Improved quantitative analysis of hard coatings by radiofrequency glow discharge optical emission spectrometry (rf-GD-OES)

Quantitative depth profiles are presented for a variety of hard coatings on tool steel. The coatings include TiN, TiC, TiCN and Cr7C3 coatings, produced in a commercial furnace by chemical vapour deposition (CVD), and TiAlN, CrN and MoS2 + Ti coatings, prepared in a laboratory coater by physical vapour deposition (PVD). The profiles were obtained using rf-GD-OES and are the first to use a dc bias voltage correction and a hydrogen correction. These corrections involve a term called the 'inverse relative emission yield' and are simple functions of the dc bias voltage and hydrogen signal. These corrections mean bulk and coated samples with different electrical characteristics can be combined in a single calibration. The correct quantitative depth profile can now be obtained even in the presence of significant amounts of hydrogen in the coating.