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Atomic oxygen interaction with nickel multilayer and antimony oxide doped MoS{sub 2} films

Description: Sputtered MoS{sub 2} is a solid lubricant capable of ultralow friction coefficients (below 0.05) load-bearing capacity. Since it exhibits low friction in vacuum, low outgassing rate, is non-migrating and lacks organic binders, this material is an attractive lubricant for space mechanisms. To exploit these new materials to their fullest potential, designers of space-based motion systems require data on the effects of atomic oxygen exposure on dense, sputtered MoS{sub 2}. This paper describes the effects of atomic oxygen in low earth orbit on the friction and surface composition of sputtered MoS{sub 2} films. Sputtered multilayer films of MoS{sub 2} with nickel (0.7 nm Ni per 10 nm MoS{sub 2}, for 1 {mu}m total film thickness), and MoS{sub 2} cosputtered with antimony oxide (nominally 2 {mu}m thick) were exposed to 2.2 to 2.5 x 10{sup 20} oxygen/cm{sup 2} over a period of 42.25 hours in earth orbit on the United States space shuttle. Identical specimens were kept as controls in desiccated storage for the duration of the mission, and another set was exposed to an equivalent fluence of atomic oxygen in the laboratory. The friction coefficient in air and vacuum, and the composition of worn surfaces, were determined prior to the shuttle flight and again after the shuttle flight. Results are described.
Date: December 31, 1994
Creator: Dugger, M.T.
Partner: UNT Libraries Government Documents Department

Friction and wear in surface micromachined tribological test devices

Description: We report on the design, construction, and initial testing of surface micromachined devices for measuring friction and wear. The devices measure friction coefficients on both horizontal deposited polysilicon surfaces and vertical etched polysilicon surfaces. The contact geometry of the rubbing surfaces is well-defined, and a method is presented for the determination of the normal and frictional forces. Initial observations on test devices which have been dried with supercritical CO{sub 2} and devices coated with octadecyltrichlorosilane suggest that the coatings increase the lifetime of the devices and the repeatability of the results.
Date: August 1, 1997
Creator: Senft, D.C. & Dugger, M.T.
Partner: UNT Libraries Government Documents Department

Lubricant replacement in rolling element bearings for weapon surety devices

Description: Stronglink switches are a weapon surety device that is critical to the nuclear safety theme in modem nuclear weapons. These stronglink switches use rolling element bearings which contain a lubricant consisting of low molecular weight polytetrafluoroethylene (PTFE) fragments. Ozone-depleting solvents are used in both the manufacture and application of this lubricant. An alternate bearing lubrication for stronglink switches is needed that will provide long-term chemical stability, low migration and consistent performance. Candidates that were evaluated include bearings with sputtered MoS{sub 2} on the races and retainers, bearings with TiC-coated balls, and bearings with Si{sub 3}N{sub 4} balls and steel races. These candidates were compared to the lubricants currently used which are bearings lubricated with PTFE fragments of low molecular weight in a fluorocarbon solvent. The candidates were also compared to bearings lubricated with a diester oil which is representative of bearing lubricants used in industrial applications. Evaluation consisted of cycling preloaded bearings and subjecting them to 23 gRMS random vibration. All of the candidates are viable substitutes for low load application where bearing preload is approximately 1 pound. For high load applications where the bearing preload is approximately 10 pounds, bearings with sputtered MoS{sub 2} on the races and retainers appear to be the best substitutes. Bearings with TiC-coated balls also appear to be a viable candidate but these bearings did not perform as well as the sputtered MoS{sub 2}.
Date: May 1, 1996
Creator: Steinhoff, R.; Dugger, M.T. & Varga, K.S.
Partner: UNT Libraries Government Documents Department

