Oxidation and creep behavior of textured Ti2AlC and Ti3AlC2

The oxidation and creep behaviors of textured Ti₂AlC and Ti₃AlC₂ ceramics were characterized. The oxidation behavior of the two materials, which was studied in air at temperatures ranging from1000 to 1300 °C, was observed to be anisotropic and the materials exhibited a better oxidation resistance along a direction transverse to the c-axis. The correlation between the overall parabolic rate constant and oxidation temperature of both textured materials was characterized, providing new insights into the oxidation kinetics. The results indicate that the texturing has a negligible influence on the creep behavior in the assessed temperature range of 1000?1200 °C in air, for the applied stresses ranging from 40 to 80 MPa. In this stress regime, the creep behavior of textured Ti₂AlC and Ti₃AlC₂ appears to be controlled by grain boundary sliding. This behavior can be rationalized based on a model for superplastic deformation, indicating pure-shear motion under stationary conditions accommodated by lattice or grain-boundary diffusion.     

Gradient HfB2-SiC multilayer oxidation resistant coating for C/C composites

The gradient HfB₂ modified SiC coating was prepared on the surface of SiC-coated C/C composites by in-situ synthesis. Anti-oxidation behaviors of the coated C/C samples at 1773, 1873 and 1973?K were investigated. The results show that the gradient HfB₂ modified SiC coatings possess excellent oxidation resistance, which can protect C/C substrates from oxidation for 800, 305 and 100?h at 1773, 1873 and 1973?K, respectively. In addition, with the oxidation temperature increasing, the evaporation of the Hf-Si-O glass layer and the active oxidation of SiC were accelerated, which is the reason for the worst oxidation resistance of the sample at 1973?K among the three temperatures.     

Oxidation resistance up to 2600 K under air plasma of (Zr/Hf)B2 composites containing 20 vol% AlN for hypersonic applications

Fully-dense ZrB₂ and HfB₂ composites were elaborated by Spark Plasma Sintering with 20 vol% AlN to replace SiC or TaSi₂ with the objective to improve the oxidation resistance at very high temperature. This study follows the ones on (Zr/Hf)B₂-SiC and (Zr/Hf)B₂-TaSi₂ systems carried out in the same conditions (Pellegrini et al. 2022a; Pellegrini et al. 2022b). Oxidation behavior of several samples in air plasma conditions, at 1000 Pa total pressure and from 1980 K up to 2600 K, was studied using the MESOX facility implemented at the focus of a solar furnace. The mass variation of the samples during oxidation duration of 300 s on a temperature plateau was measured. The characterization of the oxidized samples was done using SEM, EDS, XRD, XPS and Raman. A better oxidation resistance was obtained with these new compositions as, for example, no mass loss up to 2600 K was measured for the ZrB₂-20 vol% AlN composite due to the protective effect of the aluminum-rich phase formed by oxidation and confirmed by the cross-section analysis.     

Oxidation resistance and thermal shock properties of self-healing SiCN/borosilicate glass-B4C-Al2O3 coatings for C/C aircraft brake materials

SiCN/borosilicate glass-B₄C-Al₂O₃ coating was deposited on carbon fiber-reinforced carbon matrix (C/C) brake materials to protect them from oxidation. Microstructural analysis revealed that the coating was dense and uniform. Fabricated coating showed excellent oxidation resistance and significantly low weight losses after oxidation in dry air for 10?h than SiCN/borosilicate glass-B₄C coated samples (ca. 0.12%, 0.51%, and 0.29% at 700, 800, and 900?°C, respectively). B₄C is believed to react with the oxygen diffused into the coating to produce B₂O₃, which could heal cracks of the coating and improve its self-sealing ability and oxidation resistance. The Al₂O₃ present in the outer glass layer is believed to inhibit volatilization of B₂O₃, thereby reducing weight losses in air. Fabricated coating also possessed excellent oxidation resistance under fresh and sea water conditions, with cracks and pores generated during oxidization process being effectively healed. Prepared coating materials showed excellent thermal shock resistances after 50 thermal shock cycles, with weight losses being as low as 0.23%.     

