Study of preceramic compositions based on modified polycarbosilane and polyorganosilazanes

2021 ◽  
Vol 87 (9) ◽  
pp. 30-37
Author(s):  
A. M. Shestakov ◽  
N. I. Shvets ◽  
V. A. Rosenenkova
Keyword(s):  
Nuclear Power ◽  
Ceramic Composite ◽  
Physical And Mechanical Properties ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Amorphous Structure ◽  
Ceramic Fibers ◽  
Liquid Polymer ◽  
The Matrix ◽  
Monolithic Ceramics

Ceramic matrix composites (CMC) exhibit increased crack resistance and resistance to mechanical and thermal shock impacts retaining at the same time the valuable properties of monolithic ceramics. Therefore, they are widely used as parts of heat-loaded elements of aviation and rocket technology, in nuclear power industry, etc. LPI-method (liquid polymer infiltration) of CMC production is based on the impregnation of a skeleton of ceramic fibers with an organosilicon polymer, formation of a preceramic matrix by polymer technology, and subsequent high-temperature pyrolysis resulting in formation of a reinforced ceramic matrix. Ceramics obtained from polymer precursors have a predominantly amorphous structure which determines its high thermal stability. Moreover, introduction of the nanosized particles of carbides, borides and nitrides of refractory metals (Zr, Ti, Hf) into the matrix of a ceramic composite stabilizes its amorphous structure up to temperatures of 1500 - 1600°C. We present the results of studying the preceramic compositions based on polycarbosilane and polyorganosilazanes modified with Hf and Ta atoms. It is shown that introduction of the modifying additives Hf and Ta into the polyorganosilazane composition shifts the curing interval of the compositions towards lower temperatures. The yield of the gel fraction is 73.3 and 82.7 wt.%, respectively. The weight loss of pyrolysate samples heated to 1400°C in air does not exceed 0.5%. The physical and mechanical properties, as well as the thermal oxidative stability of novel ceramic composite materials obtained on the base of the studied compositions and carbon reinforcing filler are analyzed. It is shown that the density of CMC samples increases by 1.5 times with an increase in the number of impregnation cycles and reaches the maximum value of 1950 kg/m3 with five impregnation cycles of the filler with a composition based on polyorganosilazane modified with Ta. The results obtained can be used in the development of new CMCs.

Effect of Microporosity on Damage Initiation in Ceramic Matrix Composites

2019 ◽  
Author(s):  
Suhasini Gururaja ◽  
Abhilash Nagaraja
Keyword(s):  
Gas Turbines ◽  
Ceramic Matrix Composites ◽  
Local Stress ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Damage Initiation ◽  
The Matrix ◽  
Homogenization Approach ◽  
Matrix Porosity ◽  
Monolithic Ceramics

Abstract Ceramic matrix composites (CMC) are a subclass of composite materials consisting of reinforced ceramics. They retain the advantages of ceramics such as lower density and better refractory properties but exhibit better damage tolerance compared to monolithic ceramics. This combination of properties make CMCs an ideal candidate for use in high temperature sections of gas turbines. However, modeling the damage mechanisms in CMCs is complex due to the heterogeneous microstructure and the presence of processing induced defects such as matrix porosity. The effect of matrix pore location and orientation on damage initiation in CMCs is of interest in the present work. CMCs fabricated by various fabrication processes exhibit matrix pores at different length scales. Microporosities exist within fiber bundles in CMCs have a significant effect on microscale damage initiation and forms the focus of the current study. In a previous work by the authors, a two step numerical homogenization approach has been developed to model statistical distribution of matrix pores and to obtain the effective mechanical properties of CMCs in the presence of matrix porosity. A variation of that approach has been adopted to model matrix pores and investigate the severity of pores with respect to their location and orientation. CMC microstructure at the microscale has been modeled as a repeating unit cell (RUC) consisting of fiber, interphase and matrix. Ellipsoidal pores are modeled in the matrix with pore distance from the interphase-matrix interface and pore orientation with respect to the loading direction as parameters. Periodic boundary conditions (PBCs) are specified on the RUC by means of constraint equations. The effect of the pore on the local stress fields and its contribution to matrix damage is studied.

