Steam Oxidation Resistance Research Articles

Experimental study on steam oxidation resistance at 600 °C of Inconel 625 coatings deposited by HVOF and laser cladding

Inconel 625 (IN625) coatings were deposited by High-Velocity Oxy-fuel (HVOF) and laser cladding, on a 10.50–12%Cr steel to improve its oxidation resistance. Both as-deposited coatings exhibited a γ-Ni-Cr matrix and two protective oxides (Cr2O3 and NiCr2O4). In addition, laser cladding as-deposited coatings also presented precipitates A2B-type Laves phases due to the dilution effect from laser cladding technique. Coated and uncoated steel were oxidized under isothermal conditions at 600 °C for 2000 h and subsequently analyzed using gravimetry, SEM-EDS and XRD techniques. The application of IN625 coatings revealed a weight gain ten times lower than that registered for the uncoated steel, this improvement being mainly due to the presence of protective and stable Cr2O3 and NiCr2O4 oxides. Additionally, the XRD analysis showed that the initial Laves phases present in the laser cladding coating, were re-dissolved and transformed in δ-Ni3Nb compound suggesting that that the temperature and exposure time are enough to induce this transformation.

Improvement of steam oxidation resistance of the γ-TiAl alloy with microarc oxidation coatings at 900–1200 ℃

A dense ceramic coating of ∼30 µm on the γ-TiAl alloy was fabricated using the microarc oxidation (MAO) technique. The coated alloy was oxidized under 900–1200 ℃ steam environments for 3600 s. The oxidation rate for the MAO-coated TiAl alloy is significantly lower than the pristine TiAl alloy. The MAO coating remains intact through the oxidation tests, while the layered structures are formed beneath the MAO coating, which are characterized in detail with X-ray diffraction, scanning and transmission electron microscopy. The improvement of steam oxidation resistance is attributed to the barrier effect of the MAO coating.

Effect of N content on microstructure and properties of (AlTiCrNiTa)N coatings for accident-tolerant fuels

The (AlTiCrNiTa)N coatings were successfully deposited on Zr-4 substrates by magnetron sputtering technology as a function of N2/Ar gas pressure ratio Γ. The microstructure, wettability properties, mechanical properties, corrosion properties and high-temperature steam oxidation resistance of the coatings were investigated. With the decrease of Γ, N content and the thickness of the coating decreased. All coatings show a simple NaCl-type face-centered cubic (FCC) structure, exhibit hydrophobic surface and own high hardness. When Γ is 1/8, the (AlTiCrNiTa)N coating had excellent corrosion properties and high-temperature steam oxidation properties.

Active Crack Obstruction Mechanisms in Crofer® 22H at 650 °C.

Increased cyclic loading of components and materials in future thermal energy conversion systems necessitates novel materials of increased fatigue resistance. The widely used 9–12% Cr steels were developed for high creep strength and thus base load application at temperatures below 620 °C. At higher temperature, these materials present unstable grain structure, prone to polygonization under thermomechanical fatigue loading and limited resistance to steam oxidation. This seminal study compares thermomechanical fatigue resistance and long crack propagation of the advanced ferritic-martensitic steel grade 92 and Crofer® 22H, a fully ferritic, high chromium (22 wt. %) stainless steel, strengthened by Laves phase precipitation. Crofer® 22H features increased resistance to fatigue and steam oxidation resistance up to 650 °C. Both thermomechanical fatigue (crack initiation) and residual (crack propagation) lifetime of Crofer® 22H exceeded that of grade 92. The main mechanisms for improved performance of Crofer® 22H were increased stability of grain structure and “dynamic precipitation strengthening” (DPS). DPS, i.e., thermomechanically triggered precipitation of Laves phase particles and crack deflection at Laves phase-covered sub-grain boundaries, formed in front of crack tips, actively obstructed crack propagation in Crofer® 22H. In addition, it is hypothesized that local strengthening may occur near the crack tip because of grain refinement, which in turn may be impacted by testing frequency.

