Multilayer Ceramic Coatings Research Articles

Microstructural evolution and ablation behaviors of NbSi2/SiO2–Nb2O5/X (X=MoSi2, MoSi2-Yb2O3, MoSi2-Yb2O3–ZrC) multilayer coatings on Nb alloy in different ablation environments

To improve the high-temperature ablation resistance of Nb alloys, multiphase-multilayer ceramic coatings were prepared using a novel strategy combining halide activated pack cementation (HAPC) and liquid plasma-assisted particle deposition and sintering (LPDS) methods. The MoSi2, Yb2O3, and ZrC particles were deposited individually or co-deposited on the NbSi2 bottom layer to obtain NbSi2/SiO2–Nb2O5/MoSi2 (Mo), NbSi2/SiO2–Nb2O5/MoSi2-Yb2O3–SiO2 (MoYb), NbSi2/SiO2–Nb2O5/MoSi2-Yb2O3–ZrO2–ZrC (MoYbZr) multilayer ceramic coatings, respectively. Results showed that all three coatings remained intact after propane ablation (1500 °C), exhibiting excellent ablation resistance. For the harsher oxyacetylene ablation environments with higher temperatures (1800 °C), Mo coating suffered from long cracks, bubbling, and localized spalling and MoYb coating sprouted massive cracks without spalling. The oxide scale integrity of the MoYbZr coating was well maintained without cracks, exhibiting excellent resistance to oxyacetylene ablation attributed to the incorporation of Yb2O3 and ZrC. The mass and linear ablation rates of MoYbZr coating were only 0.137 mg/s and 0.196 μm/s after oxyacetylene ablation, which were 25.14 % and 49.61 % lower than that of MoYb coating, and 88.01 % and 75.37 % lower than that of the Mo coating, respectively. The Yb2O3 strengthened the Si–O bonding in the SiO2 network and increased the viscosity of the SiO2 scale, thus enhancing the self-healing ability of the oxide scale and slowing down the evaporation of SiO2. The oxidation products (ZrO2 with SiO2) from MoSi2 and ZrC further reacted to produce ZrSiO4, which can inhibit microcrack creation and extension. Micropores in the Zr–Si–O oxide scale mitigated thermal stresses, inhibited crack initiation and extension. The Yb2O3, Yb2SiO5, and ZrSiO4 embedded in the SiO2–ZrO2 scale acted as pinning effects, enhancing the high-temperature structural stability, thereby improving the ablation resistance of the MoYbZr coatings.

Accelerated thermal property mapping of TRISO advanced nuclear fuel

TRistructural ISOtropic (TRISO) fuel is a leading-edge nuclear fuel form representing a departure from the more traditional nuclear fuel forms utilized in the reactor fleet of today. Rather than a monolithic fuel pellet of uranium dioxide, integral fuel forms containing TRISO fuel are composed of thousands of microencapsulated uranium-bearing fuel kernels and individually coated with multiple layers of pyrolytic carbon and silicon carbide. These multilayered ceramic coatings serve as an environmental barrier to ensure radioactive and chemically reactive fission products are contained within the reactor fuel elements, but also participate in the transfer of heat generated in the nuclear fuel to the coolant – the primary purpose of a nuclear reactor. Since traditional thermal property measurement techniques, such as laser flash analysis, would be unable to resolve the thermal properties of the individual TRISO coating layers, a simplified frequency-domain thermoreflectance technique has been developed to rapidly map the thermal properties of TRISO particles. Using this technique, the thermal properties of TRISO particles have been mapped from room temperature up to 1000 °C to examine the spatial variation and temperature-dependency of the thermal properties within each layer. Additionally, spatial-domain thermoreflectance was used to examine the anisotropy of the thermal properties for each layer at different locations within a single TRISO particle, and across multiple TRISO particles to assess the intra- and inter-particle uniformity of thermal properties, respectively. To elucidate the underlying causes for the measured variations in thermal properties, scanning electron microscopy and Raman spectroscopy were used to examine variations in microstructure and chemical bonding within the different coating layers. Results from this work are then compared with previous examinations of TRISO fuel particles and microstructurally driven mechanisms for the variations in the measured thermal properties of the different carbonaceous layers are discussed.

