ICMCTF1998 Session B2: CVD Hard Coatings & Technologies - Plasma & Duplex Coatings, Ion Nitriding & Surface Modifications

Wednesday, April 29, 1998 8:30 AM in Room Golden West
Wednesday Morning

Time Period WeM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF1998 Schedule

Start Invited? Item
8:30 AM B2-1 Duplex TiN Coatings Deposited by Arc Plating for Increased Corrosion Resistance of Stainless Steel Substrate
S. Rudenja, C. Leygraf, J. Pan (The Royal Institute of Technology, SWEDEN); P. Kulu, E. Talimets, V. Mikli (Tallinn Technical University, ESTONIA)

Deposition of the hard coatings onto steel substrate can produce a surface with specific properties such as hardness, wear resistance.

However, corrosion resistance of the coated steel substrate can decrease as a result of galvanic coupling between the substrate and the electrochemically nobler coating. Once it has started, corrosion propagates at the bottom of the structural defects in the coating generally named pinholes or at the interface between substrate and coating.

This interface between the coating and substrate is responsible for adhesion properties and partly also for the high wear resistance of the coated substrate. Besides, the interface can play an important role in corrosion prevention of the coated substrate.

Duplex coating technique performed with arc plating can result in substantial increase of the corrosion performance of the coated substrate. Duplex coatings can be divided into two groups based on the principles by which they are produced: - structure- dense coatings, that are produced by deposition of thick pure metal layer (e.g. Ti) followed by nitriding the surface, - interfacial coating, that are produced by an initial plasma treatment (e.g. nitriding or implantation) of the substrate followed by deposition of the coating. The interface between the steel substrate and the coating consists of plasma treated upper layer of the substrate and an interlayer between substrate and coating.

This paper presents a study of corrosion performance of duplex coating in different aqueous solutions. The coatings were produced in one set in an arc plating PVD- plant. Electrochemical evaluation of the coating was done by polarization methods and electrochemical impedance spectroscopy (EIS).

T. Michler (Fraunhofer Institute for Surface Engineering and Thin Films, Germany); J. Vetter (Metaplas Oberflaechenveredelungstechnik GmbH, Germany); H. Steuernagel (Hartmann Armaturen KG, Germany)
The combination of thermochemical heat treatment (e. g. nitriding or carburizing, with or without plasma enhancement) and hard coating (e. g. TiN, CrN) is known as „duplex treatment“. It offers the possibility of improving the functional properties of tools and machine parts compared to a mono treatment. The combination of plasmanitriding and PVD hard coating has been investigeted by various groups mostly for the increase of the wear resisrance of tools. However, machine parts seem to be very promising candidats for duplex treatments, especially when they are made of soft steels such as stainless steels. This paper will show that functional behaviour of duplex treated parts are both determined by the application oriented optimization of the thermochemical heat treatment and by the selection of the appropriate hard coating. The hard coatings include Titanium Nitride (TiN), Chromium Nitride (CrN) and Diamond Like Carbon (DLC). For demonstration this paper is focused on the valve steel X20Cr13 but includes also some information about similar procedures when applying duplex coatings for forming tools and gears.
9:10 AM Invited B2-3 Low Pressure, High Density Plasma Nitriding. Mechanisms, Technology and Results.
H.M Michel, T.C Czerwiec (Laboratoire de Science, France); E. Bergmann (Ecole d'Ingenieurs de Geneve, Switzerland)

Plasma nitriding is now widely used in manufacturing for surface hardening of ferrous and non ferrous materials. For that purpose, plasma generation is most frequently fulfilled by a dc glow discharge with the underlying limitations associated with this technology. First, the temperature of the substrate to be treated is strongly coupled with the discharge parameters that control the plasma reactivity and secondly, the processing pressure is relatively high (100-1000 Pa). Nevertheless, more flexibility and control are required for plasma nitriding of promising non-ferrous materials such as titanium, aluminium and their alloys. In the case of aluminium, low temperature and low pressure nitriding processes associated with high plasma reactivity are necessary.

These requirements are fulfilled by the recently developed enhanced or intensified plasma nitriding processes such as : triode arrangements, electron cyclotron resonance microwave plasma or high current, low voltage thermionic arcs. The purpose of this paper is to review these new nitriding processes from both technological and fundamental point of view. Particular attention will be paid to the metallurgical results obtained on austenitic stainless steels, titanium and aluminium.

