SiC-bonded diamond composite materials, which are produced by reactive infiltration of diamond preforms with liquid silicon, have excellent wear and thermal properties. During infiltration, SiC and residual silicon (2–10 vol.%) are formed. The residual silicon has a negative effect on the properties. To minimize this influence, the infiltration of the diamond preforms with eutectic mixtures of Si and TiSi2, and VSi2, as well as the infiltration of TiC-containing diamond preforms, was tested. The structures were analyzed in detail using scanning electron microscopy (including EDX and EBSD) and X-ray phase analysis. In the case of infiltration with TiSi2/Si and the TiC-containing preforms, the formation of TiC and the MAX phase (Ti3SiC2) was detected. The Si content in dense, completely infiltrated materials can thus be almost completely eliminated. This is mainly due to the changed passivation of the diamonds by the Ti-containing melts compared to the pure Si melt. The results show that SiC-bonded diamond composite materials with interesting mechanical and electrical properties can be produced in this way.

Cubic boron nitride (cBN) is valued for industrial applications such as cutting tools and abrasives due to its excellent thermal and mechanical properties. To kinetically suppress the phase transformation from cBN to the stable hexagonal modification (hBN), Spark Plasma Sintering (SPS) was applied to Al2O3-cBN ceramic composites using high heating rates (50 K/min) and short isothermal holding times (5 min) at temperatures up to 1600 °C. X-ray diffraction (XRD), scanning electron microscopy (SEM), hot gas extraction, and differential scanning calorimetry (DSC) were used to study the microstructure of composites with an Al2O3 matrix and an Al2O3 matrix containing 5 vol.% of a glassy phase. Effective densification is achieved once the glassy phase is fully melted. However, this accelerates the transformation of cBN into hBN at temperatures ≥ 1350 °C (1400 °C in the pure Al2O3 matrix). Microcracks, due to residual stress, can be mitigated by reducing the cBN grain size.

For high performance circuit boards, the combination of Si3N4 and copper, joined by an Active Metal Brazing process (AMB) has become the standard material combination due to high thermal conductivity combined with very high flexural strength. These properties ensure high stability at thermal cycles which are necessary for high packing densities and charging of electric vehicles. In micrometer cantilever beam experiments at the interface between a hypereutectic silver copper active filler metal and Si3N4 ceramic, the strength of the individual components of the joining interface where investigated.

To improve the performance of superhard ceramic composites, this study aims to develop a dense, phase-pure, and uniform TiN coating on cubic boron nitride (cBN) particles with a target thickness of at least 150 nm. TiN coatings were applied using atomic layer deposition (ALD) alone, as well as a combined ALD/chemical vapor deposition (CVD) process. While ALD produced uniform and dense coatings, the thickness remained below 50 nm. The combined ALD/CVD approach achieved greater thicknesses up to 500 nm, though coating homogeneity remained a challenge. Optimization efforts, including increased ALD cycles and reduced CVD pressure, led to improved coating uniformity, with 25%–30% of particles coated to thicknesses ≥ 80 nm. Structural analysis confirmed dense, pore-free TiN1−x layers for all synthesized powders. In contrast, the commercial reference powder showed a non-uniform, multiphase coating (α − Ti, Ti2N, and TiN0.53) with defects. While the ALD/CVD powders exhibited better phase purity than the commercial sample, further optimization is needed to achieve consistent coatings above 150 nm. These results suggest the ALD/CVD route is promising for producing coatings suitable for use in ceramic matrix composites.

The influence of spark plasma sintering (SPS) on the phase stability and bandgap of single-phase HEO ceramics with the composition CeO2-delta center dot(Dy,La,Sm,Y)2O3 was studied. Single phase HEO powders were prepared by combustion synthesis. The powders were consolidated by SPS at temperatures 1300 degrees C, 1400 degrees C, and 1600 degrees C to prepare dense bulk ceramics. At 1600 degrees C, a complete cubic-to-monoclinic phase transformation occurred, driven by Ce4 + to Ce3+ reduction under reducing SPS conditions. The change in the oxidation state of Ce resulted in an increase of the average ionic radius driving the cubic-to-monoclinic phase transition. Annealing the monoclinic samples at 1200 degrees C in air led to a reversible transformation to the cubic structure. The phase transformations coupled with the presence of oxygen vacancies resulted in a bandgap energy reduction.

