Materials Flashcards
What are the two types of hardness tests and explain them?
The Brinnell Test: Uses a steel sphere that is pressed into the surface of the material. The relationship between the diameter of the sphere and the diameter of the indent forms the hardness value.
The Rockwell hardness test. For softer materials a steel sphere is used and for harder materials a diamond cone is used. The depth and force are automatically determined by the tester and produces a corresponding hardness value.
What test is used to test microhardness?
The Knoop hardness test
What is the definition of ductility?
The ability of a material to be permanently deformed without breaking when a force is applied.
What is fracture toughness?
Measures the ability of a material containing a flaw to withstand an applied load.
What are Weibull statistics?
The likelihood of material failing under a given load.. Brittle materials have a much wider distribution that ductile
How do brittle and ductile materials fail?
Ductile: Necking occurs, leaves cup and cone fracture, and failure surface leaves dimples from microvoids pointing in the direction of failure.
Brittle: No necking, chevron pattern fans away from the origin of the crack
What constitutes a ferrous metal?
Based upon carbon-iron alloys
What are the components of the AISI or SAE Distinctions for Ferrous Metals
The first two numbers indicate the governing alloying element.
The last two or three numbers indicate the percent Carbon
What is the carbon percent that distinguishes Carbon Steels and Cast irons?
2.11 %C
What is the carbon percentage that distingusihes hypo and hyper-euctectoid steels?
0.77%
What happens to 5 key properties when the percet carbon increases?
- Tensile Strength Up
- Yield Strength Up
- % Elongation Down
- Ductility Down
- Impact Toughness Down
What are the basic solid solutions of ferrous alloys?
Austeninte, Ferrite, Cementite, and Pearlite
What are the four methods of cooling a ferrous alloy to produce variations in solid solution strengthening and what is the resulting solid solution?
- Quenching- Martensite
- Austempering-Bainite
- Normalizing- Fine Pearlite
- Annealing- Coarse Pearlite
How are pearlite and bainite different?
Pearlite is a lamellar structure of cementite and ferrite while Bainite is non-lamellar with significantly more dislocations
What benefits arise from using an alloying element in steel?
- Solid-solution strengthening of Ferrite
- Cause precipitation of alloy carbides instead of cementite
- Improve corrosion resistance and other special characteristics
- Improve hardenability
What is hardenability?
Depth to which a material is hardened after putting it through a heat treating process
What is the Jominy Test?
It compares the hardenability of different steels by austenitizing a steel and then cooling one end with water.
What is the Jominy Distance?
It evaluates the hardness of material at a given distance away from the water cooled end.
What is the grossman chart used for?
To determine the hardenability at the center of a steel bar for different quenchants
What is galvanized steel?
Steel covered with zinc for improved corosion resistance.
What makes it stainless steel?
Contains at least 11% Chromium that forms a protective layer of chromium oxide
What additional solid solution is introduced when cast irons are cooled?
Graphite
What is the specific strength?
Strength/density
What are the pros and cons of aluminum alloys?
Pros:
- Great specific strength
- No ductile to brittle transition at low temps
- Easily formed
- Resistance to oxidation and corrosion (aluminum oxide)
Cons:
- Potential to fail by fatigue
- Poor wear resistance
What are the two kinds of aluminum alloys and what makes them distinct?
Wrought Alloys- Properties controlled by strain hardening, solid-solution strengthening, and grain size control
Casting Alloys- Enough silicon is present to cause an eutectic reaction
What are the pros and cons of magnesium alloys?
Pros:
- Lighter than aluminum
- Good corrosion resistance in most environments
- Good specific strength
Cons:
- Poor corrosion resistance with salt
- Poor resistance to creep, fatigue, and wear
- Poor Strengthening capabilities
What are the pros and cons of beryllium alloys?
Pros:
- Lighter than aluminum
- Stiffer than steel
- High Specific strength
Cons:
- Expensive
- Brittle, reactive, and toxic
What are the pros and cons of copper alloys?
