L. Ipaz

Influence of the microstructure on the electrochemical properties of Al-Cr-N coatings deposited by co-sputtering method from a Cr-Al binary target

In the present paper, aluminum chromium nitride (Al-Cr-N) films were deposited onto AISI H13 steel substrates by a reactive d.c magnetron co-sputtering system in an atmosphere of Ar/N2 (90/10) gas mixture from a binary target composed of chromium (99.95%) and aluminum (99.99%). Different powers (40, 50, 60, and 70 W) were applied to the target, in order to study the effect of this parameter and the sputtering yield of binary target, on the microstructure and the electrochemical properties of the Al-Cr-N coatings. The corrosion behavior in 3.5 wt. (%) NaCl solution was investigated by electrochemical corrosion tests (Tafel polarization curves and Electrochemical Impedance Spectroscopy (EIS)), and the chemical composition, microstructure and the absorption bands by means of Energy Dispersive X-ray Spectroscopy (EDX), X-ray diffractometry (XRD) and Fourier Transform Infrared Spectroscopy (FTIR), respectively. EIS results showed that the Al-Cr-N coating deposited at 40 W, exhibited the lower porosity and the highest polarization resistance, and subsequently, when the power applied to the binary target increased, the corrosion rate and the porosity increase.

Correlation Between Mechanical Properties and Nanofriction of [Ti–Cr/Ti–Cr–N] n and [Ti–Al/Ti–Al–N] n Multilayers

In this work, thin films deposited by pulsed DC magnetron sputtering of [Ti–Al/Ti–Al–N]n and [Ti–Cr/Ti–Cr–N]n multilayers of nanometric periods were analyzed by AFM in contact mode to measure values of lateral and normal forces. From these measurements, the coefficient of friction (COF) of these materials in contact with the AFM tip was calculated. Measurements were made with three types of silicon tips, diamond-coated, Pt–Cr-coated, and bare silicon. Significant differences between the tip materials in contact with the samples, which affected the COF, were observed. The effect of the environmental layer of water covering the surface sample and the tip appears as the most important factor affecting the tribology behavior of the tip-sample contact. For diamond-coated and bare silicon tips there is an additional adherence force increasing the normal load. But for tips platinum–chromium-coated there is a repulsive force due to this water layer, which behaves as a lubricant layer before a threshold load.

A Practical Application of X-Ray Spectroscopy in Ti-Al-N and Cr-Al-N Thin Films

Binary and ternary transition metal nitrides coatings have been used in numerous applications to increase the hardness and improve the wear and corrosion resistance of structural materials, as well as in various high-tech areas, where their functional rather than tribological and mechanical properties are of prime importance (Munz, 1986; Chen & Duh, 1991; PalDey & Deevi, 2003; Ipaz et al., 2010). Up to now, Ti-Al-N and Cr-Al-N films have been synthesized by a variety of deposition techniques including cathodic arc evaporation (Cheng et al., 2001), ion plating (Setsuhara et al., 1997), chemical vapor deposition (CVD) or plasma-enhanced CVD (Shieh & Hon, 2001) and d.c. / r.f. reactive magnetron sputtering (Musil & Hruby, 2000; Sanchez et al., 2010). Performance of these coatings is equally dependent on their chemical composition and long-range crystalline structure, as well as on the nature and amount of impurities and intergranular interactions. Significant improvement in the mechanical properties has recently been achieved with multicomponent superlattice, multilayers and nanocomposite nitride coatings. In the case of such multilayers systems, not only is close control of the elemental composition (stoichiometry) and modulation period necessary to optimize the properties of the coatings, but the influence of chemical bond formation between the components is also of prime importance. Therefore, it is necessary to take special care when the conditions of preparation are nonequilibrium, activation of CVD and PVD by plasmas or energetic particle beams are applied, occasionally leading to unpredicted deviations, both in composition and structure. As is highlighted in this study, nitride coatings or nitrided surfaces based in Chromium and Aluminium materials can be analyzed in detail by X-ray photoelectron spectroscopy (XPS) due to its excellent element selectivity, quantitative character and high surface sensitivity. More importantly, XPS reflects the atomic scale chemical interactions, i.e. the bonds between neighboring atoms Cr-N, Al-N, Ti-N, Ti-Al-N and thus it also provides reliable structural characteristics for amorphous or nano-crystalline coatings of complex composition, for which application of diffraction techniques is not straightforward.