Silicon carbide-bonded diamond materials produced by pressureless reaction infiltration of diamond preforms have high wear resistance and thermal conductivity, making them ideal for a range of industrial applications. During infiltration, the Si is typically converted to cubic β-SiC. The aim of the work was to investigate the extent to which the formation of hexagonal α-SiC can be achieved by adding α-SiC or AlN nuclei to the preform. Detailed microstructural investigations using XRD, high-resolution FE-SEM, and EBSD analyses show that both AlN and SiC serve as nuclei for α-SiC. Regardless of this, a large proportion of β-SiC forms on the surface of the diamonds. However, the added nuclei change the structure of the SiC framework that forms.

Nowadays, the fabrication of multi-material components with desired geometries and tailored microstructural properties is drawing continuous attention. By laminating or additive manufacturing and subsequent co-sintering, multi-material composites that combine a wide range of favorable properties can be produced. Examples are metal-ceramic laminates and multi-ceramic composites, which not only open the spectrum of material applications but also provide a higher degree of flexibility than single materials. However, undesired deformation that triggers delamination, curvature, cracks or even catastrophic failure frequently occurs during the co-sintering process. To solve these issues, a thermo-mechanical model that predicts densification, deformation, and delamination of multi-material components along the entire co-sintering process was developed. A multi-ceramic composite and a metal-ceramic laminate were selected to test and validate the developed model by experimental investigations. The developed model is proven to effectively describe the deformation, curvature, and stress distribution in the studied material combinations.

Materials with high thermal conductivity are required in a wide range of thermal management applications. Silicon carbide (SiC) bonded diamond materials, which can be produced without pressure, are a possible candidate for such applications. They exhibit thermal conductivities > 650 W/(m·K) depending on the diamond content, diamond grain size and residual silicon content. It is difficult to experimentally determine the influence of these factors on the thermal conductivity separately, as changing one of these parameters affects the other parameters. Therefore, a method for generating digital microstructures of SiC bonded diamond materials was developed and the thermal conductivity was calculated as a function of the grain size These data were compared with real structures.

Extremely reliable and wear-resistant components are required for subsea pump applications. For this purpose, materials and components were developed and qualified within the framework of a joint project1, which under media lubrication with water containing particles, exhibit the highest possible wear resistance and can thus achieve the longest possible service life. The developed SiC-bonded diamond ceramics have diamond contents of up to 60 % by volume and can be manufactured in the form of a solid material or as graded components containing diamonds only in the tribologically stressed areas. The results show that the investigated diamond-containing ceramics are very suitable for media-lubricated sliding bearings and mechanical seals in subsea applications. The friction values under media lubrication are very stable and independent of tribological loads. In mechanical seal application, SiC-bonded diamond shows significantly better friction performance than the reference material SiC. An outlook is given on demonstrator tests that are currently in preparation.

The wear behavior of SiC bonded diamond materials produced by liquid silicon infiltration in diamond preforms was investigated. The wear behavior in sand blasting tests (SiC abrasives, 5 bar pressure) was correlated with the microstructure. All SiC bonded diamond materials showed a wear, which was approximately 10 times less than the wear behavior of the reference SiC material.Systematic changed microstructures were created by increasing the infiltration temperature. As the infiltration temperature increases, a graphite layer is formed at the diamond-SiC interface. At the highest infiltration temperature (1670 °C), the layer thickness reaches approx. 580 nm. The results show that wear resistance is not negatively affected by the graphite layer. On the contrary, for materials with a graphite layer thickness of up to 70 nm, the wear resistance increases by up to 30 %. The wear increases again only at the highest infiltration temperature. However, this is probably caused more by the internal damage to the diamonds and not by the graphite layer at the interface.

The uniaxial viscosity is an important material property that has to be determined in order to understand the densification of a material during the sintering process. It depends simultaneously on temperature, relative density and grain size which complicates its determination. To determine its dependence on these three factors, bending creep tests are performed on pre-sintered 3Y-TZP specimens with different relative densities and grain sizes up to the corresponding pre-sintering temperatures. The uniaxial viscosity of 3Y-TZP specimens is calculated after obtaining the deflection rates. It is found that the uniaxial viscosity decreases with temperature according to the Arrhenius equation. In addition, the tetragonal to cubic phase transformation at temperature above 1300 degrees C leads to a decrease of the activation energy. Apart from that, the contribution of densification and grain growth to the increase of the uniaxial viscosity is quantitatively determined. When grain boundary diffusion dominates, the contribution of grain growth is up to 1.8 times that of densification to the uniaxial viscosity. Furthermore, it is found that Rahaman's model best fits the normalized uniaxial viscosity. At the end, an evolution profile of the uniaxial viscosity for polycrystalline materials during the sintering process is proposed to facilitate the analysis of the sintering shrinkage rate.

