Micro hardness

Hardness in the micro range of a material. In contrast to macro hardness, which is an integral hardness value for the overall metal matrix of the examined material, micro hardness provides hardness values for individual structural components (Fig. 1). This makes it possible, to perform for example the following material tests:

  • Hardness comparison between individual phases in homogenous alloys
  • Determination of segregation in individual crystals
  • Examination of mixed crystals
  • Determination of the hardness profile in the cross section of thin layers (e.g. nitrided, case-hardened layers, galvanic coatings, oxide layers)
  • Determination of the orientation and structures at crystallites
  • Examination of diffusion processes,
  • Detection of internal stress
  • Detection of creeping processes

For micro hardness testing, most laboratories apply the Vickers hardness test.

The indenter in this test is a straight diamond pyramid (square base) with a plane angle of 136°. At this shape of the indenter, the test force and the impression surface are proportional and the hardness value according to Vickers is respectively independent of the selected test force. The Vickers hardness value is determined from the test force F and the impression surface A of the left impression (see Hardness test). Figs. 2 and 3 show micro hardness testing machines.

An overview camera enables a range of vision of 60 μm to 52 mm by combining a macro objective lens with high-quality measuring objective lenses. This technology is used to display an overview of the sample (40 x 52 mm) on which all test lines are clearly displayed. To considerably facilitate this process, grids, auxiliary lines and reference lines with edge offsets can be displayed.

An important factor for the accuracy of the test result is the measurement of the test impression. Exact results can only be ensured by perfectly visible test impressions with optimum contrast and ideal light conditions. The electronic system of the camera controls the image ratios independently from the operator and ensures optimum visibility.

This machine applies IPC (Indentor Parallel to Contour) technology (Fig. 4). The fully automatic rotating indentor is the first system that enables exact measurements in the surface layer hardness profile. Test points can be placed even closer to the edge/contour.

  • Fig. 1: Micro hardness impressions to mark the differences in hardness, 1 = carbide;  2 = pearlite; 3 = ferrite , magnification 300:1, etched with HNO3
  • Fig. 2:  DuraScan micro hardness testing machine (EMCO-TEST Prüfmaschinen GmbH, Kuchl-Salzburg, Austria)
  • Fig. 3: Q10 micro hardness testing machine (Qness GmbH, Golling, Austria)
  • Fig. 4: IPC technology (Qness GmbH, Golling, Austria)
Movie 1