Tribology of Coatings for Automotive and Aerospace Applications

Thursday, May 2, 2013 1:30 PM in Room Golden West

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1:30 PM E3-1+G-1 Friction Reduction Through Thermal Spray Coatings on Cylinder Running Surfaces of Internal Combustion Engines
Peter Ernst (Sulzer Metco AG (Switzerland), Switzerland)
More stringent environmental laws in the field of vehicle emissions such as nitrogen oxides, particulate matter and carbon dioxide increase the pressure on the internal combustion engine manufacturers to develop, validate and apply technologies, which contribute to a reduction in these emissions. As a result, the interest in low friction coatings for cylinder running surface has risen significantly over the past few years. Among others, the SUMEBore® coating solution from Sulzer Metco can provide such properties. Current commercial applications range from small 2-stroke engines for motorcycles and other leisure vehicules, (downsized) lightweight passenger car engines up to highspeed diesel truck and medium speed diesel engines for power generation, marine propulsion, locomotives, etc.SUMEBore coatings are applied by a powder based air plasma spraying (APS) process. The APS process is extremely flexible when it comes to freedom of materials choice and can also process materials to which wire-based coating methods – such at Plasma Transferred Wire Arc (PTWA) or Twin Wire Arc Spray (TWAS) - do not have access, particularly metal matrix composites (MMC) and pure ceramics.The compositions can be tailored to the specific challenges in an engine, e.g. reducing friction and excessive abrasive wear, addressing scuffing issues, corrosion attack caused by adulterated fuels, improve the heat transfer into the water jacket, etc. Up to date a number of engines have been tested successfully. Most of the tested engines achieved significant reductions in lubricant oil consumption (LOC), sometimes in excess of 75%, reduced fuel consumption, very low wear rates and corrosion resistance on the cylinder running surfaces. The paper will give an introduction into the APS coating application on cylinder running surfaces. It will be underlined with recent examples of engines that achieved significant reduction in friction and LOC and improved corrosion resistance. One specific example will be highlighted from the industrialization of the APS process on a 3-cylinder, 1.5l high performance engine for a leisure vehicle with start of industrial production (coating application) in September 2012.
2:10 PM E3-1+G-3 Thermal Treatment and Tribological Behaviour of Hybrid Coatings Deposited by Sol-gel Route on Martensitic Stainless Steel
Souphiane Rahoui, Viviane Turq, Jean-Pierre Bonino (Université Paul Sabatier, France)

Stainless steels are widely used in the aeronautical field. Among these steels, the 15-5 PH martensitic stainless steel (X5CrNiCu15-5), known for high strength and good corrosion resistance, presents poor tribological behavior, particularly in high temperature environment. Moreover, in the field of surface treatments and coatings, recent environmental regulations encourage working on new non polluting process.

In this study, a process was developed to improve the tribological behavior of the martensitic stainless steel until 500°C. Organic-inorganic hybrid coatings were prepared via sol-gel route and deposited onto stainless steel by dip-coating technique.

The effects of an additional thermal treatment, under different temperatures and in air or in nitrogen atmospheres was then studied. Combined analysis was conducted by thermal analysis (DTA/TGA), Nuclear Magnetic Resonance (of 29Si and 13C) and Raman Spectroscopy on the xerogel and on the coating.

The mechanical properties and the tribological behavior (evaluated with a pin-on-disk tribometer) of the coated samples were also studied.

2:30 PM E3-1+G-4 Tribological Behavior of New Coatings for High Temperature Aeronautical Applications
Marine Bernard, Vincent Fridrici, Philippe Kapsa (LTDS - Ecole Centrale de Lyon, France)

In aeronautics tribology, mechanical parts are required to operate with increasing temperature. The increased functioning temperature (up to 700°C) of the contacts prone to friction and wear (such as bearings and other structural parts) is a direct consequence of the increasing power of jet engines. In the case of ball bearings, the substrate materials as well as the coating durability are affected by temperature. There is then a pressing need to introduce new coatings demonstrating effective tribological behavior at high temperature (e.g. 600°C instead of 150°C for some aeronautical joints), especially in order to replace silver coating used at normal temperature but that cannot work at higher temperature. In partnership with Airbus Aerospace and SKF Aerospace, the durability of ball bearings functioning under extreme conditions in terms of temperature and sliding friction was studied.

