1
Q
Grain boundary
A
- Within any particular grain, all units of the cell are arranged with one orientation and one pattern
- grain boundary, two different oriented crystals meet, there is a mismatch between the atoms as well as empty space
- can be seen with a metallurgical microscope
2
Q
Strain Hardening
A
- An increase in deformation causes an increase in dislocations making a material harder to deform: becomes stronger and more brittle
- occurs during plastic deformation at room temp
3
Q
Slip
A
- The process by which dislocations move and causes material to deform
4
Q
Erosion- Assisted corrosion
A
- Impingment cavitation are examples of this type of corrosion
5
Q
Etching
A
- metal is first smoothly polished then chemically attacked
6
Q
Activation energy
A
- Energy necessary to break bonds between atoms is called activation energy
7
Q
Four main Categories of engineering materials
A
- Metals, ceramics, semiconductors, polymers
8
Q
line dislocation/ Edge dislocation
A
- If one extra line of atoms is squeezed in the part of the crystal
9
Q
Dislocation
A
- A line imperfection, representing a missing row or an extra row of atoms in an otherwise perfect crystal
10
Q
Interstitial alloys
A
- Smalller atoms squeeze the lives between metallic atoms
11
Q
Grain boundary embrittlement
A
- When some ductile and strong metals are brought into contact with low melting point metals, they can become brittle and crack under low stresses
12
Q
Orange peel
A
materials with a large grain size are weaker at room temp and often during processing cause products to have a granular surface
13
Q
diffusion
A
- Just a stepwise migration of atoms from one position to another
14
Q
Flow assisted Corrosion
A
- Protective layer of oxide on a metal surface is dissolved or removed by win or water exposing the metal
15
Q
Environmentally Induced corrosion
A
- Result if a corrosive or chemicallly reactive environment
- SCC, hydrogen embrittlement, Liquid Metal embrittlement and corrosion fatigue alternate names
16
Q
galvanic Corrosion
A
- Occurs only when two electrochemically dissimilar metals are in contact in an electrolyte solution and one metal becomes the anode while the other the cathode
17
Q
Filiform corrosion
A
- occurs when under painted or plated surfaces when water breaches the coating
18
Q
localized Corrosion
A
- Attacks or targets one area of the material.
- Pitting, crevice and deli form are localized type of corrosion
19
Q
pitting
A
- when a small hole, or cavity, forms in the metal, difficult to detect
20
Q
Crevice Corrosion
A
- occurs in confined spaces where the access of working fluid from the environment is limited
- Occurs under gaskets or seals, inside cracks and seams or in spaces filled with deposits and under sludge piles
21
Q
Corrosion
A
- Degredation of a material due to a reaction with its environment
22
Q
Z-number
A
- Strongly affects the penetrating ability of ionization radiation
- Number of protons in the nucleus, atomic number
23
Q
Malleability
A
- Can be extensively deformed without producing cracks and voids in structure
- make different shapes without fracturing them.
