facilitate the diffusion of ions through the lattice. The grain growth was controlled by lattice diffusion under reducing atmosphere, and the apparent activation energy was 168 ± 6 kJ/mol. The mechanical results show that the crush load of Li 2 TiO 3 pebbles decreased with the increase of temperature, and the average crush load at 500 °C was 13.9 N. In addition, the thermal cycling and long-time annealing experiments suggested that Li 2 TiO 3 pebbles have good structural and performance stability. The Li 2 TiO 3 ceramics prepared by wet process were satisfactory tritium breeder materials with ideal application potential. [ABSTRACT FROM AUTHOR]

• HPT-processed Mg-Gd-Y-Zn-Zr nanostructure exhibits an excellent thermal stability. • Mg-Gd-Y-Zn-Zr nanostructure exhibits an unique phase transformation upon annealing. • The formation of solute segregation and β phase retards grain growth during annealing. • A hardness peak is achieved by annealing due to the effects of solute segregation. A Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr (wt.%) alloy is processed by solution treatment and high pressure torsion (HPT) at room temperature to produce a nanostructured light material with high hardness. The stability of this alloy is subsequently tested through isochronal annealing for 0.5 h at 373 K to 673 K. The results reveal a thermal stability that is vastly superior to that of conventional Mg-based alloys processed by severe plastic deformation: the grain size remains at around 50 nm on heating to 573 K, and as the temperature is increased to 673 K, grain growth is restricted to within 500 nm. The stability of grain refinement of the present alloy/processing combination allowing grain size to be limited to 55 nm after exposure at 573 K, appears to be nearly one order of magnitude better than for the other SPD processed Mg-RE type alloys, and 2 orders of magnitude better than those of SPD processed RE-free Mg alloys. This superior thermal stability is attributed to formation of co-clusters near and segregation at grain boundaries, which cause a thermodynamic stabilization of grain size, as well as formation of β-Mg 5 RE equilibrium phase at grain boundaries, which impede grain growth by the Zener pinning effect. The hardness of the nanostructured Mg-Gd-Y-Zn-Zr alloy increases with increasing annealing temperature up to 573 K, which is quite different from the other SPD-processed Mg-based alloys. The high hardness of 136 HV after annealing at 573 K is mainly due to solute segregation and solute clustering at or near grain boundaries. [ABSTRACT FROM AUTHOR]

The Th 1- x Sc x O 2- x /2 (0 ≤ x ≤ 0.1) ceramic system with high density was originally prepared via a co-precipitation route and simple sintering method. XRD analysis indicates that the Th 1- x Sc x O 2- x /2 ceramics exhibited a single cubic fluorite structure and a slight increase of cell parameters. SEM images show that Sc doping contributed a decreasing pores and more uniform grain distribution. The calculated relative densities could reach up to a value higher than 99.0% for x = 0.01 during the isothermal process while the maximum actual relative density was only about 77.4% during the non-isothermal sintering process. And the analysis of grain growth kinetics demonstrates that Th 1- x Sc x O 2- x /2 was a solid solution with a high solubility of Sc for x = 0.01 and a low solubility of Sc for both x = 0.05 and x = 0.1, which resulted in a strongly slow grain growth for x = 0.1 due to the solute drag effect. The sintering mechanism investigation also illustrates that low amount (x = 0.01) of Sc doping could significantly enhance the densification sintering of ThO 2 -based ceramics and reduce the sintering temperature by nearly 150 °C. Such strategy has issued the bottleneck problem existed in the densification sintering of ThO 2 -based ceramics at a lower temperature without any other special sintering atmosphere, which even could be applicable for other ceramics difficult to sinter. [ABSTRACT FROM AUTHOR]

Numerical simulation has disclosed a strong influence of the size distribution of fine particles on grain growth in polycrystalline materials. It is shown that growth of its width causes lowering of the time exponent in the kinetic equation of normal grain growth and reduction of the incubation period of abnormal grain growth. [ABSTRACT FROM AUTHOR]

