Ceramic Layer Research Articles

Crystalline Structure Assessment of Ceramic Veneered Co-Cr-W Dental Alloy Substructures Obtained by Selective Laser Melting—A Pilot Study

The aim of this work is to assess the crystalline structure modification of an SLM Co-Cr-W dental alloy, veneered with two different ceramics, by means of X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy, coupled with energy-dispersive spectroscopy (SEM-EDS). Ten identical plates were fabricated using SLM and were subsequently subjected to ceramic veneering. Following the repeated firing of the ceramic layers, carried out at temperatures exceeding 900 °C, new crystalline phases and variations in the crystallite sizes in the SLM Co-Cr-W dental alloy used for the substructure were detected via XRD. The two veneering ceramics showed significant differences in their behavior, beginning with the first firing, accompanied by structural changes. AFM micrographs and histograms of the surface heights over the whole scanned area of the samples showed that the surface of the Co-Cr-W dental alloy is strongly affected by the repeated firings necessitated by the ceramic firing process, a finding in accordance with the XRD results. The SEM investigation revealed that the different firing parameters had an impact on the alloy, the ceramic microstructure, and the surface quality. The differences in the chemical composition of the ceramics, highlighted by EDS, are reflected in their behavior. The crystalline alloy structure is influenced by the repeated firings of the ceramic layers.

The Effect of Ceramic Coating on Performance and Emission of Diesel Engine Operated on Diesel Fuel and Biodiesel Blends

In this work, the effect of ceramic coating on performance, exhaust gas temperature and gases emissions of diesel engine operated on diesel fuel and biodiesel blends was investigated. A conventional four stroke, direct injected, single cylinder, diesel engine was tested at constant speed and at different load conditions using diesel fuel and biodiesel blends. The inlet and exhaust valves, the head of piston and cylinder head of the engine were coated by ceramic materials. Ceramic layers were made of (210-240) μm of Al2O3 and (30-60) μm of 4NiCr5Al as a bond coat for inlet and exhaust valves and (350-400) μm of YSZ and (50-100) μm of 4NiCr5Al as a bond coat for head of piston and (280-320) μm of Sic and (40-80) μm of 4NiCr5Al as a bond coat for cylinder head. The coating technique adapted in this work is the flame spray method. The engine with valves, piston and cylinder head ceramic coated research was tested for the same operation conditions of the engine (without coating). The results showed that a reduction in brake specific fuel consumption of 19.29%, 15.91%, 14.65% and 7.06%, an increase in brake thermal efficiency of 23.68%, 19.77%, 16.51% and 6.32%, the increase in exhaust gas temperature of 9.01%, 7.22%, 15.7% and 11.42%, the reduction of CO emission of 18.57%, 20%, 20.5% and 27.77%, the reduction of HC emission of 28.97%, 43.9%, 38.88% and 36.41% for diesel, B5,B10 and B100 respectively.

Thermo-metallurgical-mechanical modeling of FG titanium-matrix composites in powder bed fusion

The build-up of residual stress plays a crucial role in the formation quality of as-built parts fabricated by powder bed fusion (PBF). However, the comprehensive understanding of residual stress and distortion fields in PBF-printed functionally graded titanium matrix composites (FGTMCs) has not been achieved. Furthermore, the effect of metallurgical transformation on thermo-mechanical behavior of these materials during the PBF remains unclear. In this paper, considering the phase transition effect due to thermal evolution in the PBF process, a thermo-metallurgical-mechanical coupled model of printed FGTMCs is developed. The equivalent temperature-dependent elastic modulus and heat conductivity of FGTMCs are calculated based on the homogenization method. The differential quadrature method is first employed to efficiently predict the temperature, residual stress, and distortion distributions of PBF-printed FGTMCs. The accuracy of the proposed model is verified by a comparison with predictions in the literature. Furthermore, the effect of crucial process and geometrical parameters on the thermo-mechanical behaviors of FGTMCs is analyzed. The results indicate that the residual stress and vertical distortion of FGTMCs increase as the laser penetration, energy densities, and power index increase, while decreasing significantly with the increased ceramic content, preheating temperature, and layer thickness. These results provide valuable insights for guiding the process optimization of additively manufactured FGTMCs.

