Malmö högskola
Avd. För Materialvetenskap
Ämneskod-linje MT7150
Tentamensdatum 2006-01-12
Skrivtid
14.15-18.15
Tentamen I Tillämpad Materialteknik
Examination in: Applied Engineering Materials
Number of questions: 8
Examiner: Liu-Ying Wei (telephone 57136)
Aids: pocket calculator, “ENGLSK-SVENSK ORDLISTA”
Summary of questions:
I. Crystalline structure
II. Stress and strain
III. Fe-C system
IV. Cast irons
V. Creep
VI. Ni-base superalloys
VII. Polymers
VIII. Titanium alloys
3p
7p
12p
6P
10P
6P
3P
12P
Total
59P
Pass minimum:
28P
Mark: 5: >49P; 4: >39P; 3: >28P
I. Crystalline structure (3p)
Sketch a (210) plane and a [1 1 2] direction in a cubic unit cell (see Fig. 1).
z
y
x
Fig. 1 A cubic unit cell
II. Stress and strain (7p)
Fig. 2 is a stress-strain curve obtained from a tensile test of Al alloy 2024.
1. Calculate the elastic modulus E of the alloy; (2p)
2. Calculate the yield strength (Y.S), tensile strength (T.S) and percent
elongation of the alloy; (3p)
3. Calculate the elastic recovery for the specimen upon removal of the
load at point A (see Fig. 2) in the curve, what is the plastic deformation
at point A? (2p)
A
fracture
Fig. 2 stress-strain curve of Al alloy 2024
III. Fe-C system (12p)
1. Fe-Fe3C phase diagram is shown in Fig. 3; fill the phase name(s) in the
regions (1) – (8). (4p)
2. What is the maximum solubility of carbon in the austenite? (1p)
3. What is a eutectoid reaction? Using the attached Fe-Fe3C phase
diagram give the eutectoid temperature, eutectoid composition and the
product of the eutectoid reaction in the Fe-C system. (2p)
4. A TTT diagram for AISI-SAE 1080 steel (containing 0.8 wt% C) is
shown in Fig. 4. Predict the microstructures of the steel subjected to the
following treatments i) rapidly quenched from austenitic region to
470ºC, ii) held for 4 seconds, iii) quenched to room temperature, iv)
reheated to 300 ºC for 5 hours, v) cooled to room temperature. (5p)
1
3
2
5
4
6
7
Fig. 3 Fe-Fe3C phase diagram
8
Fig. 4 TTT diagram for 1080 steel
IV Cast irons (6p)
1. What is the function of silicon (Si) in grey iron? (1p)
2. What is the function of magnesium (Mg) in ductile iron? (1p)
3. Fig. 5 (A-D) illustrates the microstructures for four types of cast irons;
identify which one is grey iron and which is ductile iron. (2p)
4. Describe the differences of the two cast irons, in microstructure and in
mechanical property. (2p)
A
B
C
D
Fig. 5 Four different types of cast irons. Optical micrographs.
V. Creep (10p)
1. A common creep requirement is a 100h creep life to 0.2% strain,
calculate the strain rate ( ) for this creep requirement. (1p)
2. From the figure below (Fig. 6) make a comparison of the relative creep
resistance of IMI Ex 834, 6246 and 64 (Ti-6Al-4V), by estimating their
lifetime to failure at 500ºC and an applied stress of 300 MPa. Note that
the Larson Miller parameter (LM = T(20+logt)) refers to temperature
in Kelvin and time in hours and that the criterion for life is 0.2% strain.
(4p)
3. What is the lifetime for alloy 6246 if the service temperature decreases
to 450 ºC provided that the applied stress remains at 300 Mpa. (2p)
4. Explain qualitatively why, in general, short-term yield strength
increases while creep strength decreases with decreasing grain size. (3p)
III Creep
Fig. 6
VI. Ni-base superalloys (6p)
1. The composition of the alloy Hastelloy X is as follow,
Ni-0.1C-1Si-22Cr-18Fe-1.5Co-9Mo-0.6W
What are the main strengthening mechanisms in the alloy? Why? (3p)
2. What is the function of the ’ phase in Ni-base superalloys, give the
compound formula and draw a schematic unit cell for the ’ phase. (3p)
VII Polymers (3p)
1. What are thermosetting polymers? (1p)
2. Vinylidene fluoride, as shown below, is one of the common
thermosetting polymers, give the formulas for the mer and the
monomer of vinylidene fluoride. (2p)
F
H F
H F
H F
H
F
H F
H
-C-C-C-C-C-C-C-C -C-C-C-CF
H F
H F
H F
H
F
H F
H
VIII Titanium alloys (12p)
1. What is  stabilizer in titanium alloys? Give two examples of the
alloying elements for the  stabilizer. (2p)
2. Using the attached (Ti-6Al)-V phase diagram (Fig. 7) to predict the
microstructure of the alloy Ti-6Al-4V subjected to the following three
different treatments, draw schematically the final microstructure,
indicate the composition of each phase in the final microstructure and
calculate the amount of each phase:
a. Held at 1020ºC for 2h + water quench to room temperature, (2p)
b. Held at 1020ºC for 2h + slowly cooled to room temperature, (3p)
c. Quench to 950 ºC + held at 950 ºC for 2h + air cool to room
temperature. (5p)
Temperature (ºC)

1000


500
Ms
Mf
5
10
20
Fig. 7 (Ti-6Al)-V phase diagram
Vanadium wt%