EG 326 - Materials Science
Determine which microstructure goes with each location labeled on the phase diagram. Write the answer in the blanks provided below lines. Note: some microstructures may be used more than once. 1. _________ 2._________ 3._________ 4._________
#1_________A___________ #3________F____________ #5________C___________ #2_________E___________ #4_________B___________
In a hexagonal crystal a = b not equal to c, and all angles alpha, beta, and gamma are 90 degrees. ________________ True or False
False
Metals contain both ionic and covalent bonds. ________________ True or False
False
Tempering increases the amount of martensite in steel. True or False
False
The activation energy for the diffusion of carbon in chromium is 111,000 J/mol. Calculate the diffusion coefficient at 1100 K, given that D at 1400 K is 6.25 x 10-11 m2/s. R=8.314 J/mol-K a) 4.6x10-12 m2/s b) 8.7x10-7 m2/s c) 5.4x10-7 m2/s d) 9.2x10-12 m2/s
To solve this problem it first becomes necessary to solve for D0 from Equation 5.8 as = 4.6 E -12 m^2/s
Coring occurs as a result of rapid (i.e. non-equilibrium) solidification. True or False
True
The metal iridium has an FCC crystal structure. If the angle of diffraction for the (220) set of planes occurs at 69.22 (first-order reflection) when monochromatic x-radiation having a wavelength of 0.1542 nm is used, compute the interplanar spacing for this set of planes. a) 0.1357 nm b) 0.0824 nm c) 0.2180 nm d) 0.1649 nm
a) 0.1357 nm
The attractive force between two ions, FA, is given by the following formula: Fa = dEa/dr = A/r^2 where A = A0(Z1e)(Z2e), A0 = 9 x 10^9 V/C, and e = 1.602 x 10^-19 C. The atomic radii of Li+ and O2 ions are 0.068 and 0.140 nm, respectively. Calculate the force of attraction between a Li+ and an O2- ion. Note that 1 nm=10-9 m and 1N=1VC/m2 a) 1.07x10-8 N b) 3.14x10-8 N c) 2.2x10-10N d) 6.9 N
a) 1.07x10-8 N
The coordination number for a FCC unit cell is _______________ a) 12 b) 3 c) 8 d) 6
a) 12
Which type of fracture is associated with transgranular crack propagation? a) Brittle b) Ductile c) Either ductile or brittle d) Neither ductile or brittle
a) Brittle
Metals can ________ the light beams. a) Reflect b) Refract c) Transmit d) None of these
a) Reflect
A eutectoid reaction involves which of the following phases? a) Three solid b) One liquid and one solid c) Two liquids and one solid d) One liquid and two solid
a) Three solid
A specimen of a 4340 steel alloy having a plane strain fracture toughness of45 MPa/m is exposed to a stress of 1000 MPa. Will this specimen experience fracture if it is known that the largest surface crack is 0.75 mm long? Why or why not? Assume that the parameter Y has a value of 1.0. a) Yes, this specimen will experience fracture under this load because applied stress is higher than the critical stress b) No, this specimen won't experience fracture under this load because applied stress is lower than the critical stress c) Cannot be predicted
a) Yes, this specimen will experience fracture under this load because applied stress is higher than the critical stress Fracture will most likely occur because this specimen will tolerate a stress of 927 MPa psi before fracture, which is less than the applied stress of 1000 MPa
Consider a single crystal of some hypothetical metal that has the FCC crystal structure and is oriented such that a tensile stress is applied along a direction. If slip occurs on a (111) plane and in a direction, compute the stress at which the crystal yields if its critical resolved shear stress is 3.42 MPa. a) 4.65 MPa b) 11.42 MPa c) 6.98 MPa d) 6.75 MPa
b) 11.42 MPa This problem asks for us to determine the tensile stress at which a FCC metal yields when the stress is applied along a direction such that slip occurs on a (111) plane and in a direction; the critical resolved shear stress for this metal is 3.42 MPa. To solve this problem we use Equation 7.4; however it is first necessary to determine the values of phi and lambda. These determinations are possible using Equation 7.6. Now, lambda is the angle between and directions. Therefore, relative to Equation 7.6 let us take u1 = -1, v1 = 0, and w1 = 2, as well as u2 = -1, v2 = 0, and w2 = 1. This leads to
