POWDER METALLURGY

TEAM MEMBERS:

VIDHIDUHITA RAUL(111021008)

GAYATRI VORA (111021024)

DEVASHRI VAGHOLKAR (111021037)

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INTRODUCTION

Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape or form, and then heating the compressed material in a controlled atmosphere to bond the material.

Basically a chipless metalworking process, P/M typically uses more than 97% of the starting raw material in the finished part and hence it is an energy and materials conserving process.

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3PROCESS

1 •Characterization

2 •Powder Production

3 •Mixing - Blending

4 •Processing - Compacting

5 •Sintering Operation

6 •Finishing Operation

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A. CHARACTERIZATION AND TESTING OF POWDERS

Obtaining desired properties in a component depends on the properties of metal powders used and hence it is essential to test the powders.

It helps in the selection of the right type of powder for a given application.

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1. Chemical Composition and Impurity

2.Shape, Size and

Distribution

3. Particle Porosity and

Microstructure

4. Specific Surface

5.Density

6. Flow Rate

7. Compacting or Pressing Properties

8. Sintering Characteris

tics

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1. Chemical Composition and Impurity

Impurities not only affect the component properties but also influence the pressing and sintering characteristics and hence its determination is very important.

It can be determined by several standard techniques like :a) Gravimetric Analysisb) Volumetric Analysisc) Colourometric Analysisd) Spectroscopy

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2.Shape, Size and DistributionIt can be measured by the following methods:

1. Sieve Method : It is the simplest method in which sieves of different mesh numbers are used.

2. Microscopic Method : Optical (2,000 x) and Electron (5,00,000 x) Microscopes are used.

3. Sedimentation Method : Classification is based on the settling velocities of powders in a fluid.

4. Elutriation Method : The metal powder is allowed to settle in a moving liquid or gas of a constant velocity to determine size distribution of fine particles.

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83. Particle Porosity and Microstructure

It is determined by using microscopy by mounting the powders in a suitable medium.

1. HOT MOUNTING : Powder + BakeliteThe medium is mounted, polished, etched, washed with water and alcohol and dried using blast of hot air and then examined under microscope.

2. COLD MOUNTING : Powder + Polymeric Liquid + Hardener

The medium is poured in a steel tube in which the liquid polymerizes and becomes hard in 10-15 mins. Then it is polished, etched, washed and examined.

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4. Specific Surface Total surface area of powder per unit

weight (cm2/gm).

The compacting and sintering properties are highly dependent on the contact area.

Methods of evaluation :1. Permeability Method2. Adsorption Method

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5.Density1. APPARENT DENSITY : It is defined as the mass per unit volume of a loosely or

unpacked powder. It includes internal pores only and strongly influences the

pressing characteristics. It is measured by using standard flow meter funnel or

volumeter.

2. TAP DENSITY : It is the apparent density of the powder after it has been

mechanically shaken or tapped until the level of powder remains constant.

It is measured by Ro tap machine.

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VOLUMETER

RO-TAP MACHINE

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6. Flow Rate It is defined as the rate at which metal powder will flow

under gravity from a container through an orifice having specific shape and size.

It is measured by using a flow meter which is a conical brass funnel with an internal angle of 60 D.

It depends on : Size and shape Distribution Amount of adsorbed gases Moisture Coefficient of friction

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7. Compacting or Pressing Properties

It is represented in terms of :

Compressibility : Ability to undergo deformation under the

applied pressure.

Compactibility :The minimum pressure required to produce a compact.

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148. Sintering Characteristics

The sintering characteristics and quality can be determined by testing the following properties :

Dimensional Change i.e. % Shrinkage Density and Porosity Mechanical Properties Microstructure

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B. POWDER MANUFACTURING

There are various ways to manufacture powder and each method gives a power of different size, shape, distribution and has different characteristics.

Therefore, a right type of powder in the correct proportion should be used for obtaining the desired properties in the final sintered product.

The proper choice of method depends on the type of raw material, desired properties, final component and economy of the process.

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MECHANICAL PROCESSES

PHYSICAL PROCESSES

CHEMICAL PROCESSES

ELECTRO-CHEMICAL PROCESSES

POWDER

MANUFACTURI

NG

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17I. MECHANICAL PROCESSES

MACHINING

CRUSHING

MILLING

SHOTTING

GRAINING

AUTOMIZATION

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TYPES OF CRUSHERS

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MILLING

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SHOTTING

Solidification by air or neutral gas

GRAINING

Solidification by water

Molten metal is poured on a vibrating screen and the liquid droplets are solidified.

In both the methods powders contained are coarse

Other pulverization methods required.

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AUTOMIZATION

The process of metal spraying against a stream of compressed air or inert gas is Atomization.

