ICMCTF2015 Session G3: Coatings Pre-/Post Treatments

Thursday, April 23, 2015 8:00 AM in Room Sunset

Thursday Morning

Start	Invited?	Item
8:00 AM		G3-1 Duplex Electron Beam Surface Treatment and PVDHard Coating - the Key for Wear-resistant Cast Irons and Al Alloys Rolf Zenker, Anja Buchwalder, Anne Jung, Erik Zaulig (TU Bergakademie Freiberg, Germany) PVD hard coating of steels is a well-known surface technology for significantly improving friction and wear behavior. In principle, hard coating can also be carried out on cast irons and Al alloys, but due to the insufficient load-supporting capacity of the soft base materials, i.e. of the microstructural constituents, this technology is inapplicable for wear protection of cast iron and Al alloys. This paper deals with research activities into using electron beam (EB) liquid-phase surface treatments both without additives (remelting) and with additives (alloying) to improve the conditions for the deposition of thin PVD hard coatings on these different groups of materials. The EB remelting of cast irons is already used for wear protection on an industrial scale. The ledeburitic microstructure of the remelted layer led to increased hardness up to a value of 700 HV0.1. Moreover, EB alloying using Ni-based additives allows the generation of a broad range of different microstructures, with hardness values ranging from 400 to 900 HV0.1. The specific layer thickness (0.3 to 1 mm) depended on the energy input. The graphite was eliminated in the layer transformed by the EB, and complete coverage with PVD coatings could be achieved. In the case of Al alloys, the EB alloying was carried out using Co-based additives. The hardness of the layers could be increased up to 400 HV0.1, with thicknesses between 0.5 and 1.0 mm. Comparative studies of single (PVD hard coating of base materials) and duplex technologies (EB surface treatment with subsequent PVD hard coating) were carried out. The different load capacities resulting from the surface treatments were investigated, and the hardness, friction behavior, and wear behavior (ball-on-flat test) were measured. Apart from the influence of the EB layer configurations, the effect of different PVD coatings (TiN, TiAlN, TiCN) was taken into consideration. Special attention was focused on the influence of the temperature-time cycles during the subsequent PVD hard coating on the different material-specific microstructures and hardness values of the EB-treated layers. In addition, the research activities were focused on specific aspects and effects of the chemical composition directly at the material surface on the formation, roughness, and adhesion of the PVD coatings, especially in the case of the Al alloys. For this purpose, XPS analyses and scratch tests under increased loading conditions were performed. Through a combined duplex EB surface treatment and PVD hard coating, cast irons and Al alloys can be used for applications with high demands in relation to friction and wear.
8:20 AM	Invited	G3-2 Pre-treatments and Post-treatments of Hard Coatings for Better Performance Saleh Abusuilik, Junichi Nishida (Hitachi Metals, Ltd., Japan) Hard coatings deposited using cathodic arc evaporation are widely used in forming and cutting tools industry. The hard coatings show good tribological and mechanical properties, which have improved the working life and performance of such tools. Nevertheless, improving coating adhesion and surface roughness are among the main challenging issues of the coatings. In this regard, pre-treatment and post-treatment processes, including variety of plasma and mechanical treatments are commonly used to enhance coating adhesion and surface roughness. In this talk, pre-treatment and post-treatment methods used for hard coatings will be reviewed with concentration on industrial applications. Particularly, plasma nitriding and etching, shot peening, and micro-blasting finishing were studied and their role in improving adhesion and performance of CrN-based coatings were evaluated. In addition, tribological properties of the coatings were evaluated using ball-on-disk tests. Likewise, adhesion properties of the coatings were examined using HRC indentation and scratch tests. Furthermore, corrosion and erosion resistance of the coatings were tested in corrosive environments, including acidic aqueous solutions and molten aluminum. We found that plasma nitriding and intermediate post-treatment improved corrosion and erosion resistance of coated components against H₂SO₄ aqueous solutions and molten aluminum. Shot peening and micro-blasting finishing improved adhesion of the coatings. In conclusion, pre-treatments and post-treatments of hard coatings showed good solutions for better performance of the coatings.
