Oxidation Protective Ability Research Articles

LaB6 modified MoSi2 ceramic coating of SiC coated carbon/carbon composites for oxidation resistance at high temperature

To protect carbon/carbon (C/C) composites from oxidation at high temperature, a LaB6 modified MoSi2 outer coating was produced on SiC coated C/C composites by pack cementation technique. The phase composition, microstructure and oxidation protective ability of the LaB6–MoSi2/SiC ceramic coatings were investigated. Results show that the LaB6–MoSi2/SiC coating possesses dense and crack-free microstructure and can effectively protect C/C composites from oxidation for 750h at 1773K in air. The weight loss of the as-received coated C/C composites is only 0.108% after oxidation process.

Anti-oxidation properties of ZrB2 modified silicon-based multilayer coating for carbon/carbon composites at high temperatures

To improve the anti-oxidation ability of silicon-based coating for carbon/carbon (C/C) composites at high temperatures, a ZrB2 modified silicon-based multilayer oxidation protective coating was prepared by pack cementation. The phase composition, microstructure and oxidation resistance at 1773, 1873 and 1953 K in air were investigated. The prepared coating exhibits dense structure and good oxidation protective ability. Due to the formation of stable ZrSiO4–SiO2 compound, the coating can effectively protect C/C composites from oxidation at 1773 K for more than 550 h. The anti-oxidation performance decreases with the increase of oxidation temperature. The mass loss of coated sample is 2.44% after oxidation at 1953 K for 50 h, which is attributed to the decomposition of ZrSiO4 and the volatilization of SiO2 protection layer.

SiC–MoSi2/ZrO2–MoSi2 coating to protect C/C composites against oxidation

To improve the oxidation resistance of carbon/carbon (C/C) composites in air at high temperatures, a SiC–MoSi2/ZrO2–MoSi2 coating was prepared on the surface of C/C composites by pack cementation and slurry method. The microstructures and phase compositions of the coated C/C composites were analyzed by scanning electron microscopy and X-ray diffraction, respectively. The result shows that the SiC–MoSi2/ZrO2–MoSi2 coating is dense and crack-free with a thickness of 250–300 μm. The preparation and the high temperature oxidation property of the coated composites were investigated. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 260 h at 1773 K in air. The excellent anti-oxidation performance of the coating is considered to come from the formation of ZrSiO4, which improves the stability of the coating at high temperatures.

Oxidation protection of C/C composites with in situ bamboo-shaped SiC nanowire-toughened Si–Cr coating

An in situ bamboo-shaped SiC nanowire-toughened Si–Cr coating was prepared on the carbon/carbon composites by pack cementation and heat treatment with ferrocene as the catalyst. The microstructures and oxidation behavior of the coating were investigated. Results showed that the coating had a dense microstructure, without the penetrating microcracks, which was primarily attributed to the unusual toughening effect of the bamboo-shaped nanowires resulting from the mechanical interlocking between the nodes and the matrix. The coating exhibited good oxidation protection ability at high temperature. The weight gain of the samples was 0.79% after isothermal oxidation at 1500°C for 185h.

Multi-layer CVD-SiC/MoSi2–CrSi2–Si/B-modified SiC oxidation protective coating for carbon/carbon composites

To further improve the oxidation resistance of coating for carbon/carbon (C/C) composites, a multi-layer CVD-SiC/MoSi2–CrSi2–Si/B-modified SiC coating was prepared on the surface of C/C composites by pack cementation and chemical vapour deposition method, respectively. The microstructures, oxidation and thermal shock resistance of the coating were studied. The influence of B content in pack powder on the microstructure and oxidation resistance of B-modified SiC coating was also investigated. The results show that the B-modified SiC coating prepared with 10 wt.% B exhibited the best oxidation protection ability for C/C composites at 1173 K. The multi-layer coatings could protect the C/C composites at 1173 K for 30 h and 1873 K for 200 h, and endure 30 thermal cycles between 1873 K and room temperatures. The oxidation resistance and thermal shock resistance is mainly attributed to their dense structure and self-sealing property.

