Phase equilibria in aluminium-rich alloys of aluminium-gadolinium and aluminium-terbium

JOIJRh’AL OF THE LESS-COMMON

PHASE EQUILIBRIA GADOLINIUM AND

0.

5. C. RUNNALLS

METALS

431

IN ALUMINIUM-RICH ALUMINIUM-TERBIUM

AND R.

R.

ALLOYS

OF

ALUMINIUM-

ROUCHER

Chalk Rioev A’uclear Labovatovies. Atowzic Energy o_fCanada Limited, Chalk Riuw, O&ario (Canada) (Ibxeived

April I 5th, 1967)

SUMMARY

The aluminium-rich compounds GdA14 and TbA14 precipitate in aluminiumgadolinium and aluminium-terbium alloys cast from the liquid and decompose by a peritectoid reaction at 400’ and 42o”C, respectively, to form ol-aluminium plus GdAla and TbAla. The latter mately IO wt.24 Thermal analysis formation

possibly

compounds

form eutectic

mixtures

with Al at approxi-

Gd and Tb with melting points of 643” and 644”C, respectively. and X-ray diffraction experiments indicate that a solid-state transinvolving

on cooling GdA13 to 641’C

a rearrangement

or clustering

of vacancies

is initiated

and TbA13 to 642°C.

GdA14 and TbA14 are isostructural with orthorhombic UAl4. Both GdA13 and TbA13 have structures based on an assembly of close-packed layers containing a ratio of one lanthanide

to three aluminium

atoms in each layer. The stacking

the layers are ABA. for GdA13 (SnNis TbAlz (rhombohedral PuA13 structure).

structure)

sequences

and ABABCBCACA

of

. . for

Ii’iTRODUCTION

Since isotopes of the rare-earth or lanthanide elements are found in abundance among the fission products, the nuclear properties of the lanthanides are of considerable interest

to reactor

physicists.

Such properties

are often studied using thin alloy

foils containing a small amount of the rare earth in a diluent with a low-neutroncapture cross-section. Thus for recent physics experiments at Chalk River several compositions of the binary alloys aluminium-gadolinium and aluminium-terbium were prepared and fabricated ture on the two alloy systems

into foils. Since there was little published in the literasome phase equilibria studies were carried out and were

reported briefly earlierr. The purpose of the present plete account of the data obtained.

paper is to provide a more com-

EXPERIMENTAL

The alloys were prepared by heating super-pure aluminium (gg.g90/6 +) obtained from the Aluminum Company of Canada, in air to IOOO’C in a graphite cruJ. Less-Common

Metals, 13 (1967) 431-442

0. J. C.

432

RUNNALLS, R. R. BOUCHER

cible surrounded by an induction coil. Gadolinium or terbium metal of 99.9% purity produced by the American Potash and Chemical Corporation was dropped into the liquid aluminium and was dissolved, usually within fifteen minutes. The liquid alloys were poured into water-cooled molds to provide castings of uniform composition from which samples could be cut for heat treatment and thermal-analysis experiments. The thermal analyses were carried out using the time-temperature method on machined alloy cylinders 1.5 cm diam. x 1.5 cm high in a tungsten coil furnace capable of operation at 10-5 torr at elevated temperatures, A small axial hole was drilled into the centre of each cylinder to accommodate a Pt/Pt-10% Rh thermocouple sheathed in graphite. Thermocouples were connected to a Rubicon potentiometer, Leeds and Northrup amplifier and Speedomax recorder assembly and were calibrated frequently against the melting points of aluminium (660°C) and gold (1063°C). The power to the furnace was supplied through motor-driven Variac transformers so that the furnace temperature could be raised or lowered at a linear rate of I’-2’C per min. Alloy filings were examined in a Philips X-ray powder diffraction camera of 11.46 cm diam. Intermetallic phases were separated from the alloys by dissolving away the aluminium matrix in dilute NaOH. The resulting crystals were friable and could be ground readily to a fine powder in a mortar and pestle. The powdered

