Silicon Carbide Ceramic Matrix Composites Research Articles

ITO:SiC Ceramic Matrix Composite Thermocouples for Engine Components

Surface temperature measurements of ceramic matrix composite (CMC) based engine components within the hot section of a gas turbine engines are needed to verify engine designs and cooling requirements. Traditional temperature sensors cannot be applied to silicon carbide (SiC) based CMC's for this purpose, since they cannot be welded or embedded in the material. For these reasons, a novel thermocouple was developed for surface temperature measurement of p-type SiC-SiC CMC's. This novel thermocouple uses the p-type SiC-SiC CMC itself as one of the thermoelements and indium-tin-oxide (ITO) as the other thermoelement. Since both thermoelements are wide bandgap semiconductors, this thermocouple has exceptional thermoelectric output. A thermoelectric output of 272 μV/°K was observed for this ITO:SiC CMC thermocouple, which is an order of magnitude larger than that of type-K thermocouples. A drift rate of 3.28 °C/h was measured for this ITO:SiC CMC thermocouple. In addition, indium tin oxynitride (ITON) protective coatings deposited via reactive sputtering enabled these thermocouples to operate at 1000 °C. The ITON coating served as an oxygen diffusion barrier to prevent oxidation at the ITO:SiC CMC junction. Nitrogen and air anneals at 550 and 1000 °C, respectively, were used to improve the high temperature stability of the ITO and ITON coatings. Performance, fabrication details, and challenges using these ITO:SiC CMC thermocouple are discussed within.

Mechanical model and removal mechanism of unidirectional carbon fibre-reinforced ceramic composites

Numerous scholars have researched the influences of grinding parameters on the surface quality and grinding forces of carbon fibre-reinforced silicon carbide ceramic matrix (Cf/SiC) composites. Nevertheless, the relevant mechanical model and removal mechanism have not been investigated from a microscale perspective. To develop a mechanical model, the area of formation of the grinding chips should be analysed in detail and discussed. The supporting conditions and debonding depth are critical to the grinding forces. To validate the reliability of the mechanical model, experiments with the same grinding parameters were performed. The differences between the theoretical and experimental results were small, which indicated that the mechanical model was accurate and reasonable. Based on the theoretical analyses and experimental results, the material removal mechanism was explored in detail. Based on the topographies of the grinding chips and surfaces, the failure processes of the fibre and matrix due to the forward motion of the abrasive grains were analysed. As the grinding depth increased, the evaluation indexes of the debonding depth, grinding forces and grinding chips gradually increased. Moreover, the increasing proportions of fibre pullout and fibre outcrop indicated that the quality of the grinding surface decreased. Based on the research findings, the debonding depths, grinding forces, grinding chips and surface topographies of unidirectional Cf/SiC composites can be determined, which is expected to significantly improve the machining ability of Cf/SiC composites.

Damping Capacity and Storage Modulus of SiC Matrix Composites Infiltrated by AlSi Alloy

In this paper, we describe how an aluminum alloy-reinforced silicon carbide ceramic matrix composite (SiCCMC) with excellent damping capacity and storage modulus was fabricated by infiltration. The effects of silicon (Si) on the microstructure and damping capacity of the composite were studied. The interface bonding and damping mechanism involved were also discussed. The results show that composites with high damping capacity can be obtained by infiltrating SiC ceramics with aluminum alloy. The residual Si in the SiC ceramic had little effect on the damping capacity, and it provided the passage of aluminum alloy into the interior of the SiC ceramic. The aluminum atoms penetrate the SiC particles by diffusion. Optimal composite damping capacity was obtained when the Si content in the aluminum alloy was 15 wt. %, because the AlSi/SiC interface friction dissipated most of thermal energy. Ti3SiC2 formed on the surface had little effect on the damping capacity. Additionally, by changing the Si content in the aluminum alloy, the strength and damping capacity of the composites can be controlled.