Metallurgical, erosion, and sensitization performance of TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings on AISI 304 boiler steel

In the present work, TiAlN monolayer and TiAlN/TiN multilayer ceramic coatings were deposited on AISI 304 austenitic stainless steel by plasma arc physical vapor deposition (PAPVD) process. The metallurgical, erosion, and sensitization performance of these coatings were compared with uncoated 304 boiler steel. Metallurgical studies depicted formation of Al and Ti nitrides on monolayer and multilayer coated steel surfaces, which resulted into higher nitriding at the surface and dense coating formation on boiler steel substrate. Multilayer film exhibited comparatively lesser porosity, lower surface roughness, and higher hardness than monolayer coated and uncoated steel. The erosion performance was evaluated at 30° and 90° besides 2 g/min and 3 g/min flow rates of Al2O3 erodent material for coated and uncoated steel substrate. Multilayer coated 304 steel possessed lower erosion wear rate as evaluated through lesser weight loss before and after erosive wear, smaller crater formation, and minimal adherence of erodent material along with lesser Fe content on eroded surface relative to monolayer coated and uncoated steel. Multilayer coated steel thermally aged at 750° for 24 h had least degree of sensitization (DOS) compared to monolayer coated and uncoated aged boiler steel. Although monolayer coated steel performed better than uncoated one in erosion and sensitization performance but multilayer coating performance was best among all coated and uncoated steel used for present study. Thus, it was established that TiAlN/TiN multilayer coating on AISI 304 boiler steel has improved its metallurgical, erosion, and sensitization performance.

изико-механические свойства керамических покрытий, получаемых короткоимпульсной лазерной наплавкой порошковой смеси на основе бора

Modern repair production that implements traditional technologies for making restorative coatings has lost its relevance, since it cannot provide the necessary physical and mechanical properties of the coatings. The problem is that in modern metallurgy there is no line of repair additive materials with high strength and technological properties. Therefore, the issues of searching for innovative materials and technologies for their application on the surface of worn parts are relevant and require fundamental research. The aim of the work is to study the physical and mechanical properties of ceramic coatings obtained by short-pulse laser treatment. To achieve this goal, ceramic compositions based on boron carbide, additionally doped with boron nitride (0 to 40% BN), magnesium oxide (2 to 10% MgO) and lithium (5 to 25% LiO), were used. The scientifi c novelty of the research lies in the application of selective laser sintering technologies in the formation of thin coatings (up to 200 μm) under conditions of a short-pulse laser refl ow of powder media. To assess the physical and mechanical properties, laboratory research methods were used, in particular, analysis of the microhardness of the created restorative coatings, microstructure and tribological performance indicators using modern techniques and instrumentation. The research results confi rm the possibility of practical implementation of restorative coatings based on ceramic compounds. The multi-layer ceramic coatings (B4C-BN- MgO-Li2O) up to 200 μm thick showed good workability, low coeffi cient of friction (0.18) and the ability to work under high dynamic loads in the absence of intensive lubrication. The structure of the coatings has a dense adhesive zone with no visible defects. The presented results of studying the physic-mechanical properties of ceramic coatings have high research credentials and practical signifi cance, and their application will improve the durability of machine parts in the conditions of their operation.

Effect of mechanical properties of CrN/CrCN coatings and uncoated 1.402 stainless steel on the evolution of degradation and surface roughness in cavitation erosion

The effect of the mechanical properties of CrN/CrCN multilayer ceramic coatings on cavitation degradation and surface roughness was investigated. Three coatings with comparable thickness and modulus but the different thicknesses of the CrCN layer, and uncoated 1.402 steel were tested. Increasing the thickness of the CrCN layer increased hardness (H) and Young's modulus (E), but decreased the LC1 force at which the first cracks appear. No correlations were found with LC2 force, at which coating is completely removed. The H3/E2 ratio of better correlated with erosion rate and eroded area than the ratio of H/E. The eroded area of CrN/CrCN coatings was related to the erosion rate. For the H3/E2 ratio bigger than 0.1 GPa, the erosion rate increased with increasing this parameter. The failure mechanism influenced the nature of the relationship between roughness and volume loss in cavitation erosion studies. In the case of systems with hard and rigid coatings, the increase in surface roughness was accompanied by a decrease in volume loss. Changing the degradation mechanism during the tests leads to a loss of correlation between roughness and erosion rate.

