Oxidation-protective and mechanical properties of SiC nanowire-toughened Si–Mo–Cr composite coating for C/C composites

Oxidation-protective SiC nanowire-toughened Si–Mo–Cr composite coating prepared on the carbon/carbon (C/C) composites by chemical vapor deposition and pack cementation was investigated in this study. After incorporating SiC nanowires, the hardness, elastic modulus and fracture toughness of the composite coating were increased by 6.12%, 20.89% and 35.78%, respectively, due to the toughening and strengthening mechanisms including nanowire pullout, nanowire bridging, microcrack deflection and good interaction between nanowire/matrix interface. Thermogravimetric analysis revealed that the maximum weight loss of the coated C/C samples was decreased from 5.87% to 3.93% by incorporating SiC nanowires from room temperature to 1500 °C.     

Oxidation and ablation resistance of ZrB2–SiC–Si/B-modified SiC coating for carbon/carbon composites

ZrB₂–SiC–Si/B-modified SiC coating was prepared on the surface of carbon/carbon (C/C) composites by two-step pack cementation. The coating could efficiently provide protection for C/C composites from oxidation and ablation. The improvement of oxidation resistance was attributed to the self-sealing property of the multilayer coating. A dense glassy oxide layer could afford the high temperature up to 2573 K and efficiently protect C/C composites from ablation.     

Oxidation protection and behavior of C/C composites with an in situ SiC nanowire–SiC–Si/SiC–Si coating

An in situ SiC nanowire–SiC–Si/SiC–Si protective coating was prepared on C/C composites by pack cementation and heat treatment. SiC nanowires suppressed the cracking of the coating by nanowire pullout and bridging and microcrack deflection, avoiding the oxidation of C/C composites. Results showed that the oxidation of the samples was a continuous weight gain process. The oxidation behavior was fitted to the parabolic–linear model and the final weight gain was 1.8% during thermogravimetric analysis from 50 to 1600 °C. The oxidation behavior was fitted to the parabolic model and the final weight gain was 0.51% during isothermal oxidation at 800 °C.     

Phase transformation and properties of quasicrystal particles/Al matrix composites

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Effect of SiC/ZrC ratio on the mechanical and ablation properties of C/C–SiC–ZrC composites

The effect of SiC/ZrC weight ratio on the mechanical and ablation properties of carbon/carbon composites modified by SiC nanowires reinforced SiC–ZrC ceramics (C/C–SiC–ZrC) was studied. Results showed that C/C–SiC–ZrC composites with a SiC/ZrC ratio of 1:1.5 exhibited good mechanical and ablation properties. The flexural strength and modulus were 201 ± 20 MPa and 18 ± 1 GPa, respectively. After ablation for 120 s, the linear and the mass ablation rate were 0.012 mm/s and 0.0019 g/s. The good performance is attributed to a higher density, the reinforcing effect of SiC nanowires and the proper SiC/ZrC ratio.     

C/SiC/MoSi2–SiC–Si multilayer coating for oxidation protection of carbon/carbon composites

C/SiC/MoSi₂–SiC–Si oxidation protective multilayer coating for carbon/carbon (C/C) composites was prepared by pack cementation and slurry method. The microstructure, element distribution and phase composition of the as-received coating were analyzed by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the multilayer coating was composed of MoSi₂, SiC and Si. It could effectively protect C/C composites against oxidation for 200 h with the mass loss of 3.25% at 1873 K in static air. The mass loss of the coated C/C composites results from the volatilization of SiO₂ and the formation of cracks and bubble holes in the coating.     

Oxidation protection of SiC-coated C/C composites by SiC nanowire-toughened CrSi2–SiC–Si coating

Oxidation protective SiC nanowire-toughened CrSi₂–SiC–Si coating was prepared on SiC-coated carbon/carbon composites by chemical vapor deposition and pack cementation. SiC nanowires in the coating suppressed the cracking of the coating via various toughening mechanisms including nanowire pullout, microcrack bridging by nanowire and microcrack deflection, resulting in a good oxidation inhibition for the coated samples. The results showed that the maximal weight loss of the coated samples was only 2.55% in thermogravimetric analysis from room temperature to 1500 °C, and the weight loss of the coated samples was only 1.24% after isothermal oxidation at 1500 °C for 316 h.     

