Phase Diagrams Introduction

Question 1

Phase

Answer 1

All parts of a material with the same atomic structure are a phase

Question 2

Three forms of binary alloy

Answer 2

• Single solid solution
• Two separated solid solutions
• Compound (phase 1) and solid solution (phase 2)

Question 3

Metallic alloy

Answer 3

Mixture of metal and something else (metal or non-metal)

Question 4

Ceramic alloy

Answer 4

Mixture of ceramic and somethings else

Question 5

Component

Answer 5

The chemical elements that make up an alloy, usually denoted by capital letters (A, B, C…) or element symbols

Question 6

Binary alloy

Answer 6

Contains two components (ternary, quaternary etc also exist)

Question 7

Composition measures

Answer 7

Composition of alloys components or phase can be measured by weight % (wt%) or atom % (at%)

Question 8

Calculate Wa

Answer 8

100 x [Weight of component A]/[Sum of al component weights]

Question 9

Calculate Xa

Answer 9

100 x [number of atoms/moles of component A]/[Total number of atoms/moles of all components]

Question 10

What describes constitution of an alloy?

Answer 10

• Phases present
• Weight fraction of each phase
• Composition of each phase

Question 11

Define G (Gibbs free energy) for given composition at fixed T and p

Answer 11

G = U + pV - TS = H - TS

Question 12

Equilibrium constitution

Answer 12

The state of lowest Gibbs free energy G for a given composition, temperature and pressure - there is no tendency for an alloy in this state to change, since it is thermodynamically stable

Question 13

Phase diagram

Answer 13

Diagram showing equilibrium constitution, with T and composition as axes (since p can generally be neglected in manufacturing processes (for solid and liquid manufacturing)