Deuterium permeation through multi-layer ceramic coatings under liquid lithium-lead exposure condition

Corrosion of tritium permeation barrier ceramic coatings by liquid tritium breeders is an unavoidable concern in a high thermal efficiency fusion reactor. In this study, we have established a deuterium permeation measurement system under static Li-Pb exposure conditions to investigate the deuterium permeation behavior of multi-layer ceramic coatings under corrosive environments. The system successfully detected the coating degradation on the moment by measuring an irregular increase in deuterium permeation. The permeation behaviors showed that the coating degraded more seriously as the number of the interfaces between the different ceramics increased.

The effect of nickel on the high-temperature properties of multilayer ceramic coatings

The structure and composition of multicomponent TiCrMoN-Ni arc-PVD coatings with high nickel concentration (more than 8 at.%) are studied at bias potentials of 80-140 V. All coatings are characterized by a layered structure, the modulation period tends to decrease as increasing the bias potential. After annealing at 850 °C in vacuum, the coatings retain their layered structure without signs of dissolution of layers in each other. Nickel sublayers retain their polycrystalline structure, at the same time, the monolayer CrN are formed due to recrystallization.

Corrosion tests of multi-layer ceramic coatings in liquid lithium-lead

Tritium permeation through structural materials in fusion reactor blanket systems is a critical issue from the viewpoints of fuel loss and radiological safety. Ceramic coatings have been investigated to prevent tritium permeation; however, corrosion of the coatings by blanket materials, especially corrosive liquid tritium breeders such as lithium-lead is serious. In our previous study, the improvement of permeation reduction performance using an erbium oxide (Er2O3)-zirconium oxide (ZrO2) two-layer coating was confirmed, but it did not show substantial corrosion resistance. In this study, various multi-layer coatings were fabricated by metal organic decomposition and then exposed to lithium-lead under static conditions to investigate precise corrosion behaviors of multi-layer coatings. After lithium-lead exposure for 1000 h at 600 °C, the outermost Er2O3 layer almost disappeared, while the outermost ZrO2 layer remained, indicating that ZrO2 is more suitable as the outermost layer. However, many cracks and peelings were observed on the outermost ZrO2 layer in the cases of the samples having four coating interfaces. The optimization of layer combination and the control of adhesion between the coatings are required to reduce the degradation of multi-layer coatings.

Corrosion-Resistant Ceramic Coatings that are Promising for Use in Liquid Metal Environments

This Article Presents the Results of the Development of Multilayer Ceramic Coatings to Protect Metal Products from Corrosion in Aggressive Liquid Metal Environments. the Development is Based on the Integrated Use of Low-Temperature Heterophase Transfer and Microarc Oxidation Methods. the Results of Corrosion Tests of Coatings in the Interaction with Molten Lead in the Temperature Range of 400-600°C are Presented. the Structural Characteristics of the Coatings are Considered.

Mechanical and corrosion performance of multilayer ceramic coatings deposited on an austenitic stainless steel using plasma spray

This research investigated consecutive multilayer thermal barrier coatings, including \(\hbox {Ni}_{3}\hbox {Al}\)–\(\hbox {Al}_{2}\hbox {O}_{3}\)–\(\hbox {Al}_{2}\hbox {O}_{3}/\hbox {MgO}\), produced by plasma spray with outer layer thicknesses of 50, 100 and \(150\,\upmu \hbox {m}\) deposited on an AISI 316 stainless steel. X-ray diffraction, scanning electron microscopy, Rockwell-B hardness measurements, pin-on-disk wear test and potentiodynamic polarization test were performed to evaluate the specimens. The results revealed that the structure of the produced coatings was completely crystalline. An increase in the coating thickness formed a smooth surface and a low degree of roughness and promoted grain growth. According to the Hall–Petch equation, the degree of hardness decreased from 99 to 92 HRB, and the friction coefficient decreased from 1.25 to 0.6 because of low surface roughness. An adherence test performed with a Brinell hardness test showed that an increase in the layer thickness improved the coating adherence coefficient (\(\hbox {d}p/\hbox {d}r\)) from 0.083 to \(0.118\,\hbox {kg}\,\upmu \hbox {m}^{-1}\). The corrosion test results indicated that the increase in the coating thickness caused a decrease in corrosion current density from 1.1 to \(0.008\,\hbox {mA}\, \hbox {cm}^{-2}\).