Pros:
- Better resistance to creep, fatigue, and wear
- Excellent ductility, corrosion resistance, and conductivities
Cons:
1. Low specific strength
What is brass?
Copper and Zinc
What is bronze?
Copper and tin
What are the pros of nickel and cobalt alloys?
Pros:
- High Melting Temp
- High Strength
- Excellent corrosion resistance
What are monels?
Copper-Nickel alloys known for exceptional strength and corrosion resistance
What are superalloys?
Nickel, iron-nickel, and cobalt allows that contain a large amount of alloying element to produce high strength at elevated temperatures
What are the pros of titanium alloys?
- Excellent corrosion resistance
- High Specific strength
- Good High-Temper Properties
What does it mean if a material is allotropic?
The crystal structure changes based on the temperature.
What constitutes a “Light Metal” and what are examples?
Metals that have a low density but high specific strength.
- Aluminum
- Magnesium
- Titanium
- Beryllium
What constitutes a “Nobel Metal” and what are examples?
Resists corrosion and makes very good conductors of electricity.
- Gold
- Silver
- Palladium
- Platinum
- Rhodium
What constitutes a refractory metal and what are examples?
Exceptionally high melting temperature and high temp service. High density so low specific strength. BCC crystal structure.
- Tungsten
- Molybdenum
- Tantalum
- Niobium
What is the definition of glass?
Metastable material that has hardened and become rigid without crystallizing
What does amorphous mean?
No crystalline structure and only short-order of atoms
What are glass modifiers?
Additional elements that break up the network structure and cause glass to crystallize by introducing a shortage of available silicone. They allow for glass to be made at a lower temperature
What are the three temperature and viscosity ranges of glasses?
- Liquid range- sheet and plate glass formed in molten state
- Working range- shapes formed by pressing, drawing, or blowing into molds
- Annealing range- annealed to reduce residual stress and prevent cracks from forming and potentially causing devitrification
What is devitrification?
Precipitation of a crystalline phase from the glass
What is tempered glass?
Glass that had its surface cooled faster than the center which introduced a residual compressive stress
What is laminar glass?
Two pieces of annealed glass with a polymer between them
What is a glass-ceramic?
Crystalline materials derived from amorphous glasses
What percentage of crystallinity do glass-ceramics have?
> 70-99%
How do glass-ceramics get their crystallinity?
Controlled crystallization forms a combination of amorphous glass and ultra-fine crystalline phases
What are glazes?
Ceramic coatings applied to glasses
What are enamels?
Ceramic coating applied to metals
What are examples of common ceramics? What are they used for?
- Diamond- Abrasives for grinding and polishing
- Silica-glasses
- Silicon carbide- coating for metals and ceramics at high temps
How are ceramics made?
- Starts as a fine powder
- Formed into shape to produce a green ceramic
- Fired to harden
What is an example of a glass-ceramic?
Corning Ware- The ceramic top of ovens
What are the most important defect in a polycrystalline ceramic?
Pores- They are pre-existing locations for crack growth
What are technical ceramics?
High-performance/engineered ceramics, that are made of inorganic ceramic materials have superior properties. They have incredibly high purity made from a metal compound combined with oxides, carbides, or nitrides
What are examples of technical ceramics?
Alumina Oxide, Zirconium Oxide
What is polymerization?
The process by which small molecules consisting of one or a few units are chemically joined to create giant molecules
Are polymers traditionally organic or inorganic?
Organic meaning they contain carbon
What are the three kinds of plastics/polymers?
Thermoset, thermoplastics, and elastomers
How are polymers classified?
- By how the molecules are synthesized
- By their molecular structure
- By their chemical family
What are the two types of polymerization? Briefly explain them?
- Addition- Atoms are added in chain-like fashion to build the polymer (Polyethylene)
- Condensation- A relatively small molecule is formed as a result of the polymerization reaction, typically make much more complex structures (Polycarbonates)
What are the two formations that polymer chains can form?
