ICMCTF2008 Session H3: Surface Engineering to Address Environment and Life-Cycle Issues

Thursday, May 1, 2008 1:30 PM in Room Terrace Pavilion

Thursday Afternoon

Start	Invited?	Item
1:30 PM	Invited	H3-1 Nanopatterning Interfaces for Toughness and Reliability N.R. Moody (Sandia National Laboratories); M.S. Kennedy (Clemson University); A.A. Talin (Sandia National Laboratories); D.F. Bahr (Washington State University); E.D. Reedy (Sandia National Laboratories) Coatings and films are often used to enhance performance and reliability of micro and nanoscale devices fabricated using micosystem technologies. In all environments, performance depends on adhesion. Variations in surface topology are used to great advantage in improving film and coating adhesion at the micron and sub-micron scales. However, limitations in test capabilities have prevented a direct measure of surface topology contributions to adhesion at the nanoscale. Understanding these contributions to adhesion is a key factor to enhancing performance and reliability of nanostructured materials and devices especially in active environments. As a result, we are combining nanomechanical tests and finite element-based simulations to develop an understanding of how patterns of small-scale interfacial heterogeneities affect interfacial crack nucleation and crack propagation. The nanomechanical tests show that the nanopatterns alter film fracture morphology while markedly increasing interfacial fracture energies. The simulations show that the increased resistance to interfacial film fracture is controlled by pattern morphology and mode mixity. In this presentation, we will use the test results and finite element simulations to show how small-scale variations in topology affect resistance to fracture thereby providing a means to tailor nanoscale film device performance and reliability. This work is supported by Sandia National Laboratories, a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
2:10 PM		H3-3 Galvanic Corrosion Protection for Mg Against Biofuel E85 and Engine Coolant via Electrolytic Plasma Oxidation (EPO) Process P. Zhang, X. Nie, D.O. Northwood (University of Windsor, Canada) Recently, magnesium (Mg) alloys have gained the attention of automotive industry especially in the aspect of weight reduction. However, in the case of an Mg engine block having been developed, Mg alloys are subjected to general and galvanic corrosion when exposed to biofuel E85 and engine coolant which contact the Mg engine block, cylinder head steal gasket, and aluminum cylinder head. In this research, Electrolytic Plasma Oxidation (EPO) process was used to produce thin ceramic coatings on the surface of Mg and Al 319 alloys to battle the corrosion problem occurring in the vicinity of the cylinder head gasket. Corrosion testing specimen, comprising of uncoated or coated Al 319 coupon, stainless steel gasket, and uncoated or coated Mg coupons, were coupled with stainless steel bolts, aluminum washers and aluminum nuts. Potentiodynamic corrosion tests were conducted to assess the corrosion property of each individual uncoupled sample in E85 and engine coolant, respectively. ASTM D1384 and immersion tests were employed to reveal the galvanic corrosion performance of the coupled specimen against those two corrosive solutions. Weight loss of each part in each coupling due to corrosion was determined by analysis balance. SEM with EDX analysis was used to investigate the surface morphologies and corrosion products after corrosion tests. The results showed that the EPO process could provide an efficient protection from corrosion of E85 and engine coolant. Keywords: Electrolytic plasma oxidation; Corrosion, Galvanic corrosion; Mg.
2:30 PM		H3-4 Pulsed Current Deposition of Zn-based Coatings on Steel Substrates using Plasma Assisted Electrolysis A.L. Yerokhin, A. Pilkington, A. Matthews (University of Sheffield, United Kingdom) Plasma assisted electrochemical processes attract increasing interest due to a possibility of combining advantages of conventional electrolytic and plasma-based treatments. In this work, plasma electrolytic deposition of Zn based coatings on AISI 4340 steel substrates under pulsed current conditions is discussed. The coatings with thickness 10 to 20 microns were deposited for 0.5-5 min by a brush technique using a ZnSO₄ based electrolyte operated at the temperature 80 to 90 ^oC. Negative voltage pulses were applied with amplitude, frequency and duty cycle varied within 200 to 500 V, 0.1 to 15 kHz and 0.8 to 0.2, respectively. The methods of surface profilometry, optical microscopy, XRD, SEM and EDX analyses were employed, together with microhardness tests to evaluate effects of process parameters on the characteristics of the coating microstructure, morphology, chemical and phase composition. Corrosion studies included open circuit potential measurements, potentiodynamic corrosion scans and electrochemical impedance spectroscopy analysis. Salt fog corrosion tests were also carried out. Capabilities of the plasma assisted technology compared to conventional Zn coatings are discussed, with optimal ranges of process parameters identified.
