ICMCTF2009 Session B6-1: Hard and Multifunctional Nano-Structured Coatings

Thursday, April 30, 2009 8:00 AM in Room Sunrise

Thursday Morning

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8:00 AM B6-1-1 Processes, Properties and Application Potential of Ti-Al-X-N and Cr-Al-X-N Thin Films
P.H. Mayrhofer (Montanuniversität Leoben, Austria)

Thin films based on transition metal aluminum nitrides, like Ti-Al-N and Cr-Al-N, are increasingly important for industrial applications due to their outstanding chemical and physical properties including high hardness, toughness and thermal stability. Prepared by low-temperature (substrate temperatures below 500°C) plasma-assisted vapor deposition techniques, such materials possess metastable phases as the atomic assembly kinetics are limited. These metastable phases in addition to the coating’s structure are often the key-components for the high-performance during testing and application. The structure and the phases formed strongly depend on the characteristics of the deposition process like substrate temperature, gas pressure, ionicity of the film forming species and ion bombardment. Consequently, this review deals with the influence of process parameters on the structure and metastable phases of Ti-Al-N and Cr-Al-N thin films and their properties. This is obtained by a variety of analyzing techniques including Langmuir measurements, x-ray diffraction, nanoindentation, high-resolution transmission electron microscopy, differential scanning calorimetry, tribological investigations and machining tests.

A further modification in properties of these ternary nitrides can be obtained by controlled alloying with specific elements to develop tailor-made coatings combining unique properties. In this review, the influence of the alloying elements (X) like B, V, Y, Nb, Hf, and Ta on the phase formation, structure, mechanical and thermal properties (including age-hardenability) of Ti-Al-N and Cr-Al-N is investigated in detail combining experimental and computational studies. Understanding the synthesis-structure-property relations in such ‘model-systems’ is indispensable to support the massive and collective move in coating industry towards the use of quarternary and multinary nitrides to be followed by carbides, borides, oxides, and oxy-nitrides.

