Using the spark plasma sintering technique, compact MgO/TiC composites were produced from the MgO-C recyclates, which were crushed, sieved, and mixed with titanium powder. The sintering temperatures were 900 degrees C, 1200 degrees C, and 1500 degrees C. The sintering times were 10-30 min. Analysis of the sintered composites using X-ray diffraction unveiled their phase composition and the progress of the TiC1-x formation. Scanning electron microscopy that was complemented by X-ray spectroscopy and electron backscatter diffraction revealed local distribution of individual phases. As TiC1-x is a product of the carbon diffusion into titanium, the sintering temperature and the sintering time play a crucial role in the phase and microstructure formation. Further important factors are the spatial distribution of MgO, graphite, and Ti in the starting powder mixture, because they influence the local availability of graphite as carbon source, and the size of the original Ti grains, which decides about the final concentration gradient of carbon in TiC and about the stoichiometry of this phase, in particular at lower sintering temperatures and/or at shorter sintering times. The presence of impurities stemming from the original MgO-C recyclates is discussed in context of the sintering temperature and sintering time.

A carbon-free MgO–316L cermet anode, suggested by an upcycling strategy for end-of-life MgO–C bricks, was evaluated with regard to its corrosion behavior in the intended application environment of aluminum electrolysis. The study investigates how the processing dependent microstructure affects chemical corrosion in a conventional Na-cryolitic melt at 1000 °C under current-free immersion conditions. Two manufacturing routes with identical nominal composition but highly different porosities were compared. Spark plasma sintering was used to produce a dense reference material, while granule-assisted cold isostatic pressing was used as the more scalable route for larger anode geometries. Thermodynamic modeling predicted favorable fluorination of MgO by AlF3 and low reactivity of the 316L steel phases with salt components. This was confirmed experimentally by ICP-OES, which identified Mg as the major element that was released from the specimens into the molten salt, whereas Fe, Cr, Ni and Mo remained quasi inert. The only exception was Mn, which also dissolved into the molten salt. EDX line scans and elemental mapping revealed a zonal degradation sequence with a Mg-depleted region, an Al-rich reaction zone, and a preserved bulk containing MgO grains. Degradation depended strongly on the processing route of the specimen, where the more porous CIP specimens showed greater corrosion depths. Molten salt related Na-signals extended beyond the region of complete Mg-depletion, showing that molten salt infiltration and corrosion progression were locally related but not identical. The results suggest that corrosion resistance depends not only on composition, but also on the microstructure resulting from processing.

This study presents the postmortem phase characterization of a metal-ceramic composite anode composed of 316L stainless steel and recycled MgO, sourced from spent refractory lining bricks, employed in aluminum molten salt electrolysis. The analysis focused on the immersed section of the anode, where direct exposure to the molten Na-cryolite melt promotes the formation of corrosion products. Raman spectroscopy was applied as a structural characterization technique, providing phase information that complements the morphological and elemental analyses obtained from SEM-EDX measurements. Due to its high spatial resolution, micro-Raman spectroscopy enabled the identification of local phases within the corrosion layer and the determination of their depth-dependent distribution. The local chemical analysis revealed an outer Fe-O-rich layer penetrating several tens of micrometers into the material, followed by a Fe-Al-O-containing zone. Raman spectroscopy identified the Fe-O layer as magnetite (Fe O) and the inner layer as hercynite (FeAlO), with a transition region consisting of Al-doped FeO. The results demonstrate the applicability of Raman spectroscopy for identifying corrosion products to provide contributions to the corrosion mechanisms of MgO-steel anodes under electrolytic conditions.

Laser powder bed fusion (PBF-LB/M) is designed for the near-net-shape fabrication of complex tool steel parts. In high-carbon steels, however, its broader application is limited by crack formation arising from severe thermal gradients and from stresses induced by austenite-to-martensite transformation. In this work, a materials designdriven strategy is presented to overcome these limitations through the development of a lean medium-carbon tool steel (Fe94.1Cr0.8Mo0.5Mn1.1Ni3.0C0.5) adapted to PBF-LB/M processing. By reducing the carbon content, transformation-induced stresses are mitigated, enabling the fabrication of crack-free components with a relative density of 99.7% without substrate preheating. The as-built microstructure consists predominantly of alpha '-martensite containing MnS precipitates, epsilon-martensite, and retained austenite, which undergoes deformationinduced transformation to martensite during mechanical loading and friction. The transformation-induced plasticity (TRIP) effect promotes work hardening and contributes to a favorable combination of strength and wear resistance. The additively manufactured steel exhibits a yield strength of 1317 MPa and an ultimate compressive strength of 2061 MPa. Benchmarked against commercial H11 tool steel, superior abrasive wear resistance is achieved despite lower macrohardness, which is attributed to a friction-induced austenite-tomartensite transformation at the worn surface. This work demonstrates the effectiveness of alloy design for enhanced processability and performance in additively manufactured tool steels.

