ICMCTF1999 Session B1-3: Hybrid and Sputter PVD Techniques and Coatings

Tuesday, April 13, 1999 1:30 PM in Room Golden West

Tuesday Afternoon

Start	Invited?	Item
1:30 PM		B1-3-1 The Incorporation of a Plasma Nitriding Treatment in an Industrial Scale PVD Equipment for Tool Coating G. Nayal, D.B. Lewis, P. Walke, W.-D. Münz (Sheffield Hallam University, United Kingdom) A newly developed low pressure plasma nitriding method (i.e. 8 x 10^-3 mbar) which is implemented within a PVD coating unit and an independent conventional pulse plasma nitriding process ⁽¹⁾ have been used to nitride both M2 high speed steel twist drills and flat coupons prior to subsequent deposition of a 3 µm TiAlCrYN PVD coating. Dry cutting data of pulse plasma nitrided and coated drills has shown that optimum results can be achieved when the surface nitrogen content and case depth in coupons, simultaneously nitrided with the drills, was between 4.5 and 5.5 at % and approximately 13 µm respectively. Both the surface nitrogen content and the case depth were closely matched to those obtained for the pulse plasma nitriding process when nitriding was carried out using the new process over a similar process duration i.e. 30 mins. This resulted in surface hardness (HK_0.01) of 1409-1455 for pulse plasma nitrided coupons compared with (HK_0.01) of 1310 for the newly developed low pressure nitriding process. However, unlike the conventional pulse plasma nitriding process which uses both nitrogen and hydrogen, only nitrogen was used during the latter method because of the relatively low nitrogen pressure and extremely efficient ionisation available in the newly developed process. This work compares the use of prior low pressure plasma and conventional pulse plasma nitriding treatments on the cutting performance of PVD coated TiAlCrYN twist drills. (1) G. Nayal D. B. Lewis M. Lembke and W.-D. Münz, Influence of Sample Geometry on the Efffect of Pulse Plasma Nitriding of M2 Steel, accepted for publication in Surface and Coating Technology.
1:50 PM		B1-3-2 Effects of Ar Pressure on Ion Flux Energy Distribution in Rf-plasma Assisted Magnetron Sputtering E. Kusano, T. Kobayashi, T. Saitoh, S. Saiki, K. Fukushima, N. Kikuchi, H. Nanto, A. Kinbara (Kanazawa Institute of Technology, Japan) An rf-plasma assist to conventional sputtering is an attractive technique to enhance ion fraction of metal particles passing through the plasma to the substrate region. In this process a dominant mechanism of metal ionization is thought to be Penning ionization. In the conventional sputtering plasma, increasing Ar pressure generally increases the probability of the Penning ionization. Thus, in the rf plasma assisted sputtering as well as in the conventional sputtering, increasing Ar pressure is thought to further increase the ion fraction of the sputtered metal. In this experiment, effects of Ar partial pressure on ion energy distribution and the number of metal ions have been investigated. The experiments have been performed by using a 55mm dia. Ti magnetron cathode and a 60mm dia. copper inductively coupled rf coil. The ion energy distribution of the depositing flux was measured by an energy-resolved mass spectrometer. Ar partial pressure was varied from 0.1 to 4.0Pa for a constant cathode current of 0.3A and a constant coil rf power of 200W. The experimental results show that the number of Ti⁺ ions increases with Ar pressure whereas that of Ar⁺ ions decreases. Further it was found that the mean energy of both Ar⁺ and Ti⁺ ions decreases with Ar pressure in conjunction with the plasma potential. These results suggest that the number of Ti⁺ ions increases with Ar pressure as a results of the increase in the probability of the Penning ionization of Ti atoms and that the number of Ar⁺ ions decreases as a result of the decrease in the probability in the electron impact ionization of the excited Ar atoms.