Influences of clearance angle and point angle on drilling performance of 2D Cf/SiC composites using polycrystalline diamond tools

Cf/SiC composite (carbon fiber reinforced silicon carbide ceramic matrix composites) is a kind of advanced composite material constituted by SiC as matrix and carbon fiber as reinforcing phase. Cf/SiC composites are being extensively used in the modern aerospace industry owing to their excellent physical and mechanical properties. The current work aims to investigate influences of clearance angle and point angle on drilling performance of 2D Cf/SiC composites using PCD (polycrystalline diamond) tools in terms of thrust force, drilling torque, hole surface quality, and material removal mechanism. PCD drill bits with different point angles and clearance angles were used in the experiment. The obtained results indicate that the 150° point angle is beneficial to improve the hole surface quality, and larger clearance angle is helpful to reduce the damage of exits. Additionally, the variation of clearance angle has little effect on the roughness of the machined surface. During the drilling process, the dominated material removal mechanisms are matrix removal, fiber breakage, and matrix-fiber debonding. The brittle fracture mode of carbon fibers, which directly affects surface roughness, can be divided into micro-brittle fractures in carbon fiber and macro-brittle fractures. Besides, the damage identification method of hole entrance and exit based on image processing technology is helping to improve the efficiency of machining quality evaluation.

Deuterium retention in silicon carbide, SiC ceramic matrix composites, and SiC coated graphite

Abstract Silicon Carbide (SiC) is a low Z material discussed as an alternative to graphite for fusion devices. The retention of hydrogenous species is an important plasma-surface interaction property. Deuterium was implanted into SiC, SiCf/SiC, Cf/C-SiC and SiC coated graphite under various particle energy and substrate temperature conditions. A TDS process was used to characterise the deuterium retention of the implanted specimens. While all SiC materials show elevated retention levels compared to graphite, the differences are limited to about a factor of two over the range of parameters investigated.

A Study on the Laser-Assisted Machining of Carbon Fiber Reinforced Silicon Carbide.

In recent years, as replacements for traditional manufacturing materials, monolithic ceramics and carbon fiber reinforced silicon carbide (C/SiC) ceramic matrix composites have seen significantly increased usage due to their superior characteristics of relatively low density, lightweight, and good high temperature mechanical properties. Demand for difficult-to-cut materials is increasing in a variety of area such as the automotive and aerospace industries, but these materials are inherently difficult to process because of their high hardness and brittleness. When difficult-to-cut materials are processed by conventional machining, tool life and quality are reduced due to the high cutting force and temperatures. Laser-assisted machining (LAM) is a method of cutting a workpiece by preheating with a laser heat source and lowering the strength of the material. LAM has been studied by many researchers, but studies on LAM of carbon–ceramic composites have been carried out by only a few researchers. This paper focuses on deducing the optimal machining parameters in the LAM of C/SiC. In this study, the Taguchi method is used to obtain the major parameters for the analysis of cutting force and surface roughness under various machining conditions. Before machining experiments, finite element analysis is performed to determine the effective depth of the cut. The cutting parameters for the LAM operation are the depth of cut, preheating temperature, feed rate, and spindle speed. The signal to noise (S/N) ratio and variance analysis (ANOVA) of the cutting force and surface roughness are analyzed, and the response optimization method is used to suggest the optimal machining parameters.

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.

Strengthening of C/SiC Composites by Electrophoretic Deposition of CNTs on a SiC Coating

The current study reports the enhancement of mechanical properties of carbon fiber-reinforced silicon carbide ceramic matrix composites (C/SiC CMCs) by the application of a carbon nanotube/silicon carbide (CNT/SiC) coating. CNTs were deposited on the surfaces of C/SiC composites using electrophoretic deposition (EPD), after which infiltration by SiC was achieved through a chemical vapor infiltration process. An EPD duration of 5 min was associated with a 40% increase in the ultimate flexural strength relative to that of composites with a pure SiC coating. The observed enhancement was rationalized by the microstructural observations of SiC infiltration into the porous CNT morphology and the subsequent formation of CNT/SiC layers on the surfaces of the composites and by the inherent toughness of the SiC whiskers. The flexural strength decreased with EPD durations greater than 5 min due to the formation of thick CNT meshes, which decreased the open porosity and thereby obstructed further SiC infiltration. This is a viable methodology for the improvement of mechanical properties of CMCs by the introduction of a ceramic coating containing CNT.