- Linear Polymer- Much stronger as they can tightly pack together
- Branched Polymer- Little branches around chain backbone prevents dense packing and therefore stiffness, density, and strength reduced
What does increased crystallization do to thermoplastics?
Increased density, resistance to chemical attack, and mechanical properties. It forms stronger bonds
What causes increased crystallization in polymers?
Deformation leads to an alignment of polymer chains in a preferred orientation
What is tacticity?
The properties of a polymer being controlled by the location of nonsymmetrical atoms or atom arrangements
What are:
- Isotactic Polymers
- Syndiotactic Polymers
- Atactic Polymers
- a type of atoms is all on the same side of the chain
- The atom type alternates between sides
- The atom type is randomly distributed (Poor packing and poor strength)
What are copolymers?
Linear-addition chains composed of two or more types of molecules. (Backbone of the chain has multiple types of molecules) This is able to blend properties of multiple chains Example ABS
What are Liquid-Crystalline Polymers?
Complex thermoplastic chains that are so stiff they act as rigid rods, even at high temps Example Kevlar
What are the two types of crystallization for a thermoplastic?
- Temperature (Slow-Cooling)
2. Stress-Induced Crystallization (Untangle chains)
What are the four viscosity stages as temperature increases?
- Rigid
- Leathery
- Rubbery (Both elastic and plastic deformation occurs)
- Viscous
Which type of thermoplastics shows the most crystallinity? (Linear or Branched)
Linear as they are less complex and able to more tightly pack together
What type of mechanical response do thermoplastics exhibit?
- Non-newtonian and viscoelastic behavior
What does viscoelastic behavior mean?
When a force is applied, both elastic and plastic deformation occurs
What causes elastic deformation in thermoplastics?
The covalent bonds are stretched when a force is applied and return to the original position when the force is removed
What causes plastic behavior in amorphous thermoplastics?
Chains stretch, rotate, slide, and disentangle
What is crazing?
Occurs in thermoplastics when localized regions of plastic deformation occur in the direction perpendicular to the direction of the applied load
How do elastomers prevent plastic deformation and allow for incredible elastic deformations?
Cross-linking/Vulcanization: Added sulfur atoms to link polymer chains
What is the relationship between cross-linking and elasticity?
As cross-linking goes up, as does the modulus of elasticity. The rubber becomes harder, more rigid, and brittle
What are thermoplastics?
Polymers composed of long chains produced by joining together monomers
What is an example of a thermoplastic?
Polyethylene
What are the two phases of an elastomer’s deformation?
Uncoiling and stretching of the bonds
What are elastomers?
Amorphous polymers that are able to reach 200% elasticity
What is an example of an elastomer?
Polyisoprene
What are thermoplastic elastomers?
Polymers that behave like thermoplastics at high temperatures (viscous) and as elastomers at lower temperatures. They do not rely on cross-linking for elastic deformation. They are comprised of certain strong and brittle areas with a high glass transition temp that burn away at elevated temps and other regions that behave like have a soft and rubbery manner Ex. Titon
What are thermosetting polymers?
Highly cross-linked polymer chains that form a 3D network structure
How are composites produced?
When two or more materials or phases are used together to give a combination of properties that cannot be attained otherwise
What type of composites are dispersion-strengthened alloys?
Nanocomposites that have a dispersion phase made of nanoparticles that are dispersed in a matrix phase
What are the two types of phases in a composite?
Matrix phase and dispersed phase
What does connectivity indicate with regards to composites?
It describes how the two or more phases are connected in the composite
How are particulate composites classified and what are they?
Classified based on the shape or nature of the dispersed phase
- Particle-Reinforced
- Whisker-reinforced
- Fiber-reinforced
What are the three types of composites? Given an example of each. This is not referencing how the dispersed phase is classified
- Particulate (Concrete- Mix of Cement and Gravel)
- Fiber (Fiberglass- glass fibers within in a polymer)
- Laminar (Plywood- alternating layers of wood veneer)
How do dispersoids increase the strength of dispersed-strengthened composites?
