Making finer powders

Making finer powders

Tungsten alloys were well represented at the PM*TEC World Congress year in Orlando, Florida. Ken Brooks was there... held earlier 2002 this Making...

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Tungsten alloys were well represented at the PM*TEC World Congress year in Orlando, Florida. Ken Brooks was there...

held earlier

2002

this

Making finer powders

T

HE

in producing

ened (ODS)

density

of lattice

promotes

of powder

ADVANTAGES

niques

alloys are well-known, defects

sintering.

Sintering of ball-milled the Laboratoire Matkriaux,

by Professor

de MCtallurgie

procedure

nanocrystalline

de Lille, for

ODS

tungsten

and yttrium-rich

Roland

A Taillard et G6nie

des

France,

described

an

with

and

of

sintering

admixed

work, however,

including

some

yttrium

by the

same

from the stainless

cal alloying,

powders.

grain

boundaries,

the

well through

which

that

oxidation

and

of yttrium

to yttria because

It was hoped

reducing

tungsten

small content

to disperse

for oxygen. in

out in wear-resis-

elemental

The

and to convert

help

mechaniof its high

this would also of

is deleterious

tungsten

at

to mechanical

properties. Supplied

by Plansee,

the as-received

tungsten

powder

had a median grain size of about Sprn and oxygen and carof 190ppm

trace of oxygen

and

was detected

The tungsten

15ppm

respectively.

No

in the 99.9 per cent pure

Milling time

Compaction

min

was mixed with 1 vol or 17 ~01% yttri-

um in an argon-filled mixed

steel balls and container.

composition

metal

was carried

employing

yttrium powder.

authors, was affected by contamination

Chemical

media,

bon contents

oxide (yttria). Earlier

yttrium

affinity

Physique

producing

WC

metal was expected

compacts

sizes also lead to finer

blends of tungsten

The new investigation tant

oxide dispersion.

Universite

original

tech-

and the high

in nanocrystalline

Finer particle

and more homogeneous

powders, presented

metallurgy

oxide-dispersion-strength-

powders

was

glovebox. carried

Ball-milling

out

in

an

of the

argon-filled

Sintering under

Pretreatment

Sintering under

hydrogen

+ sintering

vacuum

under hydrogen

Unmilled W W

w-lVOl%Y

w-17vol%Y

x

34

0

77.20

79.20

84.70

5

76.80

77.00

X

20

75.30

79.00

X

40

73.40

79.70

X

80

69.90

75.20

X

5

78.56

74-65

71.06

20

76.95

71.02

67.97

83.74

40

72.41

69.15

69.23

79.39

80

70.50

66.49

58.74

76.50

320

64.05

X

69.56

89.45

600

55.46

X

76.77

88.98

1200

X

56.82

X

75.25

91.65

1800

52.11

X

84.40

96.33

4320

51.35

X

X

88.30

5

77.93

76.02

80.11

X

20

76.28

73.75

X

40

76.91

72.81

X

77.39

80

75.95

71.84

X

X

1200

66.24

X

X

92.91

X

not measured

MPR October

2002

0026-0657/02/$

- see front matter

0 2002 Elsevier

Science

Ltd. All rights reserved.

Fritsch

Pulverisette

with sintered five

minutes

tungsten

planetary

carbide and

mill of 250ml

balls. Milling

three

was milled

days.

capacity,

times were between

For

comparison,

in air for times between

pure

five and

80 minutes.

mean grain size was smaller with the W-

lvol%Y

than

samples

and sintered

at 1800°C

dynamic vacuum (lo-2Pa) was employed,

this normally

Where

hydrogen

referred only to high tem-

peratures unless a presintering an inert atmosphere

for four hours under

or hydrogen. treatment

was given, with

at lower temperatures.

In character-

SEM-EDS

fered noticeable Whatever

agglomerated Table

“particles”.

1 compares

densities

of compacted

and sintered samples. samples were significantly

denser than those sintered in hydrogen.

