Oxidation behavior of γ-TiAl based alloy with Al2O3-Y2O3 composite coatings prepared by electrophoretic deposition

Electrophoretic deposition (EPD), a versatile and cost-effective process, was employed to prepare Al₂O₃-Y₂O₃ composite coatings on a γ-TiAl based alloy. SEM observations showed that the composite coatings were compact and consisted of uniform nano-particles. Cyclic oxidation at 1000 °C indicated that the γ-TiAl alloy exhibited a cyclic spallation-oxidation behavior under cyclic oxidation while the Al₂O₃-Y₂O₃ composite coatings improved the oxidation and scale spallation resistance of γ-TiAl alloy significantly due to the suppression of outward diffusion of Ti in the γ-TiAl substrate and the promotion of selective oxidation of Al in the γ-TiAl alloy induced by the composite coating.     

Cyclic oxidation behavior and thermal barrier effect of YSZ-(Al2O3/YAG) double-layer TBCs prepared by the composite sol-gel method

Novel YSZ (6 wt.% yttria partially stabilized zirconia)-(Al₂O₃/YAG) (alumina-yttrium aluminum garnet, Y₃Al₅O₁₂) double-layer ceramic coatings were fabricated using the composite sol-gel and pressure filtration microwave sintering (PFMS) technologies. The thin Al₂O₃/YAG layer had good adherence with substrate and thick YSZ top layer, which presented the structure of micro-sized YAG particles embedded in nano-sized α-Al₂O₃ film. Cyclic oxidation tests at 1000 °C indicated that they possessed superior properties to resist oxidation of alloy and improve the spallation resistance. The thermal insulation capability tests at 1000 °C and 1100 °C indicate that the 250 μm coating had better thermal barrier effect than that of the 150 μm coating at different cooling gas rates. These beneficial effects should be mainly attributed to that, the oxidation rate of thermal grown oxides (TGO) scale is decreased by the “sealing effect” of α-Al₂O₃, the “reactive element effect”, and the reduced thermal stresses by means of nano/micro composite structure. This double-layer coating can be considered as a promising TBC.     

Corrosion and tribocorrosion behaviour of thermally sprayed ceramic coatings on steel

This research aims at investigating the corrosion and tribocorrosion behaviour of thermally sprayed ceramic coatings deposited on steel specimens and exposed to a 3.5% NaCl solution. The coatings have been prepared by plasma spraying Cr₂O₃ and Al₂O₃/13% TiO₂ powders on a Ni/20% Cr bond coating. Combined wear-corrosion conditions have been achieved by sliding an alumina antagonist on the lateral surface of coated steel cylinders, during their exposure to the aggressive solution.Polarization resistance values monitored during 3 days exposures and polarization curves recorded at the end of the immersion period show that both coatings only partially protect steel substrate from corrosion. Sliding conditions (under 2 N load and 20 rpm or 10 N and 100 rpm) induce a limited increase of the substrate corrosion rates, likely as a consequence of an increase in the defect population of the ceramic coatings.On Cr₂O₃-coated specimens, tribocorrosion is more severe at 10 N and 100 rpm, while on Al₂O₃/13% TiO₂-coated specimens, a stronger corrosion attack is achieved at 2 N and 20 rpm. Profilometer analysis and wear track observations by optical and scanning electron microscopes evidence that on both coatings abrasion of the surface asperities produce both a surface polishing effect and, at high loads, the formation of a tribofilm, more continuous on Al₂O₃/13% TiO₂. On this coating the tribofilm reduces the amount of surface defects and limits the corrosion attack to a certain extent.     

