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Influence of Deposition Temperature on the Phase Evolution of HfNbTiVZr High-Entropy Thin Films
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
TU Wien, Inst Mat Sci & Technol, A-1060 Vienna, Austria.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-2361-959x
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
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2019 (English)In: Materials, ISSN 1996-1944, E-ISSN 1996-1944, Vol. 12, no 4, article id 587Article in journal (Refereed) Published
Abstract [en]

In this study, we show that the phase formation of HfNbTiVZr high-entropy thin films is strongly influenced by the substrate temperature. Films deposited at room temperature exhibit an amorphous microstructure and are 6.5 GPa hard. With increasing substrate temperature (room temperature to 275 degrees C), a transition from an amorphous to a single-phased body-centred cubic (bcc) solid solution occurs, resulting in a hardness increase to 7.9 GPa. A higher deposition temperature (450 degrees C) leads to the formation of C14 or C15 Laves phase precipitates in the bcc matrix and a further enhancement of mechanical properties with a peak hardness value of 9.2 GPa. These results also show that thin films follow different phase formation pathways compared to HfNbTiVZr bulk alloys.

Place, publisher, year, edition, pages
MDPI , 2019. Vol. 12, no 4, article id 587
Keywords [en]
high-entropy alloys, physical vapour deposition (PVD), metallic glass
National Category
Metallurgy and Metallic Materials Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-380494DOI: 10.3390/ma12040587ISI: 000460793300037PubMedID: 30781407OAI: oai:DiVA.org:uu-380494DiVA, id: diva2:1299790
Funder
Swedish Research Council, 2018-04834Available from: 2019-03-28 Created: 2019-03-28 Last updated: 2020-02-28Bibliographically approved
In thesis
1. Microstructure and Mechanical Properties of Magnetron Sputtered Refractory Metal Thin Films
Open this publication in new window or tab >>Microstructure and Mechanical Properties of Magnetron Sputtered Refractory Metal Thin Films
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The design and development of new multifunctional materials that exhibit a combination of high hardness and ductility, as well as a high corrosion resistance and thermal stability, is one of the key challenges in the field of material science. The focus of this thesis is on the development of novel multifunctional magnetron sputtered CrNbTaTiW–C based thin films. Carbon was selected as an alloying element to investigate if it could modify the microstructure (via grain refinement) and improve the properties (e.g. the hardness and ductility).

TaW-rich and near-equimolar high entropy alloys in the CrNbTaTiW system were selected as starting points for this study. The latter alloys were predicted, based on empirical design rules, to form a single-phase solid solution. In contrast, thermodynamic calculations showed that the films at equilibrium should be composed of a mixture of several phases at temperatures below 1100 °C.  Experimentally, however, a single-phase bcc structure was observed for the deposited films and it was concluded that the films were kinetically and not entropy stabilised. A hypothesis is that the kinetics during sputtering allow a ’direct’ phase selection by tuning the process parameters and evidence of this was found in the HfNbTiVZr alloy system.

The CrNbTaTiW–C system is, however, complex and additional studies were carried out on the W–C and TaW–C systems. All metallic films crystallised in a bcc structure with a <110> texture and the column width of these films varied between 25 nm and 80 nm. The films were very hard (~ 13 GPa), which was explained by the small grain size. A single-phase bcc structure was also obtained upon the addition of 5-10 at.% carbon for all compositions except the near-equimolar CrNbTaTiW. X-ray diffraction indicated a unit cell expansion, which was attributed to the formation of a supersaturated solid solution. Additional atom probe tomography (APT) studies on selected samples confirmed the formation of such solid solutions. The supersaturated solid solution is not thermodynamically stable and an annealing study showed that heat treatment yielded segregation and clustering of carbon at the grain boundaries. The addition of carbon had a grain refining effect in the W–C system and the multicomponent CrNbTaTiW–C system. In general, the addition of carbon increased the hardness, which was mainly caused by a reduced grain size in line with the Hall-Petch relationship. Excellent mechanical properties of carbon supersaturated films were further confirmed in pillar tests on W–C films, which showed very high yield strength (~ 9 GPa) and no brittle fracture. The results show that carbon can be used as a chemical approach to control the grain size and properties of these films. 

Multicomponent carbides with a B1 structure were formed at high carbon concentrations (~ 40 at.%). The microstructure of these films depended strongly on the process parameters and a higher deposition temperature was found to increase the film density and hardness. The TaW-rich carbide exhibited a very high hardness of ~ 35 GPa and excellent corrosion resistance.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. p. 73
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1909
Keywords
thin films magnetron sputtering, refractory metals, high entropy alloys, mechanical properties, transition metal carbides
National Category
Engineering and Technology
Research subject
Chemistry with specialization in Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-405323 (URN)978-91-513-0884-5 (ISBN)
Public defence
2020-04-17, Ångströmslaboratoriet Siegbahnsalen, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
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Available from: 2020-03-26 Created: 2020-02-28 Last updated: 2020-03-26

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Fritze, Stefanvon Fieandt, LinusMalinovskis, PauliusJohansson, KristinaLewin, ErikJansson, Ulf

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