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Multicomponent Alloying for Improved Hard Coatings
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coatings are vital to protect and to increase the productivity of cutting tools in high speed and dry cutting applications. During the cutting operation the temperature may exceed 1000 ºC it is therefore necessary that the coatings withstand high temperatures. A lot of development and research has been carried out during the last 30 years on finding new coating material systems providing enhanced properties such as adhesion, hardness and oxidation resistance at elevated temperatures. This thesis is based on multicomponent alloying of quaternary transition metal nitride hard coatings with a main focus on Ti-Cr-Al-N coatings. Many different coatings and compositions have been deposited using an industrial scale cathodic arc evaporation deposition system. All deposited coatings contain Al as this element is known to increase the hardness and the oxidation resistance of nitride coatings. The deterioration of the hardness in Al-containing nitride coatings is generally attributed to the transformation of cubic Al-N into hexagonal Al-N and the consequent domain coherency relaxation. This thesis investigates these phenomena on an atomic level providing a deeper understanding of and a way to engineer improved hard nitride coatings. The essence of this thesis is that by adding a third metal to a ternary nitride material system, for example one of the most frequently used Ti-Al-N, it is possible to tune and engineer the thermal stability of the cubic structure and the coherency strain which in turn affects the hardness and the oxidation resistance. The key point is that new intermediate phases in the decomposition process are generated so that the eventual detrimental phases are suppressed and delayed. More specifically, when Cr is added to the Ti-Al-N material system the coatings exhibit an age hardening process up to 1000 ºC caused by spinodal decomposition into coherent TiCr- and AlCr-rich cubic Ti-Cr-Al-N domains. This means that the unstable cubic Ti-Cr-Al-N phase decomposes via yet another unstable cubic Cr-Al-N phase before the detrimental hexagonal transformation of AlN takes place. The hardness is therefore retained up to a higher temperature compared to Ti-Al-N coatings.

By utilizing multicomponent alloying through addition of Ti to Cr-Al-N coatings the hardness is retained after annealing up to 1100 ºC. This is a dramatic improvement compared to Cr-Al-N coatings. Here the Ti addition promotes the competitive spinodal decomposition into TiCr- and Al-enriched domains suppressing the detrimental hexagonal AlN formation.

To investigate the effect of multicomponent alloying for other material systems with different mixing free energies and atomic sizes, Zr-containing, Zr-Cr-Al-N and Zr-Ti-Al-N, quaternary nitride coatings have also been deposited. For high Al- and high Zr-containing coatings the cubic solid solution structure is disrupted into a mix of nano-crystalline hexagonal and cubic phases with significantly lower hardness. The results show that the structure and hardness of these coatings are sensitive to the composition and in order to optimize the hardness and thermal stability the composition has to be fine-tuned. Altogether it is shown that through multicomponent alloying and through the control of the coherency strain it is possible to enhance the hardness and the oxidation resistance compared to the ternary system which may lead to new improved functional hard coatings.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2014. , 65 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1621
National Category
Physical Sciences Nano Technology
Identifiers
URN: urn:nbn:se:liu:diva-110684DOI: 10.3384/diss.diva-110684ISBN: 978-91-7519-238-3 (print)OAI: oai:DiVA.org:liu-110684DiVA: diva2:748130
Public defence
2014-10-30, Planck, Fysikhuset, Camus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2014-09-22Bibliographically approved
List of papers
1. Improving thermal stability of hard coating films via a concept of multicomponent alloying
Open this publication in new window or tab >>Improving thermal stability of hard coating films via a concept of multicomponent alloying
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2011 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 99, no 9, 091903- p.Article in journal (Refereed) Published
Abstract [en]

We propose a design route for the next generation of nitride alloys via a concept of multicomponent alloying based on self-organization on the nanoscale via a formation of metastable intermediate products during the spinodal decomposition. We predict theoretically and demonstrate experimentally that quasi-ternary (TiCrAl)N alloys decompose spinodally into (TiCr)N and (CrAl)N-rich nanometer sized regions. The spinodal decomposition results in age hardening, while the presence of Cr within the AlN phase delays the formation of a detrimental wurtzite phase leading to a substantial improvement of thermal stability compared to the quasi-binary (TiAl)N or (CrAl)N alloys.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-70747 (URN)10.1063/1.3631672 (DOI)000294489300018 ()
Note

Funding Agencies|SSF||Swedish Research Council||Gran Gustafsson Foundation for Research in Natural Sciences and Medicine||

