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Material Science 2 > Metals > Flashcards

Metals Flashcards

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1
Q

What is a ferrous alloy? Give examples.

A

An alloy with iron as its main constituent.

e.g. cast irons, steels.

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2
Q

Give three advantages of ferrous alloys

A
  • Iron-containing compounds are abundant in the Earth’s crust
  • They are very cheap to extract/refine/alloy etc.
  • They are incredibly versatile.
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3
Q

What are the major disadvantages of ferrous alloys? (3)

A
  • Poor corrosion resistance (they rust)
  • Low conductivity
  • High density
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4
Q

What are steels?

A

They are iron-carbon alloys that can contain a considerable amount of other alloying elements. Steels usually have a carbon content of less than 1 wt%.

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5
Q

What are plain carbon steels?

A

They are steels which contain very very little impurities (other than carbon and a little manganese).

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6
Q

What are alloy steels?

A

Steels which have had impurities/other alloying elements added to it in specific concentrations to change the properties.

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7
Q

Give the facts for plain low-carbon steels (6)

A
  • >0.25wt%c
  • No impurities added
  • average hardenability
  • Low tensile strength
  • some elasticity
  • used in automobiles
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8
Q

What are the facts for High-strength, low alloy steels? (6)

A
  • >0.25 wt%c
  • can contain additions of Cr, V, Ni and Mo
  • some hardenability
  • average tensile strength
  • some elasticity
  • used in bridges
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9
Q

What are the facts for plain medium-carbon steels? (6)

A
  • Carbon concentrations between 0.25 and 0.6wt%
  • no additions
  • Some hardenability
  • some tensile strength
  • average elasticity
  • used in hammers
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10
Q

What are the facts for heat treatable medium carbon steels? (6)

A
  • between 0.25-0.6wt%C
  • can contain Cr, Ni, and Mo
  • Good hardenability
  • good tensile strength
  • poor elasticity
  • used in gears
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11
Q

What are the facts for plain high carbon steels? (6)

A
  • Contains a carbon content between 0.6 and 1.4 wt%
  • no additions
  • good hardenability
  • some tensile strength
  • low elasticity
  • used in wear applications
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12
Q

What are the facts for Tool (high carbon) steels? (6)

A
  • contains between 0.6-1.4wt%C
  • can contain additions of Cr, V, Mo and W
  • very hardenable
  • good tensile strength
  • very low elasticity
  • used in drills
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13
Q

What are the facts for Austenitic stainless steels? (5)

A
  • can contain additions of Cr, Ni and Mo
  • average hardenability
  • average tensile strength
  • good elasticity
  • used in furnaces
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14
Q

What are cast irons?

A

A class of ferrous alloys with carbon contents above 2.1 wt%.

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15
Q

What is the carbon wt% of a typical cast iron?

A

Between 3 and 4.5 wt%

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16
Q

Why is casting often the most convenient fabrication technique for cast irons?

A

They have a melting point which is significantly lower than steels.

They are very brittle

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17
Q

Why is the carbon in cast irons mostly graphite?

A

The iron carbide (cementite) decomposes to form alpha-ferrite and graphite(C)

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18
Q

Why do cast irons often need slower cooling rates during solidification?

A

Slower cooling rates favour graphitization

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19
Q

How many types of cast iron are there?

A

4

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20
Q

What are the types of cast iron?

A

Gray iron, Ductile iron, White iron and Malleable iron

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21
Q

What are the facts of Gray iron? (3)

A
  • Has graphite flakes surrounded by an alpha-ferrite or pearlite matrix
  • Carbon content between 2.5 and 4 wt%
  • Silicon content between 1 and 3 wt%
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22
Q

What are the advantages and disadvantages of Gray iron? (3 advantages, 1 disadvantage)

A
  • Stronger under compression
  • Excellent vibrational dampening
  • Wear resistant
  • Weak and brittle under tension
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23
Q

Why is Gray iron weaker under tension?

A

The tips of the graphite flakes can act as points of stress concentration

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24
Q

What are the facts for ductile iron?

