Metals and Ceramics Flashcards
What is a crystalline and amorphous/non-crystalline material?
Crystalline:
A material whose molecules are arranged in a highly ordered structure.
Non-crystalline:
A lack of systematic and regular arrangement of molecules.
What are the three common lattice structure?
- Body Centered Cubic (BCC)
- Face Centered Cubic (FCC)
- Hexagonal Closed Packed (HCP)
What are some properties of ceramic crystal structures? (2)
- Composed of atleast two elements
- Electrically charged ions instead of atoms
What influences the crystal structure in ceramic crystals? (2)
- Charge of ions
- Relative size of cations and anions
What are the kinds of lattice defects? (4)
- 0-dimentional
- 1-dimensional
- 2-dimensional
- 3-dimensional
What are the 0-dimensional defects?
Point defects
What are the 1-dimensional defects?
linear defects, dislocations
What are the 2-dimensional defects?
Interfacial defects, stacking faults, grain boundaries
What are the 3-dimensional defects?
Precipitates, Impurities, Voids
What are some examples of a point defect?
Atom from crystal / foreign atom in interstitial site (Interstitial / self-interstitial atom)
Foreign atom in lattice structure (substitutional atom)
Unoccupied lattice site (vacancies)
Explain some 1-dimensional defects (2)
Edge dislocation: A line around which some atoms are misaligned
Screw dislocation: Topological defect formed by distortion due to sheer stress.
What is a process that increases the number of dislocations in a material?
Cold forming.
What are Interfacial / 2-Dimensional defects?
Regions of the material with different crystal structure or orientation.
What are some benefits of grain boundaries? (2)
- Block Migration of dislocations
- Give the material better strength behavior
What are bulk / 3-dimensional defects? Gives examples (3)
They are macroscopic defects. Like pores, cracks and inclusions.
What is slip?
The process by which plastic dislocation is produced by dislocation motion.
What is the slip plane?
The crystallographic plane along which the dislocation line traverses
What is a slip plane?
It is the combination of a slip plane and a slip direction
What is the formula for finding the number of slip systems?
Slip plane x Slip direction
What is the number of slip planes and slip directions in BCC?
6, 2
What is the number of slip planes and slip directions in FCC?
4, 3
What is the number of slip planes and slip directions in HCP?
1, 3
What are the two properties strengthening mechanisms aim to improve?
Yield point and Tensile strength
What are the strengthening methods? (3)
- Solid Solution Strengthening
- Strengthening by Grain Size Reduction
- Strain Hardening
What is solid solution strengthening?
Foreign atoms are introduced to hinder dislocation movement by distorting structure.
What is strengthening by grain size reduction?
Increasing number of grain boundaries hence hindering movement of dislocations.
What is Strain Hardening / Cold Working
Plastically deforming a metal at low enough temperature so that the atoms cannot rearrange themselves.
What is a Single Crystal?
A crystal with perfect repeated arrangement of atoms with same orientation throughout specimen.
What is a Polycrystalline material?
A material with many grains with different crystallographic orientations separated by grain boundaries.
What is an isotropic material?
Material in which physical properties are independent of direction.
What are anisotropic materials?
Material in which physical properties depend on direction.
What are the advantages of larger grain size? (3)
- Higher melting temperature
- Higher elastic modulus
- Higher creep resistance
What are advantages of smaller grain size? (2)
- Higher creep
- Better toughness and strength
What is a phase diagram?
Phase diagram in metals represents the physical states and transformations as a function of alloy constituents and temperature.
What is lever rule for liquid phase?
S/R+S
What is lever rule for solid phase?
R/R+S
What are the two microstructures in Iron-Iron Carbide Phase diagram?
Ferrite and Austenite
What are the three points of interest in Iron-Iron Carbide phase diagram and where are they located?
Peritectic – Top left intersection
Eutectic – Top right intersection
Eutectoid – Bottom left intersection
Describe Eutectoid
0.76% C at 727C
What structure is present at Eutectoid?