All-solid-state sodium-ion batteries operating at room temperature based on NASICON-type NaTi2(PO4)3 cathode and ceramic NASICON solid electrolyte: A complete in situ synchrotron X-ray study

All-solid-state sodium-ion batteries that work at ambient temperature are a potential approach for large-scale energy storage systems. Nowadays, ceramic solid electrolytes are gaining attention because of their good ionic conductivity and excellent mechanical and chemical stabilities. Furthermore, a good interface between electrode and solid electrolyte is also required to achieve successful cell performances. In this work, sintered ceramic layer electrolyte Na3.16Zr1.84Y0.16Si2PO12, with high ionic conductivity (0.202 mS/cm at room temperature), are prepared by using uniaxial pressing followed by a sintering process. The conductive carbon coated NASICON material (NaTi2(PO4)3/C) exhibits, as cathode material, enhanced rate capability and stability for sodium ion batteries for high carbon (18.95 %) coated sample. At C/10, the optimized cathode (with higher carbon content) achieves a remarkable initial discharge capacity of 107.3 mAh/g (reversible capacity of 101.4 mAh/g), a sufficient rate capability up to a rate of 10C, and a long cycle life (capacity retention of 58% after 950 cycles). The one-stage reversible biphasic reaction mechanism and potential-dependent structure–property of NaTi2(PO4)3 can be explained by employing in situ X-ray synchrotron method. Sequential Rietveld refinements of the in situ data show the evolution of the Na-poor NaTi2(PO4)3 and Na-rich Na3Ti2(PO4)3 phase fractions (wt%), unit cell characteristics, and unit cell volume. The design of an all-solid-state sodium ion half-cell with a NaTi2(PO4)3/C cathode and a Na3.16Zr1.84Y0.16Si2PO12 solid-state electrolyte interface results in stable capacity of 83.6 mAh/g at C/10 and excellent reversible capacity at high C-rate. The results show that sintered NASICON-based electrolytes can significantly contribute for the fabrication of all-solid-state sodium-ion battery due to the superior conductivity and stability.

Thickness-related failure behaviors of the thermal barrier coatings under thermal gradient cycling

The ZrO2–7 wt% Y2O3 (7YSZ) is the most commonly used ceramic layer in the thermal barrier coating (TBC) system due to its low thermal conductivity. However, the thermal stress-induced coating failure would damage its performance and limit its application. In the present study, a burner rig is employed to attain the operating temperature field and conduct the thermal gradient cycling tests of the coating. Moreover, the failure modes of the YSZ coating with different thicknesses (100, 200, and 400 μm) are investigated. The results show that the coating with 200 μm thickness has the most extended cyclic lifetime (>340 cycles), while 100 μm and 400 μm thick coatings have cyclic lifetimes of 240 and 80 cycles, respectively. The coating microstructure evolution, thermal growth oxides (TGO) thickness, and coating sintering behaviors are considered to explain the phenomenon. Furthermore, a TGO growth/sintering competitive failure model is proposed to describe the failure behaviors and elucidate the failure mechanisms of the coating with different thicknesses. The coatings with different thicknesses have different temperature distributions in the same external conditions. It results in different TGO growth rates and different degrees of coating sintering. The balance of TGO growth and coating sintering makes the 200 μm thick coating the most extended cyclic lifetime.

Simulation of metal ceramic single layer coatings for solar energy applications

The coating materials, thickness and number of layers directly influence the reflectance and absorptance properties of the thin films. However, while selecting the materials for single and coatings, the substrate’s refractive index; bond layer, functional layer and protective layer have to be carefully chosen to obtain the desired reflectance and absorptance values. Hence, modelling and simulating the thin film coatings is essential before conducting the experiments to get meaningful results. The simulation results of single coatings have been discussed. Generally, glass is one of the widely used substrate materials for solar reflectors, aluminum is the optimal functional material, with a reflection of 93 % of light. Nickel would be a preferable functional layer with a reflection of 64 % and absorptance of 36 %, Si3N4 being the acceptable bond layers and protective layers with a reflection of 68 % some solar thermal receiver tube applications however research effort is being made to find alternate lightweight materials for this application. Polycarbonate has been chosen as an alternate material for the substrate because it is light in weight with a reflection of 93 %, which is durable and not fragile.

