Previous exams/midterm theory questions, materials

Which factors affect the resistance of a conductor in ohm's law: 1)The total length of the conductor. 2)the cross-sectional area of the conductor. 3)Temperature of the conductor. Diffusion coefficient of the conductor.

1,2,3

How many phases are present at a eutectic point on a binary temperature-composition phase diagram when the system is at equilibrium? 0 1 2 3

3

Which statement best describes the Griffith Criterion for brittle materials?

A crack will propagate if the elastic energy released during fracture is greater than the surface energy created.

When metals are plastically deformed, how is the deformation energy distributed? A)0% retained internally; 100% dissipated as heat B)5% retained internally; 95% dissipated as heat C)50% retained internally; 50% dissipated as heat D)95% retained internally; 5% dissipated as heat

B

How does the theoretical strength of a solid material compare with its experimental strength? a)The theoretical strength is lower than the experimental strength. b)The theoretical strength and the experimental strength are about the same. c)The theoretical strength is higher than the experimental strength.

Correct Response c)The theoretical strength is higher than the experimental strength.

What would be an optimal strategy for developing stronger materials?

Create more obstacles to slip, such as grain boundaries, solute atoms and other dislocations.

Which type of charge carrier will be introduced into a semiconductor by the presence of a donor impurity? Electron Hole

Electron

In order for a semiconductor to exhibit extrinsic electrical characteristics, high impurity concentrations are required T/F

F

heat capacity of a metal is constant over all temps T/F?

F

Which of the following units are reasonable for Specific Heat Capacity? J/(kg.K) J/(mol.K) J/(mol.kg.K)

J/(kg.K)

The energy corresponding to the highest filled electron state at 0 K is called the Fermi energy. T/F

T

A metal which has a crystal structure with many operable slip systems will be relatively ___________________________. a) ductile b) brittle

a

As the dislocation density increases, the resistance to dislocation movement ____________________. a) increases b) decreases

a

Consider a diffusion couple between Cu and Ni. In which direction will the Cu atoms diffuse? a)The Cu atoms will move from the region of high Cu concentration to the region of low Cu concentration. b)The Cu atoms will move from the high Ni side to the low Ni side. c)The Cu atoms will not diffuse.

a

Consider the diffusion of nitrogen through a thin sheet of steel. Which of the following changes (while holding everything else constant) would increase the flux of nitrogen? (a) Increasing the temperature. (b) Decreasing nitrogen concentration difference across the sheet. (c) Increasing the thickness of the sheet. (d) All of the above.

a

To avoid brittle failure, materials that exhibit a ductile-to-brittle transition should be used at which of the following temperatures? (a)Above the transition temperature. (b) Below the transition temperature. (c) At the transition temperature.

a

Which phase fields does the liquidus line separate? a)It separates the liquid and liquid + solid regions. b)It separates the solid and liquid + solid regions. c)It separates the solid(α) and solid(α) + solid (β) regions. d)It separates the liquid + solid (α) and solid (α) + solid (β) regions.

a

a certain material is found to cause stress shielding when used as a knee replacement biomaterial. what can be done to reduce the stress shielding effect? a) change material to one with lower E b) change the material to one w lower tensile strength c) make the material porous d) a and c

a and c

Which phase regions will you find on an isomorphous binary composition-temperature phase diagram? Liquid Liquid + α α α + β All of the above. a, b, and c.

a b and c

Cork is an interesting material because it does not appreciably expand laterally (sideways) when compressed axially (from the top and bottom). Which option best describes Poisson's ratio for cork?

approximately equal to zero

A solidus line separates which of the following phase fields? a)It separates the liquid and liquid + solid regions. b)It separates the solid and liquid + solid regions. c)It separates the solid(α) and solid(α) + solid (β) regions. d)It separates the liquid + solid(α) and the solid(α) + solid(β) regions.

