HORIBA Worldwide

The first image shows a Raman map with a size of about 670x430 m, composed of approximately 10.000 single measuring points. Mapped was a wear track produced by the so-called "ball-on-disk" tribological test, where a Al₂O₃ ball is pressed against a rotating substrate. The substrate was a steel cylinder coated by a thin film of Al₅₀Cr₅₀N, deposited with an industrial-scale arc-evaporation system (RCS, BALZERS, Liechtenstein). Hard coatings in general are necessary to meet the high demands on metal cutting tools in terms of hardness, abrasive wear, oxidation and corrosion resistance and low friction. The test was performed at 700C. The spectra were recorded at room temperature using a Labram-HR800, equipped with a X-Y motorized stage, at 488 nm excitation of a Ar⁺-ion laser. After background correction, two spectra representative for hematite in the center of the wear track and for as-deposited coating out the wear track were chosen as "model"-spectra. Each original spectrum was decomposed by fitting of the sum of the two model-spectra, using the build-in routines of the Labspec4 software. The relative contribution of hematite and coating in each spectrum at every measuring point is displayed in red and green, respectively. The red areas indicate hematite from the underlying steel substrate due to total removing of the coating during the tribological test. Yellow spots indicate approximately equal contribution of both hematite and coating spectrum. The image shows that Raman maps enable the difficult decision whether the hard coating has fulfilled its main task of protecting the underlying steel from destruction. Raman maps are an important analytical method to design harder, more resistant and better lubricating hard coatings. The second image is a microphotograph of the wear track overlaid by the Raman map described before. The numbers indicate image size in m.