Electrophoretically-deposited solid film lubricants

Description: An aqueous-based process that uses electrophoresis to attract powdered lubricant in suspension to a charged target was developed. The deposition process yields coatings with low friction, complies with environmental safety regulations, requires minimal equipment, and has several advantages over processes involving organic binders or vacuum techniques. This work focuses on development of the deposition process, includes an analysis of the friction coefficient of the material in sliding contact with stainless steel under a range of conditions, and a functional evaluation of coating performance in a precision mechanical device application. Results show that solid lubricant films with friction coefficients as low as 0.03 can be produced. A 0.03 friction coefficient is superior to solid lubricants with binder systems and is comparable to friction coefficients generated with more costly vacuum techniques.
Date: April 1, 1995
Creator: Dugger, M.T.; Panitz, J.K.J. & Vanecek, C.W.
Partner: UNT Libraries Government Documents Department

Particle-surface interactions in chemical mechanical polishing

Description: Material removal in chemical mechanical polishing (CMP) occurs by a pressure accentuated chemical attack of the surface. The polishing slurry typically consists of abrasive particles and reactive chemicals that may or may not include an oxidant. Post-CMP cleaning processes must remove both the ionic contaminants and any remaining polishing slurry particles. Central to the effectiveness of a clean is the use of conditions that will minimize the binding force between the residual particles and the wafer surface. The morphology and composition of the particle, the surface from which it must be removed, and the environment surrounding the wafer will determine the magnitude of forces that hold a particle to the wafer surface. At the Sandia/SEMATECH Center for Contamination Free Manufacturing, two techniques--atomic force microscopy (AFM) and electrokinetic deposition--are being used to explore these interactions for CMP of both oxide and tungsten surfaces. A basic understanding of particle-surface interaction forces and how they are affected by the chemical/physical environment of the particle and surface is the objective of this task. Modification of the binding forces between particles and wafer surfaces may be used to maximize post-CMP cleaning effectiveness.
Date: October 1, 1996
Creator: Dugger, M.T.; Adkins, C.L.J.; Resnick, P.J.; Jeon, J.S. & Raghavan, S.
Partner: UNT Libraries Government Documents Department

Energetic-particle synthesis of high-strength Al(O) alloys

Description: High-strength Al(O) alloys, initially discovered by ion implantation, have now been produced with electron-cyclotron resonance plasma deposition and pulsed-laser deposition. The mechanical properties of these deposited alloy layers were examined with nanoindentation, and finite element modeling of the indented layer on Si substrates was used to determine yield stresses for the alloys of {approximately} 1--5 GPa. The key to these high strengths is the high density of nanometer-size {gamma}-Al{sub 2}O{sub 3} precipitates formed when high concentrations (5--30 at.%) of oxygen are introduced into aluminum as individual atoms or molecules. The strongest alloys have precipitates as small as 1 nm, implying that such small precipitates block dislocation motion. Based upon previous studies with oxygen-implanted aluminum, improved tribological properties are expected for layers made by the two new deposition methods.
Date: September 28, 1995
Creator: Follstaedt, D.M.; Knapp, J.A.; Barbour, J.C.; Myers, S.M. & Dugger, M.T.
Partner: UNT Libraries Government Documents Department

Use of pulsed high power ion beams to enhance tribological properties of stainless steel, Ti, and Al

Description: Enhanced tribological properties have been observed after treatment with pulsed high power ion beams, which results in rapid melting and resolidification of the surface. The authors have treated and tested 440C martensitic stainless steel (Fe-17 Cr-1 C). Ti and Al samples were sputter coated and ion beam treated to produce surface alloying. The samples were treated at the RHEPP-I facility at Sandia National Laboratories (0.5 MV, 0.5--1 {micro}s at sample location, <10 J/cm{sup 2}, 1--5 {micro}m ion range). They have observed a reduction in size of second phase particles and other microstructural changes in 440C steel. The hardness of treated 440C increases with ion beam fluence and a maximum hardness increase of a factor of 5 is obtained. Low wear rates are observed in wear tested of treated 440C steel. Surface alloyed Ti-Pt layers show improvements in hardness up to a factor of 3 over untreated Ti, and surface alloys of Al-Si result in a hardness increase of a factor of two over untreated Al. Both surface alloys show increased durability in wear testing. Rutherford Backscattering (RBS) measurements show overlayer mixing to the depth of the melted layer. X-ray Diffraction (XRD) and TEM confirm the existence of metastable states within the treated layer. Treated layer depths have been measured from 1--10 {micro}m.
Date: April 1, 1998
Creator: Senft, D.C.; Renk, T.J.; Dugger, M.T.; Grabowski, K.S. & Thompson, M.O.
Partner: UNT Libraries Government Documents Department