Preparation and characterization of porcupine-fish-spine-inspired AZ91/SiC composites with radial lamellar structures

There is a growing demand for lightweight, damage-tolerant, and wear-resistant structural materials, and it is difficult to produce such materials with conventional methods. In this work, we prepared AZ91/SiC composites with a porcupine-fish-spine-inspired structure through radial freeze casting and pressureless infiltration, and investigated the effect of the thermal conductivity of the freezing mold (copper, brass, and stainless steel molds) on the structure and mechanical properties of the composite prepared. Owing to a higher axial-radial temperature gradient ratio, scaffolds prepared with the steel mold had a stronger orientation of ceramic layers, and the corresponding composites had higher flexural strength and fracture toughness compared with those prepared using the copper mold. The main toughening mechanisms were crack deflection and uncracked-ligament bridging. In particular, a radially frozen composite had a lower dry wear rate (by 20%) at cross-sectional surfaces than a conventional axially frozen composite. This paper presents an economical and scalable method for the preparation of high-performance lightweight metal matrix composites.

Ultrasound-Auxiliary Preparation of Antifouling Cu-Enriched Titanium Oxide Ceramic Layer

The limited antifouling capability of Ti-based components could jeopardize their applications in petroleum engineering. In this work, a Cu-enriched TiO2 coating has been fabricated using an ultrasound-auxiliary micro-arc oxidation (UMAO) method. The Cu enrichment of TiO2 affects its morphology, phase component and chemical configuration, leading to the slightly enhanced corrosion resistance of the Cu-enriched TiO2 coating relative to that free of Cu. Finally, the antifouling capability against sulphate-reducing bacteria (SRB) is significantly improved by preventing the formation of biofilm after the Cu enrichment of TiO2, which potentially widens its application in petroleum engineering.

Nonuniform Distribution of Crystalline Phases and Grain Sizes in the Surface Layers of WC Ceramics Produced by Spark Plasma Sintering

The research results conducted on binderless tungsten carbide (WC) ceramics obtained by spark plasma sintering (SPS) of WC powders with different average particle sizes (95, 800, 3000 nm) are presented. Nonuniform distribution of crystalline phases and microstructure of the WC ceramics was studied using layer-by-layer X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Surface layers of the WC-based ceramics are characterized by nonuniform distribution of W2C crystalline phase and grain sizes, including the appearance of abnormally large grains. Thickness of the nonuniform layer was at least 50 μm. The effect under study is associated with an intense carbon diffusion from graphite foil. On the one hand, this contributed to a decrease in the intensity of W2C phase particle formation, which is transformed into α-WC phase due to the carbon. On the other hand, it caused abnormal grain growth in the layer where the carbon diffused. The obtained value of the carbon diffusion depth (50 μm) exceeds the values known from the literature (up to 1 μm in the case of volume diffusion even at temperature of 2370 °C and exposure time of ~60 h). The use of boron nitride (BN) as a protective coating on graphite mold parts did not prevent the formation of nonuniform layer on the ceramic surface.

316L-toughened porous Al2O3-based ceramic functionally graded materials using binder jetting

Al2O3-based ceramic functionally graded materials (FGMs) containing 1 wt% CuO and 4 wt% TiO2 as sintering aids and 0–40 wt% 316L as a toughening phase are fabricated by binder jetting additive manufacturing, and the low-temperature co-sintering toughening mechanism was studied. According to the 3D Stereo Microscope and XRD results, the interfacial microstructure exhibited a noticeable gradient change after being sintered from 1200 °C to 1450 °C for 2 h, and the main phases were Al2O3, γ-austenitie, Fe3C and a small amount of δ-ferrite. The FGMs sintered at 1450 °C had maximum relative density, X–Z-axis dimensional shrinkage and average bending strength values of 70.05%, 4.89%, 10.15%, 17.53% and 26.9 ± 0.87 MPa, respectively. Bending cracks originated from the pure Al2O3-based ceramic layer and gradually propagated to the high-316L side, accompanied by the crack bridging and deflection phenomena. The maximum crack deflection degree was about 90° at 1200 °C and 1400 °C. Obviously, the existence of crack bridging and deflection illustrated that 316L addition effectively improves the toughness of FGMs.

