final exam 033
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8/8/2019 Final Exam 033
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KING FAHD UNIVERSITY OF PETROLEUM &
MINERALS, DHAHRAN, KSA
MECHANICAL ENGINEERING DEPARTMENT
ME 205 : MATERIAL SCIENCE
Summer semester 2003-04 (033)
Final ExamInstructor: Mr. M. Yaqub
Name____________________________Student #__________________________
Tuesday: August 17, 2004 Time Allowed: 2 hours
ME 205.01
Problem # Marks Grade
1 10
2 15
3 10
4 10
5 10
6 10
7 10
Total 75
Close books and handouts
Last page of the exam is a formula sheet
This exam contains twelve (12) pages including the cover page
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Problem # 1 10 points
Please tick the correct answer.
1. The figure shows a line defect in a crystal. This type of defect is called.
Edge dislocation
Mixed dislocation
Screw dislocation
Point defect
2. For this dislocation, dislocation line is
Inside the paper
Parallel to dislocation
Perpendicular to dislocation
Perpendicular to the paper
3. In inter-diffusion or impurity diffusion,
Atoms of the element forms a dislocation line
Atoms of same metal diffuses in the metal
Atoms of one metal diffuses in another metal
Atoms diffuses in another metal at constant rate
4. Percentage elongation is a measure of
Tensile strength
Toughness
Hardness
Ductility
5. In a slip system, normal to the slip plane and slip direction makes angles of 30
and 45 degree respectively, for this system
λ = 45 and φ = 30
λ = 30 and φ = 45
λ = 45 and φ = 45
λ = 30 and φ = 30
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6. Adding the impurity atom in pure metal
Decreases the yield strength of the metal
Increases the yield strength of the metal
Have no effect on properties of pure metal
Impurity atom can not add in pure metal
7. Isomorphous alloy systems are those in which
Alloy has more than two components
Two components of the alloy can only mix up to certain percentage
Two components of the alloy can mix in any composition
When alloy has two solid phases α and β
8. In non-equilibrium cooling of an isomorphous alloy
The composition of solid phase is non-uniform
The composition of solid phase is uniform
The composition of solid phase has a single component
The composition of solid phase is difficult to identify
9. In a lead-tin alloy system Eutectic α forms,
When solidification of the alloy starts
When half of the solidification is reached
When solidification comes to an end
None of above
10. In an Iron-Carbon alloy, the mass fraction of total ferrite is 0.93. Proeutectoid
phase for this alloy is
Ferrtire
Austinite
Cementite
Pearlite
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Problem # 2 10 points
The wear resistance of a steel gear is to be improved by hardening its surface. This is
to be accomplished by increasing the carbon content within an outer surface layer as a
results of carbon diffusion into the steel; the carbon is to be supplied from an external
carbon-rich gaseous atmosphere at an elevated and constant temperature. The initial
carbon content of the steel is 0.2 wt %, whereas the surface concentration is to bemaintained at 1.00 wt %. For this treatment to be effective, a carbon content of 0.6 wt
% must be established at a position 0.75 mm below the surface. Specify the time
required for this diffusion process at temperature of 1000oC.
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Problem # 3 15 Points
Stress-Strain behavior for steel is given in the following graph. If the initial length and
diameter of the specimen is 50.8 and 12.8 mm respectively, find the following for the
steel.
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Continue Problem # 3
a) Tensile strength, fracture strength, and 0.2% yield strength.
b) Young’s modulus
c) Ductility in terms of percentage elongation and final length of the specimen.
d) True strain at necking point and necking diameter.
e) Modulus of resilience for the steel.
f) Strain hardening exponent for the steel.
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Problem # 4 10 Points
The average grain diameter for a brass material was measured as a function of time at
650oC, which is tabulated below at two different times:
a) What was the original grain diameter?
b) What grain diameter would you predict after 150 min at same temperature?
(Specify clearly any assumption you make to solve this problem)
Time
(min)
Grain Diameter
(mm)30 3.9 x 10
-2
90 6.6 x 10-2
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Problem # 5 10 points
Following figure is the copper-nickel phase diagram. For the figure
1) Show the liquid, solid and liquid + solid region.
2) If an alloy of 50 wt % Ni – 50 wt % copper is cooled from 1400o
C, find
a) The temperature where solidification will start and the composition
of liquid and solid phase at this temperature.
b) The temperature where solidification will end and the composition
of liquid and solid phases at this temperature.
c) Weight fraction and compositions of liquid and solid phases
at temperature 1300oC
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Additional sheet for problem #5
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Problem # 6 10 points
For a lead-tin alloy of composition 80 wt % Sn-20 wt % Pb and at 180oC, do the
following.
a) Determine the mass fraction and composition of α and β phase.
b) Determine the mass fraction of primary β and eutectic microconstituents after
solidification.
c) Determine the mass fraction of eutectic β .
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Problem # 7 10 points
Consider 1.5 kg of austenite containing 1.15 wt % C, cooled to below 727oC.
a) What is the proeutectoid phase?
b) How many kg of each of total ferrite and cementite form?
c) How many kg each of pearlite and the proeutectoid phase form?
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)ln(2)1(ln 0
D
D
t =+= ε ε A
F
t =+= )1( ε σ σ
For grain Growth at constant temperature; t k d d n
o
n=−