The tensile properties of plutonium gallium alloys in the temperature range 20–100° C

JOURNALOl? NUCLEARMATERIALS17 (19%)

THE TENSILE PROPERTIES

54-59.

OF PLUTONIUM-GALLIUM RANGE D. C. MILLER

UKAEA,

The

room

temperature

flow

density

and

stress,

5 March

compositional elongation,

hardness

plutonil~-gallium

ALLOYS IN THE TEMPERATURE

20-100” C + and 5. S. WHITE

Afomic ?Vwpom l&march ~~~a~l~h~~~t, Received

U.T.S.,

NORTH-HOLLANDPUBLISHINGCO., AMSTERDAM

0

has

alloys

1965 and in revised

dependence

reduction

been

having

in

of

area,

determined

composition

for lying

Ald~~~on, form

composition don&es

26 May

comprise

jointes

concerne

were also measured at 60’ C! and 100” C for d-stabilised

solution

solide

compositions

data

together

in the range with

mined for plutonium-aluminium alloys

has

regarding

enabled the

some

La variation

ha.rdening

des proprit%&

ambiante

limite

Blastique,

teIles

mecaniques

que la charge

0 B 5.6 At

iL la traction

100” C pour

de rupture,

dans le domaine Les

propri&&

en phase

B 60” 6 de

und

der

Hlirte

wurden

zwischen

bei

der Rruchfestigkeit,

Raumtemperat~

1.1-5.6

Ihre

At.-%

die

LGsungshlrtung

fiir

Ihre

Zu-

Festigkeitseigenschaften

Zusammensetzung Gallium.

Diese

mit frtiher

Plut,onium-Aluminium-

Legierungen

wurde

lagen zwischen O-5.6 At. - “/bGallium.

ausserdem

Zusammenhang fiir

ermittelt.

60 und 100’ C fi.ir S-stabilisierte

gemessen.

einige von

Daten

zwischen

ermiigliehen

ver~ffentlichten und

Legierungen

liegt

in

Angaben

Plutonium-Cerium-

Schlussfolgerungen, S-stabilisiertem

welche Plutonium

die be-

treffen.

work to the Pu-Ga system, as well as increasing the range of testing temperatures up to 100” C.

In unalloyed plutonium the F.C.C. d-phase is stable between 319’ C and 450” C, ref. 1). It has been known for some time, that additions

2.

of aluminium 2) and eerium 3) stabilise it fully down to room ~mperature. Recently it was shown that gallium 4) also stabilises the delta phase down to room temperature. The phase diagrams of the three systems are similar, showing that the solutes have virtually no solubili~y in the LY-,,6, y or S’ phases, but are markedly soluble in both 6 and E phases. Previously, a detailed investigation has been made of the compositional dependence of the tensile properties of &stabilised Pu-AI and Pu-Ce allloys, tested at room temperature 5). The present investigation now extends this and Associates,

de

der Querschnittsreduktion

Plu~nium-Gallium-Legierungen

In~oduction

+ NOW at Rolls Royce

en

formation

par

-.__--

la densite

ainsi mesu&es

stabilis&

la

de la composition

y(, Ga.

furent

les alliages

& la temph-

la striction,

plutonium-gallium

de composition

1.

made

et plutoniumd~duetions,

stabilisci en 6.

Die Konzentrationsabhgngigkeit

Es

l’allongement,

pour des alliages

du plutonium

o/0Ga. Ces d&ermin&es

quelques

le durcissement

sammensetzungen

et la duret6 a 4% BtudiQ en fonction

et

be

&stabilised

1.1 et 5.6 At

de faire

der Spannungsverhriltnisse,

-_-.-

rature

mecaniques

to of

entre

at 7; deter-

and plutonium-cerium

deductions

solution

plutonium.

1.146

that previously

1965

It cellos ant&ieurement

cBrium ont permis ce qui

Ga. These

UK

pour 10s alliages pl~ltonium-aluminium

within the range O-5.6 at a/oGa. The tensile properties alloys having

Berks.,

2.1.

Experimental

methods

SPECIMEN PREPARATION AND HEAT TREATMENT

The alloys were chill cast in vacuum and subsequently were homogenised by vacuum annealing at 450” C for 50 h. For alloys believed to be in the two phase (a~+&) region, the 450° C anneal was followed by a further 50 h anneal at 250” C in the (y-h 6) field. This was necessary in order to obtain equilibrium proportions of the two phases. The (x+6)/6 phase boundary, where x= E, B or y is shown to be practically vertical below 250’ C in the phase diagram 4>,

Derby. 54

TENSILE thus the proportion

PROPERTIES

and

composition

OF PLUTONIUM-GALLIUM of the

2.2.

