MAT E 202 FINAL QUESTIONS & VERIFIED ANSWERS
fuel cells require __________ hydrogen. _________ of the hydrogen results in
___________. - Answers - High Purity
Contamination, decreased efficiency.
What is diffusion in Solids? - Answers - -Thermal Energy is how atom travels
-Temperature Dependant (thermally activated)
-It is when a material via motion of an atom through a unit cell
What is Interstitial Diffusion? - Answers - -An atoms moves from one interstitial site to
another
-Limited to small atoms that can fit in an interstitial site (the smaller the atom the faster
the diffusion)
-There are more interstitial sites than vacancies
What is vacancy diffusion? - Answers - -the motion of an atom from a normal lattice site
to an adjacent vacancy site
-host atom is known as the solvent, diffusing atom is called solute
-activation energy for vacancy diffusion is larger than for interstitial diffusion
Describe Fick's first law. - Answers - - atoms will move down in concentration gradient
(except hydrogen)
- hydrogen for this reason makes metals brittle, which can cause failures
Diffusion Coefficient is _________ dependant. - Answers - Temperature dependant
smaller diffusing atom = ... - Answers - less activation energy
Bcc diffusion is quicker because.... - Answers - there is more open space
what does Fick's 2nd law state? - Answers - The diffusion Gradient changes with time
If (Cx-Co)/(Cs-Co) = some constant, then - Answers - some constant = x^2/Dt
What is the case depth? - Answers - The distance x at which HRC = 50
What is carburizing? - Answers - Heating a part of low carbon steel in a carbon-rich
environment so that C is diffused into its surface.
, Essentially, its the diffusion of Carbon into steel
Define elastic and plastic deformation? - Answers - Elastic - stretching of bonds
between atoms but atomic positions are maintained when unloaded
Plastic - permanent atomic displacements
Explain how plastic deformation works on a subatomic level? - Answers - -motion of
dislocations results in permanent deformation
-linear or one dimensional defect in which atoms are misaligned
-this motion can be called 'slip', and involves breaking/reforming of bonds
What are the requirements for dislocation motion? - Answers - -dislocations present in
the metal
-a slip plane and crystallographic direction for dislocations to move
-a shear stress parallel to the slip plane that will cause dislocations to move
Why are planes and directions of plastic deformation important? - Answers - -occurs
along planes of high PPF (slip plane)
-occurs in direction with highest LPF (slip direction)
-the higher the PPF and/or LPF, the shorter the distance an atom moves before it bonds
to another atom
-all of this is called a SLIP SYSTEM
Where does slip occur on FCC planes? - Answers - On family of (111) planes, and [110]
direction
The stress level at which plastic deformation occurs (slip) occurs is related to what 2
things? - Answers - -number of slip systems available
-quality (value) of slip systems (PPF and/or LPF)
A closed packed plane has a PPF > than? - Answers - 0.90
How is thermal activation and plastic deformation related? - Answers - -does not need
thermal activation on CPP
-does need it for non CPP
Describe Shear stress to move dislocations - Answers - -dislocation motion happens on
the plane where resolved shear stress along slip plane reaches a critical value called
the critical resolved shear stress.
-Tr < Tcrss
-resolved shear stress is a function of applied load and orientation
-MAXIUMUM AT 45 and 45 deg.
-if 90 deg. slip don't occur
fuel cells require __________ hydrogen. _________ of the hydrogen results in
___________. - Answers - High Purity
Contamination, decreased efficiency.
What is diffusion in Solids? - Answers - -Thermal Energy is how atom travels
-Temperature Dependant (thermally activated)
-It is when a material via motion of an atom through a unit cell
What is Interstitial Diffusion? - Answers - -An atoms moves from one interstitial site to
another
-Limited to small atoms that can fit in an interstitial site (the smaller the atom the faster
the diffusion)
-There are more interstitial sites than vacancies
What is vacancy diffusion? - Answers - -the motion of an atom from a normal lattice site
to an adjacent vacancy site
-host atom is known as the solvent, diffusing atom is called solute
-activation energy for vacancy diffusion is larger than for interstitial diffusion
Describe Fick's first law. - Answers - - atoms will move down in concentration gradient
(except hydrogen)
- hydrogen for this reason makes metals brittle, which can cause failures
Diffusion Coefficient is _________ dependant. - Answers - Temperature dependant
smaller diffusing atom = ... - Answers - less activation energy
Bcc diffusion is quicker because.... - Answers - there is more open space
what does Fick's 2nd law state? - Answers - The diffusion Gradient changes with time
If (Cx-Co)/(Cs-Co) = some constant, then - Answers - some constant = x^2/Dt
What is the case depth? - Answers - The distance x at which HRC = 50
What is carburizing? - Answers - Heating a part of low carbon steel in a carbon-rich
environment so that C is diffused into its surface.
, Essentially, its the diffusion of Carbon into steel
Define elastic and plastic deformation? - Answers - Elastic - stretching of bonds
between atoms but atomic positions are maintained when unloaded
Plastic - permanent atomic displacements
Explain how plastic deformation works on a subatomic level? - Answers - -motion of
dislocations results in permanent deformation
-linear or one dimensional defect in which atoms are misaligned
-this motion can be called 'slip', and involves breaking/reforming of bonds
What are the requirements for dislocation motion? - Answers - -dislocations present in
the metal
-a slip plane and crystallographic direction for dislocations to move
-a shear stress parallel to the slip plane that will cause dislocations to move
Why are planes and directions of plastic deformation important? - Answers - -occurs
along planes of high PPF (slip plane)
-occurs in direction with highest LPF (slip direction)
-the higher the PPF and/or LPF, the shorter the distance an atom moves before it bonds
to another atom
-all of this is called a SLIP SYSTEM
Where does slip occur on FCC planes? - Answers - On family of (111) planes, and [110]
direction
The stress level at which plastic deformation occurs (slip) occurs is related to what 2
things? - Answers - -number of slip systems available
-quality (value) of slip systems (PPF and/or LPF)
A closed packed plane has a PPF > than? - Answers - 0.90
How is thermal activation and plastic deformation related? - Answers - -does not need
thermal activation on CPP
-does need it for non CPP
Describe Shear stress to move dislocations - Answers - -dislocation motion happens on
the plane where resolved shear stress along slip plane reaches a critical value called
the critical resolved shear stress.
-Tr < Tcrss
-resolved shear stress is a function of applied load and orientation
-MAXIUMUM AT 45 and 45 deg.
-if 90 deg. slip don't occur
