Literature

PARAMETERS FOR CENTRIFUGAL ATOMIZATION OF METAL

K Halada, et al, (National Research Institute for Metals, Tokyo, Japan). Vol 1, Paper 5, 193-199.

Parameters for centrifugal atomization of metal are discussed theoretically and from experiments using Zn. The state of atomization for liquid properties and atomization conditions are represented diagrammatically. Equations for powder diameter and stopping distance are derived.

COMPARISON OF PROCESSING OF ATOMIZED AND SPRAY DEPOSITED AI-Si-Fe-Ni ALLOY PRESSING & SINTERING E Hehmann, et al, (Ecole des Mines de Paris, France). Vol 1, Paper 8,216-226.

Gas atomized powder and spray deposited AI-20%Si-5%Fe-2%Ni (wt%) were compared using differential scanning calorimetry, X-ray diffraction and electron microscopy. Results suggest greater undercooling with spray deposition than with gas atomization. Highest values of UTS were obtained with gas atomized metal (435MPa) after hot extrusion and forging. UTS of sprayed material is lower (380MPa) but there is higher elongation. Manufacture of an automobile component was studied using four different process routes.

WATER ATOMIZED PREALLOYED HEAT TREATABLE STEEL POWDERS FOR PRODUCTION OF HIGH STRENGTH AND DIMENSIONALLY ACCURATE PM PARTS

N Dautzenberg, et al, (Marmesmann-DEMAG Pulvermetall, Munchengladbach, Germany). Vol 1, Paper 9,227-236.

Structure and properties of PM parts produced from Mannesmann prealloyed steel powder (94%Ni, 0.5%Mo 1.0-1 .5%Cu and 0.5-0.7%C) were investigated. Martensitic structure was obtained under controlled cooling conditions from sintering temperature in controlled atmosphere. Tensile strengths up to 850MPa (single pressed) and 1050MPa (double pressed) were observed. Dimensional change (shrinkage) during sintering was compensated for by expansion on formation of martensite and controlled addition of Cu. The component used in experiments was a synchronizer hub which was also plasma-nitrided for enhanced wear resistance.

PRODUCTION OF SEGREGATION-FREE POWER BLENDS: PROCESSING PARAMETERS AND PRODUCT PROPERTIES

F Gosselin, et al, (Quebec Metal Powders Ltd, Tracy, Quebec, Canada). Vol 1, Paper 16, 297-303.

Solid and liquid binders, used in the production of segregation-free powder blends, were compared. Solid binders were more effective in preventing segregation and gave a more flowable powder than those with a liquid binder. Compressibility is reduced by solid binder. Binders were found not to interfere with sintering.

ATOMIZATION OF Cu ALLOYS

K Rzesnitek, et al, (Max Planck Institute, Stuttgart, Germany). Vol 2, Paper 2, 7-10.

Principles of droplet solidification during gas atomization are described. Cooling rates and degree of undercooling are estimated. Aspects of homogeneous and heterogeneous nucleation are discussed. Experimental use was made of Cu and Cu-Sn alloys.

A STUDY OF MECHANISMS IN CENTRIFUGAL ATOMIZATION (CA)

J P Cherre, A Accary, (University of Clermont II, Clermont-Ferrand, France). Vol 2, Paper 3, 11-15.

Mechanisms of particle formation during CA have been studied using the Bi-Sn eutectic and a horizontal disc running at 60 000 rpm. Four mechanisms have been identified: centrifugal atomization, disc rim coalescence, particle collision and erosion of the molten film on the disc surface.

PRODUCTION OF AI-TRANSITION METAL ALLOYS BY ROTATING WATER FILM ATOMIZATION (RWFA) AND MATERIAL EVALUATION

J J Ramon, et al, (Technion, Haifa, Israel). Vol 2, Paper 4, 16-19.

Powders of an A1-Cr alloy were produced by RWFA and characterized by electron microscopy and differential scanning calorimetry. Powders were consolidated by extrusion and tested at various temperatures. The process gives powders comparable in

microstructure with the atomized powder, ie irregular shaped particles with an oxide film.

USE OF Ni-CARBONYL GAS TO COAT PARTICULATE MATERIALS

F W Hech, et al, (Novamet Speciality Products Corp, Wyckoff, NJ, USA). Vol 2, Paper 9, 40--46.

The decomposition of Ni(CO)4 (gas) has been used to deposit Ni on to a variety of particulate materials in heated fluidized beds. The process is described and examples of applications are given.

A QUANTITATIVE THEORY FOR SUPERSOLIDUS LIQUID PHASE SINTERING

R M German (Rensselaer Polytechnic Institute, New York, USA). Vol 1, Paper 3, 172-184.

A theory is presented for supersolidus liquid phase sintering. Densification is by a viscous flow process involving the formation of liquid films at interfaces in polycrystalline, prealloyed particles. Rigidity was determined by percolation threshold where structural integrity is lost and the particle fragments into a viscous solid-liquid mixture. The process is modelled with consideration given to time, temperature and microstructural factors. Results include suggestions for practice.

DEFECT HEALING DURING SINTER/HIP

A Frisch, et al, (Max-Planck-Institut fiJr Metallforschung, Stuttgart, Germany). Vol 1, Paper 10, 237-250.

Densification, creep properties and viscosity of the materials were measured in a load dilatometer. The materials examined were W with an intergranular Ni phase, A1203 and anorthite glass. Elimination of macropores is by a flow of grains and a fluid intergranular phase during sinter/HIP. Conditions for defect healing are quantified as a function of temperature, time, pressure and initial grain size.

784 MPR November 1990