High Temperature Oxidation Tests Research Articles

High-temperature oxidation and gas thermal shock studies of IC10 simulated specimens with thermal barrier coatings

PurposeThe purpose of this study is to investigate the effects of high-temperature oxidation tests and gas thermal shock tests on IC10 simulated components with thermal barrier coatings under different temperatures and oxidation times.Design/methodology/approachIn the high-temperature oxidation test, specimens were oxidized at three different temperatures of 850, 980, and 1,100 °C for durations of 10, 20, 50, 100, 200, and 300 h, respectively. In the gas thermal shock test, specimens were pre-oxidized for 10, 20, 50, and 100 h, followed by a high-temperature gas thermal shock test at 1,100 °C.FindingsIn the high-temperature oxidation tests, with increasing oxidation time, the oxidation layer thickened, and the air-film holes diameter decreased. The microstructure of the bond coat transitioned from strip-like to block-like, and internal cracks transformed from numerous and short to larger and deeper. Below the bond coat, a noticeable disappearance layer of strengthening phase appeared, with increasing thickness. The strengthening phase in the substrate transitioned from regular square shapes to circles as temperature increased. In gas thermal shock tests at 1,100 °C, the oxidation weight gain ratio increased with longer pre-oxidation times, whereas the erosion weight loss ratio gradually decreased.Originality/valueThe originality and significance of this study lie in its departure from the typical subjects of high-temperature oxidation and thermal shock tests. Unlike common research targets, this study focuses on IC10 simulative specimens with thermal barrier coatings and air-film holes. Furthermore, it investigates the effects of varying temperatures and oxidation durations.

Phase formation, structure and properties of quaternary MAX phase thin films in the Cr-V-C-Al system: A combinatorial study

Tailoring of individual atomic layers via alloying to synthesize quaternary MAX phases allows for expanding their chemical diversity and fine-tuning of their properties. In this study, Cr-V/C/Al multilayered precursors were deposited via combinatorial magnetron sputtering, creating nanostructured architectures with periodic stacking of nanolayers and varying Cr:V ratios. Their phase transformation and underlying reaction mechanisms during subsequent thermal annealing in argon towards the prospective quaternary solid solution (CrV)n+1AlCn MAX phases formation was systematically studied. Crystallization of (CrV)2AlC starts at approximately 500°C, while growth of higher-ordered (CrV)4AlC3 is observed from 960°C. Notably, intergrowth of (CrV)2AlC and (CrV)4AlC3 structures with coherent interface suggests that (CrV)2AlC acts as template for nucleation of (CrV)4AlC3. Thermal stability and high-temperature oxidation tests found that (CrV)2AlC exhibits higher thermal stability compared to (CrV)4AlC3 and films with Cr72.7V27.3 displayed good oxidation resistance at 1000°C, forming a protective bilayer oxide scale consisting of (Cr,Al)2O3 and Al2O3.

Oxidation resistance, corrosion behavior and grinding performance of laser-deposited TaMoCrTiAl refractory high-entropy coating

In this study, TaMoCrTiAl refractory high-entropy alloy coating without defects was successfully prepared on the Ti6Al4V substrate by laser metal deposited. Microstructure and properties were investigated systematically by multiple characterization methods. The results of phase and morphology experiments indicate that the coating comprised a BCC phase and a partial Laves phase. The coating, with an average thickness of 990 μm, exhibits good metallurgical bonding with the substrate. Further observation reveals that the cladding region consists of irregular bulk crystals. The heat-affected zone has a fine grain size, whereas the substrate has coarse and uneven grains. The high-temperature oxidation test shows that the formation of an Al2O3 oxide layer enhances the coating's high-temperature oxidation resistance. According to the results of microhardness tests, the average microhardness in the coating is about 570.98 HV (1.87 times that of the substrate) due to the formation of the leave phase particles and the fine-grain strengthening. The presence of Titanium, chromium and molybdenum elements in the coating facilitates the formation of a passivation film, thereby enhancing its corrosion resistance. Furthermore, the coating exhibits the smallest grinding force (43.637 N) and the lowest roughness (0.506 μm) at an experimental temperature of 100 °C, which demonstrates that appropriately elevating the experimental temperature can decrease the grinding force and enhance the flatness of the grinding surface.

