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Growth and Characterization of Ti-Si-N Thin Films
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [sv]

Utvecklingen inom materialforskningen går mot att framställa avancerade material vilka är skräddarsydda för olika tillämpningar. Detta har medfört att det blir allt mer populärt att belägga ytor med ett eller flera tunna lager med syfte att förbättra materialegenskaperna. Användningsområden för ytbeläggningar går att hitta inom allt från vardagliga produkter såsom teflonbeläggningar av stekpannor, förgyllning av smycken till avancerad halvledarteknik för att åstadkomma energieffektiva lysdioder. Det enskilt största tillämpningsområdet för tunna filmer är dock som skyddande skikt för verktyg inom skärande bearbetning. Utvecklingen går stadigt mot högre skärhastigheter och därmed ökade temperaturer, idagsläget kan området där verktyget och arbetsmaterialet är i kontakt nå temperaturer på mellan 800-1000 °C utan att förlora nämnvärt i styrka. Detta har gjorts möjligt genom att belägga skären med någon eller några μm (tusendels mm) av lämpligt keramiskt material i avseende att öka motståndskraften för nötning vid bearbetning vid höga temperaturer.

I den här avhandlingen har tunna filmer studerats med det övergripande målet att förbättra egenskaper hos verktyg för skärande metallbearbetning genom att öka motståndskraften hos materialen mot mekanisk och kemisk nötning vid höga temperaturer. Materialsystemet som undersökts är Ti-Si-N, där tunna filmer av både legeringar och tvåfassystem har syntetiserats och egenskapskarakteriserats. Legeringarna är belagda med varierande Si-halt från 0 till 10 atomprocent och avsedda för att studera strukturella, termiska och mekaniska egenskaper. De framställdes med en teknik som kallas arcförångning, där man i ett vakuumsystem frigör högenergetiskt material i det här fallet av Ti och Si som förångas från en solid yta kallad target. Atomerna joniseras genom kollisioner med elektroner och reagerar på sin väg mot substratet med kvävgas. Väl framme vid substratet, kondenserar jonerna och bilder den tunna filmen. Filmerna består av två strukturtyper, den första är en fast lösning där Si atomer upp till 5 at.% ersätter Ti atomer i TiN. I det andra fallet så segregerar Si till korngränserna. Värmebehandlingsexperiment visar att Si bildar SiNx som kapslar in TiN-korn vid temperaturer upp till 1000 °C. Hårdhetstester visar att filmerna bibehåller sin hårdhet upp till 1000 °C tack vare fasomvandlingen. Även vid 1100 °C är hårdheten hög. Dessa skikt besitter alltså egenskaper som gör dem väldigt användbara inom tillämpningar för skärande bearbetning.

Nanostrukturerade materials egenskaper beror på dess mikrostruktur snarare än på de grundämnen som ingår, detta exemplifieras av TiN-SiNx-nanokompositer bestående av nanokristallina TiN-korn inbäddade i några få atomlager SiNx, där materialegenskaperna helt och hållet beror på kornstorleken på TiN-kornen och tjockleken på SiNx-lagren. Ökas tjockleken på SiNx minskar hårdheten. Dessa filmer har mycket goda mekaniska egenskaper och är ett av de hårdaste materialen som finns. Nyckeln till den höga hårdheten hos skikten ligger i att bilda starka bindningar mellan TiN och SiNx. Hur dessa ser ut vet man dock inte eftersom strukturen på SiNx gränsytan inte är känd. Anledningen är att den är svår att avbilda på grund av dess krökta form och begränsade volym. I denna avhandling har TiN/SiNx multilager belagts, dvs. en lagrad struktur TiN alternerad med SiNx. Dessa filmer framställdes med sputtring, en teknik som liknar arcförångning men där man istället accelerera positivt laddade joner mot Ti och Si targets med en hög negativ potential som frigör Ti och Si. I multilagren varierades SiNx-lagrets tjocklek mellan endast några få atomlager för att göra en förenklad modell av gränsytan hos nanokompositen och med atomupplöst transmissionselektronmikroskopi samt hårdhetsmätningar konstateras sedan att de hårdaste filmerna var de där kristallin SiNx stabiliseras mellan TiNkorn. Vidare studerar jag SiNx/TiN ytor med sveptunnelmikroskopi och täthetsfunktionalteori (en kvantmekanisk simuleringsmetod). Mina resultat visar SiNx och bindningarna till TiN är mycket mer komplicerade än vad man tidigare trott, då de kan vara kristallina och anta komplexa rekonstruktioner. Detta bidrar till den starka bindningen mellan TiN och SiNx vilket i sin tur förklarar varför materialen blir så hårda.

