Reinforced Silicon Carbide Ceramic Matrix Research Articles

Measurement and evaluation of fiber bundle surface of long fiber reinforced woven composites

Long fiber reinforced woven composites (LFRWCs) are being applied to many growing fields because of their excellent properties; however, owing to their anisotropy and inhomogeneity, traditional surface measurements and evaluation methods appropriate for isotropic materials are no longer suitable to LFRWC, thus causing many difficulties in terms of their wide industrial applications. Based on this fact, a multi-scale surface evaluation system is proposed according to the LFRWC structure. This paper is mainly focused on the first scale evaluation-fiber bundle scale. First, the reasons why 2D rather than 3D measurements and evaluations should be adopted at this scale are described, and four indexes, namely, Raave, Rqave, Rskave and Rkuave are proposed to evaluate the surface roughness, damage type, and degree of damage. A method is proposed to determine the maximum sampling step (MaxSS) to ensure that the measurement data are undistorted. As a demonstration, the validity of the method is checked through the testing of a carbon fiber reinforced silicon carbide ceramic matrix composite (Cf/SiC).

Grinding characteristics and removal mechanisms of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites

The grinding performance of unidirectional carbon fibre reinforced silicon carbide ceramic matrix composites (Cf/SiC) was investigated in this paper. The effects of the fibre orientation and grinding depth on the surface integrity and grinding forces and an understanding of the grinding mechanisms are the primary concerns of this article. This problem is relatively unexplored; therefore, the main value of this research is to improve the processing quality and reduce the production cost. In the Cf/SiC grinding procedure, cracks, fibre wear, interfacial debonding, fibre pull-out and outcrop can be detected on the ground surface. The grinding depth and deflection angle have been shown to have a notable influence on the surface quality in different datum planes. A suitable grinding depth and deflection angle should be carefully chosen to achieve good surface quality in different machined surfaces. Specifically, the surface quality decreases and the grinding forces increase with increasing grinding depth. In addition, greater grinding surface quality is observed at β = 90°, i.e., γ = 0°, but poorer machined surfaces are obtained at α = 0°, i.e., γ = 90°. The surface topography, roughness and grinding forces of unidirectional Cf/SiC could be forecasted according to the analysis conclusions. This research is expected to offer guidelines for increasing the machining quality of Cf/SiC.

Friction and wear characteristics of carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composite and zirconia (ZrO2) ceramic under dry condition

Abstract To investigate the tribological properties of Cf/SiC composite with different fiber orientations and ZrO2 with ground and polished surfaces, running-in tests under dry condition were conducted in a pin-to-disc apparatus. The results show that ground surfaces of ZrO2 ceramic sliding against each fiber orientation exhibit more excellent tribological properties than the polished ones. The average coefficient of friction (COF), pin and disc wear rate decrease about 53.7%–63.3%, 59.4%–80.6% and 69.7%–88.5% respectively among all fiber orientations. Specifically, 90deg fiber orientation sliding against ground ZrO2 surface exhibits the best excellent tribological property. Wear mechanism and the reason leading to the results are researched. The work firstly proposes ground surface scratch is a kind of surface texture which hugely affects material's tribological performance.

Influence of thermal shock and environment temperature on mechanical properties of C/SiC/GH783 joint brazed with Cu-Ti + Mo

The carbon reinforced silicon carbide ceramic matrix composites (C/SiC) were brazed to Fe-Ni-Co superalloy (GH783) with Cu-Ti + Mo solder under vacuum at 1000 °C. The influence of thermal shock (in air at 800 °C) and environment temperature on mechanical properties of the joint were investigated. The joint between C/SiC composites and GH783 was dense, crack free, and was comprised of reaction layer, stress relief layer, plastoelastic layer, and diffusion layer. Thermal shock damage and oxidative damage were both existing after the thermal shock. Therefore, the flexural strength of the joint decreased dramatically with the increase of thermal shock times. After 5, 10, and 15 times of thermal shock, the flexural strength of the joint decreased to 42.9, 22.7, and 9.7% of the initial strength, respectively. The flexural strength of the joint decreased dramatically with the increase of environment temperature because of the thermal mismatch between C/SiC and the interface reaction layer. The flexural strength of the joint at 600, 800, and 900 °C was decreased to 60, 39, and 29% of that at room temperature, respectively.

Hot corrosion of RE 2 SiO 5 with different cation substitution under calcium–magnesium–aluminosilicate attack

Rare earth (RE) silicates have been applied as advanced environmental barrier coatings (EBCs) to protect silicon carbide fibers reinforced silicon carbide ceramic matrix from water vapor and molten salt corrosion in engines. This process, however, is limited by volcanic ash corrosion as assessment of ash-induced corrosion is anecdotal and quantitative data are insufficient. In this account, the corrosion behavior of RE monosilicates (RE2SiO5, RE = Y, Lu, Yb, Eu, Gd, and La) by calcium–magnesium–aluminosilicate (CMAS), with similar composition as volcanic ash, was comprehensively investigated. Results indicated that RE2SiO5 could react with CMAS at 1200 °C at the interface, where the products crystallized in CMAS glass. RE2Si2O7 was formed by the reaction between RE2SiO5 and silica (SiO2) in CMAS, which was followed by corrosion of RE2Si2O7 by CMAS. RE2SiO5 with Type B structure showed better resistance toward CMAS than RE2SiO5 with Type A structure. Moreover, RE2SiO5 with larger radii of RE3+ cations led to easy formation of oxyapatite phase; however, RE2SiO5 with smaller radii of RE3+ cations easily formed garnet phase. Besides, smaller radii RE3+ cations induced slower reactions. These findings can contribute to identifying, preventing, and minimizing the damage to matrix components with EBCs caused by volcanic ash.