Yttria-Stabilized Zirconia Composite Coating as Barrier to Reduce Hydrogen Permeation into Steel.

Hydrogen atoms can enter into metallic materials through penetration and diffusion, leading to the degradation of the mechanical properties of the materials, and the application of hydrogen barrier coatings is an effective means to alleviate this problem. Zirconia coatings (ZrO2) have been widely studied as a common hydrogen barrier coating, but zirconia undergoes a crystalline transition with temperature change, which can lead to volumetric changes in the coating and thus cause problems such as cracking and peeling of the coating. In this work, ZrO2 coating was prepared on a Q235 matrix using a sol-gel method, while yttria-stabilized zirconia (YSZ) coatings with different contents of rare earth elements were prepared in order to alleviate a series of problems caused by the crystal form transformation of ZrO2. The coating performances were evaluated by the electrochemical hydrogen penetration test, pencil hardness test, scratch test, and high-temperature oxidation test. The results show that yttrium can improve the stability of the high-temperature phase of ZrO2, alleviating the cracking problem of the coating due to the volume change triggered by the crystalline transition; improve the consistency of the coating; and refine the grain size of the oxide. The performance of YSZ coating was strongly influenced by the yttria doping mass, and the coating with 10 wt% yttria doping had the best hydrogen barrier performance, the best antioxidant performance, and the largest adhesion. Compared with the matrix, the steady-state hydrogen current density of the YSZ coating decreased by 72.3%, the antioxidant performance was improved by 65.8%, and the ZrO2 coating hardness and adhesion levels were B and 4B, respectively, while YSZ coating hardness and adhesion were upgraded to 2H and 5B. With the further increase in yttrium doping mass, the hardness of the coating continued to improve, but the defects of the coating increased, resulting in a decrease in the hydrogen barrier performance, antioxidant performance, and adhesion. In this work, the various performances of ZrO2 coating were significantly improved by doping with the rare earth element, which provides a reference for further development and application of oxide coatings.

Evaluation of high-temperature oxidation behaviour of ATF claddings during severe accidents in nuclear power plants

This work aims to evaluate the oxidation behavior and kinetics of ADSS B#51 alloy in high-temperature air and to investigate the effect of the T-ramping rate on the kinetics of ADSS B#51. Using Thermogravimetric Analyzer (TGA), the high-temperature oxidation test was performed isothermally in air at 1000 °C, 1150 °C, and 1300 °C and for T-ramping tests at 1 °C/min, 4 °C/min, 40 °C/min. We estimated weight gains of the alloy in T-ramping condition and compared with measured value. It was concluded that the oxidation rates of the alloy during T-ramping were higher than those estimated by using parameters determined from the isothermal tests. In addition, surface oxide characterization using SEM-EDS demonstrated a complex surface oxide. Where the surface oxide and the oxide compositions were randomly distributed and not following any specific pattern. The findings showed that T-ramping oxidation kinetics parameters are in between the oxidation kinetics parameters of the steady-state region and transient region of isothermal oxidation, but closer to the transient region.

Oxidation resistance of aluminized refractory HfNbTaTiZr high entropy alloy

In the present study, an equimolar HfNbTaTiZr refractory high entropy alloy was subjected to powder-pack aluminizing at 950°C for 4 h. High-temperature isothermal oxidation tests were carried out in open air on both as-cast and aluminized samples at 1000°C for the durations of 5, 25, and 125 h. Microstructural analysis and oxidation kinetics revealed the formation of a complex oxide layer consisting of (Hf,Zr)O2 and Al2O3 with AlN inclusions in the aluminized samples following oxidation. Significant cracking of the complex oxide layer occurred after the prolonged exposure of 125 h. The as-cast samples followed similar oxidation kinetics under all the conditions. However, the magnitude of mass gain for the aluminized samples was 1.18, 1.55, and 3.60 times less than the as-cast samples after 5, 25, and 125 h of oxidation, respectively. The lower mass gain in the aluminized samples indicated the formation of an adherent oxide layer on the surface of the alloy and that the molar volume of the oxide equaled or exceeded the molar volume of the alloy. As a result, the aluminized alloy was shielded from direct contact with gaseous oxygen and oxidation rate was governed by diffusion through the oxide layer.

