Switching performance of tungsten-silver electrical contacts

range of methods, described.

of Incone

Mechanical

ed by a nano-indentation shown

that

this

mechanical

powder, are

properties

can

were evaluat-

method

and it is

be used to assess the

behaviour

of

nano-crystalline

powders.

important in

for

solid

angle,

and pore size are noted.

initial

These

para-

meters were varied in a study of liquid-phase sintering trolled

of W-Ni-Cu. by particle

forming ratio

agent, and

dihedral

ratio

and distortion video

dilatometry, experiments

and

size was conpore

angle by the Ni:Cu

1iquid:solid

Densification

device.

Pore

size of a polymer

%W.

by

were studied by

imaging,

quenching

a co-ordinate

measuring

It is shown that at full density

porosity effect

and pore on

size have

distortion

Distortion

in

was reduced

volume

fraction

Experiments

initial

no detectable

W-16%Ni-4%Cu. for increased

and

indentation fracture fracture

angle.

and

relationship

hardness

illustrated

the

carried over into

based measurements at fine

grain

by refinement

stress increases

of

size.

For

of grain size the

more than the plastic

et

Attempts alloy from

heavy alloy

al.

to make a W-7%Ni-3%Co elemental

powders

properties

is attributed

heavy

are described.

The fully dense alloy is reported mechanical

to have poor

at low strain rates. This

to H embrittlement

tation of a brittle intermediate

or to precipiphase at the W-

matrix interface.

Coating of silicon carbide whiskers with alumina hydrate

that Al,O,-hydrate

on to Sic

whiskers.

cursor, Al nitrate, itant solution, is dispersed

posite.

is injected

of the

pre-

into the precipin which

and yields the required

Effects of process

erties

had been

The coating

Na bicarbonate,

deposit

the

conditions were

the com-

on prop-

investigated

conditions

tions.

W-35wt%Ag alloyed

were

for in

investigated.

loose W particles.

15 hours,

industrial and

It was found

40

X-ray

diffraction Increased

there

and also

for

a

to

smooth

550,

1500hours.

At

increases

600 550

Al,

and

were

and heat treat-

or 650°C

for up to

600°C

hardness

were found and were greatest of fine TiAl,. is

in Al

a, d, h and g

were detected

in A2.

attributed

to

and TiAl,.

Fabrication and properties of gradient material for bio-medical application M.Omori er al. (Tohoku Uniwsity, Sendai, Japan.) J.Japan Sot. Powder/Powder Metall., Vol 47, No II, 2000, 1226-1233. In Japanese. It is reported that a graded n-hydroxyapatite material,

for bio-medical

been fabricated bility

against

applications,

by PM methods. soft tissue

had

Bio-compati-

and osteogenesis

hard tissue were investigated examination

related to the composition

Evaluation of orientation of titanium aluminide platelets in aluminium base composites

response through

with

gested

Y.Watanabe et al. (Shinshu University, Ueda, Japan.) Acta Mater., Vol49, No 5, 2001, 775-783. It

is reported

material,

that

based

on

a functionally

Al-TiAU

been made by a centrifugal

part. Distribution platelets

graded

platelets,

had

casting technique.

of the platelets directions

was investigatand were found

with the planar direc-

to the radial direction and orientation

of the

of the TiAl,

are discussed.

nanocomposites

by animal

in tests.

of thin sections

by

cated by conventional

sintering

of composite

powders made by sol-gel coating

of subemicron

spine1 powders. In the composite

material ZrO,

longer suitable

had a narrow Lange of sizes and was tetragonal. The

sintered

materials

and

homogeneous.

were

of

It is sug-

control

tissue

gradient.

Thermoelectric properties of boron carbide-titanium boride composites T.Goto et al. (Tohoku Univel-sity, Se&i, Japan.) .l.Japan Sot. Pow&r/Pow&r Met&, Vol 47, No II, 2000, 1184-1188. InJapanese. It is reported

that a floating zone technique

had been used to prepare directionally

solidi-

fied B&-(0

mate-

to 35)mol%xB2

composite

rials. Electrical

and thermoelectric

were measured

parallel

properties

and perpendicular

At 25%TiB,,

conductivity

to

the eutec-

perpendicular

to

was smaller than parallel

coefficient

was larger.