Functional assignment of technological accessories for woodworking

Forming a heat and sound insulation board from wood using non-combustible binders can increase the fire protection of the material by forming a protective layer of coke. This will make it possible to develop a new type of fireproof roofing products for building structures. It is not always advisable to treat the surface of a heat and sound insulation board with fireproof coatings, since after prolonged thermal exposure, the combustion stage can be transferred to the interior of the material by smoldering. Therefore, the manufacture of fire-resistant heat- and sound-insulating wood materials, the study of fire protection and the impact of their components on this process is an unresolved component of ensuring the fire resistance of building structures. And, accordingly, they determine the need for such research.
 The paper presents the results of research into the process of protecting wood wool boards with binders based on fire-resistant coatings. Tests on model samples of a wooden board showed that the material based on wood wool and an inorganic binder is characterized by heat absorption and inhibition of oxidation in the gas and condensed phase and the formation of a thermally protective ceramic layer on the surface of the wood. Experimental studies have confirmed that a material based on wood wool and an inorganic binder at a ratio of 1:1 refers to combustible materials, since its smoldering was recorded during exposure to temperature. So, by thermal action for 90 s, the material ignited and the flame spread over the first three zones for 41 s. On the other hand, an increase in the amount of an inorganic-based binder and the use of an organic-mineral binder does not lead to a material fire. In this case, the maximum temperature of the flue gases was about 120 °C, and the flammability index was 0 due to the decomposition of fire retardants under the influence of temperature with the release of incombustible gases, which inhibit the oxidation of the material and significantly increase the formation of a heat-protective layer of coke on the surface of the material. This leads to inhibition of heat transfer of the high-temperature flame to the material. Due to this, it became possible to determine the conditions of fire resistance of the material by forming a barrier for thermal conductivity. The obtained results indicate the possibility of targeted regulation of high temperature transfer processes to organic material by using special binders for wood products.

Ballistic performance study of multilayer Al2O3 ceramic-metal composite armor under strong confinement

A multilayer constrained alumina ceramic metal composite armor is designed in this paper. The effect of interlayer steel thickness of alumina ceramic metal armor on penetration process of tungsten alloy armor piercing projectile is studied by the penetration test and finite element simulation. The results show that in the case of the same layer of ceramics and equal surface density, the thicker the thickness of the steel plate away from the impact surface is, the better the support of the metal plate to the sandwich ceramics is. It is beneficial to maintain the initial volume of ceramics and the better ballistic performance of armor. The ballistic performance of the armor structure in this paper is 26.38 % higher than that of the Q235 steel plate with equal density.

Interlaminar mechanical performance of a multi-layered photovoltaic-thermoelectric hybrid device

A concentrated photovoltaic-thermoelectric hybrid device made up of a six-layer composite structure is considered. The hybrid device is composed of, from top to bottom, photovoltaic cell, ethylene vinyl acetate (EVA) layer, tedlar polyester tedlar (TPT) layer, ceramic layer, electrode, and thermoelectric legs. Under the service condition, the poor interlaminar mechanical performance of the hybrid device induced by the high interlaminar stresses level can give rise to very poor power generation performance. To understand this, an analytical model is built to study the influence of the thermal contact resistance and interfacial slip stiffness on the interlaminar stresses of the hybrid device. In particular, effects of the material parameters and geometric dimensions of the hybrid device are also studied by using the state space method. It is found that the thermal contact resistance mainly affects the interlaminar stresses of the photovoltaic module. The interlaminar stresses without considering the temperature-dependent material properties are greater than the actual stresses. The highest interlaminar shearing stress appears at the lower surface of the photovoltaic cell and the maximum peeling stress occurs at the interface between the EVA layer and TPT layer. A lower interfacial slip stiffness is conducive to reducing the interlaminar stresses. The interlaminar stresses decrease with decreasing elastic modulus and coefficient of thermal expansion of the EVA layer. In addition, a thinner thermoelectric layer contributes to lower the interlaminar stresses. The results offer helpful suggestions for the optimization of the interlaminar mechanical performance of the hybrid device.

