Sample taking

Method used to take a sample from the raw material of the melt or the casting for the purpose of further chemical, physical or metallographic examination.
Polished specimens, for example, are taken from the relevant material by means of a separation process. In this case, there is a risk of the material structure near the later ground surface being influenced. These influences can be caused by thermal impacts, deformations, reinforcement or formation of new cracks and edge damage.

Fig. 1
shows a specimen improperly taken using a cutting wheel. The heat generated during this process resulted in the formation of bright an dark zones.

Fig. 2 and Fig. 3 show that different structures occur in these zones making an exact assessment of the strucgture no longer possible.

Wet separation of polished specimens is thus essential. Ideally, the cutting wheel consists of Al2O3, SiC or diamond and a binding agent (plastic, rubber, metal) working out the sample by grinding in a coolant (water). In case of soft materials (e.g. aluminum alloys) it must be ensured that the contact pressure is kept as low as possible by chosing a suitable separating tool. Then, the later ground surface has an excellent flatness and is not subject to change.

  • Fig. 1: Improperly taken specimen with thermal impact zones, 1:1
  • Fig. 2:  Structure formation in the bright zones from Fig. 1, 100:1, etched
  • Fig. 3: Structure formation in the dark zones from Fig. 1, 100:1, etched
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