Impact of Processing on the Creep Properties of High Performance Ferritic (HiperFer) Steels

High performance ferritic (HiperFer) stainless steels constitute a new class of low-cost, heat resistant, hardenable materials which combine high creep and fatigue strength with increased steam oxidation and wet corrosion resistance. The fundamental relationships regarding the alloy composition, microstructure, and resulting mechanical properties are largely known and already published, while relevant commercialization issues, such as the effect of processing on the microstructure, have not yet been addressed. The current paper outlines the impact of the forming parameters on the resulting microstructure and the achievable creep properties. Thermomechanical treatment is demonstrated as an effective method for increasing the creep strength for a given chemical composition. This may constitute a key enabler for cost savings in component production, e.g., for the simple machining of “drop-in” turbine blades or bolts from forged bar stock material.

Long‐term high‐temperature steam oxidation behavior of Cr‐coated Zircaloy‐4 alloy for accident tolerant fuel

AbstractThe Cr‐coated Zircaloy‐4 samples were prepared by arc ion plating to enhance the high‐temperature oxidation resistance of Zircaloy‐4 alloys for accident tolerant fuel claddings. The oxidation tests of the Cr coating were performed under 1473 K steam for 60, 120, and 240 min. The steam oxidation tests indicated that the Cr‐coated Zircaloy‐4 substrate had excellent high‐temperature steam oxidation resistance to protect the fuel cladding from damage for at least 240 min. The weight gains and the thickness of the oxidation scale of the samples were measured to evaluate the oxidation kinetics of the Cr coating in 1473 K steam. In addition, the diffusion and interfacial evolution were analyzed during the oxidation process, and the steam oxidation behaviors of the Cr coatings were also discussed in detail.

Oxidation behavior and Cr-Zr diffusion of Cr coatings prepared by atmospheric plasma spraying on zircaloy-4 cladding in steam at 1300 °C

To improve the high-temperature steam oxidation resistance of zircaloy-4 substrate, thick Cr coatings were successfully prepared on zircaloy-4 via atmospheric plasma spraying. The microstructure and oxidation behavior of Cr coatings on the zircaloy-4 in steam at 1300 °C were studied systematically. The Cr coatings showed improved steam oxidation over zircaloy up to 1300 °C. The microstructure evolution, Cr-Zr diffusion, and bubble formation were analyzed and discussed. Leaf-like Cr2O3 whiskers were formed on the surfaces of the Cr coatings. Zr-rich channels in the Cr coatings near the Cr-Zr interface can provide a diffusion path for oxygen to reach the zircaloy.

Effect of HfO2 framework on steam oxidation behavior of HfO2 doped Si coating at high temperatures

HfO2 doped Si is designed as bond coat material in thermal/environmental barrier coatings (TEBCs). In this work, the HfO2-Si composite coatings with different HfO2 contents were prepared by atmospheric plasma spraying (APS). The steam oxidation behavior of the coatings was comparatively studied at 1300 °C and 1400 °C. Volatilization of Si occurred during spraying, leading to the deviation of coating compositions. The sprayed coatings contained different HfO2 structures. During steam oxidation, HfSiO4 phase was formed at the SiO2/HfO2 interface by solid-state reaction between them. The HfSiO4 or HfO2/HfSiO4 mixture particles worked to deflect or pin micro-cracks, thus improving the resistance of the coating to cracking. At 1300 °C, a protective oxide scale was formed on the traditional Si coating or the HfO2-Si coating with isolated HfO2 particles. However, the HfO2-Si coating with inter-connected HfO2 framework revealed poor oxidation-resistance. At 1400 °C, accelerated oxidation degradation, steam corrosion volatilization, interface reaction and sintering occurred. The HfO2 framework structure played a dominating role in determining the steam oxidation resistance of the HfO2-Si coating, and the connected HfO2 framework and TGO network provided a rapid diffusion path for oxidants (H2O, O2− and OH−) and deteriorated the oxidation resistance.

