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Defect-engineered (Ti,Al)N thin films
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, Faculty of Science & Engineering.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis investigates the effect of point defects (nitrogen vacancies and interstitials) and multilayering ((Ti,Al)N/TiN) on the phase transformations in cathodic arc-evaporated cubic (Ti,Al)N thin films at elevated temperatures. Special attention is paid to the evolution of the beneficial spinodal decomposition into c-TiN and c-AlN, the detrimental formation of wurtzite AlN and the potential application as hard coating in cutting tools.

c-(Ti1-xAlx)Ny thin films with varying Al fractions and N content (y = 0.93 to 0.75) show a delay in the spinodal decomposition when increasing the amount of N vacancies. This results in a 300 °C upshift in the age hardening and a delay in the w-AlN formation, while additions of self-interstitials enhance phase separation. High temperature interaction between hard metal substrates and thin films is more pronounced when increasing N deficiency through diffusion of substrate elements into the film. Low N content films (y = 0.58 to 0.40) showed formation of additional phases such as Ti4AlN3, Ti2AlN, Al5Ti2 and Al3Ti during annealing and a transformation from Ti2AlN to Ti4AlN3 via intercalation. The multilayer structure of TiN/TiAlN results in surfacedirected spinodal decomposition that affects the decomposition behavior. Careful use of these effects appears as a promising method to improve cutting tool performance.

Abstract [de]

Diese Arbeit untersucht den Effekt von Punktdefekten (Stickstoffleerstellen und Zwischengitteratome) und Multilagen ((Ti,Al)N/TiN) auf die Phasenumwandlung in lichtbogenverdampften kubischen (Ti,Al)N-Dünnschichten bei erhöhten Temperaturen. Besonderes Augenmerk liegt auf der Entwicklung der vorteilhaften spinodalen Entmischung in c-TiN und c-AlN und der nachteiligen Bildung von Wurtzit-AlN, sowie der möglichen Anwendung als Hartstoffbeschichtung von Schneidwerkzeugen.

c-(Ti1-xAlx)Ny mit unterschiedlichem Al-Anteil und N-Gehalten von y = 0,93 bis 0,75 zeigt mit zunehmenden Stickstoffleerstellen eine Verzögerung der spinodalen Entmischung. Dadurch verschiebt sich die Ausscheidungshärtung um 300 °C zu höheren Temperaturen und die w-AlN-Bildung wird verzögert, während der Einbau von Eigenzwischengitteratomen die Entmischung beschleunigt. Die Hochtemperaturwechselwirkung zwischen Hartmetallsubstrat und Dünnschicht durch Diffusion von Substratelementen in die Schicht nimmt mit steigendem Stickstoffdefizit zu. Stickstoffarme Schichten (y = 0,58 bis 0,40) zeigen während der Wärmebehandlung zusätzliche Phasen wie Ti4AlN3, Ti2AlN, Al5Ti2 und Al3Ti und eine Umwandlung von Ti2AlN in Ti4AlN3 durch Interkalation. Die Multischichtstruktur von TiN/TiAlN führt zu einer oberflächengerichteten spinodalen Entmischung, die das Entmischungsverhalten beeinflusst. Ein gezielter Einsatz dieser Effekte erscheint als ein vielsprechender Weg, um die Leistungsfähigkeit von Schneidwerkzeugen zu verbessern.

Abstract [sv]

I denna avhandling behandlas inverkan av punktdefekter (kvävevakanser och interstitialer) och multilagring ((Ti,Al)N/TiN) på högtemperaturfasomvandlingar i tunna arcförångade skikt av kubiska (Ti,Al)N. Störst vikt har lagts på utvecklingen av det fördelaktiga spinodala sönderfallet till c-TiN och c-AlN, den ofördelaktiga omvandlingen till w-AlN och potentialen som hårda skikt i verktygstillämpningar.

