Sintered parts are manufactured by forming metallic or ceramic powders in metal moulds and then baking and hardening the moulded parts at temperatures lower than their melting points. The advantages of sintering are that only a small amount of energy is required with minimum material losses and no time and effort are required for secondary processing because metals do not need to be melted. This section provides an overview of sintering and introduces observation and measurement examples of sintered parts using digital microscopes.

Observation and Measurement of Sintered Parts Using Digital Microscopes

Advantages and Disadvantages of Sintering

Sintering is used to manufacture various parts because materials do not need to be melted.

Advantages of sintering
  • Almost any material can be used as long as it can be powdered.
  • Secondary processing is not required in many cases.
  • Material losses are small.
  • Complex shapes can be moulded.
  • Materials can be freely mixed.
  • Sintered parts are porous and thus light.
  • Even materials with high melting points can be processed.
Disadvantages of sintering
  • Powders are processed, which increases the material costs.
  • Parts shrink when sintered.
  • Mechanical properties, such as strength, are inferior to those produced by casting or pressing.

Principle of Sintering

Solid powder surfaces are unstable because atoms, molecules, and ions are not bonded. Joints called necks are formed when solid powders are heated. As atoms, molecules, and ions move (diffuse) from powder particle surfaces to necks, necks become larger and the surface areas decrease. As necks continue to grow through the initial, intermediate, and final stages, density increases and the sinter is completed.

Powder compact
Initial stage
Intermediate stage
Final stage
  1. A: Neck
  2. B: Open pores
  3. C: Closed pores

Pores that are connected to external air are called open pores and those isolated in an object are called closed pores.

Sintering Flow

  1. Determine the mixing ratio of material powders and mix them with a mixier until the mixture becomes uniform.
  2. Put the powder mixture into a metal mould and form it with a press.
  3. Heat the moulded part in a sintering furnace for several hours.
    Material powders do not melt because the moulded part is baked to harden at temperature lower than their melting points. Material powders are firmly bonded to each other when heated for a long time and become a sinter.

Sintering furnaces are filled with gases to prevent sinters from becoming oxidised.
Sinters may be cut or polished to increase accuracy or heat-treated to increase hardness.

Raw materials are powdered.
Material powders are mixed.
The mixture is moulded.
The moulded part is sintered.
Finished product
  1. A: Mixer
  2. B: Press
  3. C: Sintering furnace

Observation and Measurement Examples of Sintered Parts Using Digital Microscopes

These are the latest examples of observation and measurement of sintered parts using KEYENCE’s VHX Series 4K Digital Microscope.

Observation of particle boundaries on a sinter (ferrite core)
VH-Z100, 700×, mixed illumination + adjustable illumination attachment
Low particle boundary density (low strength)
VH-Z100, 700×, mixed illumination + adjustable illumination attachment
High particle boundary density (high strength)
The adjustable illumination attachment can be used to clearly check particle boundary sizes and density.
Observation of cracks on a ceramic sinter
1000×, coaxial illumination, without HDR
1000×, coaxial illumination + HDR
With the HDR function, it is possible to check how far cracks extend.
Observation of a sinter surface
VH-Z20, 100×, ring illumination + adjustable illumination attachment
Left: With the attachment/Right: Without the attachment
Using the adjustable illumination attachment allows for pores to be observed clearly.
Automatic area measurement of a ceramic sinter
VHX-E500, 1000×, coaxial illumination
The grains used to be visually counted by size using a scanning electron microscope (SEM). This process can now be done automatically using the automatic area measurement function.
Automatic area measurement of pores in a ceramic sinter
ZS-200, 1000×, coaxial illumination
Before measurement
ZS-200, 1000×, coaxial illumination
Automatic area measurement image
Automatic area measurement can be performed with the same settings, which improves efficiency.
Grain size analysis for a metal sinter
ZS-200, 1500×, coaxial illumination
Before measurement
ZS-200, 1500×, coaxial illumination
Automatic area measurement (grain size analysis) image
The grain sizes used to be compared with limit samples, which caused variations in evaluation.
The automatic area measurement function allows for accurate grain size analysis, significantly reducing the amount of analysis work.