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Diffusion by which mechanism occurs more rapidly in metal alloys?
A) Vacancy diffusion
B) Interstitial diffusion
B) Interstitial Diffusion
In metal alloys, interstitial diffusion takes place more rapidly than vacancy diffusion because the interstitial atoms are smaller and are more mobile. Also, there are more vacant adjacent interstitial sites than there are vacancies.
Self-diffusion is atomic migration in pure metals. Interdiffusion is diffusion of atoms of one metal into another metal.
True or False
True
As temperature decreases, the fraction of total number of atoms that are capable of diffusive motion
Increase or Decrease
Decrease
As temperature decreases, the fraction of the total number of atoms that are capable of diffusive motion decreases
If [m] atoms of helium pass through a [a] square meter plate area every [t] hours, and if this flux is constant with time, compute the flux of helium in units of atoms per square meter per second.
A) J = At/M
B) J = A/(Mt)
C) J = M/(At)
D) J = Mt/A
C) J = M/(At)
Calculate the diffusion coefficient for copper in aluminum at 600°C. \n Preexponential and activation energy values for this system are 6.5 x 10–5 m2/s and 136,000 J/mol, respectively.
(A) 5.7 x 10-2 m2/s (C) 4.7 x 10-13 m2/s
(B) 9.4 x 10-17 m2/s (D) 3.9 x 10-2 m2/s
C) 4.7 x 10-13 m2/s
After an edge dislocation has passed through some region of a crystal, the atomic arrangement of
that region is disordered.
True or False
False
Before and after an edge dislocation has passed through some region of a crystal, the atomic
arrangement is ordered and perfect. It is only during the passage of the extra half-plane that there is
disorder.
The process by which plastic deformation is produced by dislocation motion is called ____.
Slip
Relative to the direction of an applied shear stress, the direction of motion of an edge dislocation’s line is
Parallel or Perpendicular
Parallel
The direction of motion of an edge dislocations’ line is parallel to the direction of applied shear stress.
The atoms surrounding a screw dislocation experience what kind(s) of strain(s)?
A) Shear strains
B) Compressive strains
C) Tensile strains
A) Shear Strains
The atoms surrounding a screw dislocation experience only shear strains.
Dislocations move with the same degree of ease on all crystallographic planes of atoms and in all crystallographic directions?
True or False
False
Dislocations do not move with the same degree of ease on all crystallographic planes of atoms and in all crystallographic directions. Crystallographic planes and directions along which dislocations move are those that are most closely packed with atoms.
Reducing the grain size of metal improves toughness.
True or False
True
Reducing the grain size of a metal improves its toughness.
Most metals strain harden at room temperature.
True or False
True
Most metals strain harden at room temperature.
Grain growth must always be preceded by recovery and recrystallization.
True or False
False
Grain growth does not always need to be preceded by recovery and recrystallization; it may occur in materials that have not been cold worked.
If %CW of low carbon steel increases, yield strength decreases.
True or False
False
Yield strength (σy) increases.
brittle
plastic
elastomer
Ductility of a material depends on which of the following factors
A) room temperature, weight of material
B) angle of impact, duration of induced force
C) temperature of the material, strain rate and stress state
D) all of the above
C) temperature of the material, strain rate and stress state
Brittle fractures are characterized by prominent deformation of the material with low probability of crack propagation.
True or False
False
Fractures that are innate to crystalline materials that have cracks propagating along the grain boundaries are called.
A) intergranular fractures
B) crystallographic fringes
C) transgranular fractures
D) boundary line faults
C) transgranular fractures
The presence of inherent defects such as cracks and microscopic flaws does not affect the fracture strength of the material.
True or False
False
Critical stress for crack propagation in brittle materials depend on:
A) length of the internal crack
B) elastic modulus of material
C) specific surface energy
D) all of the above
D) all of the above
The measure of a materials resistance to brittle fractures in the presence of cracks, known as ______________, depends on critical stress for crack propagation and crack length.
A) elasticity
B) fracture toughness
C)surface strain
D) flaw length
B) fracture toughness
If stress level and plane strain fracture toughness are fixed by the design situation, then the maximum allowable flaw size is inversely proportional to the imposed stress.
True or False
True
A) Hackle region
B) Mist region
C) Smooth mirror region
D) Source of failure
Thermoplastic polymers endure a phenomenon called ( a ). This is associated with localized ( b ) which leads to the formation of interconnected ( c ) which grow and coalesce to form ( d ).
A) crazing
B) plastic deformations
C) microvoids
D) cracks
The number of cycles required to cause failure of a material at a specific stress level, calculated through specimen mechanical testing is called ___________.
A) fatigue limit
B) fatigue strength
C) fatigue life
D) fracture toughness
C) fatigue life