Densities

mixtures actually decreased during sintering gen,

explained

diameter

by the

chemical

grains causing gas formation factors were also involved.

reduction

and porosity,

Whatever

of W/Y

under hydroof powder though

other

the milling and sin-

amount

particles

of

were also found.

their size, they were found mainly along tungalloy, microhardness

with milling

840HV

after

time,

20 hours’

times exceeding

milling.

reduction

to a hydrogen

long

for both

in particle

size, a

and the finest micro-

of yttrium.

Four hours’ sintering per cent relative

peak at

However,

30 hours are necessary

alloys to reach a substantial scopic distribution

changed very

with a distinct

grain size of a few tens of nanometres

In all cases, vacuum-sintered

a substantial

Much of this oxide suf-

grain growth, but spheroidal

With the W- lvol%Y

milling

the relative

counter-

sten grain boundaries.

about

“grains” and

to Y,O,.

just a few tens of nanometres

tiated

monocrystalline

W-17vol%Y

analyses showed that, with any

of yttrium was converted

significantly

individual

and EPMA

route or milling duration,

ising powders and sintered products, the authors differenbetween

with their

parts. sintering

The milled powders were pressed into pellets of 1Omm diameter

tering conditions,

at 1800°C

in vacua can give 96.5

density. Thus vacuum

atmosphere,

may be preferred

though the level of densifica-

tion is affected by cobalt pickup from the carbide milling container

and balls.

Seeking sinteri ng flaws ROFESSOR Randall

P

University’s Products

German

Center

of Pennsylvania

for

introduced

Innovative

a paper on the Effect of inho-

mogeneity

on dimensional precision in liquid-phase

on behalf

of three

inhomogeneities mixing

of his students. induced

and compaction,

behaviour

Initial

during

sintering

errors, due to

powder

processing,

add up and affect the sintering

of an alloy. This is observed

ing or shape distortion

State

Sintered

as warpage, crack-

distortion.

the variation

layers,

and the total

sintered

ly induced

inhomogeneities

in a non-distorting

were deliberate-

93W/Ni/Fe(7:3)

added to the different

present

in the structure. against

density of each layer configuration.

average

All but one

sample had an average density of 98 per cent or better, the only exception

being sample

1, with no added porosity.

This was because one of the three samples had an exceplow measured

this was attributed For the investigation,

in polymer polymer

Figure 2 shows a plot of this parameter

tionally

after sintering.

These factors were the number of layers in the

sample,

samples

were

porosity

of only 92 per cent,

to experimental

above

99 per cent.

but

error as the other two No

trend

could

be

heavy

alloy, the raw materials being as listed in table 2. Previous studies had looked at the effects of porosity and pore size on densification

and

distortion,

but

the

porosity

was Sample 1

homogeneous. The

milled

amounts

homogenised cleanly,

Samples

compacted 550MPa. max,

powder

porosity with

was mixed

with

for 30min.

Acrawax

proportional

different

layers

to the (Figure

Sample 3

Sample 4

Sample 5

Sample 7

Sample 6

Sample 9

Sample 10

different

from 0.5 to 6 weight per cent and

in a Turbula

leaving

added.

muffle

alloy

of Acrawax

Sample 2

~~w~~

burns amount 1) were

in a hand press with a load of approximately The

green parts were dewaxed

furnace, after

in a hydrogen

holding

at 600°C.

dimensions,

compacts

an alumina

tube furnace

in an Inconel

atmosphere After

were sintered

Sample 6

0%

at 1000°C

measuring

0.5%

their

in dry hydrogen,

0%

in

H

at 15OO”C, after a one-hour

0.5%

hold at 900°C. To quantify

the heterogeneous

an inhomogeneity several

aspects

parameter of the porous

www.metal-powder.net

porosity of the samples,

was devised that integrated structure

contributing

to

Figure I Layer configurations inhomogeneity.

