High Temperature Corrosion Resistance Research Articles

ATLAS 316, ATLAS 316L, ATLAS 316H

Abstract Atlas 316 is a chromium-nickel-molybdenum austenitic stainless steel, second only to Atlas 304 in commercial importance. The molybdenum gives Atlas 316 better overall corrosion resistant properties than type 304 austenitic stainless steel, particularly higher resistance to pitting and crevice corrosion in chloride environments. It is readily brake or roll formed, welded, soldered, and cut by both thermal and mechanical methods. The austenitic structure gives excellent toughness, even down to cryogenic temperatures. Atlas 316L, the low carbon version of Atlas 316, is highly resistant to sensitization (grain boundary carbide precipitation) and so is extensively used in heavy gauge welded components; about 5 mm, 0.2 in., and over. Atlas 316H, with its higher carbon content, has some application at elevated temperatures, as does stabilized type 316Ti. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on high temperature performance and corrosion resistance as well as heat treating, machining, and joining. Filing Code: SS-1365. Producer or source: Atlas Steels.

A lightweight image-level segmentation method for steel surface defects based on cross-layer feature fusion

Steel is widely used in the aerospace, machinery and automotive industries. Surface defects not only have a negative impact on the appearance of steel but also significantly reduce its wear resistance, high temperature resistance, corrosion resistance and fatigue strength. Therefore, the detection of steel surface defects is very important to improve the quality of steel production. The limited availability of surface defect samples in the industrial sector poses significant challenges for the accurate detection of defects in high-quality materials. In addition, the existing defect detection model is highly complex and not easy to deploy. To solve this problem, a lightweight defect detection network suitable for steel defects is proposed. The cross-layer feature fusion (CFF) in the design enables effective utilisation of multi-layer semantic features, facilitating the detection of small defects in steel. Secondly, a new loss function is designed to make up for the problems of small data volume and uneven data distribution. The experimental results demonstrate that the steel surface defect detection method proposed in this paper achieves the highest detection performance on widely used public datasets such as RSDDS, NEUS and NRSD-CR(test), while maintaining the lowest model complexity.

Fabrication and properties of Si3N4f/RBSN porous ceramic composite

Porous Si3N4 has excellent properties such as high temperature resistance, corrosion resistance, high porosity, and high specific surface area, but the inherent brittleness limits the application of Si3N4 in some special environments. Si3N4f/RBSN porous ceramic composites were prepared by reaction bonding method using reaction-bonded silicon nitride(RBSN) as the matrix and continuous Si3N4 fibers (fiber mats) as the reinforcement. The results show that the composite with Si/Si3N4 = 70:30 in the raw material has a superior nitridation rate and flexural strength of 96.5% and 23.5 MPa, respectively. The nitridation process of the Si3N4f/RBSN matrix is dominated by the vapour-phase reaction between SiO and N2, and the products are mainly α-Si3N4 whiskers. The residual flexural strength of the composites is essentially unchanged after 10 thermal cycles in air at 800 °C. The composites have excellent thermal shock resistance and can be used as the reusable crucible.

Improving stress corrosion resistance and wear resistance of austenitic hot-stamping die steels via synergistic effects of shot peening and plasma nitriding

In this work, the effects of plasma nitriding, shot peening and their combination on the high-temperature wear resistance and stress corrosion resistance of an austenitic hot-stamping die steel were investigated. The results showed that the nitrided layer consisted of a single expanded austenite after nitriding at 560 °C for 4 h. Shot-peening pretreatment improved the surface hardness and depth of nitrided layer by 29.4 % and 36.4 % compared with the nitrided-only samples. This could be attributed to an increase in dislocation density, sub-crystal refinement, precipitation of nanoscale carbides and high strain of carbides and slip bands. Nitriding increased the stress corrosion resistance and high-temperature wear resistance of materials. Samples nitrided after shot peening showed the greatest wear and corrosion resistance. Besides, the introduction of residual compressive stresses in the nitrided layer by shot peening also improved wear and corrosion resistance to some extent.