Oxidation of Cr2AlC coatings in the temperature range of 1230 to 1410 °C

The isothermal oxidation behavior of Cr₂AlC coatings on alumina substrates was investigated in the temperature range of 1230 to 1410 °C. The structure, surface morphology, microstructure evolution and chemistry of the reaction products have been investigated. In the investigated temperature range, the Cr₂AlC films form a dense continuous oxide scale consisting of α-Al₂O₃ on Cr carbides. The oxidation rates determined by thermo gravimetric analysis (TGA) were parabolic, indicating that diffusion through the scale is the rate limiting mechanism. The activation energy for oxidation was determined to be 348 kJ mol^− 1 and the parabolic rate constant at 1230 °C was 7.1 × 10^− 10 kg² m^− 4 s^− 1. Hence, the oxidation behavior is comparable to NiAl in the temperature range and time intervals investigated. With increasing oxidation time voids form at the interface between oxide and Cr carbides and the amount of Cr₇C₃ increases at the expense of Cr₃C₂. Based on our thermodynamic calculations the oxygen partial pressure below the oxide scale increases as Al is depleted and Cr carbides oxidize, resulting in CO gas- and Cr₂O₃-formation. The formation of gas may together with the depletion of Al and Cr lead to the significant void formation observed in the Cr carbide interlayer. Observation of both Cr carbide precipitates and the formation of (Al,Cr)₂O₃ solid solution support this notion. For comparison bulk Cr₂AlC was oxidized. It is argued that the absence of pores in oxidized bulk Cr₂AlC is due to the considerably larger amount of Al available.     

Oxidation behavior of arc-sprayed FeMnCrAl/Cr3C2-Ni9Al coatings deposited on low-carbon steel substrates

FeMnCr/Cr₃C₂ and FeMnCrAl/Cr₃C₂ coatings, using Ni9Al arc-sprayed coating as an interlayer on low-carbon steel substrates, were deposited by high velocity arc spraying (HVAS) on the cored wires. The high temperature oxidation behavior of the arc-sprayed FeMnCrAl/Cr₃C₂-Ni9Al and FeMnCr/Cr₃C₂ coatings on the low-carbon steel substrates was studied during isothermal exposures to air at 800 °C. The surface and interface morphologies of the coatings after isothermal oxidation after 100 h were observed and characterized by optical microscopy, field emission scanning electron microscope, energy dispersion spectrum, and X-ray diffraction. The results showed that the oxidation weight gains of the coatings were significantly lower than that of the low-carbon steel substrate. Moreover, the FeMnCrAl/Cr₃C₂-Ni9Al coating registered the lowest oxidation rate. This favorable oxidation resistance is due to the Al and Cr contents of the aforementioned coating that inhibits the generation of Fe and Mn oxides. This is attributed to the interdiffusion between the substrates and the Ni9Al arc-sprayed coating, which can convert the mechanical bonding between substrates and coatings into a metallurgical one, thereby inhibiting the oxidation of interface between the low-carbon steel and the coating.     

A new TiB2 + CrSi2 composite – Densification,characterization and oxidation studies

A new composite of TiB₂ with CrSi₂ has been prepared with excellent oxidation resistance. Dense composite pellets were fabricated by hot pressing of powder mixtures. Microstructural characterization was carried out by XRD and SEM with EDAX. Mechanical and physical properties were evaluated. Extensive oxidation studies were also carried out. A near theoretical density (99.9% TD) was obtained with a small addition of 2.5 wt.% CrSi₂ by hot pressing at 1700 °C under a pressure of 28 MPa for 1 h. The microstructure of the composite revealed three distinct phases, (a) dark grey matrix of TiB₂, (b) black phase – rich in Si and (c) white phase – Cr laden TiB₂. Hardness and fracture toughness were measured as 29 ± 2 GPa and 5.97 ± 0.61 MPa m^1/2, respectively. Crack branching, deflection and bridging mechanisms were responsible for the higher fracture toughness. With increase in CrSi₂ content, density, hardness and fracture toughness values of the composite decreased. Thermo gravimetric studies revealed the start of oxidation of the composite at 600 °C in O₂ atmosphere. Isothermal oxidation of these composites showed better oxidation resistance by formation of a protective oxide layer. TiO₂, Cr₂O₃ and SiO₂ phases were identified on the oxidized surface. Effects of CrSi₂ content, temperature and duration of oxidation on the oxide layer formation are reported. Activation energy of the composite was calculated as ∼110 kJ/mol using Arrhenius equation. Diffusion controlled mechanism of oxidation was observed in all the composites.     

