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In this study two functionally graded cemented carbide samples with gradients in both composition and grain size have been produced and studied. The two samples are manufactured by local addition of TiC to a pressed WC-Co green body prior to sintering. The two samples differ only by the in-going WC particle size, where one sub-micron and one coarse WC particle size is used. The Ti, Co, and C concentration profiles are analysed using energy−/ and wavelength-dispersive X-ray spectroscopy; Vickers hardness profiles are also measured. Furthermore, the measured experimental concentration profiles are compared with diffusion simulations using the DICTRA software. The concentration and hardness profiles show a similar trend for both samples with decreasing Ti and C concentrations while Co concentration increases with distance from the applied TiC layer. The composition gradient affects the number of stable phases and the WC grain size. Furthermore, there are distinct differences between the samples with different initial WC particle size. The sample with an initially finer WC particle size has a shorter gamma-phase zone and the difference in WC grain size across the gradient is larger as compared to the sample with an initially coarser WC particle size. Finally, abnormal grain growth occurs in both samples but it is suppressed with increasing Ti concentration., QC 20230710

Uranium dioxide (UO2) is widely used as a fuel in commercial nuclear light-water reactors (LWRs). Rigorous control of density, pore, and grain size of UO2 pellets are important prerequisites for fuel performance. Solid lubricants, frequently used in pellets manufacturing, minimize structural defects on compaction such as cracks and end-capping, promoting grain growth during sintering. This work presents and discusses the effects of the aluminum distearate (ADS) addition on the sintering behavior and microstructure of UO2 fuel pellets. UO2 and UO2-0.2wt% ADS pellets were sintered at 1760 °C for 5.7 h for comparison purposes. The results show that the densification rate increases using the solid lubricant, but the shrinkage is lowered by 0.7% due to low homogenization. The average grain size was increased by about 35% during sintering. Based on our results and a literature review, a mechanism for grain growth by aluminum addition is proposed., QC 20230508

Uppvärmning av stål kan leda till korntillväxt vilket har en avgörande roll på materialets mekaniska egenskaper och generellt sett så resulterar det i sämre hållfasthet. I följande examensarbete har olika modeller tagits fram för att prediktera förändringar i kornstorleken som sker till följd av sätthärdning. Modellerna tas fram via en litteraturöversikt och är ämnade att prediktera korntillväxt på provbitar med tillsatser av Niob samt provbitar utan Niob. Målet med detta examensarbete är att undersöka vilka modeller som finns tillgängliga för att prediktera korntillväxt samt analysera hur predikteringen ser ut i jämförelse med observationsvärden från experimentella försök. Examensarbetet består av en experimentell del och en modelleringsdel. Den experimentella delen sker genom att provbitar analyseras med hjälp av ljusoptisk mikroskopi med avseende på förändringar i kornstorlek före och efter värmebehandling. Detta för att kunna estimera förändringar i kornstorlek och validera beräkningsmodellerna för prediktering av förändringar i kornstorlek. Modelleringsdelen används för att testa hur olika modeller predikterar korntillväxten. Beräkningsdelen och den experimentella delen jämförs sedan med varandra i resultatet där en sammanställning på alla värden sker. Resultatet visar vilka modeller som finns tillgängliga för att prediktera korntillväxt samt hur predikteringarna ställer sig mot observationsvärden från experimentella prover. För att säkerställa att modellerna kan användas för att prediktera korntillväxten så krävs en djupare analys av modellerna då alla materialparametrar inte kunde tas fram till samtliga modeller. En utveckling av arbetet är att ta fram alla parametrar för att sedan kunna avgöra vilken modell som ställer sig närmast till uppmätta värden från den experimentella delen., Heating steel may lead to grain growth, which results in deterioration of mechanical properties of the steel. In the present study, different models that predict changes in grain size, occurring in heat treatments such as case hardening, have been validated. The models were retrieved via a literature review and were intended to predict grain growth on test pieces with and without Niob precipitates. The aim of this thesis is to investigate which models that are available for predicting grain growth and to validate the models in a comparison with experimental results. This thesis consists of an experimental part and a modeling part. The experimental part is done by analyzing specimens using light-optical microscopy regarding changes in grain size before and after heat treatment. This is to be able to estimate changes in grain size and validate calculation models for predicting changes in grain size. The modeling part is used to evaluate how different models predict grain growth. The calculation part and the experimental part then compare with each other in the result where a compilation of all values takes place. The results show which models are available for predicting grain growth and how the predictions compare with observation values from experimental samples. To ensure that the models can be used to predict grain growth, a deeper analysis of the models is required; not all material parameters could be obtained for all models. A development of the work is to retrieve all parameters in order to then be able to determine which model is closest to the measured values from the experimental part.

The static recrystallization characteristics and microstructure evolution in hot-deformed austenite were evaluated for a newly developed low-carbon CrNiMnB ultrahigh-strength steel with and without molybdenum addition. The time for 50% static recrystallization (t50%) over a wide range of strains and hot-deformation temperatures were obtained using the stress-relaxation technique on Gleeble thermomechanical simulator. Moreover, effect of deformation parameters on the size distribution and average size of prior austenite grains are investigated. A novel semi-automatic stress relaxation test reading tool with a graphical user interface was created and used successfully for the current study. The obtained results of strain‘s power and the apparent activation energy are within the range stated in literature for C-Mn and microalloyed steels. Addition of molybdenum increase the power of strain and the apparent activation energy from − 1.9 to − 2.6 and 206 to 212 kJ/mol, respectively. The retardation effect of molybdenum addition was shown by a new regression equation devised for calculating t50%. The developed equations show a good agreement with the experimental data and can be used in the designing of roughing during thermomechanical processing. The deformation parameters i.e., temperature, strain and holding time have a significant effect on the size distribution and average size of prior austenite grains.

