Hard and Multifunctional Nanostructured Coatings

Monday, April 29, 2013 10:00 AM in Room Royal Palm 1-3

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10:00 AM B5-1-1 Complexity in Characterization of Self Organized Structures in Nitride Nanocomposites
Naureen Ghafoor, Magnus Odén (Linköping University, Sweden)
The present research on transition metal nitrides is focused on introducing new multifunctional materials boosting functionality such as hardness, thermal stability and corrosion resistance of coatings used for metal cutting tools. One limiting factor in understanding the structural complexity of superhard self organized nano-composites is the detection limitations of available characterization techniques. For instance, the internal interfaces and the related hardness enhancement in nc-TiN/a-Si3N4 nano-composites are heavily debated topics in literature since their individual interfacial structure has yet not been possible to determine. Similarly, there is a gap in the understanding of the onset of isostructural decomposition at elevated temperatures and the subsequent phase evolution in metastable TiAlN coatings. A well controlled synthesis of model systems of varying composition and growth temperature is an appropriate approach to elucidate phase evolution, decomposition, and interfaces in related structures. This is illustrated in the present work for Zr1-xAlxN and Zr1-xSixN alloys as well as Zr1-xAlxN/ZrN and Zr1-xSixN/ZrN superlattices synthesized by reactive magnetron sputter deposition onto single-crystal MgO(001) and Al2O3(0001) substrates at 500-800°C. High temperature epitaxial growth allows for phase separation during growth and makes it possible to design the structure of the internal interfaces by controlling the composition. It is shown that the maximum hardness in Zr0.64Al0.36N or Zr0.8Si0.2N is associated with unique self-organized nanostructures that form at higher temperatures. With the combination of aberration corrected high resolution STEM imaging, EDX elemental mapping and X-ray pole figure measurements using high energy synchrotron radiation we characterize the structure, draw conclusions regarding its growth, and discuss the underlying processes causing the ordering. Furthermore, crystallographic relationships determined in multilayer structures are related to 3D nano-composites.
10:40 AM B5-1-3 High Speed Machining of Hardened Steel Using AIP Deposited Nano-multilayer Coating
Kenji Yamamoto (Kobe Steel Ltd., Japan); German Fox-Rabonovich (McMaster University, Canada); Ben Beake (Micro Materials Ltd., UK)
Recently a family of hard mono- and multilayer TiAlCrSiYN-based PVD coatings has been introduced for improving the cutting performance at extremely high cutting speed ranges. These coatings were developed for ultra high speed machining of hardened alloy steels. The multilayer coating was deposited by AIP method. It is alternating layer of TiCrAlSiYN and TiCrAlN with period of a few tens of nanometers. Cutting test was conducted using WC-Co ball nose end-mills against hardened die Steel (H13, HRC55) with cutting speed up to 800 m/min. Result of the cutting test indicated that tool life (as defined by 300um flank wear) of monolayer TiCrAlN is 50 m at cutting speed of 300m/min. Whereas it is increased up to 150m at 500m/min in case of TiCrAlSiYN monolayer coating. However, if multilayer structure is used tool life can be increased to 180m at 600m/min and 120m at cutting speed of 700m/min. TEM analysis of the worn surface of the endmill revealed that bending of the column structure is observed for the monolayer coating suggesting microstructure if destroyed by frictional force during the cutting process. Whereas no bending of the columnar structure was observed in case of the multilayer coating. Different analytical tests were conducted to identify the difference in cutting performance between mono- and multilayer coating. Hardness at room temperature indicate that there is no substantial difference between these three coating system. Then Micro-mechanical characteristics were investigated at elevated temperatures (up to 600 C) using a Micro Materials NanoTest System. Change in the hardness depending on the temperature indicates that hardness of two monolayer coatings decreased by approximately 30 % at 450 degree C. Whereas the hardness of multilayer coating was retained up to 500 degree and hardness decrease only started at 600 degree C. The high hot hardness combined with a crack-deflection ability due to the nano-multilayer structure is very beneficial in severe cutting conditions.This is considered as one of the major reasons (together with protective tribo-films formation on the friction surface) for improved wear resistance of the multilayer coating.
11:00 AM B5-1-4 Understanding the Structure of Metastable Multicomponent Nitride Thin Films by First Principles Calculations - Possibilities and Limitations
Björn Alling (Thin Film Physics Division, IFM, Linköping University, Sweden); Igor Abrikosov (Theoretical Physics Division, IFM, Linköping University, Sweden); Lars Hultman (Thin Film Physics Division, IFM, Linköping University, Sweden)

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 M1-xAlxN (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 M1-xAlxN materials such as Ti1-xAlxN, Zr1-xAlxN, Nb1-xAlxN,Y1-xAlxN, and Sc1-xAlxN. As an example, in the latter case a NaCl structure seed layer could promote growth of cubic Sc1-xAlxN 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)

11:20 AM B5-1-5 High Temperature Wear Resistance of TiCrAlCN/TiAlN Multilayer PVD Coatings on M2 High Speed Steel
Ihsan Efeoglu, Ebru Demirci (Atatürk University, Turkey); Ozlem Baran (Erzincan University, Turkey); Yasar Totik (Atatürk University, Turkey)

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.

Key Words: TiN-based coatings, alloy elements, CFUBMS, high temperature wear resistance, M2 steels.
11:40 AM B5-1-6 Wear Characteristics of Nitrogen-doped Al-Ti-Ni Nanocomposite Coatings Deposited on Austenitic Stainless Steel
Josephine Lawal, Martynas Audronis, Allan Matthews, Adrian Leyland (University of Sheffield, UK)

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.