Search Results (245)

This study examined the relationship between microhardness, morphology, and phase composition of dental yttria-stabilized tetragonal zirconia polycrystals (Y-TZP), which directly impact their long-term clinical performance and durability. The primary objective was to investigate the effects of yttria content and polishing on the surface properties and hardness of these materials. Samples from ZirCAD Prime, Cercon ht ML, ZIRCONIA YML, and ZirCAD LT were analyzed using Vickers hardness testing, Powder X-ray Diffraction (PXRD), and Scanning Electron Microscopy (SEM). SEM analysis revealed a gradual increase in grain size and porosity with higher yttria content in unpolished samples. Polishing resulted in a relatively uniform surface morphology with observable striations across all samples, subsequently leading to similar Vickers hardness values for all polished samples. PXRD and SEM analyses identified that these similar hardness values were likely due to the predominant monoclinic phase on the surface, induced by polishing. These findings underscore the significant influence of yttria content and polishing on Y-TZP microstructure and surface hardness, highlighting their critical role in the long-term success and clinical applicability of dental restorations. Full article

The spectroscopic properties of Pr³⁺ ions in the aluminosilicate matrix were investigated for the first time. Synthesis of CaAl₂SiO₆ (CASO) polycrystals doped with Pr³⁺ ions was carried out using the sol–gel method. The crystalline structures have been confirmed with XRD measurement. The absorption, excitation, emission spectra, and time decay profiles of the praseodymium (III) ions were measured and analyzed. It was found that upon excitation with visible light, this material exhibits emission mainly in the UVC region, via an upconversion emission process. The Stokes emission in the visible range is observed mainly from the ³P₀ and ¹D₂ energy levels. The ¹D₂→³H₄ emission is very stable even at very high temperatures. The studied aluminosilicate phosphors possess characteristics that confirm their potential in upconversion emission applications. Full article

Tin(II) oxide is a promising material for photocatalytic wastewater treatment. However, the established relationships between particle size, shape, and photocatalytic activity of SnO are contradictory, indicating the influence of other factors. In this work, the effect of the SnO crystallographic texture on its band gap and photocatalytic activity was shown for the first time. The relationship between the methods (microwave and hydrothermal microwave) and synthesis conditions (time, pressure, and chemical composition of the suspension) of polycrystalline tin oxide(II) and the crystallographic texture was studied. The crystallographic texture was estimated by the Harris method using the repeatability factor and the Lotgering coefficient. The formation of crystallites oriented in the growth plane (00l) was facilitated by the carbonate medium of the suspension. In the ammonia medium, crystallites were preferably formed in the plane (h0l). Increasing the time and pressure leads to the recrystallization of SnO. The band gap energy of the SnO increases from 3.0 to 3.6 eV, and the rate of photodestruction of methyl orange decreases with the growth of crystallites in the (00l) plane from 17 to 40%. Full article

Extreme conditions induced by shock exert unprecedented force on crystal lattice and push atoms away from their equilibrium positions. Nonequilibrium molecular dynamics (MD) simulations are one of the best ways to describe material behavior under shock but are limited by the availability and reliability of potential functions. In this work, a specific embedded atom (EAM) potential of molybdenum (Mo) is built for shock and tested by quasi-isentropic and piston-driven shock simulations. Comparisons of the equation of state, lattice constants, elastic constants, phase transitions under pressure, and phonon dispersion with those in the existing literature validate the reliability of our EAM potential. Quasi-isentropic shock simulations reveal that critical stresses for the beginning of plastic deformation follow a [111] > [110] > [100] loading direction for single crystals, and then polycrystal samples. Phase transitions from BCC to FCC and BCC to HCP promote plastic deformation for single crystals loading along [100] and [110], respectively. Along [111], void directly nucleates at the stress concentration area. For polycrystals, voids always nucleate on the grain boundary and lead to early crack generation and propagation. Piston-driven shock loading confirms the plastic mechanisms observed from quasi-isentropic shock simulation and provides further information on the spall strength and spallation process. Full article