Abstract [en]

Ti-Si-N and Ti-Al-Si-N thin solid films have been studied by analytical electron microscopy, X-ray diffraction, scanning tunneling microscopy, X-ray photoelectron spectroscopy, elastic recoil detection analysis, nanoindentation, and ab initio calculations. I find that arc evaporated (Ti1-xSix)Ny films can be grown as cubic solid solutions up to x = 0.09 with a dense columnar microstructure. Films with higher Si content up to x = 0.20 assumes an extremely defect-rich, feather-like structure consisting of cubic TiN:Si nanocrystallite bundles with low-angle grain boundaries caused by thermodynamically driven Si segregation. Correspondingly, the N content in the films increases close to linear with the Si content from y = 1.00 (x = 0) to y = 1.13 (x = 0.20). Annealing of the films at 1000 °C yields a metastable crystalline SiNz (1.0 ≤ z ≤ 1.33) tissue phase in 0.04 ≤ x ≤ 0.20 films which is (semi)-coherent to TiN. These films are compositionally stable and exhibit retained hardness between 31-42 GPa up to 1000 °C. At 1100-1200 °C, the tissue phase amorphizes and all SiNz diffuse out of the films, followed by recrystallization of the cubic phase. Hard turning testing was performed on (Ti0.83Si0.17)N1.09. Analysis of the tool-chip interface prepared by focused ion beam revealed shear deformation in the film and an adhering layer consisting of the work-piece material and Si and N from the film. For (Ti0.33Al0.67)1-xSix)N (0 ≤ x ≤ 0.29) films the NaCl structure cubic (Ti,Al)N solid solution phase is predominant at low Si contents, which gradually changes to a dominating hexagonal wurtzite (Al,Ti,Si)N solid solution for 0.04 ≤ x ≤ 0.17. Additional Si results in amorphization. Annealing experiments at 600-1000 °C yields spinodal decomposition of c-(Al,Ti)N into c-AlN and c-TiN, with corresponding age hardening. The h-(Al,Ti,Si)N films exhibit precipitation of c- TiN with smaller volume than the host lattice, which results in tensile cracks formations and age hardening. Films with c-(Ti,Al)N perform best in turning applications, while films with h- (Al,Ti,Si)N form cracks and fail. Finally, I have characterized the nature of metastable crystalline SiNz phases and the interface between TiN(001) and SiNz. Magnetron sputtering was used to deposit TiN/SiNz(001) nanolaminate films with varying SiNz and TiN layer thicknesses. Maximum hardness is obtained when SiNz forms coherent interfaces with TiN. In addition, in situ surface analyses in combination with ab-initio calculations reveal that SiNz sub-monolayers grow epitaxially and form crystalline reconstructions on TiN(001) and TiN(111) surfaces. Phonon calculations predict that stoichiometric c-SiN is dynamically instable when the atoms are arranged in the NaCl and ZnS forms. However, c-Si3N4 can be stabilized with D022 or L12 ordered ZnS-like structures. These results have impact for the design of superhard nanocomposites and multilayer thin films.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi , 2008.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1190
Keyword [en]
Analytical transmission electron microscopy, Arc, Sputtering, Hard coatings, Multilayer Cutting inserts
Keyword [sv]
analytisk transmissionselektronmikroskopi, ytbeläggningar, skärande, bearbetning, Ti-Si-N, arcförångning, sputtring
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:liu:diva-11929ISBN: 978-91-7393-882-2 (print)OAI: oai:DiVA.org:liu-11929DiVA: diva2:18323
Public defence
2008-05-30, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2016-08-31
List of papers
1. Influence of Si on the Microstructure of Arc Evaporated (Ti,Si)N Thin Films: Evidence for Cubic Solid Solutions and their Thermal Stability
Open this publication in new window or tab >>Influence of Si on the Microstructure of Arc Evaporated (Ti,Si)N Thin Films: Evidence for Cubic Solid Solutions and their Thermal Stability
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2005 (English)In: Surface and Coatings Technology, ISSN 0257-8972, Vol. 200, no 5-6, 1535-1542 p.Article in journal (Refereed) Published
Abstract [en]

