Titanium aluminide: going for a space ride?

0 k!?J

15’”

INTERNATIONAL PIANSEE SEMINAR 2 0 0 1

Titanium aluminide: going for a space ride?

H

igh

Performance

PM

Metals in Transportation

Swelling

increased

with alumini-

urn content.

was the title of a short

The that

after debinding. Careful attention was paid to control of oxygen and

authors went on to show the swelling

could be sup-

carbon

during debinding Densities above

pressed by first submitting the ele-

97% were achieved

Seminar

mental

sintering.

in Reutte,

Austria,

on

May 3 1st. The scope of the session was given a wider than usual interpretation as the presentations dealt with TiAl intermetallit alloys and PM rhenium MPR October

(see

2001, p. 22), most-

ly intended

for applications

in

space vehicles. In fact the keynote paper delivered by Fritz Appel of for Materials the Institute GKSS

Research,

Research

Centre, Geesthacht, the

design

advanced

and

g(TiAl)

deal with However,

Germany, on properties

of

alloys did not

PM materials his paper,

at all. which

reviewed the physical metallurgy, processing,

and mechanical

prop-

powders to high

lamellae of about 10 microns thickness. During subsequent sin-

(see Table 2). The 50Ti-47.4Al2.6Cr alloy showed a higher UTS

tering, all the aluminium

and

extremely

short

of

development minide

of the titanium alu-

alloys

potential

because

be

achieved,

microstructure microns).

Kenji

A. Bohm

Materials,

from for

Advanced Germany,

Dresden,

ture surfaces

indicated

high creep fracture on behalf at Co.

University,

and

Institute,

Inc.,

a paper that took a

They

sintering

of

compacted mixtures of elemental spherical powders of ‘Ii and Al.

TiAl

investigated

moulding

of

(3-7 microns) aAl,O, particles carried over from the source powders. Following these tests, demonstration parts in the form of automotive

fuel injection

and

from

nozzles

the

50/50

50Ti-47.4Al-2.6Cr

the

materials. The results showed that these materials could be manufac-

high-temperature

synthesis process. (See Table 1 for compositions

the was

several

alloy powders made by the

self-propagating

that

strength

partly due to the presence of fine

TiAl

injection

studied the reaction

of 300 MPa. SEM pictures of frac-

theoretical

tion of high density T’iAl components.

alloy

ture after 1000 hours under a load

at ele-

and in hostile

and

50Ti-47,4Al-2.6Cr

samples

Heat-Treating

all of Japan,

(at

“C then

and colleagues

Research

on the

were fabricated

Institute

Manufacturing

at 1300

Kansai

elongation

with the binary

showed good creep strength in air at 700 “C, surviving with no frac-

different approach to the produc-

and colleagues

Fraunhofer

fine

size
Doi presented

Kobelco

compared

alloys, and also showed increased

(grain

of S. Terauchi

percentage

-2%)

composition

strength and ductility at elevated temperatures. Creep rupture tests

with

HIPped to over 95% density.

with

paths

Demonstration

were sintered

varied

is formed.

This approach permits oxygen and carbon levels of
results

of their

for applications

vated temperatures environments.

diffusion

and no liquid phase

Ltd.,

amount

is con-

sumed at the melting point, due to

strated

vast

after 2 hours

Room temperature and tensile temperature

elevated

Osakayakin

the

sintering.

milling, creating compound particles with titanium and aluminium

erties of wrought alloys, demonresearch effort that has gone into

energy

and

levels

session of oral presentations at the 15th International Plansee

tured in medium

sized lots with

the desired dimensional

accuracy.

Finally, Toma Vasile and Mircea

and particle sizes of

Dobrescu,

University

Politehnica

these powders.) Tensile and creep

Bucharest,

Romania,

in a poster

rupture

presentation,

test bars were injection

moulded and sintered in vacuum

ing results

gave some interestof their

studies

on

The swelling effect that prevents this being a satisfactory densification

route to

was illustrated

cross-section

by

micrographs

at criti-

cal steps in the sintering

process.

It was concluded processes

Parti& size“ ‘ D&s&y

to

3.8

1.94

3.9

12.2

3.33

1.60

3.6

5s-I-4*

12.2

3.9’c

1.66

35.6

@lGq.t.qAI-2.fXr

=9

3.95

1.79

the

swelling of Ti-Al during reactionsintering: 1) rearrangement aluminium melt and wetting titanium

18

MPR

particles,

of of

and 2) forma-

tion of a highly-porous

Al,l?

the

surfaces.

November

titanium

2001

particle

on

Binder (voro

that two main

contributed

Surface area (mz/&

0026.0657/01/$-see

bttn)

(M%lrn3l

cJ.6:

i

35.8

front matter 0 2001 Elsevier Science Ltd. All rights reserved.

X-Al-Si

intermetallics,

ing 44-48

contain-

at% Al and 0.53

at%

Si. They prepared their materials from elemental lZwt%Si cold

Al, Ti, and Al-

powders,

extrusion

HIPping

(1350

200 MPa).

densified

by

followed

by

“C for 4 hours at

Microstructures

con-

sisted mostly of duplex g, a, and xTi,(Si,Al),.

Tensile

the Ti-Al-Si

alloy decreased slow-

strength

ly with increase of temperature

of to

700 “C, above which it declined rapidly.

Room

temperature

strength (YS and UTS) markedly

decreased

as aluminium

content

was increased from 46 to 52 at%, while elongation peaked between 48 and 50 at% Al, at 2%. Heat treating at 1000 “C for 10 hours in the a+g region resulted in structures consisting of colonies of lamellar a grains with globular g regions, and gave the best combinations of strength and ductility.

Joseph M. Capus Consulting Editor

Full papers are published by Plansee Holdings AG in the Proceedings of the 15th International Plansee Seminar, 2001, Vols 1-4 (eds: G. Kneringer, P Rodhammer and H. Wildner), available from:

Plansee Holdings AG, Reutte, Tyrol, A-6600, Austria; Tel: +43-5672-6000; Fax: +43-5672-600-500; www.plansee.com.

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