thermal equilibrium diagrams

Thermal Equilibrium Diagrams

Thermal Equilibrium Diagrams show the temperatures at which phase changes take place in alloys of different percentage composition.

Thermal Equilibrium Diagrams

Phase

A Phase is a portion of a system that has uniform physical and

chemical characteristics.

Thermal Equilibrium Diagrams are made for information gained

form Cooling Curves.

When the temperature of a cooling molten metal alloy is plotted against time, a cooling curve is formed.

Cooling Curve

When cooling a solid pure metal, change from a solid to a liquid at constant temperature.

This is called the Melting Point Temperature.

The heat that is released in the transition from a solid to a liquid is called hidden or Latent Heat.

Solidification Starts

Solidification Ends

LIQUID

SOLID

The Cooling Curve of 100% Copper

Remember this only happens for pure metals.

Latent heat is the quantity of heat energy absorbed or released when a substance changes its physical phase at constant temperature.

Latent Heat

The energy that goes in breaks the bond of the atoms.

LIQUID

SOLID

Pure Metal change

directly from Liquid to Solid

at1

temperature.

The Cooling Curve of Pure Metal

If a metal is 100% pure and contains no traces of other elements then some under cooling may occur before solidification begins. Under cooling is when the temperature drops below the liquid to solid temperature for a short period.

Undercooling

1500

1000

1100

Tem

pera

ture

0 C

Time

Undercooling

Fall in temperature stops temporarily at the freezing point because of Latent heat

The Cooling Curve of an Alloy

Solidification Starts

Solidification Ends

LIQUID

SOLID

“PASTY” STATE

Alloys change from Liquid to

Solid through a pasty state

over a temperature

range.

Over a Temperature Range

1Temperature

Pure Metal Alloy

Solid Solition Alloys

Solid Solution:

When viewed under a microscope, a solid solution appears like a pure metal.

A Solid Solution is when two metals are completely soluble in each other in both the liquid and solid states.

100% LeadIron Carbon

TASK

Using the graph paper supplied:(i) Draw the equilibrium diagram according to the given data.(ii) Label the diagram and describe the main features.(iii) For the alloy with 50% Nickel determine, from the diagram, the ratio of the phases at 1250°C.

The given table shows the solidification temperatures for various alloys of Copper and Nickel. The melting point of Copper is 1083°C and Nickel is 1453°C.

Axis of Diagram

40%60%

20%80%

0%100%

60%40%

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100%

0%

TEM

PERA

TURE

(°

C)

PRECENTAGE COMPOSITION

200

400

600

800

1200

1400

1000

1600

NICKELCOPPER

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0

200

400

600

800

1000

1200

1400

Copper/Nickel Equilibrium Diagram

NICKELCOPPER

TEM

PERA

TURE

(°

C)


Equilibrium diagrams are made from taking information for cooling of different

percentage of an alloy and putting it on one graph.

How Equilibrium Diagrams Are Made

The Cooling Curve of Copper/ Nickel and alloys

This is know as a TERMAL ANALYSIS

How A Thermal Equilibrium Diagram Is Made

100% Copper


100% NICKLE


60% Copper 40% Nickel


40% Copper 60% Nickel


40%60%

20%80%

0%100%

60%40%

80%20%

100%

0%

TEM

PERA

TURE

(°

C)


Liquidus Line

Solid Phase

Liquid Phase

Liquid Phase and Solid

PhaseSolidus Line

Phases are defined as regions that differ from one another on an equilibrium diagram.

200

400

600

800

1200

1400

1000

1600

NICKELCOPPER

Phases defined by composition (not by state – solid, liquid, gas)

Liquid: the two metals are soluble in each other in the liquid state.

Liquidus Line: the change from fully liquid to pasty state. Above the liquidus line, the alloy is liquid. This is the beginning of solidification.

Liquid and Solid: the alloy is in a pasty form, there are two phases one Liquid and one Solid.

Solidus Line: the change from pasty to solid. Below the solidus line, the alloy is cooling and solid. This is the end of solidification.

Solid: alloy is in solid form.

Main Features of Equilibrium Diagram

27

Introduction To Equilibrium Diagrams Equilibrium may be defined as a state of

balance or stability.

