HYDRIDE PRECIPITATION IN ZIRCONIUM STUDIED BY LOW-FREQUENCY PENDULUM TECHNIQUES

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HYDRIDE PRECIPITATION IN ZIRCONIUM STUDIED BY LOW-FREQUENCY PENDULUM

TECHNIQUES

I. Ritchie, K. Sprungmann

To cite this version:

I. Ritchie, K. Sprungmann. HYDRIDE PRECIPITATION IN ZIRCONIUM STUDIED BY LOW-

FREQUENCY PENDULUM TECHNIQUES. Journal de Physique Colloques, 1983, 44 (C9), pp.C9-

313-C9-318. �10.1051/jphyscol:1983944�. �jpa-00223391�

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JOURNAL

DE

PHYSIQUE

Colloque C9, suppl6ment au n012, Tome 44, dCcembre 1983 page C9-313

HYDRIDE

PRECIPITATION

IN

ZIRCONIUM STUDIED

BY

LOW-FREQUENCY

PENDULUM

TECHNIQUES

I.G. Ritchie and K.W. Sprungmann

Materials Science Branch, Atomic Energy of Canada Limited, Research Company, Witheshell Nuclear Research Establishment, &-tawa, Manitoba, Canada ROE ILO, Canada

Rdsumd

-

Lors de la prdcipitation des hydrures dans le Zirconium, il apparait un pic de frottement interne et un phbnomSne d'autotorsion sur le pendule. On montre comment les rssultats obtenus peuvent servir S dtablir un diagramme de limite de solubilitd, 2 l'dtat solide, de llhydrogSne danslezirconiuma jusqu's des concentrations en hydro- gPne faibles (50

5

2pg/g) usuelles dans llindustrie nuclbaire.

Abstract

-

Measurements of the hydride precipitation peak and autotwisting strain using a torsion pendulum are reported. It is shown how the results obtained can be used to map the terminal solid solubility boundary for hydrogen in a-zirconium to the low hydrogen concentrations (50 to 2 vg/g) of practical importance in the nuclear industry.

I

-

INTRODUCTION

In recent years, internal friction (IF) techniques have been used to establish the hydrogen-rich regions of the phase diagrams of metal-hydrogen systems and to study the diffusion of hydrogen both in the metal lattice and in any hydride phases formed

[ll. In particular, pendulum techniques have been used to map the hydrogen terminal solid solubility (TSS) boundaries in the hydride forming b.c.c. transition metals vanadium, niobium and tantalum for hydrogen concentrations (I: )

>

^{0.5 atom}% [2-4) and in the h.c.p. metal a-titanium 151. Several studies of t\e ;-%r-H system have been reported also [6-101, hut in only one of these 191 were the IF measurements made over sufficientlv wide temperature (T) and CH ranges to map the TSS. Other techniques have been successfully applied to the mapping of the hydrogen TSS in a-zirconium and its allovs used in the nuclear industry. However, most of the measurements have been made in the range 300 to 500°c, corresponding to 0.5

<

^C

<

^6.3

atom b (or 35 to 700 pg/gj 111-171. H

-

The purpose of this paper is to report our attempts to use the precipitation peak [2,41 and the autotwisting phenomenon [2,18-201 to map the TSS in a-zirconium. The most important goal of the study was to extend the application of pendulum techniques to the lower CH range (2

<

^CH

^<

50 pg/g) of practical importance in the nuclear industry.

I1

-

MATERIALS AND TECHNIQUES

Some of the results described in this paper were obtained on samples of a nominally

9 9 . 9 9 9 % pure zirconium containing (pg/g): H

<

5; N, 6 and 0, 17 to 23. Other

results were obtained on Marz-grade zirconium samples, which in the "as-received"

condition contained (ug/g): Al, 10; Fe, 30; Hf, 200; 0, 120; and H, 27. A single- crystal sample in the form of a small platelet (23.5 x 6.5 x 1.4 mm ) was also in- vestigated. The orientation of this sample was such that the c-axis was parallel to the thickness direction and the longitudinal axis made an angle of 14.5' with an a- direction. After testing, this sample contained (pg/g): Al, 17; Cu, 50; Cr, 45;

Fe, 80; Hf, 50; Yn, 7; Pb, 10; Si, 12; Sb, 12; 0, 200; and H, 34.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983944

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C9-314 J O U R N A L D E PHYSIQUE

Two types of low-frequency IF pendula were employed in this study: an inverted torsion pendulum and a counterbalanced flexure pendulum. Wire qamples, typically 100 mm long and 1 mm in diameter, were tested in the torsion pendulum, while platelets of typical dimensions 25 x 3 x 1 mm were tested in the flexure pendulum. Both pendula and the electronic data-logging equipment and measurement techniques used have been described in detail elsewhere (211. Yeasurements of IF were made by two different methods: either by monitoring the amplitude in free decay of the pendulum oscillations, or by driving the pendulum at a constant amplitude and monitoring the energy input per cycle to the system.