Oxygen vacancy region formation in BaTiO3 adjacent to the interface between the internal electrode and the dielectric layer in Ni–Sn internal electrode multilayer ceramic capacitor exhibiting leakage current suppression

This study underlines the ceramic BaTiO3 dielectric layer adjacent to the electrode of long-term reliability-improved Ni–Sn alloy internal electrode BaTiO3-based multilayer ceramic capacitor to clarify the cause of electric barrier formation. Electron energy loss spectroscopy measurements of the Ti L 3,2 near the edges and the O K near the edge structure changes to characterize the existence of an oxygen vacancy region, approximately 60 nm in width, and generated in BaTiO3 adjacent to the interface. Accordingly, the n-type semiconductor layer of BaTiO3 that originated from the oxygen vacancies, led to the formation of a rigid Schottky barrier at the interface.

Spark plasma sintering of ceramic materials based on zirconates of rare-earth elements

Powders of rare-earth zirconates, La2Zr2O7 and ZrO2‒8Y2O3 were synthesized by reverse chemical precipitation to obtain ceramic materials on their basis by spark plasma sintering. The formation of the phase composition of ceramics during consolidation by spark plasma sintering has been studied. The thermal conductivity of ceramics based on REE zirconates at 400 °C is 1,79 W/(m·K), which is less than that of La2Zr2O7 ― 2,06 W/(m·K) and ZrO2‒8Y2O3 ― 2,4 W/(m·K). It is shown that the use of REE oxide concentrate is promising for obtaining a ceramic layer of heat-shielding coatings with thermal stability at temperatures above 1200 °C.

Fabrication and characterization of alumina-based bilayer dielectric high gradient insulator (DHGI)

High voltage devices suffer from electrical breakdowns that hamper their operation and shorten their lifespan. Such devices are often sealed and operate under vacuum to increase optical transmission and reduce the interaction with ambient gas molecules. The main failure mode in such devices is a surface breakdown. By introduction of a periodic structure of metal-dielectric, known as high gradient insulator (HGI), improved surface breakdown threshold is achieved. Nevertheless, local breakdown damage and metal deposition on the dielectric layers degrade the HGI performance. In this work, we demonstrate the fabrication and characterization of a novel alternative concept where we replace the HGI's metallic layers with high dielectric coefficient ceramic layers. The novel structure which is denoted as DHGI (Dielectric HGI), reshapes the electric field lines in a similar manner to common HGI. A prototype DHGI composed of two layers: (i) Al2O3 and (ii) Al2O3 with 8 wt%. addition of TiO2 co-doped with Al and Nb (TANO), was fabricated by spark plasma sintering (SPS). The dielectric constants of pure alumina and TANO are 10 and ∼104, respectively. It is shown that during sintering, unique intermediate layers are formed at the interface between the two original layers. The microstructure and composition of each layer were characterized. The decreasing TANO content in the intermediate layers induces a gradual decrease of the Al2O3 grain size across the interface. The DHGI prototype was found to have superior breakdown performance compared to conventional pure alumina insulator.

Advanced Sustainable Trilayer Cellulosic "Paper Separator" Functionalized with Nano-BaTiO3 for Applications in Li-Ion Batteries and Supercapacitors.

In the quest of developing a sustainable, low-cost and improved separator membrane for application in energy storage devices like lithium-ion batteries (LIBs) and supercapacitors (SCs), here we fabricated a trilayer cellulose-based paper separator engineered with nano-BaTiO3 powder. A scalable fabrication process of the paper separator was designed step-by-step by sizing with poly(vinylidene fluoride) (PVDF), thereafter impregnating nano-BaTiO3 in the interlayer using water-soluble styrene butadiene rubber (SBR) as the binder and finally laminating the ceramic layer with a low-concentration SBR solution. The fabricated separators showed excellent electrolyte wettability (216-270%), quicker electrolyte saturation, increased mechanical strength (43.96-50.15 MPa), and zero-dimensional shrinkage up to 200 °C. The electrochemical cell comprising graphite|paper separator|LiFePO4 showed comparable electrochemical performances in terms of capacity retention at different current densities (0.05-0.8 mA/cm2) and long-term cycleability (300 cycles) with coulombic efficiency >96%. The in-cell chemical stability as tested for 8 weeks revealed a nominal change in bulk resistivity with no significant morphological changes. The vertical burning test as performed on a paper separator showed excellent flame-retardant property, a required safety feature for separator materials. To examine the multidevice compatibility, the paper separator was tested in supercapacitors, delivering a comparable performance to that of a commercial separator. The developed paper separator was also found to be compatible with most of the commercial cathode materials such as LiFePO4, LiMn2O4, and NCM111.