A
  • Gray iron but has additions of Mg and/or Ce, which significantly changes the microstructure and properties.
  • Graphite still forms but as spherical balls
  • Matrix is often pearlite, as more ductile, but can be ferrite with excessive heat treatment
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25
Q

What are the advantages of ductile iron? (2)

A

Stronger and more ductile than Gray iron

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26
Q

What are the facts for white cast iron?

A
  • Less than 1 wt% silicon
  • Large amounts of the cementite phase
  • The inside has much slower cooling times so Gray iron usually forms
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27
Q

What are the advantages and disadvantages of white cast iron?

A
  • Very rapid cooling rates
  • Due to the large amounts of cementite, it is very hard but very brittle so it is virtually unmachinable
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28
Q

What are the facts for Malleable iron?

A
  • It is white iron if it was heat treated at 800-900 degrees for a prolonged time period in a neutral atmosphere.
  • Graphite forms in clusters (rosettes)
  • surrounded by a ferrite or pearlite matrix, depending on the cooling rate (fast = pearlitic, slow = ferrite)
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29
Q

What are the advantages of malleable iron?

A
  • High strength
  • More ductile/malleable
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30
Q

Which cast irons are made with fast cooling times? (2)

A

White, pearlitic malleable

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31
Q

Which cast irons are made with moderate cooling times? (2)

A

Pearlitic Gray, Pearlitic ductile

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32
Q

Which cast irons are made with slow cooling times? (3)

A

Ferritic Gray, Ferritic ductile and Ferritic malleable

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33
Q

What are the three copper alloys?

A
  • Brass
  • bronze
  • Cu-Be
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34
Q

What are the facts for brass? (2)

A
  • Zinc, as a substitutional impurity, is the major alloying element
  • Used as costume jewellery and coins
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35
Q

What is the advantage of brass?

A

Corrosion resistant

36
Q

What are the facts for Bronze? (2)

A
  • Alloys of copper and several other elements like tin, Al, Si and Ni
  • Used as landing gear
37
Q

What are the advantages of bronze? (2)

A

They are stronger than brasses but are still highly corrosion resistant

38
Q

What are the facts for beryllium coppers? (3)

A
  • Contain between 1 and 2.5 wt% Be
  • High strengths are obtained via precipitation-hardening heat treatments
  • Used as surgical and dental instruments
39
Q

What are the advantages and disadvantages of beryllium coppers? (5 advantages, 1 disadvantage)

A
  • Very high tensile strengths
  • Excellent electrical properties
  • corrosion resistant
  • Wear resistant
  • May be cast, hot worked or cold worked
  • They cost a lot as Be is expensive
40
Q

What are the facts for aluminium alloys? (5)

A

Low density (2.7 g/cm3)

Mechanical strength can be improved by alloying/cold working but both diminish resistance to corrosion

Can contain additions of Cu, Mg, Si, Mn, Zn

Depending on the alloy an increase in strength is achieved via solid-solution hardening or precipitation hardening

Used as aircraft parts

41
Q

What are the advantages/disadvantages of aluminium alloys? (4 ad/ 1 dis)

A
  • Low density of 2.7 g/cm3
  • High electrical and thermal conductivities
  • Some resistance to corrosion
  • High ductility
  • Low melting temperature
42
Q

What are the facts for Mg alloys? (2)

A
  • Very low density of 1.7 g/cm3
  • Cannot cold work
  • Used in aircrafts
43
Q

What are the advantages/disadvantages of Mg alloys? (3 dis 2 ad)

A
  • Low melting temp
  • Susceptible to corrosion in marine environments
  • Fine Mg powder ignites easily
  • Low elastic modulus
  • Soft
44
Q

What are the facts for Ti alloys? (3)

A
  • Low density (4.5 g/cm3)
  • Hexagonal close-packed crystal structure
  • Used in space applications
45
Q

What are the advantages/disadvantages of Ti-alloys? (5 ad 2 dis)