9:00 AM		G3-4 Effect of Surface Roughness on Galling Behaviour of Steel on Hard Coatings Thomas Klünsner, Florian Zielbauer, Stefan Marsoner (Materials Center Leoben Forschung GmbH, Austria); Martin Deller (Fritz Schiess AG, Switzerland); Marcus Morstein (PLATIT AG Advanced Coating Systems, Switzerland) Galling, the transfer of workpiece material to tool surfaces, is an important factor known to influence both wear behaviour and loading conditions of metalworking tools such as deep-drawing, blanking or fine blanking punches or dies. In the current study, the states of a range of technically rough surfaces coated by AlCrN-based thin films using rotating cathodes arc evaporation PVD were characterized with regard to their galling behaviour. Furthermore, the influence of common post-treatment methods such as blasting or polishing on the early stages of galling of mild steel on coated surfaces was investigated in detail. Repeated dry-sliding contact, such as tool surfaces do encounter during operation, was physically simulated by a carefully selected ball-on-disc test setup with an applied contact pressure resembling the conditions between a steel sheet and the lateral surface of a fine blanking punch. The initial stages of galling were investigated by comparison of the development of the friction coefficient and the morphology of early iron adhesions to a range of differently post-treated coating surfaces. Depending on the surface roughness influenced by the applied post treatment method, hard coatings show a distinctively different galling behaviour in unlubricated contact conditions. The current work demonstrates a clear connection between the ratio of peaks to valleys on the investigated surfaces determined by atomic force microscopy and the kinetics of the early stages of galling illustrated by high-resolution scanning electron microscopy.
9:20 AM		G3-5 Enhancement of the Gas Barrier Property of Polypropylene by γ-APS Coating after Plasma Treatment Kazuhisa Tsuji (Keio University, Japan); Akira Uedono (University of Tsukuba, Japan); Atsushi Hotta (Keio University, Japan) The improvement of the gas barrier properties of polypropylene (PP), one of the most frequently used materials in the packaging industry, has been greatly demanded to extend the shelf life of the packaging goods by preventing the rapid degradation of the contents. In this work, the gas barrier property of PP was significantly improved by a factor of 15 through the plasma treatment of gamma-aminopropyltrimethoxysilane (γ-APS), as compared with that of non-treated PP. It was also suggested that the γ-APS was effectively converted into crosslinked SiO_x with high gas barrier characteristics after 60 s plasma treatment. γ-APS coating is one of the silane coupling agents with an amino functional group, which is often used for the complement of coating materials. Here, the γ-APS was spin-coated on the PP substrate (γ-APS/PP) to form 1.4 μm thick film followed by the oxygen plasma treatment to induce the chemical crosslinking. Eventually, the oxygen transmission rate (OTR) of γ-APS/PP was substantially reduced to 61.0 cc/m²/day/atm, whereas that of pure PP was 886.2. The structural analyses were conducted by the positron annihilation lifetime spectroscopy (PALS) and X-ray photoelectron spectroscopy (XPS). The PALS results revealed that S-parameters, which represent the density of vacancies in the structure, were decreased from 0.517 to 0.496 by the oxygen-plasma treatment at the very surface of the γ-APS coating. The S-parameter is directly related with the size of the free volume that is actually connected to the density of the micro-vacancy in the structure, which could become an efficient transmission path for the gas molecules. Thus the smaller size of the free volume at the γ-APS surface could highly be responsible for the improvement of the gas barrier properties of γ-APS/PP. XPS also revealed that the Si and O fractions were increased from 40.2% up to 85.8% after the plasma treatment, indicating the generation of SiO_x networks by the partial cut-off of the amino side-chains in γ-APS. The γ-APS method may highly be a new simplified and low-cost method to expand the industrial utility of PP especially in the packaging food or beverage fields.