used to make compacts

with different

October

levels of

2002

35

goO I

10 /

5

15 I

20 I

25 I

Inhomogeneity

Figure 2

Sintered

density

that most compacts

variation

achieved

30

40 I

35 I

parameter

Figure 3 Plot of inhomogeneity parameter indicating a sigmoid

with inhomogeneity

parameter

geneity around

showing

the initial porosity and the final sin-

is less than the critical

standard ments. large

ues above 15, increased change

tered density. Distortion

was quantified

deviation

increase

by a parameter

of the

A small increase

between

inhomo-

on distortion.

near full density.

between

vs distortion

and distortion. The critical value for inhomogeneity is 15, above which any change has no significant effect

parameter

established

parameter relationship

normalised

based on the

radius

in inhomogeneity

in distortion

when

the

measure-

results in a

inhomogeneity

in distortion,

value of 15. With val-

inhomogeneity

causes little or no

as shown in the parameter

plot of

Figure 3. The

authors

suggest further

systems with different

experiments

inhomogeneities

on different

to validate

the

model conclusively.

High energy wins nano results

T

wo

papers on closely

sented

by Uilamo

Universidade

related

subjects

Umbelino

Fed.

Rio

G.

were pre-

Gomes de

Norte,

of

the

Natal,

fragile tungsten

component

of a W/4OCu (by weight) General

Electric

gated for electrical

Brazil.

tages include The first of these dealt with the Sintering behaviour composite

W-Cu powder produced b

described

efforts to improve,

fragmentation,

d’aspersion

high-energy

by high-energy and

milling. It

milling,

homogenisation

ofa the

of the

ductivity

in the ductile copper matrix composite.

originally contacts

low thermal

developed

the alloy investi-

as long ago as 1923. Its advanexpansion,

and good machinability.

high thermal

in demand for a variety of microelectronics However, tration

the traditional

method

of a presintered

tungsten

skeleton

Sintered relative density %

Densification SRD-GRD %

900

57

60

3

0

1000

57

62

5

0

1050

57

62

5

0

1100

57

66

9

57

92

35

58

78

20

57

88

31

57

55

-2

0

Temperature QC

0

applications.

of production,

Green relative density %

Sintering isothermal time min

con-

Thus the alloy is now by infil-

with molten

1170 30 0 1200

60

34

MPR October 2002

www.metal-oowder.net

copper, has a number

of drawbacks.

culties in making complex copper

contents,

These

include diffi-

shapes, limitations

heterogeneous

on possible

structures

and residual

porosity. Liquid-phase recognised

sintering

alternative,

of pre-mixed

powders

but this too has problems,

because of mutual insolubility

and low wettability

liquid Cu. The disadvantage

can be overcome,

by employing

high-energy

ball-milling

finer particles and greater dispersion, “sintering-active”

elements.

is a

mainly of W by

(HEBM)

method to conventional

of a porous tungsten Frequently

employed the

properties tions,

However,

as heat

to create

homogeneous

there is a choice

of milling either tungsten and copper metallic powders, or

limitations,

The

latest

process,

plasma heating

of its directionality,

by reduction

mal. Material

HEBM

consisted

of attritor milling at 500 rev/min for 48

hours in an argon atmosphere. size was 0.58um

Initial tungsten mean grain

and that of the electrolytic

copper pow-

der 50um. analysis and powder evaluation,

samples

produce

milling

in a cylin-

type

mentioned

and 6mm. The samples were sintered under hydrogen

in a

ties

fur-

techniques,

414/2 dilatometer

nace. Table 2 lists the sintering

and in a resistive

conditions

sity values derived from micrometer The

HEBM

tungsten being

produced

crystallites

much

excellent

than

dispersion.

the copper content

particles

authors

increases,

powder

The

paper continues

not long enough

especially

milling

if the copper

the copper and it

that the milling

to produce

a reduction

cle size, but it seems more likely they had simply reached

and with

state that the size of

is high, but cold work hardens

breaks.

