that it does not work at low pressures. It was reported that two new laws, one being a com- plement to Heckel, had been formulated to overconre this difficulty. These were used in study of a powder and sample testing was shown to contribute to quality control.

Characteristics and production of compound powder articles

Y.U.Kem et al. (Don State Technological University, Rostov-on-Don, Russia

Characteristics of compound powder articles were investigated. It was shown that sub-parts can be joined during sintering. Joints could be strong if structures at the joint interface are similar to the base materials. Mechanisms of joining were outlined. Properties were investi- gated as influenced by thermo-diffusion alloy- ing and effects ofNi , Cr and Si.

Improvement in ductility of welded molybdenum by addition of alloy elements

M.K.Mill*,r et al. (Oak Ridge National Laboratory, USA.)

It is reported that ductility of Mo weldments can be improved by addition of B, Zr and C, in ppm amounts. Twenty per cent ductility was attained in 6.35nmr thick plate, compared with 3% usually reached. This was attributed to increase in fracture toughness of grain bound- aries. Segregation of B, Zr and C to and deple- tion of O from grain boundaries in base metal and heat-affected zones were detected by atom probe tomography.

EURO PM 20m. The Abstracts which follow are from papers presented at the 2001 European Congress on Powder Metallurgy, which was held in Nice, France, in October 2001.

Powder production Fabrication of nano-structured sub-micron metal powders by ultrasonic atomisation

B.C.lausen et al. (Lhdversit 7 of Applied Sciences of Western Switzerland, Sion, Switzerland.)

An atomiser for production of submicron, nanostructured metal powders with melting points up to 2000°C was described. The metal or alloy is induction melted, homogenised by Ar stirring and atomised into spherical by a tubular ultrasonic resonator in Ar or He. Droplet size is determined by parameters of the ultrasonic transducers. Cooling is rapid. Powders can be passivated by addition of O or CO 2 to the atmosphere. The method is expect- ed to be comnrercially viable.

Oxidation of heat-treated mechanically alloyed powders and consolidation

A R .Jones e t al. ( University of Liverpool, Liverpool, UK. )

Oxide dispersion strengthened alloys, made by mechanical alloying and consolidation, were discussed with regard to potential appli- cations. It was found that during heat treat- ment the materials studied, ODS-Fe;A1 and a Fe-Cr-AI alloy had become oxidised. This oxidation was shown to be the source of AIzO ~. Novel processing was devised to reduce the amount of oxidation and is report- ed to be promising.

Production of selenium powder from anode slimes

L.Avramovic et al. (Copper Inst. B~r, Bor, Yugosla~.,ia.)

Developments in processing of Cu anode slimes were reported. The aim was to remove Se from the slimes and produce Se powder of commercial quality. The slimes were roasted in air to produce SeO 2, which was reduced to Se powder in H2SO 4 solution. The purity of the Se powder was 99.5%.

Production of copper-boron carbide composites

C.Camurri et al. (University of Concepcion,Concepcion, Chile.)

Cu powder, finer than 150 mesh was ener- getically mechanically alloyed with 2vol%B4C and either hot pressed at 650°C and 90MPa for two hours then hot rolled, or, processed by HIP at 850°C and 100MPa for two hours. Structures and properties of the samples made by the two methods were investigated and compared. Both methods were shown to pro- duce material with homogeneous two-phase structures. Hot pressing gave samples with the higher mechanical properties of Rockwell hardness 85 to 97B and tensile strength of 340 to 420MPa. HIP samples were hardness 79B and tensile strength 320 to 350MPa.

Preparation of silicon carbide-silicon nitride nano-composites

J.Grabis, D Jankovica. (Riga Technical Uniw'rsity, Riga, Latvia. )

It was reported that a plasma chemical syn- thesis method had been developed fur produc- tion of SiC-SigN 4 nano-composites with vari- ous proportions of constituents. SiC particle and crystallite sizes were in ranges 30 to 60nm and 27 to 58nm respectively. Dispersion of constituents depended on process conditions.

Sintering Investigation of metal powder sintering by microtomography

M.di Michiel et al. (European Synchrotron Radiation FacilityGrenoble, France.)

It was reported that information concerning sintering mechaisms could be obtained by use of synchrotron microtomography. A high energy variation of this was used to study Distaloy AE and Cu after different sintering stages. The potential of the technique was demonstrated.

Effect of sintering conditions on properties of tungsten-copper-nickel electrical contacts

D.Tarata, I.Pascu. (University of Craiova, Craiova, Romania.)

A study of the effects of material and process parameters on structures and properties of W- Cu-Ni electrical contact materials was described. Four powder types were used. Pressing was at different pressures. Cu infiltra- tion was in vacuum or H at 1250°C, 1350oC and 1450°C. Variations in shrinkage, density and hardness were described and related to process conditions.

High temperature sintering of steel

S.Wikman. (Swedish Inst. for Metals Research, Stockholm, Sweden.)

It was noted that, conventionally, steel is sintered at 1120°C and that there are benefits derived front sintering at higher temperatures. Sintering at 1 3 0 0 ° C entails changes in struc- ture and mechanical properties although not all changes are advantageous. Studies of sinter- ing of prealloyed Astaloy CrM (3%Cr, 0.5%Mo and 0.3 or 0.45%C) were described. Higher sintering temperature results in increased hardness and strength, more homo- geneous microstructure, reduced O content, fewer small pores and more rounded pores. Comparison was made with two steels, one containing 3%Mn and 0.5%Mo and the other with 1.5%Mn, and 0.5%Mo, both with the same C contents. These had less homogeneous structures.

Precision multi-operational cold forging of powder rings

H.Weinert et al. (Metal Forming lnst, Poznan, Poland.)

Production of precision PM parts was dis- cussed with regard to post sintering deforma- tion to attain high density and dimensional accuracy. Cold forging of sintered parts was investigated. It was reported that a multi- stage process had been developed for produc- tion of high- density PM steel rings. Two stages of plastic flow were identified, open and closed flow in the die cavity, were shown to be responsible for densification up to 7.2 to 7.7 gm/cm 3. Distribution of strain was made possible by optimisation of sintering conditions. The results of the study were applied to repressing of sintered DistaloyAB steel rings.

www.metal-powder.net MPR November 2002 41. I i