Microstructure and oxidation resistance of Si–Mo–B coating for C/SiC coated carbon/carbon composites

A self-sealing Si–Mo–B oxidation resistance coating was prepared on C/SiC coated carbon/carbon (C/C) composites by slurry and high temperature treatment method. The oxidation resistance of the coating increases at 1173 K and first increases then decreases at 1873 K with the increase of B content from 0 to 20 wt.%. The C/SiC/gradient Si–Mo–B multilayer coating can protect C/C composite from oxidation for 100 h at 1173 K and 125 h at 1873 K. The good oxidation resistance of the coating in broad temperature range could be attributed to its good self-sealing property.     

Mechanical properties and fractograph of SiC foam-SiC particles-Al composites

A new type of hybrid SiC foam-SiC particles-Al composites used as an electronic packaging substrate material were fabricated by squeeze casting technique. The mechanical properties and the fracture mechanism of the hybrid composites were investigated. The influence of SiC particles and foam hybrid reinforcement on the behavior of the composites was studied. The results show that the interface bonding in the hybrid composites is good for the composites with the unique double interpenetrating structure. The compressive strength of the hybrid composite reinforced by the SiC with the volume fraction of 59.9% is 680 MPa, which is higher than that of any other composites with the same volume fraction of SiC particles reinforcement.     

Effect of coating thickness on microstructures and mechanical properties of C/Cu/Al composites

The different copper coatings with thickness varying from 0.3 lain to 1.5 lain were deposited on carbon fibers using either eleetroless plating or electroplating method. The coated fibers were chopped and composites were fabricated with melting aluminum at 700 ℃. The effect of the copper layer on the microstructure in the system was discussed. The results show that the copper layer has fully reacted with aluminum matrix, and the intermetallic compound CuAl2 forms through SEM observation and XRD, EDX analysis. The results of tensile tests indicate that composites fabricated using carbon fibers with 0.7-1.1 lain copper coating perform best and the composites turn to more brittle as the thickness of copper coating increases. The fracture surface observation exhibits good interface bonding and ductility of the matrix alloy when the thickness of copper coating is about 0.7-1.1 μm.     

Oxidation behavior of C/C composites with SiC/ZrSiO4–SiO2 coating

A SiC/ZrSiO₄–SiO₂ (SZS) coating was successfully fabricated on the carbon/carbon (C/C) composites by pack cementation, slurry painting and sintering to improve the anti-oxidation property and thermal shock resistance. The anti-oxidation properties under different oxygen partial pressures (OPP) and thermal shock resistance of the SZS coating were investigated. The results show that the SZS coated sample under low OPP, corresponding to the ambient air, during isothermal oxidation was 0.54% in mass gain after 111 h oxidation at 1500 °C and less than 0.03% in mass loss after 50 h oxidation in high OPP, corresponding to the air flow rate of 36 L/h. Additionally, the residual compressive strengths (RCS) of the SZS coated samples after oxidation for 50 h in high OPP and 80 h in low OPP remain about 70% and 72.5% of those of original C/C samples, respectively. Moreover, the mass loss of SZS coated samples subjected to the thermal cycle from 1500 °C in high OPP to boiling water for 30 times was merely 1.61%.     

Influences of gas flow rates on melting of particles of HVOF sprayed CoCrW coating and coating properties

This paper discussed influences of flow rates of O2, C3H8, and compressed air on the melting degree of particles during HVOF (high velocity oxy-fuel) sprayed CoCrW coating. The O2 flow rate has the maximal effect on the melting of particles, the C3H8 floW rate has the second, and the compressed air flow rate has the minimal effect. The bond strength of the HVOF sprayed CoCrW coating is over 54 MPa. The porosity ratio of the HVOF sprayed CoCrW coating after optimi-zation of gas flow rates is less than 2%. The average microhardness of the coating is up to HV0.1 545. The oxidation amount per unit area of the HVOF sprayed CoCrW coating increases with the holding time increasing at 800℃. In the same way,the oxidation amount of the coating increases as the temperature increases. Particularly, the oxidation of the coating drastically increases over 850℃.     

