Oxidation Protective Ability Research Articles

Self-healing YSZ-La-Mo-Si heterogeneous coating fabricated by plasma spraying to protect carbon/carbon composites from oxidation

Abstract To protect carbon/carbon (C/C) composites against oxidation, YSZ-La-Mo-Si (YSZ-LMS) heterogeneous coating was prepared by the plasma spraying using YSZ (Y2O3-stabilized ZrO2), MoSi2 and LaB6 as raw materials. Microstructure and surface chemistry of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Moreover, the thermogravimetric and isothermal oxidation results indicated that the YSZ-LMS coating revealed superior oxidation protective ability at elevated temperatures, which protected the C/C composites from oxidation for 50 h at 1773 K with a mass loss of 0.58%. The generation of SiO2, ZrSiO4, Y2SiO5 and La2O3 expanded the volume of solid phase and decreased the volatilization of SiO2, forming a denser Zr-Y-La-Si-O oxide glass layer. Such volume expansion promoted the formation of compressive stress within the coating at high temperature, which restrains the initiation and propagation of cracks and facilitates the oxidation resistance of the coatings for C/C composites. The corresponding high temperature oxidation activation energy of the coated C/C composites at 1573–1773 K is calculated to be 74.466 kJ mol−1.

Oxidation behavior and microstructural evolution of a slurry sintered Si-Mo coating on Mo alloy at 1650 °C

A high-temperature oxidation-protective Si-Mo coating on a molybdenum alloy substrate was prepared by slurry sintering method. The structure, composition, phase distribution, and oxidation behavior of the coating were studied. The results show that the coating has a double-layer microstructure with an outer MoSi2 layer and an inner Mo5Si3 layer. After oxidation, the coating is composed of a SiO2 outer layer, a MoSi2 middle layer, and a Mo5Si3 inner layer. The mechanism of the phase distribution and the oxidation kinetic equation were also studied. The oxidation rate Kp determined over 12h at 1650°C, was found to be 0.061mg2cm−4h−1. The excellent oxidation protective ability of the coating at ultra-high temperatures is attributable to the formation of self-healing SiO2 on the coating surface after the oxidation of MoSi2.

A novel gradient SiC-ZrB2-MoSi2 coating for SiC coated C/C composites by supersonic plasma spraying

A gradient SiC-ZrB2-MoSi2 (SZM) coating was successfully prepared on SiC coated C/C composites using supersonic plasma spraying, which is dense and defect-free. The design of gradient structure could avoid cracking at the interface between single MoSi2 coating and SiC coated C/C substrate. Result of X-ray diffraction shows that the residual tensile stress of SZM gradient coating (48.5MPa) is much lower than that of single MoSi2 coating (490.8MPa). Finite element analysis results show that the stress concentration significantly decreased at the interface of the as-sprayed gradient coating and the inner SiC coating. After thermal cycles between 900°C and room temperature for 20 times, penetrated cracks formed in the MoSi2 coating, but no obvious defect was observed in the SZM gradient coating. The brittle cracking of MoSi2 coating could be avoided by the design of SZM gradient structure, which attributes to the thermal stress release of the coating with gradient thermal expansion coefficient (CTE). The good thermal shock resistance of the gradient SZM coating in air was ascribed to the CTE gradient structure and the formation of oxygen insulation layer (Mo5Si3) beneath the outmost oxidation layer. Superior oxidation protective ability was also obtained by gradient SZM coating at 1450°C, which is due to the formation of Zircon and SiO2 phases to restrain the crack propagation and improve the oxidation resistance.

Microstructure and ablation behavior of double anti-oxidation protection for carbon-bonded carbon fiber composites

To improve the oxidation protective ability of carbon–bonded carbon fiber (CBCF) composites, double anti-oxidation protection for CBCF composites were prepared, i.e., ceramic coating-coated CBCF composites combined with ceramic-modified carbon fiber in CBCF matrix. The ablation behavior of modified CBCF composites was tested under an oxyacetylene flame at 1600°C for 300s and 800s, respectively. The results indicate that the ZrB2 in matrix and ZrB2-based ceramic coating can play double protection for CBCF composites during ablation process. The linear ablation rate of the sample after ablation for 300s and 800s were −1.1×10−4 and 8.38×10−4cms−1, respectively. The modified CBCF composites presented excellent oxidation resistance for 300s. With the increase of the oxidation time for 800s, the ZrB2-based ceramic coating experienced catastrophic damage. However, the carbon fiber surface only exhibited some circular pits instead of complete oxidation, implying that the ZrB2 on the carbon fiber surface improved the anti-oxidation and ablation resistance of CBCF composites.

