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Department of Mechanical Engineering

University of Saskatchewan

ME324.3 Engineering Materials

Mid-Term Examination (Closed Book)

Student #: _______________________________

Instructor: I. Oguocha

Time Allowed: 2 h Friday, 20 October 2006.

1. Answer ALL questions.

2. Two formula/cheat sheets are allowed but must be turned in with your answer script(s).

WARNING: This is a very busy exam. Do not waste your time on irrelevancies and verbose

statements. Wherever applicable, go straight to the point (s).

Question 1 (84 Points)

Points

(a) List the CLASSES of engineering materials according to Prof. Ashby’s method.

12

(b) Name the FOUR main types of defects discussed in this class and give ONE example

of each.

12

(c) Use a labelled diagram to distinguish between a grain-boundary and a phase

boundary.

8

(d) What is the main difference between a phase and a component in alloy systems.

6

2

(e) What is the MAJOR difference between an edge dislocation and a screw dislocation?

6

(f) Name TWO main types of diffusion mechanisms discussed in the class. Which of the

two will consume more energy? Justify your answer.

8

(g) The maximum solubility of carbon in α-iron is ___________wt% and it occurs at

__________°C.

5

(h) The maximum solubility of carbon in α-iron at room temperature is __________wt%

3

(i) The maximum solubility of carbon in γ-iron is ______________wt%

(j) Alloys generally melt over a range of temperatures. TRUE or FALSE?

(k) An iron-carbon alloy contains 0.4 wt% of carbon. The solute in this system

is:__________

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3

3

(l) Which of the following statements is TRUE?

The solidus line in a phase diagram is:

A. The temperature below which only solid phase(s) exist.

B. The phase boundary below which only solid phase(s) exist.

C. The temperature above which only liquid phase(s) exist.

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(m) Which of the following statements is TRUE?

The liquidus line in a phase diagram is:

A. The temperature below which only liquid phase(s) exist.

B. The phase boundary above which liquid begins to form.

C. The temperature above which only liquid phase(s) exist.

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(n) An alloy consists of 87.5wt% Al, 1.6 wt% Fe, 7wt% Mg, 2.5wt% Cu and 1.4wt% Mn.

To what class of metallic alloys does it belong?

3

(o) When 22 g of Mg and 33 g of Si are melted together, what will the concentration of Si

be in weight % in the alloy?

6

3

Question 2 (120 Points)

Points

(a) Name the TWO main types of furnaces used in producing iron from its ores.

6

(b) Name the types of irons produced by each of the furnaces named in (a).

6

(c) Which of the common ores used in producing iron has the highest Fe content?

3

(d) A typical charge during iron production consists of three main components, namely:

____________, ____________ and _____________

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(e) In the production of iron, iron ores are reduced mainly with __________produced from

_________

5

(f) Write the two-stage chemical reactions that give rise to the reducing agent named in (e).

4

(g) Write a typical chemical reaction for the reduction of Fe2O3 by the agent named in (e) to

produce iron.

4

(h) Write the two-stage chemical reactions that produce slag during iron production.

8

(i) The type of furnace used by IPSCO Regina to produce steels is called

_________________

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(j) The MAIN raw material used by IPSCO Regina for producing steels is

________________

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(k) Name the THREE main forms in which steels are produced for market.

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4

(l) Using the Hume-Rothery rules, determine which type of solid solubility Nitrogen would form with

iron. There are four choices: a substitutional solid solution with complete, partial, or zero

solubility, or an interstitial solid solution. A table of properties of selected elements is attached

(Table Q2). (60 Points)

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Question 3 (214 Points)

Use the Al-Ni phase diagram shown in Figure Q3 to answer the following questions:

Points (a) How many phases are present?

(b) How many three-phase invariant reactions are present?

(c) Identify and circle the locations of all the three-phase equilibria present.

(d) State the terminal solid solutions present.

(e) How many intermetallic phases are present?

(f) How many of the intermetallic phases named in (e) are non-stoichiometric?

(g) Name any stoichiometric intermetallic compound(s) present.

(h) How many congruent transformations are present?

(i) Identify and draw a square around all congruent melting equilibria present.

(j) How many congruent melting intermetallic compound(s) are present?