Preparation and properties of nickel–zirconia nanocomposite coatings

The possibility of preparing and properties (surface morphology, microhardness, corrosion resistance) of nickel–zirconia composite coatings electrodeposited from nickel acetate solutions containing a dispersed phase in the form of a conventional polydisperse crystalline micropowder and a sol with nanoscale particles have been discussed. The effect of the particle size and concentration and the electrolysis conditions on the properties of the coatings has been determined.     

Fatigue properties of Al–Si casting alloy with cold sprayed Al/SiC coating

Abstract

The fatigue properties of Al–Si alloy cold sprayed Al and Al–SiC composite coatings have been studied. The specimens coated with composites reinforced with a large volume (25%) of fine SiC particles exhibited improved adhesion strength at the interface due to crater formation, and cyclic fatigue lives at room temperature more than three times those of uncoated specimens. In high temperature low cycle fatigue tests at 250°C, the pure Al coatings showed longer fatigue lives than the Al–SiC composite coatings, which is attributed to an increment in ductility at the surface retarding fatigue crack initiation.     

Microstructure and mechanical properties of ZrB2–SiC composites prepared by gelcasting and pressureless sintering

ZrB₂–SiC ceramic composites were prepared through water-based gelcasting and pressureless sintering. Effects of the pressureless sintering temperature (1500–2000 °C), heating rate (5–15 °C/min) and soaking time (0.5–2 h) on the relative density, microstructure and mechanical properties of the ZrB₂–SiC composites were investigated in detail. A sintering temperature of 2000 °C, a heating rate of 5 °C/min and a soaking time of 2 h were found to be the optimal pressureless sintering procedure. The relative density, flexural strength and fracture toughness of the ZrB₂–SiC composite prepared under the optimum condition were 97.8%, 403.1 ± 27.8 MPa and 4.05 ± 0.42 MPa·m^1/2, respectively.     

Microstructure and mechanical properties of TiB2–SiC ceramic composites by Reactive Hot Pressing

TiB₂–SiC ceramic composites with different contents of Ni as additive were prepared by the Reactive Hot Pressing (RHP) process at 1700 °C under a pressure of 32 MPa for 30 min. For comparison, a monolithic TiB₂ ceramic and TiB₂–SiC ceramic composite were also fabricated under the identical temperature, pressure and holding time by the Hot Pressing (HP) process. The effects of the fabrication process and Ni on the microstructure and mechanical properties of the composites were investigated. About 8 vol.% of elongated TiB₂ grains with an aspect ratio of 3–6 and a diameter of 0.5–1 μm were produced in the composite prepared by the RHP process. The improvement of the fracture toughness was attributed to the toughening and strengthening effects of SiC particles and the elongated TiB₂ grains such as crack deflection. The TiB₂–SiC–5 wt.% Ni ceramic composite had the optimum mechanical properties with a flexural strength of 858 ± 87 MPa, fracture toughness of 8.6 ± 0.54 MPa·m^1/2 and hardness of 20.2 ± 0.94GPa. The good mechanical properties were ascribed to the relatively fine and homogeneous microstructure and the strengthening effect of Ni. Ni inhibited the anisotropic growth of TiB₂.     

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 185 h.     

Residual stresses and magnetic properties of alumina–nickel nanocomposites

Nanocomposites were produced by infiltration of alumina preforms with a nickel-nitrate solution, followed by reduction and sintering. Multiple infiltration and reduction steps resulted in nanocomposites with varying Ni particle concentrations. The strain in the nickel particles was evaluated from X-ray diffraction, and correlated with the magnetic properties of the nanocomposites.     

Ablation in different heat fluxes of C/C composites modified by ZrB2–ZrC and ZrB2–ZrC–SiC particles

Carbon/carbon composites modified by ZrB₂–ZrC–SiC particles (C/C–Z–SiC), C/C–Z and C/C were ablated by oxyacetylene torch using two different heat fluxes to investigate the effect of doped ceramic particles. Results indicated that C/C–Z–SiC had the best ablation property in heat flux of 2.38 MW/m² whereas their ablation rates increased fastest when heat flux rising from 2.38 to 4.18 MW/m². C/C composites had the poorest ablation property in the lower heat flux and their ablation rates increased slowest. Thermal mismatch of Z, SiC and C and evaporation of SiO₂ induced the various ablation behavior.     

Mechanical properties and creep resistance of Mg-Li composites reinforced by MgO/Mg_2Si particles

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