fine

their

time was

in copper parti-

to your reporter

equilibrium

that

size for the

conditions.

employed

and

are general-

in this

research,

ion bombardment. gradient

uses

Because

effects

as a function

temperature,

are nor-

of heating

and isothermal

mixed

of the

could

powders,

(hold)

high-energy

was again employed, previous

that modified be

by

ball

but of a different

research.

material

produced

giving

The

presenter

with varied properfunctional

substantially

gradient

improved

thermal

conductivity. tary mill. W powder with median came from Wolfram

GmbH

plane-

grain size of 0.78um

of Austria

and atomised

Cu

powder with average grain size 150um from Metalpo Brazil. Milling rotational

in

was carried out in dry air for 51 hours at a

speed of 500 rev/min. Cylindrical

samples were

pressed from this powder, 1Omm in diameter

and 3-4mm

in thickness. The

set-up

for

plasma

sintering

Figure 4 and the experimental Table 3. Green geometrically parameters

Milling balls and residue

has

dense

W/3OCu powders were mixed in a Pulverisette

with

in copper, the crystallites

the original

The

particles

measurements.

composite

embedded

finer

as well as den-

the

to that

Netzsch

TASC

infiltration

Further treatments

determined

(HEBM)

between

3

liquid

in attaining

time.

of the milled powder were pressed at 215MPa and thicknesses

earlier,

functional

and its properties

drical die to 9.7mm

diameter

applicadevices.

with 30 wt per cent Cu was investigated,

rate up to sintering To

After chemical

electrical

other

and semiconductor

from intense

metal and copper oxide powders, the latter being the

and weld-

and

suggested

especially

structures.

tungsten

In this research

contacts

thermal

ly necessary.

followed

in hydrogen.

sinks

as mentioned

serious

by copper

for electrical

attractive

of W/Cu composite

such

infiltration

substrate.

ing electrodes,

however,

or by the addition of

For HEBM

production

bution,

and sintered

densities

(weight/volume) included

phase

porosity,

dispersion

is

conditions and

shown

in

are listed in

were determined other

measured

W/Cu particle

size distri-

and

contamination

during

milling. XRD

showed that neither

amorphous

copper nor tungsten

as a result of the milling,

fraction peaks became wider, indicating about 5nm. Chemical

though

a crystallite

respectively

milling

left from

and from

milling operation. amination terability The

a residue

According

was sufficient

investigation

to previous work, this cont-

to increase significantly

indicated

two

main

the sin-

some of the key parameters

before

and after sintering. As might have been expected,

high-energy

of the precursor powders gave a well-mixed posite powder. This was accompanied fragile tungsten

particles,

decreased

down to 17nm and their insertion

ball-milling

W/3OCu com-

by fracture

of the

mean crystallite and homogeneous

size dis-

persion in the copper matrix.

densification

In the first, the liquid phase,

flows into the pores and the agglomerates nano-grains rearrangement

rearrange.

In

continues,

Solid-state tungsten

the

second,

increasing

sintering

cent to the densification. promote

from the a previous

Table 5 summarises

of W/Cu.

mechanisms.

geneity.

size of

analysis showed the presence of 1.7

Fe and 1.8 Co per cent, introduced balls

became

the W dif-

the

structural

structural

contributes

Iron and Cobalt

grain growth,

as it forms, of tungsten homo-

about

25 per

contaminants

but may also increase

porosity. The

second

presentation

by this author described

Sintering by hollow cathode discharge of W-Cu alloys. The purpose was to investigate

www.metal-powder.net

another

the

composite alternative

MPR October

2002

37

a hot air stream at 250°C. “‘burnt out” at 500°C Sample

Green

Sintered

density %

1 2

3 4

ed salt components

Mass loss

density %

Densification %

63

92

29

5

63

69

6

13

1lOmm continued

For ball-milling, of sintered hexane

73

10

3

62

66

4

20

and unwant-

and leave a composite

W/Cu oxide

6009 of desalted oxide powder, 6600g

carbide balls of 9mm diameter

long and

130mm

of heating

sintered

product.