Oxidation and frictional performance of solid lubricants used in weapon stronglinks

Description: The oxidation and performance of the solid film lubricant used in a majority of the surety devices in the enduring stockpile have been investigated. Oxidation of this lubricant in air at 150 C produces a significant increase in the molybdenum oxide to sulfide ratio, indicative of degradation of the primary lubricating constituent of the composite lubricant. Oxidation is more extensive on samples that were burnished such that the substrate is exposed over a fraction of the surface, relative to those which were only lightly burnished. Friction results indicate that oxidation in air did not increase the initial or steady-state friction coefficient for lightly burnished surfaces. However, surfaces burnished to expose substrate material experienced a significant increase in both initial and steady-state friction. Oxidation of lubricated parts retrieved from aged stronglinks has also been demonstrated.
Date: May 1, 1996
Creator: Dugger, M.T.; Peebles, D.E.; Ohlhausen, J.A.; Varga, K.S. & Steinhoff, R.
Partner: UNT Libraries Government Documents Department

Energetic-particle synthesis of nanocomposite Al alloys

Description: Ion implantation of O into Al and growth of Al(O) layers using electro-cyclotron resonance plasma and pulsed laser depositions produce composite alloys with a high density of nanometer-size oxide precipitates in an Al matrix. The precipitates impart high strength to the alloy and reduced adhesion during sliding contact, while electrical conductivity and ductility are retained. Implantation of N into Al produces similar microstructures and mechanical properties. The athermal energies of deposited atoms are a key factor in achieving these properties.
Date: November 26, 1996
Creator: Follstaedt, D.M.; Knapp, J.A.; Barbour, J.C.; Myers, S.M. & Dugger, M.T.
Partner: UNT Libraries Government Documents Department

The Effect of Humidity on the Reliability of a Surface Micromachined Microengine

Description: Humidity is shown to be a strong factor in the wear of rubbing surfaces in polysilicon micromachines. We demonstrate that very low humidity can lead to very high wear without a significant change in reliability. We show that the volume of wear debris generated is a function of the humidity in an air environment. As the humidity decreases, the wear debris generated increases. For the higher humidity levels, the formation of surface hydroxides may act as a lubricant. The dominant failure mechanism has been identified as wear. The wear debris has been identified as amorphous oxidized silicon. Large slivers (approximately 1 micron in length) of debris observed at the low humidity level were also amorphous oxidized silicon. Using transmission electron microscopy, we observed that the wear debris forms spherical and rod-like shapes. We compared two surface treatment processes: a fluorinated si- lane chain, (FITl) and supercritical C02 dried (SCC02). The microengines using the SCC02 process were found to be less reliable than those released with the FIX process under two humidity levels.
Date: February 2, 1999
Creator: Dugger, M.T.; Eaton, W.P.; Irwin, L.W.; Miller, S.L.; Miller, W.M.; Smith, N.F. et al.
Partner: UNT Libraries Government Documents Department

Electrical Contact Performance Degradation in Electromechanical Components

Description: Detailed materials evaluations have been performed for MC2969 Intent Stronglink switch monitor circuit parts returned from the field out of retired weapon systems. Evaluations of local contact resistance, surface chemical composition and surface roughness and wear have been determined as a function of component level contact loop resistance testing position. Several degradation mechanisms have been identified and correlated with the component level measurements. Operational degradation produces surface smoothing and wear with each actuation of the monitor circuit, while aging degradation is observed in the segregation of contaminant species and alloy constituent elements to the surface in the stressed wear regions.
Date: March 23, 1999
Creator: Peebles, D.E.; Dugger, M.T.; Neff, S.G.; Sorroche, E.H.; Robinson, J.A.; Fanska, J. et al.
Partner: UNT Libraries Government Documents Department

