ICMCTF2007 Session G4/E4: Tribological Study of Coatings for Green Manufacturing and Dry Machining

Thursday, April 26, 2007 8:00 AM in Room Royal Palm 4-6

Thursday Morning

Start	Invited?	Item
8:00 AM		G4/E4-1 TiAlCN/VCN Nanoscale Multilayer PVD Coatings Deposited by the Combined High Power Impulse Magnetron Sputtering / Unbalanced Magnetron Sputtering, (HIPIMS/UBM) Technology Dedicated to Machining of Al and Ti Alloys P.Eh. Hovsepian, A.P. Ehiasarian (Sheffield Hallam University, United Kingdom); I. Petrov (Frederick-Seitz Materials Research Laboratory and University of Illinois); C. Schimpf (Technical University of Freiberg, Germany) TiAlCN/VCN has been deposited by the combined High Power Impulse Magnetron Sputtering / Unbalanced Magnetron sputtering technology using a Hauzer HTC 1000-4 PVD system. Macroparticle-free V ion flux has been generated by HIPIMS discharge to sputter clean the substrates prior to the coating deposition. High Resolution Transmission Electron Microscopy, Scanning Transmission Electron Microscopy and Energy Dispersive Spectroscopy, analyses revealed that V ⁺ HIPIMS etching produced atomically clean interface and V implantation resulting in enhanced coating adhesion, (L_C = 58N). Excellent performance was achieved due to the synergy between V and C and the nanoscale multilayer structure of the coating. Vanadium provides for low coefficient of friction due to the formation highly lubricious V₂O₅ during sliding. Introduction of Carbon increases the chemical inertness between cutting tool and workpiece material and reduces build up edge formation. The coating combines low friction, (µ = 0.42 against Al₂O₃) with high hardness (H_V= 2900 kgmm^-2) and unique wear mechanism. HRTEM and Electron Energy Loss Spectroscopy revealed that in TiAlCN/VCN, Carbon is segregated laterally between the individual layers of the superlattice, (bi layer thickness Δ = 2.2 nm) producing low shear strength interfaces Provision of low shear strength interfaces results in a well defined nanometer scale layer by layer wear mechanism, which turned out to be the key for prevention of tribofilm and consequently thick build up layer formation. In dry milling of Al 7010-T 7651 alloy, TiAlCN/VCN nanoscale multilayer PVD coating outperformed state of the art Diamond Like Carbon (DLC, Cr/WC/a-CH) coated and uncoated end mills by factor of 4 and 8 respectively. In turning of Ti-alloys the TiAlCN/VCN coated cemented carbide inserts produced 2-3 times more components (orthopaedic implants), as compared to uncoated tools.
8:20 AM	Invited	G4/E4-2 A Review of the Developments in PVD Coatings for Machining High Temperature Alloys A.T. Santhanam (Kennametal Inc.) High temperature alloys, such as nickel-base and titanium alloys are difficult to machine because of their high hardness and strength at elevated temperatures, low thermal conductivity, reactivity with tool materials, high capacity for work hardening, and the presence of hard phases in their microstructure. This paper addresses the specific machining challenges from the point of view of tool wear mechanisms observed on cemented carbide tools and the remarkable progress achieved in recent years in combating these tool wear modes. PVD hard coatings from single layer TiN, TiCN, TiAlN, AlTiN, and AlCrN coatings to ternary (Ti,Cr,Al)N and (Ti,Al,Y)N nitride coatings, nanolayer TiN/AlTiN, and nano-composite (Ti,Al,Si)N coatings have significantly contributed to delay the onset of various tool failure modes and thus increase tool life. The impact of these developments on increased machining productivity and reduced manufacturing cost will be discussed.
9:00 AM		G4/E4-4 Application of Nano Multilayered PVD Coatings M. Arndt, H. Westphal (Kennametal Technologies GmbH, Germany); R.M. Penich (Kennametal Inc., USA); H. van den Berg (Kennametal Technologies GmbH, Germany) The performance of sophisticated carbide cutting tools is strongly influenced by the surface engineering, i.e. the substrate hard metal and geometry together with the coating. In order to improve wear and oxidation resistance hard coatings deposited by PVD have to be designed for the application concerned, considering abrasive impact, operation temperature, necessary toughness, as well as frictional and chemical interaction between tool and machined material. This paper deals with different applications of modern cutting tools in the field of automotive industry like milling of engine blocks, cylinder heads or crankshafts, where PVD coatings are applied. For this, AlTiN-based coatings on inserts for indexable milling cutters are optimized regarding the main wear mechanisms under the particular machining conditions, leading to a distinct increase of lifetime of the tools.