24
Q
rare earth elements
A
- Some metals because they are rarer or more difficult to extract from ore such as titanium, silver and gold
- Not necessarily rare in quantity just difficult to extract
25
general Corrosion
* general attack or uniform corrosion most common type of corrosion
* entire surface of the metal shows a uniform spongelike appearance
26
Hot- Worked
* if it is plastically deformed( pressed, rolled, drawn, extruded) above its recrystallization temp
* New grains are formed, which are mostly free of dislocations
* harder materials such as steel or parts where reduction in area is large are hot worked
27
atomic Weight
* Weight is mass multiplied by gravitation
* can be represented in grams or kilograms
28
Screw Dislocation
* Crtsyalline lattice is distorted in a spiral form
* When dislocations formed? During solidification of crystalline solids, permanent or plastic deformation, atomic mismatch
29
point Defect ( Vacancies)
* If crystals have missing or have a few extra atoms, called point defect
* if one or few atoms are missing it is termed vacancy
30
cathodic protection
* passing anodic or cathodic currents in the metal
* electrons are passed into the metal and reach the metal/ electrolyte interface ( Cathodic current) the anodic reaction will be stiffied while the cathodic reaction rate increases
31
Equilibrium phase Diagram
* illustrates the relationship between temperature composition and the phases present in the particular alloy system
*Collection of curves showing solubility limits for different composition at different temps
* Upper line: 100 percent liquid
* Lower line: Solid
*above liquidous: One phase liquid
32
Thermosetting Polymers
* Thermosetting like a cake and thermoplastic like Ice
* once a part becomes thermoset it cannot be remelted or recycled
* Long chained molecules are cross linked in a 3D spatial arrrangement so product becomes one molecule
* cross linking also called curing can be done at high as well as room temps
33
polymorphism
* Ability of a solid material to exist in multiple forms of a crystallographic structure
* Pure iron metals at 2800F as it cools takes a BCC Structure. At 2541 Changes to FCC then upon further cooling changes to BCC
* BCC Structure has a lower packing number than FCC Structure
34
Amorphous structure
* Solids which have no particular order
* Tend to soften slowly over a wide temp range
* if maintained at temp just below the melting point for long periods of time gradually will re arrange into a more highly ordered crystalline form
35
Cold worked
* Grains are deformed, large number of dislocations are jammed along grain boundaries
* products are harder and stronger than hot worked
* less ductile, if further deformation needed, need to be annealed, where they are heated to their recrystalization temp so new grains are formed
* have better surface finish, dimensional accuracy of cold working is better because of uneven thermal expansion
36
Thermal Expansion
* When atoms Increase in temperature, they gain kinetic energy and vibrate
* Temp is essentially a measurement of the kinetic energy of atoms
* why most materials minus polymers expand when heated
37
Chemical bonding between atoms
* Every object seeks to decrease its potential energy
* chemical bonding can be divided into two groups: primary or strong bonds- Ionic, covalent and metallic or secondary or weak bonds
* Strong bonds mean large amount of energy have to be spent to separate atoms. Can be mechanical or thermal
38
Electropositive elements
* Given to metals because they easily “give up” their valence electrons and become positively charged
* Most elements in the periodic table are metals
* elements located on the right side of the periodic table are electronegative meaning they readily accept electrons to form anions
39
Fretting Corrosion
* Results of repeated wearing, vibrations on an uneven rough surface
* often found in rotation or machinery balked assemblies and bearings, surface exposed to vibration
40
properties of metals
* Good conductor of heat and electricity, often malleable
* hard and strong at room temp
* cannot be made of transparent, unless metal is thinner than the wavelengths of visible light, aluminum can be made transparent
* Fe, Co, Ni have desirable magnetic properties
* can be reflected and recycled
41
Conditioning the corrosive environment
* Removal of oxygen: oxygen one of the main agent in corrosion
* sulphite or any other such solution can work as a strong reducing agent
* Corrosion Inhibitors: a chemical additives, which when added to a corrosive aqueous environment reduces the rate of metal wastage
42
Intergranular Corrosion