Available from: 2011-09-16 Created: 2011-09-16 Last updated: 2017-12-08
2. Decomposition and phase transformation in TiCrAlN thin coatings
Open this publication in new window or tab >>Decomposition and phase transformation in TiCrAlN thin coatings
2012 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 30, no 6Article in journal (Refereed) Published
Abstract [en]

Phase transformations and mechanisms that yield enhanced high temperature mechanical properties of metastable solid solutions of cubic (c)-(TixCryAlz)N coatings are discussed in this paper. Coatings grown by reactive arc evaporation technique with metal composition range y<17 at. % and 45<z<62 at. % are studied and compared with the parent TiAlN material system. The coatings exhibit age hardening up to 1000 ºC which is higher compared to what is observed for TiAlN. In addition, the coatings show a less pronounced hardness decrease when hexagonal (h)-AlN is formed compared to TiAlN. The improved thermal stability is discussed in terms of a lowered coherency stress and a lowered enthalpy of mixing due to the addition of Cr, which results in improved functionality in the working temperature range of 850-1000 ºC of for example cutting tools. Upon annealing up to 1400 ºC the coatings decompose into c-TiN, bcc-Cr and h-AlN. The decomposition takes place via several intermediate phases, c-CrAlN, c-TiCrN and hexagonal (β)-Cr2N. The microstructure  evolution investigated at different stages of spinodal decomposition and phase transformation is correlated to the thermal response and mechanical hardness of the coatings.

Place, publisher, year, edition, pages
American Vacuum Society, 2012
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-80179 (URN)10.1116/1.4757953 (DOI)
Note

On the day of the defence day the status of this article was: Manuscript

Available from: 2012-08-22 Created: 2012-08-22 Last updated: 2017-12-07Bibliographically approved
3. Nanostructuring and coherency strain in multicomponent hard coatings
Open this publication in new window or tab >>Nanostructuring and coherency strain in multicomponent hard coatings
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2014 (English)In: APL MATERIALS, ISSN 2166-532X, Vol. 2, no 11, 116104- p.Article in journal (Refereed) Published
Abstract [en]

Lattice resolved and quantitative compositional characterizations of the microstructure in TiCrAlN wear resistant coatings emerging at elevated temperatures are performed to address the spinodal decomposition into nanometer-sized coherent cubic TiCr- and Al-rich domains. The domains coarsen during annealing and at 1100 ºC, the Al-rich domains include a metastable cubic Al(Cr)N phase containing 9 at.% Cr and a stable hexagonal AlN phase containing less than 1 at.% Cr. The cubic and the hexagonal phases form strained semi-coherent interfaces with each other.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
Keyword
Age hardening; Spinodal decomposition; Cathodic arc evaporation; Aberration corrected TEM
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110678 (URN)10.1063/1.4901125 (DOI)000345638800023 ()
Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2015-03-09Bibliographically approved
4. Coherency strain engineered decomposition of unstable multilayer alloys for improved thermal stability
Open this publication in new window or tab >>Coherency strain engineered decomposition of unstable multilayer alloys for improved thermal stability
2013 (English)In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 24, 244303- p.Article in journal (Refereed) Published
Abstract [en]

A concept to improve hardness and thermal stability of unstable multilayer alloys is presented based on control of the coherency strain such that the driving force for decomposition is favorably altered. Cathodic arc evaporated cubic TiCrAlN/Ti 1−x Cr x N multilayer coatings are used as demonstrators. Upon annealing, the coatings undergo spinodal decomposition into nanometer-sized coherent Ti- and Al-rich cubic domains which is affected by the coherency strain. In addition, the growth of the domains is restricted by the surrounding TiCrN layer compared to a non-layered TiCrAlN coating which together results in an improved thermal stability of the cubic structure. A significant hardness increase is seen during decomposition for the case with high coherency strain while a low coherency strain results in a hardness decrease for high annealing temperatures. The metal diffusion paths during the domain coarsening are affected by strain which in turn is controlled by the Cr-content (x) in the Ti 1−x Cr x N layers. For x = 0 the diffusion occurs both parallel and perpendicular to the growth direction but for x > =0.9 the diffusion occurs predominantly parallel to the growth direction. Altogether this study shows a structural tool to alter and fine-tune high temperature properties of multicomponent materials.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2013
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-103072 (URN)10.1063/1.4851836 (DOI)000329173200056 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2014-01-13 Created: 2014-01-13 Last updated: 2017-12-06Bibliographically approved
5. Effects of Ti alloying of AlCrN coatings on thermal stability and oxidation resistance
Open this publication in new window or tab >>Effects of Ti alloying of AlCrN coatings on thermal stability and oxidation resistance
2013 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 534, 394-402 p.Article in journal (Refereed) Published
Abstract [en]