Oxidation Effects on the Friction of Lubricants and Self-Lubricating Materials in the Enduring Stockpile

Description: Predictive models of solid lubricant performance are needed to determine the dynamic behavior of electromechanical devices after long periods of storage. X-ray photoelectron spectroscopy has been used to determine the kinetics of oxidation and sulfate formation for solid lubricants and self-lubricating materials containing MoS{sub 2}, exposed to a variety of oxidation conditions. The frictional performance of the lubricant has then been determined as a fi.mction of its surface chemistry and the ambient environment in which sliding takes place. Results indicate that surface sulfate formation governs the initial or start-up friction coefficient of MoS{sub 2}-containing films, while the composition of the ambient gas determines the steady-state friction coefficient. The dependence of the steady-state friction coefficient on the environment in which sliding takes place has been examined, and the results show that dynamic oxidation of surfaces having exposed metal has a major impact on friction. Surface oxidation is also shown to influence the frictional behavior of a self-lubricating composite material containing MoS{sub 2}.
Date: March 18, 1999
Creator: Dugger, M. T.; Peebles, D. E.; Ohlhausen, J. A.; Robinson, J. A.; Sorroche, E. H. & Fanska, J.
Partner: UNT Libraries Government Documents Department

Microstructure of bulk and electro-formed Ni implanted with Ti and C

Description: The microstructure of high-purity Ni implanted with overlapping concentration profiles of Ti and C was examined with transmission electron microscopy. An amorphous phase forms at concentrations of 15--18 at.% Ti and 22 at.% C, while a two-phase alloy (amorphous + fcc Ni) forms for {le} 16 at.% C. Electroformed layers with sub-micron fcc grains of Ni or Ni{sub 80}Fe{sub 20} were also found to be amorphized by Ti + C implantation, a key requirement for applying this treatment to Ni-based micro-electromechanical systems to reduce their friction and wear.
Date: October 13, 1997
Creator: Follstaedt, D.M.; Myers, S.M.; Knapp, J.A.; Dugger, M.T. & Christenson, T.A.
Partner: UNT Libraries Government Documents Department

Aging model for solid lubricants used in weapon stronglinks: tribological performance and hardware review

Description: The solid lubricant used most extensively in strong links throughout the enduring stockpile contains MoS{sub 2}, which is known to react with oxygen and water vapor resulting in a change in the material`s friction and wear behavior. The authors have examined the frictional behavior of this lubricant as a function of oxidation, in support of efforts to quantify the impact of changes in the material on the dynamic behavior of the MC2969 strong link. Their results show that the friction response of oxidized lubricant is strongly influenced by the amount of burnishing performed on the lubricant after deposition. Low levels of burnish leave a thick film, of which only the near surface degrades during oxidation. Rapid wear of the oxidized material leaves a surface whose properties are the same as non-oxidized material. Higher levels of burnish leave a thinner film of lubricant such that the entire film may be oxidized. The friction coefficient on this surface reaches a steady state value greater than that of non oxidized material. In addition to these fundamental differences in steady state behavior, they have shown that the initial friction coefficient on oxidized surfaces is related to the amount of sulfide converted to sulfate, regardless of the oxidation conditions used. Measurements on parts returned from the stockpile show that the friction behavior of aged hardware is consistent with the behavior observed on controlled substrates containing thin lubricant films.
Date: September 1, 1997
Creator: Dugger, M. T.; Peebles, D. E.; Sorroche, E. H.; Varga, K. S. & Bryan, R. M.
Partner: UNT Libraries Government Documents Department