Tunna c-(Ti1-xAlx)Ny skikt med olika Al-andel och en N-halt mellan (y = 0.93 och 0.75) uppvisar ökad undertryckning av det spinodala sönderfallet med ökat kvävevakanshalt. Detta resulterar i bildandet av w-AlN skiftas upp i temperatur vilket gör att åldershärdningen höjs med 300 °C. Däremot medför närvaron av självinterstitialer ett snabbare sönderfall. Växelverkan mellan hårdmetallsubstraten och de tunna skikten vid hög temperatur ökar med minskad kvävehalt i skiten genom diffusion av atomer från substratet in i filmen. Filmer med låg kvävehalt (y = 0.58 till 0.40) bildar även andra faser så som Ti4AlN3, Ti2AlN, Al5Ti2 och Al3Ti under värmebehandling och fasomvandlingen från Ti2AlN till Ti4AlN3 sker via en mekanism kallad intercalation. Multilagring av TiN/TiAlN resulterar i ett ytriktad spinodalt sönderfall vilket påverkar det totala sönderfallsförloppet. Nyttjande av dessa resultat syns som lovande vägar till förbättrade verktygsegenskaper.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2017. , p. 73
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1878
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:liu:diva-142116DOI: 10.3384/diss.diva-142116ISBN: 9789176854563 (print)OAI: oai:DiVA.org:liu-142116DiVA, id: diva2:1151267
Public defence
2017-11-14, House D3 3, Saarland University, DE-66123 Saarbrücken, Germany, Saarbrücken, 14:15 (English)
Opponent
Supervisors
Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2017-10-23Bibliographically approved
List of papers
1. Impact of nitrogen vacancies on the high temperature behavior of (Ti1-xAlx)N-y alloys
Open this publication in new window or tab >>Impact of nitrogen vacancies on the high temperature behavior of (Ti1-xAlx)N-y alloys
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2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 119, p. 218-228Article in journal (Refereed) Published
Abstract [en]

Substoichiometric solid solution alloys of cubic (Ti1-xAlx)N-y with x = 0.26, 0.48 and 0.60, and y ranging from 0.93 to 0.75 were grown by cathodic arc deposition. The influence of nitrogen deficiency on their thermal stability was studied by X-ray diffractometry, differential scanning calorimetry, scanning electron microscopy, and atom probe tomography. The nitrogen deficiency did not significantly affect the columnar growth nor the as deposited hardness. At elevated temperatures, alloys with x = 0.48 and 0.60 decompose isostructurally into cubic c-TiN and cubic c-AlN domains, which is consistent with spinodal decomposition. The decomposition is retarded by decreasing the nitrogen content, e.g. the formed isostructural domains in (Ti0.52Al0.48)N-0.92 at 900 degrees C are similar in size to (Ti0.52Al0.48)N-0.75 at 1200 degrees C. The formation of hexagonal w-AlN is shifted to higher temperatures by decreasing nitrogen content. Nucleation and growth of Al-Ti clusters in a Ti rich matrix were observed for the alloys with high Ti content, x = 0.26. These results suggest that nitrogen deficiency reduces the driving force for phase separation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2016
Keyword
TiAlN system; Nitrogen vacancies; Spinodal decomposition; Atom probe tomography; Thin films
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:liu:diva-132334 (URN)10.1016/j.actamat.2016.08.024 (DOI)000384778300021 ()
Note

Funding Agencies|Erasmus Mundus doctoral program DocMASE; Swedish Research Council VR [621-2012-4401]; Swedish Foundation for Strategic Research, SSF via MultiFilms program [RMA08-0069]; Swedish government strategic research area grant AFM - SFO MatLiU [2009-00971]; VIN-NOVA (M - Era.net) [2013-02355(MC2)]; DFG; federal state government of Saarland [INST 256/298-1 FUGG]; AME-Lab (European Regional Development Fund) [C/4-EFRE-13/2009/Br]

Available from: 2016-11-12 Created: 2016-11-01 Last updated: 2018-01-03
2. Solid state formation of Ti4AlN3 in cathodic arc deposited (Ti1-xAlx)N-y alloys
Open this publication in new window or tab >>Solid state formation of Ti4AlN3 in cathodic arc deposited (Ti1-xAlx)N-y alloys
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2017 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 129, p. 268-277Article in journal (Refereed) Published
Abstract [en]

