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Questions and Answers
What causes the microcracks in PSZ?
What causes the microcracks in PSZ?
What is the optimum volume percentage of tetragonal phase in a cubic zirconia matrix for toughening?
What is the optimum volume percentage of tetragonal phase in a cubic zirconia matrix for toughening?
What happens to tetragonal ZrO2 inclusions under stress at the crack tip?
What happens to tetragonal ZrO2 inclusions under stress at the crack tip?
What temperature range does the monoclinic CTE apply up to?
What temperature range does the monoclinic CTE apply up to?
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At what critical size do tetragonal particles remain stable down to room temperature?
At what critical size do tetragonal particles remain stable down to room temperature?
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What is the preferred toughening mechanism in ZrO2?
What is the preferred toughening mechanism in ZrO2?
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Which factor does NOT contribute to the fracture toughness of composite materials?
Which factor does NOT contribute to the fracture toughness of composite materials?
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What happens in a weak interface between fibers and the matrix in fiber-reinforced composites?
What happens in a weak interface between fibers and the matrix in fiber-reinforced composites?
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What is the purpose of adding about 10% MgO when manufacturing partially stabilized zirconia?
What is the purpose of adding about 10% MgO when manufacturing partially stabilized zirconia?
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How is the toughness of PSZ (Partially Stabilized Zirconia) improved?
How is the toughness of PSZ (Partially Stabilized Zirconia) improved?
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What temperature is typically used to sinter the cubic phase of partially stabilized zirconia?
What temperature is typically used to sinter the cubic phase of partially stabilized zirconia?
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What is a consequence of cooling the material to room temperature too quickly after sintering?
What is a consequence of cooling the material to room temperature too quickly after sintering?
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Which type of composite interface is better for transferring stress from the matrix to the fibers?
Which type of composite interface is better for transferring stress from the matrix to the fibers?
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What is the primary advantage of using the bending test for material strength measurement?
What is the primary advantage of using the bending test for material strength measurement?
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What does the variable 'a' represent in the equation for 4-point bending strength?
What does the variable 'a' represent in the equation for 4-point bending strength?
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Which variable does NOT affect the hardness of a material?
Which variable does NOT affect the hardness of a material?
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What is the formula used for calculating bending strength in a 3-point test?
What is the formula used for calculating bending strength in a 3-point test?
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Which hardness test method is commonly used for ceramics?
Which hardness test method is commonly used for ceramics?
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In the context of microhardness, what typically happens at lower loads?
In the context of microhardness, what typically happens at lower loads?
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What type of deformation does hardness primarily measure?
What type of deformation does hardness primarily measure?
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Which external variable can influence a material's hardness?
Which external variable can influence a material's hardness?
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What happens to the failure stress as the crack size increases?
What happens to the failure stress as the crack size increases?
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What is the condition named when specimen thickness is much greater than crack dimensions?
What is the condition named when specimen thickness is much greater than crack dimensions?
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Which mode of crack surface displacement is denoted by Mode I?
Which mode of crack surface displacement is denoted by Mode I?
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What applies to the Kc value for a thick specimen under plane strain conditions?
What applies to the Kc value for a thick specimen under plane strain conditions?
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What is the symbol for plane strain fracture toughness?
What is the symbol for plane strain fracture toughness?
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What is the relation between relative density and fracture toughness for brittle materials mentioned?
What is the relation between relative density and fracture toughness for brittle materials mentioned?
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Which modes apply when the load is applied tangentially to the fracture?
Which modes apply when the load is applied tangentially to the fracture?
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Which materials were investigated for their effects on fracture toughness?
Which materials were investigated for their effects on fracture toughness?
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What is the critical particle size for ZTA (Zirconia-Toughened Alumina)?
What is the critical particle size for ZTA (Zirconia-Toughened Alumina)?
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Which of the following parameters should not be optimized for maximizing toughening in zirconia?
Which of the following parameters should not be optimized for maximizing toughening in zirconia?
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What characterizes glass as an amorphous solid?
What characterizes glass as an amorphous solid?
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Which materials are traditionally used in the production of glass?
Which materials are traditionally used in the production of glass?
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When does surface crystallization occur in glass?
When does surface crystallization occur in glass?
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Which process can be used to create sol-gel glasses?
Which process can be used to create sol-gel glasses?
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Which statement about glass is false?
Which statement about glass is false?
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What happens to unstabilized zirconia particles larger than the critical size during cooling?
What happens to unstabilized zirconia particles larger than the critical size during cooling?