The phenomenon of primary recrystallization in metallic materials is a complex process that involves nucleation and growth of new grains from the deformed microstructure during post-deformation annealing heat treatment. In this study, we compare the experimental and numerical simulation results of primary recrystallization in metallic materials. The experimental tests were carried out on ARMCO iron samples extruded to 10, 20, and 30% of deformation degree and annealed at 973 K for 300 s. Microsections of the deformed and annealed specimens were analyzed using a metallographic microscope and Joyce-Loebl image analyzer. The numerical simulations were performed using a Monte Carlo algorithm to model the primary recrystallization of variable nucleation rate. On the basis of the classification given by Christian, four types of nucleation were simulated: site-saturated nucleation, constant nucleation rate, increasing nucleation rate, and decreasing nucleation rate, with different magnitudes of stored energy. Our results show that the decreasing nucleation rate model best fits the experimental data. The comparison between the experimental and numerical simulation results provides insights into the nucleation and growth of new grains during primary recrystallization in metallic materials. [ABSTRACT FROM AUTHOR]

In the present study, detailed investigation on postdeposition halides treatment using CdCl2, CdI2, MgF2, MgCl2 and MgI2 is undertaken over thermally evaporated CdTe films. As-deposited films are subjected to halide treatment and subsequent annealing at 385°C. Halide activation induced grain growth mechanism is presented along with anions and cations roles on change in films properties and formation of different complexes. XRD patterns of all CdTe thin films exhibited polycrystalline nature with preferential cubic phased (310) plane except for CdI2 treated films where preferred reflection is appeared corresponding to (220) plane. Grain growth is observed with treatment employing amicable estimation tools. All films have a conspicuous ohmic character owing to linear I–V plots. Optical study reveals that CdCl2 treated CdTe films have higher absorbance and optical energy band-gap is measured out in the range 1.42–1.53 eV with halide treatment. Surface topography and PL study revealed to variations in surface roughness and photoluminescence peaks intensity with halide treatments. Film growth and treatment are validated by EDS analysis and FESEM images demonstrated explicit grain growth. Findings warrant amazing role of halide activation on film properties and CdCl2 is found a suitable surface treatment agent to CdTe films in order to develop better devices. [ABSTRACT FROM AUTHOR]

The effects of both nuclear energy loss and electronic energy loss need to be taken into consideration in the ceramic-based waste forms under repository environment. However, the irradiation responses of ceramic-based waste forms to each type of energy loss are somewhat different. In this study, the microstructure evolutions of ultrafine nano and micro Gd 2 Zr 2 O 7 -based waste forms were systematically studied under predominant electronic energy loss simulated by multi-energy He+ irradiation, and compared to those under predominant nuclear energy loss. The results reveal that the fewer He bubble chains, ribbon-like He bubbles and smaller microcracks were observed in the irradiated nano-grained sample. Additionally, nano-grained sample displayed a lower degree of amorphization and higher atomic order compared to micro-grained samples when subjected to predominant electronic energy loss. Moreover, the irradiation dominated by nuclear energy loss can easily induce the grain growth of nano-grained Gd 2 Zr 2 O 7 -based waste form, but in the present study this phenomenon was not observed under multi-energy He+ irradiation. Consequently, under predominant electronic energy loss, the thermodynamic instability and driving force for grain growth due to excess surface energy in the ultrafine nano sample can be suppressed. As a result, the sample demonstrated enhanced irradiation resistance due to the more efficient absorption and elimination of defects at grain boundaries induced by electronic excitation. We elucidated that enhanced irradiation resistance of the waste forms by tailoring the grain size requires the consideration of the effects of electronic energy loss and nuclear energy loss, which can provide guidance for the design and optimization of highly irradiation-resistant nuclear waste forms. [ABSTRACT FROM AUTHOR]