Fig. I. Polished section of a slow-cooled a matrix of Al and GdA13. (X zoo) J. Less-Common

Metals,

Al-40 wt.% Gd alloy showing primary crystals of GdAlsin

13 (1967) 431-442

PHASE EQUILIBRIA IN Al-RICH Al-Gd ANDAl-Tb

433

samples were mounted both in the Philips camera and on a Norelco diffractometer. Separated single crystals were studied using a Unicam rotation camera, a Unicam Weissenberg goniometer and a Supper precession camera. RESULTS ANDDISCUSSION

When aluminium-rich alloys were cooled slowly at 1°C per min from the liquid a thermal arrest due to the eutectic solidification of ~-aluminium and an inte~ediat~ phase, GdAl3 or TbAls, was observed at 643” and 644X, respectively. Each eutectic mixture contained approximately IO wt.% Gd or Tb. The GdAl3 primary crystals in slow-cooled hyper-eutectic alloys were of hexagonal cross-section (Fig. I). Once separated from the matrix they proved to be rodshaped (Fig. 2). X-ray diffraction studies showed that the rod axis paralleled the sixfold axis in the hexagonal SnNia structure (Dois type). Measured lattice parameters are compared with those of other investigators in Table I. S-ray powder diffraction data are listed in Table II. The morphology of the TbAl3 differed markedly from that of GdAls (Fig. 3). The phase proved to be isostructural with rhombohedral PuAla, a structure composed

Fig. 2. Si@e TABLE

crystals of Gd.413. (x

20)

1

LATTICE PARAMETERS

OFHEXAGONAL

GdAls alA)

c 60

Present investigation

6.331 :t: 0.003

BAENZIGERAND MORIARTY* VAN VUCHTANDBUSCHOW~

6.308 & 0.003

4.600 & o.003 4.5%+ 0.009

6.320

4-592

J. Less-ComftOtZ &/i&k,

13 (1967) 43X-442

CuKa

POWDER

TABLE

a .F. N

6

g

2

;:

3.

3i;

I.575 I.534 I.513 I.470 I.440 1.426

I.367 x.334 1.310 1.302 x.266

I.254 1.229 1.210

I.371 I.338 1.314 I.304 1.268

1.258 I.233 1.213

I.754 I.687

1.583 1.540 1.521 I.477 I.444 I.431

1.762 1.698

1.877 I.850 1.8x7

2.106 2.063

2.282

5.454 3.482 3,140 2.7’9 2.339

DATA

41.3 22.4 31.4 60.0 10.5

VW w W+

33.2 42.2

30.4 32.3 51.1

40.3 42.1 21.4 50.2

33.0 42.0

m+ w-

sm

w w-

m w+ wm m+

mVW

w+

m

30.3 41.1 00.4 50.0 II.4

In m S+ m+ ww+ m 31.3 50. I 41.2 20.4

41.0 40.2

GclAl:,

ws

FOR HEXAGONAL

s-strong; In-medium; w-weak; VW-very weak. :* dabs.< 0.9437 A obtained with CuKix~ radiation. *** Coincident with CYZline.

