Metallographic preparation of powder metallurgy parts

The main characteristic of powder metallurgy parts

Powder metallurgy is a more common parts production method, especially in the automotive industry, because it can be mass production structure and complex shape of small parts.In powder metallurgy, metal (sometimes including nonmetal) powder mixture is compacted, and then sintered.The production costs are high, but compared with forging or casting parts, finished parts have special advantages.

The powder metallurgy method, can:

• Production are generally not easily alloy alloy metal
• The production of various properties of different alloys
• Particle size is very fine uniform structure
• The shape of the complex
• In the production of excellent finish parts

Figure 1: experimental powder metallurgy stainless steel, color etching

Powder metallurgy of common applications include:

• Mechanical and structural components, such as connecting rod, sprocket and CAM
• Hard by melting and casting for the production of refractory metal
• Controllable porosity of porous material with a specific purpose
• Could not form alloy composite material, such as cu/w
• Special high strength alloy, such as nickel and cobalt base superalloy (used as a jet engine components)
• With isotropic uniform distribution of high-speed tool steel and carbide

The production of powder metallurgy parts

A lot of different metal can be used in the production of powder metallurgy parts, including iron, copper and steel powder.

The production process of iron and steel powder

Powder production
There are two kinds of powder production methods: chemical method and spray method.

• Chemical method: under the temperature below the melting point of metal oxides directly from the ore into metal powder.
• Through the nozzle atomization method: molten metal alloy, and the high pressure water or gas jet impact.Of granular form droplets, and curing.

The generation, mixed metal powder.At this stage, you can add other elements, including lubricants, carbon and/or alloying elements.

In cemented carbide die medium pressure tight powder
In order to production parts, mixed powder under high pressure in cemented carbide die medium pressure tight.At this stage, the parts have the shape of the final product, but do not have the strength of the requirements.These parts is known as the "green" parts.

Sintering parts
In order to provide the necessary mechanical and physical properties, in the protective gas in high temperature sintering process was carried out on the parts.Through cooperation with diffusion between adjacent grain produce key.

The final processing
According to the application, some parts may be additional processing, including hot isostatic pressing, immersion, the surface hardening or plating.


Figure 4: sponge iron powder, SEM

Advice about cutting of powder metallurgy parts

Powder metallurgy parts available to a variety of materials, including iron, copper and steel powder.The choice of the cutting wheel depends on the material type.

• When cutting a single material of powder metallurgy parts, choose suitable for the cutting wheel of the material.
• If you select the suitable for cutting parts of hybrid material, main material cutting wheel.
• For sintered carbide, the use of resin bond diamond cutting wheel.

Figure 7: sintered tungsten carbide (WC/Co), by Murakami reagent.the, 1500 x

Tips Mosaic powder metallurgy parts

In order to ensure the resin with good adhesion of sample material, Mosaic Mosaic sample thoroughly degreased with acetone and toluene.

And cutting, the best way to set sample depends on the material you want to deal with.

• For sintering parts (Mosaic sample) :
  - during hot compression set samples, using phenolic resin (MultiFast), or contains a hard filler material resin (DuroFastorLevoFast).
  - during cold set sample, can use acrylic resin containing packing (DuroCit - 3orLevoCit).
• After cutting, green parts must be in a vacuum environment with cold inlaid epoxy resin (CaldoFix - 2,EpoFixorSpeciFix - 40) to dip.
• Powder can be mixed with a small amount of powder inlaid with slow curing epoxy resin.The mixture sample can be set directly into the cup.
• Hard metal powder can be through the sample and fine-grained impregnated resin (DuroFast) mixed hot compression set.The mixture into sample set in the cylinder, and pour on phenolic resin.

Figure 8: the traditional method of the distribution of carbide in steel production


Figure 9: the distribution of the carbide in powder metallurgy steel

To learn more

• In ourcuttingandWith the sampleSection for more knowledge, expertise and insights
• Check our cuttingequipmentandconsumablesA series of
• Check our samplesequipmentandconsumablesA series of

Powder metallurgy copper metallographic sample preparation method

Table 1:6 powder metallurgy (P/M) copper sample method of sample preparation, Mosaic, 30 mm in diameter, with semi-automaticTegraminDiameter of 300 mm

As aDiaProAlternative, polycrystalline diamond slurry P (9 mu mu m and 3 m and 1 mu m) can be used together with the red, green or blue lubricant.

Powder metallurgy steel metallographic sample preparation method

Table 2:6 powder metallurgy (P/M) steel sample method of sample preparation, Mosaic, 30 mm in diameter, using semi-automatic Tegramin, 300 mm in diameter

As alternative DiaPro, polycrystalline diamond slurry P (9 mu mu m and 3 m and 1 mu m) can be used together with green or blue lubricant.
* you can also use the MD - Dac/DiaPro Dac. 3.

Metallographic sample preparation method of sintered carbide

Table 3:6 sample preparation method of sintered carbide sample, Mosaic, 30 mm in diameter, using semi-automatic Tegramin, 300 mm in diameter

As alternative DiaPro, polycrystalline diamond slurry P (9 mu mu m and 3 m) can be used together with the green/blue lubricant.
* optional step.


Figure 10: in MD - Allegro after fine grinding on the surface of the powder metallurgy steel


Figure 11: the same sample, as figure 10 shows the polishing is insufficient, according to the surface of the powder metallurgy steel


Figure 12: same as the figure 11 samples, after polishing for a longer time, shows that the pore is correct


Figure 13: the surface of the figure 11. A higher magnification, showed a metal cover pore "cover"

Cleaning and drying of powder metallurgy parts

After polishing, we should use water/cleaning detergent mixture powder metallurgy sample, to remove polishing slurry and residue of lubricant.Application of water washing sample, then rinse thoroughly with isopropyl alcohol.


Figure 14: cleaning the water damage may lead to structural interpretation is not correct

To learn more

• In ourGrinding and polishingSection for more knowledge, expertise and insights
• Check our grinding and polishingEquipment and productsA series of
• Get the metallographic grinding and polishingconsumablesandaccessories

Etching solution

Can use the ordinary chemical etching liquid metal or alloy.When using chemicals, must comply with the standard of security considerations.

Figure 18: etching for too long time


Figure 19: correct etching

Download contains the preparation of a complete application instructions

conclusion

Powder metallurgy for using usually not easy to form alloy metal to produce parts.Common materials including iron, copper and steel powder.

The density of powder alloy parts will affect the strength, toughness and hardness.Therefore, the porosity of the metallographic control is an integral part of quality control.

In the process of metallographic grinding and fine grinding, the metal may be pushed into the pore, leave impact assessment of the residual metal "cover".Therefore, in order to ensure that truly represent the structure of the material, it is necessary to carefully by diamond grinding and polishing.


Figure 20: infiltrated copper powder metallurgy steel

In-depth understanding of other materials

Learn more about other metal material phase information and materials.Visit ourMaterials page

All images by Danish application specialists Birgitte Nielsen
About the details of the metallographic sample preparation of powder metallurgy parts,Please contact our application specialists.