Week 1

Question 1

Primary interatmoic bonds?

Answer 1

Ionic, covelent, metallic

Question 2

Secondary bonding

Answer 2

Van der waals, hydrogen bonding

Question 3

Bonding energy E0

Answer 3

The separation of atoms/ions with an equillibrium distance r0 where the interatomic energy is minimum

Question 4

Materials w/ high bonding energies…

Answer 4

Have high melting temperature and high strengths

Question 5

Forming of atoms are either…

Answer 5

Crystalline materials or non-crystalline/amorphous (no definite form)

Question 6

Define:
1) crystalline materials
2) non-crystalline materials

Answer 6

1) periodic arrangement of atoms (long range order). They are formed by, all metals, many ceramics and some polymers.
2) short range order only. Has complex structures.

Question 7

What is a Polycrystalline material?
What happens during solidification? What is the atomic mismatch where two grains meet?

Answer 7

1) Collections of many small crystals or grains
2) Small nuclei crystals form at various locations during solidification. These small grains grow by addition of surrounding liquid.
3) grain boundaries

Question 8

What is anisotropy?

Answer 8

The directionality of properties

Question 9

What’s polymorphism?

Answer 9

Some materials have more than one crystal structure

Question 10

What’s alloytropy?

Answer 10

When polymorphism is found in elemental solids

Question 11

Types of defects?

Answer 11

Point defects, Line defects, Surface defects

Question 12

what are the?…

1) Point defects
2) Line defects
3) Surface defects

Answer 12

1) Vacancies, Intersitials, Impurities
2) Dislocations
3) Material surface, Grain boundaries, Stacking faults, Twin boundaries

Question 13

Interstitial atom?
What it causes?

Answer 13

an extra atom/ion inserted at an interstitial site (small void space normally not occupied)

Surrounding crystal region gets distorted compressed. Stress strengthens the material

Question 14

Substitutional defect?
What it causes?

Answer 14

A lattice atom/ion replaced by a different atom/ion, either larger or smaller than host atom.

It distorts local vicinity and often increase the strength of metallic materials.

Question 15

Frenkel defect?

Answer 15

a vacancy-interstitial pair, formed when a lattice atom/ion jumps to an interstitial site creating a vacancy.

Question 16

Schottky defect?

Answer 16

removal of stoichiometric number of anions and cations to preserve the electrical/charge neutrality

Question 17

Types of line defects?

Answer 17

1) Edge dislocations (An extra half plane is inserted and the bottom edge of it is edge dislocation)

2) Screw dislocations (Crystal is sheared one atom spacing)

3) Mixed dislocations (The screw dislocation at the front face of the crystal gradually changes to an edge dislocation at the side of the crystal)

Question 18

Types of Surface defects?

Answer 18

1) Material surface: Crystal abruptly ends, the atomic bonding is disrupted and each atom at the surface no longer has a proper coordination number

2) Grain boundaries: narrow zones where the atoms are not properly space, separating the individual grains

Question 19

What happens when grain size is reduced?

Answer 19

Grain boundaries increase, making dislocations travel a short distance before stopping. Therefore, increasing a materials strength.

Question 20

In surface defects, what’s…

1) Stacking faults
2) Twin boundaries

Answer 20

1) an error in the stacking sequence of close-packed planes

2) a plane in which there is a mirror image misorientation of the crystal structure

Question 21

Strain hardening process?

Answer 21

Strengthening a material by deforming it, increasing dislocation density

Question 22

Interdiffusion (impurity diffusion)?

Answer 22

Process of atoms of one metal diffusing into another

Question 23

Self-diffusion?

Answer 23

All atoms exchanging positions are of the same type

Question 24

Two dominant mechanisms of metallic diffusion?

Answer 24

Vacancy diffusion, interstitial diffusion

Question 25

Explain: 1) Unstable 2) Metastable 3) Stable

Answer 25

1) a small perturbation causes the system to move to a state of lower energy 2) a small perturbation restores equilibrium 3) will never have a perceptible change

Question 26

When is there equilibrium?

Answer 26

When driving force for the reaction is zero

Question 27

What is a Cottrell atmosphere?

Answer 27

Cluster of interstitial atoms blocking dislocations

Question 28

What’s… 1) Vacancy diffusion 2) Interstitial diffusion?

Answer 28

1) An atom from a normal lattice site moves to an adjacent vacancy. (Both self-diffusion and interdiffusion/impurity diffusion occur by this mechanism. 2) Atoms migrate from an interstitial position to a neighboring interstitial position. This mechanism is only found for diffusion of impurities (hydrogen, carbon, nitrogen, oxygen).

Question 29

What affects diffusion?

