Engr. Materials Exam 2

Phase Diagram

A temperature vs composition map showing phases.

Phase

A physically uniform region (solid, liquid, etc.).

Component

A chemical species in a system (e.g., Cu, Ni).

System

The material body under study (e.g., Cu-Ni alloy).

Liquidus

Line above which the alloy is completely liquid.

Solidus

Line below which the alloy is completely solid.

Tie-line

Horizontal line at fixed temperature used to read phase compositions.

Phase composition

The composition of a particular phase (wt% of a component).

Phase amount

The fraction (or percent) of each phase present.

Solubility limit

Maximum solute amount that dissolves in a phase.

Lever rule

Formula to calculate phase fractions from tie-line distances.

Isomorphus

Complete solid solubility between two components.

Eutectic

A point where liquid transforms to two different solids simultaneously.

Invariant point

A temperature/composition where the number of phases doesn’t change with T (e.g., eutectic).

Solvus

Boundary line separating single solid and two-solid regions.

Metastable

A non-equilibrium state that persists for some time.

Cored structure

Non-uniform composition across a grain due to fast cooling.

Equilibrium cooling

Slow cooling allowing phases to reach equilibrium compositions.

Non-equilibrium cooling

Fast cooling that prevents full diffusion and equilibrium.

Unary phase diagram

Phase diagram for a single component (T vs. P or T vs. phase).

Binary phase diagram

Phase diagram for two components.

Microstructure

Amount, size, and arrangement of phases in a material.

Liquid phase (L)

Molten state of the alloy.

Solid solution (α, β)

A solid where solute atoms substitute or fit into the host lattice.

Volume fraction

Fraction of the material’s volume occupied by a phase.

Mass fraction (wt%)

Fraction of the mass made by a component (weight percent).

Triple point

Condition where three phases coexist in equilibrium (more common in unary diagrams).

Sublimation

Solid → vapor transition without passing liquid (unary feature).