A
  • High density
  • Extremely strong
  • Highly ductile
  • Easily forged and machined
  • Very corrosion resistant
  • Is very reactive at high temps
  • Very expensive
46
Q

Facts about refractory metals (2)

A
  • Group consisting of Niobium(Nb), Molybdenum(Mo), Tungsten(W) and Tantalum(Ta)
  • Ta and Mo are alloyed with stainless steel to improve corrosion resistance
47
Q

What are the advantages of the refractory metals (4)

A
  • Very high melting points
  • Large elastic moduli
  • High strength
  • Very hard
48
Q

Facts for Noble Metals (3)

A
  • Group of 8 metals, but most common are Gold (Ag), Silver (Au) and Platinum (Pt)
  • Used in jewellery
  • Au and Ag may be strengthened by solid-solution alloying w/ Cu
49
Q

What is the general description for forming operations

A

Forming operations are those in which the shape of a piece of metal is changed by plastic deformation

50
Q

What are the 4 forming operations?

A

Forging, Extrusion, Rolling and drawing

FERD

51
Q

What is the difference between hot and cold working?

A

When the treatment occurs above the temperature at which recrystallization occurs, otherwise it is hot working

52
Q

What are the benefits and weaknesses of hot-working? (2 ben 1 weak)

A
  • Large deformations are possible and may be repeated because the metal is soft and ductile
  • Deformation energy requirements are less
  • BUT most metals experience surface oxidation, which leaves a poor finish
53
Q

What are the benefits and weaknesses of cold-working? (4 ben 2 weak)

A
  • Increases strength but decreases ductility
  • Higher-quality surface finish
  • Greater variety (and mostly better) mechanical properties
  • Closer dimensional control
  • Expensive
  • Inconvenient
54
Q

Describe the process of forging

A
  • Usually done on hot metal
  • Application of excessive blows or by continuous squeezing
  • {Think classic hammering blacksmith and see image}
55
Q

Describe the process of rolling (2)

A
  • Piece of metal passes between two rollers results in a reduction in thickness
  • Can use cold to create high-quality sheets of metal
56
Q

Describe the process of Extrusion

A

Metal is pushed through a slit and can make stuff with complicated cross-sectional geometries

See pic

57
Q

Describe the process of drawing (2)

A

Pulling a piece of metal through a tapered/slanted die

Multiple dies can be combined to thin the metal gradually

58
Q

What is the general description for casting?

A

Fabrication process where a completely molten metal is poured into a mold cavity having the desired shape; upon solidification, the metal assumes the shape of the mold but experiences some shrinkage.

59
Q

When are the casting techniques used? (3)

A
  • When the finished shape is so large or complicated that any other method would be impractical
  • A particular alloy is so low in ductility that forming by either hot or cold working would be difficult
  • In comparison to other fabrications, this is the most economical.
60
Q

What are the 3 casting techniques?

A

Sand casting, Die casting, Investment casting and continuous casting

61
Q

Describe the process of sand casting and give some products it produces. (3 and 1 product)

A
  • Ordinary sand is the mold material
  • A two-piece mold is formed by packing sand around a pattern that has the shape of the intended cast
  • A gating system is involved to expedite the molten metal into the cavity and to minimise defects.
  • Produces large things like fire hydrants
62
Q

Describe the process of die casting and when is it used? (3 and one)

A
  • Liquid metals are forced into a mold under pressure at a high velocity and allowed to solidify
  • The mold is then taken apart to leave the metal structure
  • The mold can then be used again
  • This technique is used for high volume, low-temperature alloys like Zn, Al and Mg
63
Q

Describe the process of investment casting and when is it used? (4 steps one use)

A
  • Pattern made from paraffin
  • Mold made by enclosing in plaster of Paris
  • Melt wax and hollow mold is left
  • Pour in metal
  • Used for low volume complex shapes like jewellery
64
Q

Describe the process of continuous casting and give a use (two points and a use)

A
  • The refined and molten metal is cast directly into a continuous strand that can have a rectangular or circular cross-section; solidification occurs in a water-cooled die
  • The mechanical and chemical properties are constant throughout
  • Used to make big slabs efficiently
65
Q

What are the two miscellaneous fabrication techniques?