2:10 PM		B1-3-3 The Development of a Functionally Graded TiC-Ti Multilayer Hard Coating. I. Dahan (Colorado School of Mines); U. Admon, N. Frage, M.P. Dariel (Ben-Gurion University of the Negev, Israel); J.J. Moore (Colorado School of Mines) A functionally graded transition zone between a hard TiC coating and a WC-Co substrate, e.g., a cutting tool, can be formed by taking advantage of the stability range of the titanium carbide phase that extends from TiC_0.5 to TiC. The transition zone is formed by sputter deposition of a multilayer stack of nanometric TiC and Ti layers. The composition gradient within the carbide layer is generated by varying the relative thickness of the as-deposited Ti and TiC layers within the stack. A subsequent short diffusion treatment eliminates the interfaces between the adjacent layers yet maintains an overall carbon composition gradient across the thickness of the coating. The relative thickness of the individual sputtered layers is adjusted to yield a low carbon composition in the coating close to the substrate and a stoichiometric composition near the external surface. The composition profile within the coating can be further optimized with respect to residual stresses that arise during cooling after the diffusion anneals. In this approach, different graded coatings of Ti-TiC multilayers were deposited on WC-Co substrates in two steps. This two steps process involved, find the deposition of 0.5µm graded Ti-TiC multilayers followed by a 2.5µm outer layer of stoichiometric TiC. The relevant diffusion parameters were obtained by x-ray diffraction study of the structural evolution in a multilayer stack with uniform layer thickness, as a function of the temperature and the duration of the diffusion anneal. The connection between the tribological properties and the different graded composition profiles will be presented.
2:30 PM		B1-3-4 Deposition of BN:C Films Using a B₄C Target M.U. Guruz, V.P. Dravid, Y.-W. Chung (Northwestern University) Boron Nitride films on Si (001) substrates were deposited by dc magnetron sputtering using a conducting B₄C target. Ion bombardment of the substrate was accomplished through pulsed dc biasing of the substrate. At low temperature and substrate bias, the films have the turbostatic boron nitride (t-BN) structure as evidenced by transmission electron microscopy. A strong preferred texture is observed in the films with the basal plane aligning parallel to the growth direction. Nanoindentation measurements indicate these films have a hardness in the 25-30 GPa range. The films are highly insulating (ρ˜10¹⁰ ohm.cm) and smooth (surface roughness ˜1Å rms). When the ion bombardment was enhanced by increased substrate bias, evidence of cubic boron nitride (c-BN) was found.
2:50 PM		B1-3-5 Deposition and Characterization of Ti-B-N Coatings M.S. Wong (National Dong Hwa University, ROC); Y.C. Lee, K.Y. Hsiao (National Dong Hwa University, Taiwan, ROC) Ti-B-N and TiB2 single-layer films as well as TiB2/Ti and Ti-B-N/TiN nanolaminates on various substrates were prepared using dc-magnetron sputtering technique. The structure and properties of the films were affected by several reactive sputtering process variables such as substrate bias and total pressure and by the substrate materials. Well-crystallized TiB2 films with strong (0001) texture and with hardness up to 44 GPa were produced. Small amount of nitrogen doping into TiB2 films enhanced their crystallinity, but excessive amount of nitrogen rendered amorphous films of lower hardness. However, Ti-B-N/TiN nanolaminates with high hardness up to 43 GPa were prepared and their hardness values are affected by nanolaminate period. The structure, morphology, stress and tribological properties of the coatings will be presented.