High rate deposition of thick CrN and Cr2N coatings using modulated pulse power (MPP) magnetron sputtering

As a variation of high power pulsed magnetron sputtering technique, modulated pulse power (MPP) magnetron sputtering can achieve a high deposition rate while at the same time achieving a high degree of ionization of the sputtered material with low ion energies. These advantages of the MPP technique can be utilized to obtain dense coatings with a small incorporation of the residual stress and defect density for the thick coating growth. In this study, the MPP technique has been utilized to reactively deposit thick Cr₂N and CrN coatings (up to 55 μm) on AISI 440C steel and cemented carbide substrates in a closed field unbalanced magnetron sputtering system. High deposition rates of 15 and 10 μm per hour have been measured for the Cr₂N and CrN coating depositions, respectively, using a 3 kW average target power (16.7 W/cm² average target power density), a 50 mm substrate to target distance and an Ar/N₂ gas flow ratio of 3:1 and 1:1. The CrN coatings showed a denser microstructure than the Cr₂N coatings, whereas the Cr₂N coatings exhibited a smaller grain size and surface roughness than those of the CrN coatings for the same coating thickness. The compressive residual stresses in the CrN and Cr₂N coatings increased as the coating thickness increased to 30 μm and 20 μm, respectively, but for thicker coatings, the stress gradually decreased as the coating thickness increased. The CrN coatings exhibited an increase in the scratch test critical load as the thickness was increased. Both CrN and Cr₂N coatings showed a decrease in the hardness and an increase in the sliding coefficient of friction as the coating thickness increased from 2.5 to 55 μm. However, the wear rate of the CrN coatings decreased significantly as the coating thickness was increased to 10 μm or higher. The 10-55 μm CrN coating exhibited low wear rates in the range of 3.5-5 × 10⁻⁷ mm³ N⁻¹ m⁻¹. To the contrary, the Cr₂N coating exhibited relatively low wear resistance in that high wear rates in the range of 3.5 to 7.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹ were observed for different thicknesses.     

Oxidation resistance of TiAl3-Al composite coating on orthorhombic Ti2AlNb based alloy

The TiAl₃-Al composite coating on orthorhombic Ti₂AlNb based alloy was prepared by cold spray. Oxidation in air at 950 °C indicated that the bare alloy exhibited poor oxidation resistance due to the formation of TiO₂/AlNbO₄ mixture and intended to scale off at the TiO₂ rich zone. A nitride layer about 2 µm was formed under the oxide layer. The oxygen invaded deeply into the alloy and caused severe microhardness enhancement in the near surface region. The TiAl₃-Al composite coating exhibited parabolic oxidation kinetics and showed no sign of degradation after oxidized up to 1098 h at 950 °C in air under quasi-isothermal condition. No scaling of the coating was observed after oxidized at 950 °C up to the tested 150 cycles. The major oxide in the oxidized coating was Al₂O₃. The AlTi₂N, TiAl and small amount of TiO₂ were also observed in the oxidized coating. The EPMA and microhardness tests showed that inward oxygen diffusion was prevented by the interlayer, which was formed between the composite coating and the substrate during heat-treatment. Microstructure analyses demonstrated that the interlayer play a major role in protecting the substrate alloy from high temperature oxidation and interstitial embrittlement.     

Al2O3-nanodiamond composite coatings with high durability and hydrophobicity prepared by aerosol deposition

We attempted the room-temperature fabrication of Al₂O₃-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al₂O₃ powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al₂O₃ to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al₂O₃ powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al₂O₃-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al₂O₃-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al₂O₃-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al₂O₃-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates.     

Korrosionsbeständigkeit von plasmagespritzten Aluminiumoxid- und Chromoxidüberzügen. Wirkung von NiCr und NiAl als Haftgrund

Corrosion resistance of plasma sprayed aluminia and chromia coatings. Effect of coating sublayers NiCr and NiAl The corrosion resistance of plasma sprayed Al₂O₃ and Cr₂O₃ coatings has been studied in 3.5% NaCl and 10% NaOH solutions. In this context the effect of intermediate coatings (NiCr and NiAl) on the protective efficiency of the ceramic coatings has been evaluated, too. The corrosion rates were determined by gravimetry, corrosion potential and polarisation resistance measurements. The two ceramic coatings afford efficient protection. In the alkaline solutions NiCr is superior, while in the chloride solution NiAl offers better protection.     

