High Temperature Oxidation Tests Research Articles

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.

Improving the high-temperature oxidation resistance of CrN coating by gradient deposition considering internal stress effects

In this study, two different CrN coatings were deposited on the surface of Zr-4 via a multi-arc ion-plating method using gradient and non-gradient deposition processes. The effects of two deposition processes on the high-temperature oxidation resistance and internal stress of the coatings were investigated. The microstructure and phase structure of the coatings were characterized by scanning electron microscopy, X-ray diffraction (XRD), and energy dispersive spectrometry. The high-temperature oxidation resistance of the specimens was investigated by performing thermal shock experiments and simulated loss-of-coolant accident high-temperature steam oxidation experiments. The residual stresses of both coatings during deposition were determined by XRD analysis. In addition, the thermal stresses of both coatings during the high-temperature oxidation tests were modeled and calculated. Under long-term high-temperature oxidation conditions, the gradient-deposited CrN coating exhibited improved high-temperature oxidation resistance performance than that exhibited by non-gradient-deposited CrN coating. In addition, the residual stresses of gradient-deposited CrN coating during deposition and thermal stresses during high-temperature oxidation were significantly lower than those of the non-gradient-deposited CrN coating. The results obtained herein confirm the promising potential of gradient-deposited CrN coating as an accident-tolerant fuel cladding material.

Effect of Si content on the microstructure and properties of CrSi coatings for ATF cladding

Microstructure, mechanical properties, corrosion resistance and high-temperature oxidation resistance of four CrSi coatings with different Si content ranging from 0 at% to 67 at% were investigated. With increasing Si content from 11 at% to 67 at%, the main forms of Si exist the coatings were detected to be Cr3Si, Cr5Si3 and CrSi2, respectively. All the CrSi coatings own higher nano-hardness due to the formation of intermetallic. For Si content ≤33 at%, the CrSi coatings showed good corrosion resistance in static pure water of high temperature and pressure. However, the higher Si content (67 at%) led to the dissolution of Si in the form of [Si(OH)]4, as well as insufficient Cr to form a continuous Cr2O3 layer. The high-temperature oxidation tests showed that the coating with 11 at% Si content exhibited the best oxidation resistance than other coatings, due to the formation of outermost Cr2O3 layer, stable Cr3Si phase and inner Zr2Si. Our study indicates that the coating with 11 at% Si content displays good comprehensive properties and could be used as a candidate material for ATF coatings.

Development, Characterization and High-Temperature Oxidation Behaviour of Hot-Isostatic-Treated Cold-Sprayed Thick Titanium Deposits

In this work, thick deposits of pure titanium (Ti), with a thickness of around 15 mm, were additively manufactured using high-pressure cold spraying. Nitrogen was employed as the process gas. Subsequently, the deposits were subjected to hot isostatic pressing (HIP). The HIP-treated Ti deposits were analyzed for their metallurgical and mechanical characteristics with the aim of exploring the viability of using cold spraying for the additive manufacturing of Ti components. Moreover, high-temperature cyclic oxidation testing was also performed on the HIP-treated Ti deposit to understand its stability at high temperatures. SEM/EDS showed a dense structure with marginal porosity for the HIP-treated Ti deposits, without any oxide formation, which was further confirmed via XRD analysis. An average microhardness of 214 HV was measured for the HIP-treated Ti deposits, which is close to that of the commercially available bulk titanium (202 HV). The high-temperature oxidation studies revealed that the cold-sprayed HIP-treated Ti has very good oxidation resistance, which could be attributed to the formation of protective titanium dioxide in its oxide scale.

Review on performance of chromium-coated zirconium and its failure mechanisms

The conventional Zircaloy cladding may react with coolant in light water reactors and elicit severe accident at high temperature, which constraint the safe and efficient development of nuclear energy. To avoid the tragedy happened in Fukushima, the concept of Accident Tolerant Fuel (ATF) was developed around the globe to secure the steady operation for nuclear power plants. As a short-term solution, deposition of protective coatings upon the cladding tubes are proved to be effective. Among the coatings, Chromium is one of the most outstanding choices. This paper reviews the recent study results about the performance and failure mechanisms of Cr-coated Zr cladding, including mechanical, irradiation, high-temperature oxidation tests, etc. under normal and/or accident conditions. The experiments and tests collectively suggest that Cr coating possesses excellent comprehensive properties for integrity protection of claddings and provides a promising future of the commercial application in reactor cores. Finally, this review proposes ambiguities and questions needed to be analyzed and clarified in future works.

