Oxidation Resistance Of Coatings Research Articles

A novel plasma-sprayed Cr/FeCrAl dual-layer coating on Zr alloy for potential high‐temperature applications

To better meet the requirements in loss-of-coolant accidents (LOCA) and conventional operating conditions in nuclear applications, this work prepared Cr, FeCrAl, and Cr/FeCrAl composite coatings on Zr alloys using plasma spraying technology. The microstructures, hardness, and high-temperature oxidation resistance of coatings are examined. The high-temperature oxidation of coatings was conducted at 1200 °C in air for 20, 40, and 60 min. All coatings exhibited characteristic lamellar microstructures accompanied by small pores. The inner layers of the coatings, benefiting from the “compacting effect” of subsequently deposited particles, displayed lower porosity and higher hardness. The order of high-temperature oxidation resistance among the coatings was determined as follows: Cr/FeCrAl coating > Cr coating > FeCrAl coating. Notably, the Cr/FeCrAl composite coating demonstrated exceptional durability even after a 60-min exposure, with no ZrO2 formation and negligible Fe and Cr diffusion. However, oxygen could still reach the Zr substrate due to inherent pores and the lamellar structure in the as-sprayed coatings. Therefore, post-treatments are suggested to mitigate or eliminate these pores, thereby improving high-temperature oxidation resistance.

Corrosion resistance characteristics of silicide coating on Nb[sbnd]Si based alloy exposed to CMAS at high temperature

Niobium disilicide shows good oxidation resistance in high-temperature oxidizing atmosphere and can be used as oxidation resistant coatings. However, these coatings are also required to have good environmental resistance, where corrosion by calcium‑magnesium-alumina-silicate (CMAS) represents a potential threat to the coating during the application. The aim of this work is to clarify the interaction between the AlY modified silicide coating on NbSi based alloy and the CMAS. The results indicate that the coating consists mainly of a disilicide layer and a transitional layer. The disilicide layer is mainly composed of (Nb,X)Si2 with (Zr,X′)Si2 particles dispersed in it. During the CMAS exposure, both the silicide coating and the as-formed SiO2-based composite oxide scale can be dissolved by the melted CMAS. The increase of temperature accelerates the CMAS corrosion process. The accumulation of dissolved Si at the interface between the CMAS and coating leads to the in-situ crystallization of Cristobalite-SiO2, which can arrest the melted CMAS, offering a good protection against CMAS attack. The (Nb,X)Si2 coating exhibits a two stage of CMAS corrosion process. The first one is the dissolution of the coating until SiO2 crystallization. The second one is the growth of the Cristobalite-SiO2 layer, during which the coating elements will be oxidized and can then diffuse into the melted CMAS through the Cristobalite-SiO2 layer.

Self-densification behaviors and oxidation resistance properties of a slurry-derived ZrB2-SiC coating with kyanite additive

The great advantages of component designability, operation convenience, and cost reduction make the slurry-sintering method promising for preparing oxidation resistant coatings. However, the porous structure caused by the volatilization of liquid in the slurry and shrinkage of particles in the pressureless sintering limits its practical and wide application. Herein, a dense ZrB2-SiC coating with improved oxidation resistance was fabricated via a slurry-sintering method on C/SiC composites by introducing kyanite into the slurry. The self-densification of the coating is achieved due to the volume expansion of 26.1 % related to the irreversible thermal transformation from kyanite to mullite during sintering. The resultant dense coating with a thickness of 150 μm shows the good interfacial bonding strength of 19.2 MPa and the low weight changes of 1.7 %, −0.6 %, and −1.7 % at 800 °C, 1000 °C, and 1200 °C for 40-h oxidation, respectively.

Structural Сharacteristics, Mechanical Properties, Wear and Oxidation Resistance of Coatings in the Mo–Y–Zr–Si–B System Obtained on Molybdenum by Magnetron Sputtering in the DCMS and HIPIMS Modes

Structural Сharacteristics, Mechanical Properties, Wear and Oxidation Resistance of Coatings in the Mo–Y–Zr–Si–B System Obtained on Molybdenum by Magnetron Sputtering in the DCMS and HIPIMS Modes

Microstructural evolution and high-temperature oxidation resistance of NiCoCrAlYSiHf coatings after surface thermal modification with millisecond laser

NiCoCrAlYSiHf coatings prepared by arc ion plating was thermally modified via millisecond laser technique. The microstructural evolution and oxidation resistance of the coatings before and after laser thermal modification were compared. Laser thermal modification significantly reduces the surface roughness of the coating, modifies the microstructure (introduction of dislocations, nano-particle precipitation), regulates the elemental distribution (Y-Al oxides), and forms ultrafine-grained particles on the surface. The experimental results show that these evolutions provide conditions for the improvement of the oxidation resistance of the coatings. In particular, Y-Al oxides can play an effective pinning role during long-term oxidation. And the ultrafine-grained particles formed on the surface promote the formation of Al2O3 oxide scale. Therefore, laser thermal modification can be an effective processing method to extend the service life of NiCoCrAlYSiHf coatings.

