Papers by Author: John J. Moore

Abstract: TiC/a:C nanocomposite thin film has proven to be a worthy material selection as a thin film for tribological applications due to its low coefficient of friction, good wear resistance and high hardness. In the current study TiC/a:C thin films with carbon concentration near 55-62 at % were deposited via pulsed closed field unbalanced magnetron sputtering (P-CFUBMS) in pure argon atmosphere with different substrate bias voltages and onto 440C stainless steel substrate with different substrate roughness. It was found that the TiC/a:C film hardness and elastic modulus were increased from 18.5 GPa to 33.8 GPa by increasing the substrate bias from floating to -150 V. However higher substrate bias can also decrease the film tibological properties. The substrate roughness has a strong effect on TiC/a:C film wear behavior. When the Ra (Mean surface roughness values) is less than 110 nm, the COF values are in low range (0.18-0.28). Further increase the Ra value to above 300 nm will result in a higher COF (>0.33). Films deposited on higher surface roughness substrate need longer time to reach the sliding equilibrium state.

Abstract: Self-propagating high temperature (combustion) synthesis (SHS) is being used to develop several synthesis and processing routes for the next generation of ceramic nuclear fuels. These fuels are based on an actinide nitride within an inert matrix. The application of SHS is particularly important in the synthesis of americium (Am) based ceramics; since the rapid heating and cooling cycles used in this process will help to minimize vaporization loss of Am, which is a major problem in synthesizing Am-based ceramics. Manganese, praseodymium, and dysprosium are being used as physical and chemical surrogates for various actinides. Actinide nitride powders produced using auto-ignition combustion synthesis (AICS) are subsequently reacted with zirconium powder using SHS to produce a final fuel pellet. This paper will discuss the research to date on the synthesis of Am-N powders as well as the production of dense Zr-Am-N pellets as a model ceramic fuel system.

Abstract: Porous equiatomic Nickel-Titanium (NiTi) is a strong candidate material for bone engineering applications because its mechanical properties are within the range of bone and its porosity allows for biologic interlock of the material to the surrounding tissue. Self-propagating high-temperature synthesis (SHS) is one method for producing porous NiTi. Nickel and titanium powders, -325 mesh, were mixed for 24 hours then pressed into cylindrical pellets (0.5 inch diameter, 0.5 inch height) to a theoretical green density of approximately 53%. The pellets were preheated in flowing argon for one hour then ignited using a tungsten coil. Scanning electron microscopy and electron dispersive spectroscopy (EDS) show localized differences of stoichiometry suggesting variations in the crystal structure where the Ni to Ti atomic ratio varied between 48.5:51.5 and 50.7:49.3. X-ray diffraction (XRD) (Philips X’Pert PRO) confirmed the presence crystalline equiatomic NiTi as well as other intermetallic compounds including NiTi2 and Ni4Ti3. Nanoindentation (MTS Nano Indenter XP) of this heterogeneous material indicates a mean range indentation modulus of 89.6 ± 9.4 GPa. This is on the same order of magnitude as bone, which has an elastic modulus range of 14-20 GPa.

Abstract: Ti–B–C–N and Ti–Si–B–C–N nanocomposite coatings were deposited on AISI 304 stainless steel substrates by DC unbalanced magnetron sputtering from two (80mol% TiB2–20mol% TiC and 40mol% TiB2–60mol% TiC) composite targets in various Si target powers. The relationship among microstructures, mechanical properties, and tribologiacal properties was investigated. The synthesized Ti–B–C–N and Ti–Si–B–C–N coatings were characterized using x–ray diffraction (XRD) and x–ray photoelectron spectroscopy (XPS). These analyses revealed that the Ti–Si–B–C–N coatings are nanocomposites consisting of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous TiSi2, SiC, and SiB4 matrix including some carbon, BN, CNx, TiO2, and B2O3 components. The addition of Si to the Ti–B–C–N coating led to percolation of amorphous TiSi2, SiC, and SiB4 phases. The Ti–Si–B–C–N coatings exhibited high hardness and H/E values, indicating high fracture toughness, of approximately 35 GPa and 0.098, respectively. Furthermore, the Ti–Si–B–C–N coatings exhibited very low wear rates ranging from ~3×10-7 to ~16×10-7 mm3/(N·m). The minimum friction coefficient of the Ti–Si–B–C–N coatings was approximately 0.15 at low Si target power between 25W and 50W. A systematic investigation on the microstructures, mechanical properties, and tribological properties of Ti–Si–B–C–N coatings prepared from two TiB2–TiC composite targets and one Si target is reported in this paper.

Abstract: High-temperature oxidation behaviors of Ti-Al-Si-N and Ti-Al-N films were comparatively investigated in this work. Two kinds of Ti0.75Al0.25N and Ti0.69Al0.23Si0.08N films were deposited on WC-Co substrates by a DC magnetron sputtering method using separate Ti3Al(99.9%) and Si(99.99%) targets in a gaseous mixture of Ar and N2. Si addition of 8 at.% into Ti-Al-N film modified its microstructure to a fine composite comprising, Ti-Al-N crystallites and amorphous Si3N4, and to a smoother surface morphology. While the solid solution Ti0.75Al0.25N film had superior oxidation resistance up to around 700
, the composite Ti-Al-Si-N film showed further enhanced oxidation resistance. Both Al2O3 and SiO2 layers played roles as a barrier against oxygen diffusion for the quaternary Ti-Al-Si-N film, whereas only the Al2O3 oxide layer formed at surface did a role for the Ti-Al-N film. Oxidation behavior and mechanical stability of the films after oxidation were compared between two films using instrumental analyses such as XRD, GDOES, XPS, and scratch test.

Abstract: The paper will present the methodology used to design optimized die coatings employed in material forming processes in an effort to extend the life and effect efficient operation of the dies. An optimized die coating 'architecture' requires that the coating system be essentially non-wetting with the material (metal, glass, polymer) being formed in the die, coupled with good wear and oxidation resistance Other factors, such as delaying the onset of thermal fatigue cracking (heat checking), and an acceptably low coefficient of friction. And, possibly, self-lubricating, also need to be considered based on the processing and forming conditions that include both liquid and solid materials. Many different die coatings have and are being used with different levels of success. This paper presents the current understanding that has been gained in laboratory testing, in-plant trials, and modeling in an effort to generate a fundamental understanding of how such optimized die coating systems may be designed for specific forming operations and conditions, with examples based on dies used in aluminum pressure die casting, glass molding, and metal forming operations.