* Result of a localized attack at or nearer to the grain boundary in a metal or alloy
43
Dealloying or selective leachry
* Selective dissolution of the active metal phase from an alloy in a corrosive environment
44
Foams
* made from metals and graphite
* metal foams made from aluminum and less frequently titanium or tantalum
* solid metal represents only 5 to 20 percent of the volume of
* however specific strength and stiffness are larger than for soild metal
45
Erosion Corrosion
* Accelerated or increased rate of deterioration or attack on a metal because of relative movement between a corrosive fluid and the metal surface resulting from the combination of mechanical and chemical wear
46
Smart (intelligent) materials
* Nonorganic materials that are able to sense and respond to changes in their environment in predetermined manners
* 1. Shape memory alloys: can be deformed at room temp but change to their original shape when heated
* 2. Piezoelectric ceramics: materials that produce a voltage when they experience a change in dimension ( strain ) under and applied load ( Stresses)
* 3. magnetostrictive materials: same as piezoelectric except for a response to a magnetic field
47
Nano- engineered material
*nano refers to the size of the particles which are 10 to the 9 power or 1 billion of a meter
* ability to arrange atoms
48
Biomaterial
* Can be implanted in the human body without causing adverse biological reactions or rejection
* ceramics used in the human body are called bio-ceramics
* Nearly Inert
* Porous Growth- Bone Ingrown occurs
* surface reactive- attach themselves directly
* absorbable are absorbed into and replaced by the bone
49
Thermoplastic polymers
* 85% of polymers are thermoplastic
* Produced at low cost using injection molding, blow molding and thermoforming processes
* Generally less strong and melt at lower temps than thermosetting polymers
* big advantage is that they can be remelted and recycled, thermosetting cannot
* two types of thermoplastics: Semi-crystalline and amorphous
50
Polymers
* often called plastics, composed of long chain repeating molecules
* bond between chains can be much weaker forming thermoplastic polymers or equally strong thermosetting
* elastomer (rubbers) adhesive coatings, fibers for composites are only called polymers
* Phenol formaldencle (balkeltic ) first thermosetting polymer
* Thermoplastics used 5 times more than thermosetting polymers
51
Extrinsic semiconductors
* Impurities are added in small, controlled amounts ( # of atoms) to provide either electrons near the conduction band ( N-type ) or the valence band ( p-type semiconductors )
* combination of N and P type of extrinsic semiconductors are used for junction devices ( diodes) Diodes allow high current flow in one direction
* light- emitting diode ( LED) electrons in the conduction band move to the valence band, light is emitted
* transistor: consisting of 3 semiconductors arranged P-n-p or N-P-N serve either as a gate or an amplifier, chips
52
Fluorescence
* Electrons that are excited into the conduction band with the vehicles light “ fall down” almost immediately to the valence band, releasing light
53
Intrinsic semiconductors
* Material that have two energy states close enough for electrons to jump over from fill state to empty conduction
* Only two elements silicon (Si) and germanium ( Ge) have that property. Compounds formed have the same ( gallium arsenide) indium antennite ( INSP) Cadium sulfide ( CDS) and Zinc telluride ( ZnTe)
* precise measurements of elevated temps made using thermistors which are made form intrinsic semiconductors
54
Semi Conductors
* Conduct electricity better than insulators ( ceramics and polymers) but not as well as most metals
* Ceramic semiconductors can be modified with chemical impurities adding these is called doping, similar to alloying except doping is usually on the order of parts per billion to parts per thousand
55
Normalizing
* Process sued to homogenize alloy steels
* austentization is performed at 50 to 60 C ( 122 to 140 F)
* temp higher than full anneal to accelerate for diffusion needed for dissolution of the alloying elements
* held at normalizing temps for sufficient time to effectively dissolve most alloying elements
* long soaking times avoided to not allow grain growth, followed by circulating air cooling
56
Stress relief
* Process designed to eliminate internal stresses in the part, residual stresses
* Due to process in which ends with the outer region under tension and the interior under compression at equilibrium
* most common method of residual stresses mitigation is by heating to temp substantially below austentite to ferrite transformation to allow some diffusion
57
Age hardening