RaMap is an open-source Python workflow for phase identification and mapping in Raman spectroscopy. It integrates multivariate analysis with mathematical similarity metrics and reference datasets to perform phase identification in a consistent and reproducible manner, with minimal sample-specific prior knowledge. The workflow supports the construction of Raman phase maps and can be applied as a tool for materials characterization.

Mechanisms of the lattice strain relaxation in molybdenum thin films that were grown heteroepitaxially on (001)- and (011)-oriented MgO wafers using magnetron sputtering were studied using a combination of X-ray and electron diffraction and transmission electron microscopy. For the Mo film grown on (001)-oriented MgO, the X-ray diffraction pole figure measurements revealed (001)Mo ∥ (001)MgO & [110]Mo ∥ [100]MgO as the main orientation relationship. On the (011)-oriented MgO, the Mo film grew with the orientations (112)Mo ∥ (011)MgO & ±[110]Mo ∥ [100]MgO. In all cases, the stress generated by the lattice misfit exceeded the elastic deformation limit of Mo, which activated the lattice strain relaxation mechanisms, mainly the formation of dislocations and slip and twinning on the lattice planes {112}. The dominant relaxation mechanism depends on the mutual orientation between the film and the substrate, which defines the direction of the deformation force in the film. In the (001)-oriented film, the lattice strain produced by the lattice misfit was reduced by twinning and dislocations. In the film having the (112) orientation, the main relaxation mechanism was the formation of dislocations. In both cases, the deformation energy was additionally reduced by the small lateral size of the Mo crystallites.

Compact steel-spinel composites with a specific microstructure were produced by spark plasma sintering, using powder mixtures of high-alloy steel AISI 316L, MgO, and Cr2O3 or Fe2O3 as starting materials. The reaction diffusion between MgO and Cr2O3 or Fe2O3 always led to the formation of an Mg-based spinel. The thermodynamic phase stability of the respective corundum-like oxide with respect to the oxygen partial pressure decided about the presence or absence of side reactions, which were utilized as an efficient tool for microstructure design of the steel-spinel composites.The use of Fe2O3 as one of the starting compounds initiated various redox reactions that promoted the formation of mixed spinel phases at the steel/ceramic interface and the transformation of MgO to (Mg, Fe)O, which accommodates, in addition to iron, also other divalent alloying elements from the steel. The phase composition of the composites and the spatial distributions of individual phases and their chemical compositions were investigated using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and electron probe microanalysis. The microstructure formation was substantiated by thermodynamic calculations. The role of oxidizing and reducing agents that are involved in the microstructure design is discussed.

The possibilities of producing protective spinel coatings on the surface of an AISI 316L-MgO composite via high-temperature oxidation at 800 degrees C, 900 degrees C and 1000 degrees C were explored using a combination of structure and microstructure analyses, and thermodynamic calculations. The structure and microstructure of the coatings were analyzed in situ and ex situ using high-temperature and conventional X-ray diffraction, scanning electron microscopy, electron backscatter diffraction and X-ray spectroscopy. The ex situ analyses identified the oxidation and reaction products and revealed their spatial distribution within the surface coating. The in situ analyses helped to describe the oxidation and reaction kinetics. It was found that Cr2O3, which forms on the surface of oxidized austenite grains, reacts quickly to the MgCr2O4 spinel, when it comes in contact with MgO. Longer oxidation times and higher oxidation temperatures facilitate the formation of Fe2O3 and MgFe2O4, which partially intermix with Cr2O3 and MgCr2O4. As the spinel phases are formed via interdiffusion and as their molar volume is larger than the molar volume of the original phases (MgO, Cr2O3/Fe2O3), they overgrow the surface of the MgO grains. This mechanism provides a basis for controlled growth of protective spinel coatings on the surface of the AISI 316L-MgO composites.