In this study,microstructure and mechanical characterization of as-built Hastelloy X (HX) samples produced by laser powder bed fusion (LPBF) process and post-heat-treated samples were investigated. Two sets of samples, horizontal and vertical to build direction, were considered in as-built condition to understand the effect of build direction and two solution heat-treatment temperatures, 1177°C and 1220°C, followed by fast cooling were considered to study the effect of solution heat-treatment temperature on microstructure and mechanical properties. Microstructure characterization of as-built sample horizontal to build direction revealed a typical multi-layer molten pool boundaries and the sample vertical to build direction revealed multi-layered and multi-tracked molten pool boundaries. Electron backscatter diffraction results reveal a disrupted epitaxial grain growth for the as-built samples vertical to build direction whereas equiaxed grain structure with varying twin grain boundary fractions was observed for heat-treated HX samples. As-built LPBF HX samples exhibit higher mean hardness and yield strength than post-heat-treated samples. Higher elongation and lower yield strength were observed for the sample solution treated at 1220°C as compared to the sample solution annealed at 1177°C. Microstructural evolution at 20% engineering strain for the exact positions before the tensile test was presented for solution treated at 1220°C samples, which reveals distinct slip lines within each grain as well as increased dislocation density at grain boundaries. © 2022 The Authors. Published by Elsevier B.V.

In this study,microstructure and mechanical characterization of as-built Hastelloy X (HX) samples produced by laser powder bed fusion (LPBF) process and post-heat-treated samples were investigated. Two sets of samples, horizontal and vertical to build direction, were considered in as-built condition to understand the effect of build direction and two solution heat-treatment temperatures, 1177°C and 1220°C, followed by fast cooling were considered to study the effect of solution heat-treatment temperature on microstructure and mechanical properties. Microstructure characterization of as-built sample horizontal to build direction revealed a typical multi-layer molten pool boundaries and the sample vertical to build direction revealed multi-layered and multi-tracked molten pool boundaries. Electron backscatter diffraction results reveal a disrupted epitaxial grain growth for the as-built samples vertical to build direction whereas equiaxed grain structure with varying twin grain boundary fractions was observed for heat-treated HX samples. As-built LPBF HX samples exhibit higher mean hardness and yield strength than post-heat-treated samples. Higher elongation and lower yield strength were observed for the sample solution treated at 1220°C as compared to the sample solution annealed at 1177°C. Microstructural evolution at 20% engineering strain for the exact positions before the tensile test was presented for solution treated at 1220°C samples, which reveals distinct slip lines within each grain as well as increased dislocation density at grain boundaries. © 2022 The Authors. Published by Elsevier B.V.

The topological transitions of the grain boundary network during grain growth under uniform grain boundary energies are believed to be known. However, this is not true for more realistic materials with varying grain boundary energies that, in principle, allow many different grain boundary configurations. A grain growth simulation for such a material therefore requires a procedure to enumerate all possible topological transitions and select the most energetically favorable one. Such a procedure is developed and implemented here for a microstructure represented by a volumetric finite element mesh. The method is implemented as a C++ library called VDlib based on SCOREC, an open source massively parallelizable library for finite element simulations with adaptive meshing. To test the implementation, a Voronoi tessellated microstructure composed of one hundred grains is generated and evolved under constant grain boundary properties until half of the grains remained. The evolution of the individual grains is compared to what is expected from the MacPherson-Srolovitz relation and is found to be in good match.As with all numerical techniques, it is important to identify systematic sources of error. Such studies for grain growth simulations are either missing from or not uniform across the literature. To address this issue and enable comparison across grain growth simulations, a set of benchmark cases, one for each boundary type of surfaces, lines, and points with analytical solutions are identified. These are used to compare a recently developed discrete-interface method for microstructure evolution to a state of the art diffuse interface (multiphase field method). In each case, the discrete method is found to meet or outperform the multiphase field method in terms of accuracy for comparable levels of refinement, demonstrating its potential efficacy as a numerical approach for microstructure evolution.Last, a novel invariant of ideal grain growth process is defined that idea

In this study,microstructure and mechanical characterization of as-built Hastelloy X (HX) samples produced by laser powder bed fusion (LPBF) process and post-heat-treated samples were investigated. Two sets of samples, horizontal and vertical to build direction, were considered in as-built condition to understand the effect of build direction and two solution heat-treatment temperatures, 1177°C and 1220°C, followed by fast cooling were considered to study the effect of solution heat-treatment temperature on microstructure and mechanical properties. Microstructure characterization of as-built sample horizontal to build direction revealed a typical multi-layer molten pool boundaries and the sample vertical to build direction revealed multi-layered and multi-tracked molten pool boundaries. Electron backscatter diffraction results reveal a disrupted epitaxial grain growth for the as-built samples vertical to build direction whereas equiaxed grain structure with varying twin grain boundary fractions was observed for heat-treated HX samples. As-built LPBF HX samples exhibit higher mean hardness and yield strength than post-heat-treated samples. Higher elongation and lower yield strength were observed for the sample solution treated at 1220°C as compared to the sample solution annealed at 1177°C. Microstructural evolution at 20% engineering strain for the exact positions before the tensile test was presented for solution treated at 1220°C samples, which reveals distinct slip lines within each grain as well as increased dislocation density at grain boundaries. © 2022 The Authors. Published by Elsevier B.V.

