ICMCTF1999 Session E3-2: Coatings Resistant to Severe and Unusual Environments

Monday, April 12, 1999 1:30 PM in Room California

Monday Afternoon

Start	Invited?	Item
1:30 PM		E3-2-1 Combined Cathodic Arc/ Unbalanced Magnetron Grown CrN/NbN Superlattice Coatings For Corrosion Resistance Applications P.E. Hovsepian, D.B. Lewis, W.-D. Münz (Sheffield Hallam University, United Kingdom); S.B. Lyon, M. Tomlinson (University of Manchester, United Kingdom) CrN/NbN superlatiice coatings have been developed as a potential alternative to electroplated hard chrome for specialised industrial applications. The coatings have been grown at 400⁰C by combined cathodic arc/unbalanced magnetron technique. An industrially sized 4-target PVD coater was used to etch the substrates in a Cr ⁺ ion plasma ( cathodic arc : 1 target), to deposit a 0.3µm -0.4µm thick CrN base layer ( 2 Cr targets ) and subsequently the CrN/NbN superlattice by unbalanced magnetron sputtering ( 2 Cr targets and 2 Nb targets). Single phase f.c.c. structured CrN/NbN coatings with superlattice period in the range of 0.3nm-0.7nm have been deposited on f.c.c. CrN base layer. The coating structure, composition , residual stress and texture have been investigated by XRD, SEM and EDX techniques. Potentiodynamic polarisation measurements in two corrosive media, de-aerated 0.1 M acetic acid/sodium acetate buffer solution with 0.2 M added NaCl ( pH of 4.5-4.8 ) and 3% NaCl aqueous solution have been carried out to evaluate the corrosion performance of the coatings. CrN/NbN superlattice coatings performance in the two investigated media was compared to that of 304L stainless steel and commercially available electroplated hard chrome. In chloride solutions CrN/NbN superlattice coatings deposited on single phase CrN base layer showed an approximate 14 times improvement in passive current and 180 mV higher pitting potential compared with 304 L stainless steel. The sub- stoichiometric CrN/NbN coatings are more noble ( Eco.= - 320 mV ) and show lower passive current density ( i_p = 2.6 x 10^-7A/cm² ) when compared to stoichiometric ones ( Eco. = - 512 mV, i_p= 3.4 x 10^-7A/cm²), however the pitting occurs at lower potentials ( Ep. = + 250 mV ) due to the higher residual stress in such coatings. In 3% NaCl, the corrosion resistance of CrN/NbN superlattice coatings been enhanced by a very stable passive film, with no pitting potential observed prior to oxygen evolution occurring. The pitting potential of hard chrome is approximately + 700mV is lower than the superlattice. Additionally the passive current density is of the same order, implying the superlattice coating performance better than the hard chrome.
1:50 PM		E3-2-2 Corrosion of CrN and TiAlN Multilayered Hard Coatings in Cl Containing Atmospheres at 350°C M. Andritschky, L. Cunha (Universidade do Minho, Portugal); K. Pishow (Surfcoat, Finland) Hard coatings CrN and TiAlN were prepared by reactive magnetron sputtering in the form of multilayered thin films. The coatings consisted in CrN-Cr and TiAlN - Al multilayers with a layer thickness from 4 to 50 nm. The corrosion resistance of these coatings was tested at 350°C in HCl and water containing atmospheres. Coatings with defects failed, as identified by EDX and XPS measurements, by an interfacial corrosive attack and subsequent delamination. A variation of the coating structure (reduction of the periodicity of the nanolayers) and augmenting the residual stress increased the life time of the coatings. The corrosion of these improved coatings is characterised by an oxidation of the coating surface (with the transformation of CrN into chromium oxide). This oxidation is enhanced by the HCl content in the atmosphere compared to atmospheres containing only air and water vapour. Generally, Cr containing coatings showed a better corrosion resistance than TiAl based hard coatings.