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What is a key characteristic of the glass network according to random network theory?
What is a key characteristic of the glass network according to random network theory?
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Which rule does not apply to Zachariasen's theory of glass formation?
Which rule does not apply to Zachariasen's theory of glass formation?
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Why are materials like MgO, Al2O3, and TiO2 poor glass formers?
Why are materials like MgO, Al2O3, and TiO2 poor glass formers?
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Which of the following cations is classified as a network-modifier in a glass structure?
Which of the following cations is classified as a network-modifier in a glass structure?
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What is the relationship between the bond angle of A-O-A and the periodicity of crystalline structures?
What is the relationship between the bond angle of A-O-A and the periodicity of crystalline structures?
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Study Notes
Fundamentals of Ceramic Materials
- Course title: Fundamentals of Ceramic Materials
- Instructor: Prof. Dr. Filiz Şahin
- Academic year: 2024-2025
- Semester: Fall
- Department: Metallurgical & Materials Engineering
- Institute: I.T.U
Mechanical Properties of Ceramic Materials
- Presentation on mechanical properties of ceramic materials.
Introduction - Elastic Deformation
- Elastic deformation is reversible.
- A small load causes bonds to stretch.
- Upon unloading, bonds return to their initial state.
- Elastic behavior can be linear or non-linear.
Introduction - Plastic Deformation
- Plastic deformation is permanent.
- Bonds stretch and planes shear.
- Planes still shear even after unloading.
- Linear elastic behavior is observed before plastic deformation occurs.
Introduction - Stress-Strain Curve
- Material I: High Young's modulus (E), high failure stress, low ductility, low toughness, no significant plastic deformation.
- Material II: Moderate strength, moderate ductility, deforms plastically before failure, most toughest strength of the three types. Most common for many metals.
- Material III: Low E, very ductile, low ultimate tensile strength, Common for many elastomers.
Introduction - Stress-Strain Curve - Deformation of...
- Ceramics: Critical elasticity ~ 0.01%, plasticity ~ 0%.
- Metals: Critical elasticity ~ 1–2%, plasticity up to 50-100%.
- PMMA (Acrylic Glass):* Critical elasticity ~ several %, plasticity up to several 100%. (Polymethylmethacrylate)
Introduction - Elastic Constants
- Modulus of elasticity (Young's modulus, E)
- Poisson's ratio (v or μ)
- Bulk modulus (stress to strain for hydrostatic compression)
- These constants are directly related to bonding forces, affected by microstructure (e.g., porosity).
Introduction - Modulus of Elasticity (Young's Modulus)
- Modulus of elasticity (E) is the slope of the stress-strain curve in the elastic region.
- Hooke's Law: σ = Eε
- Factors affecting E: bond strength and temperature.
- Specific values of E are provided for various ceramic substances.
Introduction - Modulus of Elasticity (Young's Modulus) - At..
- At ambient and intermediate temperatures for short-term loading, most ceramics behave elastically with no plastic deformation up to fracture.
- Most ceramic materials undergo plastic deformation at high temperatures.
Introduction - Stress-Strain Curve - 3-Point Bending Strength Measurement
- Loading rate is typically between 0.5-1.0 mm/min.
- σ = 3LF/(2bd²)
- L = specimen length
- F = loading force
- b = specimen width
- d = specimen thickness
- ASTM C1161 standard is used.
Introduction - Stress-Strain Curve - 4-Point Bending Strength Measurement
- σ = 3Fa/(bd²)
- L = specimen length
- F = loading force
- b = specimen width
- d = specimen thickness
- a = distance between supporting and loading pins
Introduction - 3- and 4-Point Bending Strength Measurement
- Bend tests are less costly than other tests due to simpler sample geometries.
- Four-point bend tests are preferred for better constant bending moment measurement.
Bending Strength
- Various ceramic materials' bending strengths (at 25°C) are tabulated.
Compressive Strength
- σc = P/A formula for compressive strength
- Stable crack propagation leads to crushing.
Hardness
- Hardness is a material's resistance to permanent deformation.
- Hardness depends on crystal structure, defects, bond type, and fractional density.
- External variables are temperature, reactive species (e.g., acids, alkalis, or water).
- Hardness tests: Brinell, Vickers, Knoop, and Rockwell.
Hardness - Indentation test is used.
- Cracking can occur upon indenting, which is related to determining fracture toughness.
Hardness - Vickers hardness is common method for ceramics
- Fine ceramics and stainless steel examples are provided.
