Copyright Dr. L. Lilensten

Complex multicomponent alloys: coupled structural and mechanical study of a bcc model alloy, and possible improvement path

Lola Lilensten1, Jean-Philippe Couzinié2, Ivan Guillot2, Guy Dirras3, Frédéric Prima1

1 IRCP Institut de Recherche de Chimie Paris – CNRS-Chimie-Paristech – 11 rue Pierre et Marie Curie – 75231 Paris Cedex 05

2 ICMPE Institut de Chimie et des Matériaux de paris Est – CNRS-UPEC – 2-8 rue Henri Dunant – 94320 Thiais

3 Université Paris 13, Sorbonne Paris Cité, LSPM (UPR 3407), CNRS, 99 avenue J-.B. Clément F-93430 Villetaneuse

A lot of research effort has now been dedicated to the study of complex multicomponent alloys (more commonly called High Entropy Alloys HEA). This family of materials introduced in 2004 breaks with the traditional alloying concept, since they explore the domain of concentrated solid solution(s) of +5 elements. Several studies sprovide fundamental understanding on the structure and the mechanical properties of some of these alloys, mostly fcc [1–3]. If the results are promising, as for example the incredible fracture toughness of FeCoCrMnNi at low temperatures [4], recent papers suggest that equiatomic fcc alloys with less than 5 elements, or non-equiatomic fcc concentrated alloys also display great, or even greater mechanical properties [2,5,6].

The sub-family of bcc complex multicomponent alloys has been less investigated. Therefore, a multi-scale characterization of a model bcc multicomponent alloy with composition Ti20Zr20Hf20Nb20Ta20 is performed. After optimization of the microstructure, investigated by SEM (EBSD), TEM and EXAFS, the mechanical properties of the alloy are studied during both tensile/relaxations tests and shear tests. Deformation mechanisms are discussed in terms of activation volume and flow stress partitioning, interpreted with the help of microstructural investigations by transmission electron microscopy.

Finally, the “HEA” concept is coupled with the chemical design based on electronic parameters Bo and Md used in Ti-alloys. This concept, first introduced by Morigana was successfully used to help predicting the structure stability, and hence the mechanical behavior – dislocation glide, twinning induced plasticity (TWIP) or transformation induced plasticity (TRIP) – of Ti-rich alloys [7,8]. The studied composition Ti35Zr27.5Hf27.5Nb5Ta5 displays a large ductility of 20% and an increased work-hardening [9]. It confirms that extending the concept of “HEAs” to non-equiatomic compositions can be highly beneficial and that the design strategy developed for Ti-alloys can be used with great results in concentrated alloys.

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Dr. L. Lilensten

IRCP Institut de Recherche de Chimie Paris

CNRS-Chimie-Paristech

11 rue Pierre et Marie Curie

75231 Paris Cedex 05

France

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