They block the movement of dislocations
How are the pros and cons of dispersed-strengthen composites over traditional age-hardened alloys?
Pros:
- Better creep resistance
- Properties hold at high temps
Cons:
1. Weaker at room temps
What are dispersion-strengthened composites meant to achieve?
Strengthen the composite
What are particulate composites used for?
Designed to produce unusual combinations of properties rather than to improve strength The particulates are coarse and therefore don’t block slip very well
What are cemented carbides and give an example?
Known as cermets. Contain hard ceramic particles dispersed in a metallic matrix (Tungsten Carbide in a cobalt matrix)
Give examples of particulate composites?
- Aluminum castings containing dispersed SiC
- Extenders like Calcium carbonate is added to polymers
- Diamonds added to a metallic matrix for abrasives
What material property benefit do Fiber-reinforced composites introduce?
Improved Strength, Young’s Modulus, strength-to-weight ratio, and fatigue resistance
How do fiber-reinforced composites work?
Introducing strong, stiff but brittle fibers into a softer, more ductile matrix. The force is transmitted to the fiber instead of the matrix
What are examples of Fiber-reinfroced composites?
- Steel-reinforcing bars
2. Glass fibers in polymers (Fiberglass)
What are the fibers traditionally made of in fiber-reinforced composites?
- Boron
- Carbon
- Polymers
- Ceramics
What is the Rule of Mixtures equation for particulate composite?
rho_c (density of the composite)= summation (f_i rho_i)
f_i volume fraction of different constituents
rho_i density of each constituent
What is the rule of mixtures equation for fiber-reinforced composites?
rho_c=f_m rho_m +f_f rho_f
f_m=1-f_f
How do you calculate the thermal conductivity and stress of a FRC when the stress is applied in the direction of the fibers?
k_c=f_mk_m+f_fk_f
sigma_c=f_msigm_m+f_fsigma_f
How do you calculate the mod of elasticity of FRC for the load applied 1. Parallel to the Fibers 2. Perpendicular to the fibers
- E_c=f_mE_m+f_fE_f
2. 1/E_c=f_f/E_f+f_m/E_m
How do you calculate the tensile strength of a FRC?
TS_c = f_f*TS_f + f_mTS_m
What is the aspect ratio of a fiber and how does it affect the strength of a FRC?
Length/diameter
Strength proportional to the aspect ratio (Small diameter= fewer flaws can propagate to lead to failure and longer fibers= fewer ends of fibers to carry less of the load
What is the equation for the critical length of fiber with diameter d?
l_c=TS_fd/(2Tau_i)
Tau_i: Correlates to the strength of bond between fiber and matrix
What is the maximum volume fraction fibers can take up?
Approx 80%
What are three methods for allowing for isotropic behavior of FRC?
- Use small randomly oriented fibers dispersed throughout the matrix
- Pile sheets aligned on top of each other with different orientations
- Using 3D weaving of fibers
Why must the coefficient of thermal expansion be considered when forming a composite?
The fibers and matrixs need to expand and contract at similar rates otherwise breaking or unbonding can occur
What is delamination?
When the bonding between plies or layers of a composite tear away. 3D weaving can help prevent this from occurring
What are advanced composites?
Traditionally polymer-matrix reinforced with high-strength polymer, metal, or ceramic fibers. (Example- Carbon fiber)
What are hybrid composites?
Composites composed of two or more types of fibers
What is unique about the bonding for ceramic-fiber-ceramic-matrix composites?
You want it to be bad to increase fracture toughness to stop cracks from continuing to propagate from the matrix to the fiber.
What are laminates?
Layers of materials joined by an organic adhesive. Such as laminated safety glass
What are laminar composites?
Composites built by stacking different composites on top of each other to provide a unique combination of properties. They always show anisotropic behavior
What are clad metals?
Metal-metal composites that stack and joins the metal on top of each other
What are the benefits of clad metals?