Numerical simulation of high-temperature erosion of heat-resistant steel considering surface scale evolution

A study was conducted on heat-treated, heat-resistant steel S51740 to understand the issues surrounding gas turbine compressors. The study included high-temperature cyclic oxidation and high-temperature erosion tests at 400 °C, 600 °C, and 800 °C. We used the oxidation test data to establish dynamic erosion models using Ansys LS-DYNA software. We focused on the target's surface morphology, stress-strain, transient temperature, and failure characteristics during high-temperature erosion after high-temperature oxidation to reveal the erosion mechanism of oxidized steel. During cyclic oxidation, the specimen's microstructure was refined at 400 °C, with a 10 μm oxidation-affected zone emerging. At 600 °C, austenite appeared, forming a 20 μm oxidation-affected zone. Performance declined at 800 °C due to decarburization and segregation, resulting in a 50 μm oxidation-affected zone. High-temperature erosion on the oxidized specimens featured cutting and a chip-like morphology at 400 °C and 600 °C. At 800 °C, the specimen experienced a notable increase in mass loss and extensive plastic deformation on the surface. Erosion simulations revealed that rising temperatures increase the target's stress distribution, strain, and temperature zones. Reduced material strength leads to lower resistance to impact particles, converting high-speed kinetic energy to internal energy during erosion. Temperature spikes in impacted zones accelerate wear and adversely affect local mechanical properties. Lower ambient temperatures exacerbate the temperature increase from erosion, significantly influencing material erosion and wear resistance.

The Effect of Cr Addition on the Strength and High Temperature Oxidation Resistance of Y2O3 Dispersion Strengthened Mo Composites.

Y2O3 dispersion-strengthened Molybdenum (Mo) composites were prepared by the mechanical alloying of Mo and Y powders then consolidation by spark plasma sintering. The effects of Chromium (Cr) addition (0 wt. %, 5 wt. %, 10 wt. % and 15 wt. %, respectively) on the mechanical performance and high-temperature oxidation resistance of Mo-Y2O3 were investigated. The introduction of Cr had a significant influence on the mechanical property and oxidation resistance of the Mo-Y2O3 composite. The highest bending strength reached 932 MPa when the addition of Cr content was 5 wt. % (Mo-5Cr-1Y sample). This improvement is likely attributable to the dual mechanism of grain refinement and solid solution strengthening. Moreover, the Mo-5Cr-1Y sample showed the thinnest oxide layer thickness after high-temperature oxidation tests, and exhibited the best oxidation resistance performance compared with the other samples. First principle calculation reveals that Cr could improve the Mo-MoO3 interface bonding to prevent rapid spalling of the oxide layer. Meanwhile, Cr also facilitates the formation of the dense Cr2(MoO4)3 layer on the surface, which can inhibit further oxidation.

High-temperature oxidation characteristics of 20CrMnTi electroplated with copper

During high-temperature forming and phase change heat treatment, the steel surface is susceptible to oxidation. This can negatively affect the surface quality of steel parts. The production of antioxidant coatings on the surface of steel parts is important for high-temperature precision forming and heat treatment. In this paper, the high-temperature oxidation tests of 20CrMnTi steel, copper, and 20CrMnTi electroplated with copper are conducted. The 20CrMnTi samples showed varying degrees of mass gain above 900 °C; the copper samples showed varying degrees of mass gain above 700 °C; and the process of mass gain for copper-plated 20CrMnTi followed the same trend as for copper during heating and holding. For heated samples of 20CrMnTi plated with copper, the copper coating was oxidized and residual copper was observed in the oxide layer. The distance between the residual copper and the surface of the sample is greater than between the residual copper and the junction of the plating layer and the substrate. Oxygen diffuses through internal defects in the material at a higher rate than copper oxidation. In this study, an oxygen diffusion model and an antioxidant protective layer model at high temperatures were suggested. The protective layer against oxidation recommended in this research is a dense coating consisting of single crystals or fine grains free of porosities and cracks.

