NGR 220 MIDTERM 2 EXAM WITH COMPLETE
SOLUTIONS 100% VERIFIED
Diffusion - ANSWER Mass Transport (movement of actual material via atomic motion)
Interdiffusion - ANSWER In alloys, atoms tend to migrate from regions of high
concentration to regions of low concentration
Self-Diffusion - ANSWER In an elemental solid, individual atoms can also migrate
Vacancy Diffusion - ANSWER Atoms exchange places with vacancies (applies to
substitution impurity atoms)
Interstitial Diffusion - ANSWER Smaller solute atoms can readily diffuse between large
solvent (or host) atoms
T/F:
Interstitial Diffusion is more rapid than vacancy diffusion - ANSWER true
What instrument can be used to confirm that a piece of steel is nanocrystalline -
ANSWER SEM and TEM
Steady-State Diffusion - ANSWER Concentration profile is NOT a function of time
Non-steady State (or Transient) Diffusion - ANSWER Concentration profile IS a function
of time
,Fick's First Law of Diffusion is used with ____________ diffusion - ANSWER steady-state
Diffusion coefficient D ____________ with increasing T - ANSWER increases
The rate of interdiffusion across an interface between 2 metals depends on? - ANSWER
Temperature and Vacancy concentration
In Non Steady State Diffusion: flux and concentration gradient _____ change with time -
ANSWER do
Fick's second law is used with ________ diffusion - ANSWER Non Steady State
What affects D? - ANSWER Temperature (Higher T = higher D)
Diffusion Mechanism
Activation Energy (High Q = Lower D)
Diffusion is FASTER for - ANSWER -Open crystal structures (BCC)
-Materials w/ secondary bonding
-Smaller diffusing atoms (C, H)
-Lower density materials
Diffusion is SLOWER for - ANSWER -Close-packed structures (FCC,HCP)
-Materials w/ covalent bonding
-Larger diffusing atoms
-Higher density materials
Elastic Deformation is ________ - ANSWER reversible
, Plastic Deformation is ______________ - ANSWER permanent
A large species diffusing through a close-packed
structure leads to what level of activation energy
for diffusion Qd and what associated impact on
diffusion coefficient D? - ANSWER . High Qd and thus lower D?
pe of stress vs. strain plot (proportional to the
elastic modulus E) depends on - ANSWER bond strength of
metal
Yield Strength - ANSWER Stress at which noticeable plastic deformation has occurred
(end of straight portion)
Tensile Strength - ANSWER Maximum stress on engineering stress-strain graph (top of
curve)
True Stress - ANSWER Occurs above engineering stress in straight line
Engineering stress σ is defined as? - ANSWER Load divided by original cross-sectional
area A0 of sample?
Toughness - ANSWER Energy need to break a unit volume of material (area under stress
strain curve)
Brittle fracture - ANSWER elastic energy
Ductile fracture - ANSWER elastic + plastic energy (more forgiving)
SOLUTIONS 100% VERIFIED
Diffusion - ANSWER Mass Transport (movement of actual material via atomic motion)
Interdiffusion - ANSWER In alloys, atoms tend to migrate from regions of high
concentration to regions of low concentration
Self-Diffusion - ANSWER In an elemental solid, individual atoms can also migrate
Vacancy Diffusion - ANSWER Atoms exchange places with vacancies (applies to
substitution impurity atoms)
Interstitial Diffusion - ANSWER Smaller solute atoms can readily diffuse between large
solvent (or host) atoms
T/F:
Interstitial Diffusion is more rapid than vacancy diffusion - ANSWER true
What instrument can be used to confirm that a piece of steel is nanocrystalline -
ANSWER SEM and TEM
Steady-State Diffusion - ANSWER Concentration profile is NOT a function of time
Non-steady State (or Transient) Diffusion - ANSWER Concentration profile IS a function
of time
,Fick's First Law of Diffusion is used with ____________ diffusion - ANSWER steady-state
Diffusion coefficient D ____________ with increasing T - ANSWER increases
The rate of interdiffusion across an interface between 2 metals depends on? - ANSWER
Temperature and Vacancy concentration
In Non Steady State Diffusion: flux and concentration gradient _____ change with time -
ANSWER do
Fick's second law is used with ________ diffusion - ANSWER Non Steady State
What affects D? - ANSWER Temperature (Higher T = higher D)
Diffusion Mechanism
Activation Energy (High Q = Lower D)
Diffusion is FASTER for - ANSWER -Open crystal structures (BCC)
-Materials w/ secondary bonding
-Smaller diffusing atoms (C, H)
-Lower density materials
Diffusion is SLOWER for - ANSWER -Close-packed structures (FCC,HCP)
-Materials w/ covalent bonding
-Larger diffusing atoms
-Higher density materials
Elastic Deformation is ________ - ANSWER reversible
, Plastic Deformation is ______________ - ANSWER permanent
A large species diffusing through a close-packed
structure leads to what level of activation energy
for diffusion Qd and what associated impact on
diffusion coefficient D? - ANSWER . High Qd and thus lower D?
pe of stress vs. strain plot (proportional to the
elastic modulus E) depends on - ANSWER bond strength of
metal
Yield Strength - ANSWER Stress at which noticeable plastic deformation has occurred
(end of straight portion)
Tensile Strength - ANSWER Maximum stress on engineering stress-strain graph (top of
curve)
True Stress - ANSWER Occurs above engineering stress in straight line
Engineering stress σ is defined as? - ANSWER Load divided by original cross-sectional
area A0 of sample?
Toughness - ANSWER Energy need to break a unit volume of material (area under stress
strain curve)
Brittle fracture - ANSWER elastic energy
Ductile fracture - ANSWER elastic + plastic energy (more forgiving)
