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Shaping Methods of Metals1- Casting cast structure **Liquid metal **Mould

2. Cold Working Fibrous or wrought Structure

1- At room temperature 2- Stresses should YIELD strength

3. Powder metallurgy (sintering)

4. Electroforming

AlloysAn alloyis a combination of two or more metals which are soluble (miscible) in the molten condition.

Phase:1. Homogeneous 2. Physically distinct 3. Mechanically separable portion of a system

Classification of alloysa. According to the number of constituting metals; Binary, ternary, quaternary etc. b. According to solubility in the solid state:

SolidSolid-Solution alloy

Intermetallic Compound

Eutectic alloy

Solid Solution Alloys olidThe metals are said to be soluble in each other in the solid state, the structure is homogenous.

Types of solid solutionsInterstitial Solid Solutions Substitutional Solid Solutions **Ordered **Ordered **Disordered **Disordered

Conditions for S.S.1. Same space lattice type. 2. Same valence. 3. Atomic size difference must be less than 15 %; other wise, interstatial S.S. may form. 4. No chemical affinity; other wise, intermetallic compounds may form

Properties of S.S.1. Due to difference in atomic size localized distortion of the lattice dislocation movement becomes more difficult, which results in: strength, Hardness and ductility

2. Being one phase system (homogenous structure), the resistance to tarnish and corrosion is high. 3. The S.S. alloy has a melting range

Equilibrium phase diagram of solid solution

Interpretation of phase diagram of solid solutionFrom the phase diagram the following can be noticed:**The melting point of silver Is 960 0C, **The 0C, that of palladium is 15550C 15550C **The line ABC is the liquidus line, **The and the line ADC is the solidus line, the solid and liquid phases exist between. **Consider an alloy of composition **Consider 65% 65% palladium and 35% silver at various temperatures: 35%--At temperature 1500 0C only liquid is present with a composition of 65% --At 0C 65% palladium and 35% silver as indicated by the dotted line PO 35% --At temperature 1400 0C liquid and solid phases are present. --At 0C To determine the composition of the alloy first solidifying, the line RM (the tie line) is drawn parallel to the base line. The tie line intersects the liquidus line at R and the solidus line at M. --At temperature 1370 0C; please identify by yourself the composition of the --At 0C; different phases.

Eutectic AlloysDefinition:**Upon solidification, the two metals show partial solubility or in extreme **Upon theoretical cases complete insolubility. -Eutectic is a Greek word that means lowest melting. melting. -For an alloy system that has a eutectic composition there is a eutectic temperature which is a melting point not a melting range. -It is the lowest solidification temperature shown in the whole system

Properties of eutectic alloys: 1. Eutectic alloys are brittle because the presence of insoluble phases definitely inhibits slip. 2. Strength and hardness surpass those of the constituent metals heterogeneous structure of the alloy 3. They have poor corrosion resistance due to the heterogeneous structure having different phases with different electrode potentials

Differences between solid solution and eutectic alloysSolid solution **Solubility in the - Complete solid state **Phases - One phase homogeneous **Melting Properties - Melting range **Properties -Similar to the parent metals with increase in strength and hardness and decrease in ductility **Resistance to - High tarnish and corrosion **Uses - Most of metallic dental restorations are solid solution alloys e.g. base metal alloys and gold alloys Eutectic Partial Two phases heterogeneous Melting point Strong, hard, brittle Very low

Only: In soldering & admixed amalgam alloy

Complete Insolubility

Intermetallic CompoundDefinition: Upon solidification, both metals have chemical affinity towards each other forming intermetallic compounds with certain composition and below certain temperature. Properties of intermetallic compound: ** They are usually very hard and brittle. ** Their properties commonly differ from those of metals making up the alloy.

Classification of alloysa. According to the number of constituting metals; Binary, ternary, quaternary etc. b. According to solubility in the solid state:

SolidSolid-Solution alloy Intermetallic Compound

Eutectic alloy

Solid Solution AlloysThe metals are said to be soluble in each other in the solid state, the structure is homogenous.