Use of THOR®115 in design of new generation combined cycle power plant

ABSTRACT Today’s deregulated and continuously changing energy market sees a steady increase of the renewables’ share. This poses several concomitant challenges to the operation of combined cycle power plants, among which the demand of high efficiency through a large load range: Conventional power plants increasingly act as dispatchable sources of electricity and are required to quickly ramp up or down their output based on the demand of electricity. This trend imposes new demands to the material industries. Under fast and frequent cycling operation ferritic steels are favoured thanks to their limited thermal expansion compared to austenitic stainless steel. Highly employed steel grades such as the 9% Cr CSEF steels are however limited in terms of service temperature, mainly due to capping their steam oxidation resistance capabilities at temperature levels required by the drive for efficiency increase. A new generation of CSEF has been developed with increased oxidation resistance and long-term stability: one of these new grades, THOR®115, has started to be used for industrial applications.

Characterisation of the austenitic steels Super 304H and HR3C after air and steam oxidation

ABSTRACT This work aimed to evaluate the effect of a long-term pre-oxidation process in the air (5000 hours at 650 °C) on the steam oxidation resistance of Cr-rich steels with around 18 wt.% Cr (Super 304H) and around 25 wt.% Cr (HR3C) content exposed for the additional 5000 hours at 650 °C. The effect showed a high impact of a long-term pre-oxidation process and a high content of Cr in the metal matrix of the exposed steels. The steel with a lower Cr content showed spallation of the oxide scale under the oxidation process in the air, and only the steel with 25 wt.% Cr showed no spallation of the oxide scale in both conditions: air and steam. The post-exposure analysis in this work was carried out using Scanning Electron Microscopy (SEM) supported by Energy Dispersive X-ray Spectroscopy (EDS) using an X-Ray mapping function. Phase analysis was performed using an XRD diffractometer.

Construction of chromium coatings with (200) preferred orientation and exploration the high-temperature steam oxidation properties

In order to improve the high-temperature steam oxidation resistance of Zircaloy-4 for accident tolerant fuel claddings (ATF), Cr coatings with (200) preferred orientation were deposited by changing argon flow using closed field unbalanced magnetron sputtering. The influences of the argon flow on the microstructure and high-temperature steam oxidation properties of Cr coatings were studied systematically. The results indicate that Cr coatings exhibit obvious preferred orientation of Cr (200) especially for 30sccm argon flow due to more adatom easy aggregation on Cr (200) plane under more ion collisions. With the argon flow increases, the grains of Cr coatings gradually becomes compact and homogeneous, which causes the formation of thicker Cr2O3 oxide layer and residual Cr layer on Cr coatings surface after 1200 °C high-temperature steam oxidation test at 8h. Above all, Cr coatings prepared by 30sccm argon flow still possess excellent steam oxidation resistance properties even after 12h exposure time. In addition, the high-temperature steam oxidation mechanism of 30sccm argon flow Cr coatings under different exposure time also was discussed in detail. The study about Cr (200) preferred orientation is expected to provide a new research idea for prolonging steam oxidation resistance and accident tolerant time.

Microstructure and multifunctionality of a 10-μm-thick dense yet smooth Cr(C) coating prepared by low-temperature magnetron sputtering

Achieving multifunctional coatings is generally difficult in single layers because the structural features required for each function are hard to consolidate. Here we report a magnetron sputtered 10-μm-thick coating consisting of a single phase of supersaturated Cr(C) solid solution (~11 at.% C). It is characteristic of a smooth surface, a high compactness, and a fibrous growth structure. The coating displays a combination of high optical reflectance, high hardness, and excellent protection for Zr alloys to high-temperature steam oxidation resistance at 1473 K. These findings open new perspectives for injecting new functions into magnetron sputtered single-layer coatings.

