ICMCTF2013 Session B5-1: Hard and Multifunctional Nanostructured Coatings

Holleck proposed that the structure of as-deposited metastable thin films of ternary nitrides could be predicted from analysis of the energetics of solid solutions. As the growth process could prevent phase separation due to limited diffusion, the most likely resulting structure was that of the disordered solid solutions having the lowest free energy.[1] The mixing enthalpies, as a first step to the free energies, of several M_1-xAl_xN (M=transition metal) was later calculated from first-principles and used to predict, analyze, and validate experimental results, see, e.g., [2-6]. However, several other aspects of the out-of-equilibrium synthesis conditions, like the structure of the substrate, the growth temperature, the nitrogen pressure, and the bias voltage are of importance and predictions based on energetic arguments should be made with caution. In this work we review theoretical calculations and compare them with experimental results for several technologically important M_1-xAl_xN materials such as Ti_1-xAl_xN, Zr_1-xAl_xN, Nb_1-xAl_xN,Y_1-xAl_xN, and Sc_1-xAl_xN. As an example, in the latter case a NaCl structure seed layer could promote growth of cubic Sc_1-xAl_xN film with Al content as high as x=0.5-0.6 [2], while calculations show that the hexagonal wurtzite structure has a lower enthalpy for x>0.4 [3]. Based on the result for those different systems we discuss the possibilities and limitations for understanding metastable phase formation in thin films using first principles calculations.

[1] H. Holleck, Surface and Coatings Technology 36, 151 (1988)

[2] C. Höglund, et al. Journal of Applied Physics, 105, 113517 (2009)

[3] C. Höglund, et al. Journal of Applied Physics 107, 123515 (2010)

[4] D. Holec, et al. Journal of Physics D: Applied Physics 43, 145403 (2010)

[5] D. Holec, et al. Surface and Coatings Technology 206, 1698 (2011)

[6] A. Zukauskaite et al. Journal of Physics D: Applied Physics. 45, in proof, (2012)

The mechanical and tribological properties of TiN-based coatings can be improved with the addition of different alloy elements such as B, Cr, Al, C, Si, etc.. For this purpose, in this study, TiN co-sputtered with Cr, Al and C were deposited on M2 steel substrates and silicon wafers by Closed-Field Unbalanced Magnetron Sputtering (CFUBMS) and TiCrAlCN/TiAlN multilayer films were obtained. The structural and properties of TiCrAlCN/TiAlN multilayer films were analyzed by using XRD and SEM. The hardness properties of films were investigated by microhardness tester. The high temperature wearproperties of TiCrAlCN/TiAlN multilayer coatings were determined by using a high temperature pin-on-disc tribometer. The effect of deposition parameters and Ti, Cr, Al, C and N content on crystallographic orientation and friction coefficient and wear rate at the high temperature was examined.

Non-ferritic engineering alloys (e.g. austenitic stainless steels, nickel alloys and alloys of Titanium, Aluminium, Magnesium) are increasingly used for engineering components, owing to combinations of desirable functional properties such as high specific strength, toughness, corrosion resistance and durability in extreme environments. However, it is well known that such alloys tend to exhibit poor tribological properties – especially under conditions of sliding wear and/or abrasion

Nanostructured coatings comprising a hard nanocrystalline phase embedded in an amorphous matrix have been found to exhibit improved tribological properties in various conditions. This study investigates the wear characteristics of nitrogen-doped Al-Ti-Ni nanocomposite coatings prepared by magnetron sputtering. The sliding and abrasive wear behaviour of the coating-substrate system were studied using a reciprocating ball-on-flat test and an abrasive wear test respectively in dry and lubricated conditions in different environments. SEM, with EDS and XRD were conducted to check the composition and measure the thickness of the coatings. Hardnesses and elastic modulii were also determined. The addition of nitrogen enhanced the formation of a hard phase in the amorphous matrix which had a significant influence on the wear behaviour of the substrate. This work provides a comprehensive report of the wear rates in different environments in both dry and lubricated conditions.