ICMCTF2006 Session B5: Surface Pre-Treatment, Coating Post-Treatment and Duplex Technology

Wednesday, May 3, 2006 1:30 PM in Room Royal Palm 1-3

Wednesday Afternoon

Start	Invited?	Item
1:30 PM	Invited	B5-1 Combination of Coating and Heat Treatment Processes O. Keßler (Stiftung Institut fuer Werkstofftechnik, Germany) For a proper use of coated tools and components excellent coating properties as well as excellent substrate properties of the coating/substrate compound are necessary. A well known example is the load support of hard steel substrates for thin wear resistant coatings. Therefore coating processes must be combined with heat treatment processes of the substrates, whereby several constraints like order and compatibility of the processes must be considered. The combination of CVD-coating plus laser beam hardening is an example of a post coating heat treatment. Applications may be possible for large forming tools made of high alloyed tool steels, which nowadays are usually through hardened after CVD-coating. Laser beam hardening offers the possibility, to harden only the highly loaded edges of the tools. The advantages of this combination are short process time, less distortion and compressive residual stresses in the substrate surface. CVD-coatings can endure laser beam hardening with suitable parameters. The influence of several CVD TiN-coated steel substrates and laser beam hardening parameters on microstructures and properties of coating/substrate compounds have been investigated. Special attention was paid to overlapping hardening zones, which may occur at the start respectively end point of a laser hardened track. The combination of case hardening plus DLC-coating is an example of a pre coating heat treatment. Applications may be possible for gears with dry lubricants. Microstructures and properties of case hardened and DLC-coated steels have been investigated. Summarizing, the combination of coating and heat treatment processes show a high potential to produce coating/substrate compounds with excellent coating properties as well as excellent substrate properties.
2:10 PM		B5-3 Study on the Effects of Microblasting on the Topography of Cemented Carbide Tools H.-G. Fuss, R. Cremer (CemeCon AG, Germany); A. Atiser, J.M. Schneider (RWTH Aachen University, Germany) Microblasting is a widely used method to treat tool’s surfaces prior to a subsequent coating process. It is well known that the surface roughness and the coating’s adhesion behavior is affected by the pretreatment conditions. In this work the influence of different microblasting techniques and pretreatment conditions on the topography of cemented carbide tools is studied by means of atomic force microscopy (AFM) using a Hysitron TriboIndenter. Correlations between the blasting pressure and the final surface topography are discussed and their relevance for coating adhesion is analyzed.
2:30 PM	Invited	B5-4 Surface Pre-Treatment and Duplex Technology F. Mumme, M. Pimenta (Balzers VerschleiBschutz GmbH, Germany) Tool-surfaces for molding and forming processes require more durability and performance to optimize customers benefit. New tool-materials, post treatments and coatings more and more used to fulfil the demands of the enduser- and toolmaker-industry. Standard hardening processes of specified toolsteel in combination with dedicated PVD-coatings improve the tribological properties and wear resistance of cold forming tools. Higher loads in forming processes e.g. cold forging, semihot forging or diecasting require improved steelgrades and additional posttreatments to increase the durability of coated surfaces. Nitriding-processes lead to a graded in hardness between hardened steel substrate and hardcoated surface. The analysis of steel grades (alloying) nitriding process (white – layer, dept of nitration) and coating process (duplex) define the most promising steps to processing.
3:10 PM		B5-6 Duplex Plasma Nitriding and Nanostructured TiAlN/CrN PVD Coating G. El Nayal (Institute of Materials Research, United Kingdom) A modified industrial sized multi arc/ unbalanced magnetron sputtering process was utilized for conducting duplex lower pressure (5-10x10^-3 mbar) plasma nitriding and nanostructured TiAlN/CrN PVD coating of M2 high speed steel (HSS) and 304 austenitic stainless steel twist drills and flat coupons. A similar duplex treatment was performed using conventional higher pressure (2-5 mbar) plasma nitriding prior to PVD coating using the same multi arc/ unbalanced magnetron sputtering process. Characterizing techniques used during this investigation included optical emission spectrometry, microhadness, adhesion, GDOES, X-RD, WDX, SEM and TEM. In the lower pressure nitriding, the reduced intensity of the nitriding species (N²⁺ and N⁺) at lower pressure combined with their increased diffusivity in the martensitic lattice of M2 HSS, relative to the austenitic lattice of 304 austenitic stainless steel, has resulted in a reduced nitrogen gradient in the diffusion layer. In contrast, the abundance of the nitriding species during higher pressure plasma nitriding together with their reduced diffusivity in the austenitic lattice of 304 austenitic stainless has readily resulted in the formation of nitride compound layer in addition to the diffusion layer with relatively steep nitrogen gradient. Dry cutting trials performed on EN9 steel demonstrated that optimum cutting results are obtained when the surface nitrogen content prior to coating is 4-8 at% and the depth of the diffusion zone is 10-25 μm. Cutting results also shown that the presence of the nitride compound layer prior to coating is unfavorable. This was attributed to the reduced substrate to coating adhesion due to the denitriding of the compound layer.