Reactive cathodic arc deposition was used to grow substoichiometric solid solution cubic c-(Ti1-xAlx)N-y thin films. The films were removed from the substrate and then heated in an argon environment to 1400 degrees C. Via solid state reactions, formation of MAX phase Ti4AlN3 was obtained. Additional phases such as Ti2AlN, c-TiN, w-AIN, Al5Ti2 and Al3Ti were also present during the solid state reaction. Ti4AlN3 formation was observed in samples with an Al metal fraction x amp;lt; 0.63 and a nitrogen content 0.4 amp;lt; y amp;lt; 0.6. Regardless of the initial composition, formation of Ti4AlN3 started in Ti2AlN crystal plates in the temperature range between 1200 and 1400 degrees C. Accompanying the onset of Ti4AlN3 was the presence of an intermediate structure identified as Ti6Al2N4, consisting of alternating layers of intergrown Ti2AlN and Ti4AlN3 phases with a half-unit-cell stacking. We suggest that the formation of Ti4AlN3 occurred via intercalation of aluminum and nitrogen along the basal plane accompanied by a simultaneous detwinning process. In addition we propose that this formation mechanism can be used to obtain MAX phases of high n order. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
Keyword
MAX phase; Intergrown phase; Thin films; Solid state reaction; Intercalation
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:liu:diva-137593 (URN)10.1016/j.actamat.2017.03.001 (DOI)000400033900026 ()
Note

Funding Agencies|European Unions Erasmus Mundus doctoral program DocMASE; Swedish Research Council [621-2012-4401]; Swedish government strategic research area grant AFM SFO MatLiU [2009-00971]; VINNOVA (M - Era.net project MC2) [2013-02355]; European Research Council under the European Communitys Seventh Framework Program (FP) [335383]; DFG; federal state government of Saarland [INST 256/298-1 FUGG, INST 256/431-1 FUGG]; European Regional Development Fund [AME-Lab C/4-EFRE-13/2009/Br]

Available from: 2017-05-22 Created: 2017-05-22 Last updated: 2018-03-19
3. Effects of nitrogen vacancies on phase stability and mechanical properties of arc deposited (Ti0.52Al0.48)Ny (y<1) coatings
Open this publication in new window or tab >>Effects of nitrogen vacancies on phase stability and mechanical properties of arc deposited (Ti0.52Al0.48)Ny (y<1) coatings
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2017 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 330, no Supplement C, p. 77-86Article in journal (Refereed) Published
Abstract [en]

Nitrogen sub-stoichiometric (Ti0.52Al0.48)Ny (0.92 ≥ y  ≥ 0.46) coatings were grown in a mixed Ar/N2 atmosphere by cathodic arc deposition on cemented carbide (WC/Co-based) substrates. The coatings present a columnar structure with decreasing column widths from 250 to 60nm, due to a corresponding reduced N content, accompanied by changes in preferred orientation from 200 to 111 to 220. Among these, coatings prepared with 0.92≥y≥0.75 exhibit spinodal decomposition and consequently age hardening at elevated temperatures. A reduced N content upshifts the hardness maximum by >300 °C. For these samples, the high temperature treatment resulted in interdiffusion of substrate elements, Co and C, mainly along column boundaries. Nevertheless, no detrimental effect in the hardness could be correlated. Conversely, a low N content sample (y=0.46) presents significant lattice diffusion of substrate elements Co, C, W, and Ta in the coating. In this case, the substrate elements are present throughout the coating, forming additional phases such as c-Ti(C,N), c-Co(Al,Ti,W), and c-(Ti,W,Ta)(C,N), with an observed increased hardness from 16 to 25GPa. We suggest that the substitution of nitrogen by carbon and the solution of W and Ta in c-TiN are responsible for the observed hardening. Our investigation shows the potential of sub-stoichiometric (Ti1-xAlx)Ny coatings for high temperature applications such as cutting tools and puts forth corresponding criteria for N content selection.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
TiAlN, Thin films, Nitrogen vacancies, Spinodal decomposition, Age hardening
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-142115 (URN)10.1016/j.surfcoat.2017.09.043 (DOI)000414819700010 ()2-s2.0-85030314026 (Scopus ID)
Note

Funding agencies: European Unions Erasmus Mundus doctoral program DocMASE; Swedish Research Council [621-2012-4401]; Swedish Government Strategic Research Area grant AFM - SFO MatLiU [2009-00971]; VINNOVA (M - Era.net project MC2 grant) [2013-02355]; DFG [INST 256/298-1 FU

