Ronald D. Ott

Structural and tribological characterization of protective amorphous diamond-like carbon and amorphous CNx overcoats for next generation hard disks

Further insight into processing-structure-property relationships have been carried out for existing and candidate carbon-based protective overcoats used in the magnetic recording industry. Specifically, 5 nm thick amorphous diamond-like carbon (a:C) and nitrogenated diamond-like carbon (a:CNx) overcoats were deposited by low deposition rate sputtering onto a thin film disk consisting of either CoCrPt/CrV/NiP/AlMg or CoCrPt/CrV/glass. The wear durability and frictional behavior of these hard disks were ascertained using a recently developed depth sensing reciprocating nanoscratch test. It was determined that the CN0.14/CoCrPt/CrV/glass disk exhibited the most wear resistance, least amount of plastic deformation, and lowest kinetic friction coefficient after the last wear event. Core level x-ray photoelectron spectroscopy (XPS) results of sputter cleaned overcoats indicated that nitrogen up to 14 at. % incorporated into the amorphous network resulted in these improvements near the overcoat/magnetic layer in...

Friction characteristics of a potential articular cartilage biomaterial

Abstract Many biomaterials are being developed to repair or replace articular cartilage. One of these materials, a poly(vinyl-alcohol) cryogel (PVA-c) may exhibit the mechanical properties required to withstand the harsh environment of diarthrodial joints. To better understand how PVA-c friction is affected by different variables employed in bench top testing to simulate joint conditions, a six-factor, two-level fractional–factorial experiment was developed. Factors included temperature, lubricant, material stiffness, load, sliding speed, and surface roughness. Static and dynamic friction were found to depend significantly on material stiffness and roughness, increasing as material stiffness and roughness increased. Dynamic friction was also inversely proportional to sliding speed. Overall static and dynamic friction for all variables was 0.285±0.091 and 0.143±0.066 (average±S.D.), respectively. Material deformation and other factors may have contributed to the higher than expected friction levels. Frictional behavior of this PVA-c against stainless steel does not follow Amonton’s friction law, nor does it follow friction models based on repulsion and adsorption theories.

The influence of a heat treatment on the tribological performance of a high wear resistant high Si Al-Si alloy weld overlay

Abstract A high silicon (Si)-containing aluminum–silicon (Al–Si) alloy surface weld overlay, deposited on 319 Al alloys, has been developed at Oak Ridge National Laboratory (ORNL) in order to improve surface-dependent properties, like resistance to wear. The overlay deposition process relies on standard techniques for Al manufacturing, therefore no unusual equipment is required. Microscopic examination of the high Si Al–Si weld overlays show a fine eutectic microstructure containing large Si particles, with the overall microstructure characteristic of a hypereutectic Al–Si alloy, similar to 390 Al alloy. The deposition process is versatile enough to be able to place the overlay in critical areas where high wear resistance is needed, thus reducing the overall cost of a component. In order to quantify the wear resistance of the high Si Al–Si overlays, they have been evaluated alongside 390 Al alloy which exhibits high wear resistance. Pin-on-disk (POD) wear tests have been performed on heat-treated (HT) and non-heat-treated specimens consisting of the high Si Al–Si overlays deposited on 319 Al alloy, bulk 390 Al alloys, and bulk 319 Al alloys. The high Si Al–Si weld overlay shows potential as a replacement of bulk 390 Al alloy for applications requiring high wear resistance.

Nanotribology and surface chemistry of reactively sputtered Ti-B-N hard coatings

Abstract The nanotribological performance of Ti–B–N protective coatings, 500 nm thick, have been studied in the range of 0–38.5 at.% N. A correlation was established amongst the chemical state, structure, mechanical properties, and nanowear resistance as a function of atomic percent nitrogen. The mechanical properties, elastic modulus and hardness, of the films were tested using a Hysitron Triboscope nanomechanical test instrument. The nanotribological performance of the films was evaluated using a Nanoindenter II with scratch capability. Single and reciprocating nanowear scratches, 10 μm in length, were performed at normal loads ranging from 50 to 750 μN. An atomic force microscope (AFM) was utilized to characterize the nanowear tracks with respect to depth and amount of plowing of material. The AFM images revealed that the reciprocating nanowear test caused grooving of the films with little to no material removal. Chemical and structural information was obtained by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction. Increasing N content correlated with increasing number of B–N bonds, structural disorder, and decreasing hardness, modulus, and wear resistance.