CMC and C/C-SiC-Fabrication

2006 ◽  
Vol 50 ◽  
pp. 130-140
Author(s):  
Roland Weiss
Keyword(s):  
Physical And Mechanical Properties ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Ceramic Materials ◽  
Matrix Composites ◽  
New Family ◽  
The Matrix ◽  
Full Conversion ◽  
Selection Of ◽  
Matrix Precursor

Ceramic Matrix Composites (CMC) have a wide interest for high temperature applications. The materials can be modified by the selection of the matrix precursor as well as of the reinforcing materials. C/C-composites can be easily modified by post-treatments with silicon in order to acquire different tribological properties from good sliding behaviour up to braking systems only depending on the manufacturing technique of these materials. It will be demonstrated during the presentation that the manufacturing depends on one hand side on the material which has to be manufactured and on the other side on the structural component and the number of parts which are required. Furthermore, it will also be shown, that silicon treatments can be performed up to a full conversion of C/C materials creating a new family of monolithic ceramic materials. Within the presentation detailed information will be given on possible processing routes as well as the resulting physical and mechanical properties of the materials.

scholarly journals Noninteractive Macroscopic Reliability Model for Ceramic Matrix Composites With Orthotropic Material Symmetry

1990 ◽  
Vol 112 (4) ◽  
pp. 507-511 ◽  
Author(s):  
S. F. Duffy ◽  
J. M. Manderscheid
Keyword(s):  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Experimental Program ◽  
Type Model ◽  
Model Parameters ◽  
Reliability Model ◽  
Matrix Composites ◽  
Physical Mechanisms ◽  
Weakest Link ◽  
Monolithic Ceramics

A macroscopic noninteractive reliability model for ceramic matrix composites is presented. The model is multiaxial and applicable to composites that can be characterized as orthotropic. Tensorial invariant theory is used to create an integrity basis with invariants that correspond to physical mechanisms related to fracture. This integrity basis is then used to construct a failure function per unit volume (or area) of material. It is assumed that the overall strength of the composite is governed by weakest link theory. This leads to a Weibull-type model similar in nature to the principle of independent action (PIA) model for isotropic monolithic ceramics. An experimental program to obtain model parameters is briefly discussed. In addition, qualitative features of the model are illustrated by presenting reliability surfaces for various model parameters.

Erosion in Gas-Turbine Grade Ceramic Matrix Composites (CMCs)

2018 ◽  
Author(s):  
N. Kedir ◽  
C. Gong ◽  
L. Sanchez ◽  
M. J. Presby ◽  
S. Kane ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Erosion Behavior ◽  
Image Mapping ◽  
Material Systems ◽  
Multiple Material ◽  
Monolithic Ceramics ◽  
Matrix Hardness

Erosion behavior of a large number of gas-turbine grade ceramic matrix composites (CMCs) was assessed using fine to medium grain garnet erodents at velocities of 200 and 300 m/s at ambient temperature. The CMCs used in the current work were comprised of nine different SiC/SiCs, one SiC/C, one C/SiC, one SiC/MAS, and one oxide/oxide. Erosion damage was quantified with respect to erosion rate and the damage morphology was assessed via SEM and optical microscopy in conjunction with 3-D image mapping. The CMCs response to erosion appeared to be very complicated due to their architectural complexity, multiple material constituents, and presence of pores. Effects of architecture, material constituents, density, matrix hardness, and elastic modulus of the CMCs were taken into account and correlated to overall erosion behavior. The erosion of monolithic ceramics such as silicon carbide and silicon nitrides was also examined to gain a better understanding of the governing damage mechanisms for the CMC material systems used in this work.

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

2020 ◽  
Author(s):  
Rajesh S. Kumar
Keyword(s):  
Elastic Properties ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Volume Shrinkage ◽  
Matrix Composites ◽  
Defect Structures ◽  
Linear Elastic ◽  
Elastic Tensor ◽  
The Matrix

Abstract Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during various phases of analysis and design of CMC components. CMCs are typically made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is that formed via Polymer Impregnation and Pyrolysis (PIP). As this process involves pyrolysis process to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This volume shrinkage leads to significant defects in the final material in the forms of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

Double Interface Coatings on Silicon Carbide Fibers

2004 ◽  
Vol 843 ◽  
Author(s):  
Jun C. Nable ◽  
Shaneela Nosheen ◽  
Steven L. Suib ◽  
Francis S. Galasso ◽  
Michael A. Kmetz
Keyword(s):  
Silicon Carbide ◽  
Surface Coating ◽  
Zirconium Oxide ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Ceramic Fibers ◽  
Oxide Coatings ◽  
Silicon Carbide Fibers ◽  
Nitride Coatings