Hessonite, a special variety of grossularite, is well-known for the heat-wave effect, which is a characteristic swirled or roiled interior appearance within the crystal. Although the heat-wave effect has been observed for a long time, it has not been studied in depth. In this study, the gemological properties, mineral compositions, fabric characteristics, and grain sizes of hessonite samples were investigated using infrared spectroscopy, electron backscatter diffraction (EBSD), and energy-dispersive X-ray spectroscopy (EDS). Hessonite exhibits the heat-wave effect and is found to be polycrystal rather than single-crystal, composed of submillimeter-sized granules with random orientation and limited variations in Fe and Al contents. Abundant micropores exist among the granules, indicating imperfect contact among them. Due to these structural features, incident light is interrupted and undergoes changes in direction and speed as it passes through the hessonite granules, grain borders, and micropores. Light reflects off the granules’ surfaces and refracts within the granules, respectively, causing the incident light to swirl and roil within the hessonite and form the heat-wave effect. This study considers that the heat-wave effect is a special optical phenomenon not caused by impurity minerals or inclusions. Full article

Aging of yttria-stabilized tetragonal zirconia polycrystal (Y-TZP) under wet conditions is known as low-temperature degradation (LTD), which is associated with phase change and decreasing mechanical strength. Herein, we studied the effects of different surface treatments on the LTD of three different commercial Y-TZP blocks utilizing CAD/CAM technology, namely, Cercon^®, e.max^® ZirCAD, and Vita In-ceram^® YZ. The blocks were immersed in 4% acetic acid at 80 °C for 0, 7, 14, and 28 days. The effects of surface treatments such as sandblasting and polishing were also examined. The results showed that the monoclinic phase increased with immersion time in all three brands. In Cercon^® blocks, a minimal amount of phase transformation was observed, with the smallest amount of degradation after immersion. Sandblasting and polishing both suppressed phase transformation. After immersion, the mechanical strength exhibited a small decrease with time. Accelerating the evaluation of the LTD of zirconia may effectively help with clinical applications. Full article

Machine learning strategies for the semantic segmentation of materials’ micrographs, such as U-Net, have been employed in recent years to enable the automated identification of grain-boundary networks in polycrystals. For example, most recently, this architecture has allowed researchers to address the long-standing problem of automated image segmentation of thin-film microstructures in bright-field TEM micrographs. Such approaches are typically based on the minimization of a binary cross-entropy loss function that compares constructed images to a ground truth at the pixel level over many epochs. In this work, we quantify the rate at which the underlying microstructural features embodied in the grain-boundary network, as described stereologically, are also learned in this process. In particular, we assess the rate of microstructural learning in terms of the moments of the k-th nearest-neighbor pixel distributions and associated metrics, including a microstructural cross-entropy, that embody the spatial correlations among the pixels through a hierarchy of n-point correlation functions. From the moments of these distributions, we obtain so-called learning functions that highlight the rate at which the important topological features of a grain-boundary network appear. It is found that the salient features of network structure emerge after relatively few epochs, suggesting that grain size, network topology, etc., are learned early (as measured in epochs) during the segmentation process. Full article

In the present work, the microstructure and texture evolution of ferritic stainless steel during unidirectional cold rolling were investigated, and the Visco-Plastic Self-Consistent (VPSC) polycrystal model was used for the simulation of texture during cold rolling. Comparison of different interaction models was made to obtain a model that better reproduces the texture evolution of ferritic stainless steels. The as-received hot-rolled samples were unidirectionally cold rolled in a laboratory rolling mill, and the thickness was reduced by 30%, 60% and 80%. Electron backscatter diffraction (EBSD) was used to observe the microstructure evolution and texture evolution, and micro-hardness was used to evaluate the work hardening of the sample. The important feature of the microstructure was the presence of shear bands (SBs), the frequency of which increased with the increase in cold-rolling reduction and was found to be orientation dependent. We found that the geometrically necessary dislocation (GND) density increased with cold-rolling reduction in accord with Ashby’s theory of work hardening, and higher GND density accumulates near the grain boundary. The grain fragmentation, Goss texture distribution and orientation gradient were found to be orientation dependent. The cold-rolled texture was composed of strong α-fiber and weak γ-fiber. The relative plastic compliance of grain and the homogeneous effective medium (HEM) were explored. The tangent interaction model was found to match reasonably well with the experimental texture. This work has great significance for achieving online monitoring of the texture of ferritic stainless steel under different industrial production processes and enhancing the intelligence level of ferritic stainless steel production process. Full article

