| 1. |
- Hörling, Anders, et al.
(författare)
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Phase stability and structural properties of Ti1-zZrzN (0<z<1) thin films
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Single-phase [NaCl]-structure Ti1-zZrzN thin films (0<z<1) have been deposited using cathodic arc plasma deposition. The films were investigated using X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, and nanoindentation. Theoretical calculations on phase stabilities using density-functional theory revealed that the pseudo-binary TiN-ZrN system exhibits a miscibility gap, with respect to phase transformation from the as-deposited single-phase [NaCl] structure into [NaCl]-strueture TiN and ZrN components up to 980°C for z=0.35. The films were found to retain their as-deposited single-phase [NaCl] structure during post-deposition annealing for 120 min at 600, 700, 1100 and 1200°C, and for as long as 195 h at 600°C. This effective thermal stability is explained by a limited driving force for phase transformation and insufficient atom diffusivity. For two film compositions deepest within the miscibility gap, however, results from nanoindentation show an essentially retained hardness at ~30 GPa after annealing at 1100-1200°C. The principal hardening mechanism for the Ti1-zZrzN fihns is thus proposed to be solid-solution hardening through localized lattice strain fields originating from difference in atomic radius of Ti and Zr. This particular system offers interesting opportunities for fundamental studies of time-temperature-transformations of ternary nitride thin films.
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| 2. |
- Hörling, Anders, et al.
(författare)
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Thermal stability, microstructure and mechanical properties of Ti1 − xZrxN thin films
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:18, s. 6421-6431
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Tidskriftsartikel (refereegranskat)abstract
- Single-phase [NaCl]-structure Ti1 − xZrxN thin films (0 < x < 1) have been deposited using cathodic arc plasma deposition. The films were investigated using X-ray diffraction (XRD), transmission electron microscopy, differential scanning calorimetry (DSC), and nanoindentation. Density functional theory calculations on phase stabilities show that the pseudo-binary TiN–ZrN system exhibits a miscibility gap, extending over 0 ≤ x ≤ 0.99 at 1000 °C, with respect to phase transformation from a solid solution into a two-phase mixture of [NaCl]-structure TiN and ZrN components. The films were found to retain their as-deposited single-phase structure during post-deposition annealing at 600 °C (18 h), 700 °C (12 h), 1100 and 1200 °C (2 h), and for as long as 195 h at 600 °C. DSC revealed no heat flow during annealing, similar to TiN, and only the x = 0.53 film exhibited a slight increase in XRD peak broadening after annealing at 1200 °C, consistent with spinodal decomposition. This effective thermal stability of the alloys is explained by the combination of a limited driving force for phase transformation and an insufficient atom diffusivity. In terms of mechanical properties, films with composition deepest within the miscibility gap showed a hardness of ∼ 30 GPa after annealing at 1100–1200 °C; a value only moderately lower than in the as-deposited condition. The principal hardening mechanism for the Ti1 − xZrxN films is proposed to be solid-solution hardening through local lattice strain fields originating from difference in atomic radius of Ti and Zr. The material system is thus promising for cutting tool applications.
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| 3. |
- Mayrhofer, P H, et al.
(författare)
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Influence of different atmospheres on the thermal decomposition of Al-Cr-N coatings
- 2008
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 41:15
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Tidskriftsartikel (refereegranskat)abstract
- Metastable cubic (c) AlCrN coatings decompose during thermal annealing into their stable phases Cr and hexagonal (h) AlN under the release of N 2. We show that the onset temperature To and amount of N2 release depend on the ambient atmosphere. For c-Al 0.56Cr0.44N only a partial dissociation into h-AlN and h-Cr2N with To ∼ 1180°C occurs during annealing in N2 up to 1450°C. Experiments in synthetic air to 1450°C yield a complete oxidation to (Al0.56Cr0.44) 2O3. © 2008 IOP Publishing Ltd.
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| 4. |
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| 5. |
- Willmann, Herbert, et al.
(författare)
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Epitaxial growth of Al-Cr-N thin films on MgO(111)
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:2, s. 598-602
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Tidskriftsartikel (refereegranskat)abstract
- Cubic rock salt structure Al0.60Cr0.40N and Al0.68Cr0.32N films of different thicknesses were grown epitaxially onto MgO(111) substrates by reactive unbalanced magnetron sputtering at 500°C. Rutherford backscattering spectroscopy reveals stoichiometric nitrides with Al/Cr ratios close to the ones of the used compound targets of 60/40 and 70/30. High resolution x-ray diffraction proves epitaxial growth over the whole film thickness up to thicknesses of ~1.8 µm. Reciprocal space maps and selected area electron diffraction show that the AlxCr1-xN films grow fully relaxed. Scanning and transmission electron microscopy imaging reveals columnar microstructures with column widths between 12–16 nm and {001} surface faceting on individual columns. The fully relaxed growth and the columnar structure can be attributed to limited ad‑atom mobility on the initial AlxCr1-xN(111) growth surface.