9:40 AM		G3-6 Dry-blasting of CVD α-Al₂O₃ Hard Coatings: Influence of Blasting Media Size, Hardness and Coating Texture on the Stress-depth Gradients Investigated by X-ray Nanodiffraction Michael Tkadletz (Materials Center Leoben Forschung GmbH, Austria); Nina Schalk, Jozef Keckes (Montanuniversität Leoben, Austria); Ivan Krajinović (Materials Center Leoben Forschung GmbH, Austria); Christoph Czettl (CERATIZIT Austria GmbH, Austria); Christian Mitterer (Montanuniversität Leoben, Austria) Recently it has been shown that the shape of the blasting media has a considerable influence on the magnitude and depth of the stress gradients introduced by dry-blasting into CVD α-Al₂O₃ hard coatings. Within this work, CVD α-Al₂O₃ coatings grown on cemented carbide cutting inserts were dry blasted with globular Al₂O₃ based blasting media with three different mesh grit sizes (<60 µm, 70 – 125 µm and 125 – 250 µm). In addition, blasting with SiO₂ and ZrO₂ based blasting media and thus different hardness but the same mesh grit size of 125 – 250 µm was performed. Further, α-Al₂O₃ coatings epitaxially grown on sapphire (0001), (112̅0) and (11̅02) substrates resulting in different mechanical properties were dry-blasted with the Al₂O₃ based 125 – 250 µm sized medium. The post treated samples were investigated using synchrotron pencil X-ray nanodiffraction, depth resolved Raman spectroscopy as well as scanning electron microscopy and focused ion beam techniques to determine the influence of the different blasting media size and composition (i.e. hardness) and the coating orientation on the stress-depth gradients. It could be shown that the size and thus, the kinetic energy of the particles significantly affects the depth of the introduced stresses, while the hardness of the medium and the contact radius have a major influence on the shape of the stress gradient. In addition, the experimental results were corroborated by finite element simulations.
10:00 AM		G3-7 Study of the Corrosion Behavior by the EIS Technique over the Surface of Borided and Non-borided AISI 316L Steels Immersed in a Simulated Body Fluid Ivvone Mejia-Caballero (Instituto Politecnico Nacional, Mexico); Manuel Palomar-Pardave (Universidad Autonoma Metropolitana, Azcapotzalco, Mexico); Jose Martínez-Trinidad (Instituto Politecnico Nacional, Mexico); Mario Romero-Romo (Universidad Autonoma Metropolitana, Azcapotzalco, Mexico); Ricardo Perez Pasten-Borja (Instituto Politecnico Nacional, ENCB, Mexico); Claudio Lopez-Garcia, IvánEnrique Campos-Silva (Instituto Politecnico Nacional, Mexico) The corrosion resistance of borided and non-borided AISI 316L steels was evaluated during 10 days of exposure in a simulated body fluid (Hanks’ solution). The boride layer was developed using the powder-pack boriding method at a temperature of 1223 K with 6 hours of exposure. The microstructure of the boride layer over the surface of the steel consisted in FeB/Fe₂B phases with a flat and smooth morphology. Optical microscopy in clear field was used to estimate the thickness of the boride layer; the total boride layer thickness (FeB + Fe₂B + diffusion zone) was approximately 52 ± 1 microns. The corrosion tests were performed over the surface of the non-borided and borided steels using the Electrochemical Impedance Spectroscopy (EIS) technique with a potentiostat (Zahner Zennium equipment) applied a frequency range from 8MHz to 2mHz (6-8 points per decade). After the corrosion tests, the surface of the borided and non-borided steels were analyzed by scanning electron microscopy (SEM), Energy Dispersive X-Ray Spectrometry (EDS) and X-Ray Photoelectron Spectroscopy (XPS) techniques to determine the corrosion mechanisms, the presence of the chemical elements on the surface of the borided and non borided steels, and the quantitative chemical composition of the specimens developed on the surface during the 10 days of exposition in the Hank’s solution. Based in the Nyquist plots estimated from the corrosion tests over the surface of borided and non-borided steels immersed in Hank’s solution during 10 days of exposure, the borided steel provided a reasonable corrosion resistance of approximately 45 KWcm², while the corrosion resistance of the AISI 316 steel reached a maximum polarization resistance of 2138 KWcm². In addition, according to the SEM and EDS results, pitting and crevice corrosion mechanisms were observed on the surface of the non-borided and borided steels respectively, whereas the phosphorus (or phosphates) content over the surface of borided steel increased as a function of the exposure time, and can be related by its low corrosion resistance compared with the values estimated in AISI 316 steel. Finally, equivalent electric circuits (EEC’s) were proposed for the analysis of the resulting impedance data for both borided and non-borided steels immersed in the simulated body fluid during 10 days of exposure.