Quantification of localised loss of material

For a better understanding of the mechanism of erosion by arcing, an accura te method of quantifying the amount of material removed is required. To ach ieve this, a Scanning White Light Interference Microscope was used to measu re the shape and Volume of craters from their local depth profiles. The cra ters were produced using single arcs with defined physical characteristics. The investigations were carried out on the polished surfaces of various ma terials, and in particular alloys and intermetallic compounds. The vertical resolution of the interferometer used was of the order of 1 nm, while the lateral resolution using white light was limited to ca. 0.5 mum. This permi ts such craters to be measured quite accurately as their size generally var ies between 20 and 500 nm in depth and 10 and 70 mum in diameter. A further advantage of this method is that in multi-phase structures the individual phases can be observed and the material loss can be distinguished between d ifferent phases.