William T. Donlon

Development of Tial-Based Automotive Engine Valves

The application of TiAl-based alloys as an exhaust valve material would allow automotive engines to operate at higher temperatures with increased efficiencies. Development of these materials at Ford initially concentrated on the Ti-48Al-1V (at%) system. This included: (1) room and elevated temperature fatigue, (2) creep and (3) tensile ductility optimization. Results from this test program in conjunction with other available data, previous ceramic experience and limited engine testing led to the conclusion that the major roadblock to implementation was not optimizing mechanical properties, but rather low cost and reliable valve manufacturing technology. When a cost effective manufacturing technology is developed, then the emphasis will shift to ensuring the product durability. Hence, the focus of the current program is the development of valve manufacturing technologies, in particular valve blank fabrication. Currently, casting appears to be the lowest cost alternative for valve blank fabrication. This paper reviews the technology development process as it pertains to TiAl-based valves.

Unusual microstructures in TiO2 ceramic pellets with asymmetrical electrical conductivity

Ceramic pellets of TiO2 (rutile), with embedded Pt wire electrodes, have been heat treated in a manner that changed the normal electrical properties of rutile at room temperature from those of an insulator to those of a semiconductor with rectifying characteristics. This change in electrical properties was accompanied by the development of unusual microstructures in the rutile grains which were analyzed by a combination of techniques including transmission electron microscopy and scanning transmission electron microscopy. These analyses indicated that, under the applied conditions of heat treatment, Pt diffused into the rutile and reacted initially with the TiO2 at oxygen vacancy sites to form point‐defect agglomerates and that these point defects blocked the normal formation of crystallographic shear planes. As the process proceeded by continued Pt diffusion, thin planar precipitates of PtTi3 were formed in epitaxial relation to the surrounding rutile matrix.

Electrical rectification caused by lamellar microstructures in platinum‐doped TiO2−x ceramics

A heat treatment combining cyclic oxidation/reduction with an applied electric field is described that enhances the diffusion of Pt into TiO2−x ceramics and causes a reaction product of PtTi3 to be formed. The PtTi3 forms as lamellar microstructures within the TiO2−x rutile grains. The ceramics produced by this heat treatment have markedly altered electrical properties showing room‐temperature conductivities increased several orders of magnitude and asymmetrical conductivity (rectification) characteristics.

Processing, X-Ray, and TEM Studies of QS87 Series 56 KΩ/Square Thick Film Resistors

Thick film resistors are glass/metal oxide nanocomposites used in hybrid microcircuits. These components have a small temperature coefficient of resistance that is useful in systems that experience a wide range of service temperatures. Test samples were produced by printing, drying, and firing resistor pastes in a laboratory process that simulated production conditions. The process parameters of peak firing temperature, time at peak temperature, and probe current were factors in a 2 3 factorial experiment that measured in-situ resistance (resistance during processing), as-fired resistance, and the temperature coefficients of resistance. As-fired resistance is shown to increase with firing time and temperature. In-situ resistance exhibited a small decrease with increasing firing temperature due to thermally-activated glass conduction at firing temperatures. The temperature coefficient of resistance measurements show that R[T] curve flattens with increasing firing time and temperature. X-ray diffraction revealed Pb-ruthenate, alumina, and Zr-silicate phases to be dispersed in the glass. Transmission electron microscopy in conjunction with energy dispersive x-ray spectroscopy revealed that the conductive phases, Pb- and CuBi-ruthenate particles, increased in size with increasing firing time and temperature. Lattice parameter measurements revealed only a small increase in the ruthenate structure. Resistance changes are attributed to increased separation of the conductive ruthenate particles by coarsening.

Microstructure and Composition of Surface Layers Formed by Ion Implantation of Nitrogen in High-Purity Aluminum

Surface layers with overall thickness + or N 2 + at energies of 50 or 100 keV in 99.99% pure aluminum. These surfaces were characterized by scanning and transmission electron microscopy, Auger electron spectroscopy, Rutherford backscattering, nuclear reaction analysis and particle-induced X-ray analysis. At doses above 2×10 17 N 2 /cm 2 , blistering of the surfaces was observed along with a reduction in the extent of the coulometric dose retained by the material. Oxygen is believed to be introduced into the near-surface region by a process of reaction and ion-beam mixing, as well as possible CO contamination of the beam. A phase, isostructural with AlN, forms semi-coherently with parent aluminum grains, however, some fraction of the metallic aluminum phase remains in the reaction layer, even at overall nitrogen contents which exceed the stoichiometry of AlN.