A

Powder metallurgy and welding

66
Q

Describe the process of powder metallurgy (4)

A
  • Powdered metals are mixed to the required composition
  • The powders are compressed to form the required shape
  • The shapes are heated to a point where they are below the melting point, but the particles are hot enough to merge into one another.
  • This decreases density as the space between the particles is smaller
67
Q

When is powder metallurgy used?

A

When dealing with materials with low ductility

68
Q

Give a general description of welding

A

Two or more metal parts are joined to form a single piece when a one-part fabrication is expensive or inconvenient.

69
Q

What is the process of welding?

A

{He skipped over it in lectures do who fucking knows}

I think its where the top/bottom of the connecting faces is melted a bit and a filler metal is put in there to seal the edges

70
Q

What is the general process of annealing?

A

Heating to the Tanneal (metal specific), then cooling slowly

71
Q

What are the 5 types of annealing?

A

Stress relief, Process annealing, Spherodizing (steels), Full anneal (steel), Normalize (steel)

72
Q

When would you need stress relief (annealing)?

A

To reduce the stress done by:

  • Plastic deformation
  • Non-uniform cooling
  • Phase transformation

Distortion and warpage and may occur if the residual stresses are not dealt with.

73
Q

When is process annealing necessary?

A

When you need to negate the effects of cold-work, so to soften and increase the ductility of a strain-hardened metal

74
Q

When is spheroidizing a metal necessary?

A

When steels contain a lot of pearlite, they may be too hard to be machined to be plastically deformed.

The steels then take on a spheroidite structure to have maximum softness and ductility

75
Q

What is the process of spheroidizing? (2)

A

Heat at just below the eutectic temperature and hold for 15-25 hrs

76
Q

Why would we need to fully anneal a metal?

A

To make a softer steel for good forming

77
Q

What is the process of a full annealing (3)

A
  • Used on low-medium carbon steels
  • Heats to get a coarse pearlite microstructure which is soft and ductile
  • This will give a microstructure with small grains and a uniform grain structure
78
Q

What is normalizing (annealing : steel) used for?

A

To make the grain size smaller

79
Q

What do you need to find to determine a hardness profile for a steel?

A
  • Find the distance from the quenched end, using the diameter of the specimen, that the centre, 1/2R, 3/4R and R are situated
  • Read off the hardness values for these distances
  • Plot this in a radial hardware profile
80
Q

Determine the radial hardness profile for a 50mm diameter cylindrical specimen of 1040 steel that has been quenched in water.

A
81
Q

What is an important fact of steels at the quenched end of a rod?

A

Alloys have identical hardness at the quenched end.

82
Q

What is hardenability?

A

The ability of an alloy to be hardened by the formation of martensite as a result of a given heat treatment

A steel with a high hardenability is one that hardens, or forms martensite, not only at the surface but throughout the structure.

83
Q

How does precipitation hardening work? (3)

A
  • Heat the metal to a higher temperature to get alpha solid solution
  • Quench it to room temp
  • Heat to an intermediate temperature to form the precipitate
84
Q

Why does precipitation hardening greatly increase the hardness and strength of an aluminium alloy?

A

The precipitate of Cu (and sometimes other metals) get evenly distributed throughout the structure.

This makes it harder for an imperfection to flow/break through the material

85
Q

What effect does precipitation hardening have on tensile strength and %Elastic Limit?

A

With time, tensile strength increases dramatically (can double) up to a time, before the precipitate becomes overly enlarged

%Elastic Limit reached minimum with precipitation time

86
Q

What is kept constant in the Jominy End-Quench test? (2)

A

Specimen size and shape and quenching treatment

87
Q

Why does the amount of martensite decrease with slower cooling rate? (2)

A

More time is allowed for carbon diffusion and the formation of the softer pearlite

Material Science 2 (4 decks)

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