Midterm 2 Vocabulary

Question 1

What are the two types of vacancies for diffusion

Answer 1

Interstitial and vacancy diffusion - interstitial diffusion is faster than vacancy diffusion because atoms are smaller

Question 2

What is self diffusion

Answer 2

process of atoms diffusing in their own crystal

Question 3

What are some factors affecting vacancy diffusion

Answer 3

number of vacancies present activation energy to hop energy in the system (arrhenius equation)

Question 4

What’s the difference between steady state diffusion and non steady state diffusion

Answer 4

Steady state diffusion concentration profile does not change as a function of time, where as concentration profile changes with time in non-steady state diffusion. In non steady state diffusion, some systems are in transient state and reach steady state after some time.

Question 5

What is the slope of a concentration to position plot

Answer 5

The concentration gradient aka the driving force for diffusion

Question 6

Explain all variables in Fick’s second law

Answer 6

D = diffusion coefficient D0 = number that ties together material dependent properties (entropic contributions, jump distance, etc) Q = activation energy R = gas constant T = absolute temperature (kelvins)

Question 7

How do the following factors affect diffusion: mechanism, temperature, species, crystal structure, polymer structure, and bonding?

Answer 7

mechanism: interstitial diffusion has higher diffusion coefficient than vacancy diffusion, temperature: higher the temperature, faster the diffusion, species: smaller the species, faster the diffusion, crystal: less APF, faster, polymer structure: more open chains faster (more permeable), bonding: stronger -> slower because higher activation energy

Question 8

In non steady state diffusion

Answer 8

flux and concentration gradient change with time at a position in the material

Question 9

What are the hume rothery rules for substitutional solid solutions

Answer 9

solubility is attained if: -> atomic radius is within 15% -> similar electronegativity -> similar valence -> same crystal structure for pure metals

Question 10

With a phase diagram and information about composition and temperature you can determine

Answer 10

The phases present, the composition of each phase, and the amount of each phase (proportion) present

Question 11

What’s the difference between a component and a phase

Answer 11

Components are elements that are present in the system (i.e. Al and Cu) while Phases are the physical or chemically distinct material regions (i.e. alpha or beta phase)

Question 12

Solubility limit is

Answer 12

the maximum concentration for which only a single phase solution exists

Question 13

Solubility limit depends on

Answer 13

Species, temperature, and pressure

Question 14

Unary phase diagrams

Answer 14

means that there is only a single component (i.e. water) in the entire phase diagram

Question 15

Isomorphic phase diagrams

Answer 15

are for complete solubility of one component in another (so same solid crystal crystal structure at all composition at some T)

Question 16

What is an isotherm

Answer 16

A temperature line in which a phase change occurs

Question 17

How do you calculate hypo/hyper eutectics

Answer 17

(See screenshot image)

Question 18

In intermetallic and ceramics we often have phases that form a line because the composition is exact

Answer 18

An intermetallic is a metal in which we have a consistent concentration of two metals mixed together

Question 19

Tell me about the ferrite phase of iron

Answer 19

one phase (alpha), soft, ductile, BCC

Question 20

Tell me about the austenite phase of iron

Answer 20

stainless, FCC

Question 21

Tell me about cementite

Answer 21

hard, brittle, Fe3C

Question 22

Tell me about pearlite

Answer 22

intermediate, 2 phases (eutectoid) of alpha and Fe3C

Question 23

What is the modulus of elasticity or Young’s modulus

Answer 23

Linear slope of stress/strain curve

Question 24

The elastic modulus with relation to the potential energy curve is

Answer 24

related to the concavity of the potential well and the slope of force (larger = more stiff) to radius in an interatomic position plot

Question 25

Yield strength is

Answer 25

the stress at which measurable plastic deformation has occurred. We compute it using the strain = 0.002 offset method.

Question 26

Given a stress and strain plot, label to me the plastic strain, elastic, elastic + plastic, and permanent stress

Answer 26

See photo

Question 27

What is ductility

Answer 27

Ductility is the degree of plastic deformation that can occur before fracture

%EL at fracture

Question 28

What is resilience

Answer 28

Resilience is the ability of a material to store energy and is the area under the stress strain curve up to the yielding stress.

Question 29

What is toughness

Answer 29

Toughness is the amount of energy needed to break up a unit of material, or the energy stored before fracture of a material (area under the whole stress strain curve)

Metals have high toughness, wheeras ceramics have small toughness and polymers have even smaller toughness.

High toughness = high ductility and tensile strength

Question 30

Compare steel between high carbon, low carbon, and medium carbon

Answer 30

High carbon steel is the strongest. Medium carbon steel is the toughest, while low carbon steel is the most ductile

Question 31

How are the berger vector and the slip direction related

Answer 31

Burger vector and slip direction are always parallel of each other

Question 32

How does the motion of the dislocaiton line relate to the berger vector direction for screw and edge

Answer 32

for edge dislocations the motion of the line is parallel to the vector while for screw dislocations the motion of the line is perpendicular to the vector

Question 33

What is the slip plane and slip direction for FCC

Answer 33

Slip Plane: [111] Slip Direction <110> for a total of 12 slip systems

Question 34

What is the slip plane and direction for BCC

Answer 34

slip plane [110] slip direction <111> for a total of 12 slip systems

Question 35

What’s the slip plane and direction for HCP

Answer 35

slip plane {0001} and slip direction <11-20>