First, SEM/EDX analyses were done on the silver coating deposited in the contact between the ball bearings rings, in order to acknowledge the actual bearings surface damage. Tribological testing of the silver coating was then performed in a standard cylinder-on-flat configuration in order to compare in situ and experimental damages.

More than ten different coatings (both soft and hard coatings, with solid lubrication properties and/or wear resistance properties) were then tested in the same configuration and conditions as the silver coating. These tests allowed us to identify the best suitable coatings for the application. An original test rig was also designed in the lab, in order to better simulate the bearings functioning conditions. This tribometer makes it possible to perform tests in ring-on-flat configuration (close contact) and to simultaneously apply a normal force up to 50 kN and a reciprocating rotating motion. Using this tribometer, the final tests were conducted on the best candidates among the different coatings, in a configuration as close to reality as possible, with a hard coating covered ring and a soft coating covered flat, the contact between the two being greased. From these tests, mechanisms of solid lubrication were examined and typical tribological damages such as adhesion and abrasion were observed. Finally, several possible solutions were determined, for two different functioning temperatures: 200°C and 600°C.

2:50 PM E3-1+G-5 Thick TiSiCN-based Nanocomposite Coatings for Aerospace and Automotive Applications
Ronghua Wei (Southwest Research Institute, US)
This paper reviews the thick nanocomposite coating research conducted at Southwest Research Institute® (SwRI®). We have been developing thick TiSiCN-based coatings (20-500 µm) for severe environments including sand erosion, sand abrasion, water droplet erosion, heavy load sliding wear and corrosion. The SwRI process utilizes magnetron sputtering of Ti from all targets in a mixture of Ar, N2 and TMS (trimethylsilane) to form the TiSiCN-based coatings. TMS is much more user-friendly than SiH4 or SiCl4; therefore, the process is suited for large-scale coating production. To increase the coating quality, a plasma enhanced magnetron sputtering (PEMS) method is used. During the deposition, in addition to the magnetron plasma, a global plasma is generated using thermionic emission for the enhanced ion bombardment. The coatings thus produced have a dense structure, good adhesion to the substrate, low internal stress and superior mechanical properties compared to those obtained with the conventional magnetron sputtering. The coatings formed have a microstructure composed of nanocrystalline TiCxN1-x (x=0, 0.3 and/or 0.7) with the grain size of 4-10 nm in a matrix of amorphous SiCyNz, or nc-TiCxN1-x/a-SiCyNz. The microstructure of the coatings results in the super-hardness (up to 4600Hv). However, the internal stress was found to be less than 1 GPa, thereby allowing the deposition of ultra-thick coatings over 500 µm for a few specific applications. The coatings also have high toughness characterized by a high value of H3/E*2. The nanocomposite coatings have been found to significantly increase erosion resistance compared to uncoated alloy substrates including Ti-6Al-4V, Inconel 718, H-13, 17-4PH stainless steel (SS), Custom 450 SS, 304 SS, carbon steels and many others. When the coatings are prepared using specific precursors, a low coefficient of friction below 0.2 in dry sliding has been achieved. These coatings have many industrial applications including compressor blades or vanes for aero engines, cylinder liners for automotive, stamping dies, and cutting tools. In this paper we review the method for preparing these coatings, discuss their microstructural, mechanical and tribological properties, and present examples for practical applications.
3:30 PM E3-1+G-7 In-situ Real Time Solid Particle Erosion Testing Methodology for Hard Protective Coatings
Etienne Bousser, Ludvik Martinu (École Polytechnique de Montréal, Canada); Jolanta Klemberg-Sapieha (Ecole Polytechnique de Montréal, Canada)

Solid Particle Erosion (SPE) degradation of engine components in aircraft operating in harsh environments is a well known issue causing severe maintenance and reliability problems. In order to enhance the lifetime of engine components many different hard protective coatings have been developed over the last two decades. While these coating systems are mostly based on TiN/Ti multilayer microstructures, they present varying material removal mechanisms depending on the phase constitution and microstructure of the target, and on the erodent characteristics (particle size, speed, composition and shape). Studying these mechanisms in detail is quite challenging given that SPE testing is notoriously inaccurate due to its aggressive nature and its many methodological uncertainties. In this presentation we will outline the work recently performed at Polytechnique Montreal on the methodological aspects of gas-blast SPE testing of hard protective coatings.

