ICMCTF1998 Session E2-2: Wear Resistance of Ceramic, Metallic and Composite Coatings (2)

Tuesday, April 28, 1998 1:30 PM in Room California

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		E2-2-1 Fracture Toughness Testing and Toughening Mechanisims of Some Commercial Cobalt-free Hardfacing Alloys B.V. Cockeram (Westinghouse-Bettis Atomic Power Laboratory) Hardfacing alloys are weld deposited to provide a wear resistant surface for structural base materials. Commercial low cobalt hardfacing alloys are being evaluated to reduce plant activation levels ¹. Since hardfacing alloys typically must be resistant to cracking to assure adequate in service performance, fracture toughness is a critical material property. Fracture toughness (K_IC) measurements of Fe-base, Ni-base, and Co-base hardfacings were performed in accordance with ASTM E399-90 procedure in an effort to identify a tough cobalt-free alternative. Reduced scatter in K_IC data was observed for the Fe-base hardfacings, and average K_IC values for Fe-base hardfacings were generally higher than the Ni-base hardfacing alloys. Preliminary crack growth data indicate that the Ni-base hardfacings possess better fatigue crack growth resistance. However, none of the Fe-base or Ni-base hardfacings have K_IC values that are comparable to the reference Co-base hardfacing. The test specimens were machined from thick (0.5") weld deposits, and the microstructures of the test specimens are compared with the more prototypic, thinnner deposits. Microstructure examinations are used to characterize the alloys and delineate the toughening mechanisms. Crack deflection and crack bridging toughening mechanisms are shown to be relevant for most of the commercial hardfacings. ¹B.V. Cockeram, R.F. Buck, and W.L. Wilso, Proc. of ICMCTF'97, 1997, to be published in Surf. Coat. Tech.
2:10 PM		E2-2-3 Wear-Resistant Monolithic and Multi-layered Cr/Cr₂N/CrN Based Films for Temperature Sensitive Substrates M.L. Kuruppu, D.M. Mihut (University of Nebraska); G. Negrea (Cluj-Napoca University, Romania); S.R. Kirkpatrick, B. Raehle (University of Nebraska); C. Rebholz, A. Matthews (University of Hull, United Kingdom); S.L. Rohde (University of Nebraska) Utilizing high-flux, low-energy ion enhanced growth conditions produced by unbalanced magnetron sputtering, monolithic and multi-layer Cr-N based film structures can be formed at substrate temperatures below 150°C, thus opening new avenues for dev elopment of wear-resistant thin films on low temperature alloy materials, such as Al-alloy, heat-treated stainless steels, etc... However, many such temperature sensitive substrates are also more compliant, and to address this tailored multi-layer structures were developed to provide built-in "load support" for the upper coating layers, while more closely matching the modulus of underlying substrates. To examine the advantages and disadvantages of various coating architectures and interface types on the mechanical properties and sliding wear performance of tailored coating/substrate systems monolithic Cr-based and multi-layered Cr/Cr₂N, Cr/CrN, and Cr₂N/CrN thin films were deposited on substrates of A2 steel, 52100 steel, and 2024-Al using controlled low-energy ion bombardment. The coating/substrate couples were analyzed by X-ray diffraction, RBS, AES, microhardness, scratch adhesion, Rockwell "C"indentation, and pin-on-disk testing. Microhardness varied from 900 to over 3000 H_K, but high hardness strongly correlated with poor adhesion. The results of pin-on-disk tests are compared for various substrates and coating architectures. The Cr-N based multi-layer films performed nearly as well on 2024-Al as on A2 steel; some running more than 48 hrs against a WC counter face with no measurable coating wear.