Proposal of self-healing coatings for nuclear fusion applications

Avoiding cracks in ceramic coatings is one of the most important problems to be solved for the thermally sprayed tritium permeation barriers in fusion reactor. In this paper, a self-healing composite coating composed of TiC + mixture (TiC/Al₂O₃) + Al₂O₃ was developed to address this problem. The coating was deposited on certain martensitic steel by plasma spraying. The morphology and phase of the coating were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD) while the porosity was analyzed by using Image Pro software. The thermal shock resistance test and residual stress measurement of the coating were also performed. In the experiment, NiAl + TiC + mixture (TiC/Al₂O₃) + Al₂O₃ and mixture (TiC/Al₂O₃) + Al₂O₃ films were also fabricated and studied respectively. The results showed that the TiC + mixture (TiC/Al₂O₃) + Al₂O₃ coating exhibited the best mechanical integrity and self-healing ability among the three samples with the porosity decreased by 90% after heat-treatment under normal atmosphere. The oxidation/expansion of TiC in the coating played an important role in the sealing of pores. This self-healing coating made by thermal spraying is proposed as a good candidate for tritium permeation barrier in fusion reactors.     

Oxidation behaviour of Ti-46.7Al-1.9W-0.5Si in air and Ar-20%O2 between 750 and 950 °C

The oxidation behaviour of an intermetallic alloy, Ti-46.7Al-1.9W-0.5Si, was studied in air and Ar-20%O₂ atmospheres at 750, 850 and 950 °C. Oxidation of the alloy followed a parabolic rate law at low temperature (750 °C) in both environments. The alloy oxidised parabolically in air and at a slower rate in Ar-20%O₂ at 850 °C. Following a parabolic oxidation for a relatively short exposure period (72 h) at 950 °C, the oxidation rate was reduced after prolonged exposure (up to 240 h) in air. The alloy oxidised in a slower manner in the Ar-20%O₂ atmosphere at 950 °C. Higher oxidation rates were observed in air than in Ar-20%O₂ at all three experimental temperatures. Multi-layered scales developed in both environments. The scale formed in air consisted of TiO₂/Al₂O₃/TiO₂/TiN/TiAl₂ layers, ranging from the surface to the substrate—whilst the scale developed in the Ar-20%O₂ atmosphere comprised of the sequence TiO₂/Al₂O₃/TiO₂/Al₂O₃/Ti₃Al/substrate. The two layers of Al₂O₃ in Ar-20%O₂ were more effective in providing protection of the substrate against high temperature corrosion than the single layer of Al₂O₃ formed in air.     

Corrosion behavior of electroless Ni-P alloy coatings containing tungsten or nano-scattered alumina composite in 3.5% NaCl solution

The corrosion protection performance of electroless deposited nickel-phosphorus (Ni-P) alloy coatings containing tungsten (Ni-P-W) or nano-scattered alumina (Ni-P-Al₂O₃) composite coatings on low carbon steel was studied. The effect of heat treatment on the coating performance was also studied. The optimum conditions under which such coatings can provide good corrosion protection to the substrate were determined after two weeks of immersion in 3.5% NaCl solution. Electrochemical impedance spectroscopy (EIS) and polarization measurements have been used to evaluate the coating performance before and after heat treatment. The Ni-P-W coatings showed the highest surface resistance compared with Ni-P-Al₂O₃ and Ni-P. The surface resistance of Ni-P-W coatings was 12.0 × 10⁴ Ω cm² which is about the double of the resistance showed by Ni-P-Al₂O₃ (7.00 × 10⁴ Ω cm²) and twenty times greater than the surface resistance of Ni-P (0.78 × 10⁴ Ω cm²). XRD analysis of non-heat-treated samples revealed formation of a protective tungsten phosphide phase. Heat treatment has an adverse effect on the corrosion protection performance of tungsten and alumina composite coatings. The surface resistance decreased sharply after heat treatment.     

