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Improving thermal stability of hard coating films via a concept of multicomponent alloying
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, The Institute of Technology. Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics.
Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
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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. Vol. 99, no 9, 091903- p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-70747DOI: 10.1063/1.3631672ISI: 000294489300018OAI: oai:DiVA.org:liu-70747DiVA: diva2:441463
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
In thesis
1. Mechanical properties and thermal stability of reactive arc evaporated Ti-Cr-Al-N coatings
Open this publication in new window or tab >>Mechanical properties and thermal stability of reactive arc evaporated Ti-Cr-Al-N coatings
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This licentiate thesis reports experimental and theoretical work on the high temperature mechanical properties and the thermal stability of cubic (c)-(Ti-Cr-Al)1-N1 coatings. It is demonstrated that it is possible to tailor and improve the properties of hard nitride coatings by different degrees of multicomponent alloying. When Cr is added to Ti-Al-N the coatings exhibit age hardening up to 1000 ºC which is higher compared to what is observed for Ti-Al-N. In addition, the coatings show a less pronounced hardness decrease when hexagonal (h)-Al-N is formed compared to Ti-Al-N. 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. When Ti is added to Cr-Al-N the formation and growth of the detrimental h-Al-N phase is suppressed and delayed improving the mechanical properties. This is discussed in terms of kinetic effects where the Ti atoms obstruct the Al diffusion and consequently the growth of h-Al-N precipitates. The microstructure evolution investigated at different stages of spinodal decomposition, coarsening and phase transformations are correlated to the thermal responses and the mechanical hardness of the coatings. 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 oxidation resistance of (Tix-Cry-Al60)1-N1 is also investigated and presented for different x/y ratios. The results show that it is possible to generate coatings with both excellent mechanical properties and oxidation resistance improving the functionality in the working temperature range of 850-1100 ºC of for example cutting tools.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2012. 37 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1546
National Category
Physical Sciences
Identifiers
urn:nbn:se:liu:diva-79579 (URN)LIU-TEK-LIC-2012:31 (Local ID)978-91-7519-832-3 (ISBN)LIU-TEK-LIC-2012:31 (Archive number)LIU-TEK-LIC-2012:31 (OAI)
Presentation
2012-09-06, Planck, Fysikhuset, Campus Valla, Linköping University, Linköping, 17:48 (English)
Opponent
Supervisors
Available from: 2012-08-22 Created: 2012-08-09 Last updated: 2014-10-07Bibliographically approved
2. Multicomponent Alloying for Improved Hard Coatings
Open this publication in new window or tab >>Multicomponent Alloying for Improved Hard Coatings
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:nbn:se:liu:diva-110684 (URN)10.3384/diss.diva-110684 (DOI)978-91-7519-238-3 (ISBN)
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
3. Theoretical understanding of stability of alloys for hard-coating applications and design
Open this publication in new window or tab >>Theoretical understanding of stability of alloys for hard-coating applications and design
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The performance of modern hard coating materials puts high demands on properties such as hardness, thermal stability and oxidation resistance. These properties not only depend on the chemical composition, but also on the structure of the material on a nanoscale. This kind of nanostructuring will change during use and can be both beneficial and detrimental as materials grown under non-equilibrium conditions transforms under heat treatment or pressure into other structures with significantly different properties. This thesis aims to reveal the physics behind the processes of phase stability and transformations and how this can be utilized to improve on the properties of this class of alloys. This has been achieved through the application of various methods of first-principles calculations and analysis of the results on the basis of thermodynamics and electronic structure theory.

Within multicomponent transition metal aluminum nitride alloys (TMAlN) a number of studies have been carried out and presented here on ways of improving high temperature stability and hardness. Most (TMAl)N and TMN prefer a cubic B1 structure while AlN is stable in a hexagonal B4 phase, but for the purposes of hard coatings the metastable cubic B1 AlN phase, isostructural with the TMN phase is desired. It will be shown how the introduction of additional alloying components, such as Cr, into (TiAl)N changes the thermodynamic stability of phases so that new intermediary and metastable phases are formed during decomposition. In the case of such a (CrAl)N phase it is shown to have greater thermodynamic stability in the cubic phase than the pure AlN, resulting in improved high temperature hardness. Also, the importance of treating not just the binodal decomposition through the formation energy relative to end products but also the impact of spinodal decomposition from its second derivative due to the topology of formation energy surfaces is emphasized in the thesis. The impact of pressure on the AlN phase has also been studied through the calculation of a P-T diagram of AlN as part of a (TiAl)N alloy.

During the study of chemical alloying of TM components into AlN the alloying of low concentrations of these TM were treated in great detail. What is generally referred to as the AlN phase in decomposition is not entirely pure and can be expected to contain traces of any alloying components, such as Ti and Cr or whatever other metals may be present. Low concentration alloying of Cr, on the order of 5-10% is also shown to be stable with regard to isostructural decomposition. Detailed analysis of the effect of Ti and Cr impurities in AlN has been carried out along with a systematic search of AlN alloyed with small amounts of other TM components. The impact of these impurities on the electronic structure and thermodynamic properties is analyzed and the general trends will be explained through the occupation of impurity states by d-like electrons.

Theoretical treatment of such impurities is not straightforward however. AlN is an s-p semiconductor with a wide band gap while TM impurities generate states of a d-like nature situated inside the band gap. Such localized impurity states are expected to give rise to magnetic effects due to spin dependent exchange, in addition strong correlation effects might have to be taken into account. For that reason the use of hybrid functionals with orbital corrections according to the mHSE+Vw scheme, developed specifically for this class of materials, has been used and shown to influence the results during calculation of impurities of Ti and Cr.

In nanocomposite multilayered structures, composed of very thin layers of one material sandwiched between slabs of another, such as layers of SiN between TiN or ZrN, the material properties are greatly affected by the interfaces. In addition to the thermodynamic effects and lattice strains of the interfaces one also has to consider the atomic vibrational motion in the interface structure. Hence, dynamical stability of these thin multilayers is of great importance. As part of this thesis, results on the thermodynamic and dynamical stability of both TiN-SiN layers and ZrN-SiN will be presented. It will be shown that due to considerable dynamical instability in the interface structure of monolayered B1 SiN sandwiched between isostructural layers of B1 ZrN along (111) interfaces this structure cannot be expected to grow, instead preferring the stable (001) direction of growth.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 73 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1647
National Category
Physical Sciences Materials Engineering
Identifiers
urn:nbn:se:liu:diva-115405 (URN)10.3384/diss.diva-115405 (DOI)978-91-7519-112-6 (ISBN)
Public defence
2015-04-10, Planck, Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2015-03-16 Created: 2015-03-16 Last updated: 2015-03-16Bibliographically approved

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