8:40 AM B6-1-3 Thermal Decomposition of Arc Evaporated ZrAlN Thin Films
L. Rogström, L.J.S. Johnson (Linköping University, Sweden); M. Johansson (SECO Tools AB, Sweden); T. Myrtveit (Sandvik Tooling AB, Sweden); L. Hultman, M. Odén (Linköping University, Sweden)
Age hardening in thin films has previously been seen for the TiAlN system where the solid solution fcc-TiAlN decomposes into fcc-TiN and hcp-AlN at elevated temperatures. The ZrAlN system is less studied but since ZrN and AlN are immiscible a phase separation can be expected. We have in this study analyzed the decomposition of ZrAlN thin films. Zr1-xAlxN thin films were deposited onto WC-Co substrates using an industrial arc evaporation system. Samples with an Al content of 00.35 in the as deposited films. After deposition the samples were annealed at temperatures between 700 and 1100°C in two hours respectively in an Ar atmosphere. The hardness of the as deposited and post annealed films was measured using nanoindentation. The hardness for the as deposited films changes with the Al content. A small amount of Al in the films lowers the hardness while a high Al content increases the hardness compared to ZrN. For the post annealed films the hardness is seen to increase with annealing temperature for high Al contents. X-ray diffractograms of the post annealed high Al content films show phase separation into fcc-ZrN and hcp-AlN.
9:00 AM B6-1-4 Growth, Annealing Behaviour and Cutting Performance of (Ti,Si)(C,N) Coatings
L.J.S. Johnson, L. Rogström (Linköping University, Sweden); M. Johansson (SECO Tools AB, Sweden); M. Collin (Sandvik Tooling AB, Sweden); J. Sjölén (SECO Tools AB, Sweden); M. Odén, L. Hultman (Linköping University, Sweden)
(Ti1-xSix)(CyN1-y) thin films have been deposited by reactive cathodic arc evaporation to investigate the influence of the addition of carbon to the widely studied Ti-Si-N system. Structure characterization by x-ray diffraction (XRD) revealed a single NaCl phase with a lattice parameter close to that of TiCN and composition analysis by elastic recoil detection analysis (ERDA) and energy dispersive x-ray spectroscopy (EDS) showed that Si ratios from x = 0 to x = 0.13 and C ratios from y = 0 to y = 0.27 were obtained. Microstructural characterization by transmission electron microscopy (TEM) revealed two distinct microstructures; one dense columnar with large grains (width of around 100-500 nm) for low Si contents, the other a fine “feathered” columnar structure for Si rich films. The hardness, as measured by nanoindentation, is influenced by both the silicon and the carbon content. After annealing at 700, 800, 900, 1000 and 1100°C for two hours each the resulting structure, composition, stress state and microstructure were investigated. No phase transformation was detected by XRD, but a significant reduction in silicon content was detected in the films at temperatures at 1000°C and above. This effect was exacerbated by the addition of carbon. Age hardening of the films was observed which increased in magnitude with carbon content, the nature of which was studied by analytical TEM. A series of cutting tests were performed with as-deposited coatings by longitudinal turning, in which the coatings with a silicon fraction x = 0.07 performed best. The worn coatings have also been characterized by analytical TEM.
9:20 AM B6-1-5 Microstructure, Mechanical and Tribological Properties of Cr-C-N Coatings Deposited by Pulsed Closed Field Unbalanced Magnetron Sputtering
Z.L. Wu (Colorado School of Mines, and Dalian University of Technology, China); J. Lin, J.J. Moore (Colorado School of Mines); M.K. Lei (Dalian University of Technology, China)
Nanocrystalline Cr-C-N coatings were deposited by pulsed closed field unbalanced magnetron sputtering (P-CFUBMS). The microstructure, composition and elemental chemical state of the coatings were investigated using transmission electron microscopy (TEM), glancing incident angle x-ray diffraction (GIXRD) and x-ray photoelectron spectroscopy (XPS). Mechanical and tribological properties of the coatings were measured by nanoindentation, Rockwell C, and ball-on-disk wear tests. The Cr-C-N coatings consist of nanocrystalline Cr7C3, Cr2N compounds embedded in an amorphous carbon and CN matrix. An increase in the hardness and a decrease in the elastic modulus of Cr-C-N coatings were identified when the N content was increased, thereby achieving a high H/E ratio of 0.098 at a N content of 24.9 at.%. The steady state dry coefficient of friction values for Cr-C-N coatings sliding against a WC-Co ball were found in the range of 0.38-0.56. The wear rates of the coatings are in the low range of 1.28-3.44×10-6mm3N-1m-1. The paper will discuss the correlation between pulsing regime, microstructure and properties of the coatings.
9:40 AM B6-1-6 Comparative Investigation of TiAlC(N), TiCrAlC(N), and CrAlC(N) Coatings Deposited by Sputtering of МАХ-Phase Ti2-хCrхAlC Targets
D.V. Shtansky, Ph.V. Kiryukhantsev-Korneev, A.N. Sheveyko, D.I. Sorokin (State Technological University “Moscow Institute of Steel and Alloys", Russia); B.N. Mavrin (Institute of Spectroscopy of RAS, Russia); C. Rojas, A. Fernandez (Instituto de Ciencia de Materiales de Sevilla, Spain); E.A. Levashov (State Technological University “Moscow Institute of Steel and Alloys”, Russia)
Previous work has demonstrated that various multicomponent nanostructured films with enhanced chemical, mechanical, and tribological properties can be deposited by sputtering of composite targets produced by self-propagating high-temperature synthesis (SHS). SHS allows fabricating ceramic targets with required chemical composition, toughness, and resistance to thermal-cycling, i.e. various properties needed for PVD targets. It is well known that MAX phases Mn+1AXn (n=1-3) are easily machinable, resistant to thermal shock, high temperature oxidation, and thermally and electrically conductive. This combination of properties makes them perspective materials as targets for deposition of hard tribological TiAlC(N), TiCrAlC(N), and CrAlC(N) coatings resistant to corrosion and high-temperature oxidation. The objective of the present study is a comparative investigation of the structure and properties of TiAlC(N), TiCrAlC(N), and CrAlC(N) coatings deposited in an Ar atmosphere or in a gaseous mixture of Ar+N2 by sputtering of SHS targets based on the МАХ-phases in the system Ti2-хCrхAlC (where x=0, 0.5, 1.5, and 2). The coatings were characterized in terms of their structure, elemental and phase composition, adhesion, hardness, elastic modulus, elastic recovery, thermal stability, friction, wear-, corrosion and high-temperature oxidation resistance. The structure of the coatings was studied by means of X-ray diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, glow discharge optical emission spectroscopy, and Raman spectroscopy. To evaluate the thermal stability and oxidation resistance, the coatings were annealed either in vacuum or in air in the temperature range 600-1000°C. The results obtained show that the Cr-doped coatings obtained under thoroughly controlled deposition parameters possess high hardness up to 35 GPa, improved oxidation resistance up to 1000°C, thermal stability up to 800°C, and good corrosion resistance. With increased chromium content the (Ti,Cr)-Al-C-N coatings demonstrated improved adhesion strength and oxidation resistance, whereas their friction coefficient against WC+Co counterpart increased from 0.3 to 0.5 and the hardness decreased down to 25 GPa.
10:00 AM B6-1-7 The Effect of Magnetron Pulsing on the Structure and Properties of Nanostructured Multifunctional Tribological Coatings
J.J. Moore, J. Lin, B. Mishra (Colorado School of Mines); W.D. Sproul (Reactive Sputtering, Inc.); J.A. Rees (Hiden Analytical, LTd., United Kingdom)

The paper will discuss the effect of pulsing unbalanced magnetrons used in three systems: (i) single magnetrons, (ii) in a closed field configuration, and (iii) in a high energy pulsing (Modulated Pulsed Power) system on the structure and properties of tribological coatings. In particular, the effect of pulsing regime (e.g, frequency, duty cycle, etc) on the plasma species and ion energy distributions (IED) will be discussed and correlated with the microstructure and tribological properties of the thin films and coatings for Cr, Al, Ti, graphite and composite TiC-TiB2 targets.