We will first present our work with respect to “traditional” erosion testing by evaluating the volume loss from the tested samples in order to accurately compare the SPE performance of different coatings without the need of obtaining coating density which is rarely accurately known. In the second part of the presentation, we will demonstrate a new in-situ real time erosion testing methodology using a quartz crystal microbalance in order to study the SPE of different hard protective coating systems. Using the previous results by volume loss measurement, we validate and discuss the advantages and challenges related to such a method. Finally, this time-resolved technique enables us to discuss some transient events present during SPE testing of hard coating systems leading to new insights into the erosion process.

3:50 PM E3-1+G-8 Characterization and Tribological Investigation of TiSixCy Wear Protective Coatings
Joël Matthey (Haute Ecole Arc Ingenierie, Switzerland)
TiSixCy hard coatings have been deposited by magnetron sputtering from a composite target that was manufactured by powder technology. Other coatings were also obtained from a Unbalanced Magnetron Sputtering unit mounted with Ti and Si targets in partial acetylene atmosphere. The attained films are principally composed of TiCx nano-crystallites and amorphous phases. Although the Ti3SiC2 phase has not been detected, the hard coating properties are yet interesting. Nanohardness values up to 1800 Hv could be obtained for coatings with friction values below 0.20 against steel in an unlubricated pin-on-disk setup. The main parameter, which governs mechanical and tribological properties, found to be the negative bias voltage applied to the substrates during the deposition process. Application of a negative bias voltage results in significant variation between the target and thin film composition. Material transfer, roughness reducing and tribo-chemical reactions between TiCx and environmental gases caused interesting tribological behavior of biased TiSixCy thin films. A strong dependence on the adhesion layer hardness and the film tribological endurance has been demonstrated. Measurements showed a thermal stability up to 400°C. Additionally, recent works showed TiSixCy could be also use as an adhesion layer for DLC coatings. Coatings have been tested in industrial applications and have been found encouraging because, in certain cases such as cold stamping and watch mechanisms, the TiSixCy coatings can compete against those currently available on the market. Compared to some industrial processes, the benefit is that no reactive gas is needed. Consequently, it has a long-term stability. This present document reports the investigation of the morphology, structure and tribological behavior of Ti-Si-C hard coatings deposited from a composite target.
4:10 PM E3-1+G-9 Effects TiN and TaN Barrier Layers on the Rmergence of Ag and Cu Particles and the Subsequent Mechanical and Antibacterial Properties of TaN-(Ag,Cu) Nanocomposite Films
Jang-Hsing Hsieh, Y.R. Cho, Yu-Tai Su (Ming Chi University of Technology, Taiwan, Republic of China)
TaN–(Cu,Ag) nanocomposite films were deposited by reactive co-sputtering on Si(001) and M2 tool steels. Prior to annealing, the films were deposited with a barrier layer of TiN or TaN (with various thickness) in order to control the amount of emerged Ag and Cu particles. As a result, the tribological and anti-bacterial behaviors can be controlled. The films were then annealed using RTA (Rapid Thermal Annealing) at 200 °C–400 °C to induce the nucleation and growth of metal particles. Thes films’ structures, surface morphologies, and mechanical properties were analyzed. The samples were tested for their anti-wear and anti-bacterial behaviors against Gram-negative Escherichia coli, as function of barrier layer thickness. It is found that, through the application of diffusion barrier, the antibacterial efficiency against E. coli as well as the tribological properties can be changed and controlled, depending on the layer thickness of TiN and TaN. In general, the films with TiN layer tended to allow more Ag and Cu particles to form on the surface.