Oxidation resistance of a SiC–ZrB2 coating prepared by a novel pack cementation on SiC-coated graphite

In this study, a functionally graded SiC layer was prepared on a graphite substrate by a pack cementation method with Si, C, and Al2O3 powders. Then a SiC–ZrB2 coating was developed by an in situ reaction method through a novel pack cementation technique at 1873 K with Zr, Si, and B4C powders to improve the oxidation protection ability of SiC-coated graphite. The phase compositions, microstructure, and element distribution of the coating were identified by X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy, respectively. The isothermal oxidation test of the coated samples was accomplished at 1773 K in air for 10 h. According to the results, a 550-μm thick graded C–SiC layer was detected at the graphite–coating interface and a SiC–ZrB2 coating was formed on the first coating. The SiC–ZrB2 coating could efficiently enhance oxidation resistance of graphite with a mass gain of +1.1 %, as compared with a −1.2 % mass loss of the first step coating. The excellent protection ability of SiC–ZrB2 coating could be ascribed to the high thermally stable ZrSiO4.

Preparation of a nanostructured SiC-ZrO2 coating to improve the oxidation resistance of graphite

A nanostructured SiC/SiC-ZrO2 coating was prepared on a graphite substrate by a two-step technique to improve the oxidation protection ability of graphite. The first step was to prepare a functionally graded SiC layer by a pack cementation process and the second one was to obtain a SiC-ZrO2 coating through a pack cementation technique at 1873K. The phase compositions and microstructure of the coating were characterized by X-ray diffraction and scanning electron microscopy. The isothermal oxidation test of the coated samples was performed at 1773K for 10h. A gradient C–SiC transition layer can be observed at the graphite-coating interface and a SiC-ZrO2 coating was formed. The SiC nanofibers with the diameter in the range of 30–160nm were observed on the coating. The SiC-ZrO2 coating could efficiently improve oxidation resistance of graphite with a weight loss of 11%, as compared with a 70% weight loss of the first step coating.

In-situ synthesis of SiC-ZrB2 coating by a novel pack cementation technique to protect graphite against oxidation

A multiphase coating was prepared on a graphite substrate by a two-step technique to enhance the oxidation protection ability of graphite. The first step was to obtain a functionally graded SiC layer and the second one was to develop a SiC-ZrB2 coating by an in-situ reaction method through a novel pack cementation technique with Zr, Si and B4C powders. The phase compositions, microstructure and element distribution of the coating were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The isothermal oxidation and thermal shock tests of the coated samples were performed at 1773 K in air for 10 h. A 650 μm thick graded CSiC layer was observed at the graphite-coating interface and a SiC-ZrB2 coating was formed on the first coating. The v coating could efficiently improve oxidation resistance of graphite with a mass gain of +1.7%, as compared with a −63.2% mass loss of the first step coating. The excellent protection ability SiC-ZrB2 coating could be attributed to the formation of the thermally stable phase ZrSiO4.

Supersonic plasma sprayed MoSi2–ZrB2 antioxidation coating for SiC–C/C composites

A dense and crack free MoSi2–ZrB2 coating was prepared on the SiC coated carbon/carbon (C/C) composites using a supersonic plasma spraying technique. The coated composites were characterised using scanning electron microscopy and X-ray diffraction. The analysis shows that the as prepared MoSi2–ZrB2 coating, with a thickness of ∼100 μm, combines well with the inner SiC coating. After oxidation at 1200°C for 72 h in air, the mass loss of MoSi2–ZrB2/SiC coated C/C is only 4.24 wt-%, which is significantly lower than that of MoSi2/SiC coated C/C (11.35 wt-%). The excellent oxidation protective ability of the MoSi2–ZrB2 coating is mainly attributed to ZrSiO4 produced by dispersive ZrO2 particles and SiO2 in the coating at high temperature.