Small grain size and near-horizontal grain boundaries are known to be detrimental to the carrier collection efficiency and device performance of pure-sulfide Cu2ZnSnS4 (CZTS) solar cells. However, forming large grains spanning the absorber layer while maintaining high electronic quality is challenging particularly for pure sulfide CZTS. Herein, a liquid-phase-assisted grain growth (LGG) model that enables the formation of large grains spanning across the CZTS absorber without compromising the electronic quality is demonstrated. By introducing a Ge-alloyed CZTS nanoparticle layer at the bottom of the sputtered precursor, a Cu-rich and Sn-rich liquid phase forms at the high temperature sulfurization stage, which can effectively remove the detrimental near-horizontal grain boundaries and promote grain growth, thus greatly improving the carrier collection efficiency and reducing nonradiative recombination. The remaining liquid phase layer at the rear interface shows a high work function, acting as an effective hole transport layer. The modified morphology greatly increases the short-circuit current density and fill factor, enabling 10.3% efficient green Cd-free CZTS devices. This work unlocks a grain growth mechanism, advancing the morphology control of sulfide-based kesterite solar cells. © 2022 The Authors. Small published by Wiley-VCH GmbH.

Uppvärmning av stål kan leda till korntillväxt vilket har en avgörande roll på materialets mekaniska egenskaper och generellt sett så resulterar det i sämre hållfasthet. I följande examensarbete har olika modeller tagits fram för att prediktera förändringar i kornstorleken som sker till följd av sätthärdning. Modellerna tas fram via en litteraturöversikt och är ämnade att prediktera korntillväxt på provbitar med tillsatser av Niob samt provbitar utan Niob. Målet med detta examensarbete är att undersöka vilka modeller som finns tillgängliga för att prediktera korntillväxt samt analysera hur predikteringen ser ut i jämförelse med observationsvärden från experimentella försök. Examensarbetet består av en experimentell del och en modelleringsdel. Den experimentella delen sker genom att provbitar analyseras med hjälp av ljusoptisk mikroskopi med avseende på förändringar i kornstorlek före och efter värmebehandling. Detta för att kunna estimera förändringar i kornstorlek och validera beräkningsmodellerna för prediktering av förändringar i kornstorlek. Modelleringsdelen används för att testa hur olika modeller predikterar korntillväxten. Beräkningsdelen och den experimentella delen jämförs sedan med varandra i resultatet där en sammanställning på alla värden sker. Resultatet visar vilka modeller som finns tillgängliga för att prediktera korntillväxt samt hur predikteringarna ställer sig mot observationsvärden från experimentella prover. För att säkerställa att modellerna kan användas för att prediktera korntillväxten så krävs en djupare analys av modellerna då alla materialparametrar inte kunde tas fram till samtliga modeller. En utveckling av arbetet är att ta fram alla parametrar för att sedan kunna avgöra vilken modell som ställer sig närmast till uppmätta värden från den experimentella delen., Heating steel may lead to grain growth, which results in deterioration of mechanical properties of the steel. In the present study, different models that predict changes in grain size, occurring in heat treatments such as case hardening, have been validated. The models were retrieved via a literature review and were intended to predict grain growth on test pieces with and without Niob precipitates. The aim of this thesis is to investigate which models that are available for predicting grain growth and to validate the models in a comparison with experimental results. This thesis consists of an experimental part and a modeling part. The experimental part is done by analyzing specimens using light-optical microscopy regarding changes in grain size before and after heat treatment. This is to be able to estimate changes in grain size and validate calculation models for predicting changes in grain size. The modeling part is used to evaluate how different models predict grain growth. The calculation part and the experimental part then compare with each other in the result where a compilation of all values takes place. The results show which models are available for predicting grain growth and how the predictions compare with observation values from experimental samples. To ensure that the models can be used to predict grain growth, a deeper analysis of the models is required; not all material parameters could be obtained for all models. A development of the work is to retrieve all parameters in order to then be able to determine which model is closest to the measured values from the experimental part.

During static recrystallization, grains often have non-constant and non-uniform growth rates, significantly affecting the recrystallization kinetics and the microstructure after recrystallization. A cellular automaton model was employed in order to evaluate the relative influences of gradients of stored energy, grain boundary curvature, and heterogeneity of grain boundary mobility on the non-uniform migration of grain boundary segments, leading to the formation of protrusions and retrusions. Electron back-scatter diffraction measurements of a cold-rolled copper microstructure served to feed the model. Orientation maps obtained after partial recrystallization were used to assess the model outcome. The model was capable to predict the shapes of recrystallized grains with retrusions and protrusions. Effects of different model assumptions were compared to reveal individual contributions of different factors to grain size distribution, grain shape and boundary roughness. The model predicted a decreasing average grain growth rate as a result of the progressive immobilization of an increasing fraction of grain boundary segments. The model prediction was compared with experimental results, explaining the origin of stationary boundaries and indicating some further improvements necessary to reach quantitative agreement.

SnSe has emerged as one of the most promising materials for thermoelectric energy conversion due to its extraordinary performance in its single-crystal form and its low-cost constituent elements. However, to achieve an economic impact, the polycrystalline counterpart needs to replicate the performance of the single crystal. Herein, we optimize the thermoelectric performance of polycrystalline SnSe produced by consolidating solution-processed and surface-engineered SnSe particles. In particular, the SnSe particles are coated with CdSe molecular complexes that crystallize during the sintering process, forming CdSe nanoparticles. The presence of CdSe nanoparticles inhibits SnSe grain growth during the consolidation step due to Zener pinning, yielding a material with a high density of grain boundaries. Moreover, the resulting SnSe-CdSe nanocomposites present a large number of defects at different length scales, which significantly reduce the thermal conductivity. The produced SnSe-CdSe nanocomposites exhibit thermoelectric figures of merit up to 2.2 at 786 K, which is among the highest reported for solution-processed SnSe.