The surface strain amplitude ( E ) at which the sample is maintained is preset by adjusting a reference voltage, N. This nominal strain amplitude N is easily related to E by a factor involving the dimensions of the sample and the geometry of the pendulum.

Where free-decay measurements have been performed, the measure of IF used is the logarithmic decrement, A. lJhere constant strain amplitude measurements have been performed, the measure of IF is the drive signal in volts, which is proportional to W for a given value of E in a given material [21].

To reduce the pick-up of gaseous impurities ( 0 , N, H an4 C), each pendulum was operated in a vacuum of better than 0.13 mPa during testing and in situ thermal treatments of the samples.

111

-

RESULTS AND DISCUSSION

Precipitation Peak

-

Curves of IF as a function of T, measured continuorisly at constant E , are shown in Fig. 1 for a sample of pure zirconium containing CR = 9 9 2 ug/g. Prior to testing, the sample was annealed for 6 h at 7 0 0 ~ ~ and strained 1% in tension before insertion in the torsion pendulum. As shown in Fig. 1, during heating there is a broad peak, situated at about 200°C, which appears to consist of at least three overlapping components. During cooling, there is a sharp rise in IF between 190 and 1 8 0 ~ ~ to a peak at about 1 6 0 ~ ~ . The shape of this cooling peak (particularly the sharp, high-temperature flank) is very similar to the shapes of the hydride-precipitation peaks in other metals 12-51. Further tesfs showed that the peak height increased with CH and the heating or cooling rate \ T I , but decreased with increasing frequency, f. In addition, the peak temperature and, more impor- tantly, the temperature of the sharp, high-temperature flank increased with C

.

^All

of the above-mentioned pr~pert~ies are characteristic of the precipitation peaas in other systems [2-51. Following the procedure adopted by other workers, we have taken the onset of the sharp increase in IF on cooling to be the position of the TSS boundary in cooling (see Fig. 1). No attempt is made to correlate a feature of the heating curve with the position of the TSS boundary in heating. Mapping of the TSS on heating must await the identification of the three components that appear to make up the heating curve. Nevertheless, it should be noted that there is a significant hysteresis between the high-temperature flanks of the heating and cooling curves, consistent with some degree of undercooling normally associated with hydride precipitation in metals. Each test of the type shown in Fig. 1 was repeated a minimum of six times on each of four samples of pure zirconium in the torsion pendulum and each of two samples of Marz-grade zirconium in the flexure pendulum.

These results are plotted in an Arrhenius dtagram (Fig. 5) of all the TSS results reported in this paper.

In a single-crystal sample tested in the flexure pendulum, a much sharper peak, or spike, was observed to be associated with the TSS boundary. Typical results are shown in Fig. 2. In this sample, which contained 34 9 2 p g / ~ of hydrogen, the peak was similar in shape on both heating and cooling with only a very slight hysteresis in the sense expected intuitively. Also, as shown in Fig. 2, the height of the peak increased with !TI. As part of an unrelated study, this sample was thermally cycled more than twenty times throuxh the temperature range 200 to 400'~ and, on each cycle, spikes similar to those shown in Fig. 2 occurred in the range 250 to 260'~ on both heating and cooling. It is possible that the spikes observed in this sinqle-

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crystal sample,,correspond to the precipitation peak in polycrystalline samples. The latter precipitation peak may be a sequence of overlapping spikes, corresponding to the precipitation of hydrides in different orientations, in different grains and in response to different levels of the local internal stress. Yore work on single- crystal samples is clearly desirable.

Fig. I

Constant E drive signal (=A) versus temperature during a thermal cvcle of pure zirconium containing 9 f 2 ug/g H.