This study presents a data-driven framework based on machine learning (ML) using extreme gradient boosting (XGBoost) for predicting the hardness of silicon nitride (Si3N4) ceramics reinforced with graphene. The XGBoost model takes into account various factors such as graphene type and content, characteristics of the raw Si3N4 powder, the parameters of the sintering process (sintering technique, temperature, pressure, holding time), and the characteristics of the sintered samples, i.e., the density, αβ content and Vickers hardness. The parameters that influence the Si3N4 hardness most strongly are identified, with sintering pressure, sintering time and density being the most influential. The addition of graphene content up to a certain threshold (1 wt%) has a positive impact on hardness. However, beyond that it leads to a lower density and a lower mechanical performance. Sintering parameters, particularly the sintering pressure, temperature, holding time and technique, strongly affect the density, final grain size, αβ Si3N4 composition and subsequently the hardness. The study highlights the importance of density and the densification process in achieving high hardness in Si3N4 ceramics. The developed ML model provides a valuable tool for predicting the hardness of Si3N4+graphene ceramics composites and offers insights into selecting suitable graphene type, content, and processing parameters. While the study primarily focuses on Si3N4+graphene composites, this novel approach holds promise for the in-silico design and analysis of diverse ceramic materials.

Structural quality of GaN layers grown on foreign substrates is usually improved by applying masks or interlayers, which interact with the crystal structure defects, mainly with threading dislocations, and consequently reduce their density. In this work, GaN interlayers with intrinsic defect structures were employed as barriers impeding the propagation of threading dislocations. The GaN samples were produced in a multistage deposition process by high-temperature vapor phase epitaxy (HTVPE). They consisted of GaN seed layers deposited on 15 x 15 mm2 (001)-oriented sapphire substrates, structured GaN interlayers and GaN top layers. The structuring of the interlayers was facilitated by changing the substrate temperature and the V/III ratio during the growth. The optical and scanning electron microscopies revealed that the structured interlayers contain pyramidal facets, vertical trenches and elongated voids. The results of X-ray diffraction and Raman spectroscopy have shown that these microstructure features are able to reduce the density of threading dislocations in the top layer and the tensile residual stress that develops in the top layer during the deposition process. These results demonstrate the potential of the intrinsic interlayer concept for the in-line defect and stress engineering in HTVPE GaN layer stacks.

Controlling the stability of colloidal nanoparticles in multicomponent systems, i.e., mixtures of colloids, is of vital importance for product formulations and separation processes of nanoparticles. However, very few studies are currently found in literature regarding the generation of binary colloids by mixing of colloidal nanoparticles, particularly small nanoparticles (< 20 nm). In this study, we report on the development of a stable binary colloid made of nanoparticles of different sizes and compositions. As a model system for this study, we mixed aqueous dispersions of gold nanoparticles (Au NPs) and ZnS quantum dots (QDs). We investigated the stability of Au NPs with three different surface ligands after mixing them with ZnS QDs, both before and after functionalization of the Au NPs with bis(p-sulfonatophenyl) phenylphosphine (BSPP). We used UV-visible spectroscopy as the primary method to monitor stability of nanoparticles in the binary mixture over time. We found out that the released thioglycerol and acetate from the surface of ZnS QDs to the binary mixture induces agglomeration in Au NPs. The surface chemistry and the purification process of Au NPs after their synthesis and surface treatment were identified as key parameters to regulate the stability in the mixture. Thus, we successfully achieved a stable mixture of BSPP-functionalized Au NPs with ZnS QDs as a model of a stable binary mixture. We believe that this study is important to stimulate research directed towards real-world multicomponent formulations including their characterization , the understanding of surface interactions.

Time-resolved imaging pump–probe reflectometry is an established technique to characterize the dynamic processes occurring during the material ablation upon ultrashort pulsed laser irradiation. In the phase explosion regime, however, the presence of an expanding liquid–vapor mixture on top of the ablated material makes an unambiguous determination of the transient ablation topography almost impossible, especially when only front-side pump–probe reflectometry is used. To circumvent this limitation, the front-side reflectometry was complemented by rear-side reflectometry, where the probe radiation does not interact with the liquid–vapor mixture, and the underneath ablation kinetics of the material becomes observable. To interpret the measured front- and rear-side reflectances, an optical multilayer model of the ablation process was developed. Its applicability is demonstrated on a thin chromium film that was ablated by a single pump pulse. The optical model replicates the Newton rings measured during spallation and phase explosion very well, which allows the reconstruction of the transient ablation topography. The combination of the front- and rear-side reflectometry with modeling offers a valuable tool for studying the ablation processes in thin metal films, because it overcomes the challenges of the phase explosion regime, and thus enhances the understanding of material dynamics upon laser irradiation.