3:10 PM		B1-3-6 Study of the Thermal Stability of Some Hard Nitride Coatings Obtained by Reactive Magnetron Sputtering C. Heau, F. Vaux (Hydromécanique et Frottement, France); R.Y. Fillit (Ecole des Mines de St-Etienne, France) In this study hard nitride coatings including Cr₂N, CrN, TiN, TiBN and TiAlN were deposited by reactive magnetron sputtering. High temperature X-ray diffraction (HTXRD) on vacuum condition of 10^-3 Pa was performed from room temperature to 1100°C. With HTXRD measurements, the temperature of re-crystallization for amorphous coatings and the temperature for transformation or decomposition of phases have been determined, then the kinetics of oxidation and grain growth have been calculated. Correlation with thermal gravimetric analysis on coatings deposited on alumina substrate pre-coated with Cr was used to determine accurate oxidation temperature. The mechanism of coating transformation as a function of temperature have been developed for each type of coating. Chromium nitride coatings are metastable, showing crystallization of Cr or decomposition of CrN into Cr₂N. TiBN coatings have the highest thermal stability, grain growth and decomposition were observed only over 900°C and no oxide was detected after thermal treating under vacuum up to 1100°C. Finely, thermally treated coatings in air for 2 hours at 400, 600 and 800°C were characterized by scratch test and hardness testing. The variation of mechanical properties as a function of temperature have been correlated with grain growth and microstructure transformation.
3:30 PM		B1-3-7 Temperature Dependence of Inductively Coupled Plasma Assisted Growth of TiN Thin Films W.J. Meng, T.J. Curtis (General Motors R&D Center); L.E. Rehn, P.M. Baldo (Argonne National Laboratory) The use of low pressure high density plasmas to assist the synthesis of ceramic thin film materials is in its infancy. We have constructed a laboratory scale inductively coupled plasma (ICP) assisted magnetron sputtering system. Using such a system, we examine the dependence of plasma-assisted growth of TiN thin films on growth temperature and the ratio of ion to neutral atom flux. We show that a temperature independent densification of TiN films occurs above a certain ion to neutral atom flux ratio. As an example of this temperature independent densification, we demonstrate the formation of dense B1-TiN crystalline thin films at growth temperatures down to 100K. The effect of growth temperature on the concentration of residual lattice defects in TiN films will also be examined.
3:50 PM		B1-3-8 About the reactive High Ion Sputtering (H.I.S.^TM) of Cristalline Al₂O₃ with Pulsed dc and r.f. PVD-process Technique G. Erkens, T. Leyendecker, R. Wenke, H.-G. Fuss, H. Thelen (CemeCon, Germany); I. Rass, M. Feldhege (Euromat, Germany); R. Cremer (RWTH Aachen LTH, Germany) The increased power and current density of the High Ion Sputtering (H.I.S.^TM) PVD process technique leads to efficiency-increasing refractory coatings. For ternary coating systems based on (Ti,Al)N a further improvement can be achieved by reactive sputtering of Al₂O₃ toplayers or oxygenous interlayers. Thermal CVD-Al₂O₃ coatings on cutting tools are distinguished by high thermal stress due to the high deposition temperature of approximately 950°-1100°C. To avoid thermal mismatch and thus crack formation lower deposition temperatures are required. The modern sputtering process modules of the PVD-system CC800^TM open up the opopertunities to deposite fine-grained crystalline Al₂O₃ at a temperature range of 500°-800°C. The pulsed dc module and the r.f. module are illustrated. The investigated coatings were deposited reactively by sputtering aluminium and controlled addition of oxygen. Both modules were campared in view of stability, process parameters and the resulting coating quality. To run the pulse module different approaches to this were selected and amounted to variations of the pulse mode and the cathode arrangement. The deposited coatings were evaluated by metallographical examinations (microhardness, film thickness, adhesion, structure (SEM, X-ray defraction) etc.). The illustrated results will show the potential of the H.I.S.^TM process modules for pulsed dc and r.f. magnetron sputtering of cristalline Al₂O₃.