Oxidation behavior of Ti3SiC2 powder synthesized by using biochar,Si and Ti

Biochar was proposed as a novel carbon source for synthesizing Ti₃SiC₂ powder with high purity by a simple pressureless sintering at 1673 K, and Ti₃SiC₂ grains exhibited the typical nanolayered structure. The oxidation behavior of Ti₃SiC₂ powder showed the parabolic law during isothermal oxidation from 1273 K to 1473 K. Dense and continuous oxidation layer consisting of mixed TiO₂ and SiO₂ was formed rapidly on the surface of Ti₃SiC₂ particles as a diffusion barrier, which effectively retarded the inward diffusion of oxygen, conferring good oxidation resistance of the powder.     

A MoSi2-SiOC-Si3N4/SiC anti-oxidation coating for C/C composites prepared at relatively low temperature

In this study, SiC coating for C/C composites was prepared by pack cementation method at 1773 K, and MoSi₂-SiOC-Si₃N₄ as an outer coating was successfully fabricated on the SiC coated samples by slurry method at 1273 K. The microstructure and phase composition of the coatings were analyzed. Results showed that a porous β-SiC inner coating and a crack-free MoSi₂-SiOC-Si₃N₄ coating are formed. Effect of Si₃N₄ content on the oxidation resistance of the coated C/C composites at 1773 K in air was also investigated. The weight loss curves revealed that introducing the appropriate proportion of Si₃N₄ could improve the oxidation resistance of coating. The MoSi₂-SiOC/SiC coated C/C sample had an accelerated weight loss after oxidation in air for 20 h. However, the coating containing 45% Si₃N₄ could protect C/C composition from oxidation for 100 h with a minute weight loss of 0.63%.     

Pursuing enhanced oxidation resistance of ZrB2 ceramics by SiC and WC co-doping

The oxidative degradation of ZrB₂ ceramics is the main challenge for its extensive application under high temperature condition. Here, we report an effective method for co-doping suitable compounds into ZrB₂ in order to significantly improve its anti-oxidation performance. The incorporation of SiC and WC into ZrB₂ matrix is achieved using spark plasma sintering (SPS) at 1800?°C. The oxidation behavior of ZrB₂-based ceramics is investigated in the temperature range of 1000?°C–1600?°C. The oxidation resistance of single SiC-doped ZrB₂ ceramics is improved due to the formation of silica layer on the surface of the ceramics. As for the WC-doped ZrB₂, a dense ZrO₂ layer is formed which enhances the oxidation resistance. Notably, the SiC and WC co-doped ZrB₂ ceramics with relative density of almost 100% exhibit the lowest oxidation weight gain in the process of oxidation treatment. Consequently, the co-doped ZrB₂ ceramics have the highest oxidation resistance among all the samples.     

High temperature oxidation behavior of ZrB2-SiC added MoSi2 ceramics

In this paper, MoSi₂, MoSi₂-20?vol% (ZrB₂-20?vol% SiC) and MoSi₂-40?vol% (ZrB₂-20?vol% SiC) ceramics were prepared using pressureless sintering. The oxidation behaviors of these MoSi₂-(ZrB₂-SiC) ceramics were investigated at 1600?°C for different soaking time of 60, 180 and 300?min, respectively. The oxidation behaviors of the MoSi₂-(ZrB₂-SiC) ceramics were studied through weight change test, oxide layer thickness measurement, and microstructure analysis. Further investigation of the oxidation behaviors of the MoSi₂-(ZrB₂-SiC) ceramics was conducted at a higher temperature of 1800?°C for 10?min. The microstructure evolution of the ceramics was also analyzed. It was finally found that the oxidation resistance of MoSi₂ was improved by adding ZrB₂-SiC additives, and the MoSi₂-20?vol% (ZrB₂-20?vol% SiC) ceramic exhibited the optimal oxidation resistance behavior at elevated temperatures. From this study, it is believe that it can give some fundamental understanding and promote the engineering application of MoSi₂-based ceramics at high temperatures.     

Oxidation resistance of Zr- and Hf-diboride composites containing SiC in air plasma up to 2600 K for aerospace applications

Microstructure-controlled and fully-dense ZrB₂ and HfB₂ composites were elaborated by Spark Plasma Sintering with two different amounts of SiC (20 and 30 vol%) added to improve their oxidation resistance using optimized sintering parameters. Oxidation of several samples in air plasma conditions, at 1000 Pa total pressure and from 1800 K up to 2600 K, was carried out. The mass variation of samples during oxidation duration of 300 s on a temperature plateau was followed. A four-step oxidation mechanism, identified by four singular mass variation behaviors depending on the oxidation temperature ranges, was proposed and detailed. The total normal emissivity was measured on pre-oxidized samples and high values around 0.90 were obtained from 1300 to 1900 K due to the presence of the oxide layer formed in air plasma conditions and this high emissivity is interesting for aerospace applications.     

