Multipass and reciprocating microwear study of TiN based films

Titanium nitride (TiN) coatings with a Cr metallic interlayer were deposited on AISI 316L stainless steel substrates using D. C. unbalanced magnetron sputtering, changing substrate temperature and gas mixture. The effect of the sliding motion in wear tests was studied, comparing multipass (unidirectional) and reciprocating (bidirectional) sliding modes. In addition, microstructure, mechanical properties and adhesion were analyzed. The structural characterization was performed by scanning electronic microscopy (SEM) and grazing incidence X-ray diffraction (GIXRD). Moreover, hardness of the coating was measured by spherical nanoindentation, and thermal residual stresses were estimated. The scratch tests were conducted using a steel ball of 1 mm of diameter. To study the effect of sliding motion, the wear tests were carried out with an alumina ball of 3 mm of diameter, in both sliding modes the same linear test geometry, a stroke length of 3 mm and loads of 0.5 and 1 N were used. TiN coatings thicknesses ranged from 1.1 to 1.8 μm, growing in preferred orientations (200) and (111). It was found that increasing the nitrogen content during the deposition cause a decrease in the adhesion of the coating. In the sliding wear tests, the coefficient of friction (COF) values ranged from 0.12 and 0.22. The effect of sliding motion in COF was more evident in the tests performed with 0.5 N load, reciprocating exhibited higher values than multipass. The specific wear coefficients k varied from 6.9 × 10⁻⁴ to 1.88 × 10⁻³ mm³ · N⁻¹m⁻¹ for all tests, the highest value was obtained in a reciprocating test.