2:50 PM		H3-5 Analysis of Corrosion Resistance of Cr-Cu-N Nanocomposite Thin Films in Sodium Chloride Aqueous Solutions Z.-F. Zeng, Y.-C. Kuo (National Taiwan University of Science and Technology, Taiwan); J.-W. Lee (Tung Nan University, Taiwan); C.-J. Wang (National Taiwan University of Science and Technology, Taiwan) The Cr-Cu-N nanocomposite thin film with sufficient hardness and antibacterial abilities can be used as a promising candidate to deposit on the surfaces of medical apparatus and food processing equipments. In this work, the Cr-Cu-N thin films with Cu contents ranging from 1.6 to 24.4 at.% have been deposited by a bipolar asymmetric pulsed DC reactive magnetron sputtering system. The surface and cross-sectional morphologies of coatings were examined with a field emission SEM, respectively. The crystalline phases of thin films were analyzed with an X-ray diffractometer. The corrosion behaviors of Cr-Cu-N thin films with different Cu contents in sodium chloride aqueous solutions were investigated. It was observed that the corrosion resistance of Cr-Cu-N thin films is improved as the Cu content increased. It was also found that more nano and micro pits formed on the corroded surface as the Cu content of thin film increased, which is attributed to the selective corrosion of Cu grains in the Cr-Cu-N thin film.
3:10 PM		H3-6 Corrosion Resistance of Thermal Sprayed Al and Al-SiC Coatings on Magnesium Alloys M. Campo, M.D. López, B. Torres, P. Rodrigo, C.J. Múnez, J. Rams, E. Otero (Rey Juan Carlos University, Spain) Magnesium and its alloys are susceptible to galvanic corrosion, which can cause severe pitting in the metal. One of the most effective ways to prevent corrosion is to coat the material base. Coatings can protect a substrate by interposing a barrier between the metal and the aggressive medium. The thermal spray technology offers a wide range of possibilities to modify the surface properties of magnesium alloys as a coating of other material can be deposited on top of them. Mg and Mg alloys were coated using the thermal spraying process. The coating deposition was carried out by flame spraying to deposit aluminium and aluminium reinforced with SiC particles. The objective of this study is to evaluate the corrosion resistance of uncoated and coated magnesium alloys in simulated marine atmospheres with chlorides (Cl-). Resistance to corrosion in 3.5 wt % NaCl solutions at room temperature was determined by using different methods. Anodic polarization measurements were carried out to study the passive behaviour of the uncoated and coated materials. The kinetic laws governing the corrosion evolution for each system were analyzed using direct current electrochemical methods and gravimetric measurements. Finally, the nature of the corrosion products was analysed by Scanning electron microscopy, Energy Dispersive X-Ray Microanalysis and X- ray diffraction after corrosion test in chloride solutions. We have observed that the presence of either aluminium or SiC reinforced aluminium coatings improve significantly the corrosion resistance of magnesium and magnesium alloys.
3:30 PM		H3-7 Microelectromechanical Systems (MEMS) Electrothermal Actuator with Out-of-Plane Motion E.S. Kolesar, T. Htun, J.S. Tippey, B.L. Least (Texas Christian University) The design, finite-element analysis (FEA) modeling, and experimental characterization of a novel microelectromechanical systems (MEMS) device, known as the out-of-plane electrothermal actuator (VLEA), is presented. This MEMS actuator can function as an assembly tool to initially elevate and position various panels and components that are often required to assemble complex 3-D MEMS technologies. The MEMS actuator investigated in this research can produce incremental out-of-plane deflections greater than 10 µm. These actuators were designed with the MEMSPro CAD program, and they were fabricated using the Polysilicon Multi-User Microelectromechanical Systems Process (PolyMUMPs) foundry operated by the MEMSCAP Corporation. The finite-element analysis (FEA) modeling was accomplished with the IntelliSuite program. An optical fiber interferometer was used to measure the actuator's out-of-plane deflection. The FEA computations and the experimental results were found to agree extremely well. A relative measure of the reliability of this MEMS actuator can be appreciated from the fact that it has been operated in its elastic regime for more than 10 million cycles, and no failures have been observed.