31.2 32.0 21.3 32.1

22.2

31.0 10.3 31.1 30.2 40.0 20.3 40. I

21.2

22.0

go.1

20.2

30.0

11.2

1.889 I.861 1.828

2.072

21.1

2.121

21.0

5483 3.524 3.166 2.74= 2.355 2.300

radiation

DIFFRACTION

II

TO.2

00.2

20.1

20.0

11.0

10.1

10.0

?2* hk.1

N

3 “x

6

F

4

1.196

I.022 I.011

1.022 I.011

0.9073

0.9138

0.9172

w+ w+

0.962 0.958 0.9437* 0.9424 0.9294 0.9161 0.9125 0.9063 W

W-

VW

m

VW

w-

m-

0.989

0.990 0.973 0.973 1 0.963 0.959 0.9447 o-9433 0.9304 0.973

1.005

1.006

mW VW

w

VW

VW

m

I.055 I.035

1.060 1 I.055 1.036

VW

1.066

W VW

VW

m

*

w W-

I.079

I.094

I.157 1.148

I.175

I.193

1.060

1.061

1.080 ) 1.067

1.081

I.097

I.177 I.175 1.158 1.150

50.4 44.0 31.5 60.3 53.0 33.4 43.3 53.1

30.5 52.2

61.1

41.4 51.3

43-2 61.0

32.4 21.5

42.3 60.2

52.1

20.5

43.0 50.3 43.1 40.4 52.0

51.2

0.7833 0.7775 0.777’ 0.7721

0.7936 0.7914 0.7872 0.7850

0.8361 0.8291 0.8286 1 0.8226 0.8218 / 0.8202

0.8392

0.8919 0.8845 0.8810 0.8780 0.8722 0.8624 0.8585 0.8492 0.8487 ) 0.8409

o.gor‘$

0.9053

0.7720

0.7774

0.7833

0.7933 0.7912 0.7871 0.7850***

0.8200***

0.8224

0.8285

-

F .?

2 m+ diffuse

m

m+ w+ VW

;=

0

? LI W-

W-

m+

m

mf

mm VW o.a357

m-

0.8490

m

VW

m

W

VW

W-

VW

VW

‘iv-

0.8404 0.8388***

0.8715 0.8618 0.8580

0.8772

0.8802

0.9043*** 0.9004 0.8910 0.8838

IO,, *

Q P

13.1

; % N

$

zz 2

w”

e” P

22.0

%

3

--_-

13.7 ro.r4

40.1

02.I3

13.4 30.9 31.5 12.11

Or.*4

2l.IO

I.558 I I.544

IO.13

s

m+ VW mm-

I.538 1.473 I.455

1.328

1.3TZ

I.316

In

t\--

xv+

m w+

1.416 I.395

I.387

m-

1.421

I.450

m-

xv-

m-

W-

I.553

I.599

I.394 I.391 I I.334 I.332 1

1.400

1.421

I.455 1.428

1.402

r.4a0

1.562

I.652

1.660

20.11

I.673

1.680

1.606

I.776 I.720

I.783 1.728

02.10 12.8

30.3 21.7

mf m m VW

I.858 I.815

XV+

m

I.957

I.873

m-

2.003 I.986 1 2.012 I.968 I.888 I.881 1 I.871 I.824

I.997

m s

2.333 2.246

w

s

2.572

2.593

In

m w s s s

2.369

2.030

2.653 2.632

2.371 2.387 I 2.352 2.261

5.ror 4.687 3.721 3.273 3.057

5.185 4.773 3.762 3.319 3.088

x s

5 stu

12.5 30.0

11.9

20.8

2r.q

10.10

12.2

02.7

21.1

20.5

00.9

01.8

02.4

20.2

10.7

02.1

11.0

or.5

10.4

01.2

I0.I

Rk.1

Cu KCXradiation

24.7 II.21 Ii.2

42.5 32.13 2.1.*g

33.6 13.16 20.20

04.14 ‘4.4 50.8

05.7 00.21

31.14 41.9 40.13 33.0 24.1

13.13 05.1 32.10 12.17

30.15 11.18 04.11

23.5 00.18 31.11 41.0 40.10 20.17 2r.16

32.4 04.8

04.5 01.17 12.14

40.4 22.9

0.958

I

O-959 0.95s

0.980 0.976

0.983

0.985

0.993

1.002

1.008

1.028

I.044 1.032

I.058

1.066

1.096

1.105

1.127

1.165

I.175

1.193

1.208

I.273

1.293 1.288

0.983 1 0.980 0.970

0.987 1 0.g8.1.