Improvement of Steam Oxidation Resistance of the Γ-Tial Alloy with Microarc Oxidation Coatings at 900 - 1200°C

Improvement of Steam Oxidation Resistance of the Γ-Tial Alloy with Microarc Oxidation Coatings at 900 - 1200°C

Thermogravimetric analysis-mass spectrometry study of steam oxidation resistance of HCM12A steel at 650°C and 700°C

ABSTRACT Ferritic/martensitic HCM12A steel specimens were subjected to 190 h of oxidation in Ar + 40% H2O at 650°C and 700°C. Simultaneous measurements of mass spectrometry and thermogravimetric analysis by a mass spectrometer and a thermobalance of symmetrical furnaces were made. Thermogravimetric measurements verified that the mass gain after oxidation at 650°C was 0.07 mg/cm2, whereas at 700°C the mass gain corresponded to ∼1.3 times that at 650°C. Mass spectrometry measurements indicated the presence of only a volatile species of low-intensity chromium (order of ppm) at 700°C (i.e. CrO2(g)) after between 175 and 190 h of oxidation. At reduced oxidation times, no volatile species were observed. We did not observe any gaseous species at 650°C. The morphology, composition, and structure of samples by scanning electron microscopy, backscattered electron detection, X-ray energy-dispersive spectrometry and X-ray diffraction are described.

Strength and rupture geometry of un-irradiated C26M FeCrAl under LOCA burst testing conditions

Ferritic iron-chromium-aluminum (FeCrAl) alloys are an accident tolerant fuel candidate to replace the incumbent Zr-based claddings. Nuclear grade FeCrAl alloys are marked by superior high temperature mechanical behavior and exceptional steam oxidation resistance , both of which increase safety margins during accident scenarios. In the present study, the loss of coolant accident (LOCA) burst behaviors of three un-irradiated commercially fabricated cladding materials in a simulated LOCA environment were compared: (1) T35Y2, a 1 st generation nuclear grade FeCrAl, (2) C26M, a 2 nd generation nuclear grade FeCrAl, and (3) Zircaloy-2. Both FeCrAl alloys showed improved mechanical strength and steam oxidation resistance compared to Zircaloy-2. C26M claddings burst at significantly higher temperatures for all tested engineering hoop stresses , had limited ballooning, and demonstrated preferential fuel retention behavior in terms of burst opening area and length. High temperature tensile data for C26M is also presented. For both un-irradiated FeCrAl alloys, it was found that a distinct “threshold” burst stress signified the transition between small and large openings. Higher threshold hoop stresses were associated with higher uniaxial strength for the FeCrAl alloys, indicating that tensile data, rather than creep data, could be useful for predicting rupture size and assessing fuel dispersal concerns.

Development of low-Cr wrought FeCrAl cladding alloys and its irradiation tolerance and steam oxidation resistance at 1200 °C

FeCrAl alloy with a low-Cr content (10%) and higher amount of Al (5%) was developed. The effects of Cr content on the mechanical properties, irradiation tolerance and the steam oxidation resistance of FeCrAl alloy were systematically investigated. The low-Cr FeCrAl alloys exhibit much better steam oxidation resistance at 1200 °C and improved radiation resistance, while maintaining comparable mechanical properties to the FeCrAl alloy with 13Cr. Stable and protective alumina scale was formed in the surface of the low-Cr alloy after the 1200 °C steam oxidation, which is different from the FeCr2O4 and Al2O3 in the surface of 13Cr alloy.

Microstructure, high-temperature corrosion and steam oxidation properties of Cr/CrN multilayer coatings prepared by magnetron sputtering

(Cr/CrN)n multilayer coatings were prepared on Zr-4 alloy using magnetron sputtering and effects of this multilayer architecture on the microstructure, mechanical properties, surface wettability, high-temperature corrosion and resistance to steam oxidation of the (Cr/CrN)n coating were studied in detail. The (Cr/CrN)n coating designed with a multilayer architecture had excellent high-temperature corrosion resistance. Steam oxidation experiments displayed that the (Cr/CrN)24 multilayer coating exhibited excellent steam oxidation resistance under high temperature of 1200 °C. Moreover, the oxidation mechanism of the Cr/CrN coating was also discussed intensively.

