5- Whole Metallurgy (Part I)

7/28/2019 5- Whole Metallurgy (Part I)

1/8

I. MetalsLight metals Heavy metals Non metals

High melting

Brittle Ductile

Inert gases

Noble Low melting


2/8

From the periodic table, it can be found that:

Metals are on the left side.

Nonmetals are on the right side.

Metalloids or semiconductors are at the

boundary between metals and nonmetals;

e.g. Carbon, Silicon and Boron.

Properties of metals:1- Ionized positively.

2- Crystalline solids at room temperature, except Hg and Ga.

3- Opaque and lustrous.

4- Thermally ad electrically conductors.

5- Hardness, melting and boiling points.

6- Density.

7- Ductile and malleable.

8- Melting range.

9- White in color except Au and Cu.


3/8

Pure metals in dentistry:

1- Au and Pt foils Restorations.

2- Pt foils Porcelain.

3- Au and Sn Ceramo metal restorations.

4- Ag and Cu Electroplated dies.

5- Hg Amalgam.

6- Ti Implantology, Cr and Br (Procera).

Shaping of metals:a) Casting:

Liquid metal Crystalline solid

Solidification and thermal shrinkage 4-6%

b) Plastic forming (Cold working):

Cast metal rod, wire, tube,


4/8

c) Sintering (Powder metallurgy):

Powder Solid

Accompanied by Shrinkage, Density and Porosity

d) Electroforming:

Ag and Cu electroplating.

C:\Documents and Settings\Mostafa A. Latif\My Documents\My

Pictures\Dr.Azza\Metallurgy\078_Electroplating.mov

HeatPressure

Temperature

Time

Time temperature cooling curve for a

pure metal

Solidification of metals:A

B\

B C

D

Tf

Liquid

PlateauL+S

Solid

Supercooling


5/8

1- Nucleus formation:

Liquid metal atomic aggregates embryos embryos

2- Crystallization:

Nuclei of crystallization Dendrites Crystals Solid metal

temp. Latent heat

Penetration of super cooling

Homogeneous Heterogeneous

Grains and grain boundaries:Poly crystalline material Crystals with various orientationCrystals or grains have: Shape

Size

Orientation

Distribution

Grain Proper

Boundary

Grain boundary:

- Transition zone (1-2 atomic distances).

- Indicates discontinuity of space lattices planes.

- Nearly noncrystalline.

- Of higher energy.

- Greater rate of diffusion.

- Greater concentration of impurities.

- More readily attacked by chemicals.

Microstructural variables of

a single phase material


6/8

Grain size:

- Size Number and location of nuclei.

- Size Grain boundary - area.

Control of grain size:

Size Physical properties.

1- Amount and rate of supercooling (Control number of grains and nuclei).

2- Rate of crystallization and rate of nucleation.

3- Nucleating agents.

1

1

r1

.... SYge

Wrought metalDeformation

Cast metal wrought metal

Deformation of metals: Elastic

Plastic

CastWrought

Recovery

Recrystallization

Grain growth

Elastic Plastic


7/8

Lattice imperfections:

a- Point defects: Vacancies

b- Line defects: Dislocations

c- Plane defects: Boundaries

Edge Dislocation Screw Dislocation Mixed Dislocation

Strain hardening: [Cold working] [Work hardening]:

Dislocation is inhibited by: 1- Point defects.

2- Collision of 2 dislocation.

3- Foreign atom lattice.

4- Grain boundaries.

Dislocation build up Stresses needed to proceed deformation

So, Hardness, Strength and P.L.

Meanwhile, Ductility and Corrosion resistance


8/8

Annealing:

It reverses the effects of cold working

It involve three stages: 1- Recovery.

2- Recrystallization.

3- Grain growth.

Factors affecting grain size and shape: 1- Rate of cooling.

2- Nucleating agents.

3- Cold working.

4- Annealing a) Recrystallization

b) Grain growth.

Grain growthRecrystallizationRecoveryFurther annealing0.3-0.6 Tm Tm

(for few minutes)

Growth of grains.

.

St., P.L.

and Ductility

Nucleation of stress free grains

at boundaries.

St., P.L., and Hardness

and Ductility

Relief of stresses

Grain

growth

Recryst.RecoveryCold

worked

A) Cold worked

B) Recovery

C) Recrystallization

D) Grain growth

Tensilestrength

Ductility

5- Whole Metallurgy (Part I)

Documents

Transcript of 5- Whole Metallurgy (Part I)