* Several Alloys ( 2024, 6061, 7075 Alu) when quenched from an elevated temp( single phase soiled solution) one supersaturated with solute atoms at room temp
* these alloys when aged at room or slightly elevated temps will strengthen by a process known as age hardening or precipitation hardening
* tensile, yield and hardness increased
58
Strain Rate
* Rate of change in strain will change with respect to time
* Strain measured on the specimen gage lenght is used to calculate the strain rate
* many material, if a gradual tensile force (low Strain rate) is applied will elongate a large amount before they break. If an impact load or sudden force is applied the material will break
59
Composites
* Composites are stronger than unreinforced matrices
* Combination of two or more materials where each material can be visually distinguished from the other
60
Metallic Glasses
* Some metallic alloys when cooled very rapidly do not have enough time to crystallize, instead form amorphous without order structures
* Atoms are randomly and tightly packed, because they do not form crystals, neither do they have grain boundaries as a result makes them 10x stronger than crystalline metals and alloys
61
Atomic structure
* atom: Smallest part of an element that retains the properties of that element
* Molecule: smallest part of the compound ( substance consisting of more than one kind of atom) that retains properties of that compound
* Sceicne that governs the system of atomic and subatomic particles and their behavior in atoms and solids is called quantum mechanics
62
Gels
* colloidal state compromised of inter-dispersed solid and liquid in which solid particles are themselves interconnected or interlaced in 3-D
63
hexagonal Closed packed structure
* this structure represents three hop unit cells which are skewed prisms
* BCC and HCP are closed packed structures packed very efficiently with the highest possible packing factor of .74
* zinc, magnesium and cobalt
64
Hot shortness
* Caued by local melting of a constituent or an impurity populating the grain boundaries of a base material below its melting point
65
Recrystallization
* Nucleation and growth of stress free grains
* Takes place only if grains are previously deformed and dislocations are piled at grain boundaries
* by eliminating the jamming dislocations and allowing them to move more easily, lowers the strength of the material, but makes it more ductile
66
grain Size
* Amount of grain boundary per unit area is rain size (N)
N= 2 to the N -1 or n= log n t1: n= grains per area
67
Annealing
* if material is heated between .3tm and .5tm where tm is the melting temp the atoms have enough energy to move slightly and form new grains
* once atoms have mobility, find new positions and relive stress by creating new grains which are free of dislocations and equal in size in all 3 directions
68
plastic deformation
* permanent or plastic deformation implies moving layers of atoms with respect to each other and changing the part without changing the volume or causing fractures or cracks
* Slip planes easier to push dominoes if they are close to each other than if they are far away from each other
* most dense directions where split occurs called slip direction made up of slip systems
* FCC have more slip systems and more malleable easier to deform
69
Residual Stress
* Can be caused by thermal gradients, crystallographic transformation and plastic deformation
* plastic D can occur across the cores section of the part ( rolling or forging) or localized to the surface
* very little load could be required before the total stress exceeds material capacity
* Can be beneficial because localized compressive stress at the surface from peening must first be overcome by applied stresses, thus extending the life of the part
70
polymorphism
* Materials that can have more than one structure are called polymorphic ( allotropic)
* Iron can be BCC and FCC, 1674-2541 F. FCC below 1674 or above 2541 has a bcc structure until melting 2800F
* titanium is BCE and HCP. HCP at low temps and BCC above 1620F
* In iron the change of volume as it cools from 1675F 913C to 1674F (912C) will change (-1.34% ) when changing from FCC to BCC
71
Ionic bonding
* Always found in compounds that are composed of both metallic and non metallic elements
* ionic bonding non directional magnitude of the bonding force equal in all directions
* hard and brittle and high melting points, electrical and thermal insulators, ceramics bonded ionically
* non-metallic are negatively charged ( anions)
72
Atomic Bonding
* Electrons that occupy the outermost shell are called valence electrons, important bonding between atoms to form atomic and molecule groups