of theoretical ing

rate

rates and isothermal

sintering

The best structure

density

of

Exudation

led to different

the spherical

-was obtained

lbK/min

and

and substantial

W03

inside diameter.

powder

TaeguTec)

hold time was increased. to evaporation The

authors

and

of 18um

was given

ion

Reduction

loss was detected

is learnt

as

mass loss was related

sputtering

homogeneous

as more

time.

during

sintering.

of materials

or functional of the

grain

was

size (Korea

the same milling

oxide was ball-

oxide powder (all percentages of the milled composite

carried out in hydrogen

to obtain

by weight).

oxide powders was

flowing at 600ml/min

at 200°C

for 1 hour followed by 700nC for an additional Measurements

treat-

addition before reduc-

tion, 49.95 wt% of desalted W/ZOCubased

from the low heatisothermal

Milling

milled for six hours with 50.05 per cent of WO, W/lOCu-based

suggest the preparation

predetermined properties

Copper

in the

e up to 92 per cent

zero

copper

times dur-

of

shell of the oxide powder. For comparison,

commercial

qualities

and 860ml

alumina container

for 6 hours at 120 rev/min in order to fragment

ment. To test the effect of a WO, Variation

powder was

moisture

were charged into a horizontal

Tungsten

ing plasma

spray-dried

powder.

%

63

The

to remove

were made of specific

8 hours.

surface area, mean

grain size and impurity levels.

with

gradient

plasma

sintering

process.

Spray-dried composites Working tent,

Dr Seong-Hyeon

Machinery W-1OCu

1

with similar alloys but of lower copper conHong

and Materials

Institute

of

dealt with the Fabrication

of the Korea

of

alloy with high thermal

ous solution of tungsten

conductivity.

An aque-

and copper salts was spray-dried,

oxidised to a homogeneous

composite

powder with nano-

sized particles, then reduced, pressed and liquid-phase

sin-

inlet

tered to near full density. The author described with

conventional

sintering

yet gain the problems

infiltration

was an effective

methods.

alternative,

as Ni or Co were normally

associated

Liquid-phase

but additives such

tion and these degraded both thermal and electrical

prop-

erties. ders produced

ball-milling

of tungsten

nano-sized

powders

could be sintered was almost elements

and copper pow-

which

to full density without

impossible

in principle

additives,

but it

to avoid contamination

by such

as Fe and Co caused by the carbide

balls and

stainless steel container tion. Thus

thermal

used in the severe milling opera-

and electrical

properties

were again

adversely affected. by producing

nano-sized

Both W/lOCu

for investigation. out additions

solutions

particles

with

of WO,

solutions

before reduction.

of 1.41

fed

metatungstate into

R

October 2002

hollow cathode discharge system.

powders

15mm

by dis-

and copper nitrate

a nozzle

rotating

in

The mixed at

11,000

and spray-dried

in

were pressed

diameter

and 3mm

at 200MPa

into

thick,

sin-

tered for one hour at 1400°C

in flowing

To evaluate

during heating

sintering

ing temperature,

activity

some compacts

temperatures

within

the

cooled

rapidly

before

more

range

then

dry hydrogen. to sinter-

were heated 900°C

to lower

-1400°C,

size and density

then

measure-

ments were made. As a result of the research, duced

by the

tent is decreased. densification combining addition

the author concluded

that,

mixed powders can be successfully methods

W/Cu powder becomes

outlined,

densification

pro-

of the

more difficult as the copper con-

This was due to pore formation

by local

of agglomerates.

Nevertheless,

g/ml were prepared

water for the desired compositions. were

ball-

and W/2OCu alloys were targeted

rev/min with a feed rate of 20ml/min

38

minimal

Two variants were tried, with and with-

solving ammonium distilled

reduced

though ultrafine

This study was an attempt to get around this limitation,

Mixed

The

compacts

High-energy

milling.