Today, 7xxx aluminum alloys are widely used in aerospace and other fields due to their excellent properties such as low density, high specific strength, and good processing performance. The heat treatment process of 7xxx aluminum alloy is crucial in controlling the strengthening phases and grain size, which is a significant way to enhance the alloy's performance. In this study, solution heat treatment tests of 7050 aluminum alloys were carried out at different temperatures, ranging from 440 °C to 470 °C, with a holding time ranging from 0.5 h to 8 h, using a DIL 805A thermomechanical test machine. The microstructural evolution during the solution heat treatment was characterized using an optical microscope (OM), a scanning electron microscope (SEM), and a transmission electron microscope (TEM). The effects of the solution parameters on the alloy's microhardness were analyzed using a digital Vickers microhardness tester. According to the ASTM E112-13 standard, The Anelli grain growth models were established to illustrate the grain size evolution during solution heat treatment, and a modified Anelli grain growth model was established. The results indicated that the grain size significantly increases with the increase in the solution heat treatment time and temperature. The Anelli grain growth model can illustrate the phenomenon of grain growth more accurately in the solution heat treatment process of 7050 aluminum alloy. It was found that prolonging the time and elevating the temperature of the solution heat treatment reduced the microhardness of the aluminum alloy because of the dissolution of the precipitates. [ABSTRACT FROM AUTHOR]

Nanostructured steels are expected to have enhanced irradiation tolerance and improved strength. However, they suffer from poor microstructural stability at elevated temperatures. In this study, Fe–21Cr–5Al–0.026C (wt%) Kanthal D (KD) alloy belonging to a class of (FeCrAl) alloys considered for accident‐tolerant fuel cladding in light‐water reactors is nanostructured using two severe plastic deformation techniques of equal‐channel angular pressing (ECAP) and high‐pressure torsion (HPT), and their thermal stability between 500–700 °C is studied and compared. ECAP KD is found to be thermally stable up to 500 °C, whereas HPT KD is unstable at 500 °C. Microstructural characterization reveals that ECAP KD undergoes recovery at 550 °C and recrystallization above 600 °C, while HPT KD shows continuous grain growth after annealing above 500 °C. Enhanced thermal stability of ECAP KD is from significant fraction (>50%) of low‐angle grain boundaries (GBs) (misorientation angle 2–15°) stabilizing the microstructure due to their low mobility. Small grain sizes, a high fraction (>80%) of high‐angle GBs (misorientation angle >15°) and accordingly a large amount of stored GB energy, serve as the driving force for HPT KD to undergo grain growth instead of recrystallization driven by excess stored strain energy. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the effect of the mechanical and metallurgical joint strength behavior of Cr-Ni-Mo steel (AISI 316) using direct drive friction welding. Experimental procedures in the study included macrostructure, microhardness, tensile test specimens with effective diameters of 4 mm, 6 mm, and 8 mm, microstructure of the fracture position, and tensile fracture morphology. The results concluded that the average microhardness values for 4 mm, 6 mm, and 8 mm diameter around the weld interface center are 298 Hv0.1, 300 Hv0.1, and 295 Hv0.1, respectively. The ultimate tensile strength ratios were of 95%, 98%, and 97% for 4 mm, 6 mm, and 8 mm, respectively, while, the ductility increased with the diameters of 41%, 50%, and 57% for 4 mm, 6 mm, and 8 mm, respectively, compared to AISI 316. The fracture position for all welded joints was in the adjacent region to the interface. The fracture surfaces had a fingerprint form and ductile mode at cleavage features. The center of the fracture revealed different forms of dimples and microcavities collected at that center. [ABSTRACT FROM AUTHOR]

Mean-field models have the ability to predict the evolution of grain size distribution that occurs through thermomechanical solicitations. This article focuses on a comparison of mean-field models under grain-growth conditions. Different microstructure representations are considered and discussed, especially regarding the consideration of topology in the neighborhood construction. Experimental data obtained with a heat treatment campaign on 316L austenitic stainless steel are used for the identification of material parameters and as a reference for model comparisons. Mean-field models are also applied to both mono- and bimodal initial grain size distributions to investigate the potential benefits of introducing neighborhood topology in microstructure prediction models. This article demonstrates that improvements in the predictions can be obtained in monomodal cases for topological models. In the bimodal test, no comparison with experimental data was performed as no data were available. But relative comparisons between models indicated few differences in the predictions. Although of interest, the consideration of neighborhood topology in grain-growth mean-field models generally results in only small improvements compared to classical mean-field models, especially in terms of implementation complexity. [ABSTRACT FROM AUTHOR]

