Readings (3)

Question 1

Single Phase

Answer 1

All parts of an alloy microstructure with the same atomic structure

Question 2

The constitution of an alloy is described by:

Answer 2

1) The phases present
2) The weight fraction of each phase
3) The composition of each phase

Question 3

Equilibrium Constitution

Answer 3

The state of lowest Gibb’s Free Energy for a given composition, temperature, and pressure.

An alloy in this state is thermodynamically stable

Question 4

Solvus Boundaries

Answer 4

Boundaries between single- and two-phase regions

Question 5

Eutectic Point

Answer 5

Lower limit of the single-phase liquid field formed by the intersection of two liquidus lines

Lowest temperature for which 100% liquid is stable - which is why casting, brazing, soldering etc. are often near eutectic in composition

Question 6

Constitution Point

Answer 6

Point of interest, consisting of multiple compositions/phases

Question 7

Intermediate Phases

Answer 7

Compounds that form between components

Question 8

Stoichiometry

Answer 8

The atomic % of components in a compound

Question 9

Eutectoid Point

Answer 9

The lower limit of a single-phase solid field formed by two falling phase boundaries intersecting in a V

Question 10

Peritectoid Point

Answer 10

inverted V corresponding to an upper limit of formation of a single solid phase - two-phase field above is formed of two solid phases

Question 11

-tic vs. -toid

Answer 11

-tic means a liquid phase is involved, -toid means all phases are solid

Question 12

Dilatometry

Answer 12

Measurement of dimensional changes at high resolution to detect changes of density and symmetry caused by phase change

Question 13

Electrical Resistivity

Answer 13

Measurement of electrical resistivity changes associated with difference in electron mean free path before and after phase change

Question 14

Calorimetry

Answer 14

Sensitive differential measurement of release or take-up of latent heat associated with phase change

Question 15

Optical Microscopy

Answer 15

Differential reflection of light, either in color or intensity, by phases or by a surface film created by chemical or electro-etching

Question 16

X-ray Diffraction

Answer 16

Diffraction of the X-radiation by the crystal lattice of each phase, giving diffraction patterns from which crystal structure and volume fraction of phases can be inferred

Question 17

Scanning Electron Microscopy (SEM)

Answer 17

Differential back-scattering of electrons by differing phases giving both an image and compositional information

Question 18

Transmission Electron Microscopy (TEM)

Answer 18

Diffraction of an electron beam by the crystal lattice of each phase, giving both an image of the structure and, from the diffraction pattern, its crystal structure

Question 19

Gibb’s Free Energy at phase boundaries

Answer 19

ΔG = 0

Question 20

Homogeneous Nucleation

Answer 20

• Spontaneous clusters/colonies of solids form within the melt
• These grow stably provided they can reach a critical radius

Question 21

Heterogeneous Nucleation

Answer 21

Solid nuclei form more readily on a pre-existing solid in contact with the liquid

Question 22

Phase Reaction

Answer 22

When any phase compositions change with temperature

Question 23

Segregation

Answer 23

The center of a grain will be of more pure substance due to cooling of the solution. As the temperature hits the liquidus line, the solid is as pure as possible (solid form), and then cooling will cause a composition gradient from the center to the outside of the grain of decreasing composition.

Question 24

Solidification Cracking

Answer 24

Segregation concentrates impurities on the grain boundaries, generating high enough thermal stresses to crack along the weakened grain boundaries

Question 25

Hybrids

Answer 25

Woven fabrics consisting of two or more types of reinforcing fibers

Question 26

Anisotropic

Answer 26

Varies with direction

Question 27

Discrete Fibers

Answer 27

Looks like “sprinkles”

Question 28

Plasticizer

Answer 28

Additive used to soften a polymer

Question 29

Thermoset

Answer 29

Become hard and rigid upon heating

Question 30

Thermoplastic

Answer 30

Become soft and deformable upon heating

Question 31

Elastomers

Answer 31

Polymers with mechanical behavior analogous to natural rubber

Question 32

Aspect Ratio

Answer 32

L/d

Question 33

Resin

Answer 33

Matrix component to help fiber interaction