Wrought metal alloys

Click here to load reader

Embed Size (px)

Transcript of Wrought metal alloys

WROUGHT METAL ALLOYS

WROUGHT METAL ALLOYS

CONTENTSDEFINITIONHOW WROUGHT METAL ALLOYS ARE MADE?USESPROPERTIESDEFORMATION OF METALSCARBON STEELGOLD ALLOYS

STAINLESS STEELTITANIUM ALLOYSCHROMIUM COBALT ALLOYSAJ WILCOCK WIRESCONCLUSION

Wrought: Beaten to shape.Alloys: A metal made by combining two or more metallic elements to give greater strength or resistance to corrosion

What are wrought metal alloys?

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

How wrought alloys are made?

How wrought metal alloys are made?

Cast alloys are made to pass through a series of dies with intermediate heat treatment to eliminate the effects of work hardening,these round wires are then made to pass through turks head to form wire with sq or rectangular cross-sections.

Work hardening: inc in strength and hardness and dec in ductility of a metal that is caused by plastic deformation,below recrystalizaion temp.7

Where all they are used?

Ortho wire.endo..prostho8

ORTHODONTIC WIRESORTHODONTIC BRACKETSPRE-FABRICATED CROWNS

PARTIAL DENTURE CLASPENDODONTIC FILESSURGICAL INSTRUMENTS

PROPERTIESStrengthStiffnessSpringbackResilienceFormability Malleability Ductility JoinabilityBiocompatibility

11

STRESSSTRAIN

ELASTIC POINT

THE RATIO OF STRESS TO STRAIN N THE LINEAR PORTION OF THE CURVE IS CALLED YOUNGS MODULUSELASTIC LIMIT

The greatest stress to which a material can be subjected, such that it returns to its original dimension when force is released is called elastic limit12

STRESSSTRAINTHE DEFORMATION MOST USED IS 0.2%YIELD STRENGTH

YIELD POINT

defined as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent.13

STRESSSTRAINULTIMATE TENSILE SRENGTH

Ultimate tensile strength is measured by the maximum stress that a material can withstand while being stretched or pulled before breaking14

STRESSSTRAINSPRING BACK

POINT OF ARBITARY CLINICAL LOADING

THE MAXIUM ELASTIC DEFLECTION. SHOWS HW FAR A WIRE CAN BE DEFLECTED WITHOUT permanent deformation.. This depends upon the elastic strain.15

STRESSSTRAINRESILENCE

THE AR UNDER STRESS-STRAIN CURVE AT MAX ELASTIC DEFORMATION. The amount of elastic energy per unit volume released on unloading of a material.16

STRESSSTRAINFORMABILITY

YIELD POINTFRACTURE POINT

THE ABILITY TO CHANGE THE SHAPE OF A MATERIAL LIKE LOOPSCOILS ETC and stops without fracture of wire.. A WIRE WHICH HAS LOW RESISTANCE TO PERMANENT DEFORMATION IS EASIEST TO FORM.17

MALLEABILITYThe material's ability to form a thin sheet by hammering or rolling.

DUCTILITYThe material's ability to be stretched into a wire.

BIOCOMPATIBILITY

Resistant to corrosion.

Since arch wire is in close contact with the oral cavity for a lengthy period they should b resistant to corrosion and should not elicit allergic response.20

JOINABILITYEase of auxillary attatchment soldering or welding

Represents the ease of either by soldering or welding21

Stress-strain curve

Proportonal limit: the maximum stress at which stress is proportional to strain above which plastic deformation occurs.22

DEFORMATION OF METALS LATTICE IMPERFECTIONS

DISLOCATIONS

STRAIN HARDENING

FRACTURE

LATTICE IMPERFECTIONS

Crystallization in metal does not occur in regular fashion but occurs as random growth with some lattice positions left vacant and others overcrowded.

24

Lattice imperfections are classified as:

POINT DEFECTS

LINE DEFECTS

POINT DEFECTS

Vacancy a vacant lattice site

Divacancy/ Trivacancy two or more missing atoms

Interstitial extra atom present in space lattice

A defect in which anatomis missing from one of the lattice sites is known as a 'vacancy' defect. It is also known as aSchottky defect, although inionic crystalsthe concepts are not identical.26

Vacancies are also known as Equilibrium defects.

This is necessary for the process of diffusion of metals

Vacancies are Equilibrium defects because a crystal lattice that is in equilibrium contains a certain number of these defects.

27

DISLOCATIONS

Edge dislocation - lattice is regular except for the one plane of atoms that is discontinuous, forming dislocation line at the edge of the half plane.