In this paper, high-purity zinc selenide (ZnSe) prepared by the Chemical Vapor Deposition (CVD) method was used as the raw material, and iron ion-doped zinc selenide polycrystals were successfully fabricated through the thermal diffusion method at 1100 °C for 30 h. The results showed that iron ions (Fe²⁺) successfully penetrated into the zinc selenide crystals, but the concentration of iron ions inside the crystals was relatively low, and the crystals exhibited numerous defects. To address this issue, we performed secondary sintering and annealing on the samples under high-temperature and high-pressure (HPHT) conditions, with the annealing temperature range set at 900–1200 °C. The results demonstrated that, under the synergistic effects of high temperature and high pressure, the lattice spacing in the crystals significantly decreased, defects were reduced, the distribution of iron ions became more uniform, and the concentration of iron ions in the central region increased. Additionally, the density and hardness of the samples were significantly improved. The method of secondary sintering under high-temperature and high-pressure provides a novel approach for the preparation of iron ion-doped zinc selenide polycrystalline ceramics, contributing to the enhancement of ceramic properties. Full article

Objectives: This study evaluates the effectiveness of laser surface texturing (LST) using a Surface Transition Machine (STM) on pre-sintered zirconia, comparing its impact on surface characteristics and shear bond strength (SBS) with resin cement to conventional sandblasting techniques. Methods: Zirconia specimens were treated with either STM or sandblasting, followed by surface analysis through scanning electron microscopy (SEM) and White Light Interferometry (WLI), wettability assessment via contact angle measurements, and SBS testing with resin cement and a 10-MDP-containing primer. Results: SEM and WLI revealed significant surface alterations in STM-treated zirconia, producing microscale textures. STM-treated surfaces exhibited significantly lower contact angles (28.4 ± 10.0°) compared to untreated (78.2 ± 8.0°) and sandblasted (79.2 ± 5.7°) surfaces, indicating enhanced wettability (p < 0.05). SBS was highest in the STM with primer group (46.3 ± 8.3 MPa) and STM without primer (43.4 ± 4.3 MPa), both of which significantly outperformed sandblasting with primer (30.06 ± 3.09 MPa) and sandblasting alone (9.8 ± 3.7 MPa) (p < 0.05). Conclusions: These findings suggest that STM-based LST is a more effective method for improving zirconia surface characteristics and adhesion in dental restorations, simplifying bonding procedures, and potentially offering better clinical outcomes than conventional sandblasting. Full article

This study evaluated the impact of glazing and multiple firing on the flexural strength, translucency, and color stability of three types of zirconia: 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP), 4 mol% yttria partially stabilized zirconia (4Y-PSZ), and 5 mol% yttria partially stabilized zirconia (5Y-PSZ). A total of 120 samples were categorized into four groups: polishing only (P), polishing + glazing (PG), polishing + glazing + one glaze firing (PGF), and polishing + glazing + two glaze firings (PGFF). A three-point bending test was used for assessing flexural strength and a spectrophotometer analysis for assessing color difference (ΔE*_ab) and translucency parameter (TP). Statistical analysis included one-way ANOVA and Kruskal–Wallis tests, with significance set at α = 0.05. The type 3Y-TZP showed the highest flexural strength (918.46 MPa) and lowest translucency (TP = 4.32), while 5Y-PSZ exhibited the lowest strength (401.58 MPa, p < 0.001) and highest translucency (TP = 6.26, p ≤ 0.012). Heat treatment resulted in a significant reduction in the flexural strength of 5Y-PSZ (p = 0.002), followed by 3Y-TZP (p = 0.04). The type 5Y-PSZ exhibited significant change in translucency (p = 0.003) and unacceptable variations in color (ΔE*_ab: 1.49–9.6). The type 4Y-PSZ exhibited the highest stability in flexural strength, translucency, and color under multiple treatments. In conclusion, while glazing and firing significantly compromised 5Y-PSZ’s flexural strength and altered its color and translucency, 4Y-PSZ demonstrated the highest stability. Full article

