Beam Technologies for Integrated Processing (1992) / Chapter Skim
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5 BEAM APPLICATIONS IN ENGINEERED MATERIALS
5 BEAM APPLICATIONS IN ENGINEERED MATERIALS
Pages 43-70
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From page 43... ...
and chemical vapor deposition (CVD)
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From page 44... ...
TiC beam, cathodic arc, and sputtering sources Corrosion-resistant coatings: PVD Steel strip A1, Zn, Sn, Cr3N2 High-rate electron beam evaporation Zn Resistance-heated source Steel fasteners, aircraft A1 PAPVD using resistance parts, etc. heated evaporation sources High-temperature Ni-Co-Cr-Al-Y, Electron beam evaporation oxidation and corrosion Co-Cr-Al-Y, resistance of turbine Ni-Cr-Al-Y, materials A1 CVD Magnetic media on tape Fe, Co, oxides Evaporation, sputtering, oblique incidence evaporation Heat barriers and moisture A1 Electron beam evaporation barrier coatings on in a continuous or polymeric films semicontinuous film Optical coatings on polymeric | Various metals, oxides, Sputter deposition film multilayers Optical coatings on MgF2, oxides Electron beam evaporation, components such as lenses sputter deposition Optical coatings on glass A1, Ag Evaporation, sputter mirrors, head lamps deposition Photovoltaic solar cells | a-Si:H PACVD l
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From page 45... ...
~3.51 ~1.~-2.0 ~ 2.26 ~ l Chemical stability l Inert, inorganic | Inert, in ganic | Inert, organic IL acids solvents, acids acids l Hardness (vickers, kg/mm2) | 7,000-10,000+ | 900-3,0 l | Thermal conductivity | 20 at 20°C I __ l (cal-cm/cm2-sec°C)
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From page 46... ...
Property Requirement Hard, transparent in visible range of the spectrum Hard, corrosion resistant, wear resistant and chemically inert Very thin films (100 i) with high hardness, corrosion resistance, and chemical inertness Hard, corrosion resistant, chemically inert, transparent in IR region Same as above and refractive index coatings for Ge Low radiation damage, transparent in visible range of the spectrum Self-standing film with high transmission and low damage threshold for x-rays, smooth surface topography Hard, chemically inert, corrosion resistant, insulating high breakdown voltage Same as above and very high thermal conductivity Same as above Same as above and with stringent requirements on optical bandgap, defect states, surface topography, etc.
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From page 47... ...
Unfortunately, it lacks the mystique associated with diamond. SURFACE MODIFICATION Two beam techniques are predominant in surface modification of materials; ion implantation and laser treatment.
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Table 5-5 lists some successful ion implantation applications. There are many new applications where ion implantation is currently under investigation.
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49 Table 5-5 Some Successful Ion Implantation Applications , .. _ Ion Species | Material | Problem | Applications Status Ti+C Ferrous alloys Wear Bearing, gears Production valves, dies Cr | Ferrous alloys Corrosion | Surgical tools Ta+C | Ferrous a l lays Scuff ing wear | Gears Pi lot production P Stainless steels Corrosions Marine products r Research chemical processing C, N Ti alloys Wear, corrosion Orthopedic Production prostheses, aerospace components N Al alloys Wear, mold release Rubber and Preproduction polymer molds evaluation Ho Al alloys Corrosion Aerospace, marine Research N Zirconium alloys Hardness, wear, Nuclear reactor Production corrosion Chemical processing N Hard chrome plate Hardness Valve seats, Pilot production godets, travellers Y
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From page 50... ...
Lasers have also been used to shape hard ceramic materials by ablation. In Si3N4, for example, high material removal rates (1 cm3 in 200 see)
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From page 51... ...
The technique has found application in prototyping and modeling with considerable interest in applying the technique to form waxes for prototype investment castings (ASM International, 1990~. There is a possibility that the technique could be extended to structural materials through application of other processes, such as sintering, melting, and laser chemical vapor deposition (LCVD)
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From page 52... ...