Shear extrusion of bismuth-tellurium thermoelectric material T.Aizawa et al. (Uniuersiry of Tokyo, Tokyo, Japan.) J.Japnn Sot. Powder/Powder Metall., Vol 47, No 11, 2000, 1189-1193. InJnpanese. The

fine-grained,

Stabilisation

to

the composition

and the Seebeck

were fabri-

gradients.

is possible

Electrical and magnetic materials

tic composition,

milling Arc

it

the growth direction

A.Dauger et al. (UMR, CRNS 6638, ENCSI, Limoges, France.) ActaMater., Vol49, No5, 2001, 81 l-816. MgA1,04-ZQ

that

the growth direction.

Ceramic nano-composites made from submicron powders coated by a sol-gel method

dense

2002

alloyed, extruded

ed at 500,

Al-

and (A3)

Composite materials

showed

and hardness.

increased

contacts.

MPR April

and

that

milling times. The alloy is considered for electrical

condi-

compacts

composition

due to W and Ag. resistance

were

morphology

times gave higher densities erosion

up to

of powders

were zones of nominal peaks

powders

under

Changes

microstructures

mechanically

Histological

tion perpendicular

University,A&pa&, Turkey.) Int. J. PowderMetall., Vol36, No 8, 2000, 35-43.

and sintered

0.25wt%C-0.35%Li-7.5%Ti02,

Al,O,

H.Nakamura et al. (Kyushu National Industrial Research Inst., Saga, Japan.) Powder Technol., Vol 117, No 3, 200 1, 270-278.

(Al), (AZ),

of A&O,

to have an orientation

Y.Karakas eral.(Sakaryn

pressed

Al-0.25wt%C-10vol%Ti02, 0.35%C-l%Mg-lO%TiO,,

strengthening

ed in 3 orthogonal

mechanically

H.Jones et al. (University of Sheffield, Sheffield, UK .) ActaMater., Vo149, No 7, 2001, 1209-1224.

Dispersion

It is reported

be

Structure hardening titanium aluminide during heat treatment of aluminium composite

polymorphs

coated

could

the grain size of the initial

fracture.

The orientation

Switching performance of tungsten-silver electrical contacts

Elemental

through

to an interface

composite

optical and physical methods showed reactions

(Defence Metallurgical Research Laboratory, Hyderabad , India.)PM Science/Technology Briefs, Vol2, No 4, 2000, 21-24.

N.Maitra

of the

due to precipitation

coating.

Development of a tungsten-nickel-cobalt

is attributed

flow stress so more plastic work is required for

determine

are planned.

was

with decrease in grain size.

mechanics

strengthening

Sic

solid

dihedral

in microgravity

The Hall-Petch

Al,O,

was found to satisfy a

relationship

increase in strength

and

sintering,

dihedral

of fine-grained

Hardness

ZrO,

Structure

spinel.

R.W.Armsaong. (AFRLIMNME, Eglin, Florida,USA.) ht. J. Refract. Metals/Hard Mater., Vol 19, No 4-6, 2001, 251-255.

Hall-Petch

densification

liquid-phase

fraction,

porosity

controlled

investigated.

R.M.German et al. (Pennsylvania State Uniwrsity, USA.) Int. J. Refract. Metals/Hard Mater., Vol 19, No 3, 2001, 149-158.

volume

Grain-size-dependent alumina fracture mechanics stress intensity

effect.

ics stress intensity

Effect of green microstructure on densification and distortion in liquid-phase sintering

distortion

tetragonal

The effects of grain size on fracture mechan-

Tungsten

Factors

Ceramics

importance

ture control

of anisotropic

in Bi-Te thermoelectric

microstrucmaterials

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