3:30 PM		B5-9 The influence of Substrate Preparation on the PVD Coating Graded Zirconium Carbide (ZrCg) K. Bobzin, E. Lugscheider, O. Knotek, N. Bagcivan (RWTH Aachen University, Germany); N. Goebbels (Surface Engineering Institute, Germany) Today tribological thin films are increasingly used on machine components. The PVD coatings chromium aluminum nitride (CrAlN) and graded zirconium carbide (ZrCg) have shown a big potential as tribological coatings. They are applied with magnetron sputter ion plating (MSIP) processes. Two different versions of ZrCg (ZrCg06, ZrCg09) with different property distributions along with CrAlN are investigated in this paper. AISI 4140 a typical material for components is used as substrate. Four different pre-treatments are applied to substrates. Annealing, tempering at 200°C and 500°C and plasma nitriding resulted in different hardnesses. It is shown that all variations revealed a good adhesion to the substrates. Tribological tests are performed in a ball on disk tribometer and an impact tester. The impact tests show clearly that tribological behaviour is correlating with the substrate hardness. Especially soft substrates which are annealed or tempered at 500°C show spherical calottes with great diameters. In the ball on disc tests all coatings show advantages to the uncoated substrates. In these tests the friction rate and the wear rates are reduced. The PVD coating ZrCg09 shows best properties in these tests.
3:50 PM		B5-10 Improvements on the Wear Resistance of High Thermal Conductivity Cu Alloys Using an Electroless Ni-P Coating Prior to PVD Deposition J.C. Avelar-Batista, E. Spain, M. Letch, J. Housden, R.N. Turner (Tecvac Ltd., United Kingdom); R. Beechey (Copperplas, United Kingdom) An attempt to improve the load support for hard PVD coatings on soft Cu alloys has been made by using a medium phosphorous content electroless Ni-P coating prior to PVD deposition. Several PVD coatings, including TiN, CrN, CrAlN, multilayered CrAlN, WC-C, multilayered CrAlN/WC-C were deposited onto an Ampcoloy 940 Cu alloy in two conditions: "standard" and electroless Ni-P plated. The effect of the electroless Ni-P coating on the coating/substrate performance was evaluated by pin-on-disc wear and impact tests. Nanohardness and surface roughness measurements were also used to characterise the resulting coating/substrate systems. The electroless Ni-P coating reduced the wear rates of the PVD-coated Cu alloys and increased the impact wear resistance. Among the PVD coatings trialled, CrN, CrAlN and multilayered CrAlN coatings on electroless Ni-P provided the lowest wear rates.
4:10 PM		B5-11 Effect of Heating Post-treatments on Nitrided Stainless Steel V.H. Baggio-Scheid, A.J. Abdalla, G. de Vasconcelos (Aerospace Technical Center, Brazil) In this work we investigate the structure and properties of plasma nitrided AISI 316 stainless steel after heating post-treatments. The samples were nitrided at 823 K during 3 h. After nitriding, heating post-treatments were made in a vacuum furnace. The influence of the heating time, ranging from 1 up to 16 h, and heating temperature, varying from 732 up to 873 K, on the surface properties was investigated. The samples were characterized using microhardness testing, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The nitriding treatment results in a compound layer of 44 mm with a hardness of 1420 HV0.1, consisting predominantly of γ [Fe4N] and CrN phases. As expected, an increase of the compound layer thickness and a decrease of the surface hardness with heating time were observed. However, the microhardness profiles shown that beneath the surface the layer hardness increases for long treatment times. New phases as Fe₃O₄ and FeCr₂O₄ appear and grow with increasing heating time.
4:30 PM		B5-13 Modeling, Production and Characterization of Duplex Coatings (HVOF and PVD) on Ti6Al4V Substrate for Specific Mechanical Applications E. Bemporad, M. Sebastiani, F. Carassiti (University of Rome, Italy); F. Casadei (Centro Sviluppo Materiali (CSM) SpA, Italy) Titanium and its alloy are extensively used in aerospace and mechanical application for its high specific strength and high fracture toughness. On the other hand, titanium alloys often show low hardness, very low load bearing capacity and poor resistance to sliding wear, so that a coating procedure is in many cases recommended, often by PVD processes. Present work deals with design, production and characterization of a duplex coating procedure, consisting in a thick HVOF WC-Co interlayer, followed by a CA-PVD deposition (multilayer Ti/TiN). The system was tested on crankpins used in high performances automotive applications. Before depositions, the contact stress field under spherical indenter have been analytically evaluated, obtaining a numerical evaluation of the load bearing capacity of the layered structure, and a finite element simulation of residual stress has been also performed, obtaining information about interfacial stress field: basing on simulations performed a thickness of 250 µm and 3 µm have been chosen for the HVOF and PVD coatings respectively. Mechanical properties of the coatings were investigated using Rockwell indentation test, micro indentation techniques and composite hardness modelling in order to obtain superficial hardness. By coupling Knoop micro-indentation, AFM analysis, Young modulus of the coatings have been evaluated. Wear rate of the coatings was measured using an implemented rotating wheel method, using the Archard model: abraded volumes were then measured with a stylus profilometer. Residual stress have been measured by means of x-ray diffraction (sin²ψ method), as a validation of the FE simulations performed. Finally corrosion rate was evaluated by salt spray technique. Results show high composite properties: high hardness, high coating adhesion, low wear rate, good corrosion resistance, making such a system particularly indicated for high performances mechanical applications.