ICMCTF2000 Session B3: Structure and Properties of Hard Coatings

Thursday, April 13, 2000 8:30 AM in Room Golden West

Thursday Morning

Start	Invited?	Item
8:30 AM	Invited	B3-1 Microstructure and Property Relationships for Hard Nanocomposite Ceramic Coatings C. Mitterer (University of Leoben, Austria); J. Musil (University of West Bohemia, Czech Republic); F. Hofer (Technical University of Graz, Austria) Recently, nanostructured and nanocomposite coatings have emerged as technologically important materials for a wide range of applications. Morphologies within the nanometre scale enable to develop materials with unusual properties which are attributed to the large internal surface area and, in the case of nanocomposites, to new strengthening mechanisms where the mechanical properties are determined by grain boundary hardening if grain boundary sliding could be avoided. During the last few years, different nanocomposite ceramic coatings have been developed with tailored properties like superhardness, toughness, friction and wear behavior and corrosion resistance. The aim of this paper is to review the results obtained in the authors laboratories on nanocrystalline and nanocomposite coatings deposited by magnetron sputtering and plasma-assisted chemical vapor deposition. Coating materials where selected with respect to optimization of hardness and toughness and include TiN-TiB₂, TiN-TiB₂-BN, TiC-TiB₂, Ti-Si-N, Ti-Al-N, W-Ti-N, ZrN-ZrB₂-BN, ZrN-Cu, ZrN-Y, CrN-Ni, Y-B and LaB₆-Zr. Coating structure was investigated using combined X-ray diffraction and energy-filtering transmission electron microscopy. Mechanical and high-temperature properties were characterized using depth-sensing Vickers microhardness measurements, thermogravimetric analysis, differential scanning calorimetry and stress measurements during thermal cycling. The main interrelationships between microstructure and properties of these coatings are presented and discussed.
9:10 AM		B3-3 Parameter Optimisation of TiN/NbN Multilayer Coatings Using Statistically Based Methods R.P. Villiger, J.A. Peters (Sulzer Innotec Ltd., Switzerland); W. Kautek, M. Handrea (Federal Institute for Materials Research and Testing, Germany) Compositional multilayer coatings were produced in a closed-loop unbalanced magnetron sputtering system. The process parameters varied included: substrate bias (-50 to -150V), nitrogen gas pressure using optical emission monitoring (OEM) and substrate rotation frequency. The influence of these parameters was analysed using two-level factorial experimental design. The TiN/NbN coatings were investigated with respect to nanolayer thickness, coating morphology and microstructure, bond strength, microhardness as well as Young ,s modulus. More detailed microstructural characterisation was performed using glow-discharge optical emission spectroscopy (GDOS), x-ray photon spectroscopy (XPS) and transmission electron microscopy (TEM) in order to better understand the nature of the nanolayer interfaces and substructure. The results indicate that the bias voltage not only influenced all mechanical properties significantly, but also affected the oxidation kinetics in the uppermost nanolayers. As the OEM and bias voltage decreased, the oxygen content increased probably due to the combined influence of an open substoichiometric columnar morphology and reduced sputter cleaning. A nano-indentation hardness of 54 GPa was achieved in the coating with a nanolayer wavelength of about 9 nm. By decreasing the substrate rotation frequency which increased the nanolayer wavelength, the hardness decreased asymptotically to common values for TiN coatings (30 GPa). The relatively high bond strengths of the nanolayer coatings were attributed to the blunting and branching of micro-cracks which finally resulted in the spallation of micro-platelets. A good correlation was exhibited between the abruptness of the interface, pronounced at high bias levels, and the coating hardness. This is an important result as it indicated that the interface played an important role in the deformation mechanisms. TEM investigations are currently being performed to understand this phenomenon.