Microstructure, surface emissivity and ablation resistance of multilayer coating for lightweight and porous carbon–bonded carbon fiber composites

To improve the oxidation protective ability of carbon–bonded carbon fiber (CBCF) composites. A multilayer coating containing ZrB2, MoSi2, SiCw and borosilicate glass was prepared on ZrB2-modified carbon–bonded carbon fiber composites (CBCFs/ZrB2) by a trace oxygen sintering method and a pre-oxidation process. The microstructure, surface emissivity and ablation resistance of the multilayer coating were studied. The coating containing dense surface layer and porous inner layer was obtained. The total emissivity of the coating in the wavelength range of 6–16 μm at 300, 500 and 800 °C was 0.72, 0.73 and 0.78, respectively. The prepared multilayer coating exhibited excellent ablation resistance for 1000 s under simulated atmospheric re-entry conditions by high frequency plasma wind tunnel test with a heat flux of 131.8 W/cm2 and stagnation pressure of 2.7 KPa.

Comparison of the oxidation behaviors of SiC coatings on C/C composites prepared by pack cementation and chemical vapor deposition

Abstract SiC coatings were prepared on carbon/carbon composites by pack cementation (PC) and chemical vapor deposition (CVD). The PC coating was composed of hexagonal platelets of α-SiC, while the CVD coating consisted of spherical particles of β-SiC. Their oxidation behaviors were investigated at 1173 K, 1473 K and 1773 K. Compared with the CVD-SiC coating, bubbles appeared in the PC-SiC coating at lower oxidation temperature and the oxide layer was thicker, which might be ascribed to the formation of aluminosilicate glass in the PC-SiC coating. With the increasing temperature, the oxidation behavior of the PC-SiC coating transformed from linear to parabolic with dramatically improved oxidation resistance, which might be attributed to the decreased viscosity of SiO 2 -rich glass and the good healing effect for cracks. The oxidation protective ability of the CVD-SiC coating was worse than that of the PC-SiC coating, because of the higher viscosity of pure SiO 2 glass and the inferior interface adhesion between the coating and the substrate.

Effect of filler on the oxidation protective ability of MoSi2 coating for Mo substrate by halide activated pack cementation

To protect molybdenum against oxidation, MoSi2 coatings were prepared by halide activated pack cementation, and the effect of filler cases, Al2O3, SiO2 and SiC, on the microstructure and oxidation resistance of MoSi2 coating was studied. The deposited coatings using Al2O3 and SiO2 filler presented a double-layer microstructure of the outer MoSi2 and the inner Mo5Si3 layer. Whereas, the coating deposited in SiC-filler case displayed only one MoSi2 layer. Lower inert ability of SiC filler in the pack and the possible reaction with molybdenum are responsible for the mono-layer structure. The coating prepared with SiO2 filler presented rough morphologies and more residual SiO2 fillers embedded on the coating surface than the Al2O3 or SiC filler cases. Attributed to the residual embedded fillers, all three kinds of deposited coatings exhibited perfect anti-oxidation property at 773K and could effectively protect molybdenum substrate against pest oxidation. As for high temperature oxidation of 1473K in air, the coating corresponding to SiO2 filler displayed the best oxidation protective ability with only 0.05% mass change after 110h oxidation. The protective SiO2 layer formed on the surface of MoSi2 coating at high temperature is responsible for the good oxidation resistance of the coating.

Design of an inlaid interface structure to improve the oxidation protective ability of SiC–MoSi2–ZrB2 coating for C/C composites

To improve the oxidation protective ability of SiC–MoSi2–ZrB2 coating for carbon/carbon (C/C) composites, pre-oxidation treatment and pack cementation were applied to construct a buffer interface layer between C/C substrate and SiC–MoSi2–ZrB2 coating. The tensile strength increased from 2.29 to 3.35MPa after pre-oxidation treatment, and the mass loss was only 1.91% after oxidation at 1500°C for 30h. Compared with the coated C/C composites without pre-oxidation treatment, after 18 thermal cycles from 1500°C and room temperature, the mass loss was decreased by 30.6%. The improvements of oxidation resistance and mechanical property are primarily attributed to the formation of inlaid interface between the C/C substrate and SiC–MoSi2–ZrB2 coating.