Corrosion resistance, strength, and lightweight
What are bimetallics? What are they used for?
Laminar composites made from two metals with different coefficients of thermal expansion. Used as temperature indicators and controllers
What are sandwich materials?
Composites with thin layers of a facing material joined to a lightweight filler material. Neither material is strong but together the composite is very strong
What is the difference between laminar and lamellar?
Laminar- Thin plates stacked on top of each other that have different grain or fiber orientation.
Lamellar- The stacking of alternating materials
What is the difference between short order and long order atomic arrangements?
- In short order the special arrangement of atoms extends only to its nearest neighbors
- In long order the special arrangement of atoms extend over a much longer length scale
What are point defects?
Localized disruptions in otherwise perfect atomic or ionic arrangements in a crystal structure
What are dislocations?
Line imperfections in an otherwise perfect crystal
What is the Burgers vector?
A vector that represents the magnitude and direction of a lattice distortion resulting from a dislocation in a crystal structure
What is a slip plane?
A plane that contains both the dislocation line and the Burger Vector.
What is slip?
Deformation of metallic materials by the movement of dislocations through the crystal
What are the two components of a slip system?
The slip direction and slip plane which are parallel to each other and the Burgers Vector
Do you use () or [] for Lattice Planes and Lattice Vectors?
()- Planes
[]-Vectors
What is the comparison of strength and ductility between FCC and BCC and what causes the differences?
BCC doesn’t have a close-packed slip systems like FCC and therefore require larger stress in order to induce a slip and therefore BCC is stronger and more brittle compared to FCC
What are surface defects?
Boundaries or planes that separate material into regions
What is a grain?
A portion of the material within which the arrangement of the atoms is nearly identical
What is a grain boundary?
The surface that separates the individual grains, a narrow zone in which the atoms are not properly spaced
What are the 3 most common forms of defects?
- Dislocations (Line defect)
- Point Defect
- Grain Boundary
How does strain hardening work?
As you plastically deform a material, slip occurs and gives rise to an increase in the number of dislocations. This increase in dislocations requires more energy to produce additional slip and therefore the material is strengthened. “Increasing defect density increases the number of stop signs for addition slip”
What is the strain hardening equation?
Simga=K*Epsilon^n
How do different crystalline structure compare with regards to the strain-hardening exponent, n
- FCC Higher
- BCC High
- HCP Low
What is the Baushinger effect?
The reduction in compressive strength of a material after it has been plastically deformed under tension. This effect can be seen in reverse as well.
What is the Frank-Read source?
A pinned dislocation that, under applied stress, produces additional dislocations
What is the equation for percent cold work?
%=A_0-A_f/A_0 *100%
What is annealing?
A heat treatment used to eliminate some or all the effect of cold working
What are the three stages of eliminating the effects of cold working?
- Recovery
- Recrystallization
- Grain Growth
What is recovery?
Heat up a material that has been cold worked. The residual stresses are reduced and the dislocations form a POLYGONIZED SUBGRAIN STRUCTURE but the dislocation density and mechanical properties remain the same.
What does recrystallization work?
When a cold-worked piece is heated above a certain temperature, known as the recrystallization temperature, new small grains start to nucleate at the cell boundaries of the polygonized subgrain structure. This eliminates most of the dislocations
What is recrystallization?
The formation of new grains by heat-treating a cold-worked material
What is grain growth?
At even higher annealing temps, the grains begin to grow and combine, which reduces the number of grain boundaries.
What is the recrystallization temperature?
The temperature at which recrystallization begins and the formation of dislocation free grains starts
What is the relationship between recrystallization temp and melting temp?
T_recrystal=0.4T_melt
What is the relationship between %cold worked and recrystallization temp?
Inversely proportional
What is the relationship between grain size and recrystallization temp?
Proportional
What is hot working?
Plastically deforming a material above the recrystallization temperature and therefore no strain strengthening occurs
What is quenching?
The rapid cooling of a metal in water, oil, or air to achieve certain desired mechanical properties. Traditionally leads to martensite forming from the austenite.
