| 1. |
- Gao, Zecui, et al.
(författare)
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Ab initio supported development of TiN/MoN superlattice thin films with improved hardness and toughness
- 2022
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Ingår i: Acta Materialia. - : Pergamon-Elsevier Science Ltd. - 1359-6454 .- 1873-2453. ; 231
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by density functional theory (DFT)-derived ductility indicators for face centered cubic (fcc, rocksalt) structured TiN/MoN0.5 superlattices and Ti0.5Mo0.5N0.75 solid solutions, TiN/MoNy superlattice (SL) thin films with bilayer periods lambda of 2.4, 3.9, 6.6, 9.9, and 23.0 nm and corresponding solid solutions were developed by DC reactive magnetron sputtering. These SLs allow for improved hardness H and critical fracture toughness K-IC, with both peaking at the same bilayer period lambda of 9.9 nm (where the MoN0.5 layers crystallize with the ordered beta-Mo2N phase); H = 34.8 +/- 1.6 GPa and K-IC = 4.1 +/- 0.2 MPa root m. The correspondingly prepared fcc-Ti0.5Mo0.5N0.77 solid solution has H = 31.4 +/- 1.5 GPa and K-IC = 3.3 +/- 0.2 MPa root m. Thus, especially the fracture toughness shows a significant superlattice effect. This is suggested by DFT-by the increase of the Cauchy pressure from -19 to + 20 GPa for the 001-direction (while that in the 100-direction remained high, above 83 GPa) upon increasing lambda from 3 to 4 nm.& nbsp;Together, experimental and computational investigations prove the importance of optimized bilayer periods for highest strength and fracture toughness, as well as optimized N-content for the solid solutions.
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| 2. |
- Kretschmer, Andreas, et al.
(författare)
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Analysis of (Al,Cr,Nb,Ta,Ti)-nitride and-oxynitride diffusion barriers in Cu-Si interconnects by 3D-Secondary Ion Mass Spectrometry
- 2023
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 197
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Tidskriftsartikel (refereegranskat)abstract
- We report on the barrier performance of a nitride, and three oxynitrides of the system Al-Cr-Nb-Ta-Ti between Cu and Si. Different high-entropy sublattice nitrides have been tested before as diffusion barriers in this system, by depositing thin barriers on single crystalline Si substrates, followed by a thick Cu layer on top, and subsequent vacuum annealing. We investigated a reversed stacking sequence, by sputtering 15-30 nm of (Al,Cr,Nb,Ta,Ti)-O-N (between 0.5 and 63.7 at.% O) on polished polycrystalline Cu substrates, followed by 200 nm of Si. The samples were then vacuum annealed at 600, 700, 800 and 900 degrees C for 30 min. All four investigated coatings perform similar. Secondary Ion Mass Spectrometry depth profiling in high-current-bunched mode (lateral res-olution +/- 1 mu m) shows breakthrough of Si even at 600 degrees C. But 3D constructed images with Burst Alignment mode (lateral resolution of +/- 2 nm) reveal that this failure is a highly localized phenomenon, likely related to coarsening effects at the Cu grain boundaries, leading to punctuation of the diffusion barrier. Aside from this penetration, the majority of the area of each barrier coating retains its function. This in-depth analysis shows that the barrier function of the nitride and oxynitride coatings mostly stays intact up to 800 degrees C and fails completely at 900 degrees C.
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| 3. |
- Kretschmer, Andreas, et al.
(författare)
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High-entropy alloy inspired development of compositionally complex superhard (Hf,Ta,Ti,V,Zr)-B-N coatings
- 2022
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Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 218
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Tidskriftsartikel (refereegranskat)abstract
- Phase stability and mechanical properties of multimetal-boronnitride (Hf,Ta,Ti,V,Zr)-B-N is investigated by ab initio computations and experimental methods. (Hf,Ta,Ti,V,Zr)-B-N shows a strong energetic preference for the fcc NaCl-type structure over other structures up to a B:N ratio of 3.5. Reactively deposited (Hf,Ta,Ti,V,Zr)-B-N coatings show formation of X-ray amorphous BN, accompanied by a drastic hardness decrease with increasing B content. But non-reactively sputtered (Hf,Ta,Ti,V,Zr)-B-N coatings exhibit a single-phase fcc solid solution, up to the maximum B:N ratio of 1.12 studied, in good agreement with calculations. All non-reactively sputtered multimetal-boronnitride coatings contain a high Zr metal-fraction and approximate to 8at% C, stemming from impurities in the target. The single-phase coatings reach superhardness up to 46.3 GPa. Even after vacuum annealing to 1200 degrees C, the hardness of the coating with a B:N ratio of 1.03 is still 43.7 GPa, while that of ZrN0.72C0.28 decreased from 36.3 to 30.2 GPa. Our results demonstrate the importance of the deposition technique to deposit single-phased coatings with exceptional hardness and thermal stability. (C) 2022 The Authors. Published by Elsevier Ltd.