(k) Name any congruent melting intermetallic compound(s) present?

(l) Name any incongruent melting intermetallic compound(s) present.

(m) Label all the two-phase fields.

(n) Is either Al or Ni allotropic? Give reasons for your answer

(o) Determine the number of degrees of freedom at the location marked •••• in the diagram?

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3

24

6

3

3

3

3

12

3

3

9

39

5

10

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(p) Draw the cooling curve of alloy X.

(q) Figure Q contains several three-phase invariant reactions. Name and completely

specify these reactions by providing the following pieces of information.

Reaction Temperature (°°°°C) Reaction Type

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60

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Question 4: (173 Points)

Figure Q4 shows the Fe-Fe3C phase diagram. Note that the temperature axis is in degree K.

(a) Label all the phase fields.

(b) Label all the critical temperatures and the phase indicated by the arrows.

(c) Identify and circle all the three-phase invariant reactions in the diagram.

(d) Write the reactions for the three invariant reactions identified in (c).

(e) Sketch and label the cooling curve for the steel alloy marked Y in the figure.

(f) Sketch and label the microstructures that will develop in alloy Y at positions 1, 2, and 3.

Points 24

12

9

18

25

24

8

(d) Distinguish between proeutectoid ferrite and eutectoid ferrite.

8

(e) A plain-carbon steel containing 0.72wt% C is cooled from 950°C to a temperature just

below the eutectoid temperature.

(i) Is this steel a hypoeutectoid, eutectoid, or hypereutectoid steel? Justify your answer.

(ii) Calculate the wt% proeutectoid ferrite in the steel.

(iii) Calculate the wt% eutectoid ferrite and eutectoid cementite in the steel.

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15

30

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Question 5: (144 Points)

(a) Name the SIX main types of cast irons. (15 Points)

(b) Give FOUR reasons why cast irons are chosen in place of steels in certain engineering designs.

(8 Points)

(c) On cooling cast irons from the liquid state, there are two possible eutectic reactions at 1154°C.

Write the equations of these two possible reactions and, for each, explain the factors that favour it.

(20 Points)

(d) The compositions of two cast irons are given as follows:

CI-A: 2.2 wt%C, 1.6 wt% Si, 0.5wt% Mn, 1.2 wt%Cr, 1.05wt%Ni

CI-B: 1.9 wt% C, 1.5 wt% Si, 0.4 wt% Mn, 1.2 wt%Cr, 6.5 wt% Cu, 2.5 wt% Mo, 1.05 wt% Ni.

What types of cast irons are these? Justify your answers. (16 Points)

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(e) Figures Q5(i)-(vi) show the micrographs of different types of cast irons. Using the qualifiers

“ferritic” and “pearlitic”, identify and name these cast irons. (24 Points)

(i) (ii)

(iii) (iv)

(v) (vi)

(vii) (viii)

(f) The chemical compositions of FIVE different cast irons are given in Table Q5.

(i) Determine the carbon equivalents of these irons. Enter your results in the column labelled

Carbon Equivalent. (30 Points)

(ii) Based on the results of your calculations in (i), name the iron(s) that will show a hypereutectic

microstructure. (6 Points)

(iii) Based on the results of your calculations in (i), name the iron(s) that will show a hypoeutectic

microstructure. (9 Points)

(g) State, giving reason(s), which of the irons in Table Q5 would:

(i) most likely solidify into white iron when cast (8 Points)

(ii) be most suitable for high-temperature applications (Hint: high graphitization favours high

temperature service). (8 Points)

Cast Iron (CI) %C %Si %Mn %P Carbon

Equivalent

CI-1 3.5 1.2 0.8 0.1

CI-2 3.3 2.2 0.5 0.3

CI-3 3.6 1.8 0.5 0.8

CI-4 3.0 5.0 0.5 0.1

CI-5 3.3 0.6 0.5 0.1

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Table Q2

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Student #: _______________________________

X

1395°°°°C 1385°°°°C

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Student #: _______________________________

Wt.% C →

Y

T (K)

1

2

3

Figure Q4.

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(i) (ii)

(iii) (iv)

(v) (vi)

(vii) (viii)

Figure Q5