Covalent-assisted construction of “scale-like” boron nitride/polyimide thermal interface materials with high thermal conductivity

Polyimide (PI) is a special engineering plastic with high strength, high modulus, high temperature resistance and corrosion resistance, but its poor thermal conductivity limits its application in high-power miniaturized electric and electronic equipment. In this study, surface-activated and modified boron nitride (m-BN) is polymerized in situ and coated to form a “scale-like” composite thermal interface material (m-BN/PI) with PI. Moreover, the m-BN@PI composite films obtained by a simple co-blending process of m-BN and PI are used as a comparison. The in-plane thermal conductivity of m-BN/PI composite reached 4.43 W m−1 K−1, when the filler content is 30 wt %, which is about 12 times higher than that of the pure PI film (0.37 W m−1 K−1). At this load, the in-plane thermal conductivity of m-BN@PI is only 3.94 W m−1 K−1. In addition, the covalent bonding between m-BN and PI molecular chains in m-BN/PI effectively reduces the interfacial thermal resistance by fitting the EMT and Foygel models. Finally, using the m-BN/PI composite film as a thermal interface material placed at the CPU location, its role in the heat dissipation process of electronic devices is demonstrated.

Molybdenum and its alloys in advanced engine applications: From material selection to surface optimization

This article explores the potential of molybdenum and its alloys for use in advanced aerospace engines, focusing on their high-temperature capabilities and corrosion resistance. It highlights the importance of enhancing oxidation resistance through methods such as alloying and the application of specialized coatings. The paper provides a detailed overview of high-temperature alloys, especially molybdenum-based alloys, discussing the benefits of various alloying elements and the types of oxidation-resistant coatings like aluminide and silicide coatings that protect against high-temperature degradation. The review of coating technologies includes modern methods like slurry sintering, atmospheric plasma spraying, and chemical vapor deposition, which improve the performance and longevity of these coatings. The paper concludes by identifying future research directions, emphasizing the need to boost the high-temperature oxidation resistance of coatings to meet the evolving demands of aerospace engine technologies.

Study of Inconel 718 deposition by high-speed Laser Cladding

This paper presents the feasibility of using High-Speed Laser Cladding technology to apply Inconel 718 as coating material for high-temperature corrosion resistance. In this study, the effect of process parameters, such as laser power, powder flow rate, speed and stepover distance, was analyzed for producing Inconel 718 coatings on 42CrMo4 steel cylinders, by means of metallographic analysis and defect identification. The coating process was optimized in terms of layer thickness, defect avoidance and powder catchment efficiency. The thickness of coating layers ranged from 0.13 mm to 0.35 mm with an average porosity between 0.12 % and 0.17 %. The powder catchment efficiency ranged from 80 % to 91 %. Finally, multilayer coatings were also produced with the best process parameters to achieve protective coatings with thickness up to 0.5 mm.

High Temperature Corrosion of Inconel 625 and Pure Nickel in Contact with Fluoride Melts

Considering the fact that fossil fuels are not inexhaustible, and they pollute the environment, the automotive industry is transitioning from internal combustion to electric engines. As a result, batteries are becoming a strategic component of cars and thus battery ingredients are considered as important raw materials. Therefore, these batteries need to be recycled as well, since the natural resources for producing them are limited and some of the elements like nickel which are used in these batteries can be hazardous if left in the environment. In order to recycle electric batteries, furnaces with high temperature corrosion resistance are necessary. Maintaining these furnaces for longer periods is of great interest and necessitates it for the challenges to be dealt with, especially in case of high temperature corrosion.In the present study, high temperature corrosion behavior of Inconel 625 is compared with pure nickel. Both metals have been exposed to fluoride melts (to mimic the recycling process) for different durations of time. The performances of these two bulk metals are investigated mainly through scanning electron microscope and X-ray diffraction. Element leaching, oxidation, depth of internal attack and depletion profile are among the main parameters studied here. Experiments are carried out both in dry and humid condition to see how humidity changes the reactions. Since there are different alloying elements in Inconel 625, and humidity is involved, pure nickel is used as the baseline to see the effect of different parameters involved. Filtered air is used as the main environment in this study and lithium fluoride is used as the main salt.