55

ALLOYS

TENSILE TESTING

two phases in the alloy at 250’ C was assumed to be maintained down to room temperature

partially

by the completion formations.

the motor drive mechanism, beam assembly and recording drum external to the Lractive” com-

After

annealing,

of

the

y + ,4 -+ oc trans-

the billets

into no. 11 type Hounsfield

were machined

tensile test pieces

having a gauge length of 0.447 in (w 12 mm) and a cross-sectional area of 0.012 5 in2 (es 0.081 cmz). The density

of each specimen

Tensile testing was

partment.

“boxed”

carried out using a

Hounsfield

tensometer,

In all cases the testing

0.075 cm/min

(corresponding

of O.O67/min). The atmosphere was high purity

argon

with

speed was

to a strain rate in the glove box

so that no oxidation

was then measured using the liquid displacement

problems were encountered when testing at 60” C and 100” C. For the tests carried out at

method

these temperatures

and its hardness

determined.

the specimen and grips were

During the present investigation the cast billets were always heat-treated before machining into tensile test specimens. This was done despite the fact that it has been shown that mechanical work, induced by f%ling, can cause a-phase precipitation in low solute Pu-Ga d-phase alloys 4). Only by adopting this procedure could specimens be obtained with a good surface finish entirely free from oxidation. However, the density of the machined specimens gave no indication of a-phase precipitation and it is apparent that if this occurred it was confined to a very shallow surface layer.

the d-phase is stabilised by aluminium the parameter is decreased in a similar manner 2).

Fig.1. The compositional

parameter

dependence

of the lattice

enclosed by a furnace and were allowed to soak at temperature for one hour prior to testing. 3. 3.1.

Experimental

results

DENSITY AND HARDNESS

Fig. 1 shows the variation of the room temperature lattice parameter of 6 stabilised plutonium with increasing gallium concentration. As can be seen, the lattice parameter decreases with increasing gallium content. When

and

density

of Pu-Ga

alloys

at

20” C.

D.

56

0'

C.

MILLER

I

I

I

2

AND

2.

The

variation

32

of

hardness

S.

WHITE

I 4

I 3

SOLUTE

Fig.

J.

at

CONCENTRATION

20” C with

I 5

6

(AT%)

composition

for Pu-Ga

alloys.

4\ I

‘O -\ \ 28

\ \

26-

\

7 o

VALUES AT IOO'C

1

\

Fig. 3.

The compositional

dependence

of the ultimate

tensile strength of Pu-Ga

alloys at 20” C, 60” C and 100” C.

TENSILE These

solutes

contrast

PROPERTIES with

cerium

OF PLUTONIUM-GALLIUM which

increases the lattice parameter a). The a-phase density values calculated from the lattice parameter measurements are in good agreement with those obtained experimentally. The effect of

equilibrium

57

ALLOYS

(y +01) structure.

If this were not

the case, lower values for both the density and hardness of unalloyed been expected

plutonium,

would have

by back extrapolation

for the two-phase

the data

alloys.

substitutionally dissolving a light atom in B-plutonium and simultaneously contracting

3.2.

the lattice parameter almost cancel. Thus the density of these alloys is approximately in-

determined at 20” C, 60” C and 100” C, is shown

dependent

concentration.

of hardness with

Gallium gives rise to a

marked solution hardening of the &phase and the rate of hardening, expressed as V.P.N./at y0 solute, is equal to 4.75. This value is the same as that previously determined for aluminium stabilised &plutonium. Back extrapolation of the density-composition and hardness-composition curves for the two phase (a + 6) alloys, to zero solute concentration, gives a density for unalloyed plutonium of 19.6 g/cm3 and a hardness value of 270 V.P.N. These are reasonable values for the a-phase of normal production metal in the as-cast condition. These results suggest that the 50 h anneal at 250” C was sufficient to produce an

I

2

The

of U.T.S. with composition,

as

the data

show that at each temperature investigated there is an increase in strength with increasing gallium content and for any composition there is a decrease in strength with increasing temperature. The data obtained at 20” C for the two phase (B +6) alloys, when back extrapolated to zero solute content, suggest that the U.T.S. of unalloyed plutonium is approximately 52 kg/mm2 (33 ton/inz). The 1 y0 flow stress curves are plotted in fig. 4. Again the d-phase alloys show a linear dependence with composition for each of the temperatures examined. The data is best represented by three parallel straight lines and thus the 1 y. flow stress is described by the empirical equation :

3 SOLUTE

Fig. 4.

The variation

in fig. 3. For &phase solid solutions,

of composition.

Fig. 2 shows the variation gallium

TENSILE DATA

4 CONCENTRATION

5

6

(AT-/o)

compositional dependence of the 1 y. flow stress of Pu-Ga alloys et 20” C, 60” C and 100’ C.

D.

58 z =

where

1.1

c-0.0162

C.

MILLER

T+8.003,

AND

(1)

content

S.