Lubrication of polysilicon micromechanisms with self-assembled monolayers

Description: Here, the authors report on the lubricating effects of self-assembled monolayers (SAMs) on MEMS by measuring static and dynamic friction with two polysilicon surface- micromachined devices. The first test structure is used to study friction between laterally sliding surfaces and with the second, friction between vertical sidewalls can be investigated. Both devices are SAM-coated following the sacrificial oxide etch and the microstructures emerge released and dry from the final water rinse. The coefficient of static friction, {mu}{sub s} was found to decrease from 2.1 {+-} 0.8 for the SiO{sub 2} coating to 0.11 {+-} 0.01 and 0.10 {+-} 0.01 for films derived from octadecyltrichloro-silane (OTS) and 1H,1H,2H,2H-perfluorodecyl-trichlorosilane (FDTS). Both OTS and FDTS SAM-coated structures exhibit dynamic coefficients of friction, {mu}{sub d} of 0.08 {+-} 0.01. These values were found to be independent of the apparent contact area, and remain unchanged after 1 million impacts at 5.6 {micro}N (17 kPa), indicating that these SAMs continue to act as boundary lubricants despite repeated impacts. Measurements during sliding friction from the sidewall friction testing structure give comparable initial {mu}{sub d} values of 0.02 at a contact pressure of 84 MPa. After 15 million wear cycles, {mu}{sub d} was found to rise to 0.27. Wear of the contacting surfaces was examined by SEM. Standard deviations in the {mu} data for SAM treatments indicate uniform coating coverage.
Date: June 1, 1998
Creator: Srinivasan, U.; Foster, J.D.; Habib, U.; Howe, R.T.; Maboudian, R.; Senft, D.C. et al.
Partner: UNT Libraries Government Documents Department

Strength and tribology of bulk and electroformed nickel amorphized by implantation of titanium and carbon

Description: Dual ion implantation of titanium and carbon was shown to produce an amorphous layer of exceptional strength within annealed bulk Ni and electroformed Ni and Ni{sub 80}Fe{sub 20} materials used in micro-electromechanical systems. The intrinsic elastic and plastic mechanical properties of the implanted region were quantified using nanoindentation testing in conjunction with finite-element modeling, and the results were interpreted in the light of microstructures observed by electron microscopy. The implantation treatment was found to produce substantial reductions in unlubricated friction and wear.
Date: October 1, 1997
Creator: Myers, S.M.; Knapp, J.A.; Follstaedt, D.M.; Dugger, M.T. & Christenson, T.R.
Partner: UNT Libraries Government Documents Department

Aging model for solid lubricants used in weapon stronglinks: Oxidation chemistry and hardware review

Description: In support of efforts to model the performance of the MC2969 strong link for stockpile life extension, the kinetics of oxidation of the MoS{sub 2} based solid lubricant coating have been determined. The lubricant oxidation is primarily influenced by the extent of burnishing of the coating after application and curing. The activation energy for lubricant oxidation is low and agrees well with reported values for MoS{sub 2} coatings and particles. The type of substrate material and the amount of H{sub 2}O vapor present have little influence on the oxidation kinetics, but do affect the chemical species found on the surface, including sulfate species which enhance substrate corrosion. The analysis of field returned hardware shows oxidation levels within the range of those obtained throughout the oxidation study.
Date: September 1, 1997
Creator: Peebles, D. E.; Ohlhausen, J. A.; Dugger, M. T.; Varga, K. S. & Bryan, R. M.
Partner: UNT Libraries Government Documents Department