Tungsten is considered as plasma-facing material in future fusion reactors. Due to the high operation temperatures, the occurrence of microstructural restoration processes as recovery, recrystallization and grain growth will unavoidably alter the desired microstructure obtained after processing and impede otherwise beneficial mechanical properties. Potassium-doping proved to be efficient in hindering or at least delaying such phenomena. Tungsten fiber-reinforced tungsten composites with drawn tungsten wires embedded in a tungsten matrix show a certain pseudo-ductility. Cylindrical single fiber composites with a single potassium-doped drawn tungsten wire in a chemically vapor deposited tungsten matrix, with or without a rare-earth oxide interlayer, were investigated as model systems. Individual specimens were annealed at 1400°C up to four weeks and changes in their microstructure tracked by electron backscatter diffraction. In the as-processed condition, the tungsten matrix showed large wedge-shaped grains stretching radially from either the interface between matrix and wire or the oxide interlayer to the outer surface with very small grains in the vicinity of the interface/interlayer. Upon heating, two zones with larger grains compared to the as-processed condition developed: in the wire regions close to its perimeter primary recrystallization led to formation of new grains with orientations deviating slightly in alignment of their crystallographic directions with the wire axis compared to the drawn wire. In the matrix, abnormally grown grains consumed the as-deposited microstructure in the vicinity of the interface/interlayer. Without an interlayer, abnormally growing grains from the matrix invaded the recrystallizing wire progressively consuming the wire. Both erbia and yttria interlayers efficiently prevented abnormally growing grains from invading the wire (except at few occasions where the oxide interlayer presented imperfections). In this manner, the presence

The dielectric properties of Neodymium zinc titanium oxide (NZT) and Neodymium magnesium titanium oxide (NMT) were investigated. The single-phase ceramic was synthesized at various temperatures below 1650 circle C. The result shows that the value of temperature of resonant frequency (tau(f)) for NMT is higher than NZT. Our findings also indicate that the rare earth materials produce high property dielectric materials, despite the fact some elements produce lower negative value of temperature of resonant frequency (tau(f)). By doping a compound such as CaTiO3 which has a very positive temperature of resonant frequency (tau(f) = 712 ppm/circle C) and a very high relative permittivity (epsilon(r) = 145), it is possible to tune NZT and MNT to achieve an excellent dielectric material. This work is under consideration. The results of this scientific research could be very important for modern advance applications in microelectronic miniaturization.

The mechanical properties of a magnesium alloy strongly depend on its grain structure. It is desirable to minimize grain growth during the post-forming annealing treatment, thereby minimizing the loss in strength while regaining ductility. In the present research, the annealing of the hot-rolled AZ61 Mg alloy at different temperatures for different times was performed to reveal the kinetics of grain growth, as affected by the precipitation or dissolution of second-phase particles. Three approaches, i.e., experimental, analytical modeling and atomistic simulation were taken and the results were compared. The predictions made from the analytical model and Monte Carlo simulation were both in acceptable agreement with experimental results in terms of the resultant grain sizes. However, the Monte Carlo simulation showed advantages over the analytical model. It was found that with increasing annealing temperature and holding time, the fraction of second-phase particles reduced, which strongly affected the kinetics of grain growth, limiting grain size and grain size homogeneity. The average grain sizes and the largest grain sizes were both taken as the characteristic parameters of the as-annealed microstructure. The results pointed out the importance of choosing an appropriate combination of annealing temperature and time in order to retain second-phase particles during annealing not only for preventing unrestricted grain growth but also for avoiding grain size inhomogeneity., Biomaterials & Tissue Biomechanics

While tremendous progress has recently been made in perovskite light-emitting diodes (PeLEDs), large-area blue devices feature inferior performance due to uneven morphologies and vast defects in the solution-processed perovskite films. To alleviate these issues, a facile and reliable interface engineering scheme is reported for manipulating the crystallization of perovskite films enabled by a multifunctional molecule 2-amino-1,3-propanediol (APDO)-triggered “anchoring effect” at the grain-growth interface. Sky-blue perovskite films with large-area uniformity and low trap states are obtained, showing the distinctly improved radiative recombination and hole-transport capability. Based on the APDO-induced interface engineering, synergistical boost in device performance is achieved for large-area sky-blue PeLED (measuring at 100 mm2) with a peak external quantum efficiency (EQE) of 9.2% and a highly prolonged operational lifetime. A decent EQE up to 6.1% is demonstrated for the largest sky-blue device emitting at 400 mm2. © 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.

Copper (Cu) as an excellent electrical conductor and the amphiphilic diblock copolymer polystyrene-block-poly(ethylene oxide) (PS-b-PEO) as a polymer electrolyte and ionic conductor can be combined with an active material in composite electrodes for polymer lithium-ion batteries (LIBs). As interfaces are a key issue in LIBs, sputter deposition of Cu contacts on PS-b-PEO thin films with high PEO fraction is investigated with in situ grazing-incidence small-angle X-ray scattering (GISAXS) to follow the formation of the Cu layer in real-time. We observe a hierarchical morphology of Cu clusters building larger Cu agglomerates. Two characteristic distances corresponding to the PS-b-PEO microphase separation and the Cu clusters are determined. A selective agglomeration of Cu clusters on the PS domains explains the origin of the persisting hierarchical morphology of the Cu layer even after a complete surface coverage is reached. The spheroidal shape of the Cu clusters growing within the first few nanometers of sputter deposition causes a highly porous Cu-polymer interface. Four growth stages are distinguished corresponding to different kinetics of the cluster growth of Cu on PS-b-PEO thin films: (I) nucleation, (II) diffusion-driven growth, (III) adsorption-driven growth, and (IV) grain growth of Cu clusters. Percolation is reached at an effective Cu layer thickness of 5.75 nm., QC 20220330