Sharp spikes in the constant E drive signal (-=A) versus temperature for a single crystal of zirconium tested in flexure pendulum.

the

1.5 Heating, 0,65'C/rnin

1.4 1.3

Autotwisting

-

Torsional strain as a function of T for a heating/cooling cycle (IT1

= 0.8"~) of a sample of Marz-grade zirconium with CH = 209 f 9 ug/g is traced in Fig. 3 . The curve can be described as a heating branch that shows little autotwisting and a cooling branch characterized by a sharp knee at 3 8 0 ~ ~ that is taken to be the position of the TSS boundary on cooling. Tn tests carried out on samples containing concentrations in the range 100 ( CR

<

700 yg/g, the heating branch was relatively flat, or contained a broad bump in the vicinity of the TSS. Repeated tests showed that the position of the knee in the cooling branch was reproducible to within

*

^10'~. 4t least five thermal cvcles were observed for each sample, and the

average position of the TSS knee in the cooling hranches is plotted in the Arrhenius plot, Pig. 5.

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JOURNAL DE PHYSIQUE

As shown in 1191 for the V-H system, the form of the autotwisting curve below the TSS knee simply reflects the fraction of precipitated hydrogen, 1.e.

+I

In 0

0 ^X- 1

z

iii - 2 - a

F

^-3-

V)

J - 4 - a z 2 - 5 -

V)

- 6 - I-

-7 -8

where T is the temperature of the TSS knee, k is Roltzmann's constant, cT, E T ~ and

E are the autotwisting strains at T, T and 0 K, respectively, and AH is the dif- fgrence between the heats of solution o? the hydride and solid solutioa phases. A test of the applicahility of eqn. (1) to the Zr-H svstem is shown in Fig. 4, where it was assumed that E RT = E (E is the autotwtsting strain at room temperature) and datum points were pickea ofp the curve in Fig. 3 at 20'~ intervals. The plot is linear from T = 3 8 0 ~ ~ down to s12o0~ where [ ~ - ( E ~ - E ~ )/(E - E ~ ) 1 becomes too small to determine gccurately. Over this linear range, theSsolu!~lit~, CH, in a-zirconium can be written

CH = 5.57 x 10 exp (-0.44 (eV)/k~) 5 (2)

0 100 200 300 400 500 600

TEMP "C

-

^209?9+q/q

-

l i l 0 B0C/mln -

-

- TSS

- -

-

I ! I I I I

for 140

<

T 1380'~ (or 2

<

^CH( 209 vg/g), which should be compared with the equation for the compilation given by Kearns (121 of

Qig. 3 Autotwisting strain versus temperature during a thermal cycle of a Marz-grade wire sample.

CH = 1.61 x 10 exp (-0.39 (eV)/kT) 5 (3)

determined over the range 260

<

^T( 550'~.

Following Ferron and Quintard [19], we attribute at least part of the autotwisting strain to the bow-out of string-like, hydride dislocations, rghich is described by

provided t9e bow-out motion is slow enough to neglect viscous damping. In eqn (41, C = 0.5 Gb is the line tension of the dislocations, o is the effective shear stress in the slip plane, b is the Burgers vector, G is the shear modulus, and x and Y are the co-ordinates along the dislocation and perpendicular to the.dislocation in the slip plane, respectively. An incorrect simplification, Cy = ob, was used for eqn. (4) by Ferron and Quintard [191, which invalidates some of their conclusions.

If the dislocation length L is set equal to the length of the hvdride needle or platelet, the solutton for y from eqn. (4), when substituted in the expression,

E~ = aAby, for the strain, finally yields

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Fig. 4

Analysis of the cooling branch of Fig. 3 in accordance with eqn. (1) of the text.

In this expression A = nNL is the density of hvdride dislocations, i.e. N is the number of hydride particles per unit volume, n is the number of dislocations per hygride p rticle, and a is a geometrical factor. Thus, in eqn. (5) the product

9

AL = nNL reflects the amount of hydrogen precipitated, if it is assumed that variations in the effective internal stress acting on the hydride dislocations remain small. Although this model is oversimplified, it does yield maxiyum str ins of !jhe order of magnitude ohserved. For example, an estimate of ( a / h ) ~ ~ = lo-' to 10- can be obtained from the height of a peak attributed to the unpinning of hydride dislocations 1221 and, if the internal stzess close to the hyd53d.e particle remains close to the yield stress, then o / G = 10

,

from which E~ = 10 to 10

,

^as

observed. Presumably, in the event of isotropic, homogeneous, hydride precipitation in a perfectly aligned, textureless sample under no external stress, a would be zero and no autotwisting would he observed. In practice, the presence of texture, and of anisotropic and inhomogeneous precipitation in response to slight variations in temperature and internal stress, leads to a net autotwisting.