9:50 AM B2-5 Influence of Sample Geometry on the Effect of Pulsed Plasma Nitriding of M2 Steel
G. Nayal (Aleppo University, Syria); D.B. Lewis, W.-D. Münz (Sheffield Hallam University, United Kingdom); J.E. Cockrem (ELTRO (GB) Limited, United Kingdom)
A comparison of pulse plasma nitrided flat coupons and complex shaped substrates such as twist drill test bits shows that the incorporation of nitrogen depends strongly on the substrate geometry. GDOES depth profiling and cross sectional WDX analyses show that the amount of nitrogen incorporated into the treated substrate might increase up to a factor of two, when flat coupon surfaces and sharp cutting edges are nitrided under identical plasma conditions. In fact, the observed increase of hardness reaches a level of Hk 1500 (base hardness HK 870) in the investigated cutting edge compared to HK 900 (base hardness HK 750) in the corresponding flat coupon measured at a depth of typically 10 μm. Bragg-Brentano XRD, SEM and optical microscopy analyses confirmed that under the used process conditions the formation of the adhesion reducing compound layer γ' CAN BE COMPLETELY SUPPRESSED. The findings clearly imply that caution must be exercised when extrapolating observations made using flat coupons to those of geometrically more complex cutting tools, eg. On twist drills.
10:10 AM B2-6 Observation of Three-Dimensional Orientational Anisotropy in an Ion Nitrided Surface Layer (m) on Stainless Steels
K. Marchev (Northeastern Uiversity); R. Hidalgo, M. Landis, R. Vallerio (Northeastern University); C.V. Cooper (United Technologies Research Center); B.C Giessen (Northeastern University)
The structure of the compound layer is of great significance for the properties of plasma nitrided samples. This is especially true for stainless steels where precipitation of chromium nitride may significantly affect some surface properties including the corrosion resistance. Following our earlier work on the formation of a nitrogen-rich single-phase compound layer (m phase) with gradually changing nitrogen concentration, lattice parameter and microhardness characteristics, we report here the observation of strong preferred orientation in those layers by pole figure studies. The key finding is the unexpected existence of an in-surface orientational anisotropy in the m phase layer, besides the more readily expected normal-to-surface anisotropy. These results may be of significance in terms of the mechanical anisotropy of compound layers. The m-phase layers are well-attached to the base material and have good mechanical (especially tribological) properties.
10:30 AM B2-7 The Use of Intensified Plasma-Assisted Processing to Enhance the Surface Properties of Ti-6Al-4V
E.I. Meletis (Louisiana State University); C.V. Cooper (United Technologies Research Center); K. Marchev (Northeastern University)
Intensified Plasma-Assisted Processing (IPAP) is a surface-modification technique developed recently in our laboratory. The technique can combine plasma-diffusion treatments with chemical-reaction synthesis. Plasma intensification is accomplished by using a triode glow discharge at low pressure. The present work focuses on applying this technique to achieving enhanced plasma nitriding of Ti-6Al-4V, a common aerospace alloy, at relatively low temperatures. The microstructures of specimens nitrided at various energetic plasma conditions have been characterized and studies conducted to investigate the growth kinetics and resulting properties. Pole-figure analysis has been performed to investigate the development of preferred orientations within the nitrided layers. IPAP-treated specimens exhibit high surface hardness values and a microstructure consisting of a TiN outermost layer, a Ti2N intermediate layer, and a nitrogen-diffusion inner zone. Tribological experiments have shown that the new plasma nitrided surfaces possess significantly higher wear resistance and lower coefficient of friction.
10:50 AM Invited B2-8 Microwave Plasma Technology for Processing of Materials
R. Gat, W. Holber (Applied Science and Technology/ASTeX Inc.)
Microwave plasmas enable a broad range of advanced materials processing including deposition, etching and surface modifications. Material systems include metals, nitrides, carbides and complex oxides. Four types of microwave sources will be discussed. Electron cyclotron resonance (ECR) sources for operation at low pressure (mTorr), downstream sources (Torr), cavity sources (10?s to 100?s of Torr), and microwave torchs for operation at atmospheric pressure. A brief review of each type of source will be presented and selected applications for each will be discussed. Recent exciting developments of a high density ECR plasma based sputtered ion source will be highlighted. The source provides high and uniform ion fluxes with low energy (20-40eV) at the substrate. Initial applications include AlN, cBN, GaN, SiC, DLC and YBCO.
11:30 AM B2-10 Dependence of Diamond-like Carbon Film Properties on Ion Energy in Plasma Deposition
A.D. Glew, M.A. Cappelli, R. Saha (Stanford University)