The behaviors of grain growth dominate the formation of the microstructure inside polycrystalline materials and thus strongly influence their practical performances. However, grain growth behaviors still remain ambiguous and thus lack a mathematical formula to describe the general evolution despite decades of efforts. Here, we propose a new migration model of grain boundary (GB) and further derive a mathematical expression to depict the general evolution of grain growth in the cellular structures. The expression incorporates the variables influencing growth rate (e.g. GB features, grain size and local grain size distribution) and thus reveals how the normal, abnormal and stagnant behaviors of grain growth occur in polycrystalline systems. In addition, our model correlates quantitatively GB roughening transition with grain growth behavior. The general growth theory may provide new insights into the GB thermodynamics and kinetics during the cellular structure evolution.

The mechanical properties of a magnesium alloy strongly depend on its grain structure. It is desirable to minimize grain growth during the post-forming annealing treatment, thereby minimizing the loss in strength while regaining ductility. In the present research, the annealing of the hot-rolled AZ61 Mg alloy at different temperatures for different times was performed to reveal the kinetics of grain growth, as affected by the precipitation or dissolution of second-phase particles. Three approaches, i.e., experimental, analytical modeling and atomistic simulation were taken and the results were compared. The predictions made from the analytical model and Monte Carlo simulation were both in acceptable agreement with experimental results in terms of the resultant grain sizes. However, the Monte Carlo simulation showed advantages over the analytical model. It was found that with increasing annealing temperature and holding time, the fraction of second-phase particles reduced, which strongly affected the kinetics of grain growth, limiting grain size and grain size homogeneity. The average grain sizes and the largest grain sizes were both taken as the characteristic parameters of the as-annealed microstructure. The results pointed out the importance of choosing an appropriate combination of annealing temperature and time in order to retain second-phase particles during annealing not only for preventing unrestricted grain growth but also for avoiding grain size inhomogeneity., Biomaterials & Tissue Biomechanics

The grain size and the ferroelectric morphology are the two most important factors in the research and development of advanced dielectric devices. It is important to synthesize nanostructures in order to achieve optimal grain size and inhibit grain growth while controlling the sintering parameters. It is also important to find new methods to study the grain growth during densification. BaTiO3 films were successfully obtained via the sol-gel spin coating method. In this paper, we report the deposition of nanostructured BaTiO3 thin film by spin coating of sol-gel precursors. The densification, grain growth and microstructure evolution have been studied. Moreover, a novel physical and mathematical fractal analysis have been applied successfully to the densification and nano grain growth of BaTiO3 thin film. The discrepancy between the fractal dimension and the grain growth with increasing temperatures and soaking time are presented and discussed.

The grain size and the ferroelectric morphology are the two most important factors in the research and development of advanced dielectric devices. It is important to synthesize nanostructures in order to achieve optimal grain size and inhibit grain growth while controlling the sintering parameters. It is also important to find new methods to study the grain growth during densification. BaTiO3 films were successfully obtained via the sol-gel spin coating method. In this paper, we report the deposition of nanostructured BaTiO3 thin film by spin coating of sol-gel precursors. The densification, grain growth and microstructure evolution have been studied. Moreover, a novel physical and mathematical fractal analysis have been applied successfully to the densification and nano grain growth of BaTiO3 thin film. The discrepancy between the fractal dimension and the grain growth with increasing temperatures and soaking time are presented and discussed.

The grain size and the ferroelectric morphology are the two most important factors in the research and development of advanced dielectric devices. It is important to synthesize nanostructures in order to achieve optimal grain size and inhibit grain growth while controlling the sintering parameters. It is also important to find new methods to study the grain growth during densification. BaTiO3 films were successfully obtained via the sol-gel spin coating method. In this paper, we report the deposition of nanostructured BaTiO3 thin film by spin coating of sol-gel precursors. The densification, grain growth and microstructure evolution have been studied. Moreover, a novel physical and mathematical fractal analysis have been applied successfully to the densification and nano grain growth of BaTiO3 thin film. The discrepancy between the fractal dimension and the grain growth with increasing temperatures and soaking time are presented and discussed.

Hierarchical mesoporous zinc oxide (ZnO) polyhedral micro-lumps were prepared by annealing zinc oxalate dihydrate (ZnC2O4 ⋅ 2H2O) precursor in an air atmosphere at various temperatures. The development of the mesoporous nanoarchitecture of the ZnO micro-lumps was studied by XRD analysis corroborated with the analysis of their specific surface area utilizing nitrogen sorption via BET method. Investigations by high-resolution SEM revealed a morphology resembling calcined mesocrystals. A description of the sintering process and the crystallite growth is given together with an analysis of the activation energy of the grain and crystallite growth, respectively. The self-diffusion coefficient, diffusion mechanisms, and its activation energy involved in the growth of crystallites were identified. The crystallite size and the specific surface area can be tuned by varying the annealing temperature, while the UV–vis and PL spectra remain nearly unchanged. The morphological and structural parameters are correlated with photocatalytic activity evaluated by the UV discolouration of the Methyl violet 2B. An interpretational framework, including three hierarchical morphology levels of the micro-lumps, was developed. The interplay between the contributions of the different promoting and impeding effects emerging on various levels can explain the non-monotonous dependence of the photocatalytic activity on the catalyst annealing temperature. © 2020

