Materials Ch 9 and 10 Quiz

Definition: Phases

The Physically and chemically distinct material regions that form. (ex α and β)

What phase is present at 1000 degC and 1.0 wt% Carbon?

1 Phase:

gamma iron; austenite

What phase is present at 1250 degC and 35 wt% Ni?

2 Phase

Liquid + alpha (FCC solid solution)

What is a tie line? How is the lever rule applied?

A tie line is drawn through the point connecting the boarder lines of two phases. Sometimes referred to as isotherm (green)

The lever rule identifies the proportions of each present phase.

Phase 1 = (C2 - C) / (C2 - C1)


Phase 2 = (C - C1) / (C2 - C1).

*C is the concentration or wt% on the graph

Definition: Eutectic

liquid transforms to two solid phases

L

Definition: Eutectoid

one solid phase transforms to two other solid phases

S_2

Definition: Peritectic

liquid and one solid phase transform to a second solid phase

S_1 + L

Iron-Carbon Phase Diagram calculations

A.) Eutectic: L -> γ + Fe_3C

B.) Eutectiod: γ -> α + Fe3C

Hypoeutectiod (left):
Wp = T/(T+U)=>(C - 0.022)/(0.76 - 0.022)

Wα = U/(T+U)=>(0.76-C)/(0.76-0.022)


Hypereutectiod (right):

Wp = X/(V+X)=>(C1-0.76)/(6.7-0.76)

WFe_3C = V/(V+X)=>(C1-0.76)/(6.7-0.76)

Where is pearlite found?

The eutectoid of the iron-carbon phase diagram

What phase does gamma (γ) represent?

Austenite

What phase does L represent?

Liquid

What does Fe_3C represent in an iron-carbon phase diagram?

Cementite

What does alpha (α) represent?

Ferrite

Reaction Rate

The rate at which a phase transformation happens. The slope on Phase Transformation Diagrams

Phase Transformation Diagrams

Tells you the time and rate at which a transformation occurs

Isothermal Transformation Diagrams

Tells you the time a transformation will take to complete at a certain temperature

Nucleation

When nuclei (seeds) act as templates on which crystals grow. Atoms are continuously added to the nuclei (seed) faster than the atoms are bring lost. Once nucleated, the growth process will proceed until equilibrium is reached.

Supercooling

one of the driving forces to nucleate. When a liquid is cooled below its melting point without it becoming a solid.

Small Supercooling

Slow Nucleation Rate --> Few Nuclei --> Large Crystals

Large Supercooling

Rapid Nucleation Rate --> Many Nuclei --> Small Crystals

How Does Temp Affect Rate of Transformation?

The higher the temp, the quicker the rate of transformation

Bainite

Fe-Fe3C Transformation Product. Results from a moderate cool from Austenite. Composed of both Ferrite and Cementite. Increases Strength but decreases ductility.

Spheroidite

Fe-Fe3C Transformation Product. Formation requires diffusion. Heat Bainite or pearlite at a temp just below eutectoid for a long time. Increases Strength but decreases ductility.

Martensite

Fe-Fe3C Transformation Product. Formation happens rapidly, no diffusion. Transformation only depends on the temp that it is rapidly cooled to. Increases Strength but decreases ductility.

Tempered Martensite

Fe-Fe3C --> Martensite Transformation Product. Heat treat martensite to form tempered martensite. Less brittle and reduces internal stress of martensite caused by quench.