Lighting technologies

Lighting technologies using the example of normalized C45 steel (Nital etching)

Bright field

  • lighting technology: bright field
  • optical path: almost vertical
  • application: approx. 50 % of all metallographic examinations
  • optical features, accessories: none
  • characterization: ferrite (bright), pearlite (dark), grain and phase boundaries (dark)
  • comment: none

Dark field

  • lighting technology: dark field
  • optical path: angular illumination
  • application: surface boundary contrast (scratches, cracks and pores), elevations and depressions (bright), planar surfaces (dark)
  • optical features, accessories: none
  • characterization: ferrite (dark), pearlite (bright), grain and phase boundaries (bright)
  • comment: translucent phases

Polarization

  • lighting technology: polarization
  • optical path: corresponds to bright field, in addition necessary: polarizer, analyzer, compensation plate (optionally)
  • application: analysis of all non-cubic phases
  • optical features, accessories: polarizer, analyzer, compensation plate
  • characterization: ferrite (dark), pearlite (bright)
  • comment: application of zinc, titanium, magnesium and their alloys; color etching; non-cubic slag inclusions

Nomarski interference contrast

  • lighting technology: Nomarski interference contrast
  • optical path: almost vertical, in addition necessary: Nomarski prism slider (Wollaston prism), polarizer, analyzer, compensation plate (optionally)
  • application: examination of slight roughnesses and differences in height (above some 10 nm), color and stereophonic imaging 
  • optical features: Nomarski prism slider, compensator, analyzer, compensation plates
  • characterization: ferrite (blue), pearlite (yellow-brown-red)
  • comment: none 

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