liu.seSearch for publications in DiVA
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Toughness Enhancement in Hard Single-Crystal Transition-Metal Nitrides: V-Mo-N and V-W-N Alloys
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Transition-metal nitrides are known for their high hardness, good wear resistance, high-temperature stability, and chemical inertness. Because of these properties, they are extensively used in many industrial applications, notably as protective wear, erosion, and scratch resistant coatings, which are often subjected to high thermo-mechanical stresses. While high hardness is essential, most applications also require high ductility, to avoid brittle failure due to cracking. However, transitionmetal nitrides, as most ceramics, generally exhibit low ductility and hence poor toughness.

Improving toughness, the combination of hardness and ductility, of ceramic materials requires suppression of crack initiation and/or propagation, both of which depend on the microstructure, electronic structure, and bonding nature of the coating material. This, however, is an extremely challenging task that requires a fundamental understanding of the mechanical behavior of materials. Theoretical studies, for example, ab initio calculations and simulations are therefore useful in the design of “unbreakable” materials by providing information about the electronic origins of hardness and ductility. Recent density functional theory calculations predicted that alloying can increase toughness in a certain family of transition-metal nitrides such as V-Mo-N and V-W-N alloys. Toughness enhancement in these alloys arises from a near optimal filling of the metallic d-t2g states, due to their high valence electron concentrations, leading to an orbital overlap which favors ductility during shearing.

This thesis focuses on the growth and characterization of V1-xMoxNy (0 ≤ x ≤ 0.7, 0.55 ≤ y ≤ 1.03) and V1-xWxNy (0 ≤ x ≤ 0.83, 0.75 ≤ y ≤ 1.13) cubic alloy thin films. I show that alloying VN with WN increases the alloy hardness and reduces the elastic modulus, an indication of enhanced toughness. I investigated the growth, nanostructure, and atomic ordering of as-deposited V1-xWxNy(001)/MgO(001) thin films. In addition, I studied the growth, structural and mechanical properties,  and electronic structure of V1-xMoxNy(001)/MgO(001) and V0.5Mo0.5Ny(111)/Al2O3(0001) thin films. I demonstrate that these alloys exhibit not only higher hardness than the parent binary compound, VN, but also dramatically increased ductility. V0.5Mo0.5N hardness is more than 25% higher than that of VN. Using nanoindentation I show that while VN and TiN reference samples undergo severe cracking typical of brittle ceramics, V0.5Mo0.5N films do not crack. Instead, they exhibit material pile-up around nanoindents, characteristic of plastic flow in ductile materials. Furthermore, the wear resistance of V0.5Mo0.5N is significantly higher than that of VN. I also show, for the first time, anion-vacancyinduced toughening of single-crystal V0.5Mo0.5Ny/MgO(001) films. Nanoindentation hardness of these alloys increases with the introduction of N-vacancies, while the elastic modulus remains essentially constant. In addition, typical scanning electron micrographs of nanoindents show no cracks, which demonstrate that N-vacancies lead to toughness enhancement in these alloys. Valence band x-ray photoelectron spectroscopy analyses show that vacancy-induced toughening is due to a higher electron density of d-t2g(Metal) – d-t2g(Metal) orbitals with increasing N-vacancy concentration, and essentially equally dense p(N) – d-eg(Metal) first neighbor bonds.

Overall, I demonstrate that it is possible to design and deposit hard and ductile transition-metal nitride coatings. My research results thus provide a pathway toward the development of new tough materials.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 69 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1578
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-106472DOI: 10.3384/diss.diva-106472ISBN: 978-91-7519-392-2 (print)OAI: oai:DiVA.org:liu-106472DiVA: diva2:716169
Public defence
2014-06-02, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-05-08 Created: 2014-05-08 Last updated: 2016-08-31Bibliographically approved
List of papers
1. Epitaxial V0.6W0.4N/MgO(001): Evidence for ordering on the cation sublattice
Open this publication in new window or tab >>Epitaxial V0.6W0.4N/MgO(001): Evidence for ordering on the cation sublattice
Show others...
2013 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 31, no 4Article in journal (Refereed) Published
Abstract [en]