Deposition of oxidation-resistant coatings by vacuum-pulse-arc melting of NiAl-based granules to protect Ni superalloys

Here we report an innovative contactless method for vacuum-pulse-arc melting of single Ni41Al41Cr12Co6Hf0.25 (at.%) granules with a size of 160 ± 20 μm using a non-consumable electrode. A dense, uniform, and oxidation-resistant coating 100 μm thick, formed by a monolayer of molten granules, was obtained on the surface of a Ni-based superalloy fabricated by laser powder bed fusion. A distinctive feature of the proposed technology is the use of high-voltage breakdown to initiate a subsequent relatively low-voltage arc discharge with adjustable duration and energy. The utilization of granules of a certain size and precise control of the discharge energy makes it possible to control the monolayer thickness and the degree of substrate melting. A mechanism is proposed for melting a single granule located on the substrate surface. The resulting coating has a submicron structure consisting of NiAl and Ni3Al intermetallic compounds. The high resistance of the coating to oxidation at 1000 °C is evidenced by the formation of an oxide scale 500 nm thick, consisting of two sublayers: an upper layer about 200 nm thick with relatively large α-Al2O3 grains up to 150 nm in size and a lower layer consisting of a mixture of α-Al2O3 and θ-Al2O3 grains smaller than 40 nm.

Preparation of VZrHfNbTa High-Entropy Alloy-Based High-Temperature Oxidation-Resistant Coating and Its Bonding Mechanism.

Ultra-high Temperature Oxidation-Resistant Alloys (UTORAs) have received a lot of attention due to the increased research demand for deep space exploration around the world. However, UTORAs have the disadvantages of easy oxidation and chalking. So, in this study, a UTORAs is prepared by hot-press sintering on VZrHfNbTa (HEA: High Entropy Alloys can generally be defined as more than five elements by the equal atomic ratio or close to the equal atomic ratio alloying, the mixing entropy is higher than the melting entropy of the alloy, generally forming a high entropy solid solution phase of a class of alloys.) a substrate coated with hafnium. The bonding mechanism, resistance to high-temperature oxidation, and hardness of the sample tests are carried out. The results show that zirconium in the matrix will diffuse into the hafnium coating during the high-temperature sintering process and form the HfZr alloy transition layer, the coating thickness of the composite is about 120 μm, and the diffusion distance of zirconium in the hafnium coating is about 60 μm, this transition layer chemically combines the hafnium coating and the HEA substrate into a monolithic alloy composite. The results of high-temperature oxidation experiments show that the oxidation degree of the hafnium-coated VZrHfNbTa composite material is significantly lower than that of the VZrHfNbTa HEA after oxidation in air at 1600 °C for 5 h. The weight gain of the coated sample after oxidation is 56.56 mg/cm2, which is only 57.7% compared to the weight gain of the uncoated sample (98.09 mg/cm2 for uncoated), and the surface of the uncoated HEA shows obvious dents, oxidation, and pulverization occurred on the surface and interior of the sample. In contrast, the coated composite alloy sample mainly undergoes surface oxidation sintering to form a dense HfO2 protective layer, and the internal oxidation of the hafnium-coated VZrHfNbTa composite alloy is significantly lower than that of the uncoated VZrHfNbTa HEA.

High-temperature oxidation behavior of laser-cladded refractory Al0.75NbNi0.1Mo0.1Cr0.5Si0.1Wx high-entropy coatings