0.993l 0.9g2 0.988

I.045 I.033 1.02g I.010 1.008 1.008 ) 1.002

I.097 I 1.068 1.061 1.060 I.059 )

I.099 1.098

1.195 1.193 ) 1.178 1.176 I.175 I 1.167 1.130 I.129 1 1.1071 1.1061

I.275 I.213 1.211 1

___-d,,l,.(‘J) ~_ I.296 I.291

33.18

31.23 40.22 21.25

34.11 30.24 00.27

52.9 61.5

32.19 43.10 15.14 16.4 01.26

40.19 42.14 12.23 60.9 41.18

24.13 25.0

34.2 51.10 20.23 21.22 Ij.11

13.19 43.1 30.21

04.17 02.22 60.0

33.9 22.18 50.11 24.10

31.17 23.14 42.8

Ilk.1

0.771-5

0.7997 0.75103 0.7839 0.7820 0.78OQ 0.7809

0.8375 0.8335 0.8283 0.8247 0.8120 0.8107 0.8061 0.8048 0.8047 I 0.8oog

0.859 0.859 0.856 0.856 0.8402

0.875 0.870 0.869

0.877 0.876

o.go5 0.891 0.891 0.878

0.954 o.g53 0.944 0.943 1 0.935 0.935 0.912 0.911 1

_.--. -dcaie.(‘lf)

0.7745

0.7809

0.7998 0.7904 0.7839 0.7820

m

w

m-r m WV VU’ w+ m+

0.8009

m+ m m-+ 111 wWf mw

m

m

m-

VW

V\”

m+

w

w

0.8046

0.8375 0.8333 0.8280 0.8245 0.81’7 0.8105 0.8060

0.8400**

0.856

0.859

0.870

0.875

0.878

0.891

0.905

n.gr*

0.935

0.943

0.953

0.

436

J. C. RUNNALLS,R. R. BOUCHER

of slightly distorted close-packed layers stacked in the sequence ABABCBCACA . . .4?5. The stacking sequence is also similar to that reported for a polymorph of YAl$ and for BaPb37. The X-ray data from both powders (Table III) and single crystals showed that the primitive cell was rhombohedral with a,=~.905f0.003 A and a,=qj.gg_t o.oxA. Independently, the structure of TbAla has been found to be rhombohedral in two other laboratories”e8. Measured lattice parameters are compared in Table IV.

Fig. 3. SingIe crystals of Tb.41~. (X 20) TABLE LATTICE

IV PARAMETERS

OR RHOMBOHEDRAL

Present investigation VAN

VUCHT

AND

KRYPIAKEWYCZ

BUSCHOWs

TbAIs*

6.176 f 0.003 6.175 6.181

AND

21.165 * 0.008 21.180

21.15

ZALUCKYJ~

*Hexagonal co-ordinates.

The proposed positions in space group R@ hexagonal axes are those reported for rhombohedral

(Intern. Tables PuAl$ i.e.,

No. 166) using

(0, 0, 0; &>g, Q; t, 4, B)+3 Tb in (a) o, o, o 6 Tb in (c) o, o, z; o, o, f with .2=0.2185 9 Al in fe) 4, o, o; 0, -5, o; 3, 3, o 18 Al in (h) x,2,

with x=o.r8r5 The above parameters J. Less-Common

Metals,

z; x, zx, z;

z_f,.T,z;R,x,

i; 2, 23

Z; 2x, x, %

and z=o.rogg. are very similar r3 (1967)

431-442

to those suggested

by KRYPXAKEWYCZ AND

PHASE EQUILIRRLJ, XNAl-RICH Al-Gd

AND Al-Tb

437

ZALUCKYJ~ of zTb=o.219, x~i=o.188 and Z_M=O.IIO. A model of the unit cell based on hexagonal co-ordinates is shown in Fig. 4. A second energy release was observed from the solidified Gd and Tb alloys on cooling to 2% below the eutectic arrest. X-ray diffraction examination of powdered specimens, both quenched from above the thermal arrest, and cooled slowly at 1°C per min to room temperature, did not reveal the presence of any new or unknown