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| 6. |
- Willmann, Herbert, et al.
(författare)
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Hardness evolution of Al-Cr-N coatings under thermal load
- 2008
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Ingår i: Journal of Materials Research. - 0884-2914 .- 2044-5326. ; 23:11, s. 2880-2885
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure and hardness evolution of arc-evaporated single-phase Cubic Al0.56Cr0.44N and Al0.68Cr0.32N coatings have been investigated after thermal treatment in Ar atmosphere. Based on a combination of differential scanning calorimetry and x-ray diffraction studies, We Can Conclude that Al0.56Cr0.44N undergoes only small structural changes without any decomposition for annealing temperatures T-a <= 900 degrees C. Consequently, the hardness decreases only marginally from the as-deposited value of 30.0 +/- 1.1 GPa to 29.4 +/- 0.9 GPa with T-a increasing to 900 degrees C, respectively. The film with higher Al content (Al0.68Cr0.32N) exhibits formation of hexagonal (h) AlN at T-a >= 700 degrees C, which occurs preferably at grain boundaries as identified by analytical transmission electron microscopy. Hence, the hardness increases from the as-deposited value of 30.1 +/- 1.3 GPa to 31.6 +/- 1.4 GPa with T-a = 725 degrees C. At higher temperatures, where the size and volume fraction of the h-AlN phase increases, the hardness decreases to 27.5 +/- 1.0 GPa with T-a = 900 degrees C.
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| 7. |
- Willmann, Herbert, et al.
(författare)
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Single-crystal growth of NaCl-structure Al-Cr-N thin films on MgO(0 0 1) by magnetron sputter epitaxy
- 2007
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 57:12, s. 1089-1092
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Tidskriftsartikel (refereegranskat)abstract
- Single-crystal NaCl-structure Al0.68Cr0.32N thin films were deposited onto MgO(0 0 1) substrates. The films exhibit cube-on-cube epitaxial growth with an initial pseudomorphic strained layer before complete relaxation into an isotropic lattice parameter of 4.119 Å as shown by symmetric high-resolution X-ray diffraction and asymmetric reciprocal space maps. The relaxation proceeds via a threading dislocation network as revealed by transmission electron microscopy. Films of 900 nm thickness have a hardness of 32.4 ± 0.5 GPa, an elastic modulus of 460.8 ± 5 GPa, and a room-temperature resistivity of 2.7 × 103 O cm as determined by nanoindentation and four-point probe measurements, respectively. © 2007 Acta Materialia Inc.
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| 8. |
- Willmann, Herbert, 1975-, et al.
(författare)
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Thermal stability and age hardening of supersaturated AlCrN hard coatings
- 2007
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Ingår i: International Heat Treatment & Surface Engineering. - : Maney Publishing. - 1749-5148. ; 1:2, s. 75-79
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Tidskriftsartikel (refereegranskat)abstract
- During advanced machining processes (high speed and dry cutting), the temperature at the cutting edge can exceed 1000°C. For modern protective hard coatings, thermal stability is of major interest. Equally important are superior mechanical properties, such as hardness, remaining at a high level over a wide temperature range. AlCrN coatings perform well in cutting tests and show excellent oxidation resistance as well as good tribological behaviour. In this work, supersaturated cubic Al0.7Cr0.3N coatings deposited by cathodic arc evaporation are studied. The phase and microstructure evolution of the material is investigated up to 1450°C using a combination of differential scanning calorimetry, thermal gravimetric analysis, mass spectrometry, X-ray diffraction and analytical transmission electron microscopy. During annealing up to 925°C, hexagonal AlN precipitates are formed at grain boundaries. At higher temperatures, a transformation of the remaining cubic AlCrN matrix into Cr via Cr2N takes place, accompanied by a release of nitrogen. After annealing up to 1450°C, the AlN grains coarsen and coalesce around the Cr and Cr2N grains. The results explain the superior cutting performance by the formation of precipitates, but also demonstrate the limitations in usage at high temperature regimes due to decomposition. Nevertheless, the substitution of Cr in the CrN lattice by Al has proven to increase the decomposition resistance significantly. Finally, nanoindentation experiments reveal that AlCrN coatings retain hardness beyond the stage of residual stress recovery up to 900°C, demonstrating an age hardening process.
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| 9. |
- Willmann, Herbert, 1975-, et al.
(författare)
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Thermal stability of Al-Cr-N hard coatings
- 2006
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 54:11, s. 1847-1851
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Tidskriftsartikel (refereegranskat)abstract
- Heat treatment of arc-evaporated cubic Al0.7Cr0.3N hard coatings in Ar up to 1450 °C causes precipitation of AlN. The Cr-enriched matrix transforms into Cr via Cr2N under N2 release. These reactions are investigated by simultaneous thermal analysis, mass spectrometry, X-ray diffraction, and analytical transmission electron microscopy.
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