Vacuum tribometer with in-situ measurement of wear track by digital holographic microscopy (DHM)

This application report presents a new ball-on-disk vacuum tribometer with in-situ and real time measurement of the wear track using Digital Holographic Microscopy (DHM). The new instrument was tested and validated by recording various types of DHM images during wear testing in vacuum at 2×10-6 mbar on polished 100Cr6 steel disks against an alumina ball. 3D wear track evolution can be analyzed by this new technique in real time without removing the sample. An excellent correlation was found between images taken on the same sample by in-situ DHM, confocal microscope, and scanning electron microscope.

Friction and wear are two of the main characteristics of a tribo-system. Friction force can normally be measured easily with load sensors. The measure of wear and determination of wear rate, however, is more complicated and it is usually determined by ex-situ and post mortem measurements using surface profilometry. It is well known that even small changes in the position of the sample during determination of wear in the course of a tribological measurement could lead to unpredictable local change of test conditions, which would affect the subsequent wear. To overcome these complications, in-situ measurement of wear is the only solution. Various methods have been proposed and studied by different researchers.

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