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Material Science 2. exam > 6 Metals and Alloys > Flashcards

6 Metals and Alloys Flashcards

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1
Q
  1. How are steels classified?
  2. What are their subfamilies?
  3. What are the main strengthening mechanisms?
  4. Where is steel used?
A
  1. steels are classified according to their carbon content and other alloying elements.
  2. subfamilies: carbon steels and alloy steels
  3. Main strengthening mechanisms: eutectoid (equilibrium) or martensitic (metastable) transformations
  4. cars, ships, trains, skysrapers, bridges, etc.

(iron density: 7,87 g/cm3, young’s modulus: ~219 GPa)

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2
Q
  1. How does the eutectoid transformation look like?
  2. What does α, δ, γ, CM stand for?
  3. What is Hypoeutetoid, Eutectoid, and Hypereutetoid?
  4. What does Pearlite mean?
A
  1. See presentation 6 slide 4
  2. α= ferrite, δ=delta iron, γ=austentite, CM=cementite
  3. Ferrite+Pearlite= Hypoetuetoid
    100% Pearlite= Eutectoid
    Cementite+Pearlite=Hypereutetoid
  4. Es ist ein Phasengemisch aus Ferrit und Zementit, das durch gekoppelte Kristallisation in Eisen-Kohlenstoff-Legierungen bei Kohlenstoffgehalten zwischen 0,02 % und 6,67 % auftritt. Der eutektoide Punkt (100%ige Umwandlung zu Perlit) liegt bei 723 °C und 0,83 % C. Bis 2,06 % C liegt der Perlit als separater Gefügebestandteil vor, oberhalb von 2,06 % C ist er Bestandteil des Ledeburits II
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3
Q

What are low carbon steels?

A

Low carbon steels:
%C below 0,2
Low cost, the highest volume used in the world.
Not heat treated, typical equilibrium microstructure: ferrite and pearlite
Hardening by cold work only
Tough and ductile, easy to machine, weldable
Typical mecanical properties LE ca. 275 MPa, R ca. 415 - 550 MPa, A% ca. 25

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4
Q

What are medium carbon- low alloy steels?

A

%C 0,25-0,6%
Higher strength, lower ductility and toughness.
Hardened by heat treatment (martensitic transformation -> to be seen 3rd year)
Low contents of Cr, Ni y Mo (-> low alloy) to facilitate heat treatment

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5
Q

What are high carbon steels?

A

%C 0,6-1,4
High strength and hardness, low ductility.
Wear resistance (cutting and forming materials)
Usually with high alloy content of Cr, V, W y Mo, to form carbides (very hard to increase further wear resistance -> tool steels)

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6
Q

Do you want to see a table of compositions of selected AISI-SAE steels? (Carbon and low-alloy steels)

A

Yes, you want. So look at the presentation 6 slide 6!

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7
Q
  1. What is the definition of stainless steel?

2. What are the different categories of stainless steels (ss)?

A
  1. stainless steel: a group of ferrous alloys that contain at least 11% Cr, providing extraordinary corrosion resistance.
  2. Ferretic (magnetic)
    Martensitic (hardest, but lowest corrosion resistance, magnetic)
    Austenitic (high Ni, high corrosion resistance, most used)
    Precipitation-Hardening (PH) (good combination of strength and corrosion resistance)
    Duplex (ferrite+austenite microstructure), good combination of props.)
    ->See pictures on slide 7
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8
Q

Do you want to see typical compositions and properties of stainless steels this time?

A

Of course you want, you little nerd. So check out presentation 6, slide 8

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9
Q
  1. What is the definition of cast irons?
  2. Which reactions can be found in cast irons?
  3. Which types of cast irons exist?
  4. What is the iron-carbon phase diagram showing?
A
  1. Cast iron: ferrous alloys containing sufficien carbon so that the eutectic reaction occurs during solidification
  2. Eutectic and Eutectoid
  3. gray cast iron, white cast iron, malleable cast iron, ductile or nodular, compacted graphite
  4. It shows the relationship between the stable iron-graphite equilibria (solid lines) and the metastable iron-cementite reactions (dashed lines). slide 9
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10
Q

How does the schematic drawings of the five types of cast iron: (a) gray iron, (b) white iron, (c) malleable iron, (d) ductile iron, and (e) compacted graphite iron look like?

A 
Just kidding. You will find the pictures on slide 10.
a graphite flakes
b Fe3C and Pearlite
c Graphite nodules
d Graphite spheroids (nodules)
e compacted (vermicular) graphite
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11
Q

What are the main characteristics of gray cast iron?

A

Main characteristics:

  • Brittle
  • Fracture gray in appaearance
  • Higher UTS in compression
  • Low cost
  • Vibration damping capacity
  • Low wear
  • Good castability

You want to see more: photomicrograph of the flake graphite in gray cast iron? click on slide 11

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12
Q

What are the main characteristics of white cast iron?

A

Main characteristics:

  • Low C, low Si, high cooling rate
  • Very brittle (cementite)
  • Fracture white in appearance
  • Very hard
  • Difficult to machine
  • Very low wear

slide 12 microstructure of white cast iron with eutectic cementite and pearlite

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13
Q

What are the main characteristics of malleable cast iron?

A

Main characteristics:

  • Obtained from white cast iron after prolonged heat treatment
  • High ductility
  • Strength depending on the matrix microstructure

slide 13 malleable cast iron showing graphite nodules in ferrite matrix

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14
Q

What are the main characteristics of ductile or nodular cast iron?