Vapor deposition techniques, discussed below, have been used to form both the reinforcing whiskers and filaments for metal and ceramic composites, and chemical vapor infiltration of fiber preforms is used for matrix formation in ceramic composites. Recent applications of beam technologies to composites are summarized in Table 5-6.
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From page 53... ...
Silicon carbide whiskers are grown today on a commercial basis from the pyrolysis of rice hulls, which are composed mostly of cellulose with hydrated amorphous silica (Lee and Cutler, 1975~. Heating rice hulls in a coking furnace at 1200° to 1800°C causes a reaction between silicon suboxide and carbon via the gas phase to form silicon carbide whiskers (Nuts, 1988~.
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From page 54... ...
For silicon carbide growth, transition metals and iron alloys satisfy this requirement (Milewski et al., 1985~. The process, operated at 1400°C using 30-pm stainless steel catalyst and methane, hydrogen, and silicon monoxide precursors, produces whiskers of a rounded triangular cross-sectional shape (4 to 6 am in diameter)
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From page 55... ...
showed that electron beam distillation is an attractive technique for depositing sheets of reactive metals such as titanium. Ceramic-Matrix Composites Fabrication Ceramic whiskers can be processed with ceramic powders to give a ceramic-matrix composite having improved fracture toughness (Milewski, 1986~.
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From page 56... ...
Thus, a metal-ceramic laminate can have the low thermal conductivity of a ceramic without the brittleness. This suggests potential use of thermal barrier coatings (Radhakrishna et al., 1988~.
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From page 57... ...
has shown that dispersions of nanoscale silicon carbide or silicon nitride particles greatly strengthen and toughen alumina, magnesia, and mullite-based ceramics (Tennery, 1989~. Synthesis of fine ceramic powders from chloromethylsilanes using pulsed excimer radiation is presently being worked on in Australia.
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From page 59... ...
This technology is presently highly advanced, achieving thickness control on each of the 20 to 30 layers in the total fiber of between 2 and 10 percent, depending on the application. Physical vapor deposition, often electron beam evaporation, is used.
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Table 5-9 Practical Optical Solar Energy Solutions Using Deposited Films Process | Material Characteristic l Sputtering TiO-Ag:TiO2 Good visible transmission, good infrared reflection Sputtering, In2O3:Sn, Snow Fair visible transmission, pyrolysis good infrared reflection Sputtering ZnO:A1 Good visible transmission, fair infrared reflection Sputtering Noble metals electron beam, Good infrared reflection evaporation I Dielectric optical waveguides on substrates (Miller and Kaminow, 1984) are used today chiefly in discrete couplers, which may be directional, star, wave-division multiplexing, or polarization retaining.
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From page 61... ...
Armor tiles' coated by CVD processes with carbon and refractory ceramic materials have been developed for this application. A codeposited coating of pyrolytic carbon and silicon carbide has proven particularly effective because of its unusually high resistance to chemical sputtering (Hopkins et al., 1984)
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American Ceramic Society Bulletin 67~2~:381-387.
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1984. Fabrication Fiber-Reinforced Ceramic Composites by Chemical Vapor Infiltration.
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1990b. Fabrication and Mechanical Behavior of Mullite Fiber Reinforced Amorphous Silicon Nitride Matrix Composites Using Chemical Vapor Infiltration.
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1977. Growth Rate of Titanium Carbide Whiskers in Chemical Vapor Deposition.
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American Ceramic Society Bulletin 68~2~:429-442. Koyama, T., and M
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American Ceramic Society Bulletin 68~2~:395-400. Radhakrishna, M
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1988. Theoretical Analysis of Chemical Vapor Infiltration in Ceramic/Ceramic Composites.
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1979. Catalytic Effects of Various Metals and Refractory Oxides on the Growth of TiC Whiskers by Chemical Vapor Deposition.
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Proceedings of the Conference on Chemical Vapor Deposition of Refractory Metals, Alloys and Compounds.
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