Papers

ICMCTF1998 Session E4/F1: Mechanical Characterization - Micromechanical Testing & Modeling

Wednesday, April 29, 1998 8:30 AM in Room California

Wednesday Morning

Start	Invited?	Item
8:30 AM		E4/F1-1 Residual Stresses and Mechanical Properties of TiCN Thin Films Deposited by Arc Evaporation L.G. Hultman (Linköping University, Sweden); L. Karlsson (SECO Tools AB, Sweden); M. Johansson, J.-E. Sundgren (Linköping University, Sweden); H. Ljungcrantz (Impact Coatings AB, Sweden) The influence of growth parameters on residual stress state (analyzed by XRD-sin²Ψ method) of arc-evaporated TiC_xN_1-x thin films deposited on cemented carbide substrates have been studied. Films with x ranging from 0 to 1 were grown by varying the ratio between the gases N₂ and CH₄. Mechanical properties, hardness (H) and Youngs modulus (E), were investigated using nanoindentation technique. The intrinsic stress, σ_int, increased rapidly with increasing negative substrate bias, V_s, up to V_s = 50 - 100 V, while for larger V_s, σ_int decreased and leveled out for V_s > 700 V at a value which increased with the order of x=0, 0.15, and 0.45. For a given V_s, a maximum in σ_int was obtained at x= 0.4-0.7. The maximum stress level was between -6 to -7 GPa and were limited by interior cracking of the films. Almost linear relationships between σ_int and H were found for each composition and with H shifting upwards in value for increasing x. For the TiN films, H ranged between 33 GPa and 26 GPa for σ_int = -5.8 and -1.2 GPa, respectively. E was constant at approx. 610 GPa for most of the films with a slight decrease for the films with the lowest stress values. It is suggested that the apparent relaxation of σ_int with increasing energy of the incident metal ions predominantly were determined by the defect annihilation processes occurring in the collision cascade at the growing film surface, and that the effective stability of defect complexes increased with increasing carbon content of the films up to x=0.4 to 0.7. The close correlation obtained between intrinsic stress and inhomogeneous strain (XRD peak broadening analysis) with the hardness shows that the obstruction effect from defects on dislocation motion together with the bond strength (affected by the composition) are the important hardening mechanisms of the films. Film microstructure was also analyzed by cross-sectional electron microscopy.
8:50 AM		E4/F1-2 Influence of Stress Distribution on Adhesion Strength of Sputtered Hard Coatings H.K. Toenshoff, B. Karpuschewski, A. Mohlfeld, H. Seegers (University of Hannover, Germany) Today's research activities in improving the properties of cutting tools are concentrated on optimizing manufacturing technologies and tool geometry, on alloying of special cutting materials and on coating of tools. As a result of the poor machinability of new cutting tool materials, the surface properties are influenced by the grinding process used during tool manufacturing. In spite of optimized coating-parameters, deposited PVD-coatings fail because of insufficient surface properties of the substrates. In this contribution influences of residual stress distribution in subsurface layers on interface strength of PVD-coated carbides were investigated. Considered topics are the influence of grinding, micro blasting and water peening of carbides on surface topography, surface composition and surface integrity. Dependencies between stress distribution in subsurface layers and interface strength of (Ti,Al)N-coatings as well as effects on wear behaviour in dry machining are highlighted. Surface properties of the tools are characterized by SEM, EDX and X-ray residual stress measurements (XRD). The X-ray measurements of the depth profile of the residual stress distribution is done by using different lattice planes and wavelengths which correspondence to different penetration depths. Film adhesion is analyzed by scratch and indentation tests. Due to increased interface strength of micro blasted tools a superior wear behaviour in dry machining is observed.