Plasma-sintering

Figure 4

added to obtain full densifica-

a W/lOCu

the powders before reduction

uniform densification trical conductivities

(weight

per cent)

of spray-dry origin

compact

with WO,

can be fully densified,

during heating.

Thermal

due to

and elec-

of these alloys were close to theoret-

ical, due to their high density and purity.

www.metal-powder.net

Heat, density and distortion

D tortion

is of interest

the PM board, and hardmetals The Effect

of heating

of W-Ni-Fe

Constance

heaoy

Schlaefer,

Center

for can

deputising

cause

was

for Ravi Bollina, Because

distortion,

of the at

liquid-phase

sintering

alloys. The

three

7

were

@215-

during the

alloys selected

test had 83, 88 and 93 wt per cent tungsten,

20 -

sin-

experiments

and limit such distortion

being nickel

by

Products

devised to quantify of heavy

and dis-

introduced

Sintered

State University. also

across

are no exception.

rate on densification alloys,

Innovative

Pennsylvania tering

during sintering

ISTORTION

d d

for

.E

and iron in the ratio 7:3. Characteristics

io-

L

the balance

6

of

the base powders are listed in Table 5. The

as-received

by rod milling two-litre

tungsten

5-

powder was deagglomerated

with pure tungsten

rods for one hour in a Temperature

plastic jar filled with argon. The W, Ni and Fe

(“C)

powders were then mixed in a Turbula mill for 30 minutes to achieve

homogeneity.

isostatically

pressed

1Omm diameter

These

into

mixed powders were cold

rods, cut

into

sections

about

and 1Omm high, then sintered at 1500°C

in dry hydrogen

(dewpoint

and hold temperatures

below -40°C).

Heating

were varied substantially

rates

density

weight per cent tungsten,

in Figure 5, as a function

During

shrinkage

rates of 1, 5, 10 and 15 K/min. The against temperature,

liquid-phase

sintering,

alloy suffers substantial

distortion

shown in Figure 7. By contrast, highly resistant to distortion To summarise

alloys by

as a function

the high-binder

heavy

under its own weight, as the low-binder

variant is

(Figure 8).

shrinkage

at any given temperature

grain boundaries,

for an 88W/Ni/Fe

alloy

Note that the

is higher for the lower heating

rate.

the aggressive liquid penetrates

causing shape loss independent

increases the amount of shrinkage

or

in W/Ni/Fe heavy

of heat-

ing rate. Over the range 1 to lSK/min, solid-state sintering has no significant

effect on final distortion.

Distortion

files are similar for alloys with the same tungsten tent leads to an increase in contiguity al rigidity

of the

compacts.

decreases with increasing In

of this investiga-

prior to liquid formation

of temperature

rates of I or 15 K/min.

but sintered at different heating rates. Increasing

as in Figure 6.

the main conclusions

tion, slower heating densification

of

for the three alloys sintered for

effects were shown in more detail for individual plotting

plotted

alloys. At melt formation,

is plotted

30 min at heating

Shrinkage

from 900°C to 1500°C at heating

for the

purposes of this research. Sinter

Figure 6 sintered

what

might

Samidipoyena Advanced

Research

at the Effect

0.8

be

distortion

solid content considered

Centre

of atmosphere

solid con-

and greater structur-

The

Chandrasekhar

pro-

content

parameter

in the alloy.

a companion of

the

in Hyderabad, in the sintering

paper,

International India, looked of heavy alloys.