Mechanical and oxidation behavior of textured Ti2AlC and Ti3AlC2 MAX phase materials

Highly textured Ti₂AlC and Ti₃AlC₂ ceramics were successfully fabricated by a two-step fabrication process, and the Lotgering orientation factors for {00l} planes of textured Ti₂AlC and Ti₃AlC₂ were calculated as 0.82 and 0.71, respectively. The effect of texturing was evaluated in terms of elastic modulus and hardness by macro- and micro-indentation. Moreover, the oxidation behavior of the MAX phases was investigated at 1300 °C in air, revealing that the oxidation was markedly anisotropic, where the textured side surface exhibited much better oxidation resistance, resulting from the rapid diffusion of Al element within its basal planes to form a protective Al₂O₃ scale on it. Furthermore, Ti₂AlC had larger difference regarding oxidation behavior between the top and side surface than Ti₃AlC₂, correlated to its higher Al ratio, leading to higher texturing degree and more diffusion pathways to the outer surface to produce an Al₂O₃ layer already at the initial oxidation stage.     

Enhancement of oxidation resistance at 1000–1400 °C of low carbon Al2O3–C refractories with pre-synthesized SiCnw/Al2O3

The oxidation resistance of low carbon Al₂O₃–C refractories with the addition of SiC_nw/Al₂O₃ composite powders and the enhancement mechanisms were investigated. The oxidation resistance was evaluated by oxidation index (O.I.) and oxidation rate constant (k). The enhancement mechanisms of SiC_nw/Al₂O₃ on oxidation resistance were analyzed based on the phases and microstructures. The results showed that the SiC_nw/Al₂O₃ can improve the oxidation resistance of Al₂O₃–C refractories, the O.I. and k of A6 (6 wt% SiC_nw/Al₂O₃ addition) were 26.0% and 34.5% lower than those of reference sample A0, respectively. The oxidation resistance of refractories was improved in a range of 1000–1400 °C due to the introduction of SiC_nw/Al₂O₃. The enhancement mechanisms can be explained that SiC_nw is more susceptible to be oxidized due to its high specific surface area, which expanded the action temperature range of other antioxidants and itself. The mullite and dense protective layer generated during oxidation is also beneficial to impede the diffusion of O₂.     

Oxidation behavior of medium-entropy (Y1/3Yb1/3Lu1/3)2O3 modified SiC ceramic at 1700 °C: Experimental and theoretical study

The medium-entropy oxide (Y_1/3Yb_1/3Lu_1/3)₂O₃ with a body-centered cubic structure was successfully synthesized by solid-state reaction process, and then it was introduced into SiC ceramic to study its effect on the oxidation behavior of SiC ceramic at 1700 °C. The (Y_1/3Yb_1/3Lu_1/3)₂O₃-modified SiC ceramic exhibited better oxidation resistance than its individual oxides (Y₂O₃, Yb₂O₃, and Lu₂O₃) modified SiC ceramic. The experimental and calculated results all indicate that the rare-earth atoms had the tendency to diffuse into the SiO₂ structure and occupy the interstitial positions within SiO₂ structure. The introduction of medium-entropy oxide (Y_1/3Yb_1/3Lu_1/3)₂O₃ reduced the initial oxidation rate of the ceramic samples (1?3 h), and enhanced the stability of SiO₂ structure, thus resulting in a better oxidation resistance at 1700 °C.     

Microstructure and oxidation resistance of a multiphase Mo-Si-B ceramic coating on Mo substrates deposited by a plasma transferred arc process

To improve the oxidation resistance of a Mo substrate, a multiphase Mo-Si-B ceramic coating was deposited using a plasma transferred arc (PTA) process. The phase constituents, microstructure, and oxidation resistance of the coating were investigated. The results show that the microstructure of the Mo-Si-B coating is characterised by rod-like Mo₅SiB₂ dendrites, a lamellar structure of Mo₃Si/Mo₅SiB₂ binary eutectics, and cellular Mo₅Si₃ dendrites. Compared with the Mo substrate, the Mo-Si-B coating exhibits a significant improvement in the oxidation resistance at 1300?°C in an air atmosphere. This is mainly owing to a dense and continuous borosilicate layer formed on the surface of the Mo-Si-B coating, which acts as an oxygen diffusion barrier. Moreover, it is observed that the Mo₅SiB₂ dendrites exhibit a higher oxidation resistance compared to Mo₃Si/Mo₅SiB₂ eutectics during high-temperature oxidation exposure. The oxidation behaviour is discussed based on the oxidation kinetics and a cross-sectional microstructure analysis of the oxidised Mo-Si-B specimen.     