2:10 PM		E3-2-3 The Corrosion Behavior and Adhesion of Ion-Plated TiN Film on AISI 304 Steel G.-P. Yu, J.-Y. Chen (Dept. of Eng. & System Science, National Tsing-Hua University, Taiwan,R.O.C.); J.H. Huang (National Tsing Hua University, Republic of China) Titanium nitride was deposited on AISI 304 steel with a hollow cathode discharge (HCD) ion plating technique. An extensive investigation on the corrosion behavior and adhesion of TiN films was performed. The corrosion resistance was evaluated by the potentiodynamic polarization in 1N H₂SO₄ + 0.05 M KSCN solution and the ASTM standard B-117 salt spray test. The ultimate shear stress, proportional to the bonding strength between coating and substrate, was measured by a periodic cracking method to stand for the adhesion. To obtain good protection of the substrate, the Ti sublayer was introduced to form Ti/TiN multiple layers. The experimental results demonstrate that the corrosion properties of TiN-coated AISI 304 steel are determined first by the influence of the synergetic effect of the packing factor and thickness associated with the coating, and second by the adhesion of TiN coating. From the results of interfacial stress measurement and SIMS depth profiles, the adhesive strength of the coating increases with increasing the thickness of interdiffusion layer. Furthermore, it also indicates that the Ti sublayer can enlarge the pseudo-diffusion layer and enhance the adhesion strength of TiN coatings. For Ti/TiN Multilayered coating, good corrosion resistance can be obtained with the measured ultimate shear stress higher than 10GPa and the interdiffusion zone higher than 0.2 µmm.
2:30 PM		E3-2-4 The Effect of Arc-PVD Metal ion Etching Pretreatment on the Corrosion Behavior of Steels M. Urgen, A.F. Cakir, M.K. Kazmanli (Istanbul Technical University, Turkey) Metal ion etching - sputtering of the substrates under high bias voltages is used both for sputter cleaning and heating in arc-PVD coating process. This sputtering process is believed to play an important role on very good adhesion properties of arc-PVD coatings. The original interface between the coating and the substrate was influenced by the high - energy metal ion bombardment during heating and sputtering under high bias. At this stage the surface was not only sputtered, but energy and momentum was also transferred to the substrate and to the very thin coating layer that was formed, creating point defects, stresses and heating in the coating and on the substrate. The aim of this work is to investigate the effect of metal - ion etching process on the corrosion behavior. Steel samples are subjected to titanium, chromium and molybdenum ion - etching process under 1000 V bias. The corrosion behavior of the ion etched samples are investigated by using standard electrochemical techniques, both in sulfuric acid and sodium chloride solutions. The beneficial effect of the metal - ion etching process on the corrosion behavior is observed. The extent of this effect depends on the type of metal ion used and the treatment time.
2:50 PM		E3-2-5 Chemical and Physical Deposition Coatings (CVD snd PVD) Exposed to Particulate Flows at High Temperature W. Tabakoff (University of Cincinnati) The design and development of high performance turbomachinery operating in an ambient with solid particles require a thorough knowledge of the fundamental phenomenon associated with particulate flows. This paper describes the overview of the jet engines performance deterioration and retention. The ingestion of solid particles over period of time, will reduce the efficiency of the propulsion system, causing increased fuel consumption and thrust decrease. The investigated coatings are produced by chemical vapor deposition (CVD), physical vapor deposition (PVD), and other methods. Experimental studies were conducted at the University of Cincinnati high temperature erosion wind tunnel to investigate the erosion behavior of coatings exposed to different types of solid particles. Some of the following coatings were evaluated: rhodium platinum aluminized, SDG-2207 (super D-gun product), CVD coatings, including TiC, TiN, Al₂O₃ and PVD coatings. The erosive wear of the samples was studied experimentally by exposing them to particle laden flow at velocities from 180 to 305 m/s, temperatures from ambient to 815°C and impingement angles from 15 through 90 degrees.
3:30 PM	Invited	E3-2-7 Erosion of Coatings by Solid Particle Impact I.M. Hutchings (University of Cambridge, United Kingdom) Surface engineering, and in particular the application of hard coatings, is commonly used to improve resistance to erosive wear caused by the impact of small hard particles. The properties of a coating material which control its behaviour under these conditions include hardness and fracture toughness. However, these are simple measures for the rather complex response which the material may show under the conditions of extremely high strain rate and very small deformation volumes which are characteristic of erosive particle impacts. Properties specific to the coated substrate system, including residual stress, coating interfacial fracture energy and coating thickness, are also important. This review will discuss all these aspects of coating behaviour, and also examine methods of testing the erosion response of coatings, which pose special problems.