-

2

E

I

+ l”C/min

LI n

5”C/m1n

0.6 -

0.4

* lO”C/min

-

e 15Wmin

86 I

88 I

Tungsten

Figure 5

Sintered

density

for 3omin at heating

of tungsten

(7:3) alloys sintered

rates of I, 5. IO or 15 K/min.

www.metal-powder.net

92 I

0

content wt.%

as a function

cent for 83, 88 and 93W/Ni/Fe

90 1

0.2-

\

0.2

0.4

R/Rmax

weight

per

at 1500°C

Figure 7 Distortion profiles of 83W/Ni/Fe(7:3) heavy alloys sintered at 1500°C for 30 minutes at heating rates of I, 5. IO or 15K/min. The X-axis represents the normalised

radius and the Y-axis the normalised

height.

MPR

October

2002

39

Powder

Nickel

Iron

Tungsten as-received

Tungsten rod-milled

Vendor

Novamet

ISP

Osram

Osram

Grade

123

CIP-R1470

M-37

M-37

Purity per cent

99.8

99.2

99;5

99.5

carbonyl

hydrogen

hydrogen

reduction

reduction

Fabrication

carbonyl

method Particle size, pm DIO

3

2

2

2

D5o D9o

10 24

6 10

6 10

3 6

spiky

spherical

irregular

irregular

faceted

faceted

Shape

Theoretical density g/cm3

8.9

7.9

19.3

19.3

Apparent density g/cm3

2.30

2.43

4.13

5.27

Tap density g/cm

33.26

4.63

6.23

7.66

Pycnometer density g/cm3

8.96

7.89

19.2

19.3

0.6

0.45

0.18

0.19

BET surface area mz/g

The

alloy

investigated

95W/3.5Ni/1.5Fe.

had

the

composition

After milling for 24 hours, 2 per cent

wax was added to the mixed powder, followed by dewax-

ing and sintering Atmospheres

tested

nitrogen/hydrogen Sintering

Our Powders Meet Your Hardmetal Needs

e on a metallic

variety of environments,

tungsten

with heating were argon,

substrate - in a

rate of 30K/min. nitrogen,

hydrogen,

and vacuum.

was incomplete

in the inert atmosphere

gave 100 per cent of theoretical vacua, density was apparently

but

density in hydrogen.

In

102 per cent of the theo-

retical value, but this was due to loss of iron and nickel binder metals. Contrary

OSRAM

Bruntal

spol. s r. o. offers:

atmosphere

‘lkqsten Metal Powder In sizes 0,s - 30 microns for various applications Tungsten Carbide Powder In sizes 0,7 - 30 microns for hardmetal

to expectations,

wettability

in the nitrogen

was not greatly inferior to that in hydrogen.

Hydrogen was definitely

the best sintering

atmosphere

for

heavy alloys, but this was due to the ease of diffusion of nickel-iron

industry

along W grain boundaries

and particle

faces. This in turn was due to the cleaner

Cobalt Metal Powder In sizes 1,l - I,8 microns

inter-

tungsten

sur-

faces, with any oxide or adsorbed oxygen freshly reduced y hydrogen.

TaC Powder In sizes 0,s - 2,0 microns TaNbC Powder 90/10, 80/20, 60/40 WCTiC 50/50,70/30 Recycling of Hardmetal Scrap into above products acxording to your

l 15”Clmin

7

1 10”Clmin A 5”CfmIn - 1”Clmin

Address: OSRAM Bruntd

spol. s r.0

Zahradni 46 CZ-792 01 Brunt8

I

0

Czech Republic Phone:

T&fax:

+420-646-793

III

New Reader

October

2002

0.6

10

1

11 63 I (sales direct)

Enquiry

Go to www.metal-powder.net MPR

I

1

06

I www.osram-bnmtal.cz

OSRAM 40

1

0.4

R/Rmax

+420-646-7 1 I 637 or +420-646-7

E-mail: [email protected]

i

0.2

Service

Figure 8 Distortion profiles of g3W/Ni/Fe(7:3) heavy alloys sintered at 15ooQCfor 30 minutes at heating rates of 1, 5,10 or 15K/min. The X-axis represents the normalised radius and the Y-axis the normalised height.

No 619.

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