Performance of Ultra Hard Carbon Wear Coatings on Microgears Fabricated by Liga

Description: Stiction and friction are of concern for the reliable, long-term application of Ni-alloy micromachines. We have found that the application of a 30-70 nm hard carbon coating produces a significant reduction in the friction coefficient and wear rate of electroformed Ni substrates in reciprocating sliding contact under simulated MEMS operating conditions. To evaluate the performance of coated components, a series of 70-pm-thick microgears ranging in diameter from 0.2 to 2.2 mm were fabricated from electroformed Ni via standard LIGA processes and fixtured on posts in preparation for the coating procedure. A pulsed vacuum- arc deposition process was used to deposit a carbon coating on the gears with the plasma incident at a shallow angle to the gears' top surface. A sample bias of -2 keV was used in order to produce a coating with relatively low stress and good adhesion while maintaining high hardness. This coating process is known to be somewhat comformal to the component surfaces. The coating uniformity, particularly in the high-aspect-ratio areas between the gear teeth, was evaluated with micro-Raman spectroscopy. It is shown that the coating can be applied uniformly on the top gear surface. Between the gear teeth the coating was the same thickness as on top of the gear down to a point 50 ~m below the top surface. Below that point (i.e. between 50 and 70 Lm), the coating thickness is somewhat thinner, but is still present. These results demonstrate that it is possible to a deposit hard carbon coating on microgears to reduce friction and wear in micromachines.
Date: December 18, 1998
Creator: Ager III, J.W.; Brown, I.G.; Christenson, T.R.; Dugger, M.T.; Follstaedt, D.M.; Knapp, J.A. et al.
Partner: UNT Libraries Government Documents Department

Fullerene-based materials research and development. LDRD final report

Description: The chemistry and physical properties of fullerenes, the third, molecular allotrope of carbon, have been studied using both experimental and computational techniques. Early computational work investigated the stability of fullerene isomers and oxides, which was followed by extensive work on hydrogenated fullerenes. Our work led to the first synthesis of a polymer containing C{sub 60} and the synthesis of the simplest hydrocarbon derivatives of C{sub 60} and C{sub 70}. The excellent agreement between theory and experiment ({plus_minus} 0.1 kcal/mol in the relative stability of isomers) has provided insight into the chemical nature of fullerenes and has yielded a sound basis for prediction of the structure of derivatized fullerenes. Such derivatives are the key to the preparation of fullerene-based materials.
Date: May 1, 1995
Creator: Cahill, P A; Henderson, C C; Rohlfing, C M; Loy, D A; Assink, R A; Gillen, K T et al.
Partner: UNT Libraries Government Documents Department

Considerations relating to pulsed-beam modification of materials

Description: Ion implantation has been shown to produce unique improvements in the properties of a wide range of materials. This technology has been extensively used for doping of semiconductors, where the required doses and implantation depths are relatively modest and readily achieved with commercial implanters. Other applications of ion implantation currently being pursued at a commercial level include the synthesis of buried second-phase layers in Si and the improvement of metal surface properties such as hardness, friction, wear rate, and corrosion. However, these applications have been severely constrained by the costs of treating large surface areas with the high ion doses required, and by the need to produce modified layers thicker than the range of the sub-MeV ions available from presently available commercial high-flux ion implanters. It therefore seems worthwhile to consider whether pulsed ion accelerators may offer advantages for such applications by providing high ion fluxes at MeV energies. The previously reported applications of pulsed accelerators to materials modification have used sub-MeV ion energies. The purpose of this article is to being these considerations the perspective of materials scientists who use ion implantation. We comment on needed extensions in implantation capabilities while leaving to others the question of whether these needs can be met with pulsed-beam technology. Further, in order to illustrate the kinds of beneficial materials modifications that can be achieved with implantation, we provide examples from recent work at Sandia National Laboratories, where large improvements have been realized in the tribological properties and strengths of Fe and A{ell} alloys. 10 refs., 6 figs.
Date: January 1, 1990
Creator: Myers, S.M.; Follstaedt, D.M.; Bourcier, R.J.; Dugger, M.T.; McIntyre, D.C. & Rader, D.J.
Partner: UNT Libraries Government Documents Department