Effect of Aging on the Toughness of Heat-Resistant 22Cr-15Ni-4Cu Austenitic Steel

As the 630°C USC power units develops rapidly, the two commonly employed austenitic steels HR3C and Super304H cannot be suitable with higher temperature and pressure any more. Due to their poor steam oxidation resistance and low strength, a new Austenitic heat-resistant steel 22Cr-15Ni-4Cu has been developed according to the strengthening mechanism of multiphase. The samples were aged for different times from 50h to 5000h under 650°C. The results show that the Charpy impact energy sharply decreases in the first 500h, and then maintains steady when aging time extends to 5000h further. Though both σ phase and M23C6 precipitated along the boundary, the sharply change of toughness was attributed to the M23C6 phase precipitation but not the σ phase. As the σ phase nearly started to precipitate after the ductile-brittle transition process. Due to the hard, large and low-plasticity M23C6 phase, it is difficult for the particles to harmonize with the matrix, which makes the composite matrix sensitive to initiation and propagation of cracks during the deformation process and then leads to the sharp decline of toughness of the steel.

Steam oxidation behavior of ZrO2/Cr-coated pure zirconium prepared by plasma electrolytic oxidation followed by filtered cathodic vacuum arc deposition

Plasma electrolytic oxidation (PEO) and filtered cathodic vacuum arc deposition (FCVAD) techniques were employed to fabricate a ZrO2/Cr composite coating on pure zirconium. The steam oxidation properties of bare and ZrO2/Cr-coated pure Zr were performed in water vapor environment at 900–1100 °C. Their morphologies, microstructures and phase constituents before and after steam oxidation were analyzed. Meanwhile, their composition depth profiles were measured by glow discharge optical emission spectroscopy (GDOES). It was found that the mass gain of ZrO2/Cr-coated Zr was about 22–45% of that of bare Zr after 3600 s steam oxidation at 900–1100 °C, and the PEO and FCVAD composite treatments significantly improved the steam oxidation resistance of Zr. After steam oxidation, the phosphorous element in the outer layer of PEO film from phosphate electrolyte diffused into the residual Cr layer, however, most of the phosphorous in the interior of PEO layer was remained although the phosphorus diffusion in the region was accelerated with the increase of steam temperature. The ZrO2 to Zr3O phase transformation in PEO intermediate layer occurred in high temperature steam. Furthermore, the PEO zirconia interlayer suppressed hydrogen permeation into the Zr substrate during steam oxidation at 900–1100 °C.

High-temperature oxidation and hydrothermal corrosion of textured Cr2AlC-based coatings on zirconium alloy fuel cladding

Alumina-forming MAX phase coatings reveal great potential for accident tolerant fuel (ATF) cladding applications due to their favorable physical and mechanical properties and excellent high-temperature oxidation resistance. The feasibility of Cr2AlC MAX phase as protective coating on zirconium-alloy fuel claddings was explored focusing on high-temperature oxidation resistance in steam and hydrothermal corrosion performance in autoclave. Single-phase and basal-plane textured Cr2AlC coatings (~6 μm thick) were synthesized on Zircaloy-4 substrate by thermal annealing of specifically designed, magnetron-sputtered Cr/C/Al elemental multilayers at 550 °C for 10 min. Additionally, a second Cr/Cr2AlC bilayer coating design was fabricated aiming to eliminate potential rapid hydrothermal dissolution of Al during normal operating conditions. Micro-cracking appeared on both annealed coatings owing to thermal expansion differences between coating layer and substrate. Growth of an adherent and dense α-Al2O3 scale during high-temperature oxidation in steam and of a thin passivating Cr2O3 layer during hydrothermal corrosion in an autoclave imply excellent combined oxidation and corrosion resistance of the textured Cr2AlC coatings on Zircaloy-4. A self-healing capability via growth of alumina filling the micro-crack (annealing-induced) gaps was observed during high-temperature oxidation. However, partial delamination was seen for both coatings after short autoclave exposure and their mechanical properties (fracture toughness and adhesion strength) need further enhancement. Overall, tailored Cr2AlC-based (multilayered) coatings can be attractive candidates as potential type of coated ATF claddings.