Ni nanocluster composites for enhanced impact resistance of multilayered arc-PVD ceramic coatings

Optimally, hard protective coatings should effectively absorb impact energy to reduce the likelihood of failure events. In this work, an arc-PVD approach was utilised for the deposition of thick ceramic multilayer AlCrTiN/CrN-based coatings containing a distribution of metallic nickel inclusions throughout sequential CrN-based interlayers. The aim of such coatings is to provide resistance to impact loading in intensive application environments, such as drop forging of steel and turbine blades exposed to abrasive particles. The structure and micro-structural development of the ceramic was first investigated using transmission electron microscopy, where discrete Ni inclusions were observed as both larger discs (d ~ 600–800nm, h ~ 200nm) and smaller (d ~ 50nm) nanoclusters. Confirmation of the distribution and nanocluster chemistry was achieved using atom probe tomography. For mono-block coatings, XRD data showed drastically reduced internal stresses as a result of the Ni inclusions, enabling the creation of thicker protective coatings which minimise substrate stress concentration upon loading. Nickel inclusion additionally provides a softening of the containing hard ceramic layer, allowing for tuning of mechanical properties. Supporting this idea, in situ micropillar compression measurements of the multi-layered coating systems showed that Ni clusters hindered crack propagation through the coating during failure, while the fracture strength could be increased by incorporating both Ti and Ni in the softer CrN-based layer. High-load impact testing highlighted the influence of Ni ‘shock absorbers’ in reducing circumferential cracking, which was further confirmed by an industrial die forging test that demonstrated a 15–22% life-time increase compared to a much thicker hard-chrome plated reference. The results of this study demonstrate an exciting way to produce Ni nanocluster integrated hard ceramic multi-layers using arc-PVD in a single processing step. Such tuneable thin-film composite systems show great promise in minimising damage from impact loading, even under severe working conditions such as in hot forging.

Multilayer (TiN, TiAlN) ceramic coatings for nuclear fuel cladding

In an attempt to develop an accident-tolerant fuel (ATF) that can delay the deleterious consequences of loss-of-coolant-accidents (LOCA), multilayer coatings were deposited onto ZIRLO® coupon substrates by cathodic arc physical vapor deposition (CA-PVD). Coatings were composed of alternating TiN (top) and Ti1-xAlxN (2-layer, 4-layer, 8-layer and 16-layer) layers. The minimum TiN top coating thickness and coating architecture were optimized for good corrosion and oxidation resistance. Corrosion tests were performed in static pure water at 360 °C and 18.7 MPa for up to 90 days. The optimized coatings showed no spallation/delamination and had a maximum of 6 mg/dm2 weight gain, which is 6 times smaller than that of a control sample of uncoated ZIRLO® which showed a weight gain of 40.2 mg/dm2. The optimized architecture features a ∼1 μm TiN top layer to prevent boehmite phase formation during corrosion and a TiN/TiAlN 8-layer architecture which provides the best corrosion performance.

Investigation on the thermal properties of the multilayered ceramic coatings deposited using atmospheric plasma spraying

Atmospheric plasma spraying was employed to deposit Zirconia/Alumina (ZrO2/Al2O3) and Zirconia/Alumina-Titania (ZrO2/Al2O3-TiO2) multilayer coatings with bonding material (Ni-Cr-Al) on the EN31 Mild Steel substrate. The investigation was carried out on multilayer ceramic coated specimen by thermal torch and shock test methods. The coated specimens were prepared as per ASTM standards. Micro structural analysis was carried out using scanning electron microscope to investigate the thermal resistance of the two different multilayer ceramic coatings. The results show that the multi-layered ZrO2/Al2O3 coating possesses improved thermal properties when compared to ZrO2/Al2O3-TiO2 multilayer coating.

Processing and characterization of CYSZ/Al2O3 and CYSZ/Al2O3 + YSZ multilayered thermal barrier coatings

CYSZ/Al2O3 and CYSZ/Al2O3+YSZ multilayer ceramic coatings were produced in 4, 8 and 12 layered with a total thickness of ~400μm by high-velocity oxy-fuel (HVOF) and atmospheric plasma spraying (APS) processes. Microstructure, thermal and mechanical properties were evaluated. The thickness of metallic bonding layer and total thickness of ceramic top layer were measured as 100±10μm and 400±20μm, respectively. Porosity levels of multilayer coatings were observed between 6 and 13%. Thermal conductivity values of the CYSZ/Al2O3 and CYSZ/Al2O3+YSZ coatings were in the range of 0.99 to 1.50W/mK. The bonding strength of as-sprayed coatings was increased from 5.4 to 10.1MPa for CYSZ/Al2O3, and 8.7 to 11.5MPa for CYSZ/Al2O3+YSZ coatings with the increasing number of layers. Existence of phase transformation (γ→α) for Al2O3 coating was observed after the thermal cycle test. The results indicated that the thermal conductivity and thermal cycle strength of CYSZ/Al2O3+YSZ TBCs were higher than CYSZ/Al2O3 based thermal barrier coatings.