Pearlite: alternating layers of Cementite and Ferrite surrounded by austenite.
What are lever rules for hypoeutectoid fraction?
Lever rule for perlite: T/T+U
Lever Rule for ferrite: U/T+U
What are lever rules for Hypereutectoid fraction?
Lever rule for perlite: X/V+X
Lever rule for cementide: V/V+X
What are lever rules for total structure?
Lever rule for cementide: T/T+U+V+X
Lever rule for ferrite:
U+V+X/T+U+V+X
What are the two main groups of heat treatment?
Hardening: Very fast cooling up to quenching for non-equilibrium microstructure
Annealing: Slow cooling rates for fully diffused equilibrium maintaining microstructure
What three structures can be produced from Austenite by hardening and what is the cooling method used?
- Pearlite: Slow cooling
- Bainite: Moderate cooling
- Martensite: Rapid quench
- Tempered Martensite:
Rapid quench + reheat
What are the six types of annealing?
- Stress relief annealing
- Homogenizing
- Coarse grain annealing
- Tempering
- Normalizing
- Spheroidizing
What is normalizing?
Removal of uneven structures of the microstructure to obtain a constant small uniform grain for an optimum strength and toughness.
What is spheroidizing?
Heat treatment to make steels more soft and ductile for machining.
What is stress relief annealing?
Annealing to dismantle internal stress from previous processes and heat treatments.
What is homogenizing?
Homogenizing of local differences in the microstructure in heterogeneous grain distribution.
What is coarse grain annealing?
Creation of a large grain structure to improve machinability.
What is tempering?
Tempering enhances ductility and toughness.
What is recrystalization?
Process for reverting from cold worked state.
What are some properties of Low-Carbon Steels?(6)
- Less than 0.25 % C
- Ferrite and Pearlite microstructure
- Strengthening performed by cold work
- Low strength and hardness, high ductility and toughness
- Machinable and weldable
- Cheap
What are some properties of medium carbon steels? (3)
- Between 0.25% and 0.6% C
- Heat treated to improve properties
- Stronger than low carbon steels, but less toughness and ductility
What are some properties of High-carbon steels? (2)
- Between 0.6% and 1.4% wrt C
- Hardest and strongest but least ductile
What are some properties of stainless steels? (3)
- Resistant to corrosion
- Atleast 11% Chromium
- High temperature resistance, low creep
What are some properties of Aluminum? (7)
- Third most common material
- Good strength with regard to density
- High resistance against weather and seawater
- Good formability and machinability
- High electrical conductivity
- High thermal conductivity
What are some properties of pure Aluminium? (3)
- High formability
- Strong corrosion resistance
- Surface can be polished using electrolysis for reflector applications
What are some Aluminum alloying elements and what properties do they improve? (6)
Silicon - Increases Castability
Magnesium - Increases strength
Copper - Increases hardenability
Zinc - Increases strength
Manganese - Increases recrystallization temperature
Lithium - Decreases density
What are some properties of Copper? (6)
- High electric conductivity
- High thermal conductivity
- Strength increased by cold deformation
- Excellent formability
- Good weldability and solderability
- High corrosion resistance
What are some properties of pure copper? (3)
- High corrosion resistance
- Low tensile strength
- Good conductivity
What are the two important copper alloys and what are their compositions?
Brass: Copper zinc with less than 50% Copper
Bronze: Copper tin with less than 60% copper
What are some properties of Magnesium? (9)
- High availability
- Low density
- Low strength
- Low elasticity
- Medium cost
- Excellent machinability
- Good dampening
- Good castability
- Low corrosion resistance
What are some properties of Pure Magnesium? (5)
- High reactivity
- Hexagonal lattice
- Poor formability
- Low toughness
- High notch sensitivity
What are some important Magnesium alloying elements and what do they do? (6)
Aluminum/Zinc:
- Increase toughness
- Decrease notch
sensitivity
Manganese:
- Increases corrosion
resistance
Cerium/Thorium:
- Increases strength at high
temperature
Zirconium:
- Grain refinement
- Increases formability and
strength
What are some properties of Titanium? (6)
- Fourth most common
- High strength
- Low density
- High cost
- High corrosion resistance
- High working
temperature
What are some properties of pure titanium? (2)
- Ductile and forgeable
- Used for corrosion resis.
