| 1. |
- Kirnbauer, A., et al.
(författare)
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Mechanical properties and thermal stability of reactively sputtered multi-principal-metal Hf-Ta-Ti-V-Zr nitrides
- 2020
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 389
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Tidskriftsartikel (refereegranskat)abstract
- Crystalline (Hf,Ta,Ti,V,Zr)N nitride thin films, with a high-entropy metal-sublattice, were synthesized at 440 degrees C by reactive magnetron sputtering using an equimolar Hf-Ta-Ti-V-Zr-compound target. The coatings are single-phase fcc structured mono-nitrides for N-2/(Ar + N-2) flow-rate-ratios (f(N2)) between 30 and 45%. For higher f(N2) a small fraction of a second phase (next to the fcc matrix) can be detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED). All coatings studied (prepared with f(N2) between 30 and 60%) show similar chemical compositions and hardness (H) values between 30.0 and 34.0 GPa with indentation moduli of similar to 460 GPa. Atom probe tomography (APT) indicates a homogenous distribution of all elements within our fcc-(Hf,Ta,Ti,V,Zr)N even after vacuum-annealing at 1300 degrees C. While H decreased from 32.5 to 28.1 GPa by this annealing treatment, the coating is still single-phase fcc structured with a defect density (expressed by XRD and SAED features, transmission electron microscopy contrast, and grain sizes) comparable to the as-deposited state. Only after vacuum-annealing at 1500 degrees C, XRD and APT reveal the formation of hexagonal structured (Ta,V)(2)N. The onset of nitrogen-loss - detected by thermogravimetric analysis - is similar to 1350 degrees C. Based on our results we can conclude that the sluggish diffusion within our fcc-(Hf,Ta,Ti,V,Zr)N warrants the single-phase fcc structure up to 1300 degrees C, although ab initio based calculations would suggest the lower-entropy products [fcc-(Hf,Zr)N, fcc-(Ta,V)N, and fcc-TiN] and [fcc-(Hf,Zr)N and fcc-(Ta,Ti,V)N] to be energetically more stable up to 1302 K.
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| 2. |
- Kohlhauser, B., et al.
(författare)
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How microalloying of the Al target can improve process and film characteristics of sputtered alumina
- 2020
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Ingår i: Surface & Coatings Technology. - : ELSEVIER SCIENCE SA. - 0257-8972 .- 1879-3347. ; 393
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Tidskriftsartikel (refereegranskat)abstract
- The outstanding thermo-mechanical and chemical stability of Al2O3 thin films attracts particular attention in academia and industry. Here we show that alloying of the powder metallurgically prepared Al targets with 2 as well as 5 at.% of Cr, Mo, or W significantly improves the process stability (e.g., reducing arcing events) for Al2O3, allowing their reactive magnetron sputtering in DC mode (substrate temperature was always 360 degrees C). Contrary to these microalloying elements, Nb did not change or improve the process characteristics of the Al target due to the relatively coarse Nb particles (< 125 mu m). Particularly the small (< 10 mu m) and fine-dispersed W particles are very effective in stopping the collision cascades to concentrate them to the near subsurface target-regions. This leads to a shift of the target-poisoning onset from O-2/(Ar + O-2) flow-rate-ratios of about 32 to 52%, specifically when adding 5 at.% to the Al target. Thereby also improved deposition rates are possible. However, detailed X-ray diffraction (XRD) and transmission electron microscopy studies show that only thin films developed from the 2 at.% W alloyed Al target have a nanocrystalline gamma-Al2O3-based structure comparable to those prepared from Al or Cr alloyed Al targets. The films are with 28.3 GPa instead of 26.8 GPa slightly harder when sputtered from Al0.98W0.02 instead of Al targets. Higher W contents (and also Nb) in the target lead to the formation of Al2O3-based films with considerably lower crystalline phase fractions and hardness (similar to 13 GPa). Hardest films, with 30.0 and 29.6 GPa, are obtained when using Al0.98Cr0.02 and Al0.98Cr0.05 targets, respectively. The formation of volatile Mo-oxides during film growth interferes the structure development, leading to rather soft films with 8.0 GPa especially when using the higher Mo alloyed Al0.98Cr0.05 target. Based on our results we can conclude that microalloying the Al targets with small and fine-dispersed Cr or W particles not just improves process stability and deposition rate during reactive sputtering of Al2O3, but also their mechanical thin film properties.
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