Residual stresses in HVOF-sprayed ceramic coatings

In this paper, the residual stress state of thermally sprayed ceramic coatings was examined by combining different experimental and analytical techniques, in order to provide a thorough characterisation of through-thickness stress profiles and a cross-verification of results. HVOF-sprayed ceramics, manufactured using commercial and nanostructured Al₂O₃ powders and commercial Cr₂O₃ powders, and atmospheric plasma-sprayed (APS) ceramics, manufactured using commercial Al₂O₃ and Cr₂O₃ powders, were investigated.The near-surface stress was measured by X-ray diffraction. The through-thickness profile and the intrinsic quenching stress were analytically computed by the Tsui-Clyne iterative model, using the X-ray measurement result as input, and results were validated by the substrate chemical removal method. Further verification was achieved by applying the in-situ curvature technique to the deposition of HVOF-sprayed Al₂O₃ coating.HVOF-sprayed Al₂O₃ coatings deposited using both conventional and nanostructured powders feature a similar, almost equibiaxial tensile stress on the top surface (116.5 MPa and 136.5 MPa, respectively) and a moderate through-thickness gradient (about 12 MPa and 20 MPa, respectively). Their intrinsic quenching stresses were analytically estimated to be 184 MPa and 205 MPa, respectively. APS Al₂O₃ possesses higher top surface stress (220 MPa) and quenching stress (311 MPa). However, it shows a less pronounced stress gradient (≈ 3 MPa) than HVOF-sprayed Al₂O₃-based coatings, because cracks, pores and weak lamella boundaries in the APS coating can accommodate the deformations induced by the bending moments arising both during coating deposition and during cooling.The model-derived quenching stress of the conventional HVOF Al₂O₃ coating was validated by the in-situ curvature measurement technique.Cr₂O₃-based coatings are significantly different. They display a lower residual stress in the near-surface region: 20 MPa in the APS coating, 27.5 MPa in the HVOF one. The HVOF coating also exhibits a very large stress gradient of ≈ 77 MPa. Machining and sliding processes (like polishing and dry sliding tribological testing) change their surface residual stresses to compressive ones.     

Phase constituents and microstructure of laser cladding Al2O3/Ti3Al reinforced ceramic layer on titanium alloy

Laser cladding of the Fe₃Al + TiB₂/Al₂O₃ pre-placed alloy powder on Ti-6Al-4V alloy can form the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer, which can greatly increase wear resistance of titanium alloy. In this study, the Ti₃Al/Fe₃Al + TiB₂/Al₂O₃ ceramic layer has been researched by means of electron probe, X-ray diffraction, scanning electron microscope and micro-analyzer. In cladding process, Al₂O₃ can react with TiB₂ leading to formation of amount of Ti₃Al and B. This principle can be used to improve the Fe₃Al + TiB₂ laser cladded coating, it was found that with addition of Al₂O₃, the microstructure performance and micro-hardness of the coating was obviously improved due to the action of the Al-Ti-B system and hard phases.     

Effect of applied current on the electrodeposited Ni-Al2O3 composite coatings

Nano-sized Al₂O₃ ceramic particles (50 nm) were co-deposited with nickel using electrodeposition technique to develop composite coatings. The coatings were produced in an aqueous nickel bath at different current densities and the research investigated the effect of applied current on microstructure and thickness of the coatings. The variation in some mechanical properties such as hardness, wear resistance, and the adhesive strength of the composite coatings is influenced by the applied current and this was also studied. The morphology of the coatings was characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The hardness, wear resistance, and bond strength of the coatings were evaluated by Vickers micro-hardness test, pin-on-disc test, and tensile test, respectively. Results showed that the Al₂O₃ particles were uniformly distributed in the coatings, and the coatings deposited at a current density of 0.01 A/cm² was most favorable in achieving a maximum current efficiency which causes the co-deposition of a maximum amount of Al₂O₃ particles (4.3 wt.%) in the coatings. The increase in Al₂O₃ particles in the coatings increased the mechanical properties of the Ni-Al₂O₃ composite coatings by grain refining and dispersion strengthening mechanisms.     