This work deals with our continued research of oxide materials for potential application in gas/humidity sensing. We have made thick film samples using iron manganite powder synthesized by a so/-gel combustion method with a net-like structure, by screen printing on alumina substrate with PdAg interdigitated electrodes. The thick film samples were fired at two temperatures 600 and 800 degrees C. The powder morphology was retained and only the organic compounds in the paste were burnt-out at 600 degrees C, while at 800 degrees C the thick film surface morphology was different where grain growth and individual particles can he observed, We measured complex impedance in a temperature and humidity chamber at room temperature (25 degrees C) in the relative humidity range 30-90% and frequency 100 Hz 1 MHz. The thick,film surface morphology has a significant influence on the effect of humidity on complex impedance. The complex impedance of thick films fired at 600 degrees C was high and did not decrease noticeably with increase in relative humidity (M., except for RH 80 and 90%, while thick film samples fired at 800 degrees C had an overall lower impedance that reduced more noticeably with increase in RH 40-70% and even more for RH 80 and 90%.

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of MgAl2O4 bodies during SPS. At the same time, such fluorides can act as a source of optically active dopants. A commercial MgAl2O4 was mixed with 0.5 wt% of LiF, MnF2, and CoF2 and, afterwards, consolidated using SPS at 1400 degrees C. Although MnF2 and CoF2 promote the densification as effectively as LiF, they cause significant grain growth.

A growing variety of microelectronic devices and magnetic field sensors as well as a trend of miniaturization demands the development of low-dimensional magnetic materials and nanostructures. Among them, soft magnetic thin films of Finemet alloys are appropriate materials for sensor and actuator devices. Therefore, one of the important directions of the research is the optimization of thin film magnetic properties. In this study, the structural transformations of the Fe73.5Nb3Cu1Si13.5B9 and Fe72.5Nb1.5Mo2Cu1.1Si14.2B8.7 films of 100, 150 and 200 nm thicknesses were comparatively analyzed together with their magnetic properties and magnetic anisotropy. The thin films were prepared using the ion-plasma sputtering technique. The crystallization process was studied by certified X-ray diffraction (XRD) methods. The kinetics of crystallization was observed due to the temperature X-ray diffraction (TDX) analysis. Magnetic properties of the films were studied by the magneto-optical Kerr microscopy. Based on the TDX data the delay of the onset crystallization of the films with its thickness decreasing was shown. Furthermore, the onset crystallization of the 150 and 200 nm films began at the temperature of about 400-420 °C showing rapid grain growth up to the size of 16-20 nm. The best magnetic properties of the films were formed after crystallization after the heat treatment at 350-400 °C when the stress relaxation took place. © 2020 by the authors.

The aim of this work was to derive new quality criteria based on steel composition and cooling pattern for continuous casting and for the subsequent cooling and reheating processes. The criteria were devised based on the outputs of multiphysics simulation tools for casting applications. The criteria were found to be good predictors of whether a steel grade combined with a given cooling pattern is prone to a specific defect. The criteria are useful in providing a theoretical justification as to why certain defects form or would form, and can be used for devising practical solutions to avoid them. In practice, the final determination of whether a defect will form depends on the cumulative impact of various single quality criteria combined with the models/data describing the developing mechanical and thermal stresses. In this paper, new quality criteria are proposed for different kinds of cracking-related and gas defects along with case examples.

The objectives of this study were to quantify the grain yield breeding progress and identify the changes in numerical yield components and grain filling traits of six-rowed winter barley (Hordeum vulgare L.) cultivars under different nitrogen (N) fertilization treatments: 0 kg ha(-1) N (0N, control) and 100 kg ha(-1) N (100N). Field trials were conducted during two (2015-2016 and 2016-2017) growing seasons in a southern Pannonian location, Novi Sad, Serbia with fifteen six-rowed winter barley cultivars. The rate of genetic gain in grain yield was 0.055 t ha(-1) yr(-1) at 0N, while at 100N genetic gain was 0.061 t ha(-1) yr(-1), indicating that modern winter barley cultivars use the applied N fertilizer more efficiently than older cultivars. Grain yield progress was mainly associated with increased grain number per unit area, grain number per spike, grain weight and harvest index. A positive linear correlation was determined between fruiting efficiency and the year of cultivar release, while changes in spike dry weight at anthesis as influenced by the year of cultivar release were not significant. Breeding progress in grain weight was more related with grain filling and maximum grain filling rate, while grain weight association with grain filling duration was less pronounced. Therefore, further grain yield improvement in six-rowed winter barley should be achieved by simultaneous increase in grain weight and grain number per spike, while maintaining high values of harvest index.

The growth of prior austenite grains (PAG) of low alloyed martensitic steel is proven to be one of the key attributes contributing to the mechanical properties of ultrahigh-strength steels. The mean linear intercept -method (MLI) is traditionally used to acquire average PAG sizes from light optical microscopy images, which are from experimental test samples. The MLI -method is arduous and time-consuming as well as a highly generalizing method, where you lose information about the grain size distribution. Therefore, a more sophisticated and computerised method is in high demand among metallurgists. A program has been developed that encompasses an importing, digitalizing and calculating tool, which provides grain sizes and their distribution from multiple images. The tool mimics the workflow of manual MLI -method so the user sets the measure lines and marks all the linear intercepts. After this the tool calculates the MLI grain sizes and their 95 % confidence limits. Additionally, the tool provides the size of each intercepted grain and combines them to create a distribution. This information has been used to study the effects of holding temperature and time on grain sizes throughout the test samples in a case where abnormal grain growth at the centreline was expected. In the present study, PAG sizes were studied before and after deformation at ¼ and ½ thicknesses at various temperatures and holding times using the grain size calculation tool. The average MLI grain sizes show very little differences between temperatures and holding times, so information about grain size distribution is needed. Traditional presentation of the grain size distributions also shows too much variation to interpret the data properly. Instead, using the grain size distribution information and grouping grains to small, medium and large instances gives more profound data, especially in cases where grain size variation is significantly large. Distribution data from the test series also

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of MgAl2O4 bodies during SPS. At the same time, such fluorides can act as a source of optically active dopants. A commercial MgAl2O4 was mixed with 0.5 wt% of LiF, MnF2, and CoF2 and, afterwards, consolidated using SPS at 1400 degrees C. Although MnF2 and CoF2 promote the densification as effectively as LiF, they cause significant grain growth.

