Finals DM | PPT Wrought Metal Alloys

Annealing

Process of controlled heating and cooling designed to produce desired properties in a metal. This process increases the ductility, stabilizes shape

increases ductility and stabilizes shape

Result of the process annealing

Cold working

Process of plastically deforming metal at room temperature

Ductility

Ability of a solid to be elongated plastically without fracture.

Malleability

Ability of a metal to be hammered into thin sheets without fracture

Wrought

Beaten to shape

Alloys

Metal made by combining two or more metallic elements to give greater strength or resistance to corrosion.

Wrought metal alloys

Cold worked metals that are plastically deformed to bring about a change in shape of structure and their mechanical properties.

Cold working

Process of strengthening a metal by changing its shape without use of heat

Strain hardening or work hardening

It involves subjecting the metal to mechanical stress to cause a permanent change to the metals crystalline structure

Rolling, bending, shearing, and drawing

Major cold working methods

Rolling

It involves metal being passed through pair of rollers to reduce its thickness

Orthodontic wires, clasp arms, performed crowns, surgical instruments

Uses of Wrought Alloys

Tensile Force

It is applied on a metal below the proportional limit, which result in small increase in separation between metal atoms

Plastic or permanent deformation

This deformation occurs when the applied stress is above the elastic limit

Crystal imperfections

These are seen within metal and has two types (point and line defects)

Point defects and line defects

What are the two types of crystal imperfections that are seen within the metal

Tensile force is applied on a metal below proportional limit = small increase in separation between metal atoms, plastic or permanent deformation, crystal impefections

Deformation of metals

Vacancy or vacant atom site

Atom site in a crystalline lattice may occur at a single site in the atomic arrangement

Divacancy

Two vacancies may occur as a divacancy

Point defects

These are equilibrium defects, and crystalline materials that is in equilibrium will contain a certain number of these defects at a given temperature 

Edge dislocation

What is the simplest type of line defect?

Wrought alloys

Contain low percentage of elements; that is, alloying elements total less than about 4 pct.

4 pct

Total alloying elements of Wrought alloys

Casting alloys

Contain same elements as wrought, but in greater amounts; for example, silicon content

Range up to 22 pct

Total amount of silicon content in cast alloys

Wrought alloys = ductile enough to be hot or cold worked during fabrication

Cast alloys = brittle to the degree that shaping by deformation is not possible and they must be fabricated by casting

Principal difference between wrought and cast alloys

Wrought alloys

Ductile enough to be hot or cold worked during fabrication

Cast alloys

Brittle to the degree that shaping by deformation is not possible and must be fabricated by casting

Lesser than 100 microns

The grain size in wrought alloys

More than 100 microns

The grain size in cast alloys

Annealing

It is a heat treatment process in which the alloy is heated up to the prescribed ___ temperature for a prescribed time followed by controlled cooling to soften the alloy

Annealing

What is the used heat treatment process for alloy to achieved controlled cooling to soften the alloy?

Annealing

Lesser ductility in metals with greater strength and hardness due to cold working) can be reversed through ____

1. Recovery stage

2. Recrystallization

3. Grain Growth

What are the 3 successive stages of annealing of wrought alloys?

The higher is the temperature needed for annealing

The higher the melting point of a metal = ____

Recovery stage

Cold working begin to disappear but not significantly

Recovery stage 

There is a slight decrease in tensile strength and no change in ductility during this stage 

Recovery stage

During this stage, there is relieving of internal strain energy resulting from cold working

Recrystallization

This occurs after recovery stage

Recrystallization

Atoms in this stage are rearranged into a lower energy configuration

Recrystallization

The old and deformed grains disappear, and new structure of strain-free grains appear

Recrystallization

The completion of this stage regains metals’ microstructure resembling that before cold working 

Grain growth

When the cold worked metal is annealed at an elevated temperature, the grain size increases and it is called ___

Grain growth

It ceases after relatively coarse grain structure is produces

Wires in orthodontic treatment

A number of wrought base metal alloys are used in dentistry, mainly as ____

A. Stainless steel (Fe-Cr-Ni)

B. Cobalt-chromium-nickel

C. Nickel-titanium

D. Beta-titanium

The wrought alloys commonly used are:

Steel

Iron based alloy with less than 1.2% carbon

Chromium (12-30%)

What is added to steel for the alloy to become stainless steel?

Stainless Steel

Chromium 12-30% + steel = ???

Less than 1.2% carbon

Total amount of carbon in steel (iron based alloy)

Stainless steel

Resistant to tarnish and corrosion because of the passivating effect of chromium

Passivating effect of chromium

Stainless steel is resistant to tarnish and corrosion because of ____

Passivating effect

It is a thin, transparent but tough and impervious oxide layer (chromium oxide) formed on the surface of the alloy, when subjected to air, which protects against corrosion

Chromium

Where does passivating effect came from?