Study on surface/subsurface breakage in ultrasonic assisted grinding of C/SiC composites

Continuous carbon fiber reinforced silicon carbide ceramic matrix composites (C/SiC) are promising materials in aerospace and space optical fields due to their excellent properties. However, poor machining quality resulted from surface/subsurface breakage is hard to meet precision requirements of some components. With an objective to study surface/subsurface breakage formation mechanism and improve machining quality of C/SiC composites, ultrasonic assisted grinding (UAG) and conventional grinding (CG) tests with a defined diamond grain distribution brazed grinding wheel were conducted. The surface/subsurface breakage types and formation mechanism were studied by comparative analysis of grinding force, micro-morphology of grinding surface/subsurface, and ground surface roughness. The results showed that main breakage types of different angle fibers in ground surface were lamellar brittle fracture and pit group originating from fracture and pullout of fibers, while breakage types of different angles fibers in ground surface were brittle fracture. Compared to CG, these breakages were reduced by UAG in varying degrees because it can reduce grinding force that determined fiber breakage. Consequently, because of the lower fiber breakages, the ground surface roughness Sa obtained by UAG was lower than CG and the maximum reduction was 12%.

Oxidation and thermal shock resistant properties of Si/Yb2SiO5/NdMgAl11O19 coating deposited on Cf/SiC composites

Yb2SiO5 and NdMgAl11O19 (NMA) powders were synthesized by solid-state reactions. Triple-layer ceramic coatings based on the Si bond layer, Yb2SiO5 interlayer and NMA top layer were prepared on carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites by atmospheric plasma spraying (APS). The coatings were subjected to thermal shock tests at 1300°C, 1400°C and 1450°C, respectively. The results showed that the Si/Yb2SiO5/NMA coating significantly improved the oxidation resistance of Cf/SiC composites. The failure mechanism of the Si/Yb2SiO5/NMA coating was closely related to the thermal shock temperature. Below 1400°C, the failure of the coating was connected with the mismatch of thermal expansion coefficient (CTE) between the coating and substrate, the reaction between Yb2SiO5 and NMA at the interface, the poor sintering property of Yb2SiO5 and NMA and the substrate itself. Above 1450°C, the coating failed after only one thermal shock cycle due to the temperature higher than the melting point of the silicon.

Strengthening/toughening of 2D C/SiC composites by coating

SiC and SiCw/SiC coatings were prepared on two-dimensional carbon fiber reinforced silicon carbide ceramic matrix composites (2D C/SiC), and strengthening/toughening of the composite by the coatings was investigated. After coating, the density of the C/SiC composites was increased effectively and the mechanical properties were improved significantly. Compared with SiC coating, SiCw/SiC coating showed the more significant effect on strength/toughness of the composites. Coatings had two effects: surface strengthening and matrix strengthening. The latter was the dominant effect. The surface strengthening can increase the crack initiation stress, while the matrix strengthening can enhance the crack propagation resistance. The former effect increased the strength and the latter effect increased the toughness.

Ceramic thin film thermocouples for SiC-based ceramic matrix composites

Conductive ceramic thin film thermocouples were investigated for application to silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiC/SiC CMC) components. High temperature conductive oxides based on indium and zinc oxides were selected for testing to high temperatures in air. Sample oxide films were first sputtered-deposited on alumina substrates then on SiC/SiC CMC sample disks. Operational issues such as cold junction compensation to a 0°C reference, resistivity and thermopower variations are discussed. Results show that zinc oxides have an extremely high resistance and thus increased complexity for use as a thermocouple, but thermocouples using indium oxides can achieve a strong, nearly linear response to high temperatures.

Silicon carbide whisker reinforced silicon carbide composites by chemical vapor infiltration

Silicon carbide (SiC) whisker reinforced SiC ceramic matrix composites were prepared by chemical vapor infiltration. Microstructure and mechanical properties of the composites were investigated. The fracture toughness of the composites was improved to 5.65–7.21 MPa m 1/2, and its flexural strength value was between 196 MPa and 305 MPa, depending on the relative density. The pullout of rough whisker, crack deflection and whisker bridging are responsible for the improvement in fracture toughness. The randomly oriented whiskers that paralleled to the crack plane, and the weak bonding strength between whisker and matrix could not have much stress transfer from the matrix, leading to the low flexural strength.