Chemical and physical properties of nanoparticles (NPs) are strongly influenced not only by the crystal structure of the respective material, including crystal structure defects but also by the NP size and shape. Contemporary transmission electron microscopy (TEM) can describe all these NP characteristics, however typically with a different statistical relevance. While the size and shape of NPs are frequently determined on a large ensemble of NPs and thus with good statistics, the characteristics on the atomic scale are usually quantified for a small number of individual NPs and thus with low statistical relevance. In this contribution, we present a TEM-based characterization technique, which can determine relevant characteristics of NPs in a scale-bridging way—from the crystal structure and crystal structure defects up to the NP size and morphology—with sufficient statistical relevance. This technique is based on a correlative multi-scale TEM approach that combines information on atomic scale obtained from the high-resolution imaging with the results of the low-resolution imaging assisted by a semi-automatic segmentation routine. The capability of the technique is illustrated in several examples, including Au NPs with different shapes, Au nanorods with different facet configurations, and multi-core iron oxide nanoparticles with a hierarchical structure.

AbstractThe reactions between newly developed filter materials and metal melts containing various inclusions were analyzed under laboratory conditions. For the melt production, a Spark Plasma Sintering (SPS) apparatus was utilized. The SPS process provides very high heating rates, which emulate the thermo-shock during a real filtration process, and variable reaction times, which allows to simulate both, short and long filtration processes. The short-time filtration processes are relevant for die-casting, where one ton of a steel passes the filter in approx. 15 s, the long-term ones for continuous casting taking several hours. In the SPS process, the convection of the steel melt is suspended, which makes the interpretation of the interfacial reactions and reaction kinetics more straightforward and trustworthy. Furthermore, the SPS process allows speeding up the reaction diffusion kinetics by using tiny diffusion couples having the form of powder mixtures that contain the metal or alloy and the functional filter material under study. In such samples, the equilibrium state that is suitable for a direct comparison with the results of thermodynamic simulations can be achieved very quickly.

Ion irradiation combined with nanoindentation is a promising tool for studying irradiation-induced hardening of nuclear materials, including reactor pressure vessel (RPV) steels. For RPV steels, the major sources of hardening are nm-sized irradiation-induced dislocation loops and solute atom clusters, both representing barriers for dislocation glide. The dispersed barrier hardening (DBH) model provides a link between the irradiation-induced nanofeatures and hardening. However, a number of details of the DBH model still require consideration. These include the role of the unirradiated microstructure, the proper treatment of the indentation size effect (ISE), and the appropriate superposition rule of individual hardening contributions. In the present study, two well-characterized RPV steels, each ion-irradiated up to two different levels of displacement damage, were investigated. Dislocation loops and solute atom clusters were characterized by transmission electron microscopy and atom probe tomography, respectively. Nanoindentation with a Berkovich indenter was used to measure indentation hardness as a function of the contact depth. In the present paper, the measured hardening profiles are compared with predictions based on different DBH models. Conclusions about the appropriate superposition rule and the consideration of the ISE (in terms of geometrically necessary dislocations) are drawn.

AbstractThe functionalization of ceramic foam filters aims typically at the enhancement of the thermal shock resistance and the reactivity of the filters with respect to specific inclusions and impurities. For this purpose, thermodynamically metastable phases are utilized that have a strongly defective crystal structure and/or nanocrystalline character. Such phases possess frequently better or even unique properties in comparison with their thermodynamically stable counterparts. However, the stability of metastable or defect-rich phases is usually impaired by microstructural changes, which occur during the contact of these phases with the metallic melt at high temperatures and which speed up finally the degradation of the functionalized filters. In general, the first step towards the stabilization of the thermodynamically metastable and/or defect-rich phases is the understanding of their microstructure and the microstructure changes accompanying the transition to the thermodynamically stable state. In this chapter, the thermally induced microstructure changes are illustrated on the examples of selected carbon containing binders and metastable alumina phases. In order to be able to describe the crystal structure and microstructure of these compounds in more details, which is required for the targeted development of the functional filter materials, complementary methods of crystal structure and microstructure analysis like X-ray and electron diffraction, X-ray and nuclear magnetic resonance spectroscopy and electron microscopy were combined and further developed.