WHITE

tensile properties were determined up to 300” C. The percentage elongation and reduction in area curves are plotted in figs. 5 and 6 respec-

t = 1 o/oflow stress in ton/ma, c = gallium

J.

(at %),

tively.

T = absolute temperature

These data were derived

by matching

together the broken tensile specimens and then

This equation only applies over the temperature

measuring

range 20-100” C, but reasonable agreement has been found between experimental and calcu-

cross sectional area. Owing to the difficulty of performing this operation in a glove box, the

Iated values for some specimens

data is subject

for which the

their

gauge

length

and

minimum

to quite large errors. However,

60 I 50

6 “t,i‘ 40

VALUES

IS -

0

0

I

2

3 SOLUTE

Fig.

5.

The

AT 6O’C

compositional

dependence

of

the

CONCENTR4?lON

percentage

5

4

6

(ATo/,)

elongation

of Pu-Ga

alloys

at 20’ C,

60” C

alloys

20” C,

and 100” C.

90

608 t

0

0’

Fig.

6.

The compositional

.

,

I

/

I

2

3

depsndenoe

of

VALUES

AT

1

I

4

5

the percentage reduction 60” C and 100’ C.

60-C

6

in area of Pu-Ga

at

TENSILE

PROPERTIES

OF

PLUTONIUM-QALLIUM

figs, 6 and 6 show that both parameters appear to be independent of temperature, for &phase alloys. 4,

59

ALLOYS

TABLET The compositional dependence of hardness UTS and 1 y0 flow stress for d-stabilised alloys 1 Pu-Al

1 Pu-Ce

1 Pu-Ga

4.75

0.53

4.75

1.06

0.18

0.98

Discussion

4.1.

THE POSITION

g OF

THE

f&+8)/8

(VPN/at %I

PHASE

BOUXDARY

The position of the (m+ S)[S phase boundary 1.02 0.15 1.09 is indicated by the change in slope of the various $ (hi/at %) properties when plotted as a function of composition. These data indicate that the boundary The values for the various properties are very oocurs at approximately 1.1 at oh Ga. This similar for Pu-Al and Pu-Ga alloys, while those contrasts with the published value of approximately 2 at o/0 Ga 4). It is interesting to note for Pu-Ce alloys are much smaller. The change however, that Ellinger, Land and Struebing 4) in the lattice parameter of the ii-phase, expressed obtained &phase lattice parameters in alloys as A/at o/o solute, is 0.0071, 0.0019 and 0.0092 with gallium contents as low as 1.06 at %. They for the Pu-Al, Pu-Ce and Pu-Ga systems did not consider that alloys containing between respectively. On the basis of a simple lattice strain solution hardening model, one would 1.06 and 2 at o/o Ga were in an equilibrium condition because severe cold work caused expect that the solution hardening observed in &-phase precipitation. However, during the Pu-Al alloys would be less than that in Pu-Ga present work it was found that d-phase alloys alloys. This is not borne out by the present containing between 1.1 and 2 at o/0 Ga were investigation. This is probably due to the quite stable at room temperature for the longest inadequacy of the solution hardening model periods of time over which their behaviour was considered. While the solute valency has been observed. It seems improbable therefore, that invoked to explain similar discrepancies in the room-~mperat~e mechanical working of other systems “), no valency effect can be such alloys induces immediate precipitation of considered here because both gallium and equilibrium a-phase, which, according to the aluminium are tri-valent. phase diagram 4) contains no dissolved gallium. It is suggested that non-equilibrium B-phase References was produced by mechanical work in the alloys 1) T. A. Sandenaw and R. B. Gibney, J. Phys. and studied by Ellinger et at. a), that is, the a-phase Chem. Solids 6 (1958) 81 was supersatura~d with gallium. It is reason- 2) F. H. Ellinger, C. C. Land and W. N. Miner, J. Nucl, Mat. 5 (1962) 165 able to conclude therefore that the eq~librium 3) F. H. Ellinger, C. C. Land and W. N. Miner, (a +8)/S phase boundary occurs at approxiExtraotive and Physical Metallurgy of Plutonium mately 1 at y. Ga. and its Alloys (Ed. W. D. Wilkinson, Interscience, 4.2.

THE

SOLUTION

HARDENING

or

(S-PHASE

PLUTONIUM

A comparison of the mechanical property data of Pu-Ga alloys with the earlier data obtained for Pu-Al and Pu-Ce alloys is given in table 1.

1960) 149 4) F. H. Ellinger, C. C. Land and V. U. Struebing, J. Nuol. Mat. 12 (1964) 226 5) D. C. Miller and J. S. White, J. Nucl. Mat. 10 (1963) 339 8) J. E. Dorn, P. Pietrokowsky and T. F. Tie&, Trans. AIME 188 (1950) 933