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of MgAl2O4 bodies during SPS. At the same time, such fluorides can act as a source of optically active dopants. A commercial MgAl2O4 was mixed with 0.5 wt% of LiF, MnF2, and CoF2 and, afterwards, consolidated using SPS at 1400 degrees C. Although MnF2 and CoF2 promote the densification as effectively as LiF, they cause significant grain growth.

Highly dense magnesium aluminate spinel bodies are usually fabricated using pressure-assisted methods, such as spark plasma sintering (SPS), in the presence of lithium fluoride as a sintering aid. The present work investigates whether the addition of transition metal fluorides promotes the sintering of MgAl2O4 bodies during SPS. At the same time, such fluorides can act as a source of optically active dopants. A commercial MgAl2O4 was mixed with 0.5 wt% of LiF, MnF2, and CoF2 and, afterwards, consolidated using SPS at 1400 degrees C. Although MnF2 and CoF2 promote the densification as effectively as LiF, they cause significant grain growth.

Most metals, ceramics, semiconductors and rocks are composed of small crystals known as grains. When annealed, this polycrystalline structure coarsens, thus allowing the properties of a material to be tailored for a particular application. The mobility of grain boundaries is thought to be determined by the crystallography of the adjacent crystals, but experimental validation in bulk polycrystalline materials is lacking. Here we developed a novel fitting methodology by direct comparison of a time-resolved three-dimensional experimental data to simulations of the evolution of 1501 grains in iron. The comparison allows reduced mobilities of 1619 grain boundaries to be determined simultaneously. We find that the reduced mobilities vary by three orders of magnitude and in general exhibit no correlation with the boundary's five macroscopic degrees of freedom, implying that grain growth is governed by other factors.

Hierarchical mesoporous zinc oxide (ZnO) polyhedral micro-lumps were prepared by annealing zinc oxalate dihydrate (ZnC2O4 ⋅ 2H2O) precursor in an air atmosphere at various temperatures. The development of the mesoporous nanoarchitecture of the ZnO micro-lumps was studied by XRD analysis corroborated with the analysis of their specific surface area utilizing nitrogen sorption via BET method. Investigations by high-resolution SEM revealed a morphology resembling calcined mesocrystals. A description of the sintering process and the crystallite growth is given together with an analysis of the activation energy of the grain and crystallite growth, respectively. The self-diffusion coefficient, diffusion mechanisms, and its activation energy involved in the growth of crystallites were identified. The crystallite size and the specific surface area can be tuned by varying the annealing temperature, while the UV–vis and PL spectra remain nearly unchanged. The morphological and structural parameters are correlated with photocatalytic activity evaluated by the UV discolouration of the Methyl violet 2B. An interpretational framework, including three hierarchical morphology levels of the micro-lumps, was developed. The interplay between the contributions of the different promoting and impeding effects emerging on various levels can explain the non-monotonous dependence of the photocatalytic activity on the catalyst annealing temperature. © 2020

The large grain boundary volume fraction of nanocrystalline metals can bestow desirable mechanical behaviors, but the same grain boundaries that impart these beneficial properties challenge their application. Excess surface energy due to the substantial interfacial volume drives grain growth, and thus a loss of the benefits gained by nanocrystalline grain sizes. Also, not all grain boundaries are equal, where material behaviors can fluctuate dramatically depending on the grain boundary structure and composition. New pathways to fundamentally alter the grain boundary structure are needed to stabilize the nanocrystalline grain size and leverage the full potential of nanocrystalline metals. “Complexion” is a term used to describe the phase-like behavior of grain boundaries, where grain boundaries, similar to bulk phases, can undergo discrete transitions in structure and composition based on external factors such as temperature. Amorphous intergranular films, a type of complexion, are of particular interest due to their ability to enhance both mechanical and radiation damage tolerance due to the excess free volume present in these structures. In this thesis, we seek to expand the current materials toolbox of alloys that can form amorphous intergranular films, and then investigate the impact of these unique damage tolerant features in applications where they can be leveraged. First, we propose a set of materials selection rules aimed at predicting the formation of amorphous intergranular films, and then apply these rules to discover new alloys that can form these features. In doing this, we also discover a counterintuitive, ultra-high temperature grain size stabilization regime driven by the formation of amorphous intergranular films. Next, we investigate the impact of these features in applications where damage tolerance is critical, particularly fatigue and radiation. We find that incorporation of amorphous intergranular films throughout the grain boundary network of n

The microstructure evolution of a martensitic Stainless steel subjected to hot compression is simulated with a physically based model. The model is based on coupled sets of evolution equations for dislocations, vacancies, recrystallization and grain growth. The advantage of this model is that with only a few experiments, the material dependent parameters of the model can be calibrated and used for a new alloy in any deformation condition. The experimental data of this work is obtained from a series of hot compression, and subsequent stress relaxation tests performed in a Gleeble thermo-mechanical simulator. These tests are carried out at various temperatures ranging from 900 to 1200⁰C, strains up to 0.7 and strain rates of 0.01, 1 and 10 s-1. The grain growth, flow stress, and stress relaxations are simulated by finding reasonable values for model parameters. The flow stress data obtained at the strain rate of 10 s-1 were used to calibrate the model parameters and the predictions of the model for the lower strain rates were quite satisfactory. An assumption in the model is that the structure of second phase particles does not change during the short time of deformation. The results show a satisfactory agreement between the experimental data and simulated flow stress, as well as less than 5% difference for grain growth simulations and predicting the dominant softening mechanisms during stress relaxation according to the strain rates and temperatures under deformation.

