shown ro depend on sub-grain ,and grain snuc-

tures. Interaction between 0 and defects delays

recrystallisation in commercial purity MO. The

0 content in recrystallised MO depended on

grain-boundary-specific surface area. Annealing

in H was effective in lowering rhe 0 content.

Mechanical alloying Synthesis of magnesium-lanthanum powders for hydrogen storage applications

J.Keskinen, S.-J’. Hnnnula.(VTT Manufacturing

Techno&?, Tamp~e, Finkmd.)

It was noted that Mg and some Mg inter-

metallic compounds, such as Mgl7La2, have

high ability to store H but some properties and

conditions limit usage. It is shown that these

properties can be improved by mechanical

alloying for which various methods were inves-

tigated. Mechanically alloyed Mg17Laz was

milled with NiSLa to improve absorption/des-

orption properties. Mg,7La,-30wt%NiSLa was

found to absorb up to 4.4wt%H of which 3.3%

was at ambient temperature.

Nitrogen behaviour and hot com- paction of high nitrogen stainless steels

H.Miuru, H.Ogarua. (College of Industrial Technology,

Hyogo, Jopan.)

It was reported that elemental Fe stainless

steel type materials could be made to absorb up

to 9.85wt%N by mechanical alloying. Cr-Mn

and Cr-Ni also absorb N. Much of the dis-

solved N was lost in subsequent processing. N

loss was reduced by increase in Cr content or

addition of Mn or Nb. Consolidation was by

spark plasma sintering.

Processing and microstructure of mechanically alloyed niobium- vanadium-aluminium

S.Dymrc et al. (Academy of Minrng and Metallurgy,

Krakow, Poland.)

Nb-24at%V-18%Al and Nb-ZO%V-

15%Al elemental powder mixtures were

mechanically alloyed and the products char-

acterized by X-ray diffraction. V and Al were

gradually taken into Nb solid solution.

Consolidated alloys contained Nb solid solu-

tion, Nb,Al and NbzAl base intermetallic

compounds and dispersed Al,O,. Properties new technology of wet chemical precipitation

depended on composition and consolidation of Cu powder for solutions had been used to

temperature. satisfy this demand.

Mechanical alloying of oxide- dispersion strengthened copper

LJ.M&n et nl. (University of Mining and TechnoJoRy,

Fyeiburg, Gel-many.)

Improvements in bonding of press-ready low alloy steel powder mixtures

U.Eng.rtrbm et al (Hizigamis AB, Hdgan&, Sweden.) Manufacture of oxide,dispersion strength-

ened Cu was discussed with regard to mechan-

ical, creep and electrical properties. Ce02 and

Y203 were considered to be the best disper-

sants. Structural evolution with time during

mechanical alloying was investigated. Uniaxial

hot pressing of mechanically alloyed powders

gave densities up to 97% and a significant

increase in 0.2% proof stress.

The demand for new powders to make parts

with improved properties to close dimensional

tolerances was discussed. It was shown that

these requirements can be met by use of bond-

ed powders, in which constituents are bonded

to Fe or steel powders. Efficient bonding gives

lower segregation, less “dusting” and better die

filling. Bonded and conventional powder mix-

tures were compared.

Modelling of mechanical alloying

1.1 .Sunol. (University of Girom, Gironn. Spain.)

Mechanical alloying was reviewed with ref-

erence to modelling of the process, in particu-

lar how energy is transferred. Collision and

attrition should be considered. Differences

between studies were dlscussed and repro-

ducibility considered. Effects of key and scale

factors were outlined. A comparison model was

applied to grain size control in mechanical

alloying of materials.

Reactive synthesis of PM materials Reactive sintering of nickel aluminide-(alumina or silicon carbide) composite materials

G .P.Cammurota, A.Catagrande. (University of Bolog~,

Bologna, Italy.)

Powder production Analysis of gas atomisation

J.J.J)unkley. (Atomisinl: Systems Ltd., Sheffield, LK.)

It was noted that there is little understand-

ing of the effects of process and material para-

meters on gas atomising. An evaluation of

equations linking particle size to process and

material conditions was presented. A dimen-

sionless gas:metal ratio, based on (volume of

gas):(volume of metal) ratio was discussed.

Mechanical and thermal energies were consid-

ered and a mechanism was discussed, from

which some predictions of effects of melt tem-

perature and gas properties were made.

An investigation of production of near-net

shape NiAl-SiC and NiAI-Al,O, composite

parts, by reactive synthesis from elemental

metal-ceramic powders was described.

Reactive synthesis was at 617°C to 637°C.

Some samples were made with addition of Fe.

Grain refinement was found to reduce hard-

ness. The presence of the ceramic raised

Vicker’s hardness from 300 to 750.

Direct synthesis of aluminium nitride

R.Pnlmer et al. (Birkbeck College, London, UK.)

Advantages of innovative large-scale metal powder production

It was noted that direct synthesis of high

purity AlN is difficult and costly. An investiga-

tion of AlN synthesis by an Al matrix . N sat-

uration process at temperatures between the

melting points of Al and AlN was described.

Chemical and thermal parameters were

analysed for the precursor materials used AI-C-

N-FeO(OH) and Al-NH,-(NH&AlF,. The

process was modelled. Advantages of the tech-

nique were outlined. S.Pkier, M.Hohmann. (ALD Vncuum Technologies AG,

Hanau, Gerr~ny.)

Inert gas atomisation was outlined.

Developments to increase operating efficiency

were described as increase in melting furnace

capacity, reduction in ‘downtime’, recovery of

used inert gas and rapid melting. Design details

were presented.

Sintering Ecological degreasing in powder metallurgy

J.A.Bas et al. (AMES SA. Barcelona, Spam.)

Sub-micron copper powder

R.Hiinert. (MicroMet GmbH Powder-Technology.

Humburg, Germq.)

The need for new Cu powders of fine parti-

cle size for injection moulding and applications

in electronics was noted. It was reported that a

The need to remove organic substances, such

as quenching oils and machining lubricants,

from PM parts was emphasised. Use of solvents

such as C,HCl, was dIscussed with reference to

environmental considerations. Some altema-

tive degreasing methods, including water-surfac-

tam solutions and ultrasonics were outlined. A

major reduction in use of C,HCl, was reported.

40 MPR September 2002 www.metal-powder.net