Operation practice in plasma rotating electrode process — Melting and droplet formation

Powder production ENVIRONMENTALLY INERT NANO-CRYSTALLINE MATERIALS T. Lowe et al. (Materials and Electrochemical Research, Tucson, Arizona, USA.) Mater. and Manux Processes, Vol 11, No 6, 1996, 1013-1028. A novel process to produce inert nanocrystalline metallic powders, coated with C, is described. The method was developed from the arc technique used to make buckyballs. Particles 10 to 50 nm are made and are stable in air. Experiments in consolidation are described and applications are discussed. OPERATION PRACTICE IN PLASMA ROTATING ELECTRODE PROCESS MELTING AND DROPLET FORMATION R. Kumagae et al. (Fukuda Metal Foil and Powder Co Ltd, Kyoto, Japan.) J.Japan Sot. Powder and Powder Metallurgy, Vol 42, No 6, 1995, 741-745. (In Japanese.) Investigations of operating practice in PREP are described. A variable studied was deflection of the plasma centre from the axis of the electrode. It is concluded that this is a controlling factor for particle size by keeping the electrode tip flat. This leads to uniform droplet size as the electrode rotates

Fundamentals TWO-PHASE FLOW MODEL FOR CLOSE COUPLED ATOMIZATION OF METALS R.S. Miller et al. (Scopi Services, Ballston Spa, NY, USA) ht. J. Powder Metallurgy, Vol 32, No 4, 1996, 341-352. Models for nozzle tip static aspiration pressure, gas and metal flows during close coupled gas atomization were reviewed. From calculations it is shown that metal flow is not solely determined by aspiration pressure. An improved model is described which provides an interpretation of the relationship between metal flow and aspiration pressure and provides a basis for operational parameters. Tests showed the validity of the model. MILLING DYNAMICS IN A REAL MILL AND A HYPOTHETICAL ONEDIMENSIONAL MILL D. Maurice, T.H. Courtney. (Michigan Technological University, Houghton, USA) Metall. and Mater. Tram A, Vol 27A, No 7, 1996, 1973-1979. Dynamics of mechanical milling are discussed in localized and generalized 50

MPR May 1997

terms. Local parameters are powder deformation, welding and fracture. Generalized descriptions consider factors such as input energy and powder segregation. A study of a particular mill is described and the study extended to a hypothetical one dimensional mill. Attention is given to mill efficiency and powder characterization. MICROMECHNICAL ANALYSIS OF PRESSURE-VOLUME RELATIONSHIP FOR POWDER COMPACTION M.J. Adams, R. McKeown. (Unilever, Port Sunlight, Wirral, UK.) Powder Technology, Vol 88, No 2, 1996, 155-163. Models for powder compaction are discussed with regard to their often empirical nature. It is shown that a lumped parameter relationship, or one due to Kawakita, can be used to estimate the strength of powder agglomerates provided that die wall friction is considered. A model is proposed which give an explicit form of Kawakita’s relationship which applies to plastic deformation rather than fracture.

Aluminium MECHANICAL PROPERTIES OF EXTRUDED BARS OF GAS ATOMIZED ALUMINIUM-SILICON-IRON POWDERS Y.S. Choi, H.Y.Ra. (Seoul National University, Seoul, Korea.) J. Korean Inst. of Metals, Vol 34, No 4, 1996, 457-462. (In Korean.) Microstructural evolution during hot extrusion of gas atomized Al-(20 or 3O)wt%Si-(3,5 or 8)%Fe powders and resulting mechanical properties were investigated. Extrusion is shown to reduce the size of the Si particles to less than 10 pm and the intermetallic particles to below 5 pm. The metastable 6 phase (A14FeSiz) decomposed and p (AlsFeSi) formed resulting in hardening. Best properties were attained in A1-2O%Si-8%Fe. EFFECTS OF TERNARY ELEMENTS ON CREEP-RUPTURE OF MECHANICALLY ALLOYED ALUMINIUM-TITANIUM S.Y. Lee, KS. Lee. (Hanyang University, Seoul, Korea.) J. Korean Znst. of Metals, Vol 34, No 4, 1996, 463-469. (In Korean.) The effects of third elements, B, V, Ce or Zr on high temperature mechanical properties of &8wt%Ti werte investigated. The third elements are reported to enhance creep properties. This is attributed to formation of a fine dispersion of ternary aluminides.

DEFORMATION OF PM SUPERPLASTIC ALUMINLUM ALLOYS K Higashi. (University of Osaka Prefecture, Osaka, Japan.) J.Japan Sot. Powder and Powder-Metallurgy, Vol42, No 6, 1995, 725. 734. (In English.) Superplasticity in nano-crystalline Al alloys is discussed. Experimental results on deformation at high strain rates are reviewed with respect to grain size and nature of grain boundaries. Optimum conditions are shown to depend on grain refinement ANALYSIS OF RESIDUAL SURFACE OXIDE FILMS ON ALUMINIUM POWDERS IN SINTERED COMPACTS T. Miyazaki et al. (University of Tokyo, Tokyo, Japan.) J.Japan Sot. Powder and Powder Metallurgy, Vol42, No 6, 1995, 752. 757. (In Japanese.) Oxide films on metal powders are discussed with reference to the fact that they may be reduced during sintering or remain to influence properties. Effects of powder characteristics and process conditions on residual 0 in Al were investigated using an electrical resistivity technique. Conditions of measurement and effects of contiguity were studied. The remaining continuous Al oxide films tended to be more stable at smaller particle sizes and lower sintering temperatures. HIGH STRAIN RATE SUPERPLASTICITY IN ALUMINIUM-ZINC-MAGNESIUM WITH SILICON NITRIDE M. Mabuchi, K. Higashi. (University of Osaka Prefecture, Osaka, Japan.) J.Japan Sot. Powder and Powder Metallurgy, Vol 42, No 6, 1995, 758-761. (In English.) Superplasticity in Al-Zn-Mg composites, reinforced with particle or whisker Si3N4, was investigated at high strain rates. Elongations of 230% for the whisker reinforced alloy and 330% for the particle material are reported.

Copper ALUMINIUM OXIDE DISPERSION STRENGTHENED WIRE H. fijimaki et al. (Yazaki Corp, Susono, Japan.) J.Japan Sot. Powder and Powder Metallurgy, Vol 42, No 5, 1995, 628-633. (In Japanese.) It is reported that Cu wire with dispersed AlzOs had been prepared by