Yoshinari and Koiwa [I81 suggest that the origin of the autotwisting strain lies in stress-induced anisotropic precipitation. Their model explains why an external shear stress enhances the observed autotwisting; the population of stress-favoured hydrides is simply increased over the popnlation of unfavoured hydrides, adding an additional component to the strains in the direction of the applied stress. This effect could also enhance the dislocation bow-out strain hy dictating the presence of more hydride dislocations on the slip planes associated with the favoured hydrides than on those associated with the unfavoured hydrides, 1.e. by dictating a higher value of a. It seems probahle that, in systems such as Zr-H where large numbers of hydride dislocations are observed, both mechanisms, combiner1 in this way, contribute to the net autotwisting.

IV

-

CONCLTJSIONS

In Fig. 5 the results are gathered together in an Arrhenius plot of En C as a function of the reciprocal temperature of the experimental feature assocaated with the TSS. These data agree well with those of some other workers. In the high hydrogen range, the data are close to the compilation reported by Kearns [121. In the lower hydrogen range, the results are within the limits of the data reported by Cann and Atrens [161. The data compiled in Fig. 5 show that the pendulum techniques employed can all he extended to determine hydrogen solubility in the loxi (CR

<

50 ug/g) concentration range of practical importance.

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JOURNAL

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TEMP°C 500 400 300

with bias Autotwisting { w~thout . bias o Single crystal 'spike'

Fig. 5

Hydrogen solubility as a function of reciprocal temperature for the TSS results obtained in this study, compared with the compilation reported hy Kearns

[121. Analysis of other autotwisting curves gave results that fall between the broken and full lines shown.

x

Precipitation Peak x Hydride Dislocation P e a k A

Data obtained from the position of the autotwisting knee in the presence of a small, tensile hias stress and a datum obtained from the study of a peak attributed to the unpinning of hydride dislocations are also shown in Fig. 5. These experiments and a discussion of the resr11.t~ will he presented elsewhere 1221.

V

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REFERENCES

111 SCHILLER P., Nuovo Cim.

33R

(1976) 226.

[21 OWEN C.V. and SCOTT T.E., Met. Trans. 3 (1972) 1715.

[ 3 1 YOSHINARI 0. anrl KOIIJA M., Acta ~eta(i982)1979.

[4] YOSHINARI 0. and KOIIJA M., Acta Met .2@1982) 1987.

[51 KOSTER IJ., BANGERT L. and EVERS Y., Z. Yetallkde 47 (1956) 564.

[6] BUNGARDT K. and PREISENDANZ H., Z. Metallkde

2

(1960) 280.

[7) POVOLO F. and RISOGNI E.A., J. Nucl. Mater.

9

(1969) 82.

[81 PROVENZANO V., SCHILLER P. and SCHNEIDERS A., J. Nucl. Mater.

52

(1974) 75.

191 MISHKA S. and ASUNDI M.K., ASTV STP

551

(1974) 63.

[lo] MAZZOLAI F.M., RYLL-NARDZEWSKI J. and SPEARS C.J., Nuovo Cim.

33B

(1976) 251 [Ill ERICKSON W.H. and HARDIE D., J. Nucl. Mater.

13

(1964) 254.

[12] KEARNS J. J., J. Nucl. Mater.

22

(1967) 292.

[I31 SLATTERY G.F., J. Inst. Metals

95

(1967) 43.

[I&] SANATZKY A. and WILKINS R.J.S., J. Nucl. Mater.

22

(1967) 304.

I151 COLEMAN C.E. and AMBLER J.F.R., Yet. Soc. CIM (1978) 81.

[16] CANN C.D. anrl ATRENS A., J. Nucl. Mater.

88

(1980) 42.

[I71 NUTTALL K., DUTTON R. and SHILLINGLAW A.J., 3rd Int. Cong. Hydrogen and Materials, Paris

1

(1982) paper A-12 p. 167.

[I81 YOSHINARI 0. and KOITJA M., J. le Phys. (1981) 893.

[I91 FERRON G. and QUIMTARD M., Scripta Metall.

13

(1979)- 923., 1201 KOIWA M. private communication.

1211 SPRUNGMANN K.W. and RITCHIE I.G., AECL-6438 (1980).

[22] RITCHIR I.G. and SPRUNGMANN K.W. in preparation for puhlikation.