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- Ben Hassine, Mohamed, 1985, et al.
(författare)
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Growth model for high-Al containing CVD TiAlN coatings on cemented carbides using intermediate layers of TiN
- 2021
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 421
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Tidskriftsartikel (refereegranskat)abstract
- This work concerns high Al-containing TixAl1-xN coatings prepared using low pressure-chemical vapour deposition (LP-CVD). The coatings were examined using electron microscopy techniques, such as scanning transmission electron microscopy (STEM), energy dispersive X-ray analysis (EDX) and transmission Kikuchi diffraction (TKD). An intermediate TiN-layer with a 〈211〉 texture consisting of twinned, needle-shaped grains influences the subsequent growth of the TiAlN layer. The TiAlN grains were columnar with a texture of 〈211〉. As the grains grow along 〈111〉, with {001} facets, this led to a tilted pyramid surface morphology. The grains developed an internal periodic epitaxial nanolamella structure. The thicknesses were 2 nm for the low (x = 0.6) and 6 nm for the high (x = 0.9) Al-containing lamellae. The TiAlN layer growth could be described by a “two-wing” model, where two TiAlN grains with a twin-related orientation grow on a twinned TiN grain, where the two TiAlN grains gradually switch sides, making the appearance of two wings of columnar grains. In general, this work shows that it should be possible to control the growth of TiAlN layers by controlling the texture and morphology of an intermediate layer, such as TiN.
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- Fazi, Andrea, 1992, et al.
(författare)
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Characterization of as-deposited cold sprayed Cr-coating on Optimized ZIRLO™ claddings
- 2021
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 549
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Tidskriftsartikel (refereegranskat)abstract
- As-produced Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray (CS) deposition process is studied. Cross-sectional electron microscopy, nano-hardness profiling, transmission electron microscopy, transmission Kikuchi diffraction, and atom probe tomography (APT) were performed to investigate the nature of the CS Cr-coating/Optimized ZIRLO™ interface, the microstructure of the coating, and the effects of the deposition on the Zr-substrate microstructure. The former surface of the Zr-substrate was found to have a highly deformed nano-crystalline microstructure, the formation of which was attributed to dynamic recrystallization occurring during coating deposition. This microstructural change, evaluated with electron backscattered diffraction and nano-hardness profiling, appeared to be confined to a depth of a few microns. Through APT analysis, a 10–20 nm thick intermixed bonding region was observed at the interface between coating and substrate. The chemical composition of this region suggests that this layer originated from a highly localized shearing and heating of a thin volume of the outermost former surface of the substrate. The study of the intermixed bonding region's crystalline structure was performed with high resolution transmission electron microscopy and revealed a distorted hexagonal close-packed structure.
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- Fazi, Andrea, 1992, et al.
(författare)
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Cold sprayed Cr-coating on Optimized ZIRLO™ claddings: the Cr/Zr interface and its microstructural and chemical evolution after autoclave corrosion testing
- 2022
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 560
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Tidskriftsartikel (refereegranskat)abstract
- Cr-coated Optimized ZIRLO™ cladding material fabricated with the cold-spray deposition process is studied. Microstructure and chemistry of this material are investigated before and after exposure to autoclave corrosion testing with scanning electron microscopy, energy dispersive spectroscopy analysis, electron backscattered diffraction, transmission electron microscopy and atom probe tomography. The results are used to assess what changes have occurred upon autoclave exposure. The formation of a compact, 80 – 100 nm thick Cr2O3 layer is observed on the surface of the exposed samples. Nucleation of ZrCr2 intermetallic phase is discovered at the Cr/Zr interface. This Laves phase nucleates inside the intermixed bonding layer that can be found in both pristine and exposed samples, and decorates the interface in the form of small particles (less than 50 nm in size). Using transmission electron microscopy and atom probe tomography the growth of a Zr-Cr-Fe phase was detected. This phase is found in the region of the Zr-substrate immediately adjacent to the coating, up to a few hundred nanometres distance from the Cr/Zr interface. A small degree of recrystallization occurs upon autoclave exposure in the 1-2 µm thick nanocrystalline layer produced on the Zr-substrate by the cold spray deposition method utilized for the fabrication of the Cr-coating.
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- Fazi, Andrea, 1992, et al.
(författare)
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Comparing CrN and TiN Coatings for Accident-Tolerant Fuels in PWR and BWR Autoclaves
- 2022
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Ingår i: Journal of Nuclear Engineering. - : MDPI AG. - 2673-4362. ; 3:4, s. 321-332
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Tidskriftsartikel (refereegranskat)abstract
- The development of coatings for accident-tolerant fuels (ATFs) for light water reactor (LWR) applications promises improved corrosion resistance under accident conditions and better performances during operation. CrN and TiN coatings are characterized by high wear resistance coupled with good corrosion resistance properties. They are generally used to protect materials in applications where extreme conditions are involved and represent promising candidates for ATF. Zr cladding tubes coated with 5 µm-thick CrN or TiN, exposed in an autoclave to simulated PWR chemistry and BWR chemistry, were characterized with SEM, EDS, and STEM. The investigation focused on the performance and oxidation mechanisms of the coated claddings under simulated reactor chemistry. Both coatings provided improved oxidation resistance in a simulated PWR environment, where passivating films of Cr2O3 and TiO2, less than 1 µm-thick, formed on the CrN and TiN outer surfaces, respectively. Under the more challenging BWR conditions, any formed Cr2O3 dissolved into the oxidizing water, resulting in the complete dissolution of the CrN coating. For the TiN coating, the formation of a stable TiO2 film was observed under BWR conditions, but the developed oxide film was unable to stop the flux of oxygen to the substrate, causing the oxidation of the substrate.
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