9:30 AM		B3-4 Sputter Deposited Nanocrystalline Cr and CrN Coatings on Steels for Wear Resistance Applications J. Seok, R.Y. Lin (University of Cincinnati) Chromium and chromium nitride coatings on steel have been deposited with a magnetron sputter deposition system. The deposition power was 200 W pulsed DC with a frequency of 185 kHz and 96% deposition duty. During deposition, the system was maintained at a pressure of 10 mTorr (1.333 Pa). The target and substrate are both 7.6cm in diameter with a 8.4 cm target-to-substrate distance. The substrate temperature was maintained at 200° C. The sputtering gas was argon mixing with 0, 3, 5 and 7% nitrogen. It was found that the deposition rate was 1.1 µmm/h and was not affected by the nitrogen content in the sputtering gas. Using X-ray diffraction analysis, it was observed that the as-deposited Cr under a pure argon condition was nanocrystalline bcc chromium with particle sizes being in the range of 40 nm. With increasing nitrogen content in the sputtering gas, the amount of CrN increased. It was also found that the microhardness of the Cr coated steel increase with increasing nitrogen content. With only less than 2 µmm Cr coating, the steel hardness increases from 126 to 198 kgf/mm² when the nitrogen content in the gas is 7%. The microhardness of Cr coated steel prepared with sputter deposition is similar to that prepared with electroplating. The coating hardness calculated from these data is 1000 kgf/mm² . Results from the scratch test of coated steels show that the sputter deposited Cr coatings indeed increase the scratch resistance of steels significantly.
9:50 AM		B3-5 Characterization of Cu-containing and Cu-free Molybdenum Nitride Hard Coatings J. Hershberger, A. Erdemir (Argonne National Laboratory); M. Urgen, M.K. KazmanliI (Istanbul Technical University, Turkey) Hard coatings of molybdenum nitride have been prepared using the arc-PVD technique. It has been found¹ that the addition of ~3at% Cu increases the hardness from 3800 HV to 6700 HV. This work has investigated the differences in morphology, structure, and stress between Cu-containing and Cu-free films ~1.6 micrometers thick deposited on substrates of Si and steel. The structure was investigated using TEM diffraction and CBED as well as XRD; the distribution of Cu was found using EDAX in an SEM. Surface and fracture cross section morphology were inspected using SEM while a laser-based substrate curvature method was used to determine stress. Results show the presence of a layer of strained small-grain-size cubic gamma-Mo₂N at the surface of the coating and a larger grain size beneath the surface. ¹¹M. Urgen et al., submitted to this conference
10:30 AM		B3-7 Mechanical Behavior of (Ti,Al)N-coatings Exposed to Elevated Temperatures and Oxidative Environments E. Schaeffer, G. Kleer (Fraunhofer-Institut fuer Werkstoffmechanik, Germany) (Ti,Al)N-coatings were deposited in different plasma and ion beam assisted deposition processes. The thermally induced and the intrinsic stresses were varied by variation of the deposition parameters, e.g. substrate temperature during deposition, gas pressure and ion energies. By in-situ measurements of the residual stresses during controlled heating up of specimens in inert gas atmosphere characteristics of the total residual stresses and variations of the intrinsic stresses due to changes in the films could be investigated. Residual stresses were also analyzed after exposing specimens to air at temperatures up to 800°C in order to study the influence of oxidation on the film stresses. For the characterization of stability and mechanical behavior scratch tests were performed on differently treated specimens. The results obtained in the experiments are described and the dependence of residual stresses and mechanical behavior on the deposition and the thermal treatment conditions, as well as influences of different layer zones formed during high temperature exposure will be discussed.
