Sorption of Hydrogen and Deuterium in a Glassy Pd-Si Alloy by a Bending-Cantilever Method
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B.H. Kear,
B.C. Giessen,
249
and M. Cohen, editors
SORPTION OF HYDROGEN AND DEUTERIUM IN A GLASSY Pd-Si ALLOY BY A BENDINGCANTILEVER METHOD
B.S. BERRY AND W.C. PRITCHET IBM T.J. Watson Research Center, Yorktown Heights, New York 10598, USA
ABSTRACT
The dilatation caused by the sorption of H and D in amorphous samples of melt-spun Pd82Si 1 8 and sputter-deposited Pd 8 1 Si 19 has been measured at room temperature for ambient charging pressures P up to 760 torr. By comparison with the strength of the Gorsky relaxation, it is concluded that (a) the dilatations per hydrogen and deuterium atom are identical and independent of 1 2 concentration and (b) the non-linearity of the dilatation vs. p / isotherms is due solely to a deviation from Sieverts' law. The isotherms exhibit a distinct isotope-dependence, of a similar nature to that for crystalline Pd. A sputterdeposited film is found to dissolve more H or D than a melt-spun ribbon, due possibly to a less structurally-relaxed configuration.
INTRODUCTION
The subject of hydrogen in metallic glasses is currently receiving increased attention from several points of view. One of these relates to the comparatively recent realization that internal friction and Gorsky relaxation measurements are available as powerful and complementary tools for studies of hydrogen in this group of materials[I,2]. The present investigation is an outgrowth of earlier work, particularly on the Gorsky relaxation, which demonstrated qualitatively that the sorption of hydrogen by a metallic glass is associated with a volume expansion or dilatation. This effect is of course well-known in crystalline materials, where it has been studied by a number of techniques that are mostly inapplicable to metallic glasses. We describe here a simple bending-cantilever method that can be applied to metallic glasses, and show that the results obtained are particularly useful when combined with complementary measurements of the Gorsky relaxation.
METHOD AND MATERIALS
The basic approach, illustrated in Fig. 1, was to utilize the bending action of a bilayer strip composed of the metallic glass bonded to an inert (non-absorbing) elastic backing or substrate. The method has proved to be both simple and sensitive, and is particularly convenient in cases where sorption can take place directly from the gas-phase, as for the Pd-Si glasses. In general, sorption involves a transient response leading eventually to an equilibrium deflection 4 (Fig. 1). The relationship between 4and the fractional volume change AV/V is [3] 3
2, 3 AV/V = 13h' + (E'lbla 1 + E' 2 b 2 a 2 )((1/Etlblal) + (1/E' 2 b 2 a2))}/h ,
,-
2 .h2
(1)
In this expression E' 1 = El/(1-Xl), and al,bl,E 1 and x 1 denote respectively the thickness, width, Young's modulus and Poisson's ratio of the metallic glass. A complementary notation is used for the backing. The sample length is e, and h is the total thickness a1 + a 2 .
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METALLIC GLASS INERT ELASTIC BACKING Fig. 1. A self-stressed bilayer cantilever, deflected into a circular arc by the sorpti
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