Malmö högskola
Avd. För Materialvetenskap
Ämneskod-linje MT7151
Tentamensdatum 2007-01-09
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.
II.
III.
IV.
V.
VI.
VII.
VIII.
Crystalline structure
Stress and strain
Creep
Fe-C system
Titanium alloys
Ceramics
Polymers
Precipitation strengthening
5p
9p
10P
12p
13P
6p
4P
7p
Total
66P
Pass minimum:
30P
Mark: 5: >54P; 4: >43P; 3: >30P
I.
Crystalline structure (5p)
1. Copper (Cu) has a face-centered cubic (fcc) structure, the atomic
radius of an Cu atom r = 0.128 nm, calculate the cube edge length
“a” of the unit cell. (3p)
2. Sketch a (212) plane and a [0 1 2] direction in a cubic unit cell (see
Fig. 1). (2p)
z
y
X
Fig. 1 A cubic unit cell
2
II. Stress and strain (9p)
Fig. 2 shows the tensile stress-strain behaviour for the brass specimen. The
specimen is a cylindrical specimen having an original diameter of 12.8 mm
and an original length of 250 mm. Determine the following:
1. The elastic modulus E of the alloy; (2p)
2. The yield strength (Y.S), tensile strength (T.S) and percent elongation
of the alloy; (3p)
3. The load applied when the specimen starts to be yielded (1 MPa =
106N/m2); (2p)
4. The change in length of the specimen originally 250 mm long that is
subjected to a tensile stress of 345 MPa; (2p)
Fig. 2 stress-strain curve of brass
3
III. Creep (10p)
1. A common creep requirement is a 1000h creep life to 2% strain at a
(shear) stress of 100 MPa. Calculate the creep rate (  ) for this creep
requirement. (Do not forget to give the unit of  ) (2p)
2. Predict the time to rupture for a 18-8 Mo stainless steel component that is
subjected to a stress of 100MPa at 600ºC (873K). (4p)
3. Consider an 18-8 Mo stainless steel component (Fig. 3) that is exposed to
a temperature of 650ºC. What is the maximum allowable stress level for a
rupture lifetime tr of one year. (4p)
Larson-Miller parameter = T(20+log tr)
Fig. 3 Logarithm stress versus the Larson-Miller parameter for an 18-8 Mo
stainless steel.
4
VI. Fe-C system (12p)
1. Fig. 4 (a-b) illustrates the microstructures for grey iron and white iron
respectively. Give the name of phases pointed by arrows in the pictures.
(3p)
2. What is the function of magnesium (Mg) in ductile iron? (2p)
Phase 1
Phase 2
Phase 3
b
a
Fig. 4 Typical microstructures of (a) grey iron; (b) white iron
3. Fe-Fe3C phase diagram is shown in Fig. 5. What phases are to be
found in an alloy containing 2 % C (wt %) at (a) 1300 ºC (b) 1000 ºC
(c) at 600 ºC.? (3p)
4. A TTT diagram for AISI-SAE 1080 steel (containing 0.8 wt% C) is
shown in Fig. 6. Design a process for heat treatment in order to
obtain a final microstructure of the 1080 steel containing about 50%
fine pearlite (+Fe3C) and 50% martensite. (4p)
5
Fig. 5 Fe-Fe3C phase diagram
Fig. 6 TTT diagram for 1080 steel (the dash-line is the 50% completion
curve)
6
V. Titanium alloys (13p)
1. What is  stabilizer in titanium alloys? Give two examples of the
alloying elements for the  stabilizer. (2p)
2. A titanium alloy Ti-6Al-4V was subjected to the following heat
treatments: (a) held at 1020ºC for 2 hours; (b) quench to 900 ºC and
held at 900 ºC for 2h; (c) slowly cooled to room temperature. Using
the attached (Ti-6Al)-V phase diagram (Fig. 7) answer the following
questions:
1) Give the composition of each phase in the alloy when the alloy
has been held at 900 ºC for 2h. (2p)
2) Calculate the amount of each phase in the alloy when the alloy
has been held at 900 ºC for 2h (2p)
3) Sketch the microstructure of the alloy when the alloy has been
held at 900 ºC for 2h (2p)
4) Sketch the final microstructure of the Ti alloy when it has
been slowly cooled down to room temperature; give the
chemical composition for each phase in the alloy. (5p)
Temperature (ºC)

1000


500
Ms
Mf
5
10
Fig. 7 (Ti-6Al)-V phase diagram
7
20
Vanadium wt%
VI. Ceramics (6p)
1. What are ceramics? (2p)
2. What is the essential difference between a ceramic and a glass? (2p)
3. What is the basic difference in mechanical properties between
ceramic materials and metallic materials? (2p)
VII Polymers (4p)
1. What are polymers, give at least four basic characteristics of polymers.
(2p)
2. The following is the structure of a monomer for propylene, give the
structure of polypropylene (C2H3-CH3)n and the structure of the mer for
polypropylene. (2p)
8
VIII. Precipitation strengthening (7p)
Cu-containing Al alloys (see phase diagram in Fig. 8) are usually
precipitation strengthened. An alloy of 96% Al – 4% Cu has been subjected
the following heat treatment: (a) heated up to 550ºC and held at 550ºC for 2
hours; (b) water quenched to room temperature; (c) heated up to 150ºC and
held at 150ºC for 20 hours, and then quenched to room temperature.
Answer the following questions:
1. describe the microstructure of the alloy after heat treatment (a); (2p)
2. describe the microstructure of the alloy after heat treatment (b); (2p)
3. what happened in stage (c), sketch the final microstructure of the
alloy after heat treatment (c). (3p)
+L

(Al)+ (Al2Cu)
Fig. 8 Al-Cu phase diagram
9
10