Molecular-Scale Lubricants for Micromachine Applications: Final Report

Description: The nature of this work was to develop the physics and chemistry base for understanding molecular-scale lubricants used to reduce of friction- and adhesion-induced failure in silicon micromachines (MEMS). We acquired this new knowledge by tailoring the molecular properties of the lubricants, applying local probes that can directly monitor the response of lubricants in contact conditions, and evaluating the performance of model lubricants MEMS devices. Model lubricants under investigation were the silane coupling agents that form monolayer films on native oxide silicon surfaces, which is the substrate in MEMS. These molecules bind via strong surface bonds and produce a layer of hydro- or fluoro-carbon chains normal to the substrate. "Tailoring" the lubricants entails modifying the chain length, the chain chemical reactivity (H or F), and the density of chain structures. Thus much effort went into understanding the surface chemistry of silane-silicon oxide coupling. With proximal probes such as atomic force microscopy (AFM), interracial force microscopy (FM), and shear force microscopy in combination with IFM, we examined the frictional and adhesive properties of the silane films with very high spatial resolution (< 100 nm) and sensitivity. MEMS structures are treated with silanes under identical conditions, and examined for friction and adhesion under operating conditions. Proper assessment of the lubricants required quantitative analysis of MEMS performance at high speeds and long operating times. Our proximal probe measurements and WS performance analyses form a very important link for future molecular dynamics simulations, that, in turn, should be able to predict MEMS performance under all conditions.
Date: December 1, 1998
Creator: Burns, A.R.; Dugger, M.T.; Houston, J.E.; Lopez, G.P.; Mayer, T.M.; Michalske, T.A. et al.
Partner: UNT Libraries Government Documents Department

The effect of frequency on the lifetime of a surface micromachined microengine driving a load

Description: Experiments have been performed on surface micromachined microengines driving load gears to determine the effect of the rotation frequency on median cycles to failure. The authors did observe a frequency dependence and have developed a model based on fundamental wear mechanisms and forces exhibited in resonant mechanical systems. Stressing loaded microengines caused observable wear in the rotating joints and in a few instances led to fracture of the pin joint in the drive gear.
Date: March 1, 1998
Creator: Tanner, D.M.; Miller, W.M.; Eaton, W.P.; Irwin, L.W.; Peterson, K.A.; Dugger, M.T. et al.
Partner: UNT Libraries Government Documents Department

Energetic Particle Synthesis of Metastable Layers for Superior Mechanical Properties

Description: Energetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finite-element simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties, i.e., the yield stress of amorphous Ni(Ti,C) exceeds that of hardened steels and other metallic glasses, and the hardness of DLC (up to 88 GPa) approaches that of crystalline diamond (approx. 100 GPa). Tribological performance of the layers during unlubricated sliding contact appears favorable for treating Ni-based micro-electromechanical systems: stick-slip adhesion to Ni is eliminated, giving a low coefficient of friction (approx. 0.3-0.2) and greatly reduced wear. We discuss how energetic particle synthesis is critical to forming these phases and manipulating their properties for optimum performance.
Date: January 1, 1998
Creator: Follstaedt, D.M.; Knapp, J.A.; Myers, S.M.; Dugger, M.T.; Friedmann, T.A.; Sullivan, J.P. et al.
Partner: UNT Libraries Government Documents Department

Ferroelectric thin film microstructure development and related property enhancement

Description: Factors that control phase evolution, microstructural development and ferroelectric domain assemblage are evaluated for chemically prepared lead zirconate titanate (PZT) thin films. Zirconium to titanium stoichiometry is shown to strongly influence microstructure. As Ti content increases, there is an apparent enhancement of the perovskite phase nucleation rate, grain size becomes smaller, and the amount of pyrochlore phase, if present, decreases. While the pyrochlore matrix microstructure for near morphotropic phase boundary composition thin films consists of two interpenetrating nanophases (pyrochlore and an amorphous phase), the pyrochlore microstructure for PZT 20/80 films deposited on MgO substrates is single phase and consists of 10nm grains. Zirconium to titanium stoichiometry also has a substantial influence on process integration. Near morphotropic phase boundary films exhibit extensive reaction with underlying TiO{sub 2} diffusion barriers; conversely, there is no chemical reaction for identically processed PZT 20/80 thin films. The authors have attempted to directly correlate the optical quality of PZT thin films to the following microstructural features: (1) presence of a second phase, (2) domain orientation, and (3) nanometer surface morphology.
Date: November 1, 1993
Creator: Tuttle, B.; Voigt, J. A.; Headley, T. J.; Potter, B. G.; Dimos, D.; Schwartz, R. W. et al.
Partner: UNT Libraries Government Documents Department