Evaluation of pressure effects on sintering

Powder

production

PLASMA-MELT TECHNIQUE ALUMINIDE

ATOMIZING FOR NIOBIUM

The production of fine Fe, Cu, Ni and Nb powders by electrically induced explosion of wires in Ar or air was investigated. Powders were less than 1 pm in size and in air were oxidized. Particle size diminished with increase in energy.

T.Kohno et al. (Mitsubishi Materials Corp, Omiya, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 11, 1996, 1265-1272. (In Japanese.) Intermetallic compounds are discussed with reference to high melting points, mechanical properties and the use of PM in fabrication. It is reported that a novel technique, plasma melt atomization, had been developed to make Nb,Al powder. Metal is melted in a pressurized container. Powders were spherical and consisted of a supersaturated body-centred cubic solid solution of Al in Nb. They had good compactibility. HIP was used for consolidation. OPTIMIZATION PULSATING

OF PROCESSING ORIFICE INJECTION

IN

R.Watanabe et al. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43: No 11, 1996, 1273-1278. (In Japanese.) It is reported that uniform spherical Pb-(2 and 63)%Sn powders had been produced by injecting droplets of molten alloy through an orifice by pulsating applied pressure. Droplets were about the same size as the orifice. Particles were coated with a 10 A thick layer of SnOz. OPERATING ROTATING

PRACTICE ELECTRODE

IN PLASMA PROCESS

R.Kumagae et aZ. (Fukuda Metal Foil and Powder Co, Kyoto, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 11, 1996, 1279-1282. (In Japanese.) A study of operation of the plasma rotating electrode atomization process is described. Ranges of metals and alloys, disc and electrode rotation speeds, and the effect of impinging the metal stream at other than the centre of the disc were investigated. PREPARATION BY EXPLOSION

OF METAL OF METAL

POWDERS WIRES

A.Kato et al. (Kyushu University, Fukouka, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43. No 11, 1996, 1283-l 288. (In Japanese.)

34 MPR June 1998

MORPHOLOGY ELECTRODEPOSITED DENDRITES

OF LEAD

K.I.Popov et al. (University of Belgrade, Belgrade, Yugoslavia.) Powder Technol., Vol93, No 1, 1997, 55-61. Dendrites of Pb were electrodeposited by a pulsating square wave overpotential. The morphology of the dendrites is shown to depend on the shape of the over-potential pulses.

Sintering EVALUATION EFFECTS

ON

OF PRESSURE SINTERING

J.Kihara et al. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 10, 1996, 1163-1170. (In Japanese.) A new analysis of sintering, based on a macro-micro coupling model, is proposed. The method allows prediction of change in microstructure, shrinkage during sintering and description of deformed material. Numerical examples were used to verify the method. SINTERING STRENGTHENED

OF OXIDE DISPERSION NICKEL POWDER

YArami, O.Iwatsu. (Fukuda Metal Foil and Powder Co, Kyoto, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 11, 1996, 1289-1293. (In Japanese.) The poor sinterability of ODS Ni powder in reducing atmospheres was noted. An investigation to improve sintering of Ni-ZrOs is described. It is reported that sintering is enhanced by pre-sintering in air before sintering in a reducing atmosphere. The effect is attributed to formation of a NiO layer which is free from ZrO,. Pre-sintering should be below 1000°C to avoid coarsening of ZrO,.

Fundamentals GRANULAR SIMULATION

MODEL FOR OF POWDER

FORMING

T.Aizawa. (University of Tokyo, Tokyo, Japan.) J. Jpn Sot. Powder Powder MetalE., Vol 43, No 10, 1996, 1159-1164. (In Japanese.) Granular modelling for simulation of compaction, part forming and coupling between powder flow and magnetic fields in compaction is discussed. Granular modelling is reported to be effective in describing powder flow and compaction in real powder forming. Extension to fine grained particles and mesoscopic modelling are considered. MICROSTRUCTURAL GRAIN GROWTH MATERIALS

IN

CONTROL SINTERED

AND

Y.Yamada, R.Watanabe. (Tohoku University, Sendai, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 10,1996, 1177-1176. (In Japanese.) A theoretical and experimental study of grain growth, in the presence of Zener type restraint, in porous compacts is described. Hillert’s rate equation for grain growth is used and grain size distribution is calculated. Three regions of grain size are identified: small shrinking grains; larger stable grain size due to pinning of boundaries by pores; and grain sizes large enough to grow at the expense of small grains. Increase of grain growth restraint displaces the maximum of the grain size distribution curve to smaller sizes. Predicted and experimental results for carbonyl Ni and carbonyl Fe are compared and good agreement is reported. IMPACT STRENGTH MATERIALS

OF

BRITTLE

T.Kaneko. (Japanese Defence Agency, Tokyo, Japan.) J. Jpn Sot. Powder Powder Metall., Vol 43, No 10, 1996, 1231-1237. (In Japanese.) A study to evaluate relationships between Charpy impact strength and other mechanical properties is described for brittle materials. Charpy tests were on notched and un-notched samples. Multiple regression was used to evaluate relationships and establish criteria. It is reported that Charpy impact strength increased in the order WC-Co, Tic-TiN, A&O, and Sic. There was a clear correlation between Charpy strength and static bend strength. TWO MECHANISMS IMPACT BREAKAGE

OF PARTICLE