Use of percolation theory to predict shape distortion in liquid phase sintering

Powder production FLUIDIZED BED NITRIDING OF FINE SILICON POWDER Y.D.Liu, SKimura. (Oregon State University, Corvallis, USA.) Powder Technol., Vol 106, No 3,1999,160-167. Batch and semi-continuous nitriding of two pm size Si powders, mixed in various proportions with 300 ,umA&O,, was investigated in a fluidized bed, at 1200 to 1300 “C, in N-H gas. When less than 5%Si was used no 8 Si nitride was formed in the product. Above 5%Si both a and 8 forms were synthesized. Excessive Si resulted in failure of the bed to fluidize.

Pressing EFFECT OF PUNCH CURVATURE ON PROPERTIES OF COMPACTED POWDERS J.M.Newton et al. (School of Pharmacy, University of London, UK.) Powder Technol., Vol 107, No l/2,2000,78-83. An investigation of compaction of powders between curved punch faces was described. Mechanical properties were found to vary with compact size and punch radius. This is attributed to variations in compact structure.

Sintering DENSIFICATION DURING LIQUID PHASE SINTERING OF PREALLOYED NICKEL BASE POWDER MIXTURES R.M.German et al. (Pennsylvania State University, USA.) Metall. Mater. Trans A., Vol30A, No 8,1999,2201-2208. Liquid phase sintering of a mixture of two prealloyed Ni base powders, one containing B to reduce the melting temperature, was investigated. Sintering was above the melting temperature of the alloy with B. Densiflcation was studied by a range of methods. Increase in the proportion of the B-free powder retarded densiflcation. A model was developed to extend models for sintering of a single prealloyed powder to mixtures of prealloyed powders. Homogenization considered. between powders is Densification is shown to depend on the extent of melting of the low melting powder and the proportion of the higher melting powder.

42 MPR November 2000

USE OF PERCOLATION THEORY TO PREDICT SHAPE DISTORTION IN LIQUID PHASE SINTERING R.M.German et al. (Pennsylvania State University, USA.) Metall. Mater. Trans A., Vol3OA, No 8,1999,2209-2220. Application of percolation theory to the onset of shape distortion during liquid phase sintering is modelled and discussed. The model considers the number of bonds per grain and the bond strength and size. Shape distortion is resisted by a rigid compact and there is a critical value for contiguity, near to 0.38, for this condition. This is shown to agree with measured values for W-Fe-Ni sintered in terrestrial and microgravity conditions. Gravity is reported to be significant only after the onset of distortion. TRANSIENT LIQUID PHASE DIFFUSION BONDING WITH IMPOSED TEMPERATURE GRADIENT A.A.Shirzadi, E.R.Wallach. (University of Cambridge, Cambridge, UK.) Acta Mater., Vol47, No 13,1999,3551-3560. It is reported that a transient liquid phase bonding procedure, with an imposed temperature gradient, had been used to make joints with good reliability and strength comparable with the parent alloys, Al alloys and composites. The process depends on diffusion through the liquid. A model is proposed for prediction of bonding time and displacement of the bond line and was validated for pure Al with a Cu interlayer.

Fundamentals EXPERIMENTAL STUDY OF DRUM MIXING KINETICS USING IMAGE ANALYSIS B.R.Young et al. (University of Calgary, Alberta, Canada.) Powder Technol., Vol 106, No 3, 1999,183-191. It is reported that mixing in a rotating drum mixer had been investigated by image analysis. The results initially showed that mixing proceeded at a uniform rate to completion but close analysis showed that mixing occurred in stages. MECHANISMSAND EINETICS OF MECIIANO-CHEMICALPROCESSES IN COMMINUTING DEVICES F.K.Urakaev, V.V.Boldyrev. (Siberian Branch of Russian Academy of Sciences,

Novosibirsk, Russia.) Powder Technol., Vol 107, No l/2,2000,93-107. Models for mechano-chemical processes, in various types of equipment, are reviewed. Pressures and temperatures at interparticle impacts are calculated. Equations for rate constants of mechano-chemical reactions and for activation of substances are deduced. THERMAL FATIGUE TEST VERIFICATION V.Pulc et al. (STU, Bratislava, Slovak Republic.) Pokroky Pras. Metal, Vol 37, No 2,1999,32-37. (In Czech.) It is reported that in thermal fatigue tests on precracked S&N, samples the measured crack depth after testing was ten times the depth predicted by computation.

Aluminium MECHANICAL PROPERTIES OF UITRAFINE ALUMINIUM-TITANIUM MADE BY DOUBLE MECHANICAL ALLOYING J.K.Yang et al. (Korea University, Seoul, Korea.) J. Korea Inst. Metals, Vol 37, No 7,1999,760-765. (In Korean.) It is reported that a double mechanical alloying technique had been applied to prepare dispersion strengthened AlTi alloys and elevated temperature properties determined. The resulting structure was finer and precipitates were smaller and more uniformly dispersed. The AlsTi phase particles were smaller than 30 nm. Extended solubility of Ti in Al was estimated to be 8.82wt%. There was no improvement in mechanical properties due to the large volume of intermetallic dispersoids. DEVELOPMENT OF SINTERED ‘Ixxx ALUMINIUM ALLOYS G.B.Schaffer, S.H.Huo. (University of Queensland, Australia.) Powder Metall., Vol47, No 3,1999,219-226. Sintering and tensile properties of 7000 Al alloys, Zn-Mg-Cu, made from elemental powders by pressing and sintering, were investigated. It is reported that microalloying with 100 ppm Pb or Sn enhanced sintering. Aspects of both transient and supersolidus liquid phase sintering are present in the alloys, making sintering characteristics sensitive to process and powder parameters. Green