Many researcher have written that the incident ion energy during chemical vapor deposition(CVD)of diamond-like carbon (DLC) effects the resulting properties. Workers effect film properties such as hardness, density, intrinsic compressive stress, and refractive index by varying the processing parameters. However, there is little agreement as to the actual ion energy during DLC deposition in self-biasing plasma chambers. Ion energies are difficult to estimate at higher operating pressures, because the energetic ions collide with low energy neutral species in the plasma sheath resulting in a broad distribution of energies. Stated ion energies for similar films range from 60 to 1200 eV 1,2,3. Some authors measure only bias voltage Vb, which is not an accurate measurement of ion energy Ei. Others estimate ion energy with electrical impedance measurements. In this work, the plasma and process chamber are characterized by the method of impedance analysis. The impedance analysis 1 predicts a variation in ion energy that is linear with applied power. Alternatively, another model2 predicts the bias voltage to vary with Power1/2Pressure-1/2. The relationship between a film property and two different processing parameters, bias versus ion energy, may well show different trends. There are other ion energy, flux and momentum measurements that are also meaningful. In this work, deposition pressure and power are varied to show dependence of ion energy and bias on processing conditions. Once the processing parameters are characterized, the processing conditions are systematically varied. Pressures are controlled from 400 to below 1 mTorr in order to achieve both collisional and non-collisional plasma sheaths respectively. Without collisions, ions strike the substrate with Ei=aVb. The films are analyzed for stress,hardness and density. Also, Raman spectrum are presented.

1 J. H. Lee, D. S. Kim, Y. H. Lee, B. Farouk, J. Electrochem Soc., 4,1451 (1996). 2 Y. Catherine, P. Couderc, Thin Solid Films, 144 265 (1986). 3 D. R. Mckenzie et al., Diamond Relat. Material, 51(1991).

11:50 AM B2-11 PACVD Thin Flms : DLC and SiOx Coatings Obtained by Low Frequency PACVD
F. Schuster, S. Anderbouhr, C. Chabrol, G. Piet, L. Filhol (CEREM/DEM/SGM, France)
DLC and SiOx coatings have been performed by Plasma Enhanced Chemical Vapour deposition (PECVD) using a pilot-scale reactor. A parametric study has been carried out in order to study the tribological behaviour and the corrosion protection of these coatings. Process control is studied with mass spectroscopy. PECVD technology provides coatings with good metallurgical quality on complex shapes industrial parts.
12:10 PM B2-12 Deposition Processes for DLC Coatings with a Great Potential for Upscaling
T. Michler, M. Grischke, K. Bewilogua, H. Dimigen (Fraunhofer Institute for Surface Engineering and Thin Films, Germany)
For engineering applications, diamond like carbon films (DLC) are the most suitable coatings, when high wear resistance and low friction is needed. One problem is their very poor adhesion on steel substrates when no intermediate layer is supplied. The most common method to deposit DLC is radio frequency PACVD (RF, 13.56 MHz), which is technically difficult and expensive to scale up to industrial dimensions. Our institute is testing different methods for plasma excitation with a great potential for upscaling. In this paper the deposition of DLC coatings by Low Frequency PACVD (LF PACVD) at pressures of several 100 Pa is presented. The parameters are very similar to the well known and industrialized plasmanitriding process. Cold work steel was used as substrate material. The experiments were carried out in a commercially available plasma nitriding plant. The adhesion was improved by an intermediate Si-C:H layer with tetramethylsilane as a precursor. Methane was used for depositing the DLC films. The mechanical properties of the films such as hardness, Young´s modulus, and wear resistance were studied as a function of the process parameters such as bias current, pressure and methane flow. The properties thus obtained are comparable to those by RF PACVD. The potential for upscaling and duplex processing is clearly demonstrated.
Time Period WeM Sessions | Abstract Timeline | Topic B Sessions | Time Periods | Topics | ICMCTF1998 Schedule