Quaternary cubic (TixCr1 − xAl~ 0.60)1 N1 coatings with 0 < x < 0.33 have been grown using reactive cathodic arc evaporation. When adding Ti the hardness was retained after annealing up to 1100 °C which is a dramatic improvement compared to CrAlN coatings. The coatings showed an age hardening process caused by spinodal decomposition into coherent TiCr- and Al-rich cubic TiCrAlN domains and the formation of hexagonal AlN precipitates and cubic TiCrN domains in the vicinity of the grain boundaries. The improved hardness was attributed to the stabilization of the cubic structure suppressing the formation and growth of hexagonal AlN. Furthermore, the presence of Ti atoms generated incoherent nanometer-sized crystallites within the hexagonal AlN precipitates disrupting the hexagonal lattice during the coarsening process.

The addition of Ti promoted the formation of a TiO2 layer over Al2O3 resulting in a lower oxidation resistance. However, by tuning the composition it is possible to design coatings to have both good oxidation resistance and good high temperature mechanical stability.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Age hardening, Spinodal decomposition, Hard coatings, TiAlN, TiCrAlN, Catodic arc evaporation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-93255 (URN)10.1016/j.tsf.2013.03.003 (DOI)000317736700066 ()
Note

Funding Agencies|SSF project Designed multicomponent coatings, MultiFilms||

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2017-12-06Bibliographically approved
6. High temperature phase decomposition in TixZryAlzN
Open this publication in new window or tab >>High temperature phase decomposition in TixZryAlzN
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2014 (English)In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 4, no 12, 127147-1-127147-9 p.Article in journal (Refereed) Published
Abstract [en]

Through a combination of theoretical and experimental observations we study the high temperature decomposition behavior of c-(TixZryAlzN) alloys. We show that for most concentrations the high formation energy of (ZrAl)N causes a strong tendency for spinodal decomposition between ZrN and AlN while other decompositions tendencies are suppressed. In addition we observe that entropic  effects due to configurational disorder favor a formation of a stable Zr-rich (TiZr)N phase with increasing temperature. Our calculations also predict that at high temperatures a Zr rich (TiZrAl)N disordered phase should become more resistant against the spinodal decomposition despite its high and positive formation energy due to the specific topology of the free energy surface at the relevant concentrations. Our experimental observations confirm this prediction by showing strong tendency towards decomposition in a Zr-poor sample while a Zr-rich alloy shows a greatly reduced decomposition rate, which is mostly attributable to binodal decomposition processes. This result highlights the importance of considering the second derivative of the free energy, in addition to its absolute value in predicting decomposition trends of thermodynamically unstable alloys.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2014
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110682 (URN)10.1063/1.4905138 (DOI)000347170100078 ()
Note

On the day of the defence date the status of this article was Manuscript.

Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2017-12-05Bibliographically approved
7. Alloying as a tool for structure and thermal stability engineering of hard coatings
Open this publication in new window or tab >>Alloying as a tool for structure and thermal stability engineering of hard coatings
2014 (English)Manuscript (preprint) (Other academic)
Abstract [en]

A large range of (ZrxAly Cr(100-x-y))1N1 coatings have been deposited using cathodic arc evaporation and annealed at temperatures up to 1100 ºC. The coatings can be divided into three different characteristic categories based on their structure, thermal stability and hardness.

The first category of coatings, (Al < ~30 % and ~40 % < Zr), are stable cubic solid solutions up to 1100 ºC. The hardness decreases upon annealing because of defect annihilation.

In the second category, (40 % < Al < 60 % and Zr < 15 %), the coatings decompose into ZrCr- and Al-rich nanometer-sized domains when annealed, which results in a hardness increase.

In the third category (~67 % < Al), the microstructure contain a mixture of 1-2 nanometer-sized nano-crystalline hexagonal (AlN) and cubic (ZrCrN) phases. These coatings have a significantly lower hardness in the as deposited state but upon annealing the hardness increases significantly.

National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-110683 (URN)
Available from: 2014-09-18 Created: 2014-09-18 Last updated: 2014-09-18Bibliographically approved

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