Wear, corrosion and oxidation characteristics of consolidated and laser remelted high entropy alloys manufactured via powder metallurgy

High entropy alloys have promising wear, oxidation, and corrosion properties compared to conventional alloys and superalloys. In the present study, CrCuFeNiAl0.5 and CrCuFeNiAl0.5Si0.5 alloys were prepared using a traditional powder metallurgy process and then remelted the surfaces via laser. The laser remelting (LR) process gains a denser and more homogeneous surface to alloys. Pressureless consolidated and laser-remelted specimens were subjected to wear, corrosion, and oxidation tests. In the wear tests, it was observed that the wear resistance of Si-containing samples was better due to higher hardness. However, the laser remelting process has mostly increased rather than reduced wear losses. The less volume loss of laser-melted samples was attributed to the almost pure Cu in its content. There is little difference among all samples in electrochemical corrosion measurements. The formation of a fragile passivation layer was observed in potentiodynamic polarization curves of CrCuFeNiAl0.5Si0.5 and LR-CrCuFeNiAl0.5Si0.5 alloys. The alloy with the best corrosion resistance is CrCuFeNiAl0.5Si0.5, whose icorr value is 0.936 × 10−6 A/cm2. After high-temperature oxidation tests, the CrCuFeNiAl0.5 alloy exhibited the worst oxidation performance due to not forming a protective oxide layer on the surface, while LR enabled the protective oxide scale in a short oxidation time. The presence of Si in this alloy relatively enhances the oxidation resistance. The best oxidation performance was observed in LR-CrCuFeNiAl0.5Si0.5 due to the forming of a protective Al2O3 layer during the oxidation tests.

Construction of Cr coatings with different columnar structure on Zircaloy-4 alloys to optimize the high-temperature steam oxidation behavior for accident tolerant fuel claddings

To optimize the oxidation behavior of chromium-coated Zircaloy-4 alloys under 1200 °C high-temperature steam for accident tolerant fuel (ATF) claddings, Cr coatings with different columnar structure are constructed by changing bias voltage using high power impulse magnetron sputtering and corresponding microstructure, mechanical and high-temperature steam oxidation properties are studied systematically. With the bias voltage increase from 0 V to − 150 V, the microstructure of Cr coatings changes from porous columnar structure to compact columnar structure. Especial for bias voltage is − 90 V, the tiny compact grains uniform distribute on the surface micrographs and optimal compact columnar structure are observed on the cross-section micrographs. The hardness and elastic modulus of as-prepared Cr coatings increase firstly and then decrease, the hardness of Cr coatings with optimal compact columnar structure is 8.65 GPa, which is elevated ∼2.28 times than Cr coatings with porous columnar structure. 1200 °C high-temperature steam oxidation test results show an interesting phenomenon that the thickness of Cr layer reduces initial and then increase with the exposure time prolong from 1 h to 4 h. The main steam oxidation mechanism, in the early oxidation stage, is formation the compact Cr2O3 oxide layer. Then, with the exposure time extend, the reduction reaction plays the significant part for steam oxidation mechanism, which is consumption of outmost Cr2O3 oxide layer and formation of subsurface Cr layer. The construction of Cr coatings with compact columnar structure and relevant oxidation mechanism are expected to offer a new idea for improving 1200 °C steam oxidation resistance of chromium-coated Zircaloy-4 alloys.

Study on high-temperature oxidation and hot corrosion characteristics of Cr60Ni40 laser cladding layer

In order to investigate the high-temperature characteristics of Cr-based alloy, Cr60Ni40 laser cladding layer (60 wt% Cr and 40 wt% Ni) were prepared and subjected to high-temperature oxidation test and hot corrosion test. The results prove that there are Cr segregation and large particles of Cr precipitated within the raw Cr60Ni40 cladding layer. During the high-temperature test, Cr2O3 protective film was generated on the surface of the cladding layer, protecting the substrate to different degrees. However, the particles precipitation of Cr caused uneven growth of Cr-rich oxide, and the Cr segregation brought about internal corrosion with Cr2O3 as the main products.

Investigations into Power Plant Alloys’ (Inconel 718) Oxidation Resistance by Compound Composite (Cr2O3 + YSZ) Coatings

As it increases the pressure and temperature of incoming steam and decreases CO2 emissions, oxidation is crucial for materials used in power plants to increase their efficiency. Compound composite (Cr2O3 + YSZ) coatings applied to Inconel 718 (EN8) substrates using the Atmosphere Plasma Spray technique are anticipated to increase structural resistance when subjected to high pressure and temperature oxidation conditions of service. The nickel-based superalloys EN8 and EN8/Yttria (8% Y2O3) Stabilized Zirconia (YSZ)/Cr2O3 were subjected to high-temperature oxidation tests in the open air at 1050 °C for approximately 12, 24, 48, and 100 h. EN8 is not appropriate for prolonged use at 1050 °C as can be seen from scanned electron microscope and energy dispersive X-ray spectroscopy analyses on isothermally oxidized samples. The findings demonstrated that the EN8 alloy exhibited more significant weight variations over 48 h at high temperatures because its chromia oxide scale was continuously smaller. With phase dispersion in the microstructure, coated EN8 exhibits a higher performance under more prolonged exposure than the EN8 alloy. Additionally, the synthesis of outer chromium oxide, YSZ, and Cr2O3 on a substrate at 1050 °C for 100 h improved the outstanding oxidation resistance while maintaining the integrity of the chromium oxide layer.