The Influence of Environmental Temperature on the Passive Oxidation Process in the C/SiC Composite

The C/SiC composite plays a crucial role in providing thermal protection for hypersonic vehicles. The SiO2 oxide layer formed via passive oxidation during ablation constitutes a typical porous medium with self-similarity. Given its significant impact on the thermal protection of the material, accurately predicting the variation in the SiO2 oxide layer thickness is of paramount importance. The growth of the oxide layer impedes the diffusion of oxygen within the material. This study considered microstructural parameters of the oxide layer based on high-temperature gas oxidation tests of the C/SiC composite. Fractal theory was utilized to construct a fractal diffusion-reaction kinetics model describing oxygen diffusion within the oxide layer and the evolution of the oxide layer under varying environmental conditions. The finding demonstrated that the existence of the oxide layer significantly influences the passive oxidation of the composite. This study underscored the significance of predicting the impact of environmental parameters on passive oxidation in the practical application of the C/SiC composite and the study result offers a valuable reference for evaluating the thermal resistance of the C/SiC composite.

High temperature oxidation and thermal properties of laminated Ti3Al(Si)C2-TiC/Nb based composites obtained by spark plasma sintering

This paper describes high-temperature oxidation behavior and thermal properties of metal-ceramic laminated composites fabricated by spark plasma sintering of Ti3Al(Si)C2-filled preceramic papers (TAC) and Nb foils. The high-temperature oxidation tests were carried out in air at 800–1300 °C. The phase composition and microstructure of the oxide layers were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The thermal properties were measured by the laser flash method in the temperature range of 30–800 °C. The evolution of the microstructure of the reaction layer (RL) formed at TAC/Nb interfaces was studied. The passive oxidation of the surface TAC layers results in the formation of outer TiO2 and inner continuous Al2O3 phase at temperatures up to 1100 °C, while local accelerated oxidation occurs above 1100 °C. As a result of breakaway oxidation, a multilayer oxide structure consisting of TiO2, Al2TiO5, Al2O3 and SiO2 phases were formed. The oxidation of inner Nb layers from the side surface can lead to high volume expansion and generation of stresses in the ceramic and metal layers due to the formation of Nb2O5 oxide phase. The stress relaxation occurred by complex mechanisms, including plastic deformation of the Nb layers, delamination at the interfaces, and formation of cracks in the reaction and TAC layers. The high temperature exposure results in slight increase in columnar grains in the reaction layers at 1200 °C, while the thickness of RL remains unchanged. The TAC/Nb composites exhibit higher thermal conductivity and diffusivity compared to monolithic TAC ceramic composites.

A Comparison Study on the Microstructure, Mechanical Features, and Tribological Characteristics of TiN Coatings on Ti6Al4V Using Different Deposition Techniques

Titanium alloys are considered lightweight alloys and are widely applied across various industries. However, their low hardness, poor wear resistance, and limited oxidation resistance restrict their prospects for wider application. In this paper, nitride coatings were prepared using three preparation processes, namely laser surface nitriding (LSN), physical vapor deposition (PVD), and plasma ion implantation (PII). Their microstructure, microhardness, tribological behavior, and high-temperature oxidation characteristics were compared. The experimental results revealed that nitrided coatings were successfully prepared using the three methods. However, a comparison of these data shows that the LSN coating exhibited superior comprehensive performance. It achieved the maximum thickness within the shortest preparation time: the thickness was about 280 μm and the deposition rate of the LSN method was 2250 and 90,000 times higher than those of the PVD and PII methods. Nitrides have high hardness, but the carrying capacity could be attributed to the thickness of the coatings: the PVD coating could withstand a force of 500 g, while the PII coating only withstood a force of less than 25 g. In addition, as hardness is the most important factor for excellent wear resistance, the average volumetric wear rate of the LSN and PVD coatings was about 9 × 10−6 mm3/m·N, and their relative wear resistance was 49.2 times that of Ti6Al4V. Meanwhile, the excellent bond between the LSN coating and the substrate was evidenced by a high-temperature oxidation test during a rapid heating–cooling cycle.

