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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