9:20 AM		G4/E4-5 Tribological Properties Investigation on Coated and Thermal Treated Surface used for Dry Machining L. Wang, X. Nie (University of Windsor, Canada); C. Yao (DaimlerChrysler Corporation Technology Center) This research is to investigate tribological properties of coated and thermal diffusion (TD) treated steels (D2) against aluminum (Al 6061) and steel (52100) counterface materials for their potential applications in dry machining/forming of aluminum/steel composite materials. The coatings included the TiN-based, CrN-based, and diamond-like carbon (DLC). Pin-on-disc tribo-tests were performed on those samples against Al and steel counter-pins under a dry sliding condition. Wyko profilemetry and SEM/EDX analysis showed that both Al and steel pin materials transferred to the coatings TiN, TiCN, CrN, CrAlN and substrate HD2, which may negatively influence product quality in machining/forming applications. The DLC coating against Al exhibited a low friction coefficient and negligible wear rate, but some wear occurred when against the steel pin due to relatively low hardness. Although CrN-MoS₂ coating had the lowest friction coefficient, a high wear rate was observed during the tests against both Al and steel pins. Coatings DLC and CrN-MoS₂ may be promising for the targeted applications, but their hardness (and also thermal stability) need to be improved.
9:40 AM		G4/E4-6 Tribological and Wetting Behaviour of a Nanolaminated PVD Tool Coating with a Nanostructured Top Layer in Interaction with a Biodegradable Lubricant for Green Metal Forming C. Warnke (Surface Eingeering Institute, Germany); P. Immich, C. Pinero, R. Nickel, T. Massmann, F. Klocke, C. Zeppenfeld, K. Bobzin (RWTH Aachen University, Germany) After many essential applications e.g. in the field of machining, PVD tool coatings materially gain in importance for metal forming processes. Coated metal forming tools may enormously reduce tool and workpiece wear, forming capacities or deliver special functions formerly provided by lubricants and often toxic additives. As main properties, the coatings have to feature a very high adhesion to the substrate, a high hardness and adequate oxidation stability. Meeting these requirements a nanolaminated TiHfCrN PVD tool coating had been developed using the Arc Ion Plating technique. After a first development step the coating delivered a high as possible hardness in combination with an as low as possible Young's modulus. These basic properties, in combination with the ability to prevent the broadening of cracks inside the coating structure, already led to outstanding performances in several metal forming processes. As a second step, this work reports on the development of an additional nanostructured CrN top layer which is used for the reduction of the friction coefficient by providing a lubricant storing functional surface. CrN shows a very high adhesion to the basic coating and is able to build passivating oxide layers. To prove the developed coating's application oriented tests were carried out, e.g. ball-on-disc and pin-on-disc tests, as well as the examinations of the wetting behaviour. Contact angle measurements and calculations of the surface free energies have been made considering the PVD coatings and a biodegradable synthetic ester as lubricant. Results of indirect impact extrusion processes are being presented including measurements of the forming capacities.
10:00 AM		G4/E4-7 Development of Nano-Columnar Carbon Coating for Dry Micro-Forming T.A. Aizawa, E.I. Iwamura (University of Toronto, Canada); K.I. Itoh (Seki-Corporation, Co., Ltd., Japan) In parallel with down-sizing of electrical devices and products, manufacturing is forced to be also miniatured to fabricate small-sized electrical parts with the characteristic size in mili-meters. This type of micro-forging and micro-stamping, suffers from two issues: forging and stamping in dry and strictly accuracy in clearance. Residual lubricating oils and cleansing agents are completely disliked by electrical parts; elimination of these oils and agents becomes absolutely severe and costly task after forging and stamping. Since the clearance is designed to be equal to or less than 10% of sheet material thickness, the conventional hard coating has a risk of break-away, or, the formability is significantly shortened. Nano-columnar carbon coating is developed to solve the above two issues in micro-forming. Amorphous carbon film with defective inter-columnar structure is employed as a starting film. Electron-beam irradiation is performed to chemically modify this microstructure having a fine nano-structured columnar carbon. After precise HRTEM observation and Raman spectroscopy, this nano-columnar carbon film is found to be composed of graphitized inter-columnar network with amorphous columns. Nano-indentation proves that this film has remarkable reversibility in deformation up to 8 to 10 % of film thickness after loading and unloading. Micro-scratching test also demonstrates that this coating has nearly the same wear resistance as cubic boron nitride coating. Furthermore, a micro-stamping test is performed to demonstrate the feasibility of this coating in practical operation.