Mechanical, electrochemical corrosion, and high-temperature oxidation properties of stir-cast and heat-treated AZ80 magnesium alloy

This study aims to produce a stir-cast AZ80 magnesium alloy and to correlate the phases and microstructure of the as-cast, T4, and T6 conditions with the alloy's mechanical, corrosion, and oxidation properties. Microstructure was analysed using Field Emission Scanning Electron Microscopy (FE-SEM) with Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and High-Resolution Transmission Electron Microscopy (HRTEM), and X-ray diffraction (XRD) technique was employed to examine at the alloy’s phases. A Vickers microhardness, tensile, and impact test specimens were meticulously prepared according to ASTM specifications. The electrochemical corrosion was tested in 0.6 M NaCl and 0.05 H2SO4, simulating the salty seawater and low-sulphur air environments. Based on the eutectic temperature of the Mg-Al alloy system, which is 437 ℃, the high-temperature oxidation test was carried out at 400 ℃, 410 ℃, and 420 ℃. Microstructural study confirms that both T4 and T6 alloys undergo grain coarsening with a grain size of 72.64 µm, and the orientation of the grains shifted from the pyramidal plane (2−1-10) to the basal plane (0001). The TEM investigation helps pinpoint the GP zone's genesis in T4 heat-treated AZ80. T4 AZ80 has a maximum ultimate tensile strength of 306 MPa and a ductility of 29.77% because of the dispersion-strengthening effect. The T6 AZ80, on the other hand, has a minimum corrosion rate of 0.158 mm/year in NaCl solution and an oxidation rate constant of 4.19 mg2.cm−4h−1 at 420 ⁰C. Notably, the T6 AZ80 shows significant peaks of Mg2Al3, and the as-cast shows more peaks of Mg17Al12. Magnesium alloy AZ80 is significantly affected by intermetallic phases like Mg17Al12 and Mg2Al3. The Mg2Al3 phase shows the latter tendency to resist corrosion and oxidation.

Steam oxidation properties of graphene reinforced bioinspired laminated CoCrFeNiMn high-entropy alloy matrix composites at 1000 ℃

Laminated CoCrFeNiMn high-entropy alloy (HEA) matrix composites reinforced with 1.0 wt% graphene nanoplatelets (GNPs) were fabricated by mechanical ball milling and flake powder metallurgy, and were isothermal oxidized at 1000 ℃ for 100 h. Vacuum hot-pressure sintering (VHPS) shows a distinct nacre structure with the microstructure composed of FCC matrix phase, Cr23C6, CrMn1.5O4 precipitated phases, numerous dislocations and twins. High-temperature oxidation tests showed that the composites had mass gains at 12 h intervals from 12 to 100 h respectively. The oxidation kinetic curve changes from a linear pattern in the early stages to an exponential pattern in the later stages, which demonstrates better long-term oxidation resistance. The anisotropy of the laminated structure results in excellent resistance to high-temperature steam oxidation in the vertical lamellar direction. Observation of the cross-section reveals that although Cr2O3 (inner layer) is present, (Mn, Cr)3O4 and Mn3O4 are the dominant oxides (outer layer). Elemental depletion zones for Mn and Cr exist in the region of the matrix near the oxide scales. The results show that the oxidation resistance of the laminated GNPs/CoCrFeNiMn composites is mainly influenced by the diffusion of Mn and Cr elements, the microstructure of the laminations and the internal oxidation.

(Invited) Pt-Modified Aluminide Coatings for Ni-Base Single Crystal Superalloy

Single phase (Ni,Pt)Al coating has been widely employed as state-of-the-art bondcoat for protecting hot-sectional components in commercial aero engines, especially for the parts made of Ni-base single crystal (SX) superalloys. For high temperature protective coating serving on SX superalloy, two interfaces are vitally essential for acquiring reliably long service life: the interface growing thermally-grown oxide (TGO) and the interface connecting coating and substrate alloy. Normally, the excellent performance of PtAl coating derives from high Al content and the incorporation of Pt, which ensures formation of exclusively adherent oxide scale, α-Al2O3. To further improve the performance of Pt-modified aluminide coating, in present study reactive elements are introduced using co-electroplating method. Compared with singular doping, co-doping of Hf-Y demonstrated superior oxidation resistance. The oxide scale growth rate and spallation tendency of Hf-Y co-doped (Ni,Pt)Al coating were much smaller, as well as the surface rumpling extent. Besides, the grain size of Hf-Y co-doped (Ni,Pt)Al coating was finer than that of Hf- or Y- doped coatings in as-received state, indicating the capability of grain refinement. With the benefits of RE co-doping, the desirably thin/smooth TGO is thus accessible for Pt-modified aluminide coatings. The other issue is the element interdiffusion at high temperature, which would affect the mechanical property of SX superalloy. According to Fick′s law of diffusion, J Al = - D Al · δμ Al / δ x ,to reduce diffusion coefficient ( D Al ) or chemical potential ( δμ Al / δ x ) would both decrease the diffusion extent ( J Al ). Therefore, two strategies are employed: adding a diffusion barrier between coating and substrate, or designing a γʹ-PtAl coating. The performance of these modified aluminide coatings are evaluated in high temperature oxidation test. At last, doping behavior of some elements were explained by First-Principle Calculations.

