ICMCTF2010 Session G2: Coatings for Automotive and Aerospace Applications
Wednesday, April 28, 2010 8:00 AM in Pacific Salon 3
G2-1 Plasma Coatings for High Efficient Power Train in Automobile
Kirsten Bobzin, Nazlim Bagcivan (RWTH Aachen University, Germany); Nico Goebbels, Koray Yilmaz (Surface Engineering Institute RWTH Aachen, Germany)
There is a great motivation to increase the efficiency of automobiles. This motivation mainly arises from the fulfillment of Kyoto protocol, which states the participating countries to reduce their CO2 emission until 2012. A reasonable amount of CO2 is produced by transporting vehicles; hence, increasing their efficiency enables reducing CO2 emission significantly. Enhancing of the efficiency can be achieved by decreasing the friction behavior or increasing the load carrying capacity of the power train elements. These requirements can be fulfilled by means of plasma coating technologies like PACVD (plasma activated chemical vapor deposition) and MSIP (magnetron sputter ion plating). Using PACVD technology, it is possible to deposit DLC (diamond like carbon), which shows excellent tribological performance, i.e. low friction and high wear resistance, under boundary and mixed lubrication regime. The low temperature ternary coating system Cr-Al-N promises to improve the load carrying capacity and wear resistance of the power train elements, with which same performance can be achieved for decreased weight that leads in return to reduction of CO2 emission. Introduction of new tribological surfaces for the sake of efficiency increase leads to the question, how lubricants are compatible with these new surfaces, which are normally developed for steel surfaces. Therefore the wettability of the new surfaces with conventional lubricants is still a challenging question. DLC and CrAlN show chemical inactive behavior, therefore the physical interactions can be considered for their wettability with lubricants.
In this study, the physical interactions between the plasma coatings and lubricants are investigated by spreading coefficients and adhesion energy, which are determined by contact angle measurement technique. The plasma coatings are a-C:H (DLC-Star®, Oerlikon Balzers) and CrAlN. The lubricants investigated are mineral oil, polyalphaolefin, synthetic ester, polyether and polyglycol. The tribological behavior of the coatings a-C:H and CrAlN with lubricants are determined in a pin-on-disk tribometer. The tribological results are compared with the physical interactions of the lubricants with the plasma coatings. For an optimum wettability of the plasma coated surfaces with lubricants, it is found that it is important to adapt both the adhesion energy and spreading coefficient, such that increasing the adhesion energy of the lubricants on DLC and CrAlN, whilst decreasing their spreading coefficients leads to a significant decrease of the friction coefficient.
G2-2 Wear and Corrosion Protection of AJ62 Mg Alloy by Plasma Electrolytic Oxidation (PEO) Process for Mg Engine Application
Peng Zhang, Xueyuan Nie (University of Windsor, Canada)
In order to reduce the fuel consumption and pollution, automotive companies are developing magnesium-intensive engines. However, due to the low wear and corrosion resistance of the Mg alloys, Mg cylinder bore and Mg engine coolant channels are vulnerable to the sliding wear and corrosion attack, individually. In this paper, Plasma Electrolytic Oxidation (PEO) process was used to produce oxide coatings on AJ62 Mg alloy, developed for Mg engine block, to battle against wear and corrosion attack. The PEO coatings exhibited a much better wear resistance, as well as a smaller friction coefficient, than the AJ62 substrate. According to the potentiodynamic polarization corrosion tests, the PEO coatings had a much higher corrosion resistance than the substrate. The galvanic corrosion property of AJ62 Mg coupled with stainless steel and aluminum (Al) was also investigated via immersion corrosion test in an engine coolant. With proper coating thickness, the PEO coatings can effectively protect the Mg alloy from the galvanic corrosion attack without significantly affecting the thermal conductivity of the Mg.