2:30 PM		E2-2-4 Fabrication, Characterization, and Testing of Hybrid Bearings Containing TiC-coated Balls M.R. Hilton, W. Park, N. Presser, G. Radhakrishnan (The Aerospace Corporation); P.C. Ward (MPB Corp.) In order to confidently design bearings for high-stress, high-cycle applications, one must obtain endurance statistics using full-scale bearing tests. Limited data has been reported to date for hybrid bearings consisting to TiC-coated balls with steel raceways. In this paper, we report on the fabrication of bearings made of M62 steel raceways with TiC-coated balls of the same steel, including aspects of heat treatment processing to maintain adequate sphericity of the balls. Post-test characterization of components from preliminary bearing tests will be reported, including plain-view and cross-sectional microscopy and profilometry. Materials damage developed during extended rolling contact will be described.
2:50 PM		E2-2-5 Microstructural Changes in DLC Films Due to Tribological Contact J. Koskinen, H. Ronkainen, K.G. Holmberg (VTT Manufacturing Technology, Finland); H.J. Scheibe, D. Schneider, P. Burck, H. Ziegele (Fraunhofer-Institut, Germany) Diamond-like carbon (DLC) films have been successfully applied as wear resistant coatings in a growing number of applications. In the literature several reports on the tribological performance on the films can be found, but the microstructural characterisation of the DLC-film subjected to repeated tribological contact has not been reported yet. In this paper hydrogenated (a-C:H) and hydrogen free (a-C) films have been subjected to sliding contact in the reciprocating wear tests. The tests have been carried out both in air (22 °C, 50% RH) and at elevated temperatures (100 - 200 °C). In the latter case the coefficient of friction was greater than about 0.2 which is a typical value in air. The wear volume of the DLC films was sufficiently low to enable the direct comparison of the film properties of the worn film to the original film. The microstructure of the films after wear tests has been characterised by nano indentation, micro RAMAN and elastic modulus measurements. The changes in the microstructure and mechanical properties of the films as a function of the tribological properties has been investigated and the role of the degradation mechanisms of the DLC films are discussed.
3:30 PM		E2-2-7 Characterization of Multilayered Ti/TiB₂ Coatings on Cemented Carbides M. Berger, M. Larsson, S. Hogmark (Uppsala University, Sweden) PVD titaniumdiboride and titaniumnitride multilayered coatings were deposited on cemented carbide using DC magnetron sputtering and e-gun evaporation respectively. The coatings were evaluated, with respect to their morphology (SEM), microstructure (SEM), phase composition (XRD), residual stress (beam deflection and XRD). Coating cohesion/adhesion and abrasive wear resistance was studied using scratch testing and the dimple grinder test. Singlelayered PVD TiN and TiB₂ were used as reference coatings througout the test. We have characterized the coatings as a function of the lamella thickness, substrate bias and the power of the DC magnetron. The investigation showed that the coatings were dense and well adhering and had a high hardness and abrasive wear resistance. Detailed results will be presented.
3:50 PM		E2-2-8 Some Effects of Ion Beam Treatments on Titanium Nitride Coatings of Commercial Quality R.R. Manory (Royal Melbourne Institute of Technology, Australia); A.J. Perry (A.I.M.S. Marketing); R. Nowak (Hiroshima University, Japan); D. Rafaja (Charles University, Czech Republic) The present work presents the effects of ion implantation into several types of TiN coatings used in the cutting tools industry: The films are monolithic TiN coatings, deposited onto cemented carbide by chemical vapor deposition or on steel by physical vapor deposition and implanted with gas or metal ions at different implantation regimes. The results considered together confirm that large changes in the residual stress and strain distributions are introduced into the implanted zone (IZ) and extend well beyond forming an implantation affected zone (IAZ) which extends to a depth of several microns. Some effects observed on the PVD deposited coatings differ from those observed for the CVD type coatings. Amorphization was noticed in the former, but not in the latter. Metallic ions implants appear to increase the IZ hardness, whereas light ions induce softening or amorphization. The residual stress in the IZ is high, tensile or compressive depending on whether vacancy generation and atom peening effects dominate and is accompanied by concomitant high, irregular, distributions of strain caused by a high dislocation density and/or grain comminution and include high fractions of lattice vacancies. The forward momentum of the ions introduces a dense dislocation network and high residual stress in the IAZ corresponding to the so-called long range effect. The dislocation density increases and the residual stress becomes more compressive with increasing ion momentum. Tribological data shows a marked improvement in wear after ion beam treatment with nitrogen at an energy of around 90keV, with an apparent threshold below a dose of 6x10¹⁷ions/cm² The correlation between the tribological data, microhardness and the observed structural changes in the IZ and IAZ zones will be presented and discussed.