* Some atoms have stable configurations, valence electron shells are completely filled. He, Ar, Kr and Xe do not react chemically with other elements
* Atoms that have an electrical charge are called ions positively charged are called cations, negatively charged called anions. Cations smaller atomic radii, anions larger
73
Atomic number
* referred to as the Z-number is the number of protons in the nucleus
* neutral atom- the number of protons is equal to the number of electrons
74
Covalent Bonding
* Stable electrical configuration is achieved by the sharing of electrons between adjacent atoms
* Two atoms that are covalently bonded will each contribute at least 1 electron to the bond, shared electron belongs to both atoms
* is directional, it exist only in the direction between one atom and another that participates in electron sharing
* most covalent bonds are very strong, but also due to the directional bonding and lack of sharing in 3D many molecules containing dissimilar atoms are gasses or liquids
75
Atomic Mass
* Protons and neutrons have approximately the same mass 1.67 x 10 to the -27 KG
* mass of an electron is 1/1836 the mass of the proton
* Total mass of an atom is found when the masses of protons and neutrons are added together
* atoms of the same element that have a different # of neutrons in their nucleus are called isotopes
* atomic mass unit (AMU) 1.67 X 10 to the -24
* mass per one mole atom 6.023 X 10 to the 23
76
Conditioning the metal ( corrosion protection )
* 1. Coating the metal : corrosion resistant coating is applied to the metal to avoid the contact between the metal and a corrosive environment
2. Alloying the metal: corrosion- resistant alloy is added to the metal to provide more protection to corrosion
77
ceramics
* Composed of oxides( metal and oxygen), Nitrides ( metal and nitrogen) and carbides ( metal and carbon)
* electrons are more tightly bonded to specific atoms
* electrons immobile, ceramics tend to be poor conductors of heat and electricity
* brittle
* makes ceramics hard ( resistant to penetration ) Strong capable of carrying significant load without deformation
* low toughness due to their brittle nature
* Electrical and thermal insulators, Sentitive to notches, chemically stable
78
Single phase region
Multiple phase region
* 1. Particular phase has a known chemical composition
2. Chemical composition and amount of each phase in the mixture can be deduced from the phase diagram
79
1. Solid solution
2. Solid mixture
1. Solid single phase that contains more than 1 element
2. Solid material where more than 1 phase is present
80
1. Substitutional solid solution
2. Interstitial Solid solution
1. One type of atom with another in a structure
2. one foreign atom between atoms of the most material ex. Brass
81
Phase
* A material having the same composition structure and properties everywhere
82
1. Equilibrium condition
2. Nonequlibrium Condition
* 1. All reactions are completed and the structure would not change regardless of how long the material is kept at that temp
2. Represents the structure before the material transformation is finished
83
modulus of elasticity
* ratio between stress ( amount of force per unit area) and Strain( change in length per unit length)
*densest direction in a BCC unit cell is along the body diagonal, FCC the densest direction is the side diagonal
Stress/strain
84
Hooke law
* Principle of physics that states that the force needed to extend or compress a spring by some distance is proportional to the distance
* relationship between the forces applied to a spring and its elasticity
85
Ferrite
* Below 912C ( 1674F) BCC structure called ferrite
* contains max .022% carbon at 727C but at room temp is almost pure Iron
* soft and magnetic
86
Cast iron
* Iron- Cementite mixture with more than 2.11 iron
* most common iron cast has 4.30% Carbon
* can be heated at the lowest temp of any material in the iron diagram to become liquid ( 1148 to 2098F)
* why it gets used in casting practices
87
Pearlite
* Present in most steels and cast irons at room temp is cooled slowly under equilibrium conditions
* steel with approximately .77% consist entirely of a pearlite microstructure
* shimmer gives it a pearly appearance
88
Stiffness change
* As material heats up, atoms move farther apart
* Elastic modulus will decrease as the temp increases
* if stiffness of the material decreases, the Speed of the sounds or shear modulus will also decrease
* acoustic velocity with UT governed by material density
* stiffness of a material and correspondidly the speed of sound in that material are related to the strength of the atomic bonds
* steel 195-210GPA, aluminum 70GPA