Refractory High Entropy Alloys (RHEAs) have great potential for ultra-high temperature environments and are one of the potential candidates for high temperature applications. In this work, a series of Al0.75NbNi0.1Mo0.1Cr0.5Si0.1Wx (x = 1, 1.5, 2) refractory high-entropy alloy coatings is prepared by laser cladding technology. The microstructure and oxidation behavior at 1000 °C and effect of changing oxidation temperature on oxidation behavior of the coatings is investigated. The results show that Al0.75NbNi0.1Mo0.1Cr0.5Si0.1Wx RHEA coatings are composed of BCC, W5Si3 and AlNi3 phases. The microstructure of RHEA coatings exhibits dendritic-cellular grain transition with increasing W content. The specific mass gains of coatings due to high temperature oxidation is 65.5 mg/cm2 for x = 1, 8.5 mg/cm2 for x = 1.5 and 14.5 mg/cm2 for x = 2 at 1000 °C for 70 h. After oxidation in 1000 °C for 70 h under air atmosphere, a protective oxide film (such as Al2O3 and SiO2) adhere around NiWO4 on the alloy coatings, which impedes the inward oxygen transport. Moderate addition of W elements is found to be beneficial in enhancing the oxidation resistance of coatings. However, excessive addition of W elements prevents the formation of protective oxides (Al2O3 and SiO2) and reduces the high-temperature oxidation resistance of the coatings. With the increase of oxidation temperature, simple oxides are significantly reduced while compound oxides are increased on the surface of the coatings. The surface appears hill-shaped oxides with the increase of NiWO4.

Improved oxidation resistance of Cr-Si coated Zircaloy with an in-situ formed Zr2Si diffusion barrier

In the present study, the dense Cr and Cr0.92Si0.08 coatings have been deposited on Zircaloy-4 substrates by the magnetron sputtering technique. The high-temperature oxidation resistance of coatings is evaluated in 1200 °C steam for 1–4 h. The Cr0.92Si0.08 coating shows better oxidation resistance than the Cr coating. The in-situ formed Zr2Si diffusion barrier inhibits the mutual diffusion of Cr and Zr. And the formation of a Cr2O3/SiO2 double-layer scale effectively improves the oxidation resistance of a single Cr2O3 layer. The formation of the in-situ diffusion barrier, Cr2O3/SiO2 scales and oxidation protection mechanisms of the Cr0.92Si0.08 coating have been discussed in detail.

Electrospark deposition of metalloceramic Fe–Al/HfC coating on steel 1035

To improve the tribotechnical behavior and heat resistance of steel 1035, composite metalloceramic Fe–Al/HfC coatings were prepared by electrospark deposition. A non-localized anode was used as an electrode consisting of a mixture of iron and aluminum granules with a molar ratio of 3:2 and with the addition of HfC powder. The cathode gain had positive values indicating that HfC powder can be deposited on steel 1035 using the Fe60Al40 anode mixture. Moreover, the cathode gain monotonically increased with the increase in addition of HfC powder to the anode mixture. The coatings structure is represented by a matrix of FeAl intermetallic compound reinforced with HfC grains, which corresponds to the structure of a metalloceramic composite. Concentration of HfC in the coating increased with the addition of HfC powder to the anode mixture. Deposition of Fe–Al/HfC coatings according to the proposed technique allows reducing the friction coefficient of steel 1035 from 6 to 40 vol. %. Depending on the concentration of HfC in the anode mixture, the wear resistance of Fe–Al/HfC coatings varied nonmonotonically with a maximum at 8 vol. %. The use of Fe–Al/HfC coatings makes it possible to increase the wear resistance of the steel surface to 10 times. Comparison of the final weight gain of the samples after 100 h of oxidation resistance tests at a temperature of 700 °C allows us to conclude that electrospark deposition Fe–Al/HfC coatings can increase the oxidation resistance of steel 1035 by 1.7–2.2 times. Analysis of the study results shows that adhesion of Fe–Al composition to HfC is weak. This was reflected in decrease in hardness, wear resistance and oxidation resistance of coatings with an increase in the concentration of HfC in the anode mixture above 8 vol. %.

A review on high entropy silicides and silicates: Fundamental aspects, synthesis, properties

AbstractMetal silicides and silicates belong to the silicon‐based non‐oxide and oxide ceramics family with exceptional properties. Silicides face fatal oxidation at low temperatures and intrinsic brittleness, whereas silicates face instability in phase at high temperatures which restricts its usage in vast engineering applications. Hence, the ceramic community introduced the concept of high entropy in metal silicides and silicates. Since 2019, high entropy silicides and silicates, a multicomponent system, have created new avenues for materials discovery and design. High entropy silicides displayed elevated properties than the traditional silicides aiming its applications in microelectronic, high‐temperature oxidation resistance coatings, and structural materials. Similarly, high entropy silicates displayed improved properties than the traditional silicates making them the most promising materials for environmental and thermal barrier coating applications for hot section components in gas turbines. The review focuses on specific case studies to emphasize the latest research and developments in high entropy silicides and silicates. Synthesis approaches employed in developing high entropy silicides and silicates and their structural and microstructural outcomes are addressed. The possible application is predicted based on the overview of the properties explored to date. The review concludes with future possibilities offered by the high entropy silicides and silicates.