10:50 AM		B3-8 Mechnical and Adhesion Properties of Al/AlN Multilayered Thin Films J.H. Lee, W.M. Kim, K.B. Song, T.S. Lee, M.K. Chung, B. Cheong, S.G. Kim (Korea Institute of Science and Technology, Republic of Korea) An investigation was conducted on the mechanical properties of compositionally modulated Al/AlN thin films due to r.f. magnetron sputter deposition on Si(100) substrates. The films were made to have modulation periods ranging from 200 to 40 nm. The volume fraction of Al was varied from 0.125 to 0.625 for films with the minimum modulation period of 40 nm, but it was set to have 0.5 otherwise. Hardness and adhesion of the deposited films were examined by nanoindentation and scratch test method, respectively. Residual stress of single layer Al and AlN films of various thickness was also measured by a conventional beam-bending technique. As compared with a monolithic AlN film, films of various modulation periods with the Al volume fraction of 0.5 were found to have lower hardness and elastic moduli. On the other hand, high hardness and elastic moduli, comparable to and 13 per cent higher than those of AlN films respectively, were registered for films that have the modulation period of 40 nm and the Al volume fraction 0.125 and 0.25 as well. All the modulated films were found to have the critical loads almost twice as high as that of a single AlN film, except the one with the lowest Al volume fraction. From the scratch pattern test, a cohesive failure was observed for films with alternating layers in residual stress state of opposite signs whereas an adhesive failure was noticed otherwise. These observations indicate that a load carrying capacity of a modulated film depends not only on modulation period and individual layer thickness but on the residual stress states of alternating layers in modulation.
11:10 AM		B3-9 Morphology, Mechanical Properties, and Oxidation Behaviors of Reactively Sputtered Cr-N Films J.G. Duh, R.J. Tu (National Tsing Hua University, Taiwan) Cr-N films with various compositions and structures are deposited by reactive sputtering on A2 tool steel. Phase identification indicates that films with lower nitrogen contents exhibit Cr and Cr₂N phases, while the CrN phase is observed in films with nitrogen contents higher than 58 at.%. The morphology, surface roughness and grain size of the deposited films are evaluated with the aid of AFM. The microhardness of the deposited film ranges from 1500 to 1800HK at a load of 3gf with a Knoop indenter. The critical loads of films are determined by the detected acoustic emission signal in a Revetest. Both adhesive and cohesive failures are observed in films with poorer adhesion. However, in films with good adhesion, only localized failures are detected. For the oxidation test, Cr₂O₃ are formed on top of films. The phase analysis of the oxidized samples indicates that the pre-existed Cr and Cr₂N phases in the deposited films are transformed to CrN due to the incorporation of nitrogen released by the oxidation layers. It is observed that the oxidation resistance of films with CrN phase is better than that with Cr or Cr₂N phases.
11:30 AM		B3-10 Role of Thickness and Deposition Technique in the Corrosion Resistance of Chromium Nitride Coatings R.E. Hawbaker, N.E. Barr, C.Q. Dam (Caterpillar Inc.) For thin coatings, such as those deposited by PVD methods, thickness can have a significant influence on corrosion resistance. In addition, the specific deposition method, such as sputtering or arc evaporation, may influence corrosion behavior of the coatings. In this study, steel coupons were coated with different thicknesses of chromium nitride (1-9 µm) by both sputtering and arc evaporation. Electrochemical corrosion, salt spray exposure, and immersion techniques were utilized to quantify the corrosion resistance of the coated substrates. Coating properties such as hardness, adhesion, and morphology were also evaluated as functions of coating thickness and deposition method. Coating defects were characterized and related to the corrosion behavior. The results are discussed in terms of the need to balance corrosion resistance, other performance requirements, and cost.
11:50 AM		B3-11 Magnetron-sputter Deposition of Metastable Thin Films in the Ternary System Chromium-Aluminium-Nitrogen S. Ulrich, R. Loos, M. Stüber, H. Leiste, C. Kunisch, H. Holleck (Forschungszentrum Karlsruhe, Germany) Ternary chromium aluminium nitride thin films are deposited by magnetron sputtering of a chromium aluminium nitride target in a nitrogen and an argon discharge, respectively. The chemical composition of the films is measured by electron microprobe analysis. The metastable, nanocrystalline structure of the films is shown experimentally by X-ray diffraction, electron diffraction, and high resolution transmision electron microscopy in agreement with thermodynamic cosiderations. The developement of metastable nanocrystalline ternary chromium aluminum nitride thin films can lead to improved chromium nitride antiwear coatings with tailored properties characterized for example by a particular toughness and a high hardness. Furthermore, the dependence of the mechanical properties such as hardness and compresive stress on ion bombardment during film growth is described by the subplantation model.