Effect of yttrium on the stability of aluminide-yttrium composite coatings in a cyclic high-temperature hot-corrosion environment

A composite coating of aluminide-yttrium has shown excellent corrosion resistance in a cyclic high-temperature hot-corrosion environment. To understand the effect of yttrium on the stability of the composite coating, the specimens were prepared with various coating parameters of Y thickness, sequence of post heat treatment and surface condition before Y-ion plating. Performance of the composite coating was evaluated by isothermal oxidation and cyclic high-temperature hot corrosion. Isothermal-oxidation-test results show that the Y in the composite coating helps to form a thick and dense Al₂O₃ scale which is ductile and resistant to thermal stress. The Y in Al₂O₃ may act as a donor which leads to an increase in concentration of interstitial oxygen and, thus, increases in oxidation rate. The presence of Y₂O₃ and (Y, Al) O-type compounds in grain boundaries of Al₂O₃ and boundaries between the Al₂O₃ and NiAl effectively prohibits the fast diffusion of oxidants (such as O and S) and Al along grain boundaries. Consequently, it may induce slow diffusion through the matrix, and thus the corrosion resistance of the composite coating under cyclic hot corrosion increases substantially.     

Intermediate temperature tribological behavior of carbon nanotube reinforced plasma sprayed aluminum oxide coating

Tribological behavior of plasma sprayed carbon nanotube (CNT) reinforced aluminum oxide (Al₂O₃) composite coatings was examined at room temperature, 573 K and 873 K using tungsten carbide (WC) ball-on-disk tribometer. The weight loss due to wear of Al₂O₃ coating was found to be increasing with the temperature while Al₂O₃-CNT coating showed a decreasing trend in the weight loss with the temperature. Relative improvement in the wear resistance of Al₂O₃-CNT coating compared to Al₂O₃ coating was found to be 12% at room temperature which gradually increased to ∼ 56% at 573 K and ∼ 82% at 873 K. Protective layer as a result of tribo-chemical reaction was observed on the wear track of both of the coatings. The improvement in the wear resistance of Al₂O₃-CNT coating was attributed to three phenomena viz. (i) higher hardness at the elevated temperature as compared to Al₂O₃ coating, (ii) larger area coverage by protective film on the wear surface at the elevated temperature and (iii) CNT bridging between splats. The coefficient of friction (COF) of Al₂O₃ coating was nearly constant at room and elevated temperature whereas COF for Al₂O₃-CNT coating decreased at the elevated temperature (873 K).     

Phase segregation and its effect on the adhesion of Cr-Al-N coatings on K38G alloy prepared by magnetron sputtering method

Cr_1 − xAl_xN (0 < x < 1) coatings were fabricated by a reactive magnetron sputtering method on a K38G alloy. The composition and microstructure of the coatings were investigated. Phase segregation of cubic AlN was considered in Cr_0.65Al_0.35N using X-ray diffraction analyses. This segregation of cubic AlN from CrAlN matrix might be induced by the high micro-stress. The critical failure load determined by scratch tests of the coating with c-AlN segregation was highest among all the coatings studied in the present work, which indicated that the coating has the best adhesion.     

Deposition, characterization and performance evaluation of ceramic coatings on metallic substrates for supercritical water-cooled reactors

A series of ceramic coatings have been prepared on P91 substrates by spray pyrolysis processes and on Zr-2.5Nb substrates by a plasma electrolytic oxidation process. Preliminary results show that coatings obtained with different solution compositions and procedures can reduce the oxidation weight gain of P91 samples by factors of 2-10 for exposure times up to 500 h in deaerated supercritical water at 500 °C and 25 MPa. Results also show that the weight gain of a P91 sample with an alumina (Al₂O₃) coating is about nine times less than that of uncoated P91 after exposures for 400 h in deaerated supercritical water at 650 °C and 25 MPa. These results indicate that the Al₂O₃ coating shows promising results for preventing oxidation of P91 under supercritical water conditions. The samples with ceramic coatings on Zr-2.5Nb substrates show marginally improved corrosion resistance compared to the bare substrates.