Analysis of the microstructure of electro-porcelain is important to better understand its influence on mechanical, electrical and aging behavior. The microstructures of two electro-porcelain materials with low and high quartz contents were analyzed with respect to the distribution of quartz. Using an adequate evaluation of EDS (energy dispersive spectroscopy) mapping data, a reproducible analysis of the size distribution and quantity of quartz was achieved. The method allows the analysis of large areas (12.5 mm2). Therefore, the probability of occurrence for a few large quartz grains could be determined. Independent of the overall amount of quartz in the materials, a wide distribution of the grain size was observed. The size of the large detected quartz grains in both materials was very similar. Around the large quartz particles, microcrack systems with lengths of several 100 µm were observed. They are linearly correlated with the equivalent circle diameter of the quartz grains. The evaluation of the cracks allowed us to determine the critical size below which no cracks around the quartz particles are formed. This size is approximately 10 µm.

Solid-state sodium batteries are currently gaining enormous interest as a lower-cost and more environmentally friendly alternative to lithium batteries. They contain significantly less critical rare elements in both the electrolyte and the active material. However, to date, there is no efficient material combination of metallic anode, cathode, and solid electrolyte for room temperature applications that does not require an additional liquid electrolyte while maintaining high energy density. NaPSiO-based glass-ceramics show high ionic conductivity at room temperature, good corrosion resistance against ambient humidity and CO2, and stability against metallic sodium. However, the conductivity mechanisms of this promising class of materials are currently poorly understood. Herein, high frequency impedance measurements up to 108 Hz shed light on the contributions of grains and grain boundaries to the total impedance, including the distribution of relaxation time constants of the fully crystallized material. In addition, analysis of the temperature dependence allows separation of electrode contributions and determination of activation energies for grain and grain boundary conductivities. Our study provides the basis for fine-tuning the stoichiometry of NaPSiO-based glass-ceramics in terms of maximizing the conductive phase fraction to optimize the performance of future solid-state sodium batteries.

The potential combinations of favorable properties give metal–ceramic laminates (MCLs) a high degree of application flexibility. However, the different thermal expansion coefficients (CTEs) and shrinkage rates of the metals and ceramics during the co-sintering process often lead to large internal stresses that cause undesired deformation or even production failures. In practice, the identification of manufacturable MCLs relies on the “trial and error” principle, which usually requires a long development period. Therefore, there is a great demand for analytic and numerical methods that allow the prediction of the deformation and manufacturability of MCLs during the co-sintering process. The main objective of this study is to investigate the curvature and stress distribution in the MCLs (steel 17-4PH/ ceramic 3Y-TZP) based on the analytic solution and finite element (FE) simulation. To achieve this, the Young’s moduli (E) and shear moduli (G) at high temperatures and the CTEs of both materials were measured. In addition, the curvatures and stress distributions of the two-layer and three-layer laminates were obtained based on the analytic method and FE simulation, which were in very good agreement. Furthermore, the influence of the CTE, Young’s modulus, height ratio, and interface on the curvature were studied. The results showed that the CTE and height ratio have a higher influence on the curvature in comparison to the Young’s modulus. The interface prevents the curvature significantly by assuming it to be a cohesive surface in the FE simulation. This provides hints to avoid delamination during the manufacturing process.

Three WC-Ti powder mixtures with 5, 10 and 15 wt% titanium were sintered by the spark plasma sintering technique. The microstructures and phase compositions of the samples were investigated by SEM, STEM, EBSD and XRD. The samples consisted of WC, W2C and a (W1-xTx)C phases when the starting amounts of titanium were 5 and 10 wt%. At the titanium content of 15 wt% the microstructure of the samples included W2C, (W1-xTx)C phases and elemental tungsten. The solubility of WC in TiC with the appearance of the (W1-xTx)C phase depended on the stoichiometry of the starting powder composition and sintering temperature. The results of EBSD phase mapping and the XRD investigation are in good agreement with the molar analysis. The best combination of hardness and fracture toughness was achieved with 5 wt% titanium. The appearance of elemental tungsten after sintering the WC-15Ti composition led to a significant reduction in hardness.

