MATSE 259 Exam 1 PSU Questions and Answers Graded A+
Elastic Modulus (e) - Answers measure of stiffness, or a material's resistance to elastic
deformation ... slope of elastic portion of stress-strain curve
Crystalline Materials - Answers small group of atoms that are repeated by translation to form 3-
D arrangements
Antisotropic - Answers properties that vary with direction. Ex: E(edge) isn't equal to E(diagonal)
Polycrystal - Answers properties that may or may not vary with direction
Isotropic - Answers the grains are randomly orientated
The Three Crystal Structures - Answers Body Centered Cubic (BCC), Face Centered Cubic (FCC),
Hexagonal Centered Prism (HCP)
Co-ordination Numbers - Answers number of atoms in a crystal lattice touching a given atom
Co-ordination Numbers for each Structure - Answers BCC = 8 FCC = 12 HCP = 12
Polymorphism - Answers same atoms can have more than one crystal structure
Close Packed Structures - Answers atoms in close touch as many as possible.
Which crystal structures are tightly packed vs ones that aren't? - Answers BCC is NOT packed
compared to HCP and FCC (most packed)
FCC layer structure - Answers A, B, C repeat
HCP layer structure - Answers A, B repeat
Linear Density - Answers Linear Density = # of atoms/ unit length of the vector
Planar Density - Answers density across a plane; # of atoms in the plane/area of plane
What are the three type of point defects? - Answers Vacancies, Interstitial Atoms, Substitutional
Atoms
Vacancies - Answers very important during diffusion!! Basically open spots in the plane
Substitutional Atoms - Answers these make solid solutions if atoms can bond together must
follow of one these rules;
Interstitional - Answers makes solid solutions; if the alloying atom is very small it'll sit in
between small crevices of the plane. Usually happens with H,C,O,N.
Edge Dislocation - Answers extra plane of atoms inserted into the crystal
, Burgers Vector - Answers measure of lattice distortion, perpendicular to distortion line
Screw Dislocation - Answers material is twisted so some atoms are above and below each other
Why do dislocations make plastic deformation possible? - Answers The crystal structures for
FCC sow its very packed so when it breaks not a big chunk does like it will with BCC and HCP.
Twin Boundary Plane - Answers a reaction of atom positions across the twin plane
Stacking Faults - Answers when they layers of stacking has an error
Diffusion - Answers transport atoms under a concentration gradient; induces atom movement
Case Hardening - Answers diffusing carbon atoms into iron atoms at surface. Results into
higher concentration of carbon
Diffusion in gases and liquids - Answers move to area of higher to lower as long as no bulk
motion
Interdiffusion - Answers in an alloy, atoms tend to migrate from regions of high concentration to
regions of low
Self-Diffusion - Answers happens with pure metals, atoms exchange positions
Vacancy Diffusion - Answers atoms exchange vacancies; depends on number of vacancies and
activation energy
Interstitial Diffusion - Answers migration of an interstitial atom to an adjacent vacant interstitial
site. This is faster than vacancy diffusion
Why is interstitial diffusion faster than vacancy diffusion? - Answers 1) Interstitial are more
mobile.
2) Probability of an empty adjacent interstitial is greater than for a vacancy
Activation Energy Barrier - Answers energy is needed to move, highest in intermediate states.
Bonds are broken then reformed.
Diffusion Welding - Answers heating two components and applying pressure, combines two
pieces of metal to make items.
Diffusion Flux - Answers measures how fast atoms or molecules diffuse through the membrane
Difusion is faster for.... - Answers 1) Open crystal structures
2) Smaller diffusing atoms
3) Lower density materials
Elastic Modulus (e) - Answers measure of stiffness, or a material's resistance to elastic
deformation ... slope of elastic portion of stress-strain curve
Crystalline Materials - Answers small group of atoms that are repeated by translation to form 3-
D arrangements
Antisotropic - Answers properties that vary with direction. Ex: E(edge) isn't equal to E(diagonal)
Polycrystal - Answers properties that may or may not vary with direction
Isotropic - Answers the grains are randomly orientated
The Three Crystal Structures - Answers Body Centered Cubic (BCC), Face Centered Cubic (FCC),
Hexagonal Centered Prism (HCP)
Co-ordination Numbers - Answers number of atoms in a crystal lattice touching a given atom
Co-ordination Numbers for each Structure - Answers BCC = 8 FCC = 12 HCP = 12
Polymorphism - Answers same atoms can have more than one crystal structure
Close Packed Structures - Answers atoms in close touch as many as possible.
Which crystal structures are tightly packed vs ones that aren't? - Answers BCC is NOT packed
compared to HCP and FCC (most packed)
FCC layer structure - Answers A, B, C repeat
HCP layer structure - Answers A, B repeat
Linear Density - Answers Linear Density = # of atoms/ unit length of the vector
Planar Density - Answers density across a plane; # of atoms in the plane/area of plane
What are the three type of point defects? - Answers Vacancies, Interstitial Atoms, Substitutional
Atoms
Vacancies - Answers very important during diffusion!! Basically open spots in the plane
Substitutional Atoms - Answers these make solid solutions if atoms can bond together must
follow of one these rules;
Interstitional - Answers makes solid solutions; if the alloying atom is very small it'll sit in
between small crevices of the plane. Usually happens with H,C,O,N.
Edge Dislocation - Answers extra plane of atoms inserted into the crystal
, Burgers Vector - Answers measure of lattice distortion, perpendicular to distortion line
Screw Dislocation - Answers material is twisted so some atoms are above and below each other
Why do dislocations make plastic deformation possible? - Answers The crystal structures for
FCC sow its very packed so when it breaks not a big chunk does like it will with BCC and HCP.
Twin Boundary Plane - Answers a reaction of atom positions across the twin plane
Stacking Faults - Answers when they layers of stacking has an error
Diffusion - Answers transport atoms under a concentration gradient; induces atom movement
Case Hardening - Answers diffusing carbon atoms into iron atoms at surface. Results into
higher concentration of carbon
Diffusion in gases and liquids - Answers move to area of higher to lower as long as no bulk
motion
Interdiffusion - Answers in an alloy, atoms tend to migrate from regions of high concentration to
regions of low
Self-Diffusion - Answers happens with pure metals, atoms exchange positions
Vacancy Diffusion - Answers atoms exchange vacancies; depends on number of vacancies and
activation energy
Interstitial Diffusion - Answers migration of an interstitial atom to an adjacent vacant interstitial
site. This is faster than vacancy diffusion
Why is interstitial diffusion faster than vacancy diffusion? - Answers 1) Interstitial are more
mobile.
2) Probability of an empty adjacent interstitial is greater than for a vacancy
Activation Energy Barrier - Answers energy is needed to move, highest in intermediate states.
Bonds are broken then reformed.
Diffusion Welding - Answers heating two components and applying pressure, combines two
pieces of metal to make items.
Diffusion Flux - Answers measures how fast atoms or molecules diffuse through the membrane
Difusion is faster for.... - Answers 1) Open crystal structures
2) Smaller diffusing atoms
3) Lower density materials
