ICMCTF2014 Session B4-1: Properties and Characterization of Hard Coatings and Surfaces

Wednesday, April 30, 2014 8:00 AM in Room Royal Palm 1-3

Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2014 Schedule

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8:00 AM B4-1-1 Development of a Systematical Methodology for Predicting Coated Milling Tools' Efficiency Including its Qualification Based on a Comparison of PVD-Coatings Deposited by the DC- and HIPIMS-Process
Marc Busch, Fritz Klocke, Thomas Bergs, Michael Ottersbach (Fraunhofer Institute for Production Technology IPT, Germany); Konstantinos-Dionysios Bouzakis, Emmanouil Bouzakis (Aristoteles University of Thessaloniki, Greece)

Eventough approximately 80% of all cutting tools applied in industrial shop floors are coated, the tools’ cutting performance very often is far behind performance potentials promoted by many researchers. A reason for this is that in demanding applications (e.g. turbomachinery manufacturing) the coating properties have to be exactly customized to cope with the individual machining conditions. If this is not the case, a reliable improvement in the tool performance cannot be guaranteed. For instance, PVD coatings’ performance varies depending on the temperature in the cutting zone. In turn, the temperatures generated during the machining process are mainly influenced by the applied machining conditions, in special the cutting velocity, as well as the definition of the tool and coating materials. In case of the cutting process milling the challenges even itensify owing to the repetitive and discontinuous tool engagement. Therefore, the objective must be to ensure the reliability of (newly) developed coatings in a production environment, without resorting to the extensive and expensive practical testing that is currently used for evaluating proper tool specifications and machining conditions.

Against this background, in this paper a systematical methodology based on analytical, experimental and numerical investigations for predicting coated tools' efficiency in milling is introduced. In the frame of the investigations different types of coatings are examined regarding their adherent cutting wedge thermal and mechanical loadings during the material removal process. The Ti-based PVD coatings are deposited using the standardized DC and the innovative HIPIMS process. After a metallographic analysis of the coatings, nano-indentation and impact tests at ambient and elevated temperatures are performed. On this base the strength properties as well as the brittleness and fatigue behaviour of the coatings can be modeled. Moreover, inclined impact tests for evaluating the films’ adhesion are applied. These results, along with FEM-based calculations of the cutting wedge thermo-mechanical loads facilitate the prediction and explanation of the coated inserts’ cutting performance at various conditions. The findings are validated by dint of endurance testing.

8:20 AM B4-1-2 Origin of Compressive Stress in CVD TiB2 Hard Coatings
Nina Schalk, Christian Mitterer, Jozef Keckes (Montanuniversität Leoben, Austria); Christoph Czettl (Ceratizit Austria GmbH, Austria); Marianne Penoy, Claude Michotte (Ceratizit Luxembourg S.àr.l., Luxembourg)

CVD hard coatings deposited on cemented carbide substrates typically exhibit tensile residual stresses, which are mainly due to differences in the thermal expansion coefficients of coating and substrate material. However, CVD TiB2 coatings have been reported to show high compressive residual stresses, although their thermal expansion coefficient is larger than that of the cemented carbide substrate. Within this work, TiB2 coatings were deposited on TiN base-layers using thermally activated CVD. The coating composition was examined using wave-length dispersive X-ray spectroscopy and electron energy-loss spectroscopy, yielding compositions close to stoichiometry. Slices of the coating were prepared and synchrotron X-ray nanodiffraction experiments were performed in transmission geometry to illuminate the origin of the compressive stresses. Thus, the gradients of stresses and texture could be determined as a function of the coating thickness with a resolution of 100 – 200 nm. Coating microstructure as well as mechanical and tribological properties were investigated by scanning and transmission electron microscopy, the sin²ψ method, nanoindentation and ball-on-disc tests. Pole figure measurements revealed no pronounced texture for the TiN base-layer and a (111) texture for the TiB2 top-layer, evidencing that there is no epitaxial relation between both layers. Hardness and compressive residual stresses of ~45 GPa and ~2.4 GPa, respectively, could be determined for the morphologically almost featureless TiB2 coatings. The combination of high hardness and compressive residual stresses results in excellent wear properties.