9:30 AM		E4/F1-4 Tribological Properties of TiAlN-Based Alloy and TiAlN-CrN Superlattice Hard Coatings at Elevated Temperatures E. Pflueger (CSEM Centre Suisse d'Electronique et de Microtechnique SA, Switzerland); A. Schroeer, P. Voumard (CSEM Centre Suisse d'Electronique et de Microtechnique SA, Neuchatel, Switzerland); L.A. Donohue (Sheffield Hallam University, Great Britain); W.-D. Münz (Sheffield Hallam University, United Kingdom) Cr and Y containing TiAlN films \|1\| as well as superlattice structured TiAlN-CrN hard coatings \|2\| deposited by the combined steered arc evaporation/ unbalanced magnetron sputter technique exhibit excellent oxidation resistance up to 900°C. The microhardness values of the TiAlN based alloys range from HK2400 to HK2700 whereas the hardness of the TiAlN-CrN superlattice coatings depends on the individual thickness of the respective TiAlN and CrN layers reaching a maximum of HK3500 at an equi-thickness layer period of 3.5 nm.Tribological tests in the temperature range 25-750°C show a decay in friction coefficient from 0.6 to 0.35 at elevated temperatures. Comparison of both types of coating against TiN reveals superior performance particularly when tests were undertaken within the highest temperature regimes. \|1\| L.A.Donohue, I.J.Smith, W-D.Münz, I.Petrov, J.E.Greene - ICMCTF97, In Press Surf.Coat.Tech. \|2\| I.Wadsworth, I.J.Smith, L.A.Donohue, W-D.Münz, - ICMCTF-97, In Press Surf.Coat.Tech.
9:50 AM		E4/F1-5 A Transmission Electron Microscope Study of the Long Range Effect in Titanium Nitride After Metal Ion Implantation Yu.P. Sharkeev (Institute of Strength Physics & Materials Science of RAS, Russia); A.J. Perry (A.I.M.S. Marketing); E.V. Kozlov, S.V. Fortuna (Tomsk State University of Architecture & Building, Russia); B.P. Gritsenko (Institute of Strength Physics & Materials Science of RAS, Russia) Ion implantation is a favored method to achieve controlled modification of the surface and near surface layers of constructional materials (metals, alloys, intermetallics, ceramics, coatings, and so on) The ion beam treatment is used to modify their surface mechanical, tribological, and chemical properties. At present two basic types of ions (gas ions and metal ions) are used to treat the materials with metallurgical doses (1x10¹⁶-1x10¹⁸ ion cm^-2. The gas ion beams are employed actively in the world to improve the properties of tools and parts. At the same time the metal ion implantation is not used widely. At present some ion implantation systems have been developed to treat the materials with the metal ions. The brief review of the vacuum-arc metal ion sources (Raduga, Diana, Titan, Mevva) is presented. The main feature of these systems is the possibility of forming multicomponent ion beams including ions of non-conducting materials. Examples of real applications of the metal ion implantation are discussed. The improvement of the service properties during ion implantation is connected with a formation of the particular structural- phase states both in the implanted zone and beyond this zone. The formation of defect structures beyond the implanted zone at ion implantation is called "the long-range effect". The effect occurs both in metals with high plasticity and low yield strenght and in high strength materials (for example, TiN coatings) The experimental results of the manifestation of this effect in metals, alloys and coatings after metal ion implantation are presented. The mathematical model explaining the formation of a defect structure beyond the implanted zone is presented.
10:30 AM		E4/F1-7 Modelling the Wear by Hard Particles of Coatings and Surface Teatments I.M. Hutchings (University of Cambridge, United Kingdom) Despite the widespread use of surface engineered components in applications where their tribological performance is critical, models for the combined wear of thin surface coatings and the underlying substrates are still poorly developed. This paper will present an overview and discussion of existing models for the wear of thin hard coatings, focussing on the wear processes of abrasion and erosion caused by hard particles. The special problems associated with measuring wear rates on coated materials will also be discussed.
11:10 AM		E4/F1-9 The Effects of Substrate Pretreatment on Residual Stress and Adhesion Strength of Diamond-coated Cemented Carbide Tool Inserts M.A. Taher, W.F. Schmidt, A.P. Malshe, A. Muyshondt, W.D. Brown (University of Arkansas) The challenge of improving the adhesion of CVD diamond coatings on carbide cutting tool inserts has gained much attention in recent years. Several researchers have proposed and investigated the use of different pretreatment methods to enhance the adhesion of CVD diamond coatings . Classical procedures such as mechanical scratching with diamond grit and chemical etching of cobalt with an acidic solution have been shown to enhance nucleation of diamond growth and improve adhesion. More recent pretreatment techniques such as the use of intermediate layers of refractory metals and better etching agents have resulted in additional improvements in the adhesion of CVD diamond. Qualitative examination of the effects of such pretreatment methods have been thoroughly discussed. However, systematic and quantitative experimentation on the physical and mechanical effects of substrate pretreatment has been scarcely reported. In the present work, the change in the residual stress of the carbide substrate was used as a quantitative approach. Stress measurement by x-ray diffraction was conducted on 20 samples prior to, and after each sample was processed through the different stages of pretreatment and diamond coating. Stress data for the 20 samples were correlated with their corresponding adhesion and machining test data. The 20 samples were divided into four groups each treated with a selected classical or novel method of surface pretreatment such as the use of nano-crystalline diamond seeds and WC surface heat treatment. Diamond coatings of 20 μ thickness were deposited using a hot filament CVD reactor.