Cd alloying has been theoretically proved to be an effective strategy to suppress Cu‐Zn antisite defects and related defect cluster for improving device performance of pure sulfide kesterite Cu2ZnSnS4 (CZTS) thin film solar cells. However, the potential of Cd alloying has not been fully realized by solely doping without further post heat‐treatment. Here, Cd alloying CZTS (Cu2(Zn,Cd)SnS4, CZCTS) is reported through dimethyl sulfoxide (DMSO) solution and how alloying concentration affects reaction path, grain growth, and electronic properties of the CZCTS absorbers is investigated. This study found that Cd can be incorporated into CZTS through direct phase transformation grain growth, which sufficiently suppresses band tailing. High quality CZCTS absorber films and efficient solar cells are fabricated within a wide range of alloy concentration. A champion CZCTS device with a power conversion efficiency of 12.3% is achieved at 35% Cd concentration without any post heat treatment, improved by over 70% compared to 7.0% of CZTS. This device exhibits a high VOC gain to the Shockley–Queisser (Voc/VocSQ = 59.7%), the lowest VOC deficit achieved in pure sulfide kesterite solar cells. The results demonstrate the importance of the Cd alloying strategy for mitigating band tailing and achieving high efficiency pure sulfide kesterite solar cells. [ABSTRACT FROM AUTHOR]

The development of high‐performance (K,Na)NbO3 (KNN)‐based lead‐free piezoceramics for next‐generation electronic devices is crucial for achieving environmentally sustainable society. However, despite recent improvements in piezoelectric coefficients, correlating their properties to underlying multiscale structures remains a key issue for high‐performance KNN‐based ceramics with complex phase boundaries. Here, this study proposes a medium‐entropy strategy to design "local polymorphic distortion" in conjunction with the construction of uniformly oversize grains in the newly developed KNN solid‐solution, resulting in a novel large‐size hierarchical domain architecture (≈0.7 µm wide). Such a structure not only facilitates polarization rotation but also ensures a large residual polarization, which significantly improves the piezoelectricity (≈3.2 times) and obtains a giant energy harvesting performance (Wout = 2.44 mW, PD = 35.32 µW mm−3, outperforming most lead‐free piezoceramics). This study confirms the coexistence of multiphase through the atomic‐resolution polarization features and analyzes the domain/phase transition mechanisms using in situ electric field structural characterizations, revealing that the electric field induces highly effective multiscale polarization configuration transitions based on T–O–R sequential phase transitions. This study demonstrates a new strategy for designing high‐performance piezoceramics and facilitates the development of lead‐free piezoceramic materials in energy harvesting applications. [ABSTRACT FROM AUTHOR]

A new grain growth model was developed by introducing the ultimate grain size to the traditional model. The grain growth behavior and its ultimate size under the Zenner pinning force are also discussed. This model was applied to the nickel-based superalloy and integrated into an FEM code. The grain evolution of a forged third-generation powder superalloy heat treated at different temperatures and holding times was studied. A gradient heat treatment setup was designed and implemented for a full-size turbine disc based on the model prediction to meet the accurate dual-microstructure requirements of an advanced aero-engine turbine disc design. The predicted temperature was validated by thermal couple measurements. The relative error between the prediction and the measurements is less than 2%. The metallographic examination of the whole turbine disk through sectioning showed that the grain size was ASTM 7-8 at the rim area and ASTM 11-12 at the bore region, which agrees well with the prediction. The predicted values of the three measurement areas are ASTM 12.1, ASTM 9.1, and ASTM 7.1, respectively, with a maximum error of 5% compared to the measured values. The proposed model was validated and successfully applied to help manufacture a dual-microstructure aero-engine turbine disc. [ABSTRACT FROM AUTHOR]