Ti1−xSixN (0 ≤ x ≤ 0.14) thin solid films were deposited onto cemented carbide (WC-Co) substrates by arc evaporation. X-ray diffraction and transmission electron microscopy showed that all films were of NaCl-structure type phase. The as-deposited films exhibited a competitive columnar growth mode where the structure transits to a feather-like nanostructure with increasing Si content. Films with 0 ≤ x ≤ 0.01 had a 111 crystallographic preferred orientation which changed to an exclusive 200 texture for 0.05 ≤ x ≤ 0.14. X-ray photoelectron spectroscopy revealed the presence of Si–N bonding, but no amorphous Si3N4. Band structure calculations performed using a full potential linear muffin tin orbital method showed that for a given NaCl-structure Ti1−xSixN solid solution, a phase separation into cubic SiN and TiN is energetically favorable. The microstructure was maintained for the Ti0.86Si0.14N film annealed at 900 °C, while recrystallization in the cubic state took place at 1100 °C annealing during 2 h. The Si content influenced the film hardness close to linearly, by combination of solid-solution hardening in the cubic state and defect hardening. For x = 0 and x = 0.14, nanoindentation gave a hardness of 31.3 ± 1.3 GPa and 44.7 ± 1.9 GPa, respectively. The hardness was retained after annealing at 900 °C, while it decreased to below 30 GPa for 1100 °C following recrystallization and W and Co interdiffusion.

Keyword
Nitrides; Arc evaporation; Transmission electron microscopy (TEM); Thin films; Solid solution; Microstructure
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14144 (URN)10.1016/j.surfcoat.2005.08.096 (DOI)
Available from: 2006-11-15 Created: 2006-11-15 Last updated: 2016-08-31
2. Phase Transformations in Arc-Evaporated Ti-Si-N Thin Films
Open this publication in new window or tab >>Phase Transformations in Arc-Evaporated Ti-Si-N Thin Films
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Manuscript (Other academic)
Identifiers
urn:nbn:se:liu:diva-13313 (URN)
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-01-13
3. Microstructure of the tool-chip interface investigated by focused ion beam and analytical transmission electron microscopy
Open this publication in new window or tab >>Microstructure of the tool-chip interface investigated by focused ion beam and analytical transmission electron microscopy
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Manuscript (Other academic)
Identifiers
urn:nbn:se:liu:diva-13314 (URN)
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-01-13
4. Structure and thermal stability of arc evaporated (Ti0.33Al0.67)1 − xSixN thin films
Open this publication in new window or tab >>Structure and thermal stability of arc evaporated (Ti0.33Al0.67)1 − xSixN thin films
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2008 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 517, no 2, 714-721 p.Article in journal (Refereed) Published
Abstract [en]

(Ti0.33Al0.67)1 − xSixN (0 ≤ x ≤ 0.29) thin solid films were deposited onto cemented carbide substrates by arc evaporation and analyzed using analytical electron microscopy, X-ray diffraction, nanoindentation, and density functional theory. As-deposited films with x ≤ 0.02 consisted mainly of a metastable c-(Ti,Al)N solid solution for which Si serves as a veritable grain refiner. Additional Si promoted growth of a hexagonal wurtzite (Al,Ti,Si)N solid solution, which dominated at 0.02 < x < 0.17. For x ≥ 0.17, the films were X-ray amorphous. Despite these widely different microstructures, all as-deposited films had nanoindentation hardness in the narrow range of 22–25 GPa. Isothermal annealing of the x = 0.01 alloy film at a temperature of 900 °C, corresponding to that in turning operation, resulted in spinodal decomposition into c-AlN and TiN and precipitation of h-AlN. For x = 0.09 films, annealing between 600 °C and 1000 °C yielded c-TiN precipitation from the h-(Al,Ti,Si)N phase. Furthermore, the x = 0.01 and x = 0.09 films exhibited substantial age hardening at 900 °C, to 34 GPa and 29 GPa due to spinodal decomposition and c-TiN precipitation, respectively. Films with a majority of c-(Ti,Al)N phase worked best in steel turning tests, while films with x > 0.02 developed cracks during such operation. We propose that the cracks are due to tensile strain which is caused by a decrease in molar volume during the phase transformation from hexagonal wurtzite (Al,Ti,Si)N into cubic TiN phase, which results in degradation in machining performance.

Keyword
TiAlSiN, Hardness, Phase transitions, Analytical transmission electron microscopy
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-15843 (URN)10.1016/j.tsf.2008.08.126 (DOI)
Note
Original Publication:Axel Flink, J.M. Andersson, Björn Alling, R. Daniel, J. Sjölén, L. Karlsson and Lars Hultman, Structure and thermal stability of arc evaporated (Ti0.33Al0.67)1 − xSixN thin films, 2008, Thin Solid Films, (517), , 714-721.http://dx.doi.org/10.1016/j.tsf.2008.08.126Copyright: Elsevier Science B.V., Amsterdam.http://www.elsevier.com/Available from: 2008-12-11 Created: 2008-12-09 Last updated: 2017-12-14Bibliographically approved
5. Interface structure in superhard TiN-SiN nanolaminates and nanocomposites: film growth experiments and ab initio calculations
Open this publication in new window or tab >>Interface structure in superhard TiN-SiN nanolaminates and nanocomposites: film growth experiments and ab initio calculations
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2007 (English)In: Physical Review. B, ISSN 1098-0121, Vol. 75, no 15, 155437- p.Article in journal (Refereed) Published
Abstract [en]