Oxidation of HfB2–SiC ceramics under static and dynamic conditions

The kinetics and the mechanism of oxidation of ceramics based on HfB₂ and SiC, manufactured by elemental self-propagating high-temperature synthesis followed by hot pressing were investigated. The synthesis product contained HfC_(x) and HfO₂ as impurity phases. Depending on the ratio between the main components, the samples were characterized by high structural and chemical homogeneity, porosity of 3–6 vol%, hardness up to 29 GPa, bending strength of 500–600 MPa, fracture toughness of 5.6–8.9 MPa × m^1/2, and thermal conductivity of 86.0–89.7 W/(m × K). The oxidation was performed under static conditions at 1650 °C and upon exposure to a high-enthalpy gas flow. A dense layer consisting of HfO₂/HfSiO₄ grains formed on the surface of the ceramics during both oxidation conditions; the space between the grains was filled with amorphous SiO₂–B₂O₃. The best heat resistance was observed for the ceramics with 16 wt% SiC for static conditions and 8 wt% SiC for gas-dynamic conditions.     

A gradient composite coating to protect SiC-coated C/C composites against oxidation at mid and high temperature for long-life service

To improve the oxidation resistance of carbon/carbon (C/C) composites at mid and high temperature, a gradient composite coating was designed and prepared on SiC-coated C/C composites by in situ formed-SiO₂ densifying the porous SiC-ZrSi₂ pre-coating. SiO₂ gradient distribution was conducive to inhibiting the cracking of the coating. A dual-layer structure with the outer dense layer and the inner microporous layer was formed in the coating during densifying. The dense layer had excellent oxygen diffusion resistance and the microporous layer alleviated CTE mismatch between SiC inner coating and dense layer. Moreover, ZrSiO₄ particles inhibited crack propagation and stabilized SiO₂ glass. Therefore, the coating can protect the C/C composites from oxidation at 1473 K, 1573 K and 1773 K for 810 h, 815 h and 901 h, respectively. The coated samples underwent 30 thermal cycles between room temperature and 1773 K without mass loss, exhibiting good thermal shock resistance.     

Effect of TiO2 on sinterability and physical properties of pressureless sintered Ti3AlC2 ceramics

TiO₂ was selected as effective sintering aid for pressureless sintering of Ti₃AlC₂ ceramics in this study. The addition of only 5?wt% TiO₂ largely promotes the densification and nearly dense Ti₃AlC₂ ceramic was obtained by pressureless sintering at 1500?°C. Significant strengthening and toughening effects were observed with the addition of TiO₂. High Vickers hardness, flexural strength and fracture toughness of 3.22?GPa, 298?MPa and 6.2?MPa?m^?1/2, respectively, were achieved in specimen pressureless sintered with 10?wt% TiO₂. Additionally, the addition of 5?wt% TiO₂ had no deleterious effect on the excellent oxidation resistance of Ti₃AlC₂ ceramic under 1200?°C water vapor atmosphere, while addition of 10?wt% TiO₂ accelerates the oxidation rate by two orders of degree.     

Self-generating oxidation protective high-temperature glass-ceramic coatings for Cf/C‐SiC‐TiC‐TaC UHTC matrix composites

The ablation/oxidation resistance of a carbon fibre (C_f)/carbon matrix (C)-SiC-TiC-TaC ceramic matrix composite (CMC) produced by melt infiltration of alloy into a C_f/C preform and tested in severely oxidising conditions was quantitatively determined and discussed. An oxyacetylene flame shot of 7.5 s (4 MW/m² nominal heat flux), as well as oxidising conditions imposed by a radiant furnace in air at 1873 K up to 480 s were the selected testing conditions. Detailed post-test microstructure investigations of the oxidised/ablated infiltrated CMC samples, compared to unprotected CMCs tested in nominally identical conditions, enabled to establish an increase in ablation/oxidation resistance of one order of magnitude. The occurrence of a self-generating protective high-temperature glass-ceramic, disclosed by microstructure analyses, played a substantial role for that performance jump during oxidation/ablation. The C_f/C-SiC-TiC-TaC composite herein tested can be a valuable candidate for uses in severe aerospace applications (propulsion and hypersonic flight).     