b

Consider the diffusion of nitrogen through a thin sheet of steel. Which of the following factors would increase the flux of nitrogen? (a) Increasing the temperature, decreasing the nitrogen concentration difference across the sheet, decreasing the thickness of the sheet. (b) Increasing the temperature, increasing the nitrogen concentration difference across the sheet, decreasing the thickness of the sheet (c) Decreasing the temperature, decreasing the nitrogen concentration difference across the sheet, decreasing the thickness of the sheet. (d) Increasing the temperature, increasing the nitrogen concentration difference across the sheet, increasing the thickness of the sheet..

b

For an edge dislocation, the direction of motion is ____________ to the direction of an applied shear stress. a)perpendicular b)parallel

b

We have two samples, one made of iron and the other is made of copper. Which of the following statements is the most accurate? a)The iron sample has a higher thermal conductivity than the copper sample. b)The copper sample has a higher thermal conductivity than the iron sample. c)By increasing the temperature, thermal conductivity of both iron and copper increase. d)The copper sample has higher thermal conductivity but lower thermal diffusity.

b

Which of the following is present in higher concentration in a solution? a) solute b) solvent

b

Which of the following statements is TRUE? (a) The Burgers vector is parallel to the dislocation line in an edge dislocation. (b) A screw dislocation results when parallel planes join together to form a helical ramp. (c) Dislocations are always thermodynamically stable and will first appear at high temperatures. (d) Dislocations are static and thus impossible to move.

b

which is false? a)Ceramics generally experience less plastic deformation before fracture compared to polymers. (b) Ceramics generally require greater energy to fracture compared to metals per unit volume of material. (c) Polymers generally require less energy to fracture compared to metals per unit volume of material. (d) Metals generally experience more plastic deformation before fracture compared to ceramics.

b

Consider a p-type semiconductor. In which region of the charge carrier concentration vs. temperature diagram does the number of charge carriers resulting from electron excitations across the band gap overwhelm the number of holes created with the aid of the acceptor atoms? a) freeze out region b) extrinsic region c) intrinsic temperature region

c

Which of the following statements best describes vacancies? (a) The formation of vacancies will always increase the Gibbs energy of the material. (b) The formation of vacancies will always decrease the Gibbs energy of the material. (c) The formation of vacancies will decrease the Gibbs energy of the material if the number of vacancies is less than the equilibrium concentration of vacancies. (d) The formation of vacancies will decrease the Gibbs energy of the material if the number of vacancies is greater than the equilibrium vacancy concentration.

c

Which of the following statements is INCORRECT: (a) Dislocations always increase the energy of the crystal. (b) Twin boundaries have a lower energy than free surfaces. (c) Vacancies always decrease the energy of a crystal. (d) Solute atoms are considered as point defects.

c

Which of the following statements is TRUE? (a) Interstitial diffusion is slower than vacancy diffusion because interstitial atoms are larger than normal lattice atoms. (b) The motion of normal lattice atoms occurs in the same direction as vacancy motion during diffusion. (c) Interstitial diffusion is more rapid than vacancy diffusion because interstitial atoms are smaller than normal lattice atoms.

c

consider grain growth in pure aluminum. which is false? a) the driving force for grain growth is the reduction of the total grain boundary energy b) grain growth will result in a decrease in yield stress c) the dislocation density decreases during grain growth d)some grains decrease in size during grain growth while other increase in size

c

the conductivity of a semi conductor increases with: a) increasing temperature in the intrinsic region b) increasing dopant concetration c) a and b

c

under which of the following conditions is the contribution of holes to the electrical conductivity negligible? a) intrinsic semiconductor at room temp b) n type semiconductor at high temp c) n type semiconductor at very low temperature d) b and c

c

What is the predominant type of bonding within a polymer chain? Ionic Hydrogen Covalent Van der Waals Metallic

covalent

9. Which of the following statements is INCORRECT: (a) Iron is polymorphic/allotropic because it has more than one crystal structure. (b) When an amorphous material is studied by X-rays, no diffraction pattern will be observed. (c) Single crystals can have different properties in different directions. (d) Most engineering materials are made of single crystals.