lines. However, there were significant differences between the two in the intensities of powder diffraction rings as illustrated by Fig. 5 for GdAlz which at first appeared due to an order-disorder transformationl. Later, once single crystals had been examined in Weissenberg and precession cameras the differences in the powder diffraction patterns could be related solely to preferred orientation effects, since the lattice parameters and diffracted intensities were identical for both quenched and slow-cooled crystals. ~~icroscopic examination of the powdered specimens confirmed that there was a pronounced difference in the two powders that could have produced the patterns observed. The quenched GdAl3 had become equi-axed during grinding whereas the slow-cooled and ground crystals fractured to form many acicular rods with smooth, cleaved faces (Fig. 6). The latter material tended to become aligned along the axis of the 0.3 mm diam. fused silica X-ray specimen tube, thus producing a distortion from the intensities expected for crystals randomly-oriented. The differences between powdered specimens of quenched and slow-cooled TbA13 were not so striking. The most significant dissimilarity was that slow-cooled crystals appeared to cleave more readily on the basal or close-packed planes. This was evident from the diffractometer examination of ground crystals sprinkled onto a glass microscope slide. As shown in Fig. 7 the enhancement observed for the oo ‘9 reflection of slow-cooled and ground TbA13 was quite striking. The contrast in cleavage behaviour between the quenched and slow-cooled GdAls and TbAI3 appeared similar to that observed earlier for El=114and Pu41~“. In the latter case an appreciable energy release on cooling coupled with a marked change in cleavage was attributed to the rearrangement of vacancies (-1021 per cma) from a random distribution in the high temperature phase to an ordered or clustered one in the low temperature phase.

Fig. 5. X-ray powder diffraction patterns of primary GdAlB crystals separated from Al-zo wt.% Gd alloys and then ground in a mortar and pestle (CL&~ radiation). {a) Crystals from alloy quenched into water from 7120°C. (b) Crystals from alloy cooled at 1°C per min to room temperature.

”

PHASE EQUILIWIA

IN &RICH

AlLGd rllvu Al-Tb

and pestle, which wcrc Fig. 6. Photographs of primary Gdhla crystals, after grinding in a mortar used to obtain the powder diffraction patterns in E’ig, 5. (X zoo) (a)Crystals from alloy quenched into water from 7oo”C. (b) Crystals from alloy cooled at 1°C per min to roam temperature.

Fig. 7. X-ray diffractometer traces of primary TbA13 crystals separated from Al-zo mt.O/, Tb alloys and then ground in a mortar and pestle (CuKo: radiation). (a) Crystais from alloy quenched into water from 7oo’C. (b) Crystals from alloy cooled at 1°C per min to room temperature.

0. J. C. RUWNALLS, R. R. BOUCHER

440

The vacancy concentration in GdAls and TbAls appears considerably lower than in UAL and PuA14 however, judging from density measurements on separated crystals. The densities calculated from the observed lattice parameters were in agreement with the measured values of 4.87 and 5.09 g per cm3 for assumed compositions of Gdo. 97Als and Tbo. 99Ala, respectively. As mentioned earlier10 once a transformation in TbA& was suspected, experiments were carried out with the isostructural Pm&-phase to search for a similar phenomenon. The consequence was that two nine-layer rhombohedral PuAI3 polymorphs were identified, ~Htx and gH0. The only dissimilarity observed between the two was that the high-temperature form, 9H0, had a slightly shorter threefold axis.

X-ray powder diffsaction patterns of filings from as-cast aluminium-rich alloys consisted of lines from a-aluminium and an intermetallic phase isostructural with orthorhombic UAlb (I& type) 11. Single crystal fragments such as those observed metallographically (Fig. 8) were separated from the aluminium matrix and were used to obtain the lattice parameters listed in Table V. The X-ray densities were calculated assuming 4 formula weights in the orthorhombic unit cell of space group Imma (Intern. Tables No. 74). It is not known if there is a Janthanide deficiency in the phases similar to the actinide one reported for UAL and PuAL9.