Consider a material with an average grain size of 50 nm. After subjecting it to heat treatment, the average grain size reduced to 35 nm. Under which condition, will the material exhibit higher strength? a) 50 nm b) 35nm c) Cannot be predicted
b) 35nm
The room-temperature electrical conductivity of a semiconductor specimen is 2.8 x 10^4 (m)^-1. If the electron concentration is 2.9 x 10^22 m^-3 and electron and hole mobilities are 0.14 and 0.023 m2/V-s, respectively, calculate the hole concentration. a) 1.24 x 1024 m^-3 b) 7.42 x 1024 m^-3 c) 7.60 x 1024 m^-3 d) 7.78 x 1024 m^-3
b) 7.42 x 1024 m^-3
As the atomic bond energy decreases, the melting point generally _______________ a) Stays same b) Decreases c) Cannot be predicted d) Increases
b) Decreases
A metal having a cubic structure has a density of 2.6 g/cm , an atomic weight of 87.62 g/mol, and a lattice parameter of 6.0849 Angstrom (Ao). One atom is associated with each lattice point. Determine the crystal structure of the metal. Note that 1 Ao=10-8cm and Aogadros number is 6.023x1023 atoms/mol. a) SC b) FCC c) BCC
b) FCC
On a cold day, the metal door handle of a car feels colder to the touch than a plastic steering wheel, even though both are at the same temperature. Please circle the reason why. a) Plastic has a higher thermal conductivity and therefore conducts heat away from one's skin more rapidly. b) Metal has a higher thermal conductivity and therefore conducts heat away from one's skin more rapidly. c) Plastic has a lower thermal conductivity and therefore conducts heat away from one's skin more rapidly. d) Metal has a lower thermal conductivity and therefore conducts heat away from one's skin more rapidly.
b) Metal has a higher thermal conductivity and therefore conducts heat away from one's skin more rapidly.
Luminescence is because of ____________________ a) Knocking out of electrons by photons b) Photons emitted while excited electrons drop down c) Photons stimulated by photons d) All of above
b) Photons emitted while excited electrons drop down
Consider a single crystal of some hypothetical metal that has the FCC crystal structure and is oriented such that a tensile stress is applied along a direction. If slip occurs on a (111) plane and in a direction, compute the angle between the slip and the stress direction () and the angle between the normal to the slip plane and the applied stress direction ( ) if its critical resolved shear stress is 3.42 MPa. a) lambda=18.4o phi=39.2o b) lambda=18.4o phi=71.6o c) lambda=50.8o phi=39.2o d) lambda=24.6o phi=40.7o
b) lambda=18.4o phi=71.6o
A solidus line separates which of the following phase fields? a) Liquid and liquid+α b) α and liquid+α c) Liquid+α and α+β d) αandα+β
b) α and liquid+α
What is the plane bound by the dash lines? a) (1 1 2) b) (1 2 1) c) (1 1 2 repeating) d) (1 2 repeating 1)
c) (1 1 2 repeating)
If a rod of 1025 steel 0.5 m long is cooled from 20°C to -10°C while its ends are maintained rigid, what type and magnitude of stress will result? Assume that at 20°C the rod is stress-free. E=207x 103 MPa, αl=12x10-6 (oC)-1 a) +24.84 MPa, Tensile b) -24.84 MPa, Compressive c) +74.5 MPa, Tensile d) -74.5 MPa, Compressive
c) +74.5 MPa, Tensile
The metal iridium has an FCC crystal structure. If the angle of diffraction for the (220) set of planes occurs at 69.22 (first-order reflection) when monochromatic x-radiation having a wavelength of 0.1542 nm is used, determine the atomic radius for an iridium atom. a) 0.3838 nm b) 0.1542 nm c) 0.1357 nm d) 0.1649 nm
c) 0.1357 nm
Calculate the APF for a BCC structure __________________. a) 0.52 b) 0.74 c) 0.68 d) 0.35
c) 0.68
A simple cubic crystal structure has ______________atom/atoms per unit cell. a) 4 b) 2 c) 1 d) 6
c) 1
Below is the Silver-Copper (Ag-Cu) phase diagram. Determine the Tm for pure Cu. a) 962oC b) 780oC c) 1085oC d) Cannot be predicted
c) 1085oC
Consider the TTT diagram for a eutectoid steel. In each case assume that the specimen begins at 800°C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. Find the final microstructure if the eutectoid steel is rapidly cool to 640oC, hold for 10 s, then quench to room temperature. a) 50% Bainite, 50% Martensite b) 50%Bainite, 50%Austenite c) 50% Coarse Pearlite, 50% Martensite d) 50%Coarse Perrlite, 50%Austenite
