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Questions and Answers
What are the advantages of ceramic matrix composites in terms of wear and corrosion resistance?
What are the advantages of ceramic matrix composites in terms of wear and corrosion resistance?
Excellent wear and corrosion resistance in a wide range of environments and temperatures.
What is the main disadvantage of monolithic ceramics that ceramic matrix composites are designed to improve?
What is the main disadvantage of monolithic ceramics that ceramic matrix composites are designed to improve?
Brittleness
Why are ceramic matrix composites more expensive to process than other materials?
Why are ceramic matrix composites more expensive to process than other materials?
High processing temperature results in complexity in manufacturing and hence expensive processing.
What is the primary reason for thermal stresses in ceramic matrix composites during cooling?
What is the primary reason for thermal stresses in ceramic matrix composites during cooling?
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What is the primary mechanism of crack arrest in ceramic matrix composites?
What is the primary mechanism of crack arrest in ceramic matrix composites?
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What is the benefit of ceramic matrix composites in terms of strength retention at elevated temperatures?
What is the benefit of ceramic matrix composites in terms of strength retention at elevated temperatures?
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What happens when a crack propagates in the matrix of a composite material?
What happens when a crack propagates in the matrix of a composite material?
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What is the result of high transverse fracture toughness in fibers during fiber pull-out?
What is the result of high transverse fracture toughness in fibers during fiber pull-out?
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What is the purpose of Chemical Vapour Infiltration (CVI) in developing Ceramic Matrix Composites?
What is the purpose of Chemical Vapour Infiltration (CVI) in developing Ceramic Matrix Composites?
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What is the difference between Chemical Vapor Deposition (CVD) and Chemical Vapor Infiltration (CVI)?
What is the difference between Chemical Vapor Deposition (CVD) and Chemical Vapor Infiltration (CVI)?
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What is the role of the heating chamber in a Chemical Vapor Infiltration reactor?
What is the role of the heating chamber in a Chemical Vapor Infiltration reactor?
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What is the advantage of the Temperature Gradient (TG-CVI) process over the isothermal/isobaric CVI process?
What is the advantage of the Temperature Gradient (TG-CVI) process over the isothermal/isobaric CVI process?
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Study Notes
Ceramic Matrix Composites (CMCs)
- Exhibit excellent wear and corrosion resistance in various environments and temperatures
- Offer higher strength-to-weight ratio
- Retain higher strength at elevated temperatures
- Possess higher chemical stability
- Fail in a non-catastrophic manner
- Have high hardness and are lightweight
Disadvantages of CMCs
- Processing routes involve high temperatures, limiting their use with high-temperature reinforcements
- Designed to improve toughness of monolithic ceramics, which are brittle
- High processing temperature leads to complex and expensive manufacturing
- Coefficient of thermal expansion differences between matrix and reinforcement cause thermal stresses during cooling
Toughening Mechanisms in CMCs
- Crack impeding: crack arresting mechanism due to fibers' higher fracture toughness than the matrix
- Fiber (or whisker) pull-out: fibers have high transverse fracture toughness, causing failure along the fiber/matrix interface
- Crack deflection: weak fiber/matrix interfaces deflect the crack
Chemical Vapour Infiltration (CVI)
- Widely used to develop CMCs
- Deposits solid materials like carbon, silicon carbide, and boron nitride in a porous structure by vapor decomposition
- Similar to Chemical Vapor Deposition (CVD), but involves deposition within a body
CVI Process
- Prepares a ceramic continuous fiber structure (porous preform) as the reinforcement phase
- Reactant gases or vapors are supplied to the reactor, flowing around and diffusing into the preform
- Decomposition of reactants fills the space between fibers, forming a composite material
CVI Reactor
- Consists of three main parts: feed system, heating chamber, and effluent system
- Can be modified to include forced gas flow and a temperature gradient to avoid restriction of gas flow
Types of CVI Processes
- Isothermal/isobaric CVI process: uniform temperature and pressure, but slow due to low diffusion rate
- Temperature gradient (TG-CVI) process: enhances gas diffusivity by leveraging temperature differences
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Description
Explore the advantages and disadvantages of ceramic matrix composites, including their excellent wear and corrosion resistance, high strength to weight ratio, and more. Learn about the properties and applications of CMCs.