V0.6W0.4N alloys are grown on MgO(001) by ultrahigh vacuum reactive magnetron sputtering from V and W targets in 10 mTorr pure-N-2 atmospheres at temperatures T-s ranging from 600 to 900 degrees C. Based on x-ray diffraction and transmission electron microscopy results, all films have the B1-NaCl crystal structure and grow with a cube-on-cube epitaxial relationship to the substrate, (001)(VWN)parallel to(001)(MgO) and [100](VWN parallel to)[100](MgO). Rutherford backscattering spectrometry analyses show that the N content in V0.6W0.4Nx alloys decreases with increasing T-s from overstoichiometric with x = 1.13 at 600 degrees C, to approximately stoichiometric with x = 1.08 at 700 degrees C, to understoichiometric at 800 degrees C (x = 0.80) and 900 degrees C (x = 0.75). High-resolution scanning transmission electron microscopy, Z-contrast, and selected-area electron diffraction investigations of V0.6W0.4N(001) alloys grown at 600 and 700 degrees C reveal the onset of W ordering on adjacent 111 planes of the metal sublattice; no ordering is observed for understoichiometric films grown at higher temperatures.

Place, publisher, year, edition, pages
American Vacuum Society, 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-95955 (URN)10.1116/1.4807654 (DOI)000321516400002 ()
Note

Funding Agencies|Knut and Alice Wallenberg Foundation||Swedish Research Council (VR)||Swedish Government Strategic Research Area Grant in Materials Science (SFO Mat-LiU) on Advanced Functional Materials||

Available from: 2013-08-19 Created: 2013-08-12 Last updated: 2017-12-06
2. Effect of WN content on toughness enhancement in V1–xWxN/MgO(001) thin films
Open this publication in new window or tab >>Effect of WN content on toughness enhancement in V1–xWxN/MgO(001) thin films
Show others...
2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 32, no 3, 030603- p.Article in journal (Refereed) Published
Abstract [en]

The authors report the growth and mechanical properties of epitaxial B1 NaCl-structure V1-xWxN/MgO(001) thin films with 0 ≤ x ≤ 0.60. The Gibbs free energy of mixing, calculated using density functional theory (DFT), reveals that cubic V1-xWxN solid solutions with 0 ≤ x ≤ 0.7 are stable against spinodal decomposition and separation into the equilibrium cubic-VN and hexagonal-WN binary phases. The authors show experimentally that alloying VN with WN leads to a monotonic increase in relaxed lattice parameters, enhanced nanoindentation hardnesses, and reduced elastic moduli. Calculated V1-xWxN lattice parameters and elastic moduli  (obtained from calculated C11, C12, and C44 elastic constants) are in good agreement with experimental results. The observed increase in alloy hardness, with a corresponding decrease in the elastic modulus at higher x values, combined with DFT-calculated decreases in shear to bulk moduli ratios, and increased Cauchy pressures (C12–C44) with increasing x reveal a trend toward increased toughness.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106347 (URN)10.1116/1.4867610 (DOI)000335965300003 ()
Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-12-05Bibliographically approved
3. Toughness Enhancement in Hard Ceramic Thin Films by Alloy Design
Open this publication in new window or tab >>Toughness Enhancement in Hard Ceramic Thin Films by Alloy Design
Show others...
2013 (English)In: APL MATERIALS, ISSN 2166-532X, Vol. 1, no 4, 042104- p.Article in journal (Refereed) Published
Abstract [en]

Hardness is an essential property for a wide range of applications. However, hardness alone, typically accompanied by brittleness, is not sufficient to prevent failure in ceramic films exposed to high stresses. Using VN as a model system, we demonstrate with experiment and density functional theory (DFT) that refractory VMoN alloys exhibit not only enhanced hardness, but dramatically increased ductility. V0.5Mo0.5N hardness is 25% higher than that of VN. In addition, while nanoindented VN, as well as TiN reference samples, suffer from severe cracking typical of brittle ceramics, V0.5Mo0.5N films do not crack. Instead, they exhibit material pile-up around nanoindents, characteristic of plastic flow in ductile materials. Moreover, the wear resistance of V0.5Mo0.5N is considerably higher than that of VN. DFT results show that tuning the occupancy of d-t2g metallic bonding states in VMoN facilitates dislocation glide, and hence enhances toughness, via the formation of stronger metal/metal bonds along the slip direction and weaker metal/N bonds across the slip plane.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-91373 (URN)10.1063/1.4822440 (DOI)000332277600006 ()
Available from: 2013-04-23 Created: 2013-04-23 Last updated: 2016-08-31Bibliographically approved
4. Vacancy-induced toughening in hard single-crystal V0.5Mo0.5Nx/MgO(001) thin films
Open this publication in new window or tab >>Vacancy-induced toughening in hard single-crystal V0.5Mo0.5Nx/MgO(001) thin films
Show others...
2014 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 77, 394-400 p.Article in journal (Refereed) Published
Abstract [en]