c) 50% Coarse Pearlite, 50% Martensite
A specimen of a 4340 steel alloy having a plane strain fracture toughness of 45 MPa/m is exposed to a stress of 1000 MPa. If the largest surface crack is 0.75 mm long, what is the critical stress? Assume that the parameter Y has a value of 1.0. a) 190 MPa b) 2602 MPa c) 927 MPa d) 1424 MPa
c) 927 MPa
The bonding in polymers is/are _______________ a) Ionic bond b) Metallic bond c) Covalent and secondary bonds d) Ionic and secondary bonds
c) Covalent and secondary bonds
Which of the following describes the formation of martensite? a) Diffusion dependent with no change in phase composition b) Diffusion dependent with a change in phase composition c) Diffusionless d) None of them
c) Diffusionless
Frenkel and Schottky defects occur in pairs within ionic solids because of: a) The differences in radii b) The need to maintain mass balance within the lattice c) The need to maintain charge balance within the lattice d) They do not occur in pairs
c) The need to maintain charge balance within the lattice
In which of the following phenomena do free electrons play a role? a) Melting b) Thermal expansion c) Thermal conduction d) Thermal decay
c) Thermal conduction
Determine the weight fraction of each phase in Cu-40% Ni alloy in the figure below at 1250oC. a) WL=0.20, Wα=0.80 b) WL=0.62, Wα=0.38 c) WL=0.38, Wα=0.62 d) WL=0.80, Wα=0.20
c) WL=0.38, Wα=0.62
Determine the weight fraction of each phase in Cu-40% Ni alloy in the figure below at 1250oC. a) WL=0.20, Wα=0.80 b) WL=0.62, Wα=0.38 c) WL=0.38, Wα=0.62 d) WL=0.80, Wα=0.20
c) WL=0.38, Wα=0.62
Consider the TTT diagram for a eutectoid steel. In each case assume that the specimen begins at 800°C and that it has been held at this temperature long enough to have achieved a complete and homogeneous austenitic structure. Find the final microstructure if the eutectoid steel is rapidly cool to 300oC, hold for 104 s, then quench to room temperature. a) 100% Martensite b) 50% Bainite, 50% Martensite c) 50% Pearlite, 50% Austenite d) 100% Bainite
d) 100% Bainite
Using the table below, determine the coordination number of potassium chloride (KCl). RK+=0.133 nm and RCl-=0.181 nm. a) 3 b) 4 c) 6 d) 8
d) 8
The two main factors driving the formation of a new phase are: a) Nucleation and deformation b) Eutectic composition and growth c) Nucleation and deformation d) Growth and nucleation
d) Growth and nucleation
Which of the following sets of properties leads to a high degree of thermal shock resistance? a) High fracture strengthHigh thermal conductivityHigh modulus of elasticityHigh coefficient of thermal expansion b) Low fracture strengthLow thermal conductivityHigh modulus of elasticityHigh coefficient of thermal expansion c) Low fracture strength Low thermal conductivity Low modulus of elasticityLow coefficient of thermal expansion d) High fracture strengthHigh thermal conductivityLow modulus of elasticityLow coefficient of thermal expansion
d) High fracture strengthHigh thermal conductivityLow modulus of elasticityLow coefficient of thermal expansion
This pencil looks like it is broken because of light refraction. What property of light causes refraction? a) Light is reflecting two different pencils in the water. b) Light makes objects float in water. c) Cannot be predicted. d) Light travels at different speeds through different materials.
d) Light travels at different speeds through different materials.
Once a system is at a state of equilibrium, a shift from equilibrium may result by alteration of which of the following? a) Pressure b) Composition c) Temperature d) Pressure,compositon, and temperature
d) Pressure, composition, and temperature
What fundamental tpe of dislocation has it Burgers ector parallel to the dislocation line? a) Edge b) Mixed c) Cannot be predicted d) Screw
d) Screw
Consider the unit cell drawn below. Please select the correct Miller indices for Vector A. a) [1 0 1] b) [1 0 1] c) [0 1 1] d) [1- 1 0]
d) [1- 1 0]