89
Cementite ( iron Carbide Fe3C)
* Contains 6.67% Carbon
* very hard and brittle
* if it consist mostly of iron and carbon and has less than 2.1% carbon, called plain carbon steel
* if other elements added called alloyed steel if mostly iron and carbon
90
Process Anneal ( intermediate Annealing)
* remove hardening due to previous cold working and restore ductility so that additional cold working can be performed on the product
* too high a temp or too long duration and process causes excessive grain growth which makes material brittle
91
full anneal
* normally used for steels with medium carbon content to improve machinability and formability
* steel 1st fully austenized, heated to 25 to 30C 9 77F to 86F) then cooled slowly in the furnace
* Furnace cooling produces very coarse pearlite that has softest microstructure possible for the steel
92
Austentite
* Below the the S-region, FCC structure
* depending on the temp, small amounts of carbon can dissolve austentite
* max amount of carbon called gamma iron is 2.14W% at 1147 C ( 2097F)
* 727C ( 1341F) lowest temp austentite can exist , 76%W carbon
* single phase, non magnetic ductile at high temps
* in plain carbon steel at room temp cannot exist adding manganese makes it stable at room temp
93
Secondary bonding
* Secondary or van Der waals bonds are much weaker than primary bonds
* are always present, evident in inert gases but are obscured by primary bonds if present
* are important in covalent bonding, they act between large molecules of polymers making 3D solids
94
Crystallization
* Essentially all metals except when cooled at an extremely rapid rate, forming metallic glasses, major fraction of ceramic materials and certain polymers crystallize when they solidify
* those that do not recrystallize called amorphous
* posses a periodicity and long range order
95
metallic bonding
* Found in metals and their alloys
* is non directional in character, bonding and temp (tm) are proportional
* if metal not connected to source of electricity movement is random. If electricity electrons are attracted to the positive electrode
* most metals and their alloys are ductile at room temperature. Atoms can change positions without metallic bonds being broken while in covalent and ionic they have to be making them brittle
* farther apart elements form ionic, closer tend to form metallic or covalent
96
1. Mixture
2. Matrix
3 solute
1. Boundary between the two phases is a surface at which the atomic arrangement is not perfect
2. Base material called the Matrix ( larger component) in the structure
3. Added material is called solute
- good properties of a mixture, the mature should be soft and tough and the solute should be hard Finley dispersed and round
97
Martensite
* when steel is quenched cooled rapidly from austentizing temp turns to martensite
* metastable and same comp as austentite but has a body centered tetragonal structure (BCT)
* starts forming at 230C ( 436F) or lower
* can form at such low temps due to the formation of martensite no change in somposition
* has potential for very high hardness 65 Rockwell
* volumetric increase as austentite transforms to martensite
97
face centered cubic structure
* majority of metals have a FCC structure
* there is a total of four whole atoms in the FCC structure, six 1/2 atoms in the center of each side and 8 1/8 atoms at each corner
* lattice constant of FCC is larger than that for the BCC but it contains four atoms resulting in a higher packing factor. Bigger means more densely packed
* 74% of the space of a FCC packed with atoms
* Iron has a fcc at higher temps, aluminum copper, nickel, silver, lead, gold
98
Body centered cubic structure
* iron has a cubic structure but 3 different type of unit cells at different temps
* body diagonal can be written as 4R= a BCC unit cells to the 3 square root
* 8 atoms are placed in the corners at of the dimple model only 1/8 belong to the unit cells. Remaining 7/8 belong to the neighboring unit cells
* 2 whole atoms make up the BCC unit cell packing factor equals
* 68 % of the space in BCC occupied by atoms, 32% empty
* iron most common, chromium, tungsten, titanium, lithium, sodium, potassium
99
Equilibrium phases
* Red cloth( pure primary color) only one phase, single phase metal such as copper or iron
* Purple Cloth ( mixture of blue and red) sub alloy such as brass or interstitial alloy such as austentite in steel, cannot distinguish between red or blue
*red or purple cloth with blue dots- mixture such as spheroidate
*Red cloth with blue stripes = different microstructures such as pearlite
100
Pure Iron not used as in cast state
101
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