Elastic Properties of Three Bulk Metallic Glasses. Evolution Versus Temperature in the Glass Transition Region and Influ
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ELASTIC PROPERTIES OF THREE BULK METALLIC GLASSES. EVOLUTION VERSUS TEMPERATURE IN THE GLASS TRANSITION REGION AND INFLUENCE OF CRYSTALLISATION.
B. VAN DE MOORTELE*, J.M. PELLETIER*, J.L. SOUBEYROUX**, I.R. LU*** *GEMPPM, INSA, Bat. 502, INSA, 69621 Villeurbanne Cedex, France. **CRETA, CNRS, Grenoble, France. ***DLR, Köln, Germany.
ABSTRACT Three bulk metallic glasses, with different resistance against crystallisation, were investigated using DSC experiments, X-ray diffraction, transmission electron microscopy and mechanical spectroscopy. Like in other non-crystalline materials, the elastic modulus exhibits a large decrease above the glass transition temperature. In materials with a large supercooled region (Pd-Ni-Cu-P for instance), this decrease can reach three decades, leading to an attractive glass forming ability. In contrast, in bulk metallic glasses in which onset of crystallisation occurs very rapidly above Tg, this decrease is on less than one decade. A correlation is made with the microstructure evolution revealed by X-Ray diffraction and transmission electron microscopy.
INTRODUCTION During the last decade, new multicomponent glass forming alloys have been developed, which exhibit a good glass forming ability [1-21]. Some of these bulk metallic glasses (BMG) have a wide supercooled region (SLR), with high resistance against crystallisation. This stability is usually characterised by the parameter ∆Tx = Tx – Tg, where temperature Tx corresponds to the onset of crystallisation and Tg to glass transition temperature. Values of ∆Tx depend on alloy composition : Pd-Ni-Cu-P BMG exhibit the highest one [18-21]. However, due to the excessive cost of this material, other alloys were developed. Many studies have been performed in Zr- base materials : Zr-Ti-Cu-Ni-Be (vitreloy) [3, 6, 8-10, 15, 17] and Zr-Ti-Cu-Ni-Al (Al replaces the expensive and toxic Be element) [1, 2, 7, 11, 13, 14, 16]. Desirable properties may include mechanical features or high corrosion resistance, for instance for athletic equipment or aerospace components. In many cases, the forming ability is a pertinent characteristics and, consequently, temperature evolution of the mechanical properties has to be investigated (elastic behaviour, viscosity, …). For instance, it is well-known that in non-crystalline materials, elastic modulus exhibits a large decrease above Tg. Unfortunately, in BMG, thermal ability to keep the non-crystalline state is not always ensured, in contrast to polymers or oxide glasses. This thermal stability depends on composition and especially on oxygen content [12]. The present study reports on elastic properties versus temperature of three BMG : Pd-NiCu-P, Zr-Ti-Cu-Ni-Be and Zr-Ti-Cu-Ni-Al. Characteristic temperatures (Tg and Tx) were determined by classical DSC experiments and information on microstructure was provided by X-ray diffraction experiments and transmission electron microscopy. L10.6.1
EXPERIMENTAL PROCEDURE Ingots of amorphous materials were prepared by induction melting in controlled atmosphere and rapid q
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