Ceramic composites based on Ce-TZP/Al2O3/H6A were sintered in order to promote grain growth and to study the effects of ZrO2 grain size on the properties of this material. A mixture of ZrO2-CeO2-Al2O3 powders was sintered at 1450 °C-2 h, following the manufacturer's recommendations. Then, the samples were further treated at 1500 or 1600 °C, for 0, 2, 8, or 24 h. The sintered specimens were characterized by X-ray diffraction, relative density, and grain size distribution. Vickers nanohardness, Young's modulus (E), and fracture toughness were measured. The materials showed complete densification for all sintering conditions studied. t-ZrO2, α -Al2O3, and cerium hexaluminate (H6A) were observed. The alumina and hexaluminate grains had average grain sizes of 0.7 and 4.5 μm (AR>3), respectively, without significant variations during the additional heat treatments. However, significant growth took place for the ZrO2 grains with increasing temperature and holding time, increasing the average grain size from 0.6~1.4 μm, when sintered at 1500 °C-2 h to 1600 °C-24 h, respectively. The materials exhibited Vickers nanohardness of 1800 HV and E=241 ± 15 GPa. On the other hand, the considerable grain growth of the ZrO2 grains as a function of holding time reflected in a reduction of the fracture toughness, which decreased from 8.5 to 5.7 MPa.m1/2 for samples sintered at 1500 °C-2 h to 1600 °C-24 h, respectively. [ABSTRACT FROM AUTHOR]

Ruthenium (Ru)—a high-melting-point precious metal—has attracted attention for use as ultrafine interconnections in large-scale integrations. This is because the resistivity of Ru interconnects is not expected to increase with a reduction in the interconnect width owing to their short mean free path for electrons. In this study, we investigated electroless plating of Ru using hydrazine hydrate as a reducing agent to obtain low-resistivity Ru films. We obtained polycrystalline Ru films on a thin (10-nm) catalytic chemical-vapor-deposited Ru underlayer. The electroless Ru films exhibited significant grain growth upon annealing at 600°C in a forming gas (N2:H2 = 9:1). The Ru (101) and (100) crystalline orientations were strengthened by annealing, and the resistivity decreased from 160 µΩ cm to 22 µΩ cm concomitantly. Thermal desorption spectroscopy showed that the electroless Ru films contained impurities, such as CO, CO2, NH3, O, C, and H2. Desorption of C, CO, CO2, and NH3 showed peak maxima at approximately 450–500 K. These impurity molecules likely came from the inclusion of the complexing agents (tartaric acid: C4(OH)4O2, and ammonium chloride: NH4Cl) and reducing agent (hydrazine: N2H2) into the Ru film. Desorption of these molecules during annealing may improve the grain growth of polycrystalline Ru and reduce its resistivity. [ABSTRACT FROM AUTHOR]

This work presents a Monte Carlo Potts grain growth model in which the grain boundary (GB) energies depend on the GB inclination. The inclination is calculated using a linear smoothing approach developed by the authors. In bicrystal simulations with a shrinking grain, the grain changes shape to prefer low energy GB inclinations. However, in polycrystal simulations the preferred inclinations depend on the approach used to assign the triple junction (TJ) energies. Approaches that produce unimodal TJ energy distributions result in the expected behavior of preferring low energy GB inclinations. However, approaches that produce bimodal TJ energy distributions result in medium energy or even high energy inclinations being preferred. Overall, this study underscores the importance of TJs in anisotropic grain growth.

Recent research has focused on the ultrafast laser welding of metal and glass due to its diverse applications in aerospace, medicine, and optical sensing. However, the significant material property differences between metals and glass, along with strict surface requirements, pose challenges to the development of metal-glass welding and limit its industrial utility. Utilizing high-pulse-energy lasers has proven effective in mitigating these challenges. This study comprehensively analyzes a millijoule (mJ)-level femtosecond pulse laser welding technique applied to aluminum alloy and fused silica, with a primary emphasis on understanding the characteristics and mechanism of joint. During the welding process, aluminum and fused silica mutually diffuse, leading to the formation of five distinct zones at the joint's cross-section. Within the aluminum molten pool in rapid cooling, aluminum grains undergo continuous growth along a temperature gradient and then transform into smaller epitaxial grains with altered grain orientations and HAGBs. An amorphous Al2O3 phase coexists with aluminum, forming a lamellar structure. Besides, silicon nanoparticles and transitional γ-Al2O3 precipitate near the center of the weld. This study examines the underlying causes of these phenomena and provides a detailed discussion of the associated strengthening mechanisms, ultimately resulting in a maximum shear strength of 8.94 MPa.