Enhanced hardness of CrAlSiN/W 2 N superlattice coatings deposited by direct current magnetron sputtering
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CrAlSiN/W2N nanolayered coatings were prepared by direct current magnetron sputtering. The modulation periods of multilayer coatings were controlled in the range from 3 to 20 nm. From the low angle x-ray diffraction and high angle x-ray diffraction (XRD) satellite peaks, the superlattice structure of these coatings was evidenced. The modulation periods of multilayer coatings were obtained precisely by the low angle XRD and high angle XRD satellite peaks methods. The detailed layered structure was further investigated by high-resolution transmission electron microscopy. Because of the dense and smooth nanolayered microstructure, the CrAlSiN/W2N multilayer films exhibited excellent microhardness. With an appropriate modulation period of 8 nm, the hardness reached a maximum around 40 GPa. The hardness enhancement is attributed to the large lattice mismatch and strengthening of superlattice structure, which is confirmed by XRD and transmission electron microscopy.
I. INTRODUCTION
Transition metal nitrides have been used for hard protective coating because of the excellent performance in hardness, wear, and corrosion resistance.1 In the nitride systems, chromium nitride (CrN) coatings with low friction coefficient, high microhardness, and high toughness have been extensively investigated and applied to improve the useful lifetime of tool steels and components.2–4 In the literature, many researchers doped a third element (such as Al, W, Zr, and. . .) in the binary CrN system for raising mechanical, thermal, and anticorrosion behavior.5–7 The ternary CrAlN coatings exhibit beneficial hardness and oxidation resistance.5 Recent studies also reveal that multilayer coatings composed of two kinds of transition nitride films show superior mechanical strength, such as hardness, adhesion, and wear resistance, as compared to a single layer nitride coating due to their specific interfaces.8–12 Some new material systems, including CrN/WN, CrN/NbN, TiN/ NbN, AlN/TiN, and CrN/AlN, exhibit evident enhancement of microhardness.10–15 Theoretically, the enhanced hardness could be interpreted by dislocation blocking between interfaces, due to the shear moduli difference, and by coherency strain from lattice mismatch of the two different nitride material systems.16 A previous work revealed that CrAlSiN coatings performed high hardness and good thermal stability.17 The a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2010.0296 J. Mater. Res., Vol. 25, No. 12, Dec 2010
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positive effect of doping Si in the nitride coating system was evidenced. To further improve the coating performance, another hard nitride coating, tungsten nitride (W2N) was introduced. In this work, CrAlSiN and W2N were chosen to fabricate the CrAlSiN/W2N multilayer coating. The mechanical strengthening of superlattice multilayer structure was expected. II. EXPERIMENTAL PROCEDURE
CrAlSiN, W2N single layer coatings and CrAlSiN/ W2N multilayer coatings were fabricated on the si
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