d

According to Matthiessen's rule the conductivity of a metal decreases with: (i) Increasing temperature (ii) increasing impurity content (iii) increasing number of dislocations a)i only b)ii only c)i and ii only d)i, ii and iii

d

Choose the most accurate statement: (a) Metals and polymers are usually crystalline, ceramic are always amorphous. (b) Metals are usually crystalline, polymers and ceramics are always amorphous. (c) Metals and ceramics are usually crystalline, polymers are usually amorphous. (d) Metals are usually crystalline, ceramics can be crystalline or non-crystalline, polymers will always have amorphous regions.

d

Consider the diffusion of nitrogen through a thin sheet of steel. Which of the following factors would increase the flux of nitrogen? (a) Increasing the temperature, decreasing the nitrogen concentration difference across the sheet, decreasing the thickness of the sheet. (b) Decreasing the temperature, decreasing the nitrogen concentration difference across the sheet, decreasing the thickness of the sheet. (c) Increasing the temperature, increasing the nitrogen concentration difference across the sheet, increasing the thickness of the sheet. (d) Increasing the temperature, increasing the nitrogen concentration difference across the sheet, decreasing the thickness of the sheet.

d

Which of the following properties could not be inferred from the interatomic potential? (ie. energy vs. distance curve) a) bond length b)bond energy c)elastic constant d) yield strength

d

Which of the following types of point defect would you expect to be the most mobile, meaning it would be easiest to move around in the structure? a)self- interstitial atom b)vacancy c)substitutional solute d)interstitial solute

d

Which statement is TRUE? (a) Brittle fracture is induced by elastic deformation. (b) Cleavage is crack propagation by the breaking of atomic bonds along random crystallographic planes. (c) Brittle fracture occurs slowly. (d) Ductile fracture is caused by damage accumulation.

d

which of the following statements best describes the temperature dependence of electrical conductivity? a) conductivity of metals and intrinsic semiconductors increases with increasing temp b) the conductivity of metals and intrinsic semiconductors increases with decreasing temperature c) the conductivity of metals increase with increasing temperature and the conductivity of intrinsic semiconductors increases with decreasing temperature d) the conductivity of metals increases with decreasing temp and the conductivity of intrinsic semiconductors increases with increasing temperature

d

which of the following statements is true? a)nucleation at grain boundaries reduces the interfacial free energy increase caused by nucleation b) nucleation in the solid state may occur heterogenously or homogenously c) nucleation in solidification is almost always heterogeneous d) all of the above

d

which of the following will promote crack propogation? a) larger crack length b) larger radius of curvature at the crack tip c) larger applied stress d) both a and c

d

As a metal is strain hardened, its ductility __________________. increases decreases

decreases

During the recovery of a cold-worked material, highly strained grains are replaced with unstrained grains. t/f

f

Generally speaking, strain hardening or work hardening, can improve the strength as well as the ductility of the metals. T/F

f

In edge dislocation, an extra half plane of atoms can cause lattice distortion to happen. As a result, there is only compressive lattice strain on the neighboring atoms. T/f

f

Increasing the concentration of the impurities increases both the strength and the ductility. t/f

f

Is the following statement correct? Resilience is the capacity of a material to absorb energy when it is deformed plastically and then, upon unloading, to have this energy recovered.

f

The word amorphous implies having ordered arrangements over long distances. True False

f

True or False: Amorphous (Non-crystalline) materials have grain boundaries.

f

True or False: Higher bonding energies generally correspond to lower melting points.

f

True or False: The introduction of impurity atoms into a highly pure metal is never desirable. The properties of the metal are always adversely affected.

f

True or False? Dislocations move with the same degree of ease on all crystallographic planes and in all crystallographic directions.

f

True or False? During the recrystallization of a cold-worked metal, its ductility remains unchanged.

f

True or False? In order for a semiconductor to exhibit extrinsic electrical characteristics, high impurity concentrations are required.