Plasma forming multilayer ceramics for ultra-high temperature application

Multilayer ceramic coatings that incorporate mullite, yttria stabilized zirconia (YSZ) and ultra-high temperature zirconium diboride (ZrB2) are suited for thermal protection systems in rocket exhaust cones, insulating tiles for the space shuttle, engine components and ceramic coatings that are embedded into the windshield glass of many airplanes. The coatings were plasma sprayed simultaneously on roughened mild steel cylinder where ZrB2 was firstly deposited followed by mullite and YSZ coatings. A net-shape multilayer ceramic cylinder has been formed by chemical dissolution of the metallic cylinder in acidic medium. The net-shape multilayer ceramics can be simulated with metallic structure and used as a burner for a scramjet engine. The SEM micrographs showed the typical lamellar structure of plasma sprayed coatings. Cracks were evident at the lamella boundaries due to thermal stresses of ZrB2 and YSZ. ANSYS version 12.1 was used to perform the finite element analysis of the TBC. A theoretical modeling for the time to mullite melting at different heat fluxes (1, 1.5, 2, 2.5 W/mm2) was investigated.

Evaluated benchmark experiments at critical assemblies simulating features of an HTHR at the ASTRA facility

The design of the ASTRA facility and critical assemblies that simulate physics features of modular high-temperature reactors (HTHR-Ms) with a graphite moderator and reflectors loaded with fuel particles having multilayer ceramic coatings is described in detail. Geometrical dimensions of the main elements and regions of the critical assemblies, composition of the materials used, and experimental results for various configurations of the critical assemblies are presented. A detailed computational benchmark model allowing for the structural and compositional features of the critical assembly configurations in question is developed on the basis of all the above data. The results are to be used for verification of the neutronics codes used for calculations of high-temperature helium-cooled reactors.

The Investigation of Hot-Dip Aluminum and Micro-Arc Oxidation Multilayer Coating on 080A15 Steel

By the combined process of hot-dip aluminum and micro-arc oxidation, multilayer ceramic coatings were obtained on the surface of commercial 080A15 steel plates. The microstructures and chemical elements of the coatings were investigated by means of scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS), respectively. The results show that the conversion coating on the surface of 080A15 steel plate is mainly composed of three layers, they are the outer layer of alumina ceramic coating, the middle layer of pure aluminum, and the inner layer of FeAl intermetallic compound. The FeAl intermetallic compound layer appears as branch-like to grow into the steel substrate. The alumina ceramic layer is a porous structure attached on the pure aluminum layer. The distribution of composition elements on the interface between the each layer is gradient transition, which is one of metallurgical adhesive characteristics.

Optimizing substrate and intermediate layers geometry to reduce internal thermal stresses and prevent surface crack formation in 2-D multilayered ceramic coatings

In order to avoid the formation of normal cracks in the external layer of multilayered ceramic coatings during cooling, determination of the residual thermal stress field is essential. Concerning the effect of the intermediate layers (transition zone) on a possible reduction of stress in the external layer, it has been shown that in the case of a symmetrical (or constrained in-plane strain) system, reduction only occurs over a critical substrate thickness. In order to investigate the effect of the substrate geometry, the residual thermal stress field has also been determined in other configurations such as an asymmetrical arrangement (one side coating) allowing bending and a concentric-cylinder structure. In these last two configurations, a strong stress reduction is obtained. For practical applications such as gas turbine ceramic components, these results may provide guidelines for an optimum design of the geometry of substrate and intermediate layers of multilayered ceramic coatings.

Finite element analysis on stresses field of normalized layer thickness within ceramic coating on aluminized steel

Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al 2O 3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al 2O 3/Al interface is minimal when Al 2O 3 layer and Al layer have the same thickness.

Heat transfer in boiling of water in a fill of spherical elements

An experimental study has been made of heat exchange in bubble and transient regimes of boiling in spherical-element fills as applied to the cores of nuclear reactors with spherical fuel microelements based on uranium dioxide with multilayer ceramic coatings. Critical dependences describing experimental data and making it possible to calculate the heat-transfer coefficient in such regimes of boiling have been obtained.