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| 4. |
- Kretschmer, Andreas, et al.
(författare)
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Improving phase stability, hardness, and oxidation resistance of reactively magnetron sputtered (Al,Cr,Nb,Ta,Ti)N thin films by Si-alloying
- 2021
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 416
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Tidskriftsartikel (refereegranskat)abstract
- Reactively magnetron sputtered high-entropy metal-sublattice (Al,Cr,Nb,Ta,Ti)N coatings have been alloyed with Si concentrations between x(si) = 6.4 and 15.0 at.%. All coatings are single-phase fcc structured and their hardness initially increases from similar to 32 to 35 GPa with Si-alloying up to x(si) = 9.8 at.%, and then decreases to similar to 24 GPa for higher Si contents. Contrary, the indentation modulus E continuously decreases from similar to 470 to 350 GPa by Si-alloying. Also, the decomposition of the fcc structure during vacuum annealing is shifted from 1000 to 1200 degrees C with the addition of Si. The hardness initially increases during vacuum annealing and reaches a maximum of 37 GPa with T-a = 1000 degrees C at x(si) = 12.0 at.%. During oxidation experiments in ambient air at 850 degrees C for up to 100 h, a 2700 nm single-phase rutile-structured oxide scale forms at the Si-free (Al,Cr,Nb,Ta,TON with a parabolic growth rate. The rate changes to a logarithmic-like behavior with the addition of Si, resulting in only similar to 280 nm oxide scale after 100 h. Also, for the Si-containing coatings, the oxide scale shows only one crystalline rutile structure. The pore size in the oxide scale of the Si-free coating is considerably reduced by Si-addition. The oxides growing at the Si-containing coatings show an opposing Si- and Cr-gradient - with much smaller pores in the Si-rich inner region - which shows a gradual transition to the remaining nitride. Ab initio based calculations confirm that the formation of a single-phase rutile-structured solid solution oxide, (Al,Cr,Nb,Ta,Ti)O-2, is energetically preferred over separate phases above 509 K, due to the higher configurational entropy. Below this temperature the decomposition towards (Al,Ta,Ti)O-2 + (Cr,Nb)O-2 would be favored (when considering just chemical contributions), but kinetically restricted.
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| 5. |
- Schmid, Barbara, et al.
(författare)
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Mechanical properties of VC/ZrC and VC/HfC superlattices
- 2024
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- Face -centered cubic transition metal carbides exhibit high melting points and hardness, making them prominent candidates for protective coating applications. Vanadium carbide (VC) has typical characteristics of transition metal carbides. It serves as model material in this study, in which we showcase the effect of superlattice architecture on mechanical properties and fracture toughness. While beneficial effects of superlattice arrangement have been demonstrated for a series of nitride -based coatings, transition metal carbides remain largely unexplored territory. Following density functional theory based ab initio predictions on lattice and shear modulus mismatch, we develop VC/ZrC and VC/HfC superlattice coatings synthesized via pulsed DC sputter deposition. The bilayer periods ( Lambda ) of our fully fcc-structured polycrystalline coatings range between 2 - 50 nm (indicated by X-ray diffraction, transmission and scanning electron microscopy). The chemical composition is close to 1:1 stoichiometry (from X-ray fluorescence, elastic back -scattering spectrometry and elastic recoil detection analysis). Both superlattice series exhibit a strong dependence of hardness, elastic modulus, and fracture toughness on their bilayer periods, which can only be correlated with the in -plane stress variations for VC/ZrC. The VC/HfC superlattices provide their peak -hardness of 36.0 +/- 1.6 GPa for Lambda = 6 nm and their peak in fracture toughness of 3.5 +/- 0.5 MPa root m for Lambda = 10 nm.
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