Thermal Spray Techniques for Fabrication of Meso-Electronics and Sensors
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E. Tormey Sarnoff Corporation Princeton, NJ.
Introduction THERMAL SPRAY is a directed spray process, in which material, generally in molten form, is accelerated to high velocities, impinging upon a substrate, where a dense and strongly adhered deposit is rapidly built. In the case of ceramic deposits, it is necessary to bring the particles to well above the melting point, which is achieved by either a combustion flame or a thermal plasma arc. The deposit microstructure and, thus, properties, aside from being dependent on the spray material, rely on the processing parameters, which are numerous and complex. In recent years, through concerted, integrated efforts of the Center for Thermal Spray Research at the State University of New York at Stony Brook and others, significant fundamental understanding of the process has been achieved, allowing for an enhanced control of the process. Thermal spray coatings (i.e., thick films > 5 micrometers) are crucial for the economical, safe, and efficient operation of many engineering components. Numerous industries, in recognition of thermal spray's versatility and inherent economics, have introduced the technology into the manufacturing environment. The technology has emerged as an innovative and unique means for processing and synthesizing of high performance materials. The main advantages of the process are: (1) versatility with respect to feed materials (metals, ceramics and polymers in the form of wire, rod or powder); (2) capacity to form barrier and functional coatings on a wide range of substrates; (3) ability to create free-standing structures for net-shape manufacturing of high performance ceramics, composites and functionally-graded materials; and (4) rapid solidification synthesis of specialized materials. Opportunities exist for many novel applications in advanced materials synthesis and deposition. The technology is rapidly becoming the process-of-choice for the synthesis of advanced functional surfaces, such as electrical conductors, magnetic components, dielectrics,ferrites, bio-active materials, and solid-oxide fuel-cells. Thermal spray offers advantages for manufacture of deposits on large area substrates and for the creation of complex conformal functional devices and systems. A more complete overview is given in a recently published MRS Bulletin Issue [1]. The virtues and unique advantages of thermal spray with respect to direct write and related processes are: "* High throughput manufacturing as well as high speed direct writing capability "* In situ application of metals, ceramics, polymers or any combinations of these materials; without thermal treatment or curing incorporation of mixed or graded layers "* Useful materials properties in the as-deposited state "* Cost effective, efficient and ability to process in virtually any environment "* Limited thermal input during processing, allowing for deposition on a variety of substrates "* Adaptable to flexible manufacturing concepts "* Robotics-capable for difficult-to-access and severe environments (portable)
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