Answer 29

1) diffusing species 2) Temperature

Question 30

Types of solid solutions?

Answer 30

1) Interstitial (additional atoms positions between the atoms of the main crystal phase) 2) Substitutional (substituting one atom for another)

Question 31

Alloying atom size limits

Answer 31

•Interstitial alloying: solvent atom radius has to be at least 30% larger than solute atom for space to in atoms in between. •Substitutional alloying: radius of solvent atoms is less than 15% different in size to the solute atom to have similar sizes.

Question 32

Component?

Answer 32

Pure metals and/or compounds of which an alloy is composed

Question 33

System meaning?

Answer 33

Series of possible alloys consisting of the same components but without regard to alloy compositions. E.g., ironcarbon system.

Question 34

Phase definition?

Answer 34

A homogenous portion of a system that has uniform physical and chemical characteristics

Question 35

Intermetallics?

Answer 35

A compound formed from two or more metals that has its own unique composition, structure and properties

Question 36

Heat treatments of formed alloy?

Answer 36

Hardening: Heated into austenite phase then quenched in oil or water Annealing: heated several hundred degrees and then cooled slowly Normalising: Heated into austenite phase and cooled slowly in air Tempering (of a hardened steel) : Heat to 400-600 degrees and then cool, increasing toughness

Question 37

Selective heating treatments?

Answer 37

Hardening of a medium-carbon steel surface: Results in a hard martensite surface, and a soft center of pearlite and ferrite Carburising: Carbon is diffused into the steel suraface at temperatures above A3 (911 degrees). Then the steel gets quenched and tempered, the surface becomes a high-carbon martensite Nitrogen: Cyaniding = immersing steel in a liquid cyanide bath Nitriding = only nitrogen is diffused into steel Carbo-nitriding- CO and NH3 are generated to diffuse both C and N into the steel surface

Question 38

Case hardening can also be done with?

Answer 38

Flame or induction heating usually with rotation. Selective heating near surface results in martensite case after quench

Question 39

Types of solid solutions?

Answer 39

1) Interstitial: Additional atoms positioned between the atoms of the main crystal phase 2) Substitutional: The process of substituting of one atom for another

Question 40

Alloying atom size limits?

Answer 40

Interstitial alloying: Solvent atom radius has to be at least 30% larger than solute atom (to fit) Substitutional alloying: Solvent atom radius is less than 15% different in size to the solute atom (needs similar size)

Question 41

Explain these metal forming... 1) Bulk forming 2) Sheet forming

Answer 41

1) it's performed on large volume to surface area materials and a large shape change results. The billet undergoing formation is usually hot and malleable 2) Sheet forming is a second stage using metal sheets. The starting surface area to volume ration is higher than bulk forming

Question 42

Types of Bulk forming?

Answer 42

1) Forging: is a compressive method where two opposing dies are used to shape the material to the die 2) Drawing (of bars/wires) : is when the work material is drawn through an orifice to create the necessary diameter 3) Extrusion: is the when the bulk material is pushed through an opening (die) to produce the desired cross-section 4) Rolling: is when rollers squeeze the larger sheet material through and compress it to a desired thickness

Question 43

Types of sheet forming?

Answer 43

1) Bending: is used to physically bend sheets into required shapes 2) Deep drawing (cup drawing) : is used to punch a flat sheet into a concave die so that it tales the cup-like shape of the die 3) Sheering: is cutting of the sheets for required dimensions

Question 44

Hot forming (0.5-0.75 of melt temperature) advantages and disadvantages?

Answer 44

Advantages: 1) more deformation without cracking 2) forced required is lower 3) little work-hardening Disadvantages: 1) accuracy of shape is harder to predict 2) surface may oxidize 3) components of forming machine will have shorter life

Question 45

Cold working advantages and disadvantages?

Answer 45

Advantages: 1) superior surface finish 2) lower energy requirements 3) work-hardening may produce a harder product Disadvantages: 1) must be ductile (or it will crack) 2) may require annealing to prevent cracking 3) requires higher forces to force cold samples into shape 4) work-hardening may not be desirable

Question 46

Aluminum general properties?

Answer 46

1) high elastic modulus 2) excellent specific strength 3) high thermal and electrical conductivity (has low melting temperature) 4) recyclable and fairly non-toxic 5) non-magnetic, some resistance to corrosion

Question 47

Aluminum alloys general applications?

Answer 47

1)Transportation industry (car engines, aerospace) 2) cans, foils 3) construction applications 4) electrical applications

Question 48

Aluminum designation?

