{101̄7} Hydride habit planes in single crystal zirconium

JOURNAL

OF NUCLEAR

(iOi7)

MATERIALS

HYDRIDE

31 (1969) 233-237.

HABIT

PLANES

C. ROY

0 NORTH-HOLLAND

PUBLISRING

IN SINGLE CRYSTAL

CO., AMSTERDAM

ZIRCONIUM

and J. G. JACQUES

Faculty of Engineering Science, Univertity of Western Ontario, London, Canada Received

4 October

1968;

in revised form 2 December

1968

Hydrogen precipitation in zirconium and its alloys has been extensively studied in recent years and the results have been summarized by Ells 1). While the gross features of the primary habit planes are well established, some of the details are not; in particular there are uncertainties MI to the crystallographic planes of zirconium other than the primary {lOTO> upon which zirconium hydride can lie. The present program was undertaken to clarify the situation with regard to the identification of the secondary habit planes of hydrides in zirconium which have been reported by several investigators z-4). The study was performed on a zirconium single crystal in order to simplify the analysis and to eliminate the effect that grain boundaries may have on the precipitation of hydrogen 5). Crystallographically oriented samples were prepared from a single crystal rod * (6 cm

prepared metallographically by polishing on wet 600 grit Sic paper followed by chemical polishing in 45 vol y0 HzO, 45 vol y0 cont. RN03 and 8 vol y0 HF solution to remove the cold worked metal or the oxide film from the surface and to reveal the hydride phase. The faces of each sample were (within lo) the -(OOOl), (lOi0) and (1210) planes. The method of analysis consisted in determining the angles that the traces of the individual hydride made with a reference direction on the three surfaces ( lOiO), (i2iO), and (0001) and matching these with the angles that the same reference .direction made with the lines of intersection of the (1OiZ) planes with the surfaces. The values of the angles &angle between a pyramidal plane and the (0001) plane), oc (angle between the [1210] reference direction and the trace of a pyramidal

long x 0.6 cm diameter) which had been charged to a concentration of 150 ppm hydrogen (by weight) by reaction at 700 “C with a measured

plane on the ( lOTO) face) and p (angle between the [lOiO] reference direction and the trace of a pyramid a 1 plane on the (i2iO) face), are listed in table 1.

quantity of hydrogen followed by a homogenization at 800 “C and slow cooling ( w 2 ‘C/min) to room temperature. A number of these were heat-treated for about 2.5 h at 700 “C in an argon atmosphere to determine the effect that the subsequent cooling rate may have on the hydrogen precipitation. A few samples were slowly cooled (w 2 “C/min) as for the hydrogenated crystal rod and the others were cooled to room temperature at various rates. Before examination the sample faces were *

Zone refined single crystd

N.Y.,

zirconium

A study of the hydride orientations A:

showed:

On the (1010) surface, fig. la, the traces of the hydride platelets lay in four different directions : 1. Broad but short traces aligned parallel to the [OOOl] direction. 2. Thin traces direction.

normal

to

the

[OOOl]

3. Thin traces making an angle of 13” on either side of the [i2iO] direction.

purchased

from Materials

U.S.A.

233

Research

Corporation,

Orangeburg,

234

Fig.

C.

1.

Hydride

morphology

ROY

AND

J.

on the faces of a sample

G.

JACQUES

annealed in argon for 2.5 h followed by cooling at a

rate of 70 “C/min. (a) (1010)

surface

x 540;

(b) (0001)

surface

x

430;

x 370;

B:

On the (0001) surface, figs. lb, c, both the broad and the thin hydride traces made -angles of O”, 60” and 120” with [1210] direction. -C: On the (1210) surface, fig. Id, the broad hydrides traces were aligned parallel to the [OOOl] direction while the thin traces exhibited four directions making successively angles of 7.5” and 15” on either sides of the [lOiO] direction. From the results of these observations, (summarized in table 2) conjointly with the

(c)

right

(0001)

surface

x

800;

(d)

(1210)

surface,

left

x 80.

values of the angles in table 1, two major hydride habit planes were deduced. A: Hydride traces XC on the (1OiO) surface, -ZH on the (1210) surface and the series YE, YF and YG on the (0001) surface correspond to hydrides lying in the primary (lOTO} habit planes. These observations confirm the results of a similar analysis carried out by Westlake and Fisher 2). B: Hydride traces XA, XB and XD on the (1010) surface and YE’, YF’ and YG’ on the (0001) surface suggest that their

HYDRIDE

HABIT

235

PLANES

TABLE 1 Angles

between the lines of intersection

of the {lOfZ} planes and the reference directions.