It is an excellent means of producing metal powders from many of the low temperature metals such as lead, aluminium, zinc and tin

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2. PHYSICAL PROCESSES

CONDENSATION

THERMAL DECOMPOSITION

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CONDENSATION Metal vapours condensed to obtain powder

Highly suitable for volatile metals

Powder shape is nearly spherical

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THERMAL DECOMPOSITION Thermal decomposition of carbonyl vapours.

Fe 5COFe(co

)5

Fe(co)5 Fe 5C

O

200 to 270°70 to 200 atm

Carbonyl

vapoursSolid metal

Carbonyl

150 to 400°1 atm

Metal powder

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3. CHEMICAL PROCESSES

REDUCTION

INTERGRANULAR CORROSION

PRECIPITATION

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REDUCTION

Metal compound is reduced by suitable reducing agent to obtain metal powder.

Example: Chromium powder is produced by reduction of chromium oxide with Mg.

Powders obtained are fine.

Shape of particles is irregular.

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28INTERGRANULAR CORROSION

Grain boundaries corrode faster than grains.

Grain boundary area of metal under interest is corroded by a suitable electrolyte so as to separate out grains from the polycrystalline metal.

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PRECIPITATION FROM AQUEOUS SOLUTION

Less noble metal displaces more noble metal from an aqueous solution containing ions of more noble metal.

Example: Silver is displaced from a silver nitrate solution by Cu or Fe.

Excellent purity.

Dendritic shape.

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304. ELECTRO-CHEMICAL PROCESSES

Powder obtained by electro deposition from aqueous solution.

Similar to electroplating.

Conditions favorable for powder formation on cathode:

1. High current density2. Low metal ion concentration3. High acidity4. Low temperature

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Types of Electrodeposition

Hard and brittle, which is

subsequently ground to powder

Soft and spongy, loosely adherent and fluffy texture

which is powdered by light rubbing

Direct deposition as powder in

bottom of the cell

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C. POWDER BLENDING Powders of metals and non-metals are

carefully blended to obtain uniform mixture. This is essential for obtaining the desired

properties. Lubricants are used to reduce friction between

die walls and the punches. Various types of blenders and mixers are

available to suit particular requirements of the components produced.

For better mixing Tumbling action is necessary and hence Y cone or Double cone Blender is used.

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Types of Blenders

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D. POWDER COMPACTING

Powder compaction is the process of compacting metal powder in a die through the application of high pressures.

The tools are held in the vertical orientation with the punch tool forming the bottom of the cavity.

The powder is then compacted into a shape and then ejected from the die cavity.

The density of the compacted powder is directly proportional to the amount of pressure applied which should be between 1 to 150 kg/mm.

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Compaction Cycle

1. Cycle Start2. Charge die3. Compaction begins4. Compaction

complete5. Ejection of compact6. Recharging of die

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Compacting Tools  Tooling must be designed so

that it will withstand the extreme pressure without deforming or bending.

Materials used should be polished and wear-resistant.

There are 4 major classes of tools:

1. Single Action Compaction ( for thin, flat components)

2. Opposed Double Action with Two Punch Motions (which accommodates thicker components)

3. Double Action with Floating Die

4. Double Action Withdrawal DiePOWDER METALLURGY

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E. SINTERING Solid state sintering is the

process of taking metal in the form of a powder and placing it into a mold or die.

The material is placed under a high heat (~80% of melting temperature) for a long period of time.

Under heat, bonding takes place between the porous aggregate particles and once cooled the powder has bonded to form a solid piece.

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Sintering proceeds in three stages.1. Neck growth proceeds rapidly

but powder particles remain discrete.

2. Most densification occurs, the structure recrystallizes and particles diffuse into each other.

3. Isolated pores tend to become spheroid and densification continues at a much lower rate.

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`

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Types of Sintering

Two types of sintering :-

Solid Phase Sintering : The compacts are heated above recrystallization temperature of low melting metal.

Liquid Phase Sintering : The compact is heated above the melting point of one of the alloying elements. Alloying may take place at the interface of the particles.

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F. FINISHING Repressing:

Additional compacting operations, performed under high pressure in presses (coining, sizing).

Impregnation: Utilizes inherent porosity of P/M components

by impregnating them with a fluid (oil).

Infiltration: A slug of lower melting point metal is

placed against the sintered part, the assembly is heated to melt slug. By capillary action, the liquid slug fills the pores of the sintered part.

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ADVANTAGES

Combinations of metals and non metals powdered parts can be manufactured.

High Dimensional accuracy.

No material is wasted as scrap.

Porous parts and cemented carbide tools can be produced which is not possible by any other method.

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Highly qualified or skilled person is not required.

Large scale production is economical and gives efficient results.

Eliminates numerous machining operations.

Powder metallurgy parts can be easily brazed, welded , soldered.

Fine Surface finish is achieved.

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RECOGNISED GREEN TECHNOLOGY

In an initiative undertaken by the Metal Powder Industries Federation, the PM industry is proclaiming to the manufacturing community that powder metallurgy is a recognized "green" technology.