Surface topography and roughness of silicon carbide ceramic matrix composites

The silicon carbide ceramic matrix composite (Cf/SiC) plays an important role in aeronautic and space applications due to its excellent performance. Cf/SiC consists of silicon carbide and carbon fibers. The effects of the grinding parameters on the 3D parameters of surface roughness and surface topography when grinding 2.5D needled Cf/SiC materials have rarely been investigated. The primary purpose of this paper is to fill this knowledge gap. Cf/SiC material was ground in the direction of the orthogonal surface, and the surface topography, grinding parameters and grinding mechanism were analysed through a series of experiments. The results indicated that matrix cracks, fiber fractures, fiber wear and interfacial debonding were the primary removal methods of the material. The grinding parameters exert a substantial influence on the quality of the machined surface, primarily because of the undeformed chip thickness and the length of the contact arc. In the grinding process of the 2.5D Cf/SiC material, the quality of the surface roughness and its parameters gradually improved with increasing grinding speed, whereas the feed speed and grinding depth produced the opposite effect. Based on the conclusions, the surface topography and roughness parameters of 2.5D Cf/SiC material can be predicted, which thus provides useful technical support for increasing the machining quality of 2.5D Cf/SiC material and all its composites.

Hydrothermal Corrosion of SiC and FeCrAl for Accident Tolerant Fuel Cladding

Since the Fukushima incident in 2011, the nuclear industry has sought to replace Zircaloy fuel cladding with a material which will better withstand a beyond-design-basis incident. A suitable material must possess superior oxidation resistance in high temperature steam (1200-1700°) to withstand a loss of coolant accident, while maintaining good hydrothermal corrosion properties for environmental compatibility during normal operating conditions (288-320°C water). In addition to corrosion issues, a suitable material must also demonstrate sufficient mechanical strength, creep resistance, radiation tolerance, and favorable neutronics. Researchers at Oak Ridge National Laboratory are engaged in testing of two leading candidates for accident tolerant fuel cladding: iron-chomium-aluminum (FeCrAl) alloys, and silicon carbide ceramic matrix composites (SiC/SiC). FeCrAl alloys have shown excellent oxidation resistance due to the formation of a passive alumina film in high temperature steam, and a protective Fe-Cr spinel layer in water. SiC/SiC has shown excellent corrosive properties in high temperature steam, but a tendency to dissolve in LWR water. To improve performance of SiC normal operating conditions, several candidate coatings are being considered, including Cr, CrN, and TiN. This work presents results of hydrothermal corrosion experiments on FeCrAl alloys and coated SiC in boiling water reactor hydrogen water chemistry (BWR-HWC) and normal water chemistry (BWR-NWC) (288°C with 150 ppb H2 or 2 ppm O2 respectively). FeCrAl samples generally exhibited low corrosion rates. Hydrothermal corrosion properties of current FeCrAl alloys are compared to older generations. CVD-SiC and SiC/SiC exhibited significant mass loss during exposure. SiC samples coated with Cr and CrN adhered well to their substrates, and effectively mitigated dissolution, with acceptable corrosion rates. This work was funded by the DOE Office of Nuclear Energy Advanced Fuels Campaign

Joining of Cf/SiC Ceramic Matrix Composites: A Review

Carbon fiber‐reinforced silicon carbide (Cf/SiC) ceramic matrix composites have promising engineering applications in many fields, and they are usually geometrically complex in shape and always need to join with other materials to form a certain engineering part. Up to date, various joining technologies of Cf/SiC composites are reported, including the joining of Cf/SiC‐Cf/SiC and Cf/SiC‐metal. In this paper, a systematic review of the joining of Cf/SiC composites is conducted, and the aim of this paper is to provide some reference for researchers working on this field.

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.

High-temperature thermal barrier-coated Sylramic-iBN/pyrolytic carbon/chemical vapor infiltration silicon carbide ceramic matrix composite behavior in a combustion environment

An environmental barrier-coated Sylramic-iBN/pyrolytic carbon/chemical vapor infiltration silicon carbide ceramic matrix composite was characterized in a harsh combustion environment under two conditions; (i) with a coating surface temperature of 1480℃, and (ii) with a combustion flame distance of 120 mm (constant flux). Three coating systems were evaluated; Coating “A” (ytterbium silicate using hafnium–silicate bond), Coating “B” (ytterbium silicate using alumina bond), and Coating “C” (ytterbium–silica compounds using alumina bond). All three coatings survived with essentially no mass loss up to 25 h when tested at 1480℃. At a flame distance of 120 mm coatings “A” and “B” experienced extensive degradation and strength loss while coating “C” had practically no degradation in retained strength. Coating “C” outperformed the other two coatings exposed to the harsh combustion environment. It performed best in terms of material loss, thermal barrier capability, and residual tensile strength.

