Phase Formation in High-Entropy Alloy Thin Films

May 18, 2016, 4:10 PM
15m
Pand

Pand

Speaker

Mr Bert BRAECKMAN (Vastestofwetenschappen, UGent)

Description

Since the beginning of the 21st century, a novel approach to design alloys with promising properties has been introduced [1]. High-Entropy Alloys (HEAs) are composed of five or more principal elements in equimolar ratios. The high mixing entropy significantly reduces the Gibbs free energy of the solid solution, hence single-phase multi-component solid solutions are thermodynamically stable, especially at high temperature. In contrast to conventional alloys, the large number of elements does not lead to complex systems but rather simple fcc and/or bcc crystalline structures or amorphous phases are formed. HEAs have excellent properties such as high hardness and strength, corrosion resistance and thermal stability, which makes them interesting materials for a range of applications. Although bulk HEAs have already been studied, the formation and properties of thin film HEAs have not yet been studied in great depth due to the alloy’s complexity. This work investigates the interplay between different elements and their chemical, topological, and thermodynamic properties on the phase formation in HEA thin films. As sputter deposition is a momentum- and energy-driven process, also the deposition conditions influence the film properties [2,3]. The 5-element CoCrCuFeNi alloy was used as a starting point and the influence of three solute elements (Nb, In and Ge) on the film growth and phase formation was studied. In this way it is possible to make a cautious set of guidelines for future alloy design.

Keywords: High-entropy alloys, multi-element thin films, sputter deposition, phase formation

References [1] J. W. Yeh et al., Adv. Eng. Mater. 6 (5) (2004) 299, [2] B. R. Braeckman et al., Thin Solid Films 580 (2015) 71, [3] B. R. Braeckman, D. Depla, J. Alloys Compd. 646 (2015) 810

Primary author

Mr Bert BRAECKMAN (Vastestofwetenschappen, UGent)

Co-author

Prof. Diederik DEPLA (Vastestofwetenschappen, UGent)

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