Nanostructured materials—the subject of much of contemporary materials research—are defined by internal interfaces, the nature of which is largely unknown. Yet, the interfaces determine the properties of nanocomposites and nanolaminates. An example is nanocomposites with extreme hardness70–90  GPa, which is of the order of, or higher than, diamond. The Ti-Si-N system, in particular, is attracting attention for the synthesis of such superhard materials. In this case, the nanocomposite structure consists of TiN nanocrystallites encapsulated in a fully percolated SiNx “tissue phase” (1 to 2 monolayers thick) that is assumed to be amorphous. Here, we show that the interfacial tissue phase can be crystalline, and even epitaxial with complex surface reconstructions. Using in situ structural analyses combined with ab initio calculations, we find that SiNx layers grow epitaxially, giving rise to strong interfacial bonding, on both TiN(001) and TiN(111) surfaces. In addition, TiN overlayers grow epitaxially on SiNx/TiN(001) bilayers in nanolaminate structures. These results provide insight into the development of design rules for new nanostructured materials.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-13316 (URN)10.1103/PhysRevB.75.155437 (DOI)
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2016-08-31
6. Growth and characterization of TiN/SiN(001) superlattice films
Open this publication in new window or tab >>Growth and characterization of TiN/SiN(001) superlattice films
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2007 (English)In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 22, no 11, 3255-3264 p.Article in journal (Refereed) Published
Abstract [en]

We report the layer structure and composition in recently discovered TiN/SiN(001) superlattices deposited by dual-reactive magnetron sputtering on MgO(001) substrates. High-resolution transmission electron microscopy combined with Z-contrast scanning transmission electron microscopy, x-ray reflection, diffraction, and reciprocal-space mapping shows the formation of high-quality superlattices with coherently strained cubic TiN and SiN layers for SiN thickness below 7–10 Å. For increasing SiN layer thicknesses, a transformation from epitaxial to amorphous SiNx (x ? 1) occurs during growth. Elastic recoil detection analysis revealed an increase in nitrogen and argon content in SiNx layers during the phase transformation. The oxygen, carbon, and hydrogen contents in the multilayers were around the detection limit (~0.1 at.%) with no indication of segregation to the layer interfaces. Nanoindentation experiments confirmed superlattice hardening in the films. The highest hardness of 40.4 ± 0.8 GPa was obtained for 20-Å TiN with 5-Å-thick SiN(001) interlayers, compared to monolithic TiN at 20.2 ± 0.9 GPa.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-13317 (URN)10.1557/JMR.2007.0412 (DOI)
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2017-12-13
7. “SiNx 1x5/TiN(001) surface reconstructions studied by scanning tunneling microscopy and ab initio calculations
Open this publication in new window or tab >>“SiNx 1x5/TiN(001) surface reconstructions studied by scanning tunneling microscopy and ab initio calculations
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Manuscript (Other academic)
Identifiers
urn:nbn:se:liu:diva-13318 (URN)
Available from: 2008-05-27 Created: 2008-05-27 Last updated: 2010-01-13
8. Metastability of fcc-related Si-N phases
Open this publication in new window or tab >>Metastability of fcc-related Si-N phases
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2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 13, 132103-132103 p.Article in journal (Refereed) Published
Abstract [en]

The phenomenon of superhardening in TiN/SiNx nanocomposites and the prediction of extreme hardness in bulk gamma-Si3N4 have attracted a large interest to this material system. Attempts to explain the experimental findings by means of first-principles calculations have so far been limited to static calculations. The dynamical stability of suggested structures of the SiNx tissue phase critical for the understanding of the nanocomposites is thus unknown. Here, we present a theoretical study of the phonon-dispersion relations of B1 and B3 SiN. We show that both phases previously considered as metastable are dynamically unstable. Instead, two pseudo-B3 Si3N4 phases derived from a L1(2)- or D0(22)-type distribution of Si vacancies are dynamically stable and might explain recent experimental findings of epitaxial SiNx in TiN/SiNx multilayers.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16093 (URN)10.1103/PhysRevB.78.132103 (DOI)
Note
Original Publication: Björn Alling, Eyvas Isaev, Axel Flink, Lars Hultman and Igor Abrikosov , Metastability of fcc-related Si-N phases, 2008, Physical Review B. Condensed Matter and Materials Physics, (78), 13, 132103. http://dx.doi.org/10.1103/PhysRevB.78.132103 Copyright: American Physical Society http://www.aps.org/ Available from: 2009-07-03 Created: 2009-01-07 Last updated: 2017-12-14Bibliographically approved

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