Search

A series of 20 and 100 nm Fe53Pt47 thin films sputter-deposited onto Si substrates have been thermally annealed using a pulsed thermal plasma arc lamp. A series of one, three or five pulses were applied to the thin films with widths of either 50 or 100 ms. The microstructure and magnetic properties of these annealed Fe53Pt47 films are discussed according to the various annealing conditions and A1 to L10 phase transformation. Upon pulse annealing, the average in-plane grain size of 15 nm (nearly equivalent for both film thicknesses) was observed to increase to values near 20 nm. In general, increasing the pulse width or number of pulses increased the L10 order parameter, tetragonality of the c/a ratio and coercivity of the specimen. The exception to this trend was for five pulses at 100 ms for both film thicknesses, which indicated a reduction of the order parameter and coercivity. This reduction is believed to be a result of the interdiffusion of Fe and Pt into the Si substrate and the formation of iron oxide clusters in the grain boundaries characterized by atom probe tomography.

Pulse thermal processing (PTP) of FePt nanoparticle films was studied using a high density infrared (HDI) plasma arc lamp. FePt nanoparticle films on silicon substrates were processed using 0.25- second infrared (IR) pulses. The processing was aimed at reaching a peak target temperature for multiple pulses of 550 C. Numerical simulations of the heat transfer for the PTP were performed to determine the operating power levels for the plasma arc lamp. Infrared measurements were conducted to obtain experimental data for the surface temperature of the FePt nanofilm. Parameters needed for the heat-transfer model were identified based on the experimental temperature results. Following the model validation, several numerical simulations were performed to estimate the power levels. It was shown that the FePt nanoparticle films were successfully processed using the power levels provided by the heat-transfer analysis.

Sputter-deposited, equiatomic PtMn thin films have application in giant magnetoresistive spin valves, tunneling magnetoresistive spin valves, and magnetic random access memory. However, the as-deposited films are found to be a disordered A1 phase in a paramagnetic state rather than an antiferromagnetic phase with L10 structure, which is needed for device operation. Therefore, a postannealing step is required to induce the phase transformation from the asdeposited A1 face-centered-cubic phase to the antiferromagnetic L10 phase. The A1 to L10 metastable transformation was studied by x-ray diffraction and differential-scanning calorimetry. An exothermic transformation enthalpy of −12.1 kJ/mol of atoms was determined. The transformation kinetics were simulated using the Johnson-Mehl-Avrami analysis.

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

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.

A new high density infrared based coating process has been developed to produce wear resistant coatings on AISI 4340 steel substrates that are of commercial interest. The process combines infrared heating, with power densities up to 35 MW m -2, with room temperature precursor spray deposition processes to rapidly form wear resistant coatings. Here, the process is demonstrated using a 20 vol.-%WC reinforced coating in a Ni-11 wt-%P binder on a AISI 4340 steel substrate, to produce a smooth, high density, 10 μm thick coating with minimal degradation of the WC reinforcement or base steel and a hardness seven times greater than that of the substrate.

The stereographic scanning electron microscopy (SEM) imaging was used to investigate the wear mechanism in wire electrical discharge machining (EDM) truing of metal bond diamond wheels for ceramic grinding. A piece of the grinding wheel was removed after truing and grinding to enable the examination of wheel surface and measurement of diamond protrusion heights using a SEM and stereographic imaging software. The stereographic SEM imaging method was calibrated by comparing with the profilometer measurement results. On the wheel surface after wire EDM truing and before grinding, some diamond grain protruding heights were measured in the 32 μm level. Comparing to the 54 μm average size of the diamond grain, this indicated that over half of the diamond was exposed. During the wire EDM process, electrical sparks occur between the metal bond and EDM wire, which leaves the diamond protruded in the gap between the wire electrode and wheel. These protruding diamond grains with weak bond to the wheel were fractured under a light grinding condition. After heavy grinding, the diamond protrusion heights were estimated in the 5–15 μm range above the wear flat. A cavity created by grinding debris erosion wear of the wheel bond could be identified around the diamond grain.

Covering a light-emitting diode (LED) with quantum dots (QDs) can produce a broad spectrum of white light. However, current techniques for applying QDs to LEDs suffer from a high density of defects and a non-uniform distribution of QDs, which respec-tively diminish the efficiency and quality of emitted light. Oak Ridge National Laboratory (ORNL) has the unique capability to thermally anneal QD structures at extremely high power densities for very short durations. This process, called pulse thermal proc-essing (PTP), reduces the number of point defects while main-taining the size and shape of the original QD nanostructure. Therefore, the efficiency of the QD wavelength conversion layer is improved without altering the emission spectrum defined by the size distribution of the quantum dot nanoparticles. The cur-rent research uses a thermal model to predict annealing tempera-tures during PTP and demonstrates up to a 300% increase in pho-toluminescence for QDs on passive substrates

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.

A novel process has been developed at Oak Ridge National Laboratory for the production of high silicon (Si) containing aluminum–silicon (Al–Si) alloy weld overlay on Al alloys. The main purpose of the overlay is to improve the wear resistance of the underlying alloy. The process is versatile enough to place the overlay only in critical areas, thus, greatly reducing the cost of a component. Instead of manufacturing a component from expensive high Si content 390 Al alloy, the component could be manufactured from an inexpensive alloy, such as 319 Al alloy, and the high Si, Al–Si alloy overlay could be placed in essential areas where high wear resistance was required. Test specimens comprised of the high Si, Al–Si alloy overlays on 319 Al alloy have been processed to mimic the wear resistance of bulk 390 Al alloys. Pin-on-disk wear tests have been performed, following ASTM standards, to quantify the wear resistance of the high Si, Al–Si alloy overlay with that of bulk 390 Al alloy. Wear tests have also been p...

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 © 2000 John Wiley & Sons, Ltd.

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.