Fig. 8. Polished section of an Al-20 wt.% Tb alloy, cast from ~ooo”C into a water-cooled primary crystals of TbA14 in an Al-TbAlI matrix. ( x 500)

showing

J. Less-Common

h!fetak, I3 (1967)

431-+$2

mold,

PHASE EQUILIBRIA

X-ray TbAl4

IN Al-RICH Al-Gd

diffraction

decomposed

AND Al-Tb

studies of heat-treated

by a peritectoid

reaction

4.11 alloys indicated

that both GdA14 and

to form aluminium

plus GdA13 and

TbA13 near 400°C. Only reflections from GdA14 and Al could be detected, for example, after heating a cast 12 wt.% Gd-AI alloy at 390°C for 14 days. After IO days at 41o”C, however, about half the GdAld in a similar specimen had been converted to GdAln. The peritectoid temperature, therefore, has been placed at 400’ f 10%. The decomposition

temperature for TbAla was estimated At temperatures near 600°C complete

to be some 20°C higher, 420~ + zo”C. conversion to GdA13 and TbA13 was

achieved in one day in alloys with eutectic-type structures (10-15 wt.% Gd or Tb). The effect of such a heat treatment on the metallographic structure was extensive as illustrated for an Al-10 wt.% Gd alloy in Fig. 9. Surprisingly, BUSCHOW in a recent study of the Gd-.41 system’” to produce minium,

GdA14. Hence,

in obvious

his claim was that GdAla is the compound

contradiction

of the earlier disclosure1

was unable

richest

and the results

in aluoutlined

above.

Phase

Lattice

paramet~vs

a Gdhl4

TbAla

4.430 *

G

b

I#.++2 + 0.001

0.001

X-vay density, (glt9G)

(A)

6.316

6.261

*

0.001

+ 0.001

13.739

13.706

4.568 4.661

+ 0.003

& 0.003

Pig. 9. Polished sections of Al-10 wt.% Gd alloys. (X 420) (a) Cast from ~ooo”C into a watercooled mold showing Al dendrites in an Al-GdA14 matrix. (b) As-cast alloy from (a) annealed for 17 h at 620°C showing Al (light phase) and GdA13 (dark phase). J. Less-Common

Metals,

13 (1967) 431-442

0. J. C. RUNNALLS,

442

R. R. BOUCHER

ACKNOWLEDGEMENT The ration

authors

wish to thank

and metallographic

Mr. L. R. NORLOCK

examination

for assistance

with

the prepa-

of the alloys.

REFERENCES I 0. 3.C. RUNNALLSAND R.R.BOUCHER, J.Metds, r5(1963)687. 2 N. CBAENZIGER AND J. L.MORIARTY, ActaCvyst.,rq fIg6s) 948. 3 J. H. VAN VUCHT AND K. H. J. BUSCHOW, Philips Res. Rept., rq (1~64) 319. 4 O.J.C.RUNNALLS,A~. EB. Canada Ltd.,Rept. r620,Sept., 1962;~sopubIis~~d as U.S.A.E.C. HW-75007, Paper 8, 1962. 5 0. J. C. RUNNALLS AND R. R. BOUCHER, Acta Cyt., 19 (1965) 184. 6 J. F. SMITH,D. BAILEY,H. A. WILHELM AND R. L. SNYDER, U.S.A.E.C., IS-rg3, Dec. 1960, 7 ;.?SAND~ D. H WOOD ANDW.J.RAMSEY,A~~~CY~~~.,17(1964)986. 8 P. I. KRYPI&W&ZZ AND I.I.ZALUCKYJ,Ann. Univ. Mariae C&e-Skloduwska, Sect. AA, rg (1964) 97. Q 0. J.C. RUNNALLS AND R. R. BOUCHER, Trans. AIME, 233 (1965) 1726. IO O.J.C.RUNNALLSAND R.R.BoucHER,J.NucE.M~~~~.,15 (1965) 57. II B. S. BORIE,Tvalas. AIME, 188 (1950) 182. IZ E(. H. J. BUSCHOW, J. Less-Common Met&, g (1965) 452. .J. Less-CommonMetals, I3 (1967) 43X-442

Lzlblin-Pal.,