Materials Science and Engineering Flashcards

Flashcards for reviewing Materials Science and Engineering lecture notes, focusing on key vocabulary related to crystallization, nucleation, solidification, phase diagrams, diffusion, and steel microstructures.

Nucleation

The formation of the first nanocrystallites from molten material.

ΔGv

The free energy per unit volume and the driving force for solidification.

σsl

Surface free energy associated with the solid-liquid interface during solidification.

Embryo

A tiny, unstable particle of solid that forms from the liquid as atoms cluster together, which may either grow or re-dissolve.

Critical Radius (r*)

The minimum size of a crystal that must be formed by atoms clustering together in the liquid before the solid particle is stable and begins to grow.

Undercooling (ΔT)

The difference between the equilibrium freezing temperature and the actual temperature of the liquid.

Homogeneous Nucleation

Nucleation that occurs when the undercooling becomes large enough to cause the formation of a stable nucleus without pre-existing surfaces.

Latent Heat of Fusion

The heat given up during the liquid-to-solid transformation.

Heterogeneous Nucleation

Nucleation on pre-existing surfaces, such as impurities in contact with the liquid or container walls.

Planar Growth

A type of solidification where a solid-liquid interface remains planar as latent heat is removed through the solid.

Dendritic Growth

A type of solidification where a small solid protuberance (dendrite) grows into an undercooled liquid, releasing latent heat which warms the liquid to the freezing temperature.

Gibbs Free Energy (G)

Thermodynamic potential that is minimized at equilibrium under constant pressure, defined as G = H - TS.

Helmholtz Free Energy (F)

Thermodynamic potential that is minimized at equilibrium under constant volume, defined as F = U - TS.

Cooling Curve

A graph that shows how the temperature of a material decreases with time.

Superheat

The difference between the pouring temperature and the freezing/melting temperature.

Recalescence

The increase in temperature of the undercooled liquid as a result of nucleation.

Thermal Arrest

A region on a cooling curve where the temperature is constant due to the evolution of latent heat balancing heat loss.

Liquidus Temperature

The temperature above which a material is completely liquid.

Solidus Temperature

The temperature below which a material is completely solid.

Interdiffusion (Impurity Diffusion)

Diffusion of atoms of one metal into another.

Self-Diffusion

Diffusion that occurs in pure metals where atoms exchange positions but are of the same type.

Vacancy Diffusion

Diffusion where an atom leaves its lattice site to fill a nearby vacancy, creating a new vacancy at the original site.

Interstitial Diffusion

Diffusion where a small interstitial atom moves from one interstitial site to another.

Concentration Gradient

The slope of the concentration profile, representing the change in concentration with position.

Fick's First Law

Describes steady-state diffusion, where the flux (J) is equal to -D(dc/dx).

Diffusion Coefficient (D)

A measure of how fast atoms can diffuse in a material (cm^2/s).

Activation Energy (Q)

The energy required for an atom to move from one lattice site to another during diffusion (cal/mol).

Solid Solution

A solid-state solution of one or more solutes in a solvent, where the crystal structure of the solvent remains unchanged.

Substitutional Solid Solution

A solid solution where solute atoms replace solvent atoms in the crystal lattice.

Interstitial Solid Solution

A solid solution where solute atoms occupy interstitial sites in the crystal lattice.

Hume-Rothery Rules

A set of rules that determine the conditions for unlimited solid solubility.

Phase

A homogeneous portion of a system that has uniform physical and chemical characteristics, bounded by a surface.

Phase Diagram

A graphical representation of the physical states of a substance under different conditions of temperature and composition.

Isomorphous Phase Diagram

A binary phase diagram where the two components display complete solid solubility.

Tie Line

A horizontal line within a two-phase region drawn at the temperature of interest, used to determine phase compositions.

Lever Rule

A method used to calculate the amounts of each phase in a two-phase region of a phase diagram.

Eutectic Phase Diagram

A binary phase diagram that explains the chemical behavior of two elements with limited solubility in the solid-state but complete solubility in the liquid-state.

Eutectic Point

A point on a binary phase diagram at which three phases are in equilibrium.

Invariant Point

A point on a binary phase diagram at which three phases are in equilibrium.

Eutectic Reaction

A reaction where, upon cooling, a liquid phase transforms into two solid phases.

Isothermal Reaction

Reaction which takes place at a constant temperature.

Austenite

An interstitial solid solution of Carbon dissolved in γ (F.C.C.) iron.

Ferrite

An interstitial solid solution of a small amount of carbon dissolved in α (BCC) iron.

Pearlite

The eutectoid mixture containing 0.80 % C and is formed at 723°C on very slow cooling, a fine mixture of ferrite and cementite.

Cementite

Iron carbide (Fe3C), a hard and brittle phase.

Martensite

A super-saturated solid solution of carbon in ferrite, formed by rapid cooling (quenching) of austenite.

Ledeburite

The eutectic mixture of austenite and cementite, containing 4.3 percent C and formed at 1130°C.

Eutectoid Reaction

A reaction where, on cooling, austenite transforms into pearlite (mixture of ferrite & cementite).

Hypo-eutectoid Steel

Steels having less than 0.8% carbon.

Hyper-eutectoid Steel

Steels that contain more than the eutectoid amount of Carbon (0.8%).

TTT Diagram

Time-Temperature-Transformation diagram; describes the time required at any temperature for a phase transformation to begin and end. AKA isothermal transformation (IT) diagram or the C-curve.

CCT Diagram

Continuous Cooling Transformation diagram is often used when heat treating steel and represent which types of phase changes will occur in a material as it is cooled at different rates.