Raman chemical imaging of tribological nitride coated (TiN, TiAlN) surfaces

A new near-infrared Raman imaging microscopy (NIRIM) is used to identify and map the distribution of hard coatings on coated steel surfaces, both before and after tribo-testing. The NIRIM instrument used for these studies combines fiber-bundle image compression (FIC) hardware and multi-variate signal processing software to identify and map chemical species on surfaces. The materials studied consist of H13 steel substrates coated with titanium nitride (TiN) and titanium aluminum nitride (TiAlN). The NIRIM instrument was used to identify and map the distribution of these hard coatings on tribological surfaces, both inside and outside the wear tracks generated under different load and lubrication conditions. Comparison of the NIRIM results with combined scanning electron microscopy (SEM)/X-ray micro-analysis of the same samples indicates that although the two results are in general well correlated, in some cases the two methods are clearly sensitive to different chemical structures present on the same surface.