High Temperature Oxidation of Zircaloy-4 Under Conditions Simulating a Loss of Cooling Accident in Spent Fuel Pools Examined with Raman Imaging and 18o Tracer Techniques

Since the Fukushima accident, an increased attention is continuously paid to the vulnerability of the Spent Fuel Pools (SFPs). In SFPs, for different reasons, degradation of the fuel rods induced by oxidation in air-steam mixtures after dewatering is a major safety concern: (i) the cladding material is the only barrier left against fission product dissemination, (ii) the heat released by the oxidation reactions can overcome the residual decay heat of the fuel and may become the main driving force to the accident escalation, (iii) hydrogen production is a strong concern because of the presence of steam, (iv) presence of air in the atmosphere is known to be an aggravating factor because of the “catalytic” role of nitrogen on the oxidation mechanism.In this study, high temperature oxidation tests in oxygen, air and air - steam atmospheres were performed with Zircaloy-4 cladding tubes and plates specimens. Because spent fuels are concerned, the presence of the corrosion oxide scale formed in reactor during in-service operation was also considered. The tests described in this study were restricted to the 700 – 950°C range, and mostly performed at 850°C. Raman imaging was used to examine the specimens after the oxidation tests, either directly at the oxide surface, or on metallographic preparations for cross-section examinations.We first used new opportunities given by Raman imaging to analyze, at least qualitatively, the structural and mechanical phenomena involved in this particular corrosion phenomena. Indeed, this method can provide information on the nature of phases that are present in the scale and on the stress level with sub-micron spatial resolution. The different methods used to extract this information that is present in the Raman data will be described and discussed.Moreover, isotopic substitution was also considered. Actually, Raman spectroscopy has also the ability to quantitatively extract the 18O distribution in a zirconia oxide scale after a two stage experiment with a fair accuracy. Raman imaging gave clear evidence for different characteristic distributions of 18O in the scales. Some of them have been correlated with the development of cracks and porosity in the oxide which allows the corroding medium to penetrate locally in the scales. Nitrogen appears to have no or limited influence on the oxygen diffusion, but is observed to reach the metal/oxide interface much faster than oxygen. Thus, we also emphasize the potential of this method to investigate the 18O distribution in such complex corrosion scales.

Investigation of High-Temperature Oxidation of Homogeneous and Gradient Ni-Cr-Al Coatings Obtained by Detonation Spraying

The high-temperature oxidation of homogeneous and gradient coatings based on Ni-Cr-Al obtained by detonation spraying is investigated. To assess the resistance to high-temperature oxidation of Ni-Cr-Al coatings, cyclic tests were carried out at a temperature of 1000 °C for 50 cycles. The assessment of high-temperature oxidizing ability was carried out by measuring the weight gain of samples after each cycle. After high-temperature oxidation tests, the morphology and chemical composition of the coating structure in the cross-section were investigated using SEM/EDS. The phase composition of the samples was studied by X-ray diffraction (XRD) phase analysis. Visual analysis of the sample surface under study after high-temperature oxidation showed that the surface of homogeneous or gradient Ni-Cr-Al coatings remained undamaged. The results of X-ray phase analysis showed the peaks of Al2O3 in Ni-Cr-Al gradient coatings are more expressed and intense compared to homogeneous coatings of Ni-Cr-Al. Gradient coatings also retain an increased chromium content compared to homogeneous Ni-Cr-Al coatings. This increased chromium content can slow down mixing or diffusion between different phases of the material at their boundary, which, in turn, contributes to increasing the resistance of the gradient coating to oxidation.