Although the use of protective Ti(C,N)/Al2O3 coatings produced by chemical vapour deposition (CVD) on cemented carbide (WC-Co) substrates is the state of the art in high-speed metal cutting, the effect of the substrate treatment on the microstructure of such coatings is not fully understood yet. In this study, the influence of the original substrate grain size (coarse-grained, fine-grained) and the substrate treatment (as-sintered, wet blasted, ground or polished) on the grain size, preferred orientation of crystallites and residual stress in Ti(C,N)/Al2O3 coatings was systematically investigated. The microstructure analyses carried out using scanning electron microscopy with electron backscatter diffraction and symmetrical X-ray diffraction (XRD) revealed that the utilization of fine-grained substrates and the substrate treatment reduce the grain size in both layers, and increase the preferred orientations 〈211〉 and 〈0001〉 of fcc-Ti(C,N) and α-Al2O3 crystallites, respectively. In α-Al2O3, the microstructure changes are mainly connected with the morphology of the bonding layer, as it follows the morphology of the fcc-Ti(C,N) facets. The residual stress analyses done using glancing angle X-ray diffraction (GAXRD) disclosed a reduction of the tensile thermal stress in α-Al2O3 layers that were deposited on coarse-grained substrates. The residual stress in fcc-Ti(C,N) was substantially less reduced in the whole fcc-Ti(C,N)/α-Al2O3 stacks than in the reference fcc-Ti(C,N) monolayers. Vice versa, fcc-Ti(C,N) in the full stacks contained less crystal structure defects and lower microstrain than in the reference fcc-Ti(C,N) monolayers, because they were exposed to higher temperatures.

The sintering process on Cu/ZnO/Al2O3 catalysts in the heterogeneous liquid phase assisted methanol synthesis from CO2/H2 was investigated. In order to better understand the sintering event, in addition to standard methods (XRD, XPS, BET, ICP-OES) microscopic techniques with different magnifications such as SEM-EDX, AFM, and TEM were used. Water has been identified as the sintering agent. In addition to eliminating water with CO, another way was found to remove water from the catalyst surface and therefore to counteract the sintering during catalysis. This goal can be achieved by using highly polar solvents allowing to synthesize MeOH solely from carbon dioxide and hydrogen, without deactivating the catalyst or using carbon monoxide.

Atomic-scale characteristics of individual nanocrystals (NCs), such as the crystallographic orientation of their facets and the kind and density of crystal structure defects, play a tremendous role for the functionality and performance of the whole NC population. However, these features are usually quantified only for a small number of individual particles, and thus with limited statistical relevance. In the present work, we developed the multiscale approach available in transmission electron microscopy (TEM) further, and applied it to describe features of different types of Au NCs in a statistical and scale-bridging manner. This approach combines high-resolution TEM, which is capable of describing the characteristics of NCs on atomic scale, with a semi-automatic analysis of low-magnification high-angle annular dark-field scanning TEM images, which reveals the nanoscopic morphological attributes of NCs with good statistics. The results of these complementary techniques are combined and correlated. The potential of this multiscale approach is illustrated on two examples. In the first one, the habitus of Au NCs was classified and assigned to multiply twinned nanoparticles and nanoplates. These classes were quantified and related to different stacking fault densities. The second example demonstrates the statistical determination of crystallographic orientations and configurations of facets in Au nanorods.

Although many challenges of the 21st century need solutions which are directly connected with the development of new technologies, the preferences of prospective students in Germany are often far from mathematics, physics and chemistry. Moreover, the acceptance and recognition of new achievements in these disciplines are quite low in society, even if these achievements are the basis for the development of new technologies that positively affect daily life. As a part of a campaign intended to increase the number of students in the fields of materials science and materials technology (and related fields), the authors created an escape room focused on materials science and crystallography, which illustrates the approaches used by materials scientists and the beauty of crystallography. The fundamental features of the escape room, which are presented in this contribution, are its variability and the ability to inspire participants who have different backgrounds in physics, chemistry and/or materials science. By varying the level of difficulty and the game play duration, the escape room structure makes it possible to appeal to a broad audience, offer an authentic escape room experience and impart lasting knowledge through reflection after completion. The authors' experiences with the escape room and the feedback from the attendees are summarized at the end of the contribution.