Synergistic optimization of mechanical and tribological properties of TiC modified copper-graphite composites by direct current in-situ sintering

The application of Cu-graphite composites in the field of friction materials is limited by the poor wettability between Cu and graphite and weakened mechanical properties. In this work, in-situ TiC layers were generated by interfacial resistance sintering with direct current to manipulate the interfacial bonding of the composites and enhance their comprehensive properties. The Ti added to the composites would react with graphite at the interface to generate TiC layers and form strong Cu–TiC-graphite interfaces due to interfacial reactions. When the added Ti content is 6 wt%, the composite demonstrates the most excellent mechanical properties and tribological characteristics, i.e., yield strength (168 MPa) and wear rate (2.7 × 10−10 m2/N) are 93.1% higher and 29.7% lower than those of the Cu-graphite composite without Ti addition, respectively. The dense TiC layer induces the strengthening of the Cu matrix and serves as the reinforcing phase to optimize the interfacial bonding and stress transfer, which not only greatly enhances the mechanical properties of the composite but also enables the composite to take full advantage of the hard TiC and graphite phases to obtain stable friction coefficient and low wear rate. This work provides a simpler technique to prepare modified Cu-graphite composites with excellent performance and contributes to the in-depth understanding of the enhancement mechanism of hard ceramic layers on the mechanical and tribological properties of composites.

Hot corrosion and CMAS degradation of laser-glazed YSZ coating with optimum parameter

The purpose of this research is to look into the effect of laser surface modification on the hot corrosion and hot corrosion + calcium–magnesium aluminosilicate (CMAS) resistance of YSZ thermal barrier coating. Metco AMDRY 997 (Ni–22Cr–10Al–Y) powder was coated as a bond coat on the AISI 304L stainless steel substrate using a high-velocity oxy-fuel spray technique. As a ceramic top layer, 204 NS YSZ (ZrO2·8Y2O3) particles were plasma sprayed on the bond coat. Following that, the entire coating surface was treated with a 20-kHz pulsed CO2 laser to increase the coatings’ surface performance. A corrosion test was carried out in a box furnace for 20 h at 1050 °C. SEM images of laser-glazed coatings revealed denser surfaces than those of air-spraying coatings. The laser-modified coating is more resistant to hot corrosion than unmodified coatings. The X-ray diffraction analysis revealed that the reaction between yttria (Y2O3) and V2O5 resulted in the formation of YVO4 crystals as a corrosion product. According to energy dispersive spectroscopy results, laser-glazed coatings reduced molten salt diffusion from surface to bond coat. As a result, laser-glazed coatings demonstrated improved hot corrosion resistance and decreased corrosion products on the bond coat zone. After the hot corrosion test, the laser-treated composite had a 55% lower thermally grown oxide layer than untreated APS YSZ. The optimum laser parameter was used as 77.7 W laser power, 120 mm/s scanning speed, and 215 mm laser distance.

A double-layer-coated graphite anode material for high-rate lithium-ion batteries

Graphite is currently the most widely used anode material for lithium-ion batteries. However, the rapid development of electric vehicle market puts forward higher requirements to the rate performance of graphite anode. Therefore, in this study, the double-layer-coated (hard carbon and alumina coated) artificial graphite particles (AG@HC@Al2O3) are obtained to meet the requirements above. The inner hard carbon layer improves the rate performance with its large layer spacing. For the outermost ceramic layer of alumina, it further improves the high current charging capacity by improving the wettability of electrolyte to graphite anode. On the other hand, it acts as artificial solid electrolyte interphase film to slow down the loss of coulomb efficiency caused by hard carbon coating. The AG@HC@Al2O3 presents an excellent capacity retention rate of 94.4% at the rate of 1C (1C = 372 mAh g−1) after 150 cycles.