Diagrams indicates the phases the alloy is at different temperatures.

Phases are defined as regions that differ from one another on an equilibrium diagram. Phases defined by composition.

Equilibrium refers to Balance existing in a system

In Metallurgy, Equilibrium means, that the cooling of a metal or an alloy is so slow that all the changes that might take place get the chance to do so.

The Meaning of the Term Equilibrium

Metallurgy is the study of metals and their properties

To achieve equilibrium to take place enough time for complete

diffusion is required.

Diffusion

Diffusion is the processes by which a substance spread out through another

substance. Atoms move in a solid metal in this

manner.HIGH CONSTANTRATION

LOW CONSTANTRATION

Diffusion in a vacuum

Diffusion in a Solid

Atom move form high concentration to low

concentration

Water And Sugar

A SINGLE PHASE

TWO-PHASES

How Many Phases Are There? PHOTOS

Phase

A Phase is a portion of a system that has uniform physical and

chemical characteristics.

Phases

Phases are defined as regions that differ from one another on an

equilibrium diagram. Phases defined by composition. NOT BY STATE (solid, liquid , gas)

Substitution Solid Solution Alloys

Nickel Copper


Copper

Nickel

Copper

Nickel

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0

200

400

600

800

1000

1200

1400

NICKELCOPPER

TEM

PERA

TURE

(°C)


1250°C

Ratio of Phases

Tie Line

iii)For the alloy with 50% Nickel determine, from the diagram, the ratio of the phases at 1250°C.

26%

66%

Ratio of Phases

Ratio of phases at 1250℃ for 50% Nickel

26%

66%

The ratio of Solid to Liquid is:

A CB

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0

200

400

600

800

1000

1200

1400

NICKELCOPPER

TEM

PERA

TURE

(°C)


1250°C

26% 66%

Ratio of phases at 1250°C for 35% Nickel

35%

Ratio of Phases

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0

200

400

600

800

1000

1200

1400

NICKELCOPPER

TEM

PERA

TURE

(°C)


1250°C

26% 66%

Ratio of phases at 1250ºC for 60% Nickel

Ratio of Phases

Eutectic Alloys

Eutectic Alloys

In a eutectic alloy the two metals are

completely soluble in the liquid phase but are

insoluble in the solid phase.

TASK

Using the graph paper supplied:i. Draw the equilibrium diagram according to the given

data.ii. Label the diagram and describe the main features.

The given table shows the solidification temperatures for various alloys of Cadmium and Nickel.

Axis of Diagram

40%60%

20%80%

0%100%

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100%

0%

TEM

PERA

TURE

(°

C)


200

400

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1200

1400

1000

1600

BISMUTHCABMIUM


TEM

PERA

TURE

(°

C)

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%0

50

100

150

200

250

300

350

400

BISMUTHCADMIUM

TEM

PERA

TURE

(°

C)


Cadmium / Bismuth Equilibrium Diagram

40%60%

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80%20%

100%

0%



50

100

150

200

300

350

250

400

TEM

PERA

TURE

(°

C)

Liquid Phase

Liquidus Line

Solid PhasesSolidus Line

BISMUTHCADMIMUM

Liquid Phaseand Solid Phase

EutecticPoint


40%60%

20%80%

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60%40%

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100%

0%PRECENTAGE COMPOSITION


TEM

PERA

TURE

(°C

)

Liquid Phase

Solid Cadmium and Eutectic

BISMUTHCADMIUM

Liquid and Solid Cadmium

Liquid and Solid Bismuth

EutecticPoint

Solid Bismuth and Eutectic

Green Line

Eutectic Alloy

Eutectic

50

100

150

200

300

350

250

400

Solid Bismuth Solid Cadmium

Cadmium / Bismuth∘ Cadmium Atoms∙ Bismuth Atoms

X 1 000

X 10 000 000

Eutectic Point

The point where the liquid alloy changes to solid

without going through a liquid/solid state is called the

eutectic point.

Partial Solubility Alloy

The equilibrium diagram for this type of alloy is called a Partial Solubility thermal equilibrium diagram.

It is a combination of the solid solution and eutectic diagrams and is a little more complex.

Partial Solubility AlloySome metals in an alloy only

partially dissolve in each other. Lead/Tin Alloy (Solder) is an

example of this.