What is alpha and beta titanium?
Alpha titanium has hexagonal structure
Beta titanium has cubic space centered structure
What is technical titanium?
Titanium with portions of iron and oxygen
How do properties of technical titanium vary with grade?
They are better with grade
What are some properties of alpha titanium?(3)
- Low to medium strength
- Low density
- Good weldability
What are some properties of Nickel? (5)
- Face-Centered Cubic structure
- High strength
- Very high density
- High material cost
- High working temperature
What are some properties of pure nickel? (2)
- Ferromagnetic
- Corrosion resistant
What are some important Nickel alloys and what effect do they have? (5)
Copper: Strength
Chromium: Toughness
Cobalt: Wear resistance
Iron: Temperature resistance
Molybdenum: Corrosion resistance
What are some properties of Nickel-based super alloys?(5)
- High strength
- Long fatigue life
- Resistance against creep
- Resistance against stress rupture
- Resistance against corrosion and oxidation
What are the three main types of ceramics?
Consumer, Functional, and Structural
What types of ceramics are included in consumer ceramics?
Silicate ceramics
What types of ceramics are included in Functional ceramics?
Silicate ceramics and non-oxide ceramics.
What types of ceramics are included in structural ceramics?
Oxide and non-oxide ceramics
What are some examples of Silicate ceramics?(3)
- Porcelain
- Stoneware
- Glass ceramic
What are some examples of Oxide ceramics?(3)
- Aluminum Oxide
- Zirconium Oxide
- Titanium Oxide
What are some examples of non-oxide ceramics?(3)
- Carbon
- Boron Carbide
- Silicon Nitride
What are some forming processes for ceramics? (3)
- Pressing
- Extrusion
- Injection Molding
What are the two general processes for creating ceramics?
Forming,
Sintering(burning)
What structure do silicate ceramics have after sintering?
Glassy and crystalline phases
What structure do oxide and non-oxide ceramics have after sintering process?
Polycrystalline structure
What features dominate the mechanical properties of ceramics?
Pores, inclusions, and manufacturing induced defects.
What are most common coordination numbers for ceramic materials?
4, 6, 8
What are some physical and mechanical properties of ceramics? (6)
- Disposition to brittle fracture
- Low thermal conductivity
- Low thermal expansion
- High hardness
- Low electrical conductivity
- High corrosion resistance
What is used to characterize ceramics instead of tensile strength?
Flexural strength
What is used to accurately model ceramic behavior and why is it used?
Weibull distribution, because of high degree of scatter in properties.
What are some rules for construction with ceramics?(5)
- Avoid sharp edges
- Avoid abrupt changes in cross section
- Pressure load to be preferred over tensile load
- Avoid high edge pressure
- Consider different thermal expansion coefficients
What are some important ceramic materials? (3)
- Aluminum Oxide
- Dense Silicon Nitride
- Boron Carbide
What are some properties of Aluminum Oxide? (5)
- Good mechanical and chemical properties
- High hardness
- Disposition to creep at high temperatures
- High thermal expansion
- Medium thermal conductivity
What are some properties of dense silicon nitride?(3)
- Suitable for high temperature applications
- Polyphase material
- Low chemical resistance
What are some properties of Boron Carbide? (7)
- Third hardest material in world
- High hardness at high temperatures
- Non-oxide, non-metal ceramic
- Only machinable with diamonds
- Thermal conductivity decreases with increasing temperature
- Low oxidation resistance
- High chemical resistance
