CHAPTER 1Part 2

MATERIAL STRUCTURE AND

BINARY ALLOY SYSTEM

Metal and Alloy Solidification

• is a phase transformation from liquid to solid to have the

desired shape ( semi-finished or finished products)

• Processes involving solidification : welding, soldering, casting

and glass forming

• 3 steps in solidification process:

Formation of stable nuclei in the melt

Growth of nuclei into crystals

Formation of a grain structure.

Solidification of Metals

a. Formation of stable nuclei (nucleation)b. Nucleation growth into crystalc. Formation of grain structure

a b c

Stages of Grain Growth• Crystal nuclei commence to form around microscopic impurities. This

is called nucleation.

• Dendrites begin to form crystal nuclei. These dendrites will have

primary and secondary arms.

• Dendrites continue to grow, forming tertiary arms, which meet and join.

• Dendrites thicken up and fill in. When arms of one dendrite touch those

of adjacent dendrites, growth ceases and grain boundaries are

established.

• When metal is completely solid, little evidence of dendrite growth

remains and only the grain boundaries are visible.

Formed as a result of adding of impurity atoms to a metal.

is an alloy in which one element is dissolved in another to form a single-

phase structure without changing the crystal structure and no new

structures are formed.

SOLUTE and SOLVENT

2 types of solid solutions :-

Substitutional Solid Solution

Interstitial Solid Solution

Solid Solutions

• Dissolved element or solute atoms

• Element or compound present in a minor concentration

• Can be either metallic or nonmetal

• Base element or host atoms• Element or compound present

in a greatest amount• metallic

• Solute or impurity atoms replace or substitute the solvent

atoms.

Zinc (solute)

dissolve

Copper (solvent)

Substitutional Solid Solution

Brass

Zinc is dissolved in Copper to form Brass.

Several features of solute and solvent atoms that determine the

formation of substitutional solid solution.

The atomic radii of the 2 elements must be

similar with the difference in atomic radii less than

±15%.

Their crystal structures for metals of both atoms must

be the same.

Substitutional Solid Solution

• Solute or impurity atoms fills the voids or vacant spaces among the

solvent atoms.

dissolve

Iron (solvent

)Carbon (solute)

Interstitial Solid Solution

SteelSteel

Carbon is dissolved in Iron to form Steel.

Several features of solute and solvent atoms that determine

the formation of Interstitial solid solution.

The solvent atom must have more than one valence.

The atomic radii of the solute atom must be smaller

than the atomic radius for the solvent atom.

Interstitial Solid Solution

The Difference Between

METAL and ALLOY

METAL ALLOYmade up of only one element alloy is a mixture of metals, or

metal and non-metal

High ductility Low ductility

Lack of mechanical properties (tensile strength, yield strength,

hardness)

Superior mechanical properties

Lack of strength High strength

Low melting point high melting point

Example:Copper, Zinc

Example : Brass , Steel

Cooling Curve

And

Phase Diagram

Heating and Cooling curve

• Heating curve – graph that shows phase changes as a substance is heated

• Cooling Curve – graph that shows phase changes as a substance is cooled.

** when you go

through a phase

change, the

temperature is

constant but you are

adding/losing heat

not temperature.

0 t1 t2 t3 t4

0 t1 t2 t3 t4

Cooling Curve

Cooling Curve

Equilibrium Phase Diagram

• Represents the relationship between

temperature and the compositions and the

quantities of phases at equilibrium.

• Temperature and composition are the variable

parameters for binary alloys.

• Pressure is also a parameter that influences

• A binary alloy is one that consists 2

components.

Phase Diagram

• Triple Point – point where temperature + pressure conditions allow all 3 states to exists at once.

• Critical Point – T&P above this point do not allow water to exist as liquid.

For every substance the phase diagram is different.

WaterMelting point = freezing point = 0˚CBoiling point = condensing pt=100˚C

• Phase Diagram = show at varying pressure and temperature what state or phase the substance is in.

Binary Phase diagram

Terms In Equilibrium Phase

Diagram• Phase : a homogeneous portion of a system that has uniform physical

and chemical characteristics.

• Equilibrium Phase Diagram: is a convenient and concise way of

representing the most stable relationship between phases. The state of a

system where the phase characteristics remains constant over time

periods.

• Compositions : the relative content of a particular element within an

alloy, usually expressed in weight percent or atom percent.

• Liquidus : the line or boundary separating liquid and liquid+solid

phase region on a binary phase diagram.

Cooling Curve for Cu-Ni System

Phase diagram

for Cu-Ni system

• At temperature below about 1080˚C, Cu and Ni are

mutually soluble in each other in the solid state for all

composition.

• The Cu-Ni system is termed as isomorphous (solid has the

same structure for all composition) because if this

complete liquid and solid solubility of the two components.

• Liquid L is a homogeneous

liquid solution composed

of both Cu and Ni.

• Solid phase is a

substitution solid solution

consisting both CU and Ni.

Point a

Point b

Point c

Point d

Point e

Point f

Task

Find and draw the

IRON-CARBON PHASE DIAGRAM

to discuss with your friends in next class.

** Everyone must have your own

diagram**

THE END

THANK YOU