9:00 AM B4-1-4 An In-situ Study of the Fracture Toughness and Cracking Behaviour of the CrAlN/Si3N4 Nanocomposite Coatings
Shiyu Liu, Claire Davis (University of Cambridge, UK); Xianting Zeng (Singapore Institute of Manufacturing Technology, Singapore); William Clegg (University of Cambridge, UK)

Cr-based nanocomposite coatings are attracting increasing attention as wear protection coatings in dry machining and on aero-engine compressor blades where the components are consistently subjected to high loading, high impact or heavy erosive environments. Although generally attributed to the high coating hardness, this can also be influenced by the fracture toughness, particularly in extreme applications. In this paper, we study the fracture toughness and cracking behaviour of the CrAlN/Si3N4 nanocomposite coatings and demonstrate how these properties depend on the coating composition. The nanocomposite coatings were deposited with different silicon contents using a lateral rotating cathode arc technique. Their composition, microstructure, chemical bonding states and mechanical properties were characterized using EDS, XRD, XPS and nanoindentation respectively and compared with CrN and CrAlN coatings deposited under the same conditions. The fracture toughness of the coatings was characterized by an in-situ double cantilever beam (DCB) compression method. It is found that the CrAlN/Si3N4 nanocomposite coatings are significantly tougher than the CrN and CrAlN coating, and the fracture toughness values increase with the coating’s Si content. The in-situ observations also demonstrated that the cracking of the coatings was influenced by the microstructural variability of the coatings.

9:20 AM B4-1-5 Mechanical Properties and Cutting Performance of MT-TiCN Coated Carbide Tools as a Funtion of Carbon Content
Anongsack Paseuth, Haruyo Fukui, Susumu Okuno, Hideaki Kanaoka (Sumitomo Electric Hardmetal Corp., Japan); Yoshio Okada (Motherson Techno Tools Ltd.)

Moderate temperature (MT)-TiCN is one of the most important components in modern coating systems for cutting tools. Hardness, adhesion and wear resistance can be affected strongly by the controlled adjustment of structure and chemical composition. The aim of this study is to investigate the effect of MT-TiCN coated carbide tools, as a function of carbon content, on mechanical properties and cutting performance. Deposition of high carbon contented MT-TiCN was conducted by doping a hydrocarbon gas for the CVD process with varied hydrocarbon gas to CH3CN mole fraction from 0 to 30 at 840°C and 9kPa. The carbon content x in TiCxN1-x measured from change in lattice constant, increased with hydrocarbon gas to CH3CN mole fraction and saturated at x=0.73. Crystalline size derived from XRD showed a minimum size of 39nm when carbon content x varied from 0.66 to 0.69. Hardness and adhesion was evaluated by indentation and scratch tests. Indentation hardness increased according to the increase of carbon content and maximum hardness reached 2920mgf/µm2 when carbon content x =0.69. The adhesion of film to carbide substrate showed a decrease of critical load when carbon fraction was increased. Furthermore, a cutting test for ductile cast iron (AISI:100-70-03) was performed with different kinds of carbon content x (x =0.55 to 0.73) in MT-TiCxN1-x(10µm)/Al2O3(5µm) coated carbide tools. TiC0.69N0.31/Al2O3 coated carbide tools showed significant increase in tool-life by 30-50% compared to commercially available MT-TiC0.55N0.45/Al2O3 coated carbide tools.

9:40 AM B4-1-6 Influence of Oxygen Impurities on Structural, Mechanical Properties and Age Hardening of Ti-Al-N
Helmut Riedl (Christian Doppler Laboratory for Application Oriented Coating Development at Vienna University of Technology, Austria); Anna Vlasova (Vienna University of Technology, Austria); Richard Rachbauer (Oerlikon Balzers Coating AG, Liechtenstein); Szilárd Kolozsvári (Plansee Composite Materials GmbH, Germany); Jörg Paulitsch, Paul Heinz Mayrhofer (Vienna University of Technology, Austria)