Microstructure and anti-oxidation properties of multi-composition ceramic coatings for carbon/carbon composites

To protect carbon/carbon (C/C) composites from oxidation at elevated temperature, an effective WSi₂-CrSi₂-Si ceramic coating was deposited on the surface of SiC coated C/C composites by a simple and low-cost slurry method. The microstructures of the double-layer coatings were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy analyses. The coating exhibited excellent oxidation resistance and thermal shock resistance. It could protect C/C composites from oxidation in air at 1773 K for 300 h with only 0.1 wt.% mass gain and endure the thermal shock for 30 cycles between 1773 K and room temperature. The excellent anti-oxidation ability of the double-layer WSi₂-CrSi₂-Si/SiC coating is mainly attributed to the dense structure of the coating and the formation of stable vitreous composition including SiO₂ and Cr₂O₃ produced during oxidation.     

Oxidation protection of graphite materials by single-phase ultra-high temperature boride modified monolayer Si-SiC coating

To improve the oxidation resistance of Si-SiC coating, single-phase ultra-high temperature boride (ZrB₂ or TaB₂) modified Si-SiC coating was designed and established on graphite substrates by combination of dipping and reactive infiltration process. ZrB₂ or TaB₂ phase was introduced in Si-SiC coating by directly mixing raw materials and phenol formaldehyde resin in the slurry, and then the ZrB₂-SiC-Si and TaB₂-SiC-Si coatings were fabricated on the graphite samples by dipping-curing, pyrolysis, and siliconizing. The crystalline phases and microstructure of the as-obtained multiphase coatings were investigated by X-ray diffraction analysis and scanning electron microscopy. The interrupted oxidation tests from room-temperature to 1500?°C were conducted to assess the anti-oxidation property of the prepared coatings. After 1200?h of oxidation at 1500?°C in air (30 times thermal cycles), the mass losses of the graphite substrates coated with ZrB₂-SiC-Si and TaB₂-SiC-Si coatings were 0.086% and 0.537%, respectively, and the high-temperature stability of the modified coatings was greatly improved compared to the Si-SiC coating. The excellent anti-oxidation performances of the compound coatings were attributed to the compact structure of the coatings and the formation of compound oxide layers covering on the surfaces. The compound Zr-Si-O and Ta-Si-O films possessed low oxygen diffusion rate and appropriate viscosity, which can provide appreciable oxidation protection for the internal coatings, thus obtaining the excellent oxidation and spallation resistance property.     

Effect of in situ SiC and MoSi2 phases on the oxidation behavior of HfB2-based composites

Monolithic HfB₂ and HfB₂-15vol%SiC-15vol%MoSi₂ composite samples were oxidized by a conventional electric furnace at 1700 °C for 5 h. Microstructural and phase analysis of the oxidized samples were performed by X-ray diffraction (XRD) analysis and field emission scanning electron microscope (FESEM) equipped with energy-dispersive spectroscopy (EDS). Besides, for analyzing the oxidation mechanism of the samples, thermodynamic calculations were also accomplished by HSC software. The changes in weight and thickness of the oxide scale were measured and the oxide growth rate of the oxidized samples was subsequently calculated. The results showed that HfB₂-15vol%SiC-15vol%MoSi₂ composite was much more resisted than that monolithic HfB₂ due to the formation of a thin Si-rich glass layer on the surface of the composite sample. By acting to fill the porosities between HfO₂ grains, Si-based glass phase enhanced the oxidation resistance of HfB₂-15vol%SiC-15vol%MoSi₂ composite. Conversely, the oxidized monolithic HfB₂ had only a thick porous oxide layer (HfO₂) which led to considerably lower oxidation resistance. On the other side, three layers containing HfO₂ and Si-based glass phases were formed on the oxidized HfB₂-15vol%SiC-15vol%MoSi₂ composite. Moreover, no porosities and no porous layers were also detected on the oxidized composite sample. Consequently, HfB₂-15vol%SiC-15vol%MoSi₂ composite had a parabolic behavior owing to its diffusion-controlled oxidation under the isothermal oxidation process.