Tribological, oxidation and corrosion properties of ceramic coating on AISI H13 steel by rare earth-Cr composite boronizing

In this paper, a rare earth-Cr composite boronizing method to prepare boride ceramic coatings for AISI H13 steel was proposed. The effect of rare earth elements and Cr on the microstructure, hardness, wear resistance, high temperature oxidation resistance, and corrosion of boride ceramic layers was researched. The characteristics of the boride layers were investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), electron probe microanalysis (EPMA), wear tests, high-temperature oxidation tests, and corrosion immersion tests, etc. The results showed that the boride layer comprised of Fe2B, FeB, CrB and Cr2B phases. The addition of rare earth CeO2 and Cr nanopowder promoted the growth of the boride layer, and its surface hardness increased by 3.5 times compared with that of tempered AISI H13 steel. In addition, the addition of CeO2 and Cr significantly reduced the wear rate of the boride layer, with the surface wear mechanism being abrasive oxidative wear. Furthermore, the oxidation rate of the boride layer was 71 % lower than that of AISI H13 steel, demonstrating excellent high-temperature oxidation resistance; and the boride layer showed good acid corrosion resistance in corrosion immersion tests.

High-temperature steam oxidation study of irradiated FeCrAl defueled specimens

Post irradiation examinations (PIE) were performed on irradiated iron-chromium-aluminum (FeCrAl) specimens. These FeCrAl specimens were fabricated at the US Department of Energy's Oak Ridge National Laboratory (ORNL). The experimental setup involved subjecting FeCrAl cladding, along with UO2 pellets, to irradiation in the Idaho National Laboratory Advanced Test Reactor (ATR). In parallel, the FeCrAl alloy tubing without UO2 pellets was irradiated at ORNL's High Flux Isotope Reactor (HFIR). After irradiation, the ATR-irradiated rodlet was transported to an ORNL hot cell, where it was sectioned into multiple samples for the PIE and severe-accident testing. The sectioning process revealed that the fuel was not bonded to the cladding and could be easily detached from sectioned cladding slices. Microstructural analysis of the fuel cross sections demonstrated no significant interaction between the fuel and the cladding. Additionally, high-temperature steam oxidation tests on defueled cladding segments showed minimal oxygen uptake even at 1200 °C. The ATR-irradiated specimens began to exhibit signs of enhanced oxidation upon reaching a temperature of 1300 °C. Furthermore, enhanced oxidation was observed on the inner surface of the ATR-irradiated FeCrAl specimen, which had been subjected to 1300 °C for a duration of 1 min. By contrast, high-temperature steam oxidation experiments indicated that the HFIR-irradiated FeCrAl cladding provided good thermal stability when exposed to 1300 °C for up to 4 h. Comparative analysis encompassing the oxidation behavior of the ATR-irradiated fueled FeCrAl, HFIR-irradiated unfueled FeCrAl, and unirradiated FeCrAl suggests that the fuel–cladding interaction, although not visible via standard microscale electron microscopy measurements, may accelerate the deterioration of FeCrAl cladding in beyond-design-basis accident scenarios.

High-temperature oxidation behavior of direct-aged bimodal Al2O3-reinforced Inconel625 plasma sprayed composite coatings

Plasma-sprayed (PS) coatings in industrial or aerospace applications are chosen as a technique for enhancing the high-temperature oxidation performance of parts operating under strenuous conditions. However, the presence of microstructural defects and amorphous phases developed in as-sprayed plasma coatings can restrict the potential of such coatings when exposed to thermal cycling conditions. Examining the oxidation performance and microstructural characterization of three heat-treated Inconel 625-Al2O3 plasma-sprayed composite coatings over an ASTM SA210 GrA1 (uncoated) substrate is the goal of the current study: The three prepared compositions are; a) Inconel625-30 wt% micron-sized Al2O3 (INC625-CHT) coating, b) Inconel625-30 wt% nano-sized Al2O3 (INC625-NHT) coating and c) Inconel625-15 wt% micron-sized Al2O3 + 15 wt% nano-sized Al2O3 (INC625-BHT/bimodal) coating. High-temperature oxidation tests were conducted at 900 °C temperature in air for 50 cycles in a simulated environment using a laboratory silica tube furnace. The microstructures and morphologies of the composite coatings in the as-sprayed and oxidized conditions were characterized using SEM, EDX, and XRD techniques. The furnace heat treatment (HT) improves the oxidation resistance of the coatings in order INC625-BHT, INC625-NHT, and INC625-CHT coating by healing interlamellar defects like pores and cracks.