Si–Mo–Cr coating for C/SiC coated carbon/carbon composites against oxidation

Si–Mo–Cr oxidation protective coating has been prepared on the surface of C/SiC coated carbon/carbon (C/C) composites by pack cementation technique. The phase composition and microstructure of the as prepared coatings were characterised by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersion spectrum (EDS) analyses. The oxidation behaviour of the coated C/C specimens was also investigated at 1500°C in air. The results show that the as prepared coating is mainly composed of SiC, MoSi2, CrSi2 and Si. The coating characterised by excellent oxidation resistance and thermal shock resistance can effectively protect C/C composites from oxidation for 186 h at 1500°C in air and endure the thermal cycle between 1500°C and room temperature for nine times, while the corresponding weight loss is only 0·33%. The excellent oxidation protection ability of the coating is primarily attributed to the formation of a compound glass layer, including SiO2 and Cr2O3.

A multilayer MoSi2–SiC–B coating to protect SiC-coated carbon/carbon composites against oxidation

To protect carbon/carbon (C/C) composites against oxidation, a multilayer MoSi2–SiC–B coating was prepared on the SiC-coated C/C composites by a simple and low-cost slurry method. The phase, microstructure and element distribution of the as-received coating were analyzed using X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The as-received coating could effectively protect C/C composites against oxidation at 850 °C in air for 100 h without mass loss, which exhibits better oxidation protective ability than the multilayer MoSi2–SiC coating prepared by the same method. At intermediate temperature (850 °C), the excellent oxidation protective ability of the coating is mainly attributed to the formation of the molten B2O3 for sealing the microcracks and preventing oxygen from attacking the C/C substrate.

Oxidation resistant Si–Mo–Al coating for C/SiC coated carbon/carbon composites at high temperature

A Si–Mo–Al coating for protecting carbon/carbon (C/C) composites against oxidation at elevated temperature was prepared on the surface of the C/SiC coated C/C composites by slurry method. The phase composition, microstructure and oxidation resistance of the coating at 1773 K in air were investigated. The results show that the as prepared coating was mainly composed of SiC, MoSi2, Mo(Si,Al)2 and Si. The coating provided excellent oxidation protective ability at 1773 K in air and can effectively protect the C/C composites from oxidation for 150 h. The failure of the coating at 1873 K in air is attributed to the spalling of the glass layer during the oxidation tests.

Effect of SiC Nanowires on the Mechanical and Oxidation Protective Ability of SiC Coating for C/C Composites

To protect carbon/carbon (C/C) composites against oxidation, a SiC nanowire‐toughened SiC coating with homogeneously dispersed nanowires within the coating was successfully prepared on C/C composites by a simple and low cost two‐step technique of chemical vapor deposition and pack cementation. The SiC nanowires effectively increased the mechanical properties of the coating, decreased the size of the defects in the coating, and improved the oxidation protection effectiveness of the coating. The results showed that, after introducing the SiC nanowires, the hardness, elastic modulus, and fracture toughness of the SiC coating were increased by 5%, 19%, and 48%, respectively. The mass loss of the coated C/C samples was reduced from 8.10% to 5.21% after thermogravimetric analysis in air from 873 to 1773 K. Moreover, the mass loss of the SiC nanowire‐toughened SiC coated sample was only 14.33% and 2.68% after isothermal oxidation at 1173 K for 39 h and 1773 K for 44 h in air, whereas the mass loss of the pure SiC coated sample was up to 16.12% and 7.00% after isothermal oxidation at 1173 K for 15 h and 1773 K for 20 h in air.

A SiC–Si–ZrB2 multiphase oxidation protective ceramic coating for SiC-coated carbon/carbon composites

In order to improve the oxidation protective ability of SiC-coated carbon/carbon (C/C) composites, a SiC–Si–ZrB2 multiphase ceramic coating was prepared on the surface of SiC-coated C/C composite by the process of pack cementation. The microstructures of the coating were characterized using X-ray diffraction and scanning electron microscopy. The coating was found to be composed of SiC, Si and ZrB2. The oxidation resistance of the coated specimens was investigated at 1773K. The results show that the SiC–Si–ZrB2 can protect C/C against oxidation at 1773K for more than 386h. The excellent oxidation protective performance is attributed to the integrity and stability of SiO2 glass improved by the formation of ZrSiO4 phase during oxidation. The coated specimens were given thermal shocks between 1773K and room temperature for 20 times. After thermal shocks, the residual flexural strength of the coated C/C composites was decreased by 16.3%.

