Structural and quantitative analysis of nitrured coatings deposited by DC magnetron sputtering on steels

The study concern the production of thin (4000Å) coatings and their analysis by nuclear reactions, Mössbauer spectroscopy and X-ray diffraction. The coatings are deposited by sputtering a stainless steel target in a nitrogen atmosphere; the nitrogen flux was varied between 0 and 10 sccm with increments of 1 sccm and an additional variable argon flux provided the same constant total gas flux (20 sccm) in the sputtering chamber for all depositions.

The elemental composition of coatings was studied by Rutherford backscattering (RBS), by X-ray emission induced by charged particules and by nuclear reactions (¹⁴N(³He,a₀)¹³N, ¹⁴N(a,p₀)¹⁷O, ¹⁵N(p,ag)¹²C, ¹⁴N(a,a)¹⁴N). The nitrogen content of coatings is found to increase with increasing flux up to a saturation value of 50 at.%.

A structural analysis by means of conversion electron Mössbauer spectroscopy (CEMS) and grazing incidence X-ray diffraction (GXRD) was also performed. The results indicate that the lattice expands as the nitrogen flux increases and that this expansion is caused by incorporation of nitrogen into interstitial sites. Moreover, the presence of the so-called S-phase is detected. The latter is probably due to nitrogen in solid solution at vacancies in the stainless steel. This phase is particulary interesting for industrial applications because it increases the resistance to wear without compromising the corrosion resistance of the steel.