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Effect of negative bias voltage on mechanical and electrochemical nature in Ti-W-N coatings

Abstract:

Mechanical and electrochemical surface properties of Si (100) and AISI D3 steel substrates-coated Ti-W-N, deposited by r.f. magnetron sputtering process from a binary (50% Ti, 50% W) target in an Ar/N2 (90%/ 10%) mixture, have been studied using nanoindentation.Tafel polarization curves and electrochemical impedance spectroscopy (EIS). The crystallinity of the coatings was analyzed via X-ray diffraction (XRD) and the presence of TiN(111), TiN(200), WN2 (107), and W2N(220) phases were determined. Depth sensing nanoindentation measurements were used to investigate the elasto-plastic behavior of Ti-W-N coatings. Each group of samples was deposited under the same experimental conditions (power supply, Ar/N2 gas mixture and substrate temperature), except the d.c. negative bias voltage that varied (0,-50, and-100 V) in order to study its effect on the mechanical and electrochemical properties of AISI D3 steel coated with Ti-W-N coatings. The measurements showed that the hardness and elastic modulus increase from 19 to 30 GPa and from 320 to 390 GPa, respectively, as a function of the increasing negative bias voltage. Coating track and coating-substrate debonding have been observed with atomic force microscopy (Asylum Research MFP-3D®)on the indentation sites. Finally, the corrosion resistance of Ti-W-N coatings in 3.5 wt% NaCl solution was obtained from electrochemical measurements in relation to the increase of the negative bias voltage. The obtained results have shown that at the higher negative bias voltage (-100 V), the steel coated with Ti-W-N coatings presented the lower corrosion resistance. The corrosion resistance of Ti-W-N in 3.5 wt% NaCl solution was studied in relation to the increase of the bias voltage. © Springer Science+Business Media, LLC 2010.