Answer 48

1) Wrought alloys (shaped by plastic deformation) 2) Cast alloys

Question 49

Aluminum cast alloys

Answer 49

(many contain silicon) giving alloys low melting temperatures and good fluidity and castability. Properties of aluminum cast alloys can be controlled by dispersion strengthening, solid-solution strengthening, and solidification rates. Addition of elements like boron, titanium, or magnesium changes grain size. Addition of elements like copper or zinc results in age hardening

Question 50

Magnesium properties?

Answer 50

1) lighter than Al and has comparable corrosion resistance and specific strength 2) low elastic modulus and poor fatigue and creep resistance

Question 51

Mg alloys general applications?

Answer 51

1) Aerospace 2) Machining 3) Transportation applications

Question 52

Mg alloys

Answer 52

1) Mg is less ductile than Al, but alloying Mg increases ductility 2) Mg alloys can be strengthened by heat treatment 3) Corrosion resistance can be increased by alloying or anodising

Question 53

Copper alloys properties?

Answer 53

1) higher densities than steel 2) lower specific strengths than Al or Mg alloys 3) better resistant to creep, fatigue and wear than Al or Mg alloys 4) excellent ductility, corrosion resistance, and electrical and thermal conductivities 5) colored alloys can be used for decorative effect 6) can be strengthened using heat treatment

Question 54

Solid-solution strengthened copper alloys

Answer 54

Many copper alloys remain single phase even with the addition of large mounts of alloying elements, including brass and bronze. They have good strength and ductility

Question 55

Age-Hardenable Alloys (precipitation hardening)

Answer 55

some copper alloys display an age-hardening response like, addition of Zr, Cr, Be. Copper beryllium alloys are used for high strength and stiffness, and non-sparking qualities

Question 56

Stainless Steels

Answer 56

Iron alloys containing chromium and nickel used to enhance corrosion resistance and processing properties (more ductile). 20% Cr and 10% Ni + minor elements. Excellent corrosion resistance used in areas where aggressive environment occurs

Question 57

Nickel and Cobalt Alloys:

Answer 57

Used for corrosion protection and high temperature resistance and strengths

Question 58

Nickel and Monel:

Answer 58

Nickel and its alloys: have excellent corrosion resistance and formability Monels (60% Ni + 30% Cu + Fe): alloys used for strength and corrosion resistance in salt water. They can be age-hardened, doubling their tensile strength

Question 59

Super alloys:

Answer 59

Nickel, iron-nickel, cobalt alloys have high strength at elevated temperatures, corrosion resistance, creep resistance up to 1,000 degrees. They contain alloying elements like Ti, C, Cr, Nb, Al, Mo, producing strong and stable microstructure needed at high temperatures Applications for turbine blades, jet engines, heat exchangers

Question 60

Titanium alloys properties?

Answer 60

1) excellent corrosion resistance 2) good high temperature properties 3) high strengths and low density (specific strength) 4) Allotropic material

Question 61

Titanium alloys applications?

Answer 61

1) aerospace 2) chemical processing equipment 3) biomedical implants 4) superconductors

Question 62

Pure titanium?

Answer 62

used for super corrosion resistance.

Question 63

Titanium Ti-6Al-4V ?

Answer 63

1) biomedical applications 2) harder than pure Ti 3) corrosion resistant 4) TiO2 has very good osteointegration 5) reflective properties and safe

Question 64

Refractory metals? properties?

Answer 64

include tungsten, molybdenum, tantalum, niobium 1) exceptionally high melting temperatures 2) high density (lower specific strengths)

Question 65

Refractory metals applications?

Answer 65

1) lightbulb filaments 2) rocket nozzels 3) power station components

Question 66

Precious metals? Properties?

Answer 66

1) gold 2) silver 3) platinum 4) palladium (used often as alloys for jewelry). They are corrosion resistant and excellent electric conductors

Question 67

1) Brittle fracture 2) Ductile failure

Answer 67

1) at lower temperatures (crystalline planar surface) 2) at higher temperatures ( cup and cone shape)

Question 68

Corrosion classified by environment?

Answer 68

1) Dry oxidation: hot flue pipes and scaling 2) Emulsions: oil/water mixer 3) Aerosols and Mists: costal salt air, chemical vapors 4) Aqueous corrosion: most common natural or synthetic (eg. chemical plant) environments

Question 69

Second law of thermodynamics?

Answer 69

a spontaneous process occurs if there is an increase in entropy

Question 71

Forms of corrosion?

Answer 71

Uniform attack: Oxidation and reduction reactions occur randomly across the surface. Can be predicted and designed for. Proceeds at a rate of ~0.1mm/yr for steel in water. Localised corrosion: Occurs when distinct anodic and cathodic regions are formed. Eg. pitting corrosion. Can be difficult to spot.