New sodium-based battery concepts require solid electrolytes as ion conducting separators. Besides NaSICON and β-Al2O3 in the Na2O-R2O3-SiO2 system (R = rare earth), a rarely noticed glass-ceramic solid electrolyte with the composition Na5RSi4O12 (N5-type) exists. The present study addresses the investigation of the ionic conductivity of Na5RSi4O12 solid electrolytes sintered from pre-crystallized glass-ceramic powders. The sintering behavior (optical dilatometry), the microstructure (SEM/EDX), and phase composition (XRD), as well as electrochemical properties (impedance spectroscopy), were investigated. To evaluate the effect of the ionic radii, Y, Sm and Gd rare elements were chosen. All compositions were successfully synthesized to fully densified compacts having the corresponding conducting N5-type phase as the main component. The densification behavior was in agreement with the melting point, which decreased with increasing ionic radii and specific cell volume. Alternatively, the ionic conductivities of N5-phases decreased from Y to Gd and Sm containing samples. The highest ionic conductivity of 1.82 × 10−3 S cm−1 at 20 °C was obtained for Na5YSi4O12 composition. The impact of grain boundaries and bulk conductivity on measured values is discussed. A powder-based synthesis method of this glass-ceramic solid electrolyte using different rare earth elements opens possibilities for optimizing ionic conductivity and scalable technological processing by tape casting.

The density, microstructure, and ionic conductivity of solid electrolyte Li1.3Al0.3Ti1.7(PO4)3 (LATP) ceramics prepared by cold sintering using liquid and solid sintering additives are studied. The effects of both liquid (water and water solutions of acetic acid and lithium hydroxide) and solid (lithium acetate) additives on densification are investigated. The properties of cold-sintered LATP are compared to those of conventionally sintered LATP. The materials cold-sintered at temperatures 140–280 °C and pressures 510–600 MPa show relative density in the range of 90–98% of LATP’s theoretical value, comparable or higher than the density of conventionally sintered ceramics. With the relative density of 94%, a total ionic conductivity of 1.26 × 10−5 S/cm (room temperature) is achieved by cold sintering at the temperature of 200 °C and uniaxial pressure of 510 MPa using water as additive. The lower ionic conductivities of the cold-sintered ceramics compared to those prepared by conventional sintering are attributed to the formation of amorphous secondary phases in the intergranular regions depending on the type of additives used and on the processing conditions selected.

Wear-resistant, super hard ceramic composites based on cubic boron nitride (cBN) are of great interest to industry. However, cBN is metastable under sintering conditions at normal pressure and converts into the soft hexagonal BN (hBN). Therefore, efforts are being made to avoid this process. Besides short sintering times, the use of coated cBN-particles is a way to minimize this process. Therefore, the thermal stability of TiN coated cBN powders in high purity argon and nitrogen atmospheres up to temperatures of 1600 °C was investigated by thermogravimetry, X-ray phase analysis, scanning electron microscopy and Raman spectroscopy. The TiN coating was prepared by the atomic layer deposition (ALD)-method. The investigations showed that the TiN layer reacts in Ar at T ≥ 1200 °C with the cBN and forms a porous TiB2 layer. No reaction takes place in nitrogen up to temperatures of 1600 °C. Nevertheless, the 20 and 50 nm thin coatings also undergo a recrystallization process during heat treatment up to temperatures of 1600 °C.

High quality α/β-Sialon materials were reproducible prepared using cost effective silicon nitride powders and an aqueous processing route. The influence of the powder quality (SN-E10, Silzot HQ, SicoNide P95H) on sintering and phase formation was investigated. With all 3 powders dense Sialon materials with nominal composition RxSi12-(m + n)Alm + nOnN16-n and m = 0.5 and n = 1 and 4 wt% excess rare earth additives could be prepared. The material based on Silzot HQ exhibits the highest α-Sialon content and subsequently the highest hardness due to the lower oxygen content of the starting powder. The microstructural analysis using XRD, FESEM including EDX- and EBSD-mapping reveal, that the α-Sialon grains are formed on existing α-Si3N4 grains of the starting powder. Anisotropic grain growth of the α-Sialon takes place therefore the differences in the microstructure depend strongly on the oxygen content but not from the α/β-content of the starting powders.

In addition to Gas Pressure Sintering, Field-Assisted Sintering Technology/Spark Plasma Sintering (FAST/SPS) and High-Pressure-High Temperature (HP/HT) methods (production of polycrystalline diamond) Hot Pressing (HP) and Hot Isostatic Pressing (HIP) are pressure-assisted sintering methods. The application of a uniaxial mechanical pressure during hot pressing and isostatic gas pressure during Hot Isostatic Pressing strongly enhances the densification of ceramic and powder metallurgical produced metallic materials and components. This allows materials and components with high relative density and small defect sizes to be produced. As a result, they have a particularly high reliability and strength. But at the same time they also allow the production of materials with special properties that could not be densified without pressure. This article gives an introduction to the basics and application of these technologies.