f

True or False? Thermal conduction is the phenomenon by which heat is transported from low to high-temperature regions of a substance.

f

True or False? A brittle material typically exhibits substantial plastic deformation with high energy absorption before fracture.

f

Covalent bonding is the only form of bonding in polymers. True False

false

Which of the following will increase the yield strength of a material? (i) Increasing the dislocation density. (ii) Decreasing the concentration of alloying additions. (iii) Decreasing the grain size. (iv) Decreasing the volume fraction of second phase particles.

i , iii

Consider the following statements: (i) Covalently-bonded materials may have either a high or low melting temperature. (ii) Ionic-bonded materials generally have low melting temperatures. (iii) Covalent bonding is directional. (iv) Metallic bonding is directional. Which of the following are correct?

i and iii

Consider the bonding between two ions. Which of the following statements most accurately describes the "bond length": (i) The bond length is the distance between the two ions where the net force is zero. (ii) The bond length is the distance between the two ions where the net force is at its maximum. (iii) The bond length is the distance between the two ions where the net energy is zero. (iv) The bond length is the distance between the two ions where the net energy is at its minimum.

i and iv

Which of the following statements are TRUE? (i) Increasing the dislocation density increases the stored energy in a material. (ii) Dislocation annihilation occurs when dislocations with opposite sign on the same slip plane attract each other. (iii) Dislocations always repel each other. (iv) No lattice distortions are created by screw dislocations.

i, ii

Which of the following statements is INCORRECT: i. Iron is polymorphic/allotropic because it has more than one crystal structure. ii. When an amorphous material is studied by X-rays, no long range diffraction pattern is observed. iii. Substitutional diffusion is usually faster than interstitial diffusion. iv. Single crystals can have different properties in different directions.

iii

How is the plane strain fracture toughness of a metal expected to change with rising temperature? Remain constant Increase Decrease

increase

A system is in equilibrium when its free energy is at a __________________. maximum minimum

min

Is it always possible to reach equilibrium within a reasonably short period of time (i.e. within a day)? no/yes

no

Is the following statement correct? Toughness is a measure of the ability of a material to absorb energy up to the start of plastic deformation.

no

A phase is part of a system which has uniform ______________________ characteristics. physical chemical physical and chemical none of the above

physical and chemical

Which of the energies listed below is greater? surface energy grain boundary energy

surface energy

Amorphous implies there is no long range ordering of atoms. t/f

t

Consider self-diffusion in a pure metal. The two conditions needed for a successful atomic jump are: 1) There must be an empty adjacent site. 2) The atom must have sufficient energy to break bonds with its neighbor atoms and them cause some lattice distortion during the displacement T/F

t

If a material has a high electrical conductivity, it will have high heat conductivity as well. True False

t

Ohm's law relates current density, conductivity, and electric field intensity t/f

t

Recrystallization is the formation of a new set of strain-free and equiaxed grains that have low dislocation densities. These new grains grow and consume the deformed grains. T/F

t

The process by which plastic deformation is produced by dislocation motion is called Slip. t/f

t

True or False: A metal is more likely to dissolve in a host metal that has a lower valency.

t

True or False: In metals, valence electrons are not bound to individual atoms, but are free to drift throughout the material.

t

True or False: Polymers are never completely crystalline in structure. They are always at least partially amorphous.

t

True or False? To reduce surface energy, materials can try to minimize the total area.

t

True or False? Heat capacity indicates a material's ability to absorb heat from the external surroundings. In most solids the principle mode of thermal energy assimilation is by increase in vibration energy of atoms.

t

True or false? In metals, there are significantly more vacancies than self-interstitials.

t

When the concentration of the solute in a solid solution exceeds the solubility limit, a new solid solution or phase that has a distinctly different composition than the original is formed. T/F

t

the properties of non-crystalline materials are isotropic T/F

t

The following feature is not one of the characteristics of ionic materials. Thermally insulative Electrically insulative Tough (i.e. ductile) Hard Brittle

tough