Grain size and morphology of BaTiO3-ceramics are very important characteristics in developing new dielectric devices. Samples with different additives were sintered at different temperatures and times. The microstructure of the samples was observed using scanning electron microscope (SEM). Experimental results indicated well-developed morphology of BaTiO3-ceramics from nano- to micro- scales, with the standard ceramics consolidation procedure. It is observed that the morphology of grains is the function of additives, sintering temperature and sintering time. However, image analysis of grain growth indicated that sintering temperature has a strong impact on the morphology and grain size of the samples in the temperature range 1240 °C to 1380 °C. Kinetic exponents and grain growth fractal dimensions were obtained with the collecting the parameters of same grain exposed to five magnifications by SEM imaging and using appropriate processing software for grain-shape fractal reconstruction. The main results in this paper established the relation between sintering consolidation process and fractal nature influence, as well as complex fractal correction on sintering temperature.

In nuclear fusion reactors, tungsten will be exposed to high neutron loads at high temperatures (>900 °C). The evolution and degradation of the mechanical properties under these conditions is uncertain and therefore constitutes a major risk. Here, the microstructural evolution of tungsten under combined heat and neutron loads is explored, using a multi-scale approach incorporating clusters dynamics and a mean-field recrystallization model. The mean-field recrystallization model contains both nucleation in the bulk and at the grain boundaries. The cluster dynamics model includes the incorporation of loops in the dynamics of the dislocation network as a mechanism. The effects of bulk nucleation on the microstructural evolution are explored. The simulations predict a cyclically occurring neutron-induced recrystallization at all studied temperatures. Furthermore, the evolution of the irradiation hardening during neutron-induced recrystallization is assessed from the simulated microstructures.

The mechanical properties of cemented carbides can be tuned by controlling WC grain coarsening and the simultaneous growth of the binder pocket size during the sintering. So far, bulk studies considering this phenomenon are scarce, but here, we report the first very-small angle neutron scattering (VSANS) study on cemented carbides. VSANS is supplemented with electron backscatter diffraction (EBSD) and the microstructural refinement by increasing V-doping (0, 0.02, 022, and 0.76 wt%) is quantified. The capability of VSANS as a non-destructive bulk probe for cemented carbides is shown, paving way for forthcoming in-situ studies.

In nuclear fusion reactors, tungsten will be exposed to high neutron loads at high temperatures (>900 °C). The evolution and degradation of the mechanical properties under these conditions is uncertain and therefore constitutes a major risk. Here, the microstructural evolution of tungsten under combined heat and neutron loads is explored, using a multi-scale approach incorporating clusters dynamics and a mean-field recrystallization model. The mean-field recrystallization model contains both nucleation in the bulk and at the grain boundaries. The cluster dynamics model includes the incorporation of loops in the dynamics of the dislocation network as a mechanism. The effects of bulk nucleation on the microstructural evolution are explored. The simulations predict a cyclically occurring neutron-induced recrystallization at all studied temperatures. Furthermore, the evolution of the irradiation hardening during neutron-induced recrystallization is assessed from the simulated microstructures.

Mechanical properties of microalloyed steels are enhanced by fine precipitates, that ensure grain growth control during subsequent heat treatment. This study aims at predicting austenite grain growth kinetics coupling a precipitation model and a grain growth model. These models were applied to a titanium and niobium microalloyed steel. The precipitate size distributions were first characterized by TEM and SEM and prior austenite grain boundaries were revealed by thermal etching after various isothermal treatments. From CALPHAD database, a solubility product was determined for (Ti,Nb)C precipitates. A numerical model based on the classical nucleation and growth theories was used to predict the time evolution of (Ti,Nb)C size distributions during various isothermal heat treatments. The precipitation model was validated from TEM/SEM analysis. The resulting precipitate size distributions served as entry parameters to a simple grain growth model based on Zener pinning. The pinning pressure was calculated using the whole size distribution. The resulting austenite grain growth kinetics were in good agreement with the experimental data obtained for all investigated heat treatments.

The mechanical properties of cemented carbides can be tuned by controlling WC grain coarsening and the simultaneous growth of the binder pocket size during the sintering. So far, bulk studies considering this phenomenon are scarce, but here, we report the first very-small angle neutron scattering (VSANS) study on cemented carbides. VSANS is supplemented with electron backscatter diffraction (EBSD) and the microstructural refinement by increasing V-doping (0, 0.02, 022, and 0.76 wt%) is quantified. The capability of VSANS as a non-destructive bulk probe for cemented carbides is shown, paving way for forthcoming in-situ studies.

The mechanical properties of cemented carbides can be tuned by controlling WC grain coarsening and the simultaneous growth of the binder pocket size during the sintering. So far, bulk studies considering this phenomenon are scarce, but here, we report the first very-small angle neutron scattering (VSANS) study on cemented carbides. VSANS is supplemented with electron backscatter diffraction (EBSD) and the microstructural refinement by increasing V-doping (0, 0.02, 022, and 0.76 wt%) is quantified. The capability of VSANS as a non-destructive bulk probe for cemented carbides is shown, paving way for forthcoming in-situ studies., QC 20191015