A

Main characteristics:

  • Mg or Ce added to nucleate graphite spheroids
  • Higher strength and ductility than gray iron
  • Strength similar to equivalent steels (depending on the matrix)

slide 14: (1) annealed ductile iron with a ferrite matrix, (2) As-cast ductile iron with a matrix of ferrite (white) and pearlite, (3) normalized ductile iron with a pearlite matrix

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15
Q

A table of typical properties of cast irons is fun, right?

A

You are so stupid, to think that, but here you are: slide 15, presentation 6.

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16
Q
  1. What are aluminium alloys?
  2. What are the main characteristics?
  3. Where do we use this material?
A 
1. Light alloy of extended use
Density: 2,70 g/cm3 (1/3 of steel!!!)
Young’s modulus: ~70 GPa
2. Main characteristics:
- Good corrosion resistance
- High electrical and thermal conductivity
- Main strengthening mechanisms: cold work &/or precipitation hardening (age hardening-> 3rd year)
3. planes, chair, car, ship, arenas...
17
Q
  1. Here we are again, is a table about the effect of strengthening mechanisms in aluminium and aluminium alloys interesting for you?
  2. Not enough, you also want tho see a table of the designation system for aluminum alloys?
  3. You want to see more? This time the temper designations for aluminum alloys?
  4. Next, a table of the properties of typical aluminum alloys?
A

Vale, I give up. Look on slide 17, presentation 6.

  1. check out slide 18, if you want to get bored as f***.
  2. What is wrong with you? slide 19
  3. no words. slide 20
18
Q

How do the microstructures of aluminum alloys look like? (casting alloys)

A

(a) Sand-cast 443 aluminum alloy containing coarse silicon and inclusions.
(b) Permanent-mold 443 alloy containing fine dendrite cells and fine silicon due to faster cooling.
(c) Die-cast 443 alloy with a still finer microstructure ( 350).

slide 21, presentation 6

19
Q
  1. What are magnesium alloys?
  2. What are the main characteristics?
  3. For what do you use it?
  4. You want to see an exciting table about the properties of typical magnesium alloys?
A
  1. Lightest of structural alloys
    Density: 1,80 g/cm3 (2/3 of aluminium!)
  2. Main characteristics:
    - Bad corrosion resistance
    - Good strength but low elastic modulus (~45 GPa)
    - HCP structure: difficult to form
    - Main strengthening mechanisms: cold work &/or precipitation hardening (age hardening)
  3. They are used aerospace applications, high-speed machinery, and transportation and materials handling equipment.
  4. Yes, on slide 23, presentation 6

handlebar, mobilephone, laptop, carseat, rim of wheel

20
Q
  1. What are titanium alloys?
  2. What are the main characteristics?
  3. What 3 things are titanium alloys used for?
  4. a nice table about the properties of selected titanium alloys sounds good?
A
  1. Best compromise in lightness and strength of all alloys
    Density: 4,50 g/cm3
    Young`s modulus: ~110 GPa.
  2. Main characteristics:
    - Excellent corrosion resistance. Biocompatibility
    - Best strength to density ratio of metals.
    - Very costly.
    • Titanium’s excellent corrosion resistance provides applications in chemical processing equipment and marine components,.
      - Titanium is an important aerospace material, finding applications as airframe and jet engine components.
      - Titanium alloys are considered biocompatible (i.e., they are not rejected by the body) and biomedical implants such as hip prostheses.
  4. There is nothing more exciting than on slide 25, presentation 6
21
Q

Let’s have a closer look on titanium alloys, okay?

A
  1. Both the grain boundary precipitate and the Widmanstätten plates are alpha.
  2. Microstructure of the alpha-beta titanium alloys. The structure contains primary a (large white grains) and a dark β matrix with needles of a formed during aging
22
Q
  1. What are copper alloys?
  2. What are their main characteristics?
  3. Where do you use it?
A
  1. First of metals to be used
    Density: 8,96 g/cm3 E ≈ 100 GPa
  2. Main characteristics:
    - Good corrosion resistance
    - High electrical and thermal conductivity
    - Main hardening mechanisms: cold work, solid solution, age hardening (with Be or Cr or Zr).
  3. money, statues, cable
23
Q
  1. How do the binary phase diagrams of copper alloys look like?
  2. You want to see the properies of typical copper alloys obtained by different strengthening mechanisms?
A

Binary phase diagrams for:

(a) copper-zinc (brasses)
(b) copper-tin (bronzes)
(c) copper-aluminium, (aluminium bronces)
(d) copper-beryllium

answer on slide 28

  1. slide 29
24
Q
  1. What are zinc alloys?
  2. What are the main characteristics?
  3. How does the eutectic and hypereutecitc version look like?
  4. table of zinc wrought (forging) alloys or zinc cast alloys?
A 
1. Low melting point metal with relatively low strength
Density: 7,13 g/cm3
2. Main characteristics:
- Low corrosion resistance, but is use to give corrosion protection to steels (galvanising)
- Forging and cast alloys available.
- Easy to cast.
- Low cost.
3. slide 31
4. slide 32
25
Q
  1. What are nickel and cobalt alloys used for?
  2. What are superalloys?
  3. super interesting table about compositions, properties, and applications for selected nickel and cobalt alloys?
A
  1. Nickel and cobalt alloys are used for corrosion protection and for high-temperature resistance, taking advantage of their high melting points and high strengths.
    Density: ~8,9 g/cm3
  2. Superalloys - A group of nickel, iron-nickel, and cobalt-based alloys that have exceptional properties:
    - Excelent heat resistance.
    - Outstanding oxidation (high temperature) resistance.
    - Exceptional creep resistance.
    -… but very expensive
  3. slide 34

Material Science 2. exam (7 decks)

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