4:10 PM		E2-2-9 Wear Behavior of High Energy Plasma Sprayed Nanoscale WC-Co Coatings M. Scholl (Oregon Graduate Institute of Science & Technology); M. Becker (Oregon Graduate Institute of Science and Technology); D. Atteridge (Oregon Graduate Institute of Science & Technology) The authors have previously demonstrated that nanoscale WC-Co coatings can be deposited successfully by High Energy Plasma (HEP) spraying. Nanoscale WC-Co coatings were found to have minimal porosity, high uniformity, and high hardness. Initial wear testing has shown superior performance of these nanoscale WC-Co coatings relative to conventional WC-Co coatings and common wear resistant materials. The nanoscale WC-Co coating's abrasive wear resistance was comparable to high chromium white irons despite a complete lack of large second phase constituents. Additionally, important characteristics like wear resistance were much less sensitive to variation over a broad range of plasma spraying deposition parameters for nanoscale WC-Co coatings than for conventional materials. This paper provides an examination of abrasive wear, sliding wear, and frictional behavior of HEP sprayed nanoscale WC-Co coatings and a comparison with corresponding conventional WC-Co coating properties. An ASTM G65 dry-sand-rubber-wheel abrasive wear test was used to assess abrasive wear resistance. Tests under dry pure sliding conditions were conducted using an Amsler twin roll machine with a flat-on-ring specimen configuration. The Amsler machine allowed contact pressure to varied while wear and friction forces were monitored. Results to date confirm that nanoscale WC-Co coatings provide potential for superior performance.
4:30 PM		E2-2-10 A Comparative Study of the Influence of Triode Plasma Treatments, PVD TiN, CrN and Duplex Coatings and Ion Implantation on the Impact and Abrasive Wear resistance of Ti-6Al-4V A.D Wilson, A. Leyland, A. Matthews (University of Hull, United Kingdom) Mechanical and tribological properties of plasma thermochemical heat treatments have been compared with PVD coatings and nitrogen ion implantation of the titanium alloy Ti-6Al-4V using a rubber-wheel-type abrasion tester and a pneumatic impact tester. The thicknesses of the triode plasma treatment layers were measured on polished cross-sections by scanning electron microscopy and knoop microhardness. Using a thermionic triode plasma assisted system, a hot filament supported glow discharge was produced with different compositions of nitrogen, carbon and hydrogen for the plasma treatments. The duplex system consisted of plasma nitriding followed by plasma-assisted physical vapour deposition (PAPVD) of TiN. Two groups of nitrogen implanting regimes were chosen for the study. An increased nitrogen ion dose and higher pre-implant temperature was used, to produce a larger diffused layer of nitrogen ions into the substrate to enhance load support. Generally both salt bath and gaseous methods of nitriding have been used to improve the tribological properties of Ti-6Al-4V. Diode plasmas produced in furnaces have all improved the surface properties of the alloy i.e by increasing its surface hardness and consequently improving its sliding resistance. The affinity of titanium and its alpha/beta phase stabilisers (Al and V) to nitrogen and carbon produces a compound layer of hardened precipitates at or near the surface. It has been shown that the presence of TiN and Ti₂N layers in the nitrided zone have contributed to the improved surface properties. At elevated temperatures and increased process times the surface roughness of the alloy was found to increase significantly, although this roughening effect was reduced by depositing a thin layer by PAPVD, prior to the plasma treatment. In this study we describe how it is possible to increase the substrate/surface load support with surface microhardnesses of >1000H_k and investigate this effect on the abrasion and impact resistance of the titanium alloy.