Using a combination of experiments and density functional theory (DFT), we demonstrate the first example of vacancy-induced  toughening, in this case for epitaxial pseudobinary NaCl-structure substoichiometric V0.5Mo0.5Nx alloys, with N concentrations 0.55 ≤ x ≤ 1.03, grown by reactive magnetron sputter deposition. The nanoindentation hardness H(x) increases with increasing vacancy concentration from 17 GPa with x = 1.03 to 26 GPa with x = 0.55, while the elastic modulus E(x) remains essentially constant at 370 GPa. Scanning electron micrographs of indented regions show ductile plastic flow giving rise to material pile-up, rather than cracks as commonly observed for hard, but brittle, transition-metal nitrides. The increase in alloy hardness with an elastic  modulus which remains constant with decreasing x, combined with the observed material pile-up around nanoindents, DFT-calculated decrease in shear to bulk moduli ratios, and increased Cauchy pressures (C12-C44), reveals a trend toward vacancy-induced toughening. Moreover, DFT crystal orbital overlap population analyses are consistent with the above results.

Place, publisher, year, edition, pages
Oxford, England: Elsevier, 2014
Keyword
DFT; Mechanical properties; Toughness; Transition-metal nitrides
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-106350 (URN)10.1016/j.actamat.2014.06.025 (DOI)000340303200035 ()s2.0-84903803295 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note

The authors gratefully acknowledge the financial support of the Knut and Alice Wallenberg Foundation, the Swedish Research Council (VR), the Swedish Government Strategic Research Area Grant in Materials Science (SFO Mat-LiU) on Advanced Functional Materials, and the Linköping Linnaeus Initiative LiLi-NFM (grant 2008-6572). DFT calculations were carried out on the Neolith and Triolith clusters located at the National Supercomputer Center (NSC) in Linköping, and on the Akka and Abisko clusters located at the High Performance Computing Center North (HPC2N) in Umeå, Sweden. The authors are grateful to E. Broitman and L. Martínez-de-Olcoz for fruitful discussions on nanoindentation

Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-12-05Bibliographically approved
5. V0.5Mo0.5Nx/MgO(001) layers grown at 100-900 °C: composition, nanostructure, and mechanical properties
Open this publication in new window or tab >>V0.5Mo0.5Nx/MgO(001) layers grown at 100-900 °C: composition, nanostructure, and mechanical properties
Show others...
2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

V0.5Mo0.5Nx/MgO(001) alloys with the B1-NaCl structure are grown by ultra-highvacuum reactive magnetron sputter deposition in 5 mTorr mixed Ar/N2 atmospheres at temperatures Ts which are varied from 100 and 900 °C. Alloy films grown at Ts ≤ 500 °C are polycrystalline with a strong 002 texture; layers grown at Ts ≤ 700 °C are epitaxial single-crystals. The N/Me ratio x ranges from 0.64±0.05 with Ts = 900 °C to 0.94±0.05 at 700 °C to 1.02±0.05 with Ts = 500 to 100 °C. The N loss at higher growth temperatures leads to a corresponding decrease in the relaxed lattice parameter ao from 4.212 Å with x = 1.02 to 4.175 Å with x = 0.94 to 4.121 Å with x = 0.64. V0.5Mo0.5Nx nanoindentation hardnesses H and elastic moduli E increase with increasing Ts from 17±3 GPa and 274±31 GPa at 100 °C to 26±1 GPa and 303±10 GPa at 900 °C. Films deposited at higher Ts also exhibit enhanced wear resistance. Scanning electron micrographs of nanoindents performed in single-crystal V0.5Mo0.5Nx films and films deposited at 100 and 300 °C reveal no evidence of cracking; instead they exhibit material pile-up around the indents characteristic of plastic flow in ductile materials. Valence band x-ray photoelectron spectroscopy analyses show an enhanced volume density of the shear sensitive d-t2g – d-t2g metallic states in V0.5Mo0.5Nx compared to VN and the density of these orbitals increases with increasing deposition temperature, i.e., the metallic  states become more populated with the introduction of N vacancies.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106352 (URN)
Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2016-08-31Bibliographically approved
6. Microstructure and mechanical properties of: V0.5Mo0.5Nx(111)/Al2O3(0001) thin films
Open this publication in new window or tab >>Microstructure and mechanical properties of: V0.5Mo0.5Nx(111)/Al2O3(0001) thin films
Show others...
2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

