Machining of silicon nitride materials by means of ultrasonic lapping

method (BEM) is used to analyze levelling caused by inhibitors consumed at the transport limiting rate during electrodeposition. It is predicted that (1) better levelling performance can be obtained if the microscopic surface waviness is oriented perpendicular to the convective flow, and (2) for surface roughness oriented parallel to the flow, there is an optimum boundary layer thickness, or flux of additive, which results in superior levelling performance. Profilometry and photomicrography is applied to obtain the current distribution, current efficiency and levelling performance on novel microprofiled electrodes for two orientations with respect to the fluid flow during nickel electrodeposition in the presence of Coumarin. Slightly better levelling occurs in flows transverse to grooves, and the deposit thickness increases in the flow direction. It is concluded that coumarin acts by simultaneously lowering the current efficiency, and blocking metal deposition. 331 refs., 86 figs., 8 tabs. Index Terms: Copper - electrodeposition: Electrodeposited coatings - electric conductivity; Nickel - electrodeposition; Boundary layers; Charged-particle transport: Convection; Corrosion effects; Coumarin; Electrodes; Photomicrography; Surfaces; Coatings; Computer Codes; Deposition; Electrical properties; Electrolysis; Elements; Energy transfer; Esters; Heat transfer: Hetercyclic compounds; Lactones; Mass Transfer; Metals; Organic compounds; Organic oxygen compounds; Photography; Physical properties; Pyrans; Radiation transport: Surface coating; Transition elements. 40, D. G. Chetwynd, "Linear translation mechanisms for nanotechnology applications," Measurement and Control, 24(2), pp. 52-55. (March 1991). Some approaches to the design of straight-line motion mechanisms for nanometre level metrology instruments are discussed and compared. In particular, the potential benefits of monolithic flexure mechanisms driven by compliant electromagnetic force transducers are explored. Index Terms: Electric control equipment; Physical instrumentation control; Position control; Spatial variables measurement; Linear translation mechanisms; Nanotechnology applications: Monolithic flexure mechanisms; Compliant electromagnetic force transducers. 4t, T. Baak, P. Jones, "Low expanding mirror glass," Properties and Characteristics of Optical Gla~s 11, Vol 1327, pp. 231237. Int Soc for Optical Engineering, Bellingham, WA. A series of glasses with low thermal expansion has been studied for the purpose of developing a mirror substrate. One particular composition has been found to have desirable optical fabrication characteristics of ease of grinding and polishing. The approach in tailoring the thermal expansion with the chemical composition is explained. 16 Refs. Index Terms: Mirrors - materials; Glass - optical quality; Optical materials - Glass: Thermal effects: Thermal expansion; Mirror glass; Optical glass, 42, R. A. Paquin, M. B. Magida, "Low scatter surfaces on silicon carbide," Proceedings of the 21~t Symposium on Opticai Materials for High-Power Lasers - Boulder Damage Symposium, Vol 801, pp. 256-262. Natl Inst of Standards & Technology, c/o US Department of Commerce, Gaithersburg, MD. Reaction bonded silicon carbide (RB SiC) can be readily fabricated to near net shape and mirror blanks produced by this method can potentially be less costly than those fabricated by chemical vapor deposition (CVDL However, RB SiC is two phase, SiC and up to 30% silicon (Si), and can not normally be directly polished to low scatter and roughness levels due to the difference in hardness of the two phases. We have investigated the potishability of RB SiC as a function of Silicon content and microstructure. Our results show that with a favorable microstructure, RB SiC can be polished to less than 10 rms. For reduced roughness and lower scatter surfaces, we have developed low temperature deposition techniques to apply polishabte, single phase coatings to the figured two phase surfaces. Scatter and roughness measurements show levels are comparable to CVD SiC. Index Terms: Optical materials - machining; Laser beams; Optical variables measurements; Silicon carbide: lon assisted deposition: Reaction bonded silicon carbide (RB SIC). 43, P. J. Blau, C. E. DeVore, "Machining and wear relationships in an ordered intermetallic alloy," International Conference on Wear of Materials, Vol 1, pp. 547-554. ASME, New York, NY. There are many commonalities between machining (metal cutting) and sliding friction and wear. Machining (lathe-turning) experiments and ball-on-disk wear experiments have been Conducted on a nickel aluminide alloy (IC-218 LZr). The wear tests were performed at room temperature and at 923 K (650 °C) using tungsten carbide as the slider material to simulate the cutting-tool material. The effects of cutting speed, use of a coolant, and type of cutting tool on surface finish, depth of workpiece subsurface damage, and cutting chip characteristics are reported. The depth of damage in sliding wear experiments is compared to that for lathe-turning experiments in an attempt to estimate the shear forces on the cut surface. Friction coefficients and wear factors for tungsten carbide sliding on IC-218 LZr depended on the magnitude of the normal force and on the sliding temperature. The wear rate of the nickel aluminide alloy decreased as the temperature increased. The relationship between the observed friction and wear behavior of nickel aluminide and its machining characteristics are discussed. Index Terms: Intermetallics - Wear; nickel and alloys - Wear; Metals and alloys - machining; Wear of materials - testing; Tribotogy applications; Metal cutting - Analysis; Ordered intermetallic alloys; Nickel aluminide alloy; Sliding wear testings; Ball-on-disk testing. 44, H. H. Noelke, Machining of silicon nitride materials by means of ultrasonic lapping, (Hannover Univ. (Germany, F.R.), 8 Jul 1980). Present work is to find out to what extent silicon nitride materials are machinable through ultrasonic lapping. It is to also develop technological basics for expanded kinematic technique arrangements for forming by means of geometrical producing. The examinations show that reaction-sintered silicon nitride can be machined with higher processing rate and lower formed parts wear than the hot-pressed material. For the examination of expanded technique arrangements, different cross feed motions of different kinematics were produced with the aid of specific cross feed equipment. A limiting cross feed motion must not be fallen below in the case of ultrasonic lapping with cross feed motion. A definition equation for the determination of this limiting value is specified. The result in the case of ultrasonic lapping with cross feed motion depends on wear of the formed parts more strongly than in the case of conventional ultrasonic machining. The wear form can be influenced favorably by suitable formed parts geometry or by changed kinematics of the technique arrangement. Index Terms: Silicon nitrides - ultrasonic machining; Ceramics; Grinding; Machine tools; Materials drilling; Mechanical vibrations; Surface finishing; Wear; Comminution; Machining; Nitrides; Nitrogen compounds; Silicon compounds.

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OCTOBER 1991 VOL 13 NO 4