One-step multi-compositional oxidation of YSi alloy: Experiments and ab initio computation

YSi alloy is a promising candidate as oxidation resistant coatings for both the bond coat of environmental barrier coatings (EBCs) and anti-ablation coatings at a high temperature of ∼1300 °C. In this study, a one-step multi-compositional oxidation by rapid heating oxidation mode is proposed to reduce the oxidation rate by 3.6 times compared to conventional slow heating oxidation mode. Results show that preferentially formed Y2O3 oxide initiates a multi-step oxidation, produces a cracking and porous oxides, and thereby resulting in a fast oxidation with pesting. The one-step multi-compositional oxidation with a compact and dense Y2Si2O7 scale contributes to the much better oxidation resistance for rapid heating oxidation mode of YSi alloy. The stable formation of Y2Si2O7 scale is comprehensively understood by the energy barrier, charge density and electronic level based on density functional theory. This study demonstrates a promising application of YSi alloy by rapid heating oxidation mode.

High Temperature Resistant Coatings for Strategic Aero space Applications

The aerospace components operating in hot sections of aero-engines and combustors experience extreme environments. Typically, the components are subjected to high service temperatures exceeding 1100°C and oxidizing conditions. Protective coatings are essential for preventing oxidation-induced dimensional degradation of the components and enhancing their high temperature capability as well as durability. Defence Metallurgical Research Laboratory (DMRL) has developed a variety of metallic and ceramic thermal barrier coating (TBC) systems for Ni-base superalloys, and refractory Nb-alloys for strategic aerospace applications involving ultra-high temperatures and high flow velocities. These coatings have demonstrated significant effectiveness against thermal degradation at temperatures as high as 2000 °C during oxidation in static air as well as in dynamic conditions involving high flow velocities (Mach > 2). The present article provides an overview of the advanced oxidation resistant and thermal barrier coatings developed in DMRL. The effectiveness of the TBCs in preventing dimensional degradation of the metallic and composite substrate materials has been evaluated at the laboratory scale. The developed TBCs have the potential for use in aero-engines and propulsion systems of hypervelocity vehicles.

Effects of deposition temperature on the microstructure, mechanical properties, high temperature corrosion and oxidation properties of AlCrNbTiZr high entropy alloy coatings

The AlCrNbTiZr high-entropy alloy (HEA) coatings with different deposition temperatures were prepared on Zr-4 substrate by magnetron sputtering. The effects of the deposition temperature on microstructure, mechanical properties, surface wettability, high temperature corrosion and oxidation resistance of coatings were systematically studied. The results show that the thickness of coating decreases first and then increases with the increase of deposition temperature. The coatings deposited at all temperatures is amorphous with BCC nanocrystalline domains, and the coating surface is hydrophobic. The room temperature (RT) deposition coatings have a high hardness of 25.41GPa, a good adhesion of 50 N and corrosion resistance compared with the coating at other deposition temperatures. The coating at RT deposited still has the ability to protect the substrate Zr-4 after the 1200 °C steam oxidation for 30 min. In addition, the corresponding steam oxidation mechanism is discussed in detail.

Oxidation resistance of TiSiN and AlCrN hard-coatings: Ab initio calculations and experiments

Understanding the oxidation process of hard-coating at the atomic scale is still limited. In this work, the high temperature oxidation behaviors of Ti0.86Si0.14N and Al0.66Cr0.34N coatings have been studied by ab initio molecular dynamics (AIMD) and experimental methods. The average displacement height of metal atoms bonded to O is used to reveal the morphology of oxide layers on the surface. The displacement of bonded metal atoms in ferromagnetic states changed and gradually closed to overlap, demonstrating that it is necessary to consider the magnetic property of Cr in the calculation of AlCrN system. In order to verify the simulation results, the physical vapor deposition (PVD) was used to prepare Ti0.86Si0.14N and Al0.66Cr0.34N hard coatings, and the microstructures of oxide layer at corresponding annealing temperatures are studied. It was found that the oxide layer of Ti0.86Si0.14N coatings gradually changes from a monolayer to a double layer with Ti-rich layer in the outmost as temperature increases. And the oxidation process of Al0.66Cr0.34N coating is controlled by the competition mechanism of Al-O bond and Cr-O bond. The experimental results reproduced the simulatied ones, verifying the feasibility of ab initio molecular dynamics method in quicker predicting the oxidation resistance of coatings.