We report results of growth, microstructure, and mechanical properties of V0.5Mo0.5Nx thin films deposited on Al2O3(0001) substrates by reactive magnetron sputtering. Sputtering is carried out in 5 mTorr Ar/N2 atmospheres and the growth temperatures Ts are varied between 100 and 900 °C. We find that the V0.5Mo0.5Nx/Al2O3(0001) alloy films are 111-oriented NaCl-structure. In-plane and out-of plane lattice parameters are found to decrease with increasing Ts and indicate that all alloy films are strained. V0.5Mo0.5Nx hardnesses and reduced elastic moduli increase with increasing Ts, and vary between 15-23 GPa, and 220-318 GPa, respectively. The wear resistance of the alloy films is also found to increase with increasing Ts. In addition, scanning electron micrographs of indents performed on V0.5Mo0.5Nx films show material pile-up around the indent edges and no evidence of crack arising from nanoindentation experiments. Coefficients of friction acquired at normal forces of 1000 μN are found to be of the order of 0.09.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106353 (URN)
Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2016-08-31Bibliographically approved
7. Sputter-cleaned Epitaxial VxMo(1-x)Ny/MgO(001)Thin Films Analyzed by X-ray PhotoelectronSpectroscopy: 1. Single-crystal V0.48Mo0.52N0.64
Open this publication in new window or tab >>Sputter-cleaned Epitaxial VxMo(1-x)Ny/MgO(001)Thin Films Analyzed by X-ray PhotoelectronSpectroscopy: 1. Single-crystal V0.48Mo0.52N0.64
Show others...
2013 (English)In: Surface Science Spectra, ISSN 1055-5269, E-ISSN 1520-8575, Vol. 20, no 1, 68-73 p.Article in journal (Refereed) Published
Abstract [en]

Epitaxial VxMo(1-x)Ny thin films grown by ultrahigh vacuum reactive magnetron sputter deposition on Mg(001) substrates are analyzed by x-ray photoelectron spectroscopy (XPS). This contribution presents analytical results for 300-nm-thick single-crystal V0.48Mo0.52N0.64 films deposited by reactive cosputtering from V (99.95 % purity) and Mo (99.95 % purity) targets. Film growth is carried out at 900 °C in mixed Ar/N2 atmospheres at a total pressure of 5 mTorr, with a N2 partial pressure of 3.2 mTorr; a bias of −30 V is applied to the substrate. Films composition is determined by Rutherford backscattering spectrometry (RBS). XPS measurements employ monochromatic Al K α radiation (hν = 1486.6 eV) to analyze V0.48Mo0.52N0.64(001) surfaces sputter-cleaned in-situ with 4 keV Ar+ ions incident at an angle of 70° with respect to the surface normal. XPS results show that the ion-etched sample surfaces have no measurable oxygen or carbon contamination; film composition, obtained using XPS sensitivity factors, is V0.33Mo0.67N0.64. All core level peaks, including the nearby Mo 3p3/2 (binding energy of 394.0 eV) and N 1s (at 397.6 eV) peaks, are well-resolved.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-106357 (URN)10.1116/11.20130301 (DOI)
Available from: 2014-05-05 Created: 2014-05-05 Last updated: 2017-12-05

Open Access in DiVA

Toughness Enhancement in Hard Single-Crystal Transition-Metal Nitrides: V-Mo-N and V-W-N Alloys(2843 kB)1291 downloads
File information
File name FULLTEXT01.pdfFile size 2843 kBChecksum SHA-512
544b4d5085ca290d04fbe518338601f8ab8c9c05699c56add79e327b092bacc647d6568d30464fa7cb81a4f5243eeeadfbc5b5ade2cbdb902ccb8ea1c7a48849
Type fulltextMimetype application/pdf
omslag(88 kB)22 downloads
File information
File name COVER01.pdfFile size 88 kBChecksum SHA-512
5da3829ed43d891b949c45baffb0cad7a28fa8baf9853cc88016e03fec6b9140829db47b20afccf593f73f6781f76fcadf905b2d381e93dbdbf3ef45634df0ad
Type coverMimetype application/pdf

Other links

Publisher's full text

Authority records BETA

Kindlund, Hanna

Search in DiVA

By author/editor
Kindlund, Hanna
By organisation
Thin Film PhysicsThe Institute of Technology
Natural Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 1291 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

doi
isbn
urn-nbn

Altmetric score

doi
isbn
urn-nbn
Total: 1062 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf