Ceramic Layer Research Articles

Improving fire retardancy of Ti alloys with a refractory ceramic barrier layer

Reliable service of indispensable titanium alloys in aeroengines is limited by the bottleneck problem of titanium fires. In this study, a tri-layer fire retardant coating with a bi-functional ceramic barrier layer is proposed to suppress titanium fire. Results show that the current coating can increase the fire retardant temperature by ≥ 300 K under droplet ignition. Thermal barrier effect of the YSZ refractory ceramic layer significantly reduces Ti alloy temperature, and oxygen barrier effect prevents active Ti from directly contacting oxygen during the entire ablation process. Therefore, the two barrier effects effectively prevent occurrence of titanium fire. In addition, dissolution of the Ni-based abradable seal coating makes burning TC4 molten droplet extinguished in a short time, thus further inhibiting titanium fire ignition. The present study provides an effective method for reliable service and titanium fire-resistant design of titanium alloys.

3D printing of ultra-thin veneers made of lithium disilicate using the LCM method in a digital workflow: A feasibility study.

This article highlights the feasibility of the additive fabrication of ultra-thin veneers made of lithium disilicate using the lithography-based ceramic manufacturing (LCM) method. An esthetical appealing restoration of anterior teeth with thin ceramic veneers is considered one of the ultimate challenges in restorative dental prosthetics. These sophisticated restorations can be fabricated in different ways. Both analog and digital subtractive manufacturing processes have been used to date. Either of the methods is highly demanding for the dental technician and dental engineering due to the required low ceramic layer thickness. Modern additive manufacturing methods, for example LCM technology, enable the production of ultra-thin lithium disilicate veneers with layer thicknesses of down to 0.2 mm and could therefore represent a viable alternative for this indication in the future. Digital technologies can help streamline workflows, make the outcome more predictable and reproducible, and even further optimize therapeutic restorative options such as highly esthetic veneers for anterior teeth. The reduced material thickness allows for a true non-prep solution or minimally invasive preparation.

Effects of Top Ceramic Layers with an Ultrathin Dense Layer on the Thermal–Physical Properties of Thermal Barrier Coatings

Thermal barrier coatings have been used to protect superalloys under extremely harsh conditions. The durability of TBCs with a NiCoCrAlY bond layer prepared via the air plasma spray process and an ultrathin dense layer prepared via magnetron sputtering was investigated under different corrosion conditions. This paper discusses the corrosion resistance improvement mechanism of TBCs with a dense layer produced by magnetron sputtering under corrosion conditions with environmental contaminants such as calcium–magnesium–aluminum–silicon oxide systems (CMAS) at 1300 °C and NaCl-Na2SO4-V2O5 (NV) at 900 °C. The corrosion results show that CMAS will react with the stabilizers of zirconium oxide, which will change the rate of the phase transition, as determined via X-ray diffraction tests. A thermal ablation test verified that TBCs with a dense layer have a better corrosion resistance and better thermal insulation properties. All results show that preparing TBCs with a dense layer via the magnetron sputtering method will be an efficient method to improve TBCs’ properties at high temperatures in the future.

Synergistically improving dielectric permittivity and breakdown strength of ceramic dielectric via introducing monodispersed gold nanoparticles

Ceramic dielectrics have been extensively studied due to their high-power density and fast charge/discharge rate. However, simultaneously increasing their dielectric permittivity and breakdown strength remains a formidable challenge. Here, the novel sandwich structure ceramic dielectrics are designed, in which monodisperse gold nanoparticles are sandwiched by two ceramic layers. The effects of gold nanoparticles with different sputtering times on the dielectric breakdown performance of the composite ceramics are investigated. The results show that the dielectric permittivity and breakdown strength of barium titanate composite ceramics with 3 min gold nanoparticle interlayer (BT-3Au-BT) reach 6017.5 (10 kHz) and 111.4 kV/cm, respectively, which are 9 % and 18 % higher than that of barium titanate ceramics without gold nanoparticle interlayer (BT-0Au-BT). The improved dielectric permittivity is originated from the formation of numerous micro-capacitors. The enhanced breakdown strength is attributed to the Coulomb blockade effect of gold nanoparticles. This work provides a novel, easy-to-operate and scalable approach for synergistically improving the dielectric permittivity and breakdown strength of dielectric materials, which opens up a novel way for the design of high-performance dielectric materials and would also be enlightening for the exploration of other functional nanocomposites.

Study of wear and corrosion resistance of ATO nanoparticle–doped micro‐arc oxide film layers

AbstractIn order to enhance the corrosion and wear resistance of aluminum alloys in complex and variable environments, an Al2O3 ceramic film was prepared on the surface of 7A04 aluminum alloy in a silicate electrolyte system using a micro‐arc oxidation technique. Subsequently, antimony tin oxide (ATO) nanoparticles were used to dope the micro‐arc oxidation film to enhance the protective properties of the 7A04 aluminum alloy. The structural characteristics of the film were investigated by examining the surface and cross‐sectional morphology and the composition of the physical phases. The results show that ATO nanoparticles can promote the micro‐arc oxidation reaction, improve the surface morphology of the film layer, increase the thickness of the film layer and the denseness after sintering, and enter the film layer in the form of melt wrapping, which plays a role in refining the grain. In the study of the wear resistance and corrosion resistance of ATO‐doped ceramic film layers, it was found that the introduction of ATO nanoparticles did not significantly improve the wear resistance of the micro‐arc oxide ceramic film layers but significantly improved the corrosion resistance of the film layers.

Polymer‐derived SiOC ceramic coating for corrosion protection

AbstractIn the present study, a polymer‐derived silicon oxycarbide (SiOC) ceramic layer has been coated on stainless steel 304 (SS304) to improve corrosion resistance in a seawater environment. The surface of SS304 is dip‐coated with vinyl‐functionalized polysiloxane, followed by pyrolysis under argon at 800°C to obtain SiOC layer with a thickness of about 1 μm after two‐fold coating/pyrolysis steps. Structural characterization of the samples was performed by fourier transform infrared (FTIR), X‐ray diffraction, Raman spectroscopy, and scanning electron microscopy. Electrochemical characterization of SS304 and SiOC‐coated SS304 is performed in 0.6 M NaCl solution. Potentiodynamic polarization measurements showed improved corrosion resistance of SiOC‐coated SS304 with a very low corrosion current density of 4.14 × 10−9 A/cm2 whereas for uncoated SS304 corrosion current density of 4.56 × 10−7 A/cm2 was measured. Electrochemical impedance spectroscopic study confirmed superior corrosion resistance behavior of SiOC‐coated SS304 over uncoated SS304.

Study on the protective performance of high-performance multi-scale (SiCh-p+B4Cp)/5083Al ceramic array armor with excellent ballistic properties

Ceramic array armor suffers from insufficient constrained capability of ceramic units in the embedded armor structure, leading to weak interfacial bonding at ceramic unit connections, significantly reducing the overall ballistic performance. In this study, centimeter-sized SiC hexagonal prisms and micrometer-sized B4C powders were used as reinforcing materials. A high-strength, high-toughness, and multiscale array (SiCh-p + B4Cp)/5083Al armor with strong interfacial bonding was prepared using pressure infiltration technique. The (SiCh-p + B4Cp)/5083Al armor was combined with ultra-high molecular weight polyethylene and 6252 armor steel to form an integrated armor system. To investigate the effect of constrained material on its ballistic performance, the array structures with epoxy and 5083Al as constrained material were prepared for comparison. Ballistic performance tests were conducted using 12.7 mm Armor-Piercing Incendiary (API). The damage mechanisms of the armor structure were studied through finite element simulation and a combination of macroscopic and microscopic analyses. The results demonstrate excellent overall ballistic performance of the (SiCh-p + B4Cp)/5083Al armor system. The high-strength and high-toughness 55 vol%B4Cp/5083Al composite material exhibits strong interfacial bonding with SiCh-p, providing robust support to the SiCh-p. The armor back deformation was reduced by 50 %, and the ceramic layer dissipated more than 70 % of projectile kinetic energy, The materials prepared in this study exhibit significant potential in ballistic performance.

Ablation behavior, microstructure, phase evolution and in situ ceramization mechanism of ZrC-LaB6 modified carbon fiber/phenolic resin ceramizable composite

Carbon fiber/phenolic resin composite (CF/Ph) has drawn great interest in thermal protection for its characteristics of high specific strength and easy fabrication. However, oxidation failure limits further application of CF/Ph in hostile environments. Herein, a novel carbon fiber/phenolic resin ceramizable composite modified with ZrC and LaB6 was reported. The synergistic effects between ZrC and LaB6 on high-temperature thermal degradation behavior, oxidative corrosion and ablation resistance were systematically studied based on thermal analysis and oxyacetylene ablation experiment of the resulting ceramizable composite as well as microstructure evolution, phase evolution, and thermodynamic calculation analysis of the ablated surface. The resulting ceramizable composite exhibited excellent oxidative corrosion and ablation resistance, with the residue yield at 1500 °C as high as 32.8 % and the linear ablation rate at 4.3 MW/m2 for 30 s as low as -0.00231 mm/s, respectively. Further, the ablation mechanisms were revealed. Dense B-C-O-Zr-La ceramic layers with a mosaic structure, which acted as efficient thermal protection barriers, were constructed in situ, and significantly reduced corrosion to carbon. Moreover, an intense endothermic effect during the carbothermal reaction between ZrO2, B2O3 and PyC led to an abnormally better insulation capacity.

Research and analysis of a thermal optimisation design method for aluminium alloy pistons in diesel engines

To further improve the thermal state of the piston for better thermal design, a multi-objective optimisation algorithm was used in this paper to find the best combination of design variables. The results show that thermal barrier coating (TBC) can effectively prevent heat transfer to the piston, and the thicker the ceramic layer, the better the thermal insulation effect. The maximum temperature and maximum thermal stress of the optimised piston matrix can be reduced by a maximum of 55.54 °C and 43.94 MPa, with a reduction of 15.08 % and 25.43 %, respectively, compared with that of the aluminium alloy piston of 368.39 °C and 172.76 MPa. Moreover, the thermal stress at the bottom of the combustion chamber, a larger cross-sectional area of the cooling gallery can dissipate more heat, which can have a more significant impact compared to the thickness of the ceramic layer. The large temperature gradient causes the maximum thermal stresses of the TBC piston to occur on the surface where the metal bonding layer contacts the piston matrix. Such high thermal stress is the main cause of coating delamination. The findings of this study can provide a reference for improving the thermal state of the piston and enhancing the engine performance.

The Effect of the Addition of Aluminum Nitride to the Composition of NiAl2O4 Ceramics on Hydrogenation Processes and the Increase in Resistance to Swelling and Degradation

This work examines the effects of the formation of impurity inclusions in the structure of NiAl2O4 ceramics when aluminum nitride is added to them and the occurrence of a reinforcement effect that prevents hydrogenation processes and the subsequent destruction of conductive and thermophysical characteristics. The appeal of ceramics possessing a spinel crystal structure lies in their potential use as ceramic fuel cells for both hydrogen generation and storage. Simultaneously, addressing the challenges related to ceramic degradation during hydrogenation, a critical aspect of hydrogen production, can enhance the efficiency of these ceramics while lowering electricity production costs. The selection of aluminum nitride as an additive for ceramic modification is based on its remarkable resistance to structural damage accumulation, its potential to enhance resistance to high-temperature degradation, and its ability to bolster strength properties. Moreover, an examination of the alterations in the strength characteristics of the examined samples subjected to hydrogenation reveals that the stability of two-phase ceramics is enhanced by more than three to five times compared to the initial ceramics (those without the addition of AlN). Additionally, it was noted that the most significant alterations in both structure and strength become apparent at irradiation fluences exceeding 1014 proton/cm2, where atomic displacements in the damaged ceramic layer reach over 5 dpa. During the evaluation of thermophysical properties, it was discerned that ceramics featuring an impurity phase in their composition exhibit the highest stability. These ceramics demonstrated a reduction in the thermal conductivity coefficient of less than 1% at the peak irradiation fluence.

Spectrum regulation of YAG:Ce/YAG:Cr/YAG:Pr phosphor ceramics with barcode structure prepared by tape casting

AbstractYAG:Ce/YAG:Cr/YAG:Pr composite phosphor ceramics with barcode structure were prepared by tape casting combined with the solid‐state reaction method. This structure provides a convenient and effective method for regulating the optical parameters such as luminous efficacy (LE), color rendering, and correlated color temperature (CCT) of white light‐emitting diodes/laser diodes (LEDs/LDs). For the sample with a thickness ratio of 6:6:6 for YAG:Ce, YAG:Cr, and YAG:Pr, the in‐line transmittance reaches 60% at 800 nm, and it shows a good optical performance with the LE of 106 lm/W, the color gamut (Rg) of 77, the color fidelity index (Rf) of 86, and the CCT of 7642 K. The electroluminescence spectra and color coordinates can be adjusted by changing the ratio of each component in the composite ceramic and the thickness of the ceramic because the tape casting method allows precise control of the thickness of each ceramic layer. The high tunability provides more freedom in the performance design of composite phosphor ceramics and makes them the most promising candidate for high brightness white LEDs/LDs.

Low-temperature co-fired PZNN-PZT multilayer piezoelectric ceramics with excellent electrical and bending properties

A 0.65 Pb(Zr0.47Ti0.53)O3–0.35[Pb(Zn0.1Ni0.9)1/3Nb2/3]O3 (PZNN-PZT) piezoceramic with sintering aids of Li2CO3, Bi2O3, CuO and Sm2O3 was prepared via a traditional solid reaction to achieve a high-performance multilayer actuator. The microstructure and electrical properties of ceramic bulks were systematically explored. The piezoceramics sintered at various temperatures show multi-phase co-existence. The sintering aids are beneficial for grain growth and microstructure densification. The piezoceramic sintered at 960 °C possesses relatively desirable electrical properties, including d33 ∼ 550 pC/N, kp ∼0.7 εr ∼2200, tan δ ∼0.021, Qm ∼71, Tc ∼240.5 °C, Pr ∼24.44 μC/cm2 and Ec ∼823.7 V/cm. Furthermore, we employed the tape casting and low-temperature co-fire methods to fabricate a PZT-PZNN/Ag–Pd multilayer piezoceramic of 7 × 7 × 36 mm3 in dimension with a single ceramic film of about 80 μm in thickness. The Ag–Pd electrode is effectively bonded with the ceramic layer, especially chemical binding induced by oxygen diffusion at some partial areas, which plays a crucial role in high binding strength (∼9.2 MPa). The multilayer piezoceramic exhibits outstanding actuating characteristics of high Smax ∼55.53 μm @ 150 V, and low H ∼19.8% @ 150 V together with outstanding stiffness of 70.87 N/μm @ 150 V.

Electrochemical and tribological studies of in-situ grown ceramic layers on additively manufactured Ti–50Zr alloy for load-bearing implant applications

Ti and Zr metals are the most common bio-metallic materials that are frequently employed in a variety of orthopedic applications due to their excellent biocompatibility and mechanical stability. However, these metals still suffer from poor wear and corrosion resistance in the physiological environments. To mitigate these limitations, Ti–50Zr alloy was fabricated using the Laser Engineering Net Shape (LENS™) additive manufacturing technique. At 600 °C for 2 and 6 h, the samples underwent thermal nitridation (TN) and thermal oxidation (TO), respectively. The assessment of the surface treatments on the in-situ grown nitride and oxide coating thickness, phase identifications, and in-vitro tribological properties of Ti–50Zr alloy were carried out in simulated conditions. The results showed that thermal treatments could significantly change the film thickness, hardness, wear resistance, and corrosion resistance properties of Zr–50Ti alloy. The sample that underwent nitriding at 600 °C for 6 h showed the highest in-vitro wear resistance. Compared to thermally oxidized samples, nitridation of Ti–50Zr alloy can be used for bio implant applications, with adequate mechanical stability, excellent wear, and corrosion resistance.

High Temperature Flexural Strength, Microstructure, and Phase Evolution of Quartz Fiber/Boron Phenolic Resin Ceramizable Composite Modified with W and B4C

In order to investigate the effect of refractory metal on the high temperature properties of phenolic resin matrix composites, modified quartz fiber reinforced ceramizable composites were prepared by a molding process with a refractory component, tungsten, as the functional component and boron carbide as the ceramic forming agent. The effects of the tungsten and the boron carbide on the heat resistance of the composite were investigated. The results showed that the introduced refractory metal tungsten and the boron carbide can react to form tungsten borides and tungsten carbides at high temperature, and form a ceramic layer on the surface of the composite, which can fill the defects caused by pyrolysis of matrix and improve the high temperature performance of the composite. When the content of boron carbide was 10 wt% and the content of tungsten powder was 30 wt%, the flexural strength of the composite before and after heat treatment at 1200 °C were increased by 54.6% and 30.2% respectively compared with that without filler.

Doped effect of Yb on enhancing resistance to calcium-magnesium-alumina-silicate corrosion of Sm2(Zr0.7Ce0.3)2O7

Four kinds of (Sm1−xYbx)2(Zr0.7Ce0.3)2O7 (x = 0, 0.1, 0.2, 0.3) ceramics with different contents of Yb were prepared by the solid-phase reaction. Their thermochemical reaction behaviors with calcium-magnesium-alumina-silicate (CMAS) at 1300 °C were investigated. Among them, (Sm0.7Yb0.3)2(Zr0.7Ce0.3)2O7 has the best corrosion resistance to CMAS. The increase of Yb content can accelerate the formation rate of apatite, preventing the ceramic layer from erosion of CMAS and improving the strain tolerance of the ceramic. In addition, the CMAS wetting, corrosion process and failure mechanisms were discussed by high-temperature field wetting and transmission electron microscopy.

Functional design and implementation of multilayer Ce:YAG/Cr:YAG composite transparent ceramics by tape casting for white LEDs/LDs

The shortage of red-light emission in Ce3+:Y3Al5O12 (Ce:YAG) luminescent ceramics is a bottleneck problem to realize the key applications of ceramics based white light-emitting diode (LED) and laser diode (LD) devices. However, the energy band-gap engineering for Ce3+ ion via host substitution or red-emission ions co-doping always leads to its decrease of luminescence efficiency (LE), while a spectrum overlay strategy would be simple and effective. In this study, multilayer composite structure Ce:YAG/Cr:YAG transparent ceramics (TCs) with high color rendering index (CRI) were fabricated by tape casting and vacuum sintering. An organic tape casting protocol with low toxicity and environmental protection was developed and the amounts of dispersants, binders, and plasticizers were systematically optimized to produce good quality tapes with no defects. The transmittance of ceramic reached 78% at 800 nm. By using a 455 nm blue chip, the CRI of the Ce:YAG/Cr:YAG TCs based LED device was increased from 26.7 to 77.5, and the LE was decreased from 181.5 to 10.4 lm/W. Additionally, the optimized LE and CRI for LD device were 130.2 lm/W and 78.1, respectively. Therefore, this research displays that the design and implementation of ceramic functional layer to achieve the essential enhancement of CRI in TC based white lighting is a promising method through the tape casting forming technology.

Nanodiamond Decorated PEO Oxide Coatings on NiTi Alloy.

Cardiovascular diseases (CVDs) remain a leading cause of death in the European population, primarily attributed to atherosclerosis and subsequent complications. Although statin drugs effectively prevent atherosclerosis, they fail to reduce plaque size and vascular stenosis. Bare metal stents (BMS) have shown promise in acute coronary disease treatment but are associated with restenosis in the stent. Drug-eluting stents (DES) have improved restenosis rates but present long-term complications. To overcome these limitations, nanomaterial-based modifications of the stent surfaces have been explored. This study focuses on the incorporation of detonation nanodiamonds (NDs) into a plasma electrolytic oxidation (PEO) coating on nitinol stents to enhance their performance. The functionalized ND showed a high surface-to-volume ratio and was incorporated into the oxide layer to mimic high-density lipoproteins (HDL) for reverse cholesterol transport (RCT). We provide substantial characterization of DND, including stability in two media (acetone and water), Fourier transmission infrared spectroscopy, and nanoparticle tracking analysis. The characterization of the modified ND revealed successful functionalization and adequate suspension stability. Scanning electron microscopy with EDX demonstrated successful incorporation of DND into the ceramic layer, but the formation of a porous surface is possible only in the high-voltage PEO. The biological assessment demonstrated the biocompatibility of the decorated nitinol surface with enhanced cell adhesion and proliferation. This study presents a novel approach to improving the performance of nitinol stents using ND-based surface modifications, providing a promising avenue for cardiovascular disease.

High-Modulus Laminated SiC/AZ91 Material with Adjustable Microstructure and Mechanical Properties Based on the Adjustment of the Densities of the Ceramic Layers.

To address the issue of inadequate strength and plasticity in magnesium matrix composites, SiC preforms were prepared using the freeze-casting process. The effects of sintering temperature on the microstructure, mechanical properties, and fracture behavior of SiCp/AZ91 magnesium matrix composites were studied by controlling the density of SiC preforms through low-temperature sintering. The results indicate that as the sintering temperature decreases, the reaction products in the SiC layer decrease, resulting in lower SiC preform density and increased content of AZ91 alloy filling in the layer. The increased alloy content in the ceramic layer not only inhibits crack initiation but also hinders crack propagation, thereby endowing the SiCp/AZ91 laminated material with excellent compressive strength and compressive strain. At the sintering temperature of 900 °C, the SiCp/AZ91 laminated material exhibits impressive compressive strength and strain values of 623 MPa and 8.77%, respectively, which demonstrates an excellent combination of strength and toughness.

Wet reduction-based fabrication and characterization of a Cu-Pb(MgNb)ZrTiO3 multilayer actuator

Cu–(0.7Pb(Mg0.67Nb0.33)TiO3–0.3Pb(Zr0.48Ti0.52)O3)(PMNZT) multilayer actuators were prepared using a sequence of ceramic layer tape-casting, on-ceramic electrode printing, lamination, co-firing in air, and soaking in aqueous N2H4 at 25–100 °C. The employed wet reduction protocol converted the Cu2O produced in the electrode layers upon co-firing to Cu, while keeping the composition and structure of the PMNZT ceramic layers unaffected. Nano-pores were converted into macro-pores with increasing reduction temperature and time. This reduction process was controlled by the kinetics, which is attributed to the open structure of the electrode resulting from the presence of a sacrificial polymer (polyvinylidene difluoride, PVDF) particles. This resulted in a short path of hydrogen diffusion in the inner electrode layers. The pore size and population affected the electrical conductivity of the electrode and the performance of the PMNZT ceramics. To address this issue, the sample was immersed in aqueous HSO4 at 60 °C to fill the pores in the electrode layers, thereby mitigating their effect on electrical conductivity. The samples prepared using wet reduction and filling processes exhibited the same piezoelectric properties as the bulk PMNZT sample.

Innovative powder-based wettability evaluation of HfB2-ZrB2-SiC-B4C-CNT composite: Effect of surface roughness and ambient conditions

Active metal brazing, the most common method for joining UHTCs, necessitates the wettability of diborides in contact with filler layer, which is evaluated in present work using a powder-based approach. Ni powder is placed on pre-spark-plasma-sintered HfB2-ZrB2-SiC-B4C-CNT (HZSBC) composites with varying surface roughness (0.1 and 0.7 μm) and heated to 1450°C in Ar and Ar+H2 atmosphere. Formation of gas-liquid-Ni interface for rough surface (Ra:0.7 µm) restricted the spreading of molten Ni on HZSBC surface and increased contact angle (by ∼30°) compared to smooth surface (Ra:0.1 µm). Addition of 5% H2 into Ar atmosphere suppressed the oxide formation and improved molten Ni spreading at a contact angle of ∼10°. Cross-sectional analysis of droplets supports dissolutive wetting where enhanced surface roughness has reduced the dissolution depth (by ∼50% for Ar and ∼12% for Ar+H2 atmospheres). Furthermore, brazing of HZSBC composites with Ni interlayer is performed at 1450°C, in Ar and Ar+H2 atmosphere. Lower wettability of Ni with HZSBC in Ar resulted in detachment of composites during polishing, thus, indicating poor interfacial bonding. Successful brazing of these composites in Ar+H2 atmosphere resulted in microstructural inhomogeneity with decreased hardness and Young's modulus by ∼68% and ∼58%, respectively, from HZSBC region to Ni-Si rich filler layer. Lower interfacial residual stresses (∼0.4 GPa) have provided the structural integrity between ceramic and metal layer, thus making them suitable for applications involving complex shapes.