11:30 AM		E4/F1-10 Development of a Single Pass Scratch Tester to Investigate Galling Properties of Austenitic Steels M. Joseph, A. Matthews (University of Hull, United Kingdom) The problem of galling on drill collars has been a well documented feature in the oil and offshore industries. Developments have been made with new materials able to reduce this effect significantly. However, there is a need to establish a reliable and repeatable test to study this type of failure mechanism in more detail. The aim of this investigation was to develop a reliable and repeatable test to determine the critical contact pressures at which galling occurs on materials Staballoy AG17, Datalloy and Staballoy 734. A comparison between uncoated and plasma assisted physical vapour deposited (PAPVD) TiN and CrN on Staballoy AG17 was also made. This was achieved by modifying a VTT scratch tester which allowed a greater loading range on the substrates. Different indenter configurations were investigated to determine the best conditions to simulate galling. Analysis was by measuring the Normal load, Friction Force and Acoustic Emission which were plotted on a graph plotter. The effect and extent of galling was studied by Optical and Scanning Electron Microscopy as well as, Surface Profilometry. Preliminary tests on AISI 304 stainless steel were used as a bench mark to identify the exact nature of galling and this was then used to compare and categorise the materials under investigation From the results obtained a reliable galling test was established and the materials studied were ranked according to galling resistance.
11:50 AM		E4/F1-11 Microhardness, Adhesion and Scratch Behaviour of Chromium Nitride Film Deposited on Tool Steel by Reactive Sputtering J.G. Duh, J.N. Tu (National Tsing Hua University, Taiwan) Cr-N films with various compositions and structures were deposited by reactive sputtering on A2 tool steel. Phase analysis showed that films with lower nitrogen contents exhibited the Cr and Cr₂N phases, while the CrN phase was observed in the films with nitrogen contents higher than 58 at%. With aid of Atomic Force Microscope, the surface roughness and grain sizes of the deposited films were evaluated. The microhardness of the deposited films ranged from 1482 to 1771 HK at the load of 3 gf, in which corresponding penetration depths were less thatn 1/10th of the avearge film thickness. Young's modulus obtained from the depth-sensing method were around 330 Gpa. The scratch test was also applied to evaluate the adhesion of the deposited films. The critical loads of the films were determined by the detected acoustic emission signals and the observation of the scratch channels. Serious Failures were found in the films deposited with lower nitrogen gas low rates, both cohesive and adhesive failures were observed. In the films deposited with higher nitrogen flow rates, only localized failures were observed.
12:10 PM		E4/F1-12 The Nano-scratch Tester (NST) as a New Tool for Assessing the Strength of Ultrathin Hard Coatings and the Mar Resistance of Polymer Films N.X. Randall, B. Bellaton (CSEM Instruments, Switzerland); R. Consiglio (Ecole des Mines, France) Nowadays, functional coatings are used in increasingly demanding applications that require specific resistance to damage and good adhesion. This has prompted a rising interest in improving the mechanical properties of polymer coatings, especially their scratch and mar resistance, and ultrathin hard coatings as used for protective overcoats in the magnetic storage industry. In order to overcome the limitations of both the classical stylus scratch test (normal force range) and the atomic force microscope technique (short slidig distances), a new concept has been developed. The Nano-Scratch Tester (NST) is a new instrument which uses a diamond stylus with a tip radius in the range 0.5-20um, a wide load range (10uN-IN), a scratch length of up to 10mm and which simultaneously measures the tangential force and penetration depth during the scratching process. Application of the contact mode is achieved by means of three cantilevers. Depending on the width, thickness and length of these cantilevers, the overall load range can be modified owing to the vertical displacement of the cantilever's fixed end. Furthermore, this instrument allows the study of materials in a multipass contact fatigue mode, and for high resolution inspection of the deformed or damaged area, a scanning force microscope (SFM) is integrated into the system. First experimental results are presented for very different materials; polymeric clear-coat samples which give a range of mar resistance and DLC ultra thin films used as protective overcoats for hard disks. All results indicate very good reproducibility and confirm the application of this new instrument for the accurate characterisation of elasticity, hardness, adhesion and mechanical integrity in coated systems where the film thickness is less than 1 um.