Publications

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The major focus of this study was to examine the feasibility of applying diamond-like nanocomposite (DLN) coatings on the sidewalls of Ni alloy parts fabricated using lithographie, galvanoformung and abformung (LIGA: a German acronym that means lithography, electroforming, and molding) for friction and wear control. Planar test coupons were employed to understand the friction mechanisms in regimes relevant to LIGA microsytems. Friction tests were conducted on planar test coupons as well as between LIGA-fabricated test structures in planar-sidewall and sidewall-sidewall configurations. Measurements were made in dry nitrogen and air with 50% relative humidity by enclosing the friction tester in an environmental chamber. In contrast to bare metal-metal contacts, minimal wear was exhibited for the DLN-coated LIGA NiMn alloy parts and test coupons. The low friction behavior of DLN was attributed to its ability to transfer to the rubbing counterface providing low interfacial shear at the sliding contact. The coating coverage and chemistry on the sidewalls and the substrate-coating interface integrity were examined by transmission electron microscopy, Automated eXpert Spectral Image Analysis, and electron backscatter diffraction on cross sections prepared by focused ion beam microscopy. The role of novel characterization techniques to evaluate the surface coatings for LIGA microsystems technology is highlighted. © 2009 IEEE.

In ductile metals, sliding contact induces plastic deformation resulting in subsurfaces, the mechanical properties of which are different from those of the bulk. This article describes a novel combination of nanomechanical test methods and analysis techniques to evaluate the mechanical behavior of the subsurfaces generated underneath a wear surface. In this methodology, nanoscratch techniques were first used to generate wear patterns as a function of load and number of cycles using a Hysitron TriboIndenter. Measurements were made on a (001) single crystal plane along two crystallographic directions, <001> and <011>. Nanoindentation was then used to measure mechanical properties in each wear pattern. The results on the (001) single crystal nickel plane showed that there was a strong increase in hardness with increasing applied load that was accompanied by a change in surface deformation. The amount of deformation underneath the wear patterns was examined from focused ion beam cross-sections of the wear patterns. © 2009 Materials Research Society.

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High performance soft magnetic alloys are used in solenoids in a wide variety of applications. These designs are currently being driven to provide more margin, reliability, and functionality through component size reductions; thereby providing greater power to drive ratio margins as well as decreases in volume and power requirements. In an effort to produce soft magnetic materials with improved properties, we have conducted an initial examination of one potential route for producing ultrafine grain sizes in the 49Fe-49Co-2V alloy. The approach was based on a known method for the production of very fine grain sizes in steels, and consisted of repeated, rapid phase transformation cycling through the ferrite to austenite transformation temperature range. The results of this initial attempt to produce highly refined grain sizes in 49Fe-49Co-2V were successful in that appreciable reductions in grain size were realized. The as-received grain size was 15 {micro}m with a standard deviation of 9.5 {micro}m. For the temperature cycling conditions examined, grain refinement appears to saturate after approximately ten cycles at a grain size of 6 {micro}m with standard deviation of 4 {micro}m. The process also reduces the range of grain sizes present in these samples as the largest grain noted in the as received and treated conditions were 64 and 26 {micro}m, respectively. The results were, however, complicated by the formation of an unexpected secondary ferritic constituent and considerable effort was directed at characterizing this phase. The analysis indicates that the phase is a V-rich ferrite, known as {alpha}{sub 2}, that forms due to an imbalance in the partitioning of vanadium during the heating and cooling portions of the thermal cycle. Considerable but unsuccessful effort was also directed at understanding the conditions under which this phase forms, since it is conceivable that this phase restricts the degree to which the grains can be refined. Due to this difficulty and the relatively short timeframe available in the study, magnetic and mechanical properties of the refined material could not be evaluated. An assessment of the potential for properties improvement through the transformation cycling approach, as well as recommendations for potential future work, are included in this report.

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Spectrum imaging combined with multivariate statistics is an approach to microanalysis that makes the maximum use of the large amount of data potentially collected in forensics analysis. Here, this study examines the efficacy of using spectrum imaging-enabled microscopies to identify chemical signatures in simulated bioagent materials. This approach allowed for the ready discrimination between all samples in the test. In particular, the spectrum imaging approach allowed for the identification of particles with trace elements that would have been missed with a more traditional approach to forensic microanalysis. Finally, the importance of combining signals from multiple length scales and analytical sensitivities is discussed.

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