Study on Microstructure and Oxidation Resistance Mechanism of Y-Modified NiCrAlY Coating Prepared by Pack Cementation

The existence mode of Y is an important factor affecting the oxidation resistance of NiCrAlY coating. The traditional thermal sprayed NiCrAlY coating had some problems such as internal-stress-induced coating peeling, when it was used at high temperature for a long time. In this paper, Y-modified NiCrAlY coatings were prepared on the surface of thermal-sprayed NiCrAlY coatings by halide-activated pack-cementation technology. The microstructure and oxidation resistance of the coatings after thermal insulation at 1100 °C for 100 h were analyzed. The results show that the oxidation resistance of Y-modified NiCrAlY coatings was improved significantly. When the oxidation temperature and time were 1100 °C and 100 h, the oxidation weight gain of thermal sprayed NiCrAl0.5Y and NiCrAl1.0Y coatings was 3.8 and 2.2 times that of Y-modified coatings, respectively. In addition, the NiCrAlY coatings prepared by pack cementation had better oxidation resistance than thermal sprayed coatings when the content of Y was equal. The oxidation resistance of the pack-cemented NiCrAlY coatings were increased with the increase in Y content when it was in a range of 0~1 wt.%. When oxidized at 1100 °C for 100 h, the oxidation weight gain of the pack-cemented NiCrAl0.5Y and NiCrAl1.0Y coatings was about 1.8 and 0.9 mg/cm2, respectively. The formation of highly stable intermetallic compounds Ni5Y in the pack-cemented Y-modified coatings is concluded to be the reason for improving the oxidation resistance of the coatings. This work can provide a solution to improve the oxidation resistance of traditional MCrAlY coatings.

Effect of Voltage on the Microstructure and High-Temperature Oxidation Resistance of Micro-Arc Oxidation Coatings on AlTiCrVZr Refractory High-Entropy Alloy

In order to improve the high-temperature oxidation resistance of refractory high-entropy alloys (RHEAs), we used micro-arc oxidation (MAO) technology to prepare ceramic coatings on AlTiCrVZr alloy, and the effects of voltage on the microstructure and high-temperature oxidation resistance of the coatings were studied. In this paper, the MAO voltage was adjusted to 360 V, 390 V, 420 V, and 450 V. The microstructure, elements distribution, chemical composition, and surface roughness of the coatings were studied by scanning electron microscopy (SEM), energy dispersive (EDS), X-ray photoelectron spectroscopy (XPS), and white-light interferometry. The matrix alloy and MAO-coated samples were oxidized at 800 °C for 5 h and 20 h to study their high-temperature oxidation resistance. The results showed that as the voltage increased, the MAO coating gradually became smooth and dense, the surface roughness decreased, and the coating thickness increased. The substrate elements and solute ions in the electrolyte participated in the coating formation reaction, and the coating composition was dominated by Al2O3, TiO2, Cr2O3, V2O5, ZrO2, and SiO2. Compared with the substrate alloy, the high-temperature oxidation resistance of the MAO-coated samples prepared at different voltages was improved after oxidation at 800 °C, and the coating prepared at 420 V showed the best high-temperature oxidation resistance after oxidation for 20 h. In short, MAO coatings can prevent the diffusion of O elements into the substrate and the volatilization of V2O5, which improves the high-temperature oxidation resistance of AlTiCrVZr RHEAs.

Formation and oxidation resistance of MoSi2 coating for Nb-Si based alloy prepared by slurry sintering method

The high-temperature oxidation resistant MoSi2 intermetallic coatings have been successfully prepared on the Nb-Si based alloy by slurry sintering method. The heating rate before the sintering temperature is reached has an obvious influence on the density and interface structure of the coatings. The coating prepared at a heating rate of 10 °C/min is the densest, with a porosity about 18.4 area%, and has a good adhesion strength of 22.5 MPa. After oxidation at 1250 ℃ for 10 h, the coating exhibits multi-layer structure consisted of an SiO2 scale, an MoSi2 layer, an inner oxidation layer and an (Nb,X)5Si3 transitional layer from the outer to the inner.

Influence of Yttrium Addition on Structure and Properties of MoYSiB Oxidation-Resistant Coatings

Influence of Yttrium Addition on Structure and Properties of MoYSiB Oxidation-Resistant Coatings

Effect of Nb content on microstructure, mechanical property, high-temperature corrosion and oxidation resistance of CrNb coatings for accident tolerant fuel cladding

Five CrNb coatings containing different Nb contents were deposited on zircalloy substrate by magnetron sputtering technology. The effect of Nb content on microstructure, mechanical property, high-temperature corrosion and oxidation resistance of the coatings were investigated systematically. With increasing Nb content, the surface wetting characteristics of the coating changed from hydrophilic to hydrophobic, the wear performance and the nanohardness were enhanced. The Nb addition has little effect on the corrosion resistance of the coatings. The optimal mechanical and high temperature oxidation properties were obtained for the coating with 21at% Nb content.