Synthesis, Structure and Properties of MoNbTaVW High Entropy Alloy Thin Films

Ao Xia

Research output: ThesisDoctoral Thesis

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Abstract

In recent years, high entropy alloys (HEAs) have emerged as a new class of materials. These metallic alloys consist of 5 to 13 metallic elements in an approximately equimolar ratio. Their excellent mechanical properties such as high strength, ductility, thermal diffusion, and fracture toughness are promising for future applications like as wear-resistant coatings, as thermal barrier coatings or as effective diffusion barriers in microelectronics. While research on bulk HEAs has seen quite a boost over the past years, HEAs as thin films are still a relatively unexplored area. The current work provides a detailed study about MoNbTaVW HEA thin films synthesized by physical vapor deposition. The influence of the film growth conditions was studied by synthesizing metallic films using magnetron sputter deposition, high-power impulse magnetron sputtering and cathodic arc deposition. The films present a body-centered cubic (bcc) structure in as-deposited state regardless of deposition method and angle. Variations in chemical composition and mechanical properties can be related to the energetic growth conditions encountered in the different methods. When annealed in vacuum, the bcc structure of MoNbTaVW is stable up to 1200 °C. With the addition of N2 to the discharge during deposition, a nitride phase with face-centered cubic structure forms and the hardness increases. Tensile testing of the films deposited on polyimide was performed to assess their electromechanical behavior. The crack onset strain of MoNbTaVW was determined at about 2%. The sharp rise in resistance at strains exceeding the crack onset strain indicates a brittle behavior, which is further enhanced with the addition of N and the formation of (MoNbTaVW)1-xNx films.
Translated title of the contributionSynthese, Struktur und Eigenschaften von MoNbTaVW Hochentropielegierungsschichten
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Mitterer, Christian, Supervisor (internal)
  • Mayrhofer, Paul Heinz, Assessor B (external)
  • Eckert, Jürgen, Assessor A (internal)
  • Franz, Robert, Co-Supervisor (internal)
Publication statusPublished - 2020

Bibliographical note

embargoed until null

Keywords

  • thin film
  • arc evaporation
  • sputter deposition
  • high power impulse magnetron sputtering
  • high entropy alloy
  • refractory metal
  • vacuum annealing
  • electrical resistance
  • fragmentation testing

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