Recent investigations showed that even small amounts of impurities, such as oxygen, affects the growth process, the crystal structure, and the grain size of ceramic-like hard coatings. Ti1-xAlxN is due to the excellent mechanical and thermal properties a well-established hard coating system, used for various industrial applications. We have used Ti1-xAlxN as a model system to study the influence of oxygen impurities on growth and film properties. By using Ti0.50Al0.50 targets with different oxygen contents (< 950, 950-2000, > 2000 ppm) and base pressures of either 10-5 mbar or 10-8 mbar, we are able to identify the major oxygen impurity source for reactively sputtered Ti1-xAlxN coatings. Furthermore, the coatings were prepared at 500 and 800 °C and when using the target with the highest O-content we also varied the sputtering power for 2 selected deposition conditions. Consequently, 14 different Ti1-xAlxN coatings with a similar Al content of x~0.6 have been prepared.

The crystallite sizes of the coatings, which vary between 20 and 80 nm, are strongly determined by the O content as well as deposition temperature, as proven by x-ray diffraction, transmission electron microscopy, and atom probe tomography. Coatings prepared from the highest purity target (O < 950 ppm) exhibit hardness values between 29 and 34 GPa, depending on the substrate temperature or base pressure used. A much higher variation in hardness between 18 and 35 GPa is obtained when using the target with the highest O-content of > 2000 ppm.

But not only the as-deposited structure and properties of Ti1-xAlxN are strongly influenced by the oxygen impurities, also their age-hardening behaviour and hence thermal stability strongly depends on the purity of the target as well as the base pressure and deposition temperature used.

10:00 AM B4-1-7 Structure, Mechanical and Adhesion Properties of CuZr Metallic Glass and CuZrN Nitride Thin Films
Fatiha Challali, Florent Tetard (LSPM-CNRS, Université Paris 13, Sorbonne Paris-Cité, France); Grégory Abadias (Pprime Institute - UPR CNRS 3346 - Université de Poitiers - ENSMA - France); Laurent Belliard (UPMC, Paris,France); Thierry Chauveau, Ovidiou Brinza, Philippe Djemia (LSPM-CNRS, Université Paris 13, Sorbonne Paris-Cité, France)
We investigated the structure and mechanical properties of ZrCu metallic glass and ZrCuN thin films deposited by rf magnetron sputtering from a Zr50Cu50 target in Ar or Ar+N2 plasma discharge, respectively. Process parameters such as rf power, Ar and N2 flows, and time of deposition were varied and the conditions for glass forming ability identified. Their influence on the thickness, the films microstructures, the chemical composition and the mechanical properties were explored. The structural properties of the metallic glass and nitride compounds were characterized by X-ray Diffraction and X-ray reflectivity, and chemical composition by wavelength-dispersive spectroscopy. The picosecond ultrasonic, the Brillouin light scattering and the nanoindentation techniques were employed to measure their acoustic, elastic and hardness properties whereas nanoscratch tests evaluated their adhesion performance. The strength and the ductility of the films were inferred from comparative tensile tests on coated and uncoated metallurgical substrates realized inside a scanning electron microscope.
10:20 AM B4-1-8 Evaluation of Fracture Toughness of ZrN Hard Coatings using Internal Energy Induced Cracking
Jia-Hong Huang, Yu-Hsiang Chen, Ge-Ping Yu (National Tsing Hua University, Taiwan)

The objective of this study was to evaluate the fracture toughness and to investigate the effect of texture on the fracture toughness of ZrN hard coatings. We employed a recently developed energy-based method named internal energy induced cracking (IEIC) method to evaluate the fracture toughness. ZrN film was continuously deposited until reaching the thickness at which the film was fractured due to stored energy accumulation. The residual stress before crack initiation was used to calculate the stored energy (Gs), from which fracture toughness (Gc) can be derived. The residual stress of the ZrN coating was measured by laser curvature method, the Young’s modulus of ZrN coatings was determined by nanoindentation, and the film thickness was determined from SEM cross-sectional image. The results showed that for a ZrN coating with (111) texture coefficient of 0.71, the fracture toughness was estimated to be ranged from 23.9 to 42.4 J/m2. The hardness of the ZrN coatings was not changed with increasing film thickness. Stress gradient may play an important role in the fracture mode. Fracture of the ZrN coating may be initiated at a position of local maximum stress gradient accompanying with defects. The stress gradient in the ZrN coating may be originated from the competitive stress generation mechanisms. As the film thickness was above 4.2 μm, the (200) orientation increased in the strongly (111) textured ZrN coatings, which may be related to the stress relief . When the stored energy in the ZrN coating was higher than 31.6 J/m2, it was partly released accompanying with the stress relief. The release of stored energy was considered to be the driving force of texture inversion. The advantages of this method are without externally applying stress and special sample preparation, and the substrate effect can be avoided. However, there are some disadvantages in applying the IEIC method. To insure that the fracture process is within the film, good adhesion and high residual stress are required. In addition, this method can only applied to hard coatings due to the requirement of small plastic zone size.