4:10 PM		B1-3-9 Characterization of Alumina Coatings Deposited by Conventional Reactive Magnetron Sputtering and High Ion Sputtering with Pulsed Bias R. Cremer, M. Witthaut, D. Neuschütz (RWTH Aachen, LTH, Germany); G. Erkens, T. Leyendecker (CemeCon, Germany); M. Feldhege (Euromat, Germany) In the last years alumina has gained increased attention as a hard coating material. This interest is based on the high performance of α-Al₂O₃ coatings as deposited by thermal CVD processes. In contrast to thermal CVD the deposition of alumina by Physical Vapor Deposition in general leads to the formation of amorphous or nanocrystalline γ-phases. For many applications, well crystallized α-Al₂O₃ is favored because of its hardness, wear resistance, and thermal stability. On the other hand, its deposition by thermal CVD is limited to temperature resistant substrates like cemented carbide, whereas the deposition of crystalline alumina by PVD at substrate temperatures of less than 550 °C would allow to coat heat-sensitive substrates like tempered steels. It is therefore desirable to find suitable deposition conditions for crystalline Al₂O₃ films at the moderate temperatures used in PVD. To investigate the structure of PVD alumina coatings in dependence of substrate temperature and deposition conditions Al₂O₃ films have been deposited by reactive magnetron sputtering at deposition temperatures between 100 and 600 °C on cemented carbide and high speed steel substrates using an aluminum target which was sputtered in an argon-oxygen plasma in rf and dc mode, respectively. The influence of deposition temperature and sputtering conditions upon the crystal structure of the films has been investigated by X-ray and electron diffraction, the binding states of the components were analyzed by Auger- and photoelectron spectroscopy. The constitution of the magnetron sputtered films is compared to Al₂O₃ films deposited by the High Ion Sputtering process with pulsed dc and rf technique, respectively, leading to crystalline films under specific deposition conditions.
4:30 PM		B1-3-10 Multifunctional Nanocomposite Wear-resistant PVD-coatings with High Hardness and Low Friction Coefficients M.A. Stüber, H.W. Holleck, H. Leiste, S. Ulrich, A. Martens (Forschungszentrum Karlsruhe, Germany) New coatings for tribological applications should combine high hardness values and low friction coefficients. This idea of multifunctional thin films can be realized by advanced coating concepts like metastable, multilayer, gradient and nanocomposite PVD-coatings. Especially the concept of nanocomposite coatings consisting of hard and lubricant phases is suitable for the development of tailored wear resistant coating with low friction. Preparation and properties of magnetron sputtered TiC/C nanocomposite thin films, consisting of nanocrystalline TiC and amorphous carbon phases, are presented. Hot pressed targets with 70 mol.-% TiC or 50 mol.-% TiC were applied. The specific sputtering power, the argon pressure and the substrate bias voltage were varied in a systematic manner. The samples were characterized with respect to mechanical properties (Vickers hardness, elastic modulus and residual stresses). Critical loads of failure were determined by the scratch test. The tribological behavior of the coatings was examined with a pin-on-disk arrangement modelling dry sliding wear conditions. The films show high hardness values up to 4100 HV0.05, critical loads of failure up to 40 N, maximum compressive stresses up to 4 GPa, low friction coefficients of 0.3 against 100Cr6 and low volumetric sliding wear. Preliminary results for nanocomposite thin films consisting of TiC and MoS2 phases will be shown.
4:50 PM		B1-3-11 Effect of Target Material and Process Parameters on Properties of Metal Containing DLC Coatings K. Bewilogua, C. Specht, J. Schröder, R. Wittorf, J. Brand (Fraunhofer Institute for Surface Engineering and Thin Films, Germany) Metal containing amorphous hydrogenated carbon (Me-DLC) coatings have a great potential in the field of wear and friction reduction on precision components. A large number of applications of such coatings are known so far. Today Me-DLC coatings with excellent adhesion will be produced in an industrial scale using reactive d.c. magnetron sputter techniques with argon-hydrocarbon mixtures as sputter gas. However, the knowledge on the effect of the target material is rather limited. We prepared coatings with targets consisting of transition metals like Ti and W as well as of transition metal carbides e.g. WC. Both for the substrate temperature and the properties of the deposited coatings (wear, hardness) considerable differences were revealed. Furthermore the effect of ion energy and ion current density was investigated systematically. Obviously the substrate heating during the deposition process increases with increasing atomic number of the target material. This can be explained by an effect of energetic neutrals. Also the coating properties depend on the target material. For W-C:H coatings a rather high wear resistance combined with an excellent adhesion can be achieved.