{lOiZ} pltmes { lOi8)

12” 57’

O”, f

11° 02’

f

77O 03’,

f

83” 35’

{ 1077)

14O 43’

O”, f

12O 49’

f

75O 17’,

*

82” 31’

(1076)

17; 03’

00, f

14O 53’

rt_ 72’ 57’,

f

81’ 17’

(lOT5)

2o” 12’

00, f

17O 40

f

69” 48’,

& 79’ 35’

(1014)

24’ 42’

O”, f

21° 43’

f

65’ 18’,

& 77” 06’

(loi3)

31° 30’

O’=, f

27’ 57’

f

58” 30’,

& 72” 58’

(1012)

42O 36’

0”,

f

38’ 32’

f

47” 24’,

{lOTl}

61’ 28’

0”,

f

57” 52’

& 28” 32’,

f

65’ 19’

& 47’ 24’

TABLE 2 Observed Major

angles between hydride traces and reference directions.

hydride traces

I

(1010)

face

XA

(0001)

face

0’

YE-E’

0”

XB + 13’

YF-F’

60”

xc

90”

YG-G’

120’

XD-

13”

(i2To)

face

ZH

0’

ZI +75” ZJ +82.5” ZK--82.5’ ZL - 75O

Note: traces

YE’,

YF’,

YG’

refer to the traces of broad hydrides and YE,

YE‘, YG,

to the

of thin hydrides.

habit plane is of the general form {lOiZ>. platelets were identified at high magnification However, since the angles made by the ( x 800) but were all found to lie parallel to hydride traces ZI, ZJ, ZK and ZL on the numerous planes of the {lOi?}types. Traces (i2iO) surface matched olosely (within attributed to (1Oib) and (lOi2) hydride habit 0.5”) the angles made by the lines of planes are shown in fig. 2. Some of these less intersection of the (10x7) planes (table 1) important habit planes e.g. (1Oib)and (lOi2) and this surface, it can only be concluded have been observed in earlier studies with that the secondary habit plane of zirzirconium s-4). conium hydride in zirconium is (lOi7). With decreasing the cooling rates (from This corresponds with the primary hydride 700 “C to room temperature) the platelets lying habit planes 6) in Zircaloy-2 and -4. parallel to the (1OiO)habit planes grew larger The slowly cooled samples (m 2 “C/min), and aggregated in bands with those lying whether examined after homogenization at parallel to the (lOi7) habit planes. The mor800 “C or after heat treatment at 700 “C, phology of hydrides in samples cooled at two exhibited hydride traces of minor importance different rates is shown in fig. 3. -on the (1210) and (lOi0) surfaces. These Since the present study is somewhat parallel

235

C.

ROY

AXD

J

G.

JAUQUES

to that made by Westlake snd Fisher 2) on a crystal of zirconium, it is important to

&gle

assess, either on the basis of the experimental a,pproach or the method of analysis, the ca,use of differences of our results and theirs. Westlake and Fisher suggest’ed that thG formation of a hydride layer on their crystals during the hydrogenation caused hydride precipitjation parallel t’o the [lOi5] and the (10il) planes. This doea not explain the occurrence of pyramidal habit planes in our samples Yince these were

(b) <0001) surfaw

X 80 .- cooling

rate

2 *C/Ix&

prepared from the core of the hydrogenated zirconium rod which in fa.ct shmved no peripheral hydride layer. Westlake and Fisher appear to hwve given little import,ance to the direction of the traces of broad hydrides arsd in partiodnr shape hydrides” un the “nondescript the surface of their crystal B (specimen II} whose crystallographic orientation was cioac to the basal plane. It was the carefIll study of the two forms of hydride which appeared on all faces of our cryst’als whioh enables us to identify unctmbiguously the two important families of hydride habit planes in zirconium.

to

C’i

3.

Westlake and Fisher ident&d the hydride habit planes from the angles obtained by recording the position of the rotating stags of a metallograph when an edge or a ~r~ctft

HYDRIDE

was parallel

to the cross-hair

piece. Since the orientation

HABIT

faces varied between 2” and 4’ off the low index planes e.g. (i2iO) face, it can be shown by simple geometry lead to differences observed

The

in the eye-

of their crystal

that this deviation

can

237

PL&N%iS

authors

gratefully

acknowledge

the

support for this work by a research grant from Atomic Energy of Canada Limited, D. Dillon of the Faculty of Engineering for providing

the laboratory

and to Science

facilities.

of 1" to 4’ between the

and the true values of the angles

between an edge and the hydride traces. Unless this was fully accounted for in their analysis Westlake and Fisher may have failed to identify the (lOi7) hydride habit planes which produce on the (i2iO) and (lOi0)faces traces with angular differences of less than 3” and 5” respectively with respect to those produced by the (IOi5) hydride habit planes.

References 1) C. E. Ells, J. Nucl. Mat. 28 (1968) 129 2)

D. G. W&lake 224 (1962)

and E. S. Fisher, Trans.

AIME

254

H. Babyak,

8)

W.

4)

F. W.

Kunz

(1960)

133

Trans.

AIME

and A. E. Bibb, Acta Met.

5,

J. E. Bailey,

s,

D. G. Westlake,

J. Nucl.

239

11 (1963) Mat.

(1967)

252

Trans. AIME

218

267

26 (1968)

208