| 1. |
- Johnson, Lars, 1983-
(author)
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Inside The Miscibility Gap : Nanostructuring and Phase Transformations in Hard Nitride Coatings
- 2012
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Doctoral thesis (other academic/artistic)abstract
- This thesis is concerned with self-organization phenomena in hard and wear resistant transition-metal nitride coatings, both during growth and during post deposition thermal annealing. The uniting physical principle in the studied systems is the immiscibility of their constituent parts, which leads, under certain conditions, to structural variations on the nanoscale. The study of such structures is challenging, and during this work atom probe tomography (apt) was developed as a viable tool for their study. Ti0.33Al0.67N was observed to undergo spinodal decomposition upon annealing to 900 °C, by the use of apt in combination with electron microscopy. The addition of C to TiSiN was found to promote and refine the feather-like microstructure common in the system, with an ensuing decrease in thermal stability. An age-hardening of 36 % was measured in arc evaporated Zr0.44Al0.56N1.20, which was a nanocomposite of cubic, hexagonal, and amorphous phases. Magnetron sputtering of Zr0.64Al0.36N at 900 °C resulted in a self-organized and highly ordered growth of a two-dimensional two-phase labyrinthine structure of cubic ZrN and wurtzite AlN.The structure was analyzed and recovered by apt, although the ZrN phase suffered from severe trajectory aberrations, rendering only the Al signal useable.The initiation of the organized growth was found to occur by local nucleation at 5-8 nm from the substrate, before which random fluctuations in Al/Zr content increased steadily from the substrate. Finally, the decomposition of solid-solution TiB0.33N0.67 was found, by apt, to progress through the nucleation of TiB0.5N0.5 and TiN, followed by the transformation of the former into hexagonal TiB2.
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| 2. |
- Johnson, Lars, 1983-, et al.
(author)
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Microstructure evolution and age hardening in (Ti,Si)(C,N) thin films deposited by cathodic arc evaporation
- 2010
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In: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:4, s. 1397-1403
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Journal article (peer-reviewed)abstract
- Ti1 − xSixCyN1 − y films have been deposited by reactive cathodic arc evaporation onto cemented carbide substrates. The films were characterized by X-ray diffraction, elastic recoil detection analysis, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron-energy loss spectroscopy and nanoindentation. Reactive arc evaporation in a mixed CH4 and N2 gas gave films with 0 ≤ x ≤ 0.13 and 0≤y≤0.27. All films had the NaCl-structure with a dense columnar microstructure, containing a featherlike pattern of nanocrystalline grains for high Si and C contents. The film hardness was 32–40GPa. Films with x > 0 and y > 0 exhibited age-hardening up to 35–44 GPa when isothermally annealed up to 900 °C. The temperature threshold for over-ageing was decreased to 700 °C with increasing C and Si content, due to migration of Co, W and Cr from the substrate to the film, and loss of Si. The diffusion pathway was tied to grain boundaries provided by the featherlike substructure.
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| 3. |
- Johnson, Lars, 1983-
(author)
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Nanostructuring and Age Hardening in TiSCN, ZrAlN, and TiAlN Thin Films
- 2010
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Licentiate thesis (other academic/artistic)abstract
- This thesis explores nanostructuring in TiSiCN, ZrAlN, and TiAlN thin films deposited by cathodic arc evaporation onto cemented carbide substrates, with intended applications for cutting tools. The three systems were found to exhibit age hardening upon annealing, by different mechanisms, into the superhard regime (≥30 GPa), as determined by a combination of electron microscopy, X-ray diffraction, atom probe tomography, erda, and nanoindentation tech- niques. TiSiCN forms nanocomposite films during growth by virtue of Si segregation to the surface of TiCN nanocrystallites while simultaneously pro- moting renucleation. Thus, the common columnar microstructure of TiCN and low-Si-content (≤5 at. %) TiSiN-films is replaced by a “feather-like” nanos- tructure in high-Si-content (≥10 at. %) TiSiCN films. The presence of C promotes the formation of this structure, and results in an accelerated age hardening beginning at temperatures as low as 700 °C. The thermal stability of the TiSiCN films is, however, decreased compared to the TiSiN system by the loss of Si and interdiffusion of substrate species; C was found to ex- acerbate these processes, which became active at 900 °C. The ZrAlN system forms a two-phase nanostructure during growth consisting of cubic ZrAlN and wurtzite ZrAlN. Upon annealing to 1100 °C, the c-Zr(Al)N portion of the films recovers and semicoherent brick-like w-(Zr)AlN structures are formed. Age hardening by 36 % was obtained before overageing sets in at 1200 °C. As-deposited and annealed solid solution Ti0.33Al0.67N thin films were characterized for the first time by atom probe tomography. The as-deposited film was found to be at the very initial stage of spinodal decomposition, which continued during annealing of the film at 900 °C for 2 h. N preferentially segregates to Al-rich domains in the annealed sample, causing a compositional variation between Ti-rich and Al-rich domains, to maintain the stoichiometry for the developing AlN phase. That effect also compensates for some of the coherency strain formed between cubic domains of TiN and AlN. Finally, a possible Kirkendall effect caused by an imbalance in the metal interdiffusion during the spinodal decomposition was discovered.