A review of binder phases used for sintering diamond powders under high pressure and high temperature conditions along with an outline of the properties of polycrystalline diamonds or composite materials intended for cutting tools, wire drawing dies, and drilling rocks are presented. The interaction of diamond with metals from group VIII of the periodic table, carbon-forming metals, carbides, MAX phases and with silicides, borides, and alkali carbonates is presented. The interaction of the bonding phases with diamond was determined. The influences of sintering process parameters, amounts, and methods of introducing of these phases on the basic mechanical properties and thermal resistance of diamond materials are analyzed. The investigated material properties are compared with the properties of commercial PCD with a cobalt and the SiC binder phase. Full article

The microstructural features of polycrystals determine numerous properties, whereas the evolution of crystallographic texture is responsible for the anisotropy of particular properties. Therefore, it is of crucial importance to find proper quantitative indicators, which reflect the nature of microstructure and texture characteristics. This is partially performed by the assessment of the average grain size and texture intensity that provide basic information on the microstructural features evolved; however, often, the basic quantitative indicators are not capable of revealing the complete microstructural state especially when the system is highly heterogeneous. This contribution presents various methods to assess the degree of microstructural heterogeneity, while the crystallographic aspect of microstructure evolution is characterized by several indicators of texture heterogeneity. Numerous synthetic microstructures with normal, lognormal, and bimodal grain size distributions as well as their combinations are analyzed to evaluate the applicability of the methods presented in this study. The quantitative indicators described in the frame of this contribution are likewise tested on experimentally observed microstructures. It is shown that the derived coefficients of microstructure heterogeneity correlate well with the standard deviation in grain size distribution, Gini, and Hoover coefficients, while the quantitative measures of texture heterogeneity are capable of revealing hidden aspects of microstructure evolution. Full article

Nowadays, polycrystalline lead telluride is one of the premier substances for thermoelectric devices while remaining a hopeful competitor to current semiconductor materials used in mid-infrared photonic applications. Notwithstanding that, the development of reliable and reproducible routes for the synthesis of PbTe thin films has not yet been accomplished. As an effort toward this aim, the present article reports progress in the growth of polycrystalline indium-doped PbTe films and their study. The introduction foregoing the main text presents an overview of studies in these and closely related research fields for seven decades. The main text reports on the electron-beam-assisted physical vapor deposition of n-type indium-doped PbTe films on two different amorphous substrates. This doping of PbTe is unique since it sets electron density uniform over grains due to pinning the Fermi level. In-house optimized parameters of the deposition process are presented. The films are structurally characterized by a set of techniques. The transport properties of the films are measured with the original setups described in detail. The infrared transmission spectra are measured and simulated with the original optical-multilayer modeling tool described in the appendix. Conclusions of films’ quality in terms of these properties altogether are drawn. Full article

Surface roughening (SR) has been found to occur in solid solution 2219 aluminum alloy under tensile deformation, which will deteriorate its surface quality. To make a precise study of the surface roughening (SR) behavior and mechanism, the surface morphology of annealed and solid solution 2219 aluminum alloy was compared and crystal plasticity finite element (CPFE) simulation was carried out in this study. Thereinto, representative volume element (RVE) models of polycrystals were established according to the initial grain morphology measured by electron backscatter diffraction (EBSD). The results show that the surface roughening degree of the solid solution specimen is worse than that of annealed specimen after uniaxial tension deformation. In comparison with the annealed specimen, the grains show a larger size after solid solution treatment, thus resulting in the coarse surface to a certain extent. Moreover, texture type and density also have a significant influence on surface roughness. The rotation of grains with an S and Copper orientation intensifies the surface roughening during tensile deformation. The deformation difficulty of Goss texture in the normal direction (ND) and tangential direction (TD) varies, thus contributing to the different surface morphology. The research results will provide guidance for the improvement of the surface quality of high-strength aluminum alloy aerospace components. Full article