Influence of SiC nanowires on the properties of SiC coating for C/C composites between room temperature and 1500 °C

To prevent carbon/carbon (C/C) composites from oxidation between room temperature and 1500 °C, a dense SiC nanowire-toughened SiC oxidation resistant coating was prepared by a two-step technique composed of chemical vapor deposition and pack cementation. SiC nanowires could effectively baffle the propagation of the microcracks and avoid the formation of the through-thickness microcracks in the original coating. The results indicated that, after introducing SiC nanowires, the coefficient of thermal expansion of the coating was decreased between 100 and 1500 °C, and the oxidation protective ability for the coated C/C composites was improved largely between room temperature and 1500 °C.

Oxidation Protective C/SiC/Si-SiC Multilayer Coating for Carbon/Carbon Composites Applying at 1873 K

A C/SiC/Si-SiC multilayer coating for protecting carbon/carbon (C/C) composites against oxidation was prepared by slurry and pack cementation. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis showed that the inner coating obtained from the slurry and pack cementation was a C/SiC gradient layer acting as bonding layer, and the exterior coating formed in the second pack cementation was a Si-SiC double phase coating. Oxidation tests at 1873 K in air showed that the coating exhibited excellent oxidation protective ability and thermal shock resistance. The coating could effectively protect C/C composites from oxidation at 1873 K in air for 170 h and undergo the thermal cycling between 1873 K and room temperature for 8 cycles. The weight loss of the coated C/C composites is due to the formation of cracks and holes in the coating and the volatilization of SiO2 glass at high temperature.

A modified dual-layer SiC oxidation protective coating for carbon/carbon composites prepared by one-step pack cementation

To improve the oxidation resistance of SiC coating produced by pack cementation for carbon/carbon composites, a modified SiC coating has been produced by one-step pack cementation by adding ferrocene in pack compositions. The as-received coating exhibited a dual-layer dense structure, and oxidation protective ability of SiC coating could be improved by introducing ferrocene. The modified coating could protect C/C composites from oxidation for more than 100 h at 1673 K in air. The weight loss of the coated C/C composites was considered to arise from deflection of penetrating cracks formed in outer layer from inner layer to C/C matrix.

OXIDATION RESISTANT (Mo,W)Si2 COATING FOR SiC-COATED CARBON/CARBON COMPOSITES BY IN SITU FORMATION METHOD

In order to protect carbon/carbon ( C / C ) composites against oxidation, a ( Mo , W ) Si 2 coating was prepared on the surface of SiC -coated C / C composites by a simple in situ information method using Si , Mo and W as starting materials. The microstructures and oxidation protective ability of the as-received coating were investigated. The results show that the ( Mo , W ) Si 2 outer layer coating containing free Si has a good bonding with SiC inner layer. The as-prepared SiC /( Mo , W ) Si 2 coating can protect C / C composites from oxidation in air at 1773 K for 252 h with a weight gain of 1.56 wt.%. The excellent oxidation resistant property of the double-layer coating is attributed to its dense microstructure and the formation of the stable glassy SiO 2 film on the ( Mo , W ) Si 2 coating surface during its exposure to air at high temperatures.

A Si–SiC oxidation protective coating for carbon/carbon composites prepared by a two-step pack cementation

To prevent carbon/carbon (C/C) composites from oxidation, a Si–SiC coating has been prepared by a two-step pack cementation technique. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis show that the coating obtained by the first step pack cementation is a porous β-SiC structure, and a dense structure consisting α-SiC, β-SiC and Si is obtained after heat-treatment by the second step pack cementation. By energy dispersive spectroscopy (EDS) analysis, a gradient C–SiC transition layer can be formed at the C/C-coating interface. The as-received coating has excellent oxidation protection ability and can protect C/C composites from oxidation for 166 h at 1773 K in air. The weigh loss of the coated C/C is due to the formation of bubble holes on the coating surface and through-coating cracks in the coating.