Oxidation protective ZrB2–SiC coatings with ferrocene addition on SiC coated graphite

In order to further improve the oxidation protective ability of (ZrB2–SiC)/SiC coated graphite, ferrocene was introduced into the outer ZrB2–SiC coatings during pack cementation process. The ferrocene addition increased the porosity of the outer ZrB2–SiC coatings, which was favorable to thermal shock resistance of (ZrB2–SiC)/SiC coated specimens. The ZrB2–SiC coating with 3wt% ferrocene (ZS50-3f) has optimum oxidation protective ability. Its weight retention after 15 thermal shock cycles between 1500°C and room temperature was 96. 2%. The weight loss of ZS50-3f was only 0.2% after 19h oxidation at 1500°C.

Effect of Nb on the Microstructure, Mechanical Properties, Corrosion Behavior, and Cytotoxicity of Ti-Nb Alloys.

In this paper, the effects of Nb addition (5–20 wt %) on the microstructure, mechanical properties, corrosion behavior, and cytotoxicity of Ti-Nb alloys were investigated with the aim of understanding the relationship between phase/microstructure and various properties of Ti-xNb alloys. Phase/microstructure was analyzed using X-ray diffraction (XRD), SEM, and TEM. The results indicated that the Ti-xNb alloys (x = 10, 15, and 20 wt %) were mainly composed of α + β phases with precipitation of the isothermal ω phase. The volume percentage of the ω phase increased with increasing Nb content. We also investigated the effects of the alloying element Nb on the mechanical properties (including Vickers hardness and elastic modulus), oxidation protection ability, and corrosion behavior of Ti-xNb binary alloys. The mechanical properties and corrosion behavior of Ti-xNb alloys were found to be sensitive to Nb content. These experimental results indicated that the addition of Nb contributed to the hardening of cp-Ti and to the improvement of its oxidation resistance. Electrochemical experiments showed that the Ti-xNb alloys exhibited superior corrosion resistance to that of cp-Ti. The cytotoxicities of the Ti-xNb alloys were similar to that of pure titanium.

Effect of molybdenum on the microstructure, mechanical properties and corrosion behavior of Ti alloys

Abstract In order to study the effect of Mo on the microstructure, mechanical properties and corrosion behavior of commercially pure titanium (cp-Ti), Ti-xMo (x = 5, 10, 15, and 20 wt.%) alloys were investigated. The phase and microstructures were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy. The results indicated that the Ti-5Mo alloy was mainly composed of α′ phase with a small fraction of α″ phase. The Ti-10Mo was dominated by orthorhombic α″. The Ti-15Mo alloy was mainly composed of α″ phase with a small fraction of β phase. The volume percentage of the β phase increased with increasing Mo content. The Ti-20Mo alloy was mainly composed of β phase. We also investigated the effect of alloying with Mo on the Vickers hardness and corrosion behavior of Ti-xMo alloys. The addition of Mo not only caused hardening of cp-Ti but also improved its oxidation protective ability. Electrochemical results showed that the Ti-xMo alloys exhibited improved corrosion resistance over cp-Ti.

Effect of zirconium content on the microstructure, physical properties and corrosion behavior of Ti alloys

A series of Ti–xZr alloys with Zr contents ranging from 5 to 20wt% was prepared and the effects of Zr addition on the microstructure, physical properties, and corrosion behavior of Ti alloys were investigated. The phase and microstructures were characterized using X-ray diffractometry (XRD), optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The Ti–xZr alloys exhibited α-Ti structure at Zr content of 20wt% or below. Commercially pure titanium (cp-Ti) was used as a control. We also investigated the effects of alloying element Zr on the mechanical property, oxidation protection ability, and corrosion behavior of Ti–xZr binary alloys. The physical properties and corrosion behavior of Ti–xZr alloys were sensitive to the Zr content. The addition of Zr did contribute to the hardening of cp-Ti due to solid-solution strengthening of α-Ti. Ti–xZr alloys containing up to 10wt% Zr resulted in good oxidation resistance, while Ti–xZr alloys with above 10wt% Zr demonstrated higher oxidation weight gain than cp-Ti. Electrochemical experiments showed that the Ti–xZr alloys exhibited better corrosion resistance compared to that of cp-Ti.

