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Synthesis and characterization of multicomponent (CrNbTaTiW)C films for increased hardness and corrosion resistance
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-1019-6604
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Inorganic Chemistry.ORCID iD: 0000-0002-2361-959x
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2018 (English)In: Materials & design, ISSN 0264-1275, E-ISSN 1873-4197, Vol. 149, p. 51-62Article in journal (Refereed) Published
Abstract [en]

Multicomponent carbide thin films of (CrNbTaTiW)C (30–40 at.% C) with different metal contents were depos-ited at different temperatures using non-reactive DC magnetron sputtering. The lattice distortion for the metallattice was estimated to vary from about 3 to 5%. Most films crystallized in the cubic B1 structure but Ta/W-rich films deposited at 600 °C exhibited a tetra gonal distortion. X-ray diffraction results sh ow that near-equimolar films exhibited a strong (111) texture. In contrast, Ta/W-rich films exhibited a shift from (111) to(100) texture at 450 °C. The in-plane relationship was determined to MC(111)[-12-1]//Al2O3(001)[110] with alattice mismatch of about 11% along the Al2O3[110] direction. A segregation of Cr to the grain boundaries was ob-served in all films. The microstructure was found to be the most important factor for high hardness. Less denseNb-rich and near-equimolar films deposited at low tem peratures exhib ited the low est hardnes s (12 GPa),while very dense Ta/W-rich high temperature films were found to be the hardest (36 GPa). No correlation wasfound between the lattice distortion and the hardness. Corrosion studies revealed that the multicomponentfilms exhibited excellent corrosion resistance, superior to that of a reference hyper-duplex stainless steel, in1.0 M HCl.

Place, publisher, year, edition, pages
2018. Vol. 149, p. 51-62
National Category
Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry; Chemistry with specialization in Materials Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-335985DOI: 10.1016/j.matdes.2018.03.068ISI: 000431007500006OAI: oai:DiVA.org:uu-335985DiVA, id: diva2:1165044
Funder
Swedish Research Council, 621-2012-4359Swedish Research Council, 622-2008-405Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research , RMA11-0029Available from: 2017-12-12 Created: 2017-12-12 Last updated: 2020-02-28Bibliographically approved
In thesis
1. Magnetron sputtering of binary, ternary and multicomponent thin film borides and carbides
Open this publication in new window or tab >>Magnetron sputtering of binary, ternary and multicomponent thin film borides and carbides
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Design of new thin film materials with improved properties and functionality is an important research field in materials science. In this thesis, I have used magnetron sputtering to deposit new thin film materials, which should combine high hardness and high ductility with other properties such as low friction or a good corrosion resistance. The films have been characterized with a range of techniques to determine the correlation between deposition parameters, microstructure and properties.

 The first part of the thesis is focussed on binary and ternary molybdenum-containing boride thin films with potential low-friction properties. It was found that the binary Mo-B films exhibited a nanocrystalline structure of ~ 16 nm large MoB2-x grains surrounded by an amorphous tissue phase. The special microstructure resulted in a very high hardness (29 ± 2 GPa), but limited ductility. An attempt to improve the ductility by formation of crystalline layered ternary borides such as Mo2BC and Mo2FeB2 failed due to difficulties to reach high deposition temperatures. However, the addition of carbon to the binary Mo-B films resulted initially in a reduced grain size of the MoB2-x grains. For carbon concentrations >23 at.%, a completely amorphous film was formed. Transmission electron microscopy (TEM) studies revealed that these films contained Mo-rich regions surrounded by a Mo-poor amorphous BCx phase and therefore best can be described an amorphous nanocomposite. The mechanical properties of the Mo-B-C films were strongly correlated to the amount of the softer amorphous BCx phase. Also the Mo-Fe-B films were amorphous with a hardness ranging from 19 to 26 GPa and a limited ductility. Tribological studies of the Mo-B, Mo-B-C and Mo-Fe-B films showed very high coefficients of friction (>0.8). Molybdenum and boron oxides were identified on the surface by Raman spectroscopy, but no indication of lubricating effects from these oxides could be observed. The results suggest that Mo-based borides have limited applications in future low-friction applications.

In the second part of the thesis, a high entropy alloy (HEA) of TiCrNbTaW was studied with and without the addition of carbon. The results showed that a HEA phase with bcc structure could be deposited in a wide composition and temperature range. Small amounts of carbon were dissolved into the bcc phase, while higher carbon contents resulted in a multicomponent carbide phase. The correlation between structure and properties were studied in detail. It was found that some of the films exhibited very high hardness combined with high ductility suggesting potential application of these materials as wear-resistant coatings. Finally, the corrosion resistance of these complex alloys were investigated in a very acidic environment. They were found to exhibit excellent corrosion resistance superior to hyper-duplex stainless steels.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 72
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1612
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-335987 (URN)978-91-513-0188-4 (ISBN)
Public defence
2018-02-09, 2001, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2018-01-18 Created: 2017-12-12 Last updated: 2018-03-07
2. 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)
Opponent
Supervisors
Available from: 2020-03-26 Created: 2020-02-28 Last updated: 2020-03-26

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Malinovskis, PauliusFritze, StefanRiekehr, Larsvon Fieandt, LinusCedervall, JohanRehnlund, DavidNyholm, LeifLewin, ErikJansson, Ulf

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