Hardness
- Measured hardness values are load-dependent, increasing at low loads, while at high loads they decrease due to material fracture.
Stiffness and Hardness
- A scatter plot showing the relationship between Young's modulus and hardness for ceramics, metals, and alloys.
Fracture Mechanics
- Measured fracture strength is significantly below theoretical values due to microscopic flaws and cracks.
- Crack tips are stress concentrators, the severity of strength reduction depends on various factors including pore shape and inclusion size.
Fracture Mechanics - Critical stress for crack propagation
- Brittle materials contain flaws and cracks.
- A crack forms, propagates, and fractures when the stress at the crack tip exceeds the critical stress.
- σc = (2Eys / πa)^1/2
Fracture Mechanics - Fracture Toughness
- Fracture toughness (Kc) of a material measures its resistance to brittle fracture when a crack is present.
- Kc is also referred to as stress intensity factor (at which crack propagates leading to fracture).
- Higher values mean resistance to crack propagation is greater and thus the material is more difficult to fracture.
- As crack size increases, failure stress drops; this should be accounted for in design.
Fracture Mechanics - Fracture Toughness - Thickness of specimen
- The thickness of the specimen is important in considering fracture toughness, a condition of plane strain exists when crack dimensions are much smaller than the specimen thickness.
Fracture Mechanics - 3 modes of crack surface displacement
- Mode I: Opening (tensile) mode
- Mode II: Sliding mode
- Mode III: Tearing mode
- Mode I is the most commonly encountered in a fracture test.
Fracture Mechanics - Fracture Toughness - Table 8.1
- Table showing room temperature yield strength, values of Kic for different materials.
Fracture Mechanics - Fracture Toughness - Which parameters affect Kic?
- Temperature
- Strain rate
- Microstructure (grain size)
Fracture Mechanics - Fracture Toughness - Measurement Techniques of Kic in Ceramic Materials
- Common techniques include indentation and bending tests.
Fracture Mechanics - Fracture Toughness - Measurement Techniques of Kic - Indentation
- Kic = 0.016 (E/H)^(1/2) x (P/C^(3/2))
- E: elastic modulus
- H: hardness
- P: load
Fracture Mechanics - Fracture Toughness - Measurement Techniques of Kic - Bending Test
- Four-point bending test is a common technique.
- Notches are introduced (e.g., using a diamond-tipped copper cutting wheel) into the specimens to initiate cracking.
- Types of notched specimens: SENB, CN
Fractography, Intergranular and Transgranular Fracture
- Fractography is used to analyze the failure mechanism and the origin of the fracture, including intergranular and transgranular failure types.
Conchoidal Fracture
- Conchoidal fracture exhibits no distinct cleavage plane and is common in flint, cubic zirconia, diamond, and glass.
Toughening of Ceramics
- Ceramics typically have low fracture toughness; thus, they must be modified by several methods.
- Toughening is achieved by stopping crack movement and increasing energy needed for crack propagation.
Toughening Mechanisms
- Methods to improve toughness in ceramics:
- Fiber reinforcing
- Whisker reinforcing
- Ductile network
- Transformation toughening
- Microcrack toughening
Toughening Mechanisms - Detailed mechanisms
- Crack deflection
- Crack bowing
- Crack branching
- Crack tip shielding by process zone activity
- Crack tip shielding by crack bridging
Toughening Mechanisms - Toughening achieved
- Toughening is achieved by bridging of crack surfaces behind the crack tip
- The stress intensity at the crack tip is reduced, which slows crack propagation.
Toughening Mechanisms - GNP-induced toughening mechanisms
- GNP-induced toughening mechanisms are based on methods for improving toughness through crack bridging and deflection.
- Materials like graphene sheets or carbon nanotubes are used to enhance toughness by debonding to create pullout.
Toughening Mechanisms - Crack deflection/branching
- Toughening methods involving crack deflection and branching improve ceramic toughness by causing the crack to propagate in an undesirable manner for fracture.
- Toughening happens when the crack is deflected or branched, preventing it from propagating and thus increasing toughness
Toughening Mechanisms - Transformation Toughening
- Phase transformation in zirconia (ZrO2) can enhance toughness and strength.
- Manufacturing of zirconia includes methods like adding MgO, sintering, and heat treatment to increase toughness.
- The processes affect the size of transformation-induced microcracks, which is a key factor in influencing the material's overall toughness
Toughening Mechanisms - Transformation Toughening - PSZ
- PSZ (partially stabilized zirconia) is a transformation-toughened material.