The main objective of this research is to determine the pulsing regimes that produce optimized coatings for specific applications, such as aluminum pressure die casting, and glass molding operations. In this respect the optimization of graded, multi-layer Cr-Al-N, and nanocomposite Ti-C-B-N and Ti-C coatings will be used as the main examples.

The application of Modulated Pulsed Power (MPP) deposition (an alternative to HIPIMS/HPPMS) will be discussed using some recent results.

10:40 AM B6-1-10 Thermally Enhanced Mechanically Properties of Arc Evaporated TiN/TiAlN Multialyer Thin Films
A. Knutsson (Linköping University, Sweden); M. Johansson (SECO Tools AB, Sweden); M. Odén (Linköping University, Sweden)

The cubic phase Ti1-xAlxN has been used to coat cutting tools since the late 1980’s. It has been shown that the excellent tool performance is closely related to age hardening of c-Ti1-xAlxN where it decompose to c-TiN and c-AlN at elevated temperature. In this work the possibility to control the decomposition temperature of Ti1-xAlxN with help of multilayers is investigated. Cubic metastable Ti0.34Al0.66N / TiN 3µm thick multilayers were grown by reactive arc evaporation using Ti0.33-Al0.67 and Ti cathodes in a N2 atmosphere.

The difference in decomposition between multilayers with different layer thickness (TiN/TiAlN: 50/25, 25/12 and 10/5 nm) and single layer Ti0.34Al0.66N was investigated using differential scanning calorimetry (DSC) up to 1400°C. The results revealed that the phase transformations in the multilayers are initiated at higher temperatures with decre ased Ti0.34Al0.66N thickness, suggesting a higher thermal stability compared to single layers.

The hardness increased with decreased layer period which is to be expected from Koehler and similar multilayer effects. Despite the 75 vol% TiN in the as deposited 15/5 nm multilayer a slightly higher hardness was observed compared to single layer Ti0.34Al0.66N. In addition, the multilayers exhibit a more significant age hardening effect than the single layer when annealed to 900°C, with a hardness increase of ~45 %. The hardening phenomena are discussed in terms of particle constraints from neighboring TiN-layers.

11:00 AM B6-1-11 Characterization of the Adhesion and Tribology of Ti/TiAlN Multilayer PVD Coatings Deposited on Pre-Nitrided Tool Steels
W. Tillmann, E. Vogli, S. Momeni (Dortmund University of Technology, Germany)
Employing multilayer PVD coating including ceramic and metallic inter-layers can enhance wear resistance and fracture toughness of coating systems. It is also known that the performance of the PVD coating can be enhanced by increasing hardness of the substrate. In this research work, different alloy steels were hardened using plasma nitriding process in the Arc-PVD device. The nitrided zones on steels were studied by means of XRD analysis. Afterwards, on both unnitrided and plasma nitrided substrates, different Ti/TiAlN multilayer coatings were deposited by a magnetron sputtering device. Scratch tests were performed on the duplex systems in order to characterize their adhesive properties. The failure modes of individual coating systems under various normal loads were described using light microscope, scanning electron microscope and EDX analysis. Furthermore, to study the effect of plasma nitriding on the friction coefficient and wear rate of the systems, pin-on-disc tests were carried out.
11:20 AM B6-1-12 Characteristics of Cr2N/Cu Multilayered Thin Films with Different Bilayer Thickness
C.-L. Li, J.-W. Lee (Tungnan University, Taiwan); L.-C. Chang (Mingchi University of Technology, Taiwan)
Nanostructured Cr2N/Cu multilayer coatings were deposited periodically by a bipolar asymmetric pulsed DC reactive magnetron sputtering technique. The structures of multilayer coatings were characterized by an X-ray diffractometer. The surface and cross sectional morphologies of thin films were examined by a scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. The surface roughness of thin films was explored by an atomic force microscopy (AFM). The nanohardness and elastic modulus of multilayer coatings were investigated by means of a nanoindenter. The scratch and wear testers were used to evaluate the tribological properties of thin films. The electrochemical tests in 3.5 wt. % NaCl aqueous solution were performed to evaluate the corrosion resistance of multilayered coatings with different bilayer thickness. It is observed that coatings with bilayer thickness ranges from 5 nm to 40 nm were produced in this work. The surface roughness of the multilayered coating decreased with increasing bilayer thickness. An optimal hardness and corrosion resistance were found on the coating with a critical bilayer thickness of 10 nm.
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