G2-3 A Study on the Influence of Bond Material on Honing Engine Cylinder Bores with Diamond Coated Stones
Leila Sabri, Sabeur Mezghani, Mohamed El Mansori (Arts et Métiers Paris Tech, France)
A consistent increase in demand for special tools designed to an efficient honing of engine cylinder bores is observed. Metallic Bonded Diamond Stones (MBD) are more and more used for their wear resistance and their high tool life. However, the hardness of this metallic bond leads to the degradation of the honed surface aspect by the formation of smudgy grooves edges (Blechmantel). This torn and folded metal affects the required functional performances of the cylinder bore. In this study, two new diamond coated stones with Vitrified and Resinoid Bond (respectively VBD and RBD) are tested and compared to the MBD sticks. The influences of bond material on the honing reliability are studied in terms of honed surface aspect, material removal rate and wear properties. Results reveal that the stiffness and the openness structure of the Resinoid bond lead to a better trade off between surface aspect and tool life.
G2-4 Opportunities and Challenges to Coatings Applications in the Automotive Industry - Select Case Studies
Michael Lukitsch (GM Research & Development Center)
Several case studies that showcase successful applications of coatings and thin films in the automotive industry will be examined in detail. Emphasis is on the diverse performance requirements of thin films and coatings that are unique to vehicle design and performance. These requirements are presenting challenges to materials development by physical vapor deposition (for example) and quantitative materials characterization.
Finally, existing opportunities and some exciting new challenges for coating and thin film materials related to vehicle electrification are reviewed.
G2-7 Influence of Simulated Stamping Force on Coating Failure Behavior
Jun Feng Su, Xueyuan Nie (University of Windsor, Canada); Tareena Mulholland (General Motors Company)
Due to the increasing use of advanced high strength steels, die wear prevention has become an important issue in the stamping of automotive parts. Since physical vapor deposition (PVD) coatings usually has a much higher hardness and resistance of wear than electroplated or electroless coatings and nitrided steels, PVD coatings have been considered as necessary top layers on dies surface to battle the wear problems.
Since most lab tests use operating conditions that do not correspond to actual conditions in production stamping dies, the lab tests may provide misleading results. In this work, a ball-on-plate impact fatigue test was proposed as a novel experimental technique to simulate the wear and fatigue behavior of a coating-substrate system. The simulated stamping force consists of an impact load and a pressing load, which can be adjusted by changing the distance between the impact ball and the sample (plate) surfac and by regulating air pressure in the air cylinder of the impact tester, respectively. Various hard coatings (CrN, TiAlN and TiC) were tested at various combinations of impact/pressing loads (i.e., 200N/400N, 400N/400N, 600N/400N and 800N/400N) for 10,000 cycles. The study provides experimental results concerning cohesive and adhesive failure modes. The failure mechanisms of the tested coatings are determined by means of optical microscope, scanning electron microscope and energy dispersive x-ray analysis. It was shown that among all the tested coatings the CrN coating is the best against fatigue.
G2-8 From Coatings to Electrochemical Energy Storage for Automotive Applications
Yang Cheng (University of Kentucky)
I will present an overview of our recent work on surface engineering for automotive applications, including coatings and nanostructured materials for electrochemical energy storage.
(1) Is the lotus leaf truly superhydrophobic?
This question was studied by observing water on lotus leaves and lotus-like surfaces at the micro- and macro-meter scales. Our work suggests that these surfaces can be either hydrophobic or hydrophilic. This finding may have significant ramifications on how to make and use “superhydrophobic” surfaces.
(2) Shape memory surfaces
Using micro- and nano-indentation techniques, we demonstrated the existence of shape memory and superelastic effects under complex loading conditions at the micro- and nano-meter scales. These effects form the basis for applying shape memory alloys as “self-healing” surfaces and “metallic-based adhesion” materials. The microscopic shape memory effect can also be exploited to create surfaces with reversible roughness and texture for applications such as friction control and information storage.
(3) Understanding diffusion-induced-stresses in nanostructured materials for durable lithium ion batteries
We examined the effects of surface tension and surface modulus on diffusion-induced stresses in spherical nano-particles. We showed that both the magnitude and distribution of stresses could be significantly affected by surface mechanics. In particular, a tensile state of stress may be significantly reduced in magnitude or even be reverted to a state of compressive stress with decreasing particle radius. This reduction in tensile stress may be responsible for the observed resilience to fracture and decrepitation of nanostructured materials used in electrochemical energy storage.
These examples suggest a wide range of applications of nanostructured materials for the automotive industry and beyond.