Oxidation and corrosion behaviour of CoNiCrAlY bond coats

CoNiCrAlY coating for protection against oxidation at elevated temperature was prepared on the surface of the 316L by high velocity oxygen fuel (HVOF) and cold gas dynamic spray (CGDS) techniques. The phase composition, microstructure and oxidation resistance of the coating were investigated at 900°C in air. According to the results, the CGDS coating shows low oxide growth rate as a result of low porosity, oxide content and high hardness. CGDS coating provided excellent oxidation protective ability at 900°C in air, whereas HVOF coating showed high levels of visible defects, oxide content, spinel type oxide and high oxide growth rate. Electrochemical study shows that the HVOF process provided better corrosion resistance as compared to CGDS process.

Oxidation protective TaB2–SiC gradient coating to protect SiC–Si coated carbon/carbon composites against oxidation

To improve the oxidation protection ability of the TaB2-based coatings, an oxidation protective TaB2–SiC gradient coating was prepared by in situ reaction method on SiC–Si coated C/C composites, which consists of a TaB2–SiC–Si middle buffer layer and a TaB2–SiC outer layer. The TaB2–SiC/TaB2–SiC–Si/SiC–Si coating could protect the C/C substrate from oxidation at 1773K for 1360h. During oxidation, a protective silicate glass layer consisted of an upper Ta–Si–O glass layer and a lower SiO2 glass layer would gradually formed on the surface of the coated C/C, which is responsible for the excellent oxidation resistance of the coated C/C.

Preparation of oxidation protective ZrB2–SiC coating by in-situ reaction method on SiC-coated carbon/carbon composites

In order to reduce production cost and effectively improve the oxidation protection ability of the ultra-high temperature ceramics (UHTCs) ZrB2–SiC coating for the SiC-coated carbon/carbon (C/C) composites, a ZrB2–SiC outer coating was prepared by in-situ reaction method on SiC-coated C/C. Instead of costly ZrB2 powder, inexpensive B2O3, ZrO2, Si and C powders were used as raw materials to prepare the outer ZrB2–SiC coating with well-developed microstructures. The ZrB2 and SiC phases in the outer coating were synchronously obtained during the preparation of the coating. The isothermal oxidation behavior of the coated C/C composites at 1773K was investigated. The double-layer ZrB2–SiC/SiC coating could prevent C/C composites from oxidation at 1773K for 550h. During oxidation, a kind of ‘embedding structure’ containing ZrO2 and ZrSiO4 will be formed on the surface of the compound silicate glass layer, which is responsible for the excellent oxidation resistance of the ZrB2–SiC outer coating.

ZrB2–SiC gradient oxidation protective coating for carbon/carbon composites

To improve the oxidation protective ability of carbon/carbon composites, ZrB2–SiC gradient coating was prepared on the surface of C/C composites by an in-situ reaction method. The ZrB2–SiC gradient coating consisted of an inner ZrB2–SiC layer and an outer ZrB2–SiC–Si coating. The phase composition and microstructures of the multiphase coating were characterized by XRD, EDS and SEM. Results showed that the inner coating is mainly composed of ZrB2 and SiC, while the outer multiphase coating is composed of ZrB2, SiC and Si. The multilayer coating is about 200μm in thickness, which has no penetration crack or big hole. The oxidation behavior of the coated C/C composites at 1773K in air was investigated. Results show that the gradient ZrB2–SiC oxidation protective coating could protect C/C from oxidation for 207h with only (4.56±1.2)×10−3g/cm2 weight loss, owing to the compound silicate glass layer with the existence of thermally stable phase ZrSiO4.