Types of solid solutionsInterstitial Solid Solutions Substitutional Solid Solutions **Ordered **Ordered **Disordered **Disordered

Conditions for S.S.1. Same space lattice type. 2. Same valence. 3. Atomic size difference must be less than 15 %; other wise, interstatial S.S. may form. 4. No chemical affinity; other wise, intermetallic compounds may form

Properties of S.S.1. Due to difference in atomic size localized distortion of the lattice dislocation movement becomes more difficult, which results in: strength, Hardness and ductility

2. Being one phase system (homogenous structure), the resistance to tarnish and corrosion is high. 3. The S.S. alloy has a melting range

Eutectic AlloysDefinition:**Upon solidification, the two metals show partial solubility or in extreme **Upon theoretical cases complete insolubility. -Eutectic is a Greek word that means lowest melting. melting. -For an alloy system that has a eutectic composition there is a eutectic temperature which is a melting point not a melting range. -It is the lowest solidification temperature shown in the whole system

Properties of eutectic alloys: 1. Eutectic alloys are brittle because the presence of insoluble phases definitely inhibits slip. 2. Strength and hardness surpass those of the constituent metals heterogeneous structure of the alloy 3. They have poor corrosion resistance due to the heterogeneous structure having different phases with different electrode potentials

Differences between solid solution and eutectic alloysSolid solution **Solubility in the - Complete solid state **Phases - One phase homogeneous **Melting Properties - Melting range **Properties -Similar to the parent metals with increase in strength and hardness and decrease in ductility **Resistance to - High tarnish and corrosion **Uses - Most of metallic dental restorations are solid solution alloys e.g. base metal alloys and gold alloys Eutectic Partial Two phases heterogeneous Melting point Strong, hard, brittle Very low

Only: In soldering & admixed amalgam alloy

Intermetallic CompoundDefinition: Upon solidification, both metals have chemical affinity towards each other forming intermetallic compounds with certain composition and below certain temperature. Properties of intermetallic compound: ** They are usually very hard and brittle. ** Their properties commonly differ from those of metals making up the alloy.

Cooling Curve of a pure metal:

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Cooling Curve of a pure metal:

Cooling Curve of a Solid Solution:

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Cooling Curve of a Solid Solution:

Cooling curves of a pure metal and a solid solution

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Cooling Curve of a Solid Solution :

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Cooling Curve of a Solid Solution:

Phase diagram of a solid solution

Phase diagram of a solid solution

Interpretation of phase diagram of solid solutionFrom the phase diagram the following can be noticed:**The melting point of silver Is 9600C, **The that of palladium is 15550C **The line ABC is the liquidus line, **The and the line ADC is the solidus line, the solid and liquid phases exist between. **Consider an alloy of composition **Consider 65% 65% palladium and 35% silver at various temperatures: 35%--At temperature 1500 0C only liquid is present with a composition of 65% --At 0C 65% palladium and 35% silver as indicated by the dotted line PO 35% --At temperature 1400 0C liquid and solid phases are present. --At 0C To determine the composition of the alloy first solidifying, the line RM (the tie line) is drawn parallel to the base line. The tie line intersects the liquidus line at R and the solidus line at M. --At temperature 13700C; please identify by yourself the composition of the --At different phases.

Complete Insolubility

Eutectic System:

Mechanism of Solidification

1- Nucleus formation: nuclei of crystallization. crystallization. 2- Crystallization: dendrites and grain boundary

1) Nucleus Formation:When a molten alloy is cooled and approaches its freezing temperature, the atoms try to aggregate forming initial

starting points of crystallization[nuclei of crystallization] at supper cooling point

Nucleus formation can occur byA) Homogenous nucleation The atoms of the metal itself form the nuclei of crystallization B) Heterogeneous nucleation Foreign solid metallic particles e.g. iridium, which has a higher melting temperature than that of the liquid metal are added to the liquid metal They share in the formation of the nuclei of crystallization

2) Crystallization: The metals can solidify in single crystal [grain] which is very rare, or polycrystalline

As cooling continues the nuclei of crystallization grow independently in three dimensions [tree like structure] to form crystals [grains] The growth is stopped when there is contact with adjacent growing crystals

Factors affecting grain size** Time & Temperature controlled 1- Rate of cooling 2- Rate of nucleation and crystallizationcrystallization nucleation grain size

3- Nucleating agents (grain refiner)