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.

Effects of Temperature, Oxidation and Fiber Preforms on Fatigue Life of Carbon Fiber-Reinforced Ceramic-Matrix Composites

In this paper, the effects of temperature, oxidation and fiber preforms on the fatigue life of carbon fiber-reinforced silicon carbide ceramic-matrix composites (C/SiC CMCs) have been investigated. An effective coefficient of the fiber volume fraction along the loading direction (ECFL) was introduced to describe the fiber architecture of preforms. Under cyclic fatigue loading, the fibers broken fraction was determined by combining the interface wear model and fibers statistical failure model at room temperature, and interface/fibers oxidation model, interface wear model and fibers statistical failure model at elevated temperatures in the oxidative environments. When the broken fibers fraction approaches to the critical value, the composites fatigue fracture. The fatigue life S–N curves and fatigue limits of unidirectional, cross-ply, 2D, 2.5D and 3D C/SiC composites at room temperature, 800 °C in air, 1100, 1300 and 1500 °C in vacuum conditions have been predicted.

High Temperature Oxidation Behavior of Silicon Carbide Ceramic

Oxidation thermodynamics of silicon carbide (SiC)ceramic was studied by means of HSC Chemistry code, and the weight change, morphology and phase of oxidation products were analyzed by thermogravimetric analysis(TG), scanning electron microscopy(SEM ) and X-ray diffraction (XRD). The results showed that SiC ceramic could be oxidized to silicon dioxide(SiO2) with release of small molecular gases under oxidizing atmosphere at 800°C, and the formed SiO2 film with appropriate fluidity and low oxygen diffusion coefficient could prevent the spread of oxygen with the oxidation temperature increasing up to 1200°C, which favored the anti-oxidation of SiC ceramic matrix composite.

Honeycomb Sandwich Structure of C<sub>f</sub>/SiC Ceramic Matrix Composites Prepared by PIP-CVI

continuous carbon fiber reinforced silicon carbide (Cf/SiC) ceramic matrix composites were prepared by precursor infiltration pyrolysis and chemical vapor infiltration (PIP-CVI process), in which the honeycomb sandwich structure preforms were fabricated by the three dimensional braid method. In this paper, the microstructure and the bending strength were observed and analyzed by SEM and three point bending method. The results of the study show that: The Cf/SiC ceramic matrix composites, which were lightweight and high strength, were prepared by that technique. The composite samples have a fiber volume fraction of 20%, a density of 0.38 g/cm3 and a flexural strength of 3.81 MPa. The honeycomb sandwich fiber reinforced ceramic matrix composite with a light weight, corrosion resistance and excellent physical and mechanical properties is a kind of structure and functional ceramic materials, which can realize the structure and the requirement of heat integration.

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.

Acoustic Emission Analysis on Low Velocity Impact Damage of 2D C/SiC Composites

An experimental study of low velocity impact (LVI) was carried out on 2D carbon fabric reinforced silicon carbide (C/SiC) ceramic matrix composites. The C/SiC composite specimens were impacted by using a free-drop impact machine at different energy levels ranging from 1J to 9J and acoustic emission (AE) technique was used to detect the damage process. The results indicated that AE signals could evaluate the LVI damage behaviors of C/SiC composites from the different aspects. By comparing impact load process with AE hits and AE amplitude, the damage process could be determined. In the loading stage, matrix cracking mainly occurred in the composites; when impact load reached peak load, delamination and fiber fracture started to produce; in the unloading stage, the damage modes were mainly delamination and matrix cracking. AE event count fractions could quantify the main damage modes at different impact energy levels. At lower impact energy, matrix cracking was the main damage mode; when impact energy were between 3J and 6J, delamination and matrix cracking became the main damage modes; at higher impact energy, fiber fracture was the main damage mode.