Being sustainable is a way of life and—for many of us in the PM industry—being green is now a way of doing business.

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DISADVANTAGES High tooling costs and expensive raw materials.

Difficult storing and handling of powders (degradation with time and fire hazard with particular metallic powders).

Not economical for small scale production.

Products have poor ductility, purity of powder is low and they show poor plastic properties.

Porosity makes it difficult to obtain some mechanical properties. POWDER METALLURGY

19/04/202348HOT ISOSTATIC PRESSING (HIP)

Hot Isostatic Pressing of encapsulated powder metal produces net or near net shape parts with special particle properties.

The process takes place well below the melting point of the material, typically resulting in a very fine grained structure.

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Hot Isostatic Process P/M parts are:

Isotropic Densification of powdered metal parts Elimination of porosity Improved mechanical properties Little or no secondary machining Decreased scrap loss

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APPLICATIONS Powder Metallurgy finds wide applications in the

industry and several market segments offer potential growth areas for powder metallurgy manufacturing techniques.

Automotive components Aerospace High temperature applications Healthcare sector Defence

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Automotive Components Manufacture electrical contacts, crank shaft,

piston rings, connecting rods, clutches, brakes, dynamos, etc.

Titanium is in exhaust systems using cheap commercially pure (CP) sheet. Turbochargers, valves and springs are usually made from titanium alloys.

Used as a fabrication technique for automotive components, with many cars containing up to 8-30 kilograms of parts made this way.

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Aerospace Metal powders play an important role in rockets,

missiles, satellites and space vehicles. Metal powders of Be, Al, Mg and Zr are used as solid fuels

in rockets and missiles. Tungsten parts are used in plasma jet engines and ion

engines operated at about 1800 C. Net-shape HIP titanium Powder Metallurgy products

have been developed for turbine applications where conventional processing (involving machining) is very wasteful of material and the Powder Metallurgy route can offer cost benefits.

Airframe sector: There is also growing interest in the use of titanium

Powder Metallurgy in the airframe sector.

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High Temperature Applications

Components made of W, Mo and Ta by powder metallurgy are widely used in electric light bulbs, fluorescent bulbs, radio valves, mercury arc rectifiers and X ray tubes in the form of filament,etc.

Refractory metal carbides are used for dies, rolls, cutting tools, etc. at high temperatures.

Production of super alloys is also possible by powder metallurgy.

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Healthcare Sector Titanium and titanium alloys are ideally

suited to medical implants because titanium is biocompatible and inert to human body fluids.

MRI scanners used large quantities of rare earth permanent magnets, processed from powders.

Surgical instruments and dental implants are produced.

Customized medical implants using additive manufacturing and in producing porous implant structures (to match bone stiffness and to aid osteo-integration) by PM processing.

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Defense Applications Metal powders play an important role in military

and national defense systems.

They find use in missiles, rockets, cartridge cases, bullets, etc.

Also used in military pyrotechnics like tracers, incendiaries, etc.

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62Powder Metallurgy Products

Oil-impregnated Porous Bronze Bearings Connecting Rods

Gears

19/04/2023631. Self Lubricating Bearings

Self-lubricating oil-impregnated PM bearings find their applications in mechanical and electromechanical devices, where sliding processes, especially rotary motions, are occurring. 

Friction and wear are reduced, and liquids can carry away both frictional heat and wear debris generated during the sliding process.

When the shaft is at rest all the oil is retained in the pores and the load is sustained by direct metallic contact between the two surfaces. At the beginning of movement the direct metallic rubbing between bearing and journal with its high friction coefficient raises the temperature rapidly.

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2. Cermets Cermet is "a heterogeneous combination of metals or

alloys with one or more ceramic phases in which the latter constitutes approximately 15 to 85% by volume and in which there is relatively little solubility between metallic and ceramic phases at the preparation temperature".

Cermets originally were used for cutting tool

applications.

Refractory behavior, strength, and corrosion resistance of the ceramic with the high ductility and thermal conductivity of the metallic phase are some properties.

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663. Cemented Carbides And Cemented Carbide Tipped Tools

Tungsten carbide (WC), also referred to as cemented carbide, is a composite material. Tungsten carbide powder, generally ranging in proportion between 70%-97% of the total weight, is mixed with a binder metal, usually cobalt or nickel, compacted in a die and then sintered in a furnace.

Carbides are brittle materials since it

exhibits little or no plastic deformation preceding the initiation of a crack and total failure..

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Withstand all forms of wear (including sliding abrasion, erosion, corrosion/wear and metal-to-metal galling) and exhibit a high degree of toughness.

It exhibits high compressive strength, resists deflection, and retains its hardness values at high temperatures, a physical property especially useful in metal-cutting applications.

It provides long life in applications where other materials would not last or would fail prematurely.

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THANK YOU!