4:10 PM		E3-2-9 Tribological and Thermal Evaluation of Functionally Graded Systems P.J. Huang, C. Hubbard, M.W. Cole, J.J. Swab (Army Research Laboratory); S. Sampath (SUNY at Stony Brook) The US Army is currently investigating the use of Functionally Graded Materials (FGMs) for use as liners for gun barrels. This environment has severe temperature extremes, aggressive propellant gases, and large pressure fluctuations. Candidate materials to be investigated are WC-Co and Mo2C deposited by thermal spray techniques. The objective of this paper is to evaluate the performance and advantages of using FGM (ceramic-to-metal) liners for gun barrels. This evaluation will involve microstructural and thermal characterization of the FGMs as a function of tribological and thermal fatigue tests in order to determine feasibility for this application.
4:30 PM		E3-2-10 Diamond-like Carbon Coatings for Space Tribology J. Fontaine, C. Donnet, T. Le Mogne, M. Belin (Ecole Centrale de Lyon, France); C. Héau, J.P. Terrat, F. Vaux (Hydromécanique et Frottement, France); G. Pont (Centre National d'Etudes Spatiales (CNES), France) Solid lubricant coatings for vacuum and space mechanisms are widely used when conventional liquid lubrication is prohibited, either when the operating conditions become too severe (extreme temperatures, ultrahigh vacuum) or when a clean environment is required. While the well-known MoS₂ lamellar solid lubricant is the most extensively used material today, diamond-like carbon (DLC) coatings are studied as potential candidates for a wear resistant material with low friction in vacuum conditions. DLC films have been deposited by d.c. plasma-enhanced chemical vapour deposition, in various conditions. Analytical characterization coupled with tribological tests in ultrahigh vacuum and ambient humid air have been performed to identify relationships between the deposition conditions, the composition (hydrogen content) and the properties (stress, friction) of the films. Depending on the properties of the DLC which are in turn dependent on the deposition procedure, tested DLC coatings present a wide range of tribological behavior, with friction coefficient values in UHV ranging from less than 0.01 to more than 0.5 and with various wear rates under air or UHV. Typical DLC structures and compositions allowing the achievement of extremely low friction in vacuum and good behavior under air are identified and discussed. This study has been performed with the support of the "Région Rhone-Alpes", France, and of the "Centre National d'Etudes Spatiales" (CNES), France.
4:50 PM		E3-2-11 Amorphous Carbon Coatings and Their Tribological Behaviour at High Temperatures and High Vacuum T. Krumpiegl, H. Meerkamm, W. Fruth, C. Schaufler (University, Germany); G. Erkens (CemeCon, Germany); H. Böhner (Company, Germany) Aim of the research work is a comparative study of three different types of amorphous, diamond-like-carbon (DLC) coatings performing at extreme environmental conditions (high temperature, high vacuum). A series of hard carbon coatings have been produced by PVD-magnetron sputtering and plasma decomposition (low-pressure PACVD) using standard in-house equipment. Sputtered amorphous hydrogen free carbon (a-C), RF-plasma deposited hydrogen containing amorphous carbon (a-C:H) and titanium doped hydrogen containing amorphous carbon (Ti-C:H) have been prepared on steel disks. Different tests have been carried out for the analysis and characterization of the mechanical properties and the tribological behaviour at high temperatures (500 °C) and high vacuum (10^-5 mbar). The investigated tribological coatings show good adhesion, micro hardness and friction properties at standard conditions (23 °C, 50 % r.h.). In this paper it will be reported if these coatings perform as well at elevated temperatures and high vacuum. A recently built in-house vacuum pin-on-disk test rig was used for the investigations. The results of the friction and wear tests and the possibility of applications of these coatings as solid lubricants in ball bearings are discussed. The comparison of the mechanical and tribological properties allows to rate the considered coatings in regard to the described severe environmental conditions.
5:10 PM		E3-2-12 An Investigation of the Corrosion of H13 Steel Coated with CrN; Effect of Steel Surface Preparation R. Aharonov, S. Chellapilla, B. Janoss (Multi-Arc, Inc.); R. Shivpuri (Ohio State University) Die casting dies and cores are subjected to very harsh conditions that combine high temperatures, molten metal impingement, high injection pressures, mechanical and thermal cycling. Dies fail due to a combination of corrosion, erosion, and thermal fatigue. Thin layers of CrN coating deposited by Cathodic Arc evaporation seem to provide adequate protection from some of the failure mechanisms. Accelerated corrosion tests were conducted by dipping coated core pins in an A390.2 melt. The core pins made of H-13 were treated to obtain various surface finishes prior to the coating application. The corrosion features were different depending on the surface preparation. In general, higher surface roughness resulted in a greater degree of corrosion. Possible mechanisms of corrosion are suggested.