10:20 AM		G4/E4-8 Mechanical Properties and Tool Performance of Si Doped TiAlN Coatings Deposited by Arc Ion Plating M.C. Kang, D.H. Kwon (Pusan National University, Korea); K.I. Moon (Korea Institute of Industrial Technology, Korea); M.S. Park, Y.H Jun (J&L Tech. Co., Ltd., Korea) Arc ion-plating technique is used to prepare the (TiAlSi)N films on various substrates including WC-Co coupon, Si wafer and end-mill tools. The compound alloy target is manufactured by the 33 at.% of Ti and 67 at.% of Al. The Si composition in the film is controlled by varying the ratio of SiH₄ to N₂ in the gas mixture. Mechanical properties and tool life of end-mill tools are investigated as a function of Si composition. X-ray diffraction (XRD), transmission electron microscope combined of ion-focusing beam (TEM) and Auger spectroscope are used to characterize the crystal structure and composition of films, respectively. Nano-indentor and scratch tester are used to measure the mechanical properties and film adhesion. Actually, cutting performance of coated tools under high speed cutting conditions are evaluated by the cutting force, flank wear and surface roughness of high-hardened workpiece (SKD11 in JIS, HRC60). The results show that cutting performances are significantly improved in case of a certain Si incorporation. The mechanism and role of Si incorporation on the improved milling behavior is discussed in terms of the film structure and mechanical properties.
10:40 AM		G4/E4-9 Development of Nano-Textured Self-Lubricating Adaptive Films S.M. Aouadi, C. Bradley, L. Brandon, P. Basnyat, R. Zakeri, P. Kohli (Southern Illinois University Carbondale) There have been great strides in the development and diverse utilization of hard nanocrystalline and nancomposite coatings in recent years. Research has focused primarily on multi-phase adaptive coatings that combine a hard phase that is highly wear resistant embedded with one or more phases that provide lubrication in different environments. The main challenge of the nanocomposite approach is the control of the self-lubricating process without compromising their mechanical properties. A new technique for the fabrication of adaptive self-lubricating coatings is proposed whereby nanoporous coatings are synthesized using porous alumina as a template. These coatings are subsequently filled with different potential solid lubricants (SLs) that include Ag and MoS₂. The microstructure of the produced films is evaluated using top-view and cross-sectional scanning electron microscopy. In addition, spectroscopic ellipsometry is used to collect optical data of these structures and to extract quantitative microstructural information (thickness, porosity, phase composition) through modeling based on the effective medium approximation. Finally, ball-on-disk tests were carried out using (1) the nanoprous films in lubricated conditions to investigate the potential benefit of the nanopores in diminishing the frictional contact between the contact surfaces and (2) the composite films in un-lubricated conditions to determine the performance of these coatings compared to the traditional monolithic films.
11:00 AM		G4/E4-10 Microstructure and Vacuum Sliding Behaviour of Thermally Oxidized Ti-6Al-4V Alloy A. Edrisy, M.M. Yazdanian, A.T. Alpas (University of Windsor, Canada) Lightweight titanium alloys have widespread applications in Aerospace sector which may require the operations under low atmospheric pressure conditions. Their poor tribological properties such as high wear rates, seizure, and massive transfer to the counter surfaces as well as high affinity for oxygen have been major drawbacks for the use of titanium alloy components in sliding contact situations. Several surface modification techniques are employed to improve the wear and frictional behaviour of titanium alloys. One potential solution is thermal oxidation process. In this process oxygen diffuses into Ti alloy and increases the hardness and wear resistance of surfaces. In this study the thermal oxidation (TO) treatment is carried out for Ti-6Al-4V at 600 ermined to be 4 µ. X-ray diffraction patterns of TO-treated Ti-6Al-4V exhibit peaks associated with TiO₂ in form of rutile and anatase. The sliding behaviour of treated Ti-6Al-4V discs are investigated using ball on disc configuration against AISI 52100 Steel, Ti-6Al-4V, and treated Ti-6Al-4V balls under vacuum. The wear behaviour is also compared with the untreated ones. wear rate of TO-treated Ti-6Al-4V is about three times lower than that of untreated Ti-6Al-4V in vacuum. The worn surfaces of Ti-6Al-4V tested in vacuum are rough, and exhibit severe plastic deformation and massive material transfer to counterface. The TO-treated Ti-6Al-4V reveal smoother worn surfaces and the original oxidized layer remains intact despite the fact that more wear damage is inflicted on counterface. The relationships between the microstructural basis of wear processes and the chemical properties of the thermally oxidized film are discussed to assess the suitability of this coating for wear protection of Ti-6Al-4V surfaces.