10:40 AM B4-1-9 Modified W-S Coatings for Reducing Friction in Rubber Seal Applications
Ana Manaia (Instituto Pedro Nunes, Portugal); Albano Cavaleiro (Coimbra University, Portugal); Tomas Polcar (University of Southampton, UK)

Rubber seals are commonly used in lubrication systems and bearings in order to avoid contamination of the systems and leakage of lubricants. However in dynamic contact where sliding contact conditions are present, rubber seals are easily damaged due to the high friction coefficient developed between the rubber and the seal.

The surface protection of rubber seals by applying a low friction coefficient coating is being studied in the last years; however this application requires specific materials properties either in terms of thermo-mechanical or tribological behaviours that are not yet developed.

Due to their layered structure and weak inter-layer bonding, transition metal dichalcogenides (TMD) has been studied in last decades in the field of low and super low friction coatings. Alloying TMD sputtered coatings has been the most attractive solution for improving and optimizing their friction behavior in a large range of loading environments, in order to overcome the two main drawbacks which have impeded their widespread application for reducing friction: the low loading bearing capacity and the high sensibility to moisture.

The aim of this work was to develop TMD+C coatings by PVD, in order to lowering the friction in mechanical contacts and studying the thermo-mechanical and tribological behavior of the system when applied on rubbers.

For these purposes, W-S thin films were alloyed with different C contents using magnetron sputtering and deposited on nitrile butadiene rubber (NBR) substrates.

The adhesion of the W-S-C coatings was improved by playing with the functionalization of the rubber surface by plasma etching as well as using a chemical composition gradient during the film deposition. Changing the C content of the coatings allowed to achieve hardness in the range from 6 to 10 GPa and friction coefficient as low as 0.02. Induced cracking was studied as a function of the preliminary etching substrate conditions and coatings parameters.
11:00 AM B4-1-10 Effect of Annealing Treatment on Sputtered Cobalt Sensing Response Toward Inorganic Phosphate Ion
Zulkarnain Endut (MIMOS Berhad, Malaysia); Mohd Hamdi, WanJeffrey Basirun (University of Malaya, Malaysia); AliZaini Abdullah, NorAkmaliza Rais (MIMOS Berhad, Malaysia)
Label free, reagentless and on-site analysis of phosphate ion concentration using electrochemical method has been of tremendous interest in recent years. Potentiometric based phosphate sensor by exploiting cobalt (Co) mixed potential corrosion in phosphate contained water samples has been considered as a promising solution. Mixed potential corrosion occurs when a nonequilibrium state exists at the electrode surface involving two or more electrochemical reactions. In this reaction, slow oxidation of Co and simultaneous reduction of both oxygen and Co2+ occur at the surface of electrode. This paper presents an investigation of annealing treatment on Co surface properties and its sensing response toward different phosphate concentration. Co thin film was prepared by radio frequency sputtering in room temperature and annealed in oxygen and hydrogen plasma at temperature range between 200 deg C to 500 deg C. Cobalt surface morphology, chemical composition and crystal structure after annealing treatment were analyzed using FESEM, EDX, XRD while its phosphate sensing response properties were investigated using cyclic voltammetry, linear polarization and electrochemical impedance spectroscopy (EIS). Based on the results, effect of annealing in oxygen and hydrogen plasma has a significant effect in cobalt sensing response toward phosphate concentration.
Time Period WeM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF2014 Schedule