Available from: 2017-10-23 Created: 2017-10-23 Last updated: 2018-01-03Bibliographically approved
4. Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage
Open this publication in new window or tab >>Enhanced thermal stability and mechanical properties of nitrogen deficient titanium aluminum nitride (Ti0.54Al0.46Ny) thin films by tuning the applied negative bias voltage
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2017 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 122, no 6, article id 065301Article in journal (Refereed) Published
Abstract [en]

Aspects on the phase stability and mechanical properties of nitrogen deficient (Ti0.54Al0.46)N-y alloys were investigated. Solid solution alloys of (Ti,Al)N were grown by cathodic arc deposition. The kinetic energy of the impinging ions was altered by varying the substrate bias voltage from -30V to -80 V. Films deposited with a high bias value of -80V showed larger lattice parameter, finer columnar structure, and higher compressive residual stress resulting in higher hardness than films biased at -30V when comparing their as-deposited states. At elevated temperatures, the presence of nitrogen vacancies and point defects (anti-sites and self-interstitials generated by the ion-bombardment during coating deposition) in (Ti0.54Al0.46)N-0.87 influence the driving force for phase separation. Highly biased nitrogen deficient films have point defects with higher stability during annealing, which cause a delay of the release of the stored lattice strain energy and then accelerates the decomposition tendencies to thermodynamically stable c-TiN and w-AlN. Low biased nitrogen deficient films have retarded phase transformation to w-AlN, which results in the prolongment of age hardening effect up to 1100 degrees C, i.e., the highest reported temperature for Ti-Al-N material system. Our study points out the role of vacancies and point defects in engineering thin films with enhanced thermal stability and mechanical properties for high temperature hard coating applications. Published by AIP Publishing.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
National Category
Other Materials Engineering
Identifiers
urn:nbn:se:liu:diva-140514 (URN)10.1063/1.4986350 (DOI)000407742400032 ()
Note

Funding Agencies|European Unions Erasmus Mundus doctoral program in Materials Science and Engineering (DocMASE); Swedish Research Council [621-2012-4401]; Swedish government strategic research area grant AFM - SFO MatLiU [2009-00971]; VINNOVA [2013-02355]; DFG; federal state government of Saarland [INST 256/298-1 FUGG]; European Regional Development Fund [AME-Lab C/4-EFRE-13/2009/Br]

Available from: 2017-09-11 Created: 2017-09-11 Last updated: 2018-03-27
5. Surface directed spinodal decomposition at TiAlN / TiN interfaces
Open this publication in new window or tab >>Surface directed spinodal decomposition at TiAlN / TiN interfaces
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2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 113, no 11, p. 114305-1-114305-8Article in journal (Refereed) Published
Abstract [en]

In contrast to the monolithic c-Ti1-xAlxN, the isostructural spinodal decomposition to c-AlN and c-TiN of the c-Ti1-xAlxN/TiN multilayers have the same onset temperature regardless of composition (x=0.50 and 0.66). The onset is also located at a lower temperature compared to the monoliths with the same Al-content, revealed by differential scanning calorimetry. Zcontrast STEM imaging shows a decomposed structure of the multilayers at a temperature where it is not present in the monoliths. Atom probe tomography reveal the formation of an AlN-rich layer followed by a TiN-rich area parallel to the interface in the decomposed Ti0.34Al0.66N/TiN coating, consistent with surface directed spinodal decomposition. Phase field simulations predict such behavior and show that the surface directed spinodal decomposition is affected by in the internal interfaces, as deposited elemental fluctuations, coherency stresses and alloy composition.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
Keyword
Surface directed spinodal decomposition, Titanium aluminium nitride, Phase field simulations, Atom probe tomography
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-84704 (URN)10.1063/1.4795155 (DOI)000316545200054 ()
Note

Funding Agencies|Swedish Foundation for Strategic Research (SSF) project Designed Multicomponent Coatings (MultiFilms)||Swedish Research Council (VR)||Erasmus Mundus doctoral program DocMASE||EU|C/4-EFRE-13/2009/Br|DFG||federal state government of Saarland|INST 256/298-1 FUGG|

Available from: 2012-10-17 Created: 2012-10-17 Last updated: 2018-02-23Bibliographically approved

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