Effect of Secondary Oxidants (CO2 and/or H2O) on Oxidation of Fe-20Cr-(Mn, Si)

Ferritic heat resisting alloys are widely used in industry owing to their combination of economy, reasonable strength, and high temperature corrosion resistance. Alloy design centres on forming and maintaining an external, slow growing protective oxide scale by selective oxidation of the desired metal, commonly chromium. Design methods based on diffusion theory succeed when the service environment is oxygen or clean, dry air. However, they can fail badly when secondary oxidants (like CO2 and water vapour) are present, which is commonly the case in energy production etc. This work investigates the effect of CO2 and H2O on corrosion behaviour of Fe-20Cr, in comparison with that in pure O2. The alloying effect of Si and Mn on oxidation behaviour of Fe-20Cr in different gases is also investigated.Model alloys Fe-20Cr, Fe-20Cr-1Si, Fe-20Cr-2Mn (all in wt%) were arc melted and annealed. Sample coupons were cut, ground, mechanically polished to 3mm finish, and further electro-polished to remove subsurface deformation zones. They were then exposed to Ar-2O2, Ar-20H2O-2O2, Ar-20CO2-2O2, Ar-CO2-H2O and Ar-CO2-H2O-O2 (all vol%) gas mixtures, at 650°C for 150h. Corrosion products and cross-sections were examined using optical microscopy, X-ray diffraction, Raman Spectroscopy and scanning electron microscopy equipped with energy dispersive X-ray spectrometry.The alloy behaved protectively in Ar-2O2, forming a very thin Cr2O3 layer on its surface. However, when CO2 or/and H2O was added to oxygen, breakaway oxidation resulted, forming thick multi-layered oxide scales. Detailed analysis revealed that this multi-layered structure contains four layers, where the outer layer was Fe2O3, overlying an Fe3O4 layer and FeCr2O4 spinel innermost layer, and an internal oxidation zone was formed beneath the scale. In the low environment of Ar-20CO2-20H2O, Fe3O4 layer, FeCr2O4 spinel layer and internal oxidation zone formed a three-layered structure. No Fe2O3 was found, which is attributed to the decrease in oxygen partial pressure.Carburisation of Fe-20Cr also resulted from exposure to the three CO2-bearing gases. The deepest and densest internal carburisation zone formed in Ar-20CO2-2O2. In Ar-20CO2-20H2O-2O2 and Ar-20CO2-20H2O, internally precipitated carbides were sparser, but still obvious.Silicon addition dramatically improved the oxidation resistance of Fe-20Cr. Weight gains in all gases were sharply decreased compared with those of Fe-20Cr. As with Fe-20Cr, a very thin Cr2O3 layer on the Si-bearing alloy reacted in Ar-2O2,together with a thin underlying silica layer, indicating that the alloy was fully protected. Unlike Fe-20Cr, the Fe-20Cr-1Si alloy was also protected in Ar-20CO2-2O2. However, when water vapour was present, the alloy started to go into breakaway, forming local Fe-rich oxide nodules. In Ar-20H2O-2O2, some small nodules, consisting of external Fe2O3 and inner spinel were distributed on an otherwise thin, protective chromia scale. In Ar-20H2O-20CO2-2O2 and Ar-20H2O-20CO2, an additional Fe3O4 layer was observed in nodules, between Fe2O3 and inner spinel. Thus, for Fe-20Cr-1Si samples, Fe3O4 can only be observed if 20%CO2 and 20%H2O were both present. Additionally, some small internal oxide particles were observed at breakaway nodule areas in all these three gasses. Internal carbides were found only under the big iron oxides nodules grown in Ar-20CO2-20H2O-2O2.Manganese addition did not much influence the corrosion resistance of Fe-20Cr. In general, oxide morphologies were similar to those of Fe-20Cr. In Ar-2%O2 gas, a thin Mn rich chromium oxide layer was formed over the entire alloy surface, indicating that sample was fully protected. Multi-layered thick oxides developed when CO2 or/and H2O were added. For high gases with the addition of H2O or CO2 (Ar-20H2O-2O2, Ar-20CO2-2O2, and Ar-CO2-H2O-O2), three-layered oxide structures were found to be made up of Fe2O3, Fe3O4, and spinel layers, in sequence from the outer surface to the inner alloy. It is worth noting that the oxide layers were not completely continuous in Ar-20CO2-2O2. About 15% of the cross-section area was protected which indicated that Mn can slightly improve the corrosion resistance in dry CO2 and O2 environments. In lower oxygen partial pressure gas (Ar-CO2-H2O), no Fe2O3 was found, and only Fe3O4 and spinel constituted the oxide scale. The main difference was that the internal oxidation zone became tiny on Fe-20Cr-2Mn samples. Internal carbides were still found under inner oxide in all CO2 bearing gases, most obviously in Ar-20CO2-2O2. However, in all cases the carbide quantities were far less than those in Fe-20Cr, indicating that Mn addition partially inhibited carburisation.After the thermodynamics of the reaction product phase assemblages are considered, this complex pattern of reaction products is discussed in terms of the permeability of different oxides to carbon- and hydrogen-bearing species, along with interactions between secondary oxidants on oxide surfaces and grain boundaries.

(Invited) The Internal Oxidation Mechanism of Ti60 Alloy in NaCl-coated Environment at 600o C

When serving in the marine environment, the blades of aircraft engines will suffer serious high-temperature corrosion and their service life will be shortened. This is because the water vapour and salt particles (mainly NaCl) in the marine atmosphere will inevitably be involved in the engine, resulting in severe corrosion of materials. Previous studies on the degradation of titanium alloy under NaCl mainly focused on the active oxidation mechanism, while the mechanism of internal oxidation, which can significantly damage the mechanical properties of the titanium, is not clear. In addition, internal oxidation appears microstructure sensitivity, indicating that microstructure design may be an important way to improve high-temperature corrosion resistance in the marine environment.Consequently, for further understanding the internal oxidation mechanism and the influence of microstructure on corrosion, the composition and morphology of the internal oxidized layer of the Ti60 samples, which corroded with NaCl precoated at 600 oC in moist O2 flow for 100 h, have been studied.According to the results, Ti2O formed within the internal oxidized layer. With the thermodynamic calculation results, this observation proves that internal oxides do not result from the oxidation of metal chlorides. As it is known that titanium has a high affinity to oxygen, the internal matrix turns into titanium oxides with different valence states directly, while TiCl4(g) formed from active oxidation further transports outward and is oxidized at the position with high P(O2).The α secondary phase, located inside the β phase, is more sensitive to NaCl-induced corrosion than the α lamellar outside the β phase. This is because β phase and phase boundaries provide more high-energy channels for corrosive media transport to the α secondary phase, which results in severe loss of metallic elements and oxidation. The design of the α secondary phase may be one essential point for developing titanium alloys with a good combination of mechanical properties and corrosion resistance in marine environments. Figure 1

Stability of the ternary τ11-Al4Fe1.7Si intermetallic phase from experiment and Ab initio calculations

The Al-Fe-Si ternary system provides an opportunity for the design of new lightweight low cost alloys that have high melting temperature, superior strength, and excellent high-temperature corrosion and oxidation resistance. This system is exceptionally complex and exhibits up to 21 reported binary and ternary compounds. The intermetallic compound τ11-Al4Fe1.7Si is of particular interest due to its low theoretical density, promising mechanical properties, and low cost constituent elements. Knowledge of the exact composition range and thermal stability of this phase is crucial for further development. In this study, Al-Fe-Si alloys were fabricated and equilibrated at 800 and 950 °C. The composition range of τ11-Al4Fe1.7Si was analyzed using scanning electron microscopy with energy dispersive spectroscopy and X-ray diffraction to confirm the presence of the phase. Density functional theory calculations show that entropic contributions drive and stabilize the τ11-Al4Fe1.7Si phase. Based on experimental measurements, the composition range of τ11-Al4Fe1.7Si phase was determined to be Al-(24.3–25.5)Fe-(8.2–10.8)Si at% and Al-(24.6–25.2)Fe-(9.6–11.0)Si at% at 800 °C and 950 °C, respectively.

Rhenium in the Earth's Crust: A Comprehensive Review of Mineralogy, Geochemistry and Economic Significance

Rhenium, a unique and valuable metal with exceptional properties which is vital in various industrial applications, primarily found in conjunction with minerals like molybdenite and chalcopyrite, predominantly in western countries. Despite its rarity, understanding its geological distribution, geochemical characteristics, atomic structure, and behavior is essential. This paper provides a concise overview of the geological and geographical occurrences of rhenium, shedding light on its formation within both igneous and sedimentary environments. Additionally, it examines its economic significance, emphasizing its critical role in industries like aerospace, electronics, and petrochemicals due to its high-temperature resistance, corrosion resistance, and electrical conductivity enhancement. This comprehensive exploration highlights the importance of rhenium as a byproduct of mining, contributing significantly to technological advancements and innovation across various sectors.

Development of Fe–Cr–Si deposited layer manufactured by laser directed energy deposition process

In this study, the mechanical and corrosion characteristics of a corrosion-resistant layer made of stainless steel (STS) 316 L and Fe–Cr–Si alloy powder were investigated using laser-directed energy deposition (DED). In the STS 316 L deposited specimen, both the substrate and deposited layer were face-centred cubic (FCC). The deposited Fe–Cr–Si layer was clearly separated from the substrate because it was composed of body-centred cubic (BCC). Despite the phase differences, the surface of the Fe–Cr–Si-deposited layer showed a lower corrosion rate than that of the STS 316 L. All the deposited specimens exhibited typical high-temperature tensile behavior. However, the Fe–Cr–Si deposited layer at 600 °C showed a notable reduction in strength and increased elongation compared to the room temperature (RT) and 300 °C test results owing to the carbide concentration and phase transformation in the deposited layer. Because nuclear facilities mainly operate at temperatures below 600 °C, Fe–Cr–Si materials can also be used as nuclear piping coating materials. This study provides a mechanism for the high-temperature properties and corrosion resistance of the Fe–Cr–Si deposited layer and makes it competitive for application in fourth generation nuclear power systems.

Optimized Inconel 718 pressure vessel manufactured with laser powder bed fusion

Laser powder bed fusion (L-PBF) is one of the most novel additive manufacturing methods used for a wide range of industrial grade metallic materials. The process can produce end-use metal parts with desirable qualities and mechanical properties. L-PBF however, remains a complicated and expensive manufacturing method. Design for additive manufacturing (DfAM) is a key aspect leveraging the uptake of advantages and possibilities offered by AM in augmenting its competitiveness against conventional manufacturing (CM) methods. Inconel 718 (IN718) is a nickel-based superalloy boasting high temperature strength, good oxidation, and corrosion resistance at elevated temperatures. IN718 is commonly used for high performance applications, such as power and process industry parts, and gas turbine components. High inherent toughness, hardness, work hardening, and low thermal conductivity properties make the material difficult to manufacture through conventional machining methods. The layer-by-layer building of powder metals via L-PBF makes it possible to build different geometrical intricacy. The offered manufacturing flexibility for complex high-end metal structures for variety of applications makes L-PBF an alternative manufacturing method for high performance metals. This study investigates use of DfAM for a small-scale pressure vessel with predefined geometry, dimensions, design space and load condition. The aim is to introduce and exploit contemporary design optimization methods and their feasibility with AM. Structures, such as lattices and stress field driven geometries based on finite element analysis are investigated in this study. The designs are virtually tested under predefined pressure load of 50 bar. All four design options are manufactured on EOS M290 and IN718 powder. The result of the study shows the different optimizations decrease weight and improve material savings without compromising the linear load capacity. Optimized designs could also be made in such a way that it does not increase the manufacturing duration or add additional steps to it.

The effect of Y2O3 nanoparticle addition on the microstructure and high-temperature corrosion resistance of IN718 deposited by extreme high-speed laser cladding

The microstructural evolution and 700 °C high temperature corrosion resistance of Y2O3/IN718 composite coatings with different Y2O3 contents (0, 0.5, 1.0, 1.5, 2.0, and 3.0 wt%) fabricated by extreme high-speed laser cladding (EHLC) were investigated. The results showed that the addition of 1.0 wt% Y2O3 nanoparticles to IN718 could effectively reduce the internal porosity of the specimen, reduce crack initiation, refine the grain size, and improve the high-temperature corrosion resistance. The roughness Ra was reduced by 25.9 %, from 23.93 μm to 17.73 μm, and the average grain size was reduced by 39.5 %, from 47.32 μm to 28.62 μm. The result is due to the reduction in surface roughness and porosity of the specimen after the addition of Y2O3, which forms new nucleation sites at grain boundaries, resulting in surrounding lattice distortion and grain refinement.

Microstructure, high-temperature corrosion resistance and oxidation properties of (TiVZrCrAl)N high entropy nitride coatings with different N2/Ar ratios

The (TiVZrCrAl)N high-entropy nitride coatings were prepared on Zr-4 alloy substrates by reactive magnetron sputtering with different N2/Ar pressure ratios I values. The microstructure, nanohardness, high-temperature corrosion and steam oxidation resistance properties of the coatings were investigated. The results showed that the thickness of the coating first decreaseds and then increaseds with decreasing N2/Ar pressure ratio, but the hardness first increaseds and then decreaseds. All the coatings exhibited B1-NaCl structure. When I = 1/12, the (TiVZrCrAl)N coating had excellent high-temperature corrosion resistance and steam oxidation performance. The high-temperature steam oxidation mechanisms of the (TiVZrCrAl)N coatings were analyzed in detail.

Test and Numerical Simulation of the Axial Compressive Capacity of Concrete Columns Reinforced by Duplex Stainless Steel Bars

Stainless steel has the characteristics of oxidation resistance, high temperature resistance, corrosion resistance, high strength, and high yield ratio. The use of stainless steel bars can extend the life of a structure, reduce later maintenance costs, and reduce the whole life cycle cost of the structure. In this paper, nine concrete columns reinforced with duplex stainless steel (S2205) (DSSRC) and nine ordinary reinforced concrete columns (ORC) were poured with the diameter of steel bars as the parameter, and axial compression tests were carried out on these eighteen concrete columns. The failure mode of the concrete columns is analyzed, and the compressive performance indexes of the two kinds of concrete columns are compared. The results show that, compared with the ORC, the cracking load of DSSRC is increased by 33%, the ultimate load is increased by 30.7%, and the deformation performance of the DSSRC is also improved significantly. On the basis of the test, the finite element model of DSSRC was established with the help of ABAQUS software, and the obtained failure law was consistent with the test; the experimental value, the calculated value, and the numerical simulation value of the axial compression capacity were in good agreement, which verified the feasibility of the test and provided a theoretical basis for practical engineering applications.

Multiphysics analysis of thermal mechanical behavior and tritium migration in FeCrAl and Cr-coated Zircaloy cladding under PWR normal operating and transient conditions

Both Cr-coated Zircaloy and the FeCrAl alloy have garnered attention as potential substitutes for PWR cladding materials, due to their impressive qualities, such as robust high-temperature oxidation and corrosion resistance. However, FeCrAl alloy is found to accelerate the tritium permeation throughout the cladding, this heightened tritium permeation prompts easier release from the cladding into the coolant. Consequently, the assessment of material tritium permeation becomes a crucial aspect in fuel performance analysis. In this work, the multiphysics models of Cr-coated Zircaloy and FeCrAl cladding are reviewed firstly. Then the multiphysics models are implemented in CAMPUS code and the validation of tritium migration model is presented. Subsequently, the fuel performance under normal and accident (LOCA and RIA) conditions and the tritium migration in three types of claddings are simulated and discussed. The simulation results show that the utilization of FeCrAl cladding, instead of Zircaloy, results in an overall reduction in fuel temperature under both normal and LOCA conditions. Furthermore, both the Cr-coated Zircaloy and FeCrAl cladding are found to effectively delay the cladding failure time under LOCA condition. However, the total strain of FeCrAl cladding is found to be significantly higher than that of the Cr-coated Zircaloy cladding under RIA condition. And the Cr-coated Zircaloy is found to have better tritium resistance effect than FeCrAl cladding, which greatly reduces the coolant contamination treatment. Therefore, based on the combined consideration of fuel performance and tritium resistance, Cr-coated Zircaloy emerges as the preferred candidate cladding over the FeCrAl cladding.

Corrosion behavior of AFA steel in lead-bismuth eutectic alloy with saturated oxygen at 500°C

Alumina-forming Austenitic (AFA) steel is one of the candidate corrosion-resistant structural materials for lead-cooled fast reactors, exhibiting excellent high-temperature corrosion resistance. However, its corrosion mechanisms in lead-bismuth eutectic (LBE) environment at the design operating temperature of lead-cooled fast reactors have not been fully elucidated. In this study, AFA steel was immersed in static LBE with saturated oxygen at 500 °C for 3000 hours. The corrosion behavior of AFA samples was obtained by analyzing the morphology of corrosion cross section and the distribution of elements. The results showed that the AFA steel did not form an oxide film that could effectively resist LBE. Dissolution corrosion of the matrix becomes more severe the longer the exposure time. When the NiAl phase in the matrix is located at the surface, oxide nodules are generated. It has a double-layer oxide structure, which has better resistance to LBE corrosion. Nb undergoes oxidative rupture and has a tendency to detach from the surface of the substrate when it is located on the surface. Cracks occur on the surface of the matrix after 3000 hours of corrosion, and LBE penetrates into the matrix along the cracks.

Ablation behavior, microstructure, phase evolution and in situ ceramization mechanism of ZrC-LaB6 modified carbon fiber/phenolic resin ceramizable composite

Carbon fiber/phenolic resin composite (CF/Ph) has drawn great interest in thermal protection for its characteristics of high specific strength and easy fabrication. However, oxidation failure limits further application of CF/Ph in hostile environments. Herein, a novel carbon fiber/phenolic resin ceramizable composite modified with ZrC and LaB6 was reported. The synergistic effects between ZrC and LaB6 on high-temperature thermal degradation behavior, oxidative corrosion and ablation resistance were systematically studied based on thermal analysis and oxyacetylene ablation experiment of the resulting ceramizable composite as well as microstructure evolution, phase evolution, and thermodynamic calculation analysis of the ablated surface. The resulting ceramizable composite exhibited excellent oxidative corrosion and ablation resistance, with the residue yield at 1500 °C as high as 32.8 % and the linear ablation rate at 4.3 MW/m2 for 30 s as low as -0.00231 mm/s, respectively. Further, the ablation mechanisms were revealed. Dense B-C-O-Zr-La ceramic layers with a mosaic structure, which acted as efficient thermal protection barriers, were constructed in situ, and significantly reduced corrosion to carbon. Moreover, an intense endothermic effect during the carbothermal reaction between ZrO2, B2O3 and PyC led to an abnormally better insulation capacity.