Make up of Partial Solubility Alloy Equilibrium Diagram

Eutectic Alloys

Partial Solubility Alloy

Solid Solution Alloys Solid Solution Alloys

Lead / Tin Equilibrium Diagram BASIC

Liquid Phase

Liquidus Line

Solid Phases

Solidus Line

Liquidand Solid

EutecticPoint

Liquidand Solid

40%60%

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100%

0%


TINLEAD

100

200

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400

TEM

PERA

TURE

(°

C)

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0%


Lead / Tin Equilibrium Diagram LINES

100

200

300

400

TEM

PERA

TURE

(°

C)

Liquid Phases

Liquidus Line

SolidTINLEAD

Liquidand Solid

Liquidand Solid

Solid Solution Solid

Solution

SOLVUS LINES

Solidus Line

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0%


Lead / Tin Equilibrium Diagram COMPLETE

100

200

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400

TEM

PERA

TURE

(°

C)

Liquid Phases

TINLEAD

β Solidand Liquid

α Solid and Liquidα Solid Solution β Solid

Solution

α and βSolid Solution

Interstitial Solid Solution Alloys

Lead

Tin

Task 3 (Q6 2006)Copy the given lead-tin diagram into your answer book and answer all of the following:

(i) Identify the lines labelled A, B and C; (ii) Explain what each line represents; (iii) For the alloy with 30% tin determine, from the diagram, the composition of the phases at 250°C; (iv) Indicate clearly on your diagram the eutectic point.

(i) Labelled lines A, B and C

Liquidus line

Solidus lineSolvus line

A – Liquidus line. For the alloy system this line represents the boundary between the fully liquid state and the beginning of solidification.

B – Solvus line. The transition line from one solid form to another solid form of an alloy is called the solvus line. This line indicates the maximum amount of tin

which can be dissolved in the lead.

C – Solidus line. The boundary line that determines the end of solidification. Below this line the alloy is completely solid.

(ii) Explain what each line represents?

For the alloy with 30% tin determine, from the diagram, the composition of the phases at 250°C?

A – Solid composition consisting of 8% tin and 92% lead.B – Liquid composition consisting of 43% tin and 57% lead.

A B

To determine composition

of the phases

(iv) Indicate the eutectic point

Eutectic Point


40%60%

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60%40%

80%20%

100%

0%

TEM

PERA

TURE

(°

C)


Liquidus Line

Solid Phase

Liquid Phase

Liquid Phase and Solid

PhaseSolidus Line

Phases are defined as regions that differ from one another on an equilibrium diagram.

200

400

600

800

1200

1400

1000

1600

NICKELCOPPER

Phases defined by composition (not by state – solid, liquid, gas)

40%60%

20%80%

0%100%

60%40%

80%20%

100%

0%



50

100

150

200

300

350

250

400

TEM

PERA

TURE

(°

C)

Liquid Phase

Liquidus Line

Solid PhasesSolidus Line

BISMUTHCADMIMUM


EutecticPoint


40%60%

20%80%

0%100%

60%40%

80%20%

100%

0%


Lead / Tin Equilibrium Diagram COMPLETE

100

200

300

400

TEM

PERA

TURE

(°

C)

Liquid Phases

TINLEAD

β Solidand Liquid

α Solid and Liquidα Solid Solution β Solid

Solution

α and βSolid Solution

You should know that a pure metal has one clearly defined melting point.

Mixtures tend to solidify over a temperature range, that is they start to solidify at one temperature and do not complete the process until they reach a lower point.

A mix of 80% A with 20% B will solidify over a different range than a mix of 20% A with 80% B.

A phase diagram allows us to present all this information in a single (sometime simple) diagram.

What is a Equilibrium Diagrams

68

Introduction To Equilibrium Diagrams Equilibrium may be defined as a state of

balance or stability.

Diagrams indicates the phases the alloy is at different temperatures.

Phases are defined as regions that differ from one another on an equilibrium diagram. Phases defined by composition.

thermal equilibrium diagrams

Documents

solid temperature

solid at1 temperature

constant temperature

solid pure metal

latent heatthe cooling

cooling curve of pure

cooling molten metal

melting point temperature