Powder Metallurgy

Outline

• Introduction

• Basic steps of P/M (Toz metal bilimi)

• Powder Manufacturing

• Compacting

• Sintering (külçeleme, sinterleme)

• Secondary Operations

• Repressing

• P/M forging

• Impregnation

• Infiltration

• Classification of P/M products

Powder Metallurgy

• fine metal particles are blended and pressed

• into a desired shape (compacted).

• The resulting part is then heated (sintered)

• in a controlled atmosphere for sufficient time

• to bond the compacting surfaces of the particles

• to establish desired properties.

• The temperature is below the melting point of the majorconstituent.

ksi (unit), kilopound per

square inch,

Production of Metal Powders

• The size of the particle varies from several microns to 0.5 mm.

• The most common particle size of powders 10 to 40 microns.

1. Atomization

2. Chemical reduction

3. Electrolytic process

4. Crushing

5. Milling

6. Condensation of metal vapors

7. Hydride and carbonyl processes

1. Atomization

• the molten metal is forced through an orifice

• it emerges, a high pressure stream of gas or liquid impinges on it

• causing it to atomize into fine particles.

• used mostly for low melting point metals such as tin, zinc, lead, aluminium, cadmium

2. Chemical Reduction Process

• compounds of metals are reduced with CO or H2

• at temperatures below the melting point of the metal in an atmosphere controlled furnace.

• The reduced product is then crushed and ground.

• Iron powder and Powders of W, Mo, Ni and CO can easily be produced

3. Electrolytic Process

• Production of extremely pure, powders of copper and iron.

• The electrolytic powder is quite resistant to oxidation.

• High amperage produces a powdery deposit of anode metal on the cathodes.

• the cathode plates are taken out tank,

• rinsed to remove electrolyte and are then dried.

• plates is then scraped off and pulverized to produce powder of the desired grain size.

4. Crushing Process

• requires equipment such as stamps, crushers or gyratory crushes.

• Various ferrous and non-ferrous alloys can be heat-treated

• to obtain a sufficiently brittle material

• which can be easily crushed into powder form.

5. Milling Process

• commonly used for production of metallic powder.

• using equipment such as ball mill, impact mill, eddy mill, disk mill, vortex mill,

6. Condensation of Metal Powders

• metals, such as Zn, Cd and Mg, which can be boiled

• vapors are condensed in a powder form.

• vaporized droplets of metal are allowed to condense

• On to a cool surface to which they will not adhere.

7. Hydride and Carbonyl Processes

• High hardness oriented metals such as tantalum, niobium and zirconium

• made to combine with hydrogen form hydrides that are stable at room temperature,

• but to begin to dissociate into hydrogen and the pure metal when heated to about 350°C.

Compacting of Powder

• converting loose powder in to defined shape and size.

• carried out at room temperature in a die on press machine.

• The die consists of a cavity of the shape of the desired part.

• Metal powder is poured in the die cavity and pressure is applied using

punches,

Green-State Carbide Micro-machining

400 µm 100 µm

500 µm500 µm

Sintering (Sinterleme)

• The compacts are subjected to elevated temperature in a controlled atmosphere.

• Sintering temperature should be below the melting point of the major constituent. (70-90% of Tm)

• Sintering atmosphere (N2, H2, Argon, etc.) to prevent oxidation (paslanma) and combustion (yanma).

• Sintering strips contaminants (impurities) from the surface of the powder particles.

• It permits the diffusion bonding between the powder particles, resulting in a single piece of material.

Sintering

Advantages vs. Disadvantages

• Hard to process materials such as diamond can be converted into usable components and tools

• production parts, which cannot be produced through other methods, such as sintered carbides and self-lubricating bearings.

• Simple shaped parts can be made to size with 100 micron accuracy without waste

• Highly qualified or skilled labor is not required.

• Super-hard cutting tool bits, which are impossible to produce by other processes, can be easily manufactured

Advantages vs. Disadvantages

• Ability to create complex shapes

• High production rates

• Wide variation of compositions/properties

• Low material waste

• Good microstructure control

• Eliminates machining

• Creation of residual pores• High die/tooling costs• Design limitations• High material cost

Advantages vs. Disadvantages

• not economical for small-scale production

• cost of tool and die of powder metallurgical set-up is relatively high

• size of products as compared to casting is limited

• Metal powders are expensive and in some cases difficult to store without some deterioration.

• Intricate or complex shapes produced by casting cannot be made by powder metallurgy

• metallic powders lack the ability to flow to the extent of molten metals.