Dislocation line also known as line defects. These reduce the strength of metals.28

Edge dislocation

Continuous shear stress applicationDislocation reaches edge of the crystal & disappearsLeaves ONE UNIT of slip at the crystal surface

SLIP PLANE

THE MORE THE SLIP PLANE THE EASIER TO DEFORM METAL30

Dislocationsare not equilibrium defectsit requires significant energy

Slip plane plane along which a dislocation moves

STRAIN HARDENING/ WORK HARDENING

DEFORMATION AT ROOM TEMPERATURE

INCREASE IN STRENGTH AND HARDNESS AND DECREASE IN DUCTILITY OF A METAL THAT IS CAUSED BY PLASTIC DEFORMATION AT ROOM TEMP.32

Further increase in cold work metal FRACTURE

Consequences of strain hardening

Surface hardness

Yield Strength

Ultimate tensile strength

Ductility

Resistance to corrosion of the metal

ANNEALING Controlled heating and cooling process designed to produce desired properties in a metal.

Annealing takes place in 3 successive stages

RecoveryRecrystallizationGrain growth

DURING COLD WORKING- TENSILE STRENGTH INCREASES AND DUCTILITY DECREASES.RECOVERY:Cold worked properties begin to disappear.

Slight decrease in tensile strength.

No change in ductility.No change in microstructure.

RECRYSTALIZATION

The old grains are replaced by new set of grains.The material attains its original soft and ductile condition.The fibrous structure is transformed to small grains.

GRAIN GROWTHGrain size range from fine to coarseFine grain structure if annealed further, grains begin to growLarge grains consume smaller grainsGrain growth process does not progress indefinitely to form single crystalRather, an ultimate coarse grain structure is formed

36

RECOVERYNo changes in microscopic structure.

Recrystallization

1.Rapid changes in microstructure2. On completion of recrystalization3. The fibrous structure in cold worked is transformed to small grains.

38

Grain growth

Phenomenon occurs only in wrought metals

CARBON STEELSIron-based alloys usually containing 1.2% CarbonBased on 3 possible lattice arrangements of iron, different classes of steels are:

FerriteAusteniteMartensite

Ferrite

Body centered cubic (BCC) Pure iron at room temperature Phase is stable in temperature as high as 912C Carbon has very low solubility in ferrite

Austenite

Face centered cubic (FCC) Stable form of iron at temperature between 912C & 1394C Maximum carbon solubility is 2.1% by weight.

Martensite

Body centered tetragonal crystal structure. Produced by quenching of austenite to undergo spontaneous, diffusionless transformation.This is a very strong brittle and hard alloy.The formation of martensite is actually a strengthening mechanism of carbon steel.

Produced by rapid cooling (quenching) of austenite to undergo spontaneous, diffusionless transformation.

43

Lattice is highly distorted & strained resulting in an extremely hard, strong, brittle alloy-MARTENSITE

MARTENSITE decomposes to form FERRITE & CARBIDE

Accelerated by heat treatment process called TEMPERING

Reduces hardness but increases toughness

WROUGHT GOLD ALLOYS

HISTORY

Several dental historians have referred to the discovery by Junker (2), in 1914, in a burial shaft at Giza, of two molar teeth held together by a gold wire.

seventh centry B.C., to insert a substitute tooth by replacingthe gold wire by gold bands in front of and behind the incisor teeth on each side of the gap, drilling a hole through both bands and the new tooth, and inserting a gold wire.46

GOLD WIRES WRAPPED AROUND THE NECK OF ADJACENT TEETH.

The Use of Gold in Dentistry AN HISTORICAL OVERVIEW. PART IJ. A. Donaldson British Dental Association Museum, London, U.K.

The discoveries were dated back to 550 B.C . A canine tooth like object made of two piece of calcite having hardness similar to natural teeth showing wear on the chewing surface & secured with gold wires wrapped around the neck of adjacent teeth

47

DENTAL APPLICATIONS OF GOLD ALLOYS

CONSTRUCTION OF REMOVABLE PARTIAL DENTURE CLASP.

FABRICATION OF ORTHODONTIC APPLIANCES.

AS RETENTION PINS FOR RESTORATION.

Gold wires resemble Type IV gold casting alloys in composition, but typically they contain less gold

48

Type 5 and Type 10 dental gold alloys are used as orthodontic wires.

Gold in Dentistry: Alloys, Uses and PerformanceHelmut Knosp, Consultant, Pforzheim, Germany Richard J Holliday, World Gold Council, London, UK Christopher W. Corti, World Gold Council, London, UK

PLATINUM-GOLD-PALLADIUM WIRES (P-G-P)Composition:Platinum: 40%-50%Gold: 25%-30%Palladium: 25%-30%

They possess,High fusion temper