ABSTRACTInterface coatings on fibers are important in ceramic matrix composites. In addition to providing toughness, the interface coating must also protect the reinforcing ceramic fibers from corrosive degradation. A double interface coating has been applied onto silicon carbide fibers. The double interface coating is comprised of a combination of nitride and oxide coatings. Among the nitrides, boron nitride and titanium nitride were utilized. These nitrides were deposited by CVD. The metal oxides of choice were aluminum oxide and zirconium oxide which were applied onto the nitride coatings by MOCVD. The phases on the coated fibers were determined by XRD. The surface coating microstructures were observed by SEM. The effect of the coatings on the tensile strengths was determined by Instron tensile strength measurements.

Micromechanics Approach for the Overall Elastic Properties of Ceramic Matrix Composites Incorporating Defect Structures

2021 ◽  
Author(s):  
Rajesh Kumar
Keyword(s):  
Elastic Properties ◽  
Volume Fraction ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Defect Structures ◽  
Modeling Framework ◽  
Linear Elastic ◽  
Elastic Tensor ◽  
The Matrix

Abstract Initial mechanical behavior of Ceramic Matrix Composites (CMCs) is linear until the proportional limit. This initial behavior is characterized by linear elastic properties, which are anisotropic due to the orientation and arrangement of fibers in the matrix. The linear elastic properties are needed during analysis and design of CMC components. CMCs are made with ceramic unidirectional or woven fiber preforms embedded in a ceramic matrix formed via various processing routes. The matrix processing of interest in this work is the Polymer Impregnation and Pyrolysis (PIP) process. As this process involves pyrolysis to convert a pre-ceramic polymer into ceramic, considerable volume shrinkage occurs in the material. This leads to significant defects in the form of porosity of various size, shape, and volume fraction. These defect structures can have a significant impact on the elastic and damage response of the material. In this paper, we develop a new micromechanics modeling framework to study the effects of processing-induced defects on linear elastic response of a PIP-derived CMC. A combination of analytical and computational micromechanics approaches is used to derive the overall elastic tensor of the CMC as a function of the underlying constituents and/or defect structures. It is shown that the volume fraction and aspect ratio of porosity at various length-scales plays an important role in accurate prediction of the elastic tensor. Specifically, it is shown that the through-thickness elastic tensor components cannot be predicted accurately using the micromechanics models unless the effects of defects are considered.

Whisker-Reinforced Ceramic Matrix Composites

MRS Bulletin ◽  
1987 ◽  
Vol 12 (7) ◽  
pp. 66-72 ◽  
Author(s):  
J. Homeny ◽  
W.L. Vaughn
Keyword(s):  
High Temperature ◽  
Energy Dissipation ◽  
Mechanical Performance ◽  
Ceramic Matrix Composites ◽  
Ceramic Matrix ◽  
Matrix Composites ◽  
Mechanical Reliability ◽  
Interfacial Bond ◽  
High Fracture ◽  
The Matrix

Whisker-reinforced ceramic matrix composites have recently received a great deal of attention for applications as high temperature structural materials in, for example, advanced heat engines and high temperature energy conversion systems. For applications requiring mechanical reliability, the improvements that can be realized in fracture strength and fracture toughness are of great interest. Of particular importance for optimizing the mechanical reliability of these composites is the effect of the whisker/matrix interfacial characteristics on the strengthening and toughening mechanisms. Whisker reinforcements are primarily utilized to prevent catastrophic brittle failure by providing processes that dissipate energy during crack propagation. The degree of energy dissipation depends on the nature of the whisker/matrix interface, which can be controlled largely by the matrix chemistry, the whisker surface chemistry, and the processing parameters.It is generally believed that a strong interfacial bond results in a composite exhibiting brittle behavior. These composites usually have good fracture strengths but low fracture toughnesses. If the interfacial bond is weak, the composite will not fail in a catastrophic manner due to the activation of various energy dissipation processes. These latter composites tend to have high fracture toughnesses and low fracture strengths. Generally, the interface should be strong enough to transfer the load from the matrix to the whiskers, but weak enough to fail preferentially prior to failure. Thus, local damage occurs without catastrophic failure. It is therefore necessary to control the interfacial chemistry and bonding in order to optimize the overall mechanical performance of the composites.

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