Plasma-spray forming ceramics and layered composites

In a program at the Thermal Spray Laboratory at the State University of New York at Stony Brook, both conventional gas-stabilized plasma and high-throughput water-stabilized plasma spray torches are being used to produce thick free-standing structures of oxide ceramics, metal-reinforced ceramic laminates, and multilayered or functionally graded ceramic materials. The results of the processing, microstructure, and properties of freeforms produced from ceramics in the alumina, zirconia, and alumina-zirconia system are reported.     

Properties of aluminum deposited by a HVOF process

Pure aluminum coatings deposited by a high velocity oxyfuel (HVOF) process have been produced and studied. A simple design-of-experiment (DOE) was used to assess the effect of two deposition parameters, the spray distance and oxygen-to-fuel ratio, on relevant coating properties. Porosity, surface roughness, and micro-hardness of the coatings were measured as responses to changes in the DOE parameters. The results indicated that these three properties of the aluminum coatings were normally insensitive to spray distance. Oxygen-to-fuel ratio, by flow, did appear to affect the porosity level of the coatings. Some post-coat processing of the aluminum coatings and minimization of nozzle loading are discussed.     

Comparative study of the structure of gas-stabilized and water-stabilized plasma jets

The near-field structures of a gas- stabilized plasma jet and a water-stabilized plasma jet were investigated using a nano-pulsed laser probe and stroboscopic focusing schlieren techniques. The high exit temof the gas caused laminar flow conditions at the exit of the jet, producing instability waves in the region. Significant heat conduction to the ambient fluid and volumetric expansion of the ambient gases in the near- field were observed in the schlieren images of these jets. Considerable asymmetry in the mixing and entrainment region of the water- stabilized plasma jet was also visible, whereas no significant asymmetry occurred in the luminous core of the jet. The particles injected into the plasma jet, which were visualized by the pulsed- laser technique, were confined to a narrow central core of the jet in the near- field of the jet. The combination of the two visualization techniques used in the present study allowed nonintrusive monitoring of the plasma spray process in an effort to enhance the quality of the processed deposits.     

Intelligent network evolution issues

The exchange telephone industry has developed a concept of future intelligent network characteristics that is gaining widespread acceptance. The concept is characterized by a service-independent architecture, integrated operations and service management systems, and programmable network entities. The full realization of this vision will require major advancements in the control software and signaling capabilities of existing network elements and operations systems, as well as the development of entirely new systems. Evolutionary strategies are discussed that can move the embedded network toward the ultimate goal and begin to achieve many of the benefits of the future vision in the near term. In particular, an intermediate intelligent network architecture called IN/1+, which could be implemented by 1991, is presented. IN/1+ is focused on circuit-switched capabilities and provides a significant movement toward the intended IN/2 architecture with a reasonable commitment of industry resources     

Real-time imaging of the plasma spray process—Work in progress

A LaserStrobe Control Vision system was employed to examine water-stabilized plasma (WSP), gas-sta-bilized plasma (GSP), and single-wire arc plasma (SWAP) technologies. Visualization of the plasma spray process in each of these technologies has been made possible, in some instances, for the first time. Parame-ter optimization for the three processes was accomplished. This technology has significantly added to the theoretical and scientific knowledge of plasma diagnostics and plasma processing. This summary of work in progress was presented at the NSF Design, Manufacturing and Industrial Innovation Grantees Meeting, San Di-ego, January 4–6,1995.