Oxidation protection of carbon/carbon composites with SiC/indialite coating for intermediate temperatures

In order to improve the oxidation resistance of carbon/carbon composites at intermediate temperatures, a novel double-layer SiC/indialite coating was prepared by a simple and low-cost method. The internal SiC transition layer was prepared by pack cementation and the external indialite glass–ceramic coating was produced by in situ crystallization of ternary MgO–Al 2O 3–SiO 2 glass. The microstructures and morphologies of coating were determined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Oxidation resistance of the as-coated C/C composites was evaluated in ambient air at temperature from 800 °C to 1200 °C. Nearly neglectable mass loss was measured after 100 h isothermal oxidation test, indicating that SiC/indialite coating possesses excellent oxidation protection ability. The as-coated samples have a good thermal shock resistance and no obvious damage was found in the coating even after suffered more than 11 thermal cycles between test temperature and room temperature. The oxidation protection mechanism of this coating was also discussed.

High Performance SiC Oxidation Protective Coating with ZrO2 Particle Dispersion for Carbon/Carbon Composites

High performance SiC oxidation protective coating with ZrO2 particle dispersion for C/C composites was prepared by slurry and pack cementation. Isothermal oxidation tests at 1873 K in air showed that the as-prepared coating could effectively protect C/C composites from oxidation for 100 h. The excellent oxidation protective ability can be attributed to the introduction of ZrO2 particles in the SiC coating, which can baffle the enlargement of cracks and suppress the generation of the thermal stress.

Microstructure and oxidation protective ability of MoSi2-SiC-Si coating toughened with SiC whiskers for carbon/carbon composites

To prevent carbon/carbon (C/C) composites from oxidation at high temperatures, a SiC whisker (SiCw) toughened MoSi2–SiC–Si coating was prepared on the C/C surface by a two step technique of slurry and pack cementation. Scanning electron microscopy (SEM) analysis shows that, with the content of SiCw increasing, the dimensions and frequency of cracks in the coating decrease obviously. At the same time, the thickness and compact degree of the coating reduce with the increase of the SiCw content. Oxidation tests show that, as the content of SiCw is 10 wt-%, the coating possesses a better anti-oxidation property, and the weight loss of the coated sample is only 0˙8% after oxidation at 1773 K for 200 h. The weight loss of the as-coated C/C composites is primarily due to the reaction of the C/C matrix and oxygen diffusing through the penetration cracks and holes in the coating.

Investigation of the Multi-coating for High Temperature and Long Life Oxidation Protection of C/C Composites

A SiC-WSi_2/MoSi_2 multilayer oxidation protective coating for carbon/carbon(C/C)com- posites was prepared by pack cementation.Effects of the total content of W and Mo on the microstruc- ture and high temperature anti-oxidation property of the multi-coating were studied by XRD,SEM, EDS and isothermal oxidation test.The results show that with the total content of W and Mo increas- ing in the pack powders,the as-received multi-coating thickness first increases and then decreases.The multi-coating with 10.0at%(W and Mo)has a thicker,denser structure and higher content of WSi_2 and MoSi_2 than those with 0at%,8.4at% and 13.1at%(W and Mo).A stable and dense glassy SiO_2 film can be formed on the coating surface with 10.0at%(W and Mo)during the oxidation test.The coated specimen with 10.0at%(W and Mo)has no weight loss after oxidation in air for 315h at 1500℃and no cracks after thermal cycling between 1500℃and room temperature for 18 times,which implies that the multi-coating has excellent oxidation protective ability and thermal shock resistance.

A multilayer coating of dense SiC alternated with porous Si–Mo for the oxidation protection of carbon/carbon silicon carbide composites

In order to improve the oxidation behavior of carbon/carbon silicide carbide composites prepared by liquid silicon infiltration of carbon/carbon porous preforms, a multilayer coating of dense SiC alternated with porous Si–Mo was prepared by chemical vapor deposition combined with slurry painting. Oxidation test showed that weight loss of the coated sample was only 0.25% after 150 h oxidation in air at 1673 K. And the coated sample gained weight in the course of 46 cycles of thermal shock test between 1673 K and 373 K. The coating remained intact during the two kinds of tests and no obvious failure was found. The excellent oxidation protective ability and thermal shock resistance of the SiC/Si–Mo coating can be attributed to the alternated structure.