Chromium oxide

Impervious oxide layer

Ferritic stainless steel

Austenitic stainless steel 

Martensitic stainless steel

Types of stainless steel - Based on Lattice arrangement of Iron

Ferritic steel

This steel have good corrosion resistance but less strength and hardness

Body-centered cubic (BCC)

Structure of pure iron at room temperature and stable up to 912 degrees celsius (ferritic)

Ferrite

A material that the solubility of carbon in bcc is very low and reaches a maximum of 0.02% at 723 degrees celsius

0.02% at 723 degrees celsius

Solubility of carbon in bcc (— under ferritic steel/ferrite)

Austenite

Above 723 degrees celsius, a solid solution of carbon in an fcc iron matrix

2.1%

Maximal solubility of carbon in fcc matrix

Face-centered cubic (FCC)

Structure of stable form of iron at temperature between 912 degrees celsius and 1394 degrees celsius

Austenitic Stainless Steel

Type of stainless steel that are most corrosion resistant of stainless steel

Martensitic stainless steel

This type of stainless steel has high strength and hardness and used to make surgical and cutting instruments, but have least corrosion resistance when compared to other types of steel

Used to make surgical and cutting instruments

Uses of Martensitic stainless steel

Body-centered tetragonal (BCT)

Structure when FCC is cooled very rapidly (quenched)

Martensitic

When FCC is cooled very rapidly (quenched) it transforms to a BCT structure called

Iron is major component

Chromium - 18%

Nickel - 8%

Carbon - 0.08-0.15%

Composition of Austenitic Stainless Steel

Iron

Major component of Austenitic Stainless Steel

Used to make bands and wires

Uses of Austenitic Stainless Steel

18-8 Stainless Steel

Austenitic Stainless Steel is AKA ____

18% chromium and 8% nickel

Why is Austenitic SS called 18-8 SS?

greater ductility and undergoes cold work;

ease of welding;

overcome sensitization;

ease in forming

Austenitic stainless steel is preferred over others because of:

Gold and silver soldering

Example of Soldering

Soldering

Melting a filler metal between them at a temperature below solidus temperature of the metal being joined and below 450 Celsius.

Welding

When two pieces of similar metals are joined together using heat or high temperature and fusing them together

Wrought cobalt-chromium-nickel alloys

The hardness, tensile strength, and yield the same as 18-8 steel

Wrought cobalt-chromium-nickel alloys

Tarnish and corrosion resistance are excellent

Elgiloy

AKA as Wrought cobalt-chromium-nickel alloys

Cobalt, chromium, nickel, manganese, carbon, beryllium, iron

Composition of Wrought cobalt-chromium-nickel alloys includes:

Nitinol

AKA as Nickel-titanium alloys

Nickel-titanium alloys

Have large working range or elastic deflection because of the property of shape memory and super-elasticity

Shape memory and super-elasticity

Property of nickel-titanium alloys causing it to have a large working range or elastic deflection

Memory effect

It is achieved first by establishing a shape at 482 degrees celsius > cooled = another shape > subsequent heating - lower transition temp. = wire return to its original shape

Cobalt content

Used to control the transition temperature range, which can be near mouth temperature

Cobalt content

Content of nickel-titanium alloys causing used to control transition temp.

1. Good for orthodontic wires when low force and large working range is needed

2. Good for endodontic files in curved root canals to avoid perforation

Uses of Nitinol

1. Higher friction than stainless steel

2. Difficulty in soldering

3. Expensive

4. Nickel has got some hazardous and allergic effect

Disadvantages of Nitinol

Nickel

This substance has/got some hazardous and allergic effect

1. Nickel-titanium thermal treated alloy

2. Provides sharpness and cutting ability with added flexibility

3. Ideal for enlargement for severely curved canals

Uses of nickel-titanium alloys

Beta-titanium alloys

Pure titanium

Pure titanium

Has different crystallographic forms at high and low temp.

Commercially pure titanium (CP Ti)

Exists in a stable hcp crystal structure at temp. below 882 degrees celsius and stable bcc structure above that temperature.

a-titanium

Commercially pure titanium (CP Ti) that is stable hexagonal close-packed (HCP) crystal structure at temperatures below 882 degrees celsius

Beta-titanium

Commercially pure titanium (CP Ti) that exist in a stable bcc structure above 885 degrees celsius

Beta-titanium

Crystallographic form of titanium that appears above 885 degrees celsius

Orthodontic applications

Beta form (b-titanium) is commonly used in:

Alpha and beta titanium

Have excellent corrosion resistance and environmental stability