Heat Exchangers for Heavy Vehicles Utilizing High Thermal Conductivity Graphite Foams

Approximately two thirds of the worlds energy consumption is wasted as heat. In an attempt to reduce heat losses, heat exchangers are utilized to recover some of the energy. A unique graphite foam developed at the Oak Ridge National Laboratory (ORNL) and licensed to Poco Graphite, Inc., promises to allow for novel, more efficient heat exchanger designs. This graphite foam, Figure 1, has a density between 0.2 and 0.6 g/cm 3 and a bulk thermal conductivity between 40 and 187 W/m{center_dot}K. Because the foam has a very accessible surface area (> 4 m 2 /g) and is open celled, the overall heat transfer coefficients of foam-based heat exchangers can be up to two orders of magnitude greater than conventional heat exchangers. As a result, foam-based heat exchangers could be dramatically smaller and lighter.

Direct digital additive manufacturing technologies: Path towards hybrid integration

In the past decade, additive manufacturing and printed electronics technologies have expanded rapidly on a global scale. As the additive manufacturing techniques have become more capable and affordable, and able to work with a broader range of materials, the machines are increasingly being used to make advanced products at significantly lower costs and risks. The additive manufacturing industry is populated by a broad family of technologies, and the present paper provides an overview of key additive manufacturing technologies and their impact on materials processing, device applications, and future markets. Our R&D efforts on the development of core technologies for the realization of flexible electronics, and 3D microscale structures are also highlighted.

XPS study of reactively sputtered Ti–B–N hard coatings

Thin films (500 nm) of Ti–B–N have been produced by d.c. magnetron sputtering from a TiB2 target in various Ar+N2 gas mixtures. The atomic concentration of nitrogen in the films varies between 0 and 38 at.%. The ratio of boron to titanium in the films is fixed by the relative concentration of these two elements in the TiB2 sputtering target. Bonds of B–N, B–Ti, Ti–N and Ti–B are observed in the B 1s and the Ti 2p spectra. The change of shape observed in the N 1s spectra led to the conclusion that at low nitrogen concentration the nitrogen atoms are preferentially bonded with titanium atoms, in good agreement with thermodynamical data. By using quantitative information from the B 1s, Ti 2p and N 1s curve fittings, the formation of a film containing three separate phases (TiN, BN and TiB2) is discussed. Copyright

Generation of nitrogen acceptors in ZnO using pulse thermal processing

Bipolar doping in wide bandgap semiconductors is difficult to achieve under equilibrium conditions because of the spontaneous formation of compensating defects and unfavorable energetics for dopant substitution. In this work, we explored the use of rapid pulse thermal processing for activating nitrogen dopants into acceptor states in ZnO. Low-temperature photoluminescence spectra revealed both acceptor-bound exciton (AX0) and donor-acceptor pair emissions, which present direct evidence for acceptors generated after pulse thermal processing of nitrogen-doped ZnO. This work suggests that pulse thermal processing is potentially an effective method for p-type doping of ZnO.

ADVANCED MANUFACTURING TECHNOLOGIES UTILISING HIGH DENSITY INFRARED RADIANT HEATING

Abstract Oak Ridge National Laboratory has developed a unique rapid heating capability utilising a high density infrared (HDI) radiant plasma arc lamp. Power densities ≤3.5 W cm-2 are achievable over an area 35 x 3.175 cm. The power output of the lamp is continuously variable over a range from 1.5% to 100% of available power, and power changes can occur in <20 ms. Processing temperatures ≤3000°C can be obtained in a wide variety of processing environments, making HDI a flexible processing tool. Recently, this newly developed heating method was used to investigate selective softening, i.e. hardness reduction of 6063-T6 aluminium alloy. By changing the incident power and exposure time, the percentage reduction in hardness and softened zone size can be varied. It is shown that computer modelling can be used to predict the thermal history and the resulting heat affected zone during HDI processing. In the present work, a 50% reduction in hardness was achieved and confirmed by mechanical testing and microstructural investigation. Micrographs of softened aluminium show that Mg2Si precipitates had dissolved back into solution. This new approach allows materials to be engineered for a predetermined response to dynamic loading or other environmental situations. SE/S282

XPS study of polycrystalline and epitaxial FeTaN films deposited by d.c. reactive magnetron sputtering

Thin films of FeTaN have been investigated as potential head materials for several years. However, little information related to its chemical characteristics can be found in the literature, therefore polycrystalline and epitaxial FeTaN films were synthesized by d.c. reactive magnetron sputtering. Follow-up annealing was performed on some of the thin films under vacuum conditions. The chemical compositions and elemental chemical states of both kinds of thin films were investigated by x-ray photoelectron spectroscopy. It is shown that the nitrogen content in the films can be changed and easily controlled by varying the nitrogen gas flow rates during the deposition process. There are no large chemical shifts in the binding energies of Ta 4f, Fe 2p and N Is between polycrystalline and epitaxial films. No chemical compounds among Fe, Ta and N were formed in as-deposited or even in vacuum-annealed thin films. However, a chemical shift of Ta 4f from its atomic state was found. In addition, relatively large contents of carbon and oxygen inside the films were noticed. The existing chemical states, sources and possible effects of nitrogen, carbon and oxygen on the magnetic properties were studied and discussed.