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| 4. |
- Salamania, Janella, 1992-
(author)
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Defects in Titanium Aluminum Nitride-Based Thin Films
- 2023
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Doctoral thesis (other academic/artistic)abstract
- Coatings and thin films inherently contain several types of defects. This thesis aims to enhance the understanding of the relationship of defects on the growth, structure, stability, and properties of titanium aluminum nitride films synthesized by physical vapor deposition techniques.Heteroepitaxial cubic and wurtzite films in the Ti-Al-N system grown by reactive magnetron sputtering were studied in relation to their defect structures. The dislocation structures of heteroepitaxial TiN and Ti1-xAlxNy films were analyzed by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Together with atomistic simulations, it was revealed that the presence of different dislocation types in TiN enhances the metal-metal bonds which locally weakens the directionally covalent metal-N bonds. In epitaxial cubic Ti1-xAlxN films, microstrain analysis shows that increasing N-vacancies influences the strain and compositional fluctuations in as-deposited states. During spinodal decomposition induced by annealing to high temperatures, the delay in coarsening and strain correlates with the amount of N vacancies. Detailed characterization of the decomposing domains exposed the formation of stacking faults and partial dislocations as a strain-relieving mechanism which also facilitates the known cubic-to-wurtzite transformation in Ti-Al-N.Cathodic arc deposited Ti1-xAlxN films were grown by applying a low duty cycle pulsed-substrate bias and high nitrogen pressures. This resulted into films with coarse grains and low lattice defects within them, indicating a kinetically controlled route to modify the defect structures in arc-deposited films. Applying the same technique on single crystalline TiN seed layer films kinetically stabilizes a pseudomorphic growth, allowing to form a highly textured, pseudo epitaxial wurtzite Ti1-xAlxN films by arc deposition. In combination with theoretical calculations, it was revealed that w-Ti1-xAlxN films also exhibit a miscibility gap which enables spinodal decomposition and thus age hardening when annealed. Finally, magnetron sputtered nitrogen-deficient w-Ti1-xAlxNy heteroepitaxial films were shown to exhibit a decomposition route that involves the formation of coherent intermediate MAX-like phases before transforming to pure c-TiN and w-AlN phases, which results to continued age hardening up to 1200°C.The findings in this work increase the fundamental understanding of the role of defects in Ti-Al-N films and open new routes for defect-based engineering strategies.
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| 5. |
- Johnson, Lars, 1983-, et al.
(author)
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Spinodal Decomposition of Ti0.33Al0.67N Thin Films Studied by Atom Probe Tomography
-
Other publication (other academic/artistic)abstract
- The decomposition of Ti0.33Al0.67N thin films deposited by cathodic arc evaporation have been studied by atom probe tomography. As-deposited films were found to deviate slightly from a random solid solution, and so be in the earliest stage of decomposition. After annealing at 900 °C for 2 h the films exhibited a spinodally decomposed nanostructure, in an intermediate stage. N was found to preferentially segregate to the Al-rich domains in the annealed sample, causing the TiN-domains to be understoichiometric. A possible Kirkendall effect was detected for the annealed sample, with a modulation of the local stoichiometry by 1-2 at. % along the decomposition gradient.
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| 6. |
- Salamania, Janella, 1992-, et al.
(author)
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High-resolution STEM investigation of the role of dislocations during decomposition of Ti1-xAlxNy
- 2023
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In: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 229
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Journal article (peer-reviewed)abstract
- The defect structures forming during high-temperature decomposition of Ti1-xAlxNy films were investigated through high-resolution scanning transmission electron microscopy. After annealing to 950 °C, misfit edge dislocations a/6〈112〉{111} partial dislocations permeate the interface between TiN-rich and AlN-rich domains to accommodate lattice misfits during spinodal decomposition. The stacking fault energy associated with the partial dislocations decreases with increasing Al content, which facilitates the coherent cubic to wurtzite structure transition of AlN-rich domains. The wurtzite AlN-rich structure is recovered when every third cubic {111} plane is shifted by along the [211] direction. After annealing to 1100 °C, a temperature where coarsening dominates the microstructure evolution, we observe intersections of stacking faults, which form sessile locks at the interface of the TiN- and AlN-rich domains. These observed defect structures facilitate the formation of semicoherent interfaces and contribute to hardening in Ti1-xAlxNy.
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| 7. |
- Salamania, Janella, et al.
(author)
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Influence of nitrogen vacancies on the decomposition route and age hardening of wurtzite Ti1−xAlxNy thin films
- 2023
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In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : A V S AMER INST PHYSICS. - 0734-2101 .- 1520-8559. ; 41:6
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Journal article (peer-reviewed)abstract
- The wurtzite phase of TiAlN has been known to form in industrial grade coatings with high Al content; yet, a significant knowledge gap exists regarding its behavior at high temperatures and the impact of defects on its properties. Specifically, its response to high temperatures and the implications of defects on its characteristics are poorly understood. Here, the high-temperature decomposition of nitrogen-deficient epitaxial wurtzite Ti1-xAlxNy (x = 0.79-0.98, y = 0.82-0.86) films prepared by reactive magnetron sputtering was investigated using x-ray diffractometry and high-resolution scanning transmission electron microscopy. The results show that wurtzite Ti(1-x)Al(x)Ny decomposes by forming intermediary MAX phases, which then segregate into pure c-TiN and w-AlN phases after high-temperature annealing and intermetallic TiAl nanoprecipitates. The semicoherent interfaces between the wurtzite phase and the precipitates cause age hardening of approximately 4-6 GPa, which remains even after annealing at 1200 degrees C. These findings provide insight into how nitrogen vacancies can influence the decomposition and mechanical properties of wurtzite TiAlN.
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