- Microcracks and induced stress are important factors for the toughening in partially stabilized zirconia.
Toughening Mechanisms - Transformation Toughening
- Factors like zirconia particle size, stabilizer concentration, particle distribution, and lattice mismatch are essential parameters in controlling toughening and preventing transformations that result in reduced strength and toughness.
Toughening Mechanisms - The Effect of Different Toughening Mechanisms
- A table summarizing different toughening mechanisms for ceramics and the highest toughness values achieved, exemplifying different ceramic systems.
References
- Various publications and books on ceramic materials, materials science, and nature-based composite materials.
Glass and Glass-Ceramics
- Discussion on the basics of glass and glass-ceramics.
Introduction - Definition of Glass
- Glass definition: amorphous solid with no long-range order.
- Glasses can be formed from melt cooling.
- Sol-gel glasses can also be prepared at low temperatures.
- Lack of sharp melting point and definite chemical formula are other defining characteristics.
Glass - Amorphous Solid
- Surface crystallization can occur.
- No volume crystallization is observed.
- XRD (X-ray diffraction) of a lead-silicate glass sample is presented.
Introduction - Definition of Glass
- Traditional glass composition involves inorganic materials such as silica, sodium and calcium carbonates, feldspars, borates, and phosphates.
- Certain organic glasses are also available.
Introduction - Definition of Glass
- Glass is a metastable solid which has short range order, but no long-range order.
- The material has a less stable state in the form of glass relative to a crystalline state.
Properties of Glass
- Glass is amorphous, brittle, transparent/translucent, absorbing/reflecting light
- A good electrical insulator
- Unaffected by common chemicals but susceptible to HF acid, high compressive strength.
Properties of Glass
- Mechanically strong material, strengthened by surface treatment, resist scratches, and abrasions.
- Glass is resistant to most industrial and food acids.
- Can absorb/hold heat better than metals.
- High transmittance and reflection properties for optical properties.
Volume vs Temperature
- Material volume decreases gradually as the melt cools in a steady cooling rate.
- Crystallization occurs when the cooling rate is slow enough for nucleation in the melt.
- When cooling rate is high, crystallization does not occur immediately, and the supercooled liquid volume decreases smoothly.
Glass Transition Temperature (Tg)
- Tg is where the volume-temperature curve transition occurs, parallel to the crystalline material line.
- The gradient changes.
- Viscosity is high (~1012 Pa.s) in the glass transition interval, increasing from 108 to 1012 Pa.s.
Volume vs Temperature
- Supercooled liquids cannot reach equilibrium; therefore, transformations during cooling are time and temperature dependent.
- A glass state is less stable than the crystalline state in terms of thermodynamic energy
Structural Theories of Glass Formation
- Discussion of early theories (Tammann and Goldschmidt) concerning atomic radii and ratios.
- Tammann considered glasses as strongly undercooled liquids.
- The Goldschmidt theory utilizes radius ratios of ions and assumes the structure is related to the coordination number of glass forming oxides.
- Zachariasen's random network theory is presented, explaining the structure of glasses as a network of polyhedra sharing corners with no long-range periodicity.
Structural Theories of Glass Formation
- Various types of elements are defined for their role in the glass structure: network formers, network modifiers (or intermediates),
- For instance, SiO2, B2O3, P2O5 GeO2, As2S3 and BeF2 are network formers or intermediates.
- Based on the coordination number, certain oxides are categorized either as network forming, modifiers, etc.
Structural Theories of Glass Formation
- Zachariasen formulated rules for predicting whether or not a compound can form a glass:
- Oxygen atoms are not bound to more than 2 glass formers.
- Glass formers (cations) have a coordination number of 3 or 4 (for SiO2 and various metallic oxides).
- Oxygen polyhedra is shared with each other (only at corners).
Structural Theories of Glass Formation
- Dietzel theory and field strength (Fs) of elements and their impact on the glass structure is discussed.
- Dietzel classified elements based on their field strength.
- This theory considers cation-anion interactions' effect on glass formation.
- Kinetic theory of glass formation is introduced.
- This theory studies the process related to the atomic arrangements in glass.
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Description
Test your knowledge on the key concepts related to Partially Stabilized Zirconia (PSZ) and its toughening mechanisms. This quiz covers topics like microcracks, tetragonal phase percentages, and the effects of cooling rates on material properties. Challenge yourself to understand the complexities of composite materials and their interfaces.
