Advanced Materials & Processes

NOV-DEC 2013

Covers developments in engineering materials selection, processing, fabrication, testing/characterization, materials engineering trends, and emerging technologies, industrial and consumer applications, as well as business and management trends

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i T S S e Opportunities for Thermal Spray in Functional Materials, Electronics, and Sensors 9 spray applications are in the field of protective coatings, where the principle function of the overlay coating is to protect the underlying substrate from heat, contact damage (e.g., wear), or the surrounding operational environment (corrosion). Thermal barrier coatings that protect hot section superalloys in energy and propulsion gas turbines, wide ranging hard metal cermet, and advanced alloy coatings in situations involving abrasion, sliding, or erosion wear, and passive and active (cathodic) protection in corrosive environments are among the most common applications. In most of these situations, coatings can be classified as "passive materials" and typically do not contribute to physical or chemical functional response other than providing a barrier function. As such, the application of thermal spray in truly functional systems—where deposited materials must provide an electronic or sensory function—is limited in scale and scope. However, new opportunities are emerging in advanced functional surfaces, including dielectrics, electrical conductors, magnetics, sensors, and solid oxide fuel cells. In these new applications, thermal spray offers advantages for manufacturing deposits over large area substrates and for creating complex conformal functional devices and systems. One of the most significant functional applications of thermal spray is in the manufacture of solid oxide fuel cells, involving layered material architecture of high Center for Thermal Spray Research Stony Brook University, N.Y. T hermal spray is a directed melt-spray process in which materials in the form of powder, wire, or rod are fed into a thermal source that melts and propels them onto prepared substrates. The resulting deposits are comprised of a splat-based assemblage of discrete particles resulting in a "brick wall" structure with thicknesses ranging from 50 microns to millimeter dimensions. Over the years, thermal spray technology has emerged as an innovative and unique industrial manufacturing process for fabricating advanced coatings out of a range of materials, from low melting plastics to complex multi-component alloys and refractory ceramics. The main advantages of the process include: • Versatility with respect to feed materials (metals, ceramics, and polymers in wire, rod, and powder) • Capacity to form deposits on wide ranging substrates at low substrate temperatures • Ability to apply deposits at high throughput onto complex shapes in a cost effective manner • Nonequilibrium synthesis of novel materials and phases The majority of traditional and contemporary thermal Cathode Electrolyte Anode Porous metal structure (a) (b) Routing to jxn (c) (d) (e) (f) Fig. 1 — Examples of functional coatings and patterned structures produced by thermal spray: (a) solid oxide fuel cells (courtesy Juelich Research Center), (b) direct write antenna, (c) illustration of direct write, thermal sprayed thermocouple on component (courtesy Mesoscribe Tech.), (d) actual instrumented components built, (e) multilayer inductor fabricated with blanket and direct write thermal spray, and (f) proton scintillator coatings as made and with protons. *Member of ASM International and ASM Thermal Spray Society ADVANCED MATERIALS & PROCESSES • NOVEMBER-DECEMBER 2013 69

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