What is marquenching?
A form of quencing that first brings the metal to just above the M_s temperature (Temperature at which martensite first starts to form) and once the entire metal reaches that temp, the metal is further quenched to achieve a more uniform distribution of martensite in the metal
What is the A1, A3, and Acm temps of a steel?
A1: The eutectoid temperature
A3: The temperature at which only austenite is present.
Acm: Temperature barrier between the austenite phase and the austenite cementite phase
What is tempering?
Slowly cooling a metal that has been quenched in order to provide additional toughness to the metal
What are the three steps of precipitation hardening?
- Heat to above the solvus temperature to get a complete formation of austenite.
- Rapidly quench
- Hold the metal at an aging temperature to allow the atoms to diffuse
What is the difference between natural and artificial aging?
Artificial aging involves heating the alloy up to produce the precipitation
Natural aging involves aging an alloy at room temperature
What are the four requirements for age hardening?
- The alloy must form a single phase when heated above the solvus temperature and form a double phase when cooled below it.
- The matrix must be soft and ductile while the precipitate must be hard and brittle
- The alloy must be quenchable
- A coherent precipitate must form
What is the case depth of a surface-treated metal?
The depth of a martensite layer of a metal whose surface was brought above the A3 temp and quenched but the center remained below the A1 temp
Why would you want to complete a surface heat treatment?
To achieve a hard and strong surface for superior wear and fatigue resistance while ensuring a soft and ductile, tough core
What is carburizing?
A group of surface-hardening techniques by which carbon diffuses into the steel at a temp above A3 and when the steel is quenched and tempered, it leaves a strong high carbon surface of a certain case depth and a low carbon more ductile interior
What is nitriding?
A group of surface-hardening techniques by which nitrogen is diffused into the surface of a metal at a temperature below A1.
How can you ensure that a material is crystallographically isotropic?
Make sure it is in a polycrystalline form. The random orientation of crystals will mostly cancel out any effect of anisotropy of an individual crystal structure
How can cold working lead to anisotropic behavior?
The plastic deformation can cause grains to rotate and elongate forming a fiber texture in the direction parallel to where the load is being applied. Therefore introducing an anisotropic behavior.
What is texture strengthening?
The strengthening that occurs by the development of an anisotropic texture
How does hot working introduce anisotropy to a material?
The surface of the material is cooled more rapidly than the center because of the forming rolls or dies so the surface has a finer grain size compared to the center
How does the surface finish of cold working compare to hot working?
Cold working is much better because, during hot working, the metal can contract upon cooling and the surface of a hot worked piece reacts with oxygen to form oxides which are forced into the surface
How are textures formed?
Through applied stress in a single direction that causes rotation and elongation of grains parallel to that direction
How are textures formed on thin films?
Often a mechanism of the grain growth process as compared to an applied load
What is pole figure analysis?
A technique based on x-ray diffraction used to identify textures in different materials
What is Vulcanization?
A common method for cross-linking. Strands of sulfur atoms link the polymer chains as the polymer is processed and shaped at temperatures above 100 deg C. Typically 0.5% to 5% is added
What does cross-linking do to the mechanical behavior of a polymer?
Increasing cross-linking makes it harder for polymer chains to uncoil and therefore makes polymers brittle and strong. Cross-linking can also allow for much greater elastic deformation before any plastic deformation occurs
What is cross-linking
Attaching chains of polymers together via permanent chemical bonds to produce a 3D dimensional network polymer
Describe the crystalline packing structure of thermoplastics?
When cooled below Tm, thermoplastic form regions of lamellae plates of crystalline structure with amorphous phases between
What is the molecular weight?
The term used to express the size of a molecule
What is an example of an amorphous and a crystalline polymer?
Amorphous- Polypropylene
Crystalline- Polyethylene
How do the glass transition temperature relate to the three polymers types?
- Elastomers- Very low Tg
- Thermoset- High Tg
- Thermoplastics- No Tg
