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| 7. |
- 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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| 8. |
- 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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| 9. |
- 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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| 10. |
- 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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| 11. |
- Fazi, Andrea, 1992, et al.
(författare)
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CrN–NbN nanolayered coatings for enhanced accident tolerant fuels in BWR
- 2023
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Ingår i: Journal of Nuclear Materials. - 0022-3115. ; 586
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Tidskriftsartikel (refereegranskat)abstract
- The accident tolerant fuel (ATF) concept has emerged in the years after the 2011 Fukushima accident as part of a renewed effort in research for light water reactors. The primary focus is to further improve safety measures under and beyond design basis accident conditions, and to improve fuel cladding performance in normal operation. The application of a coating on zirconium claddings can achieve both these aims without extensive changes to the reactor design. Metallic chromium coatings have been profusely studied as solution for pressurized water reactors, but the search for an effective ATF coating able to withstand the environment inside boiling water reactors (BWRs) is still ongoing. In this work, two different versions of a novel nitride coating composition were studied. Zirconium claddings coated with 8 µm thick layers of superlattice CrN–NbN and a nanolayered CrN–NbN were tested in autoclave under BWR operating conditions for 60 days. Scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, electron back-scattered diffraction, x-ray diffraction, and atom probe tomography were employed to characterize as-deposited and autoclaved samples of these two materials. During exposure, both coating versions formed a stable, dense and passivating oxide scale (200–300 nm thick) on the surface, demonstrating improved oxidation protection under operating conditions. Some differences in the oxide growth mechanism were observed between the superlattice and the nanolayered CrN–NbN coatings, which allowed to glimpse at the effect of the layer thickness on the oxidation protection provided by these coatings. The nano-structured morphology of both coatings remained unaffected by the autoclave test, but a 35 nm thick Zr-Cr-N phase was found at the coating-substrate interface of the superlattice CrN–NbN coated cladding.
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| 12. |
- Fazi, Andrea, 1992, et al.
(författare)
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Performance and evolution of cold spray Cr-coated optimized ZIRLO™ claddings under simulated loss-of-coolant accident conditions
- 2023
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 576
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Tidskriftsartikel (refereegranskat)abstract
- The performance of Cr-coated Optimized ZIRLO™ as accident tolerant fuel cladding material for pressurized water reactors (PWRs) is assessed. The coating oxidation mechanisms, oxide stability, and the transformation of the Cr-coating/Optimized ZIRLO™ interface are among the studied phenomena. For this purpose, samples were exposed at 1200°C in steam for 3 min, 20 min and 40 min. As-fabricated coated claddings, plus specimens tested in autoclave at 415°C for 90 days in simulated PWR water chemistry were employed for comparison. Characterization techniques such as scanning electron microscopy, energy dispersive x-ray spectroscopy, electron backscattered diffraction, and transmission electron microscopy were used to determine the chemistry and crystalline structure of the various phases formed during the different exposures. When exposed to loss-of-coolant accident (LOCA) conditions for 40 min, a layer of Cr2O3 up to 8 µm thick was measured on the outer surface of the Cr-coating. No significant oxidation of the underlaying Optimized ZIRLO™ alloy occurred, and the applied coating appears to be very effective at delaying the cladding degradation under accident conditions. At the coating-substrate interface, a 1–2 µm thick layer of (Cr,Fe)2Zr Laves phase was found. The presence of this phase appears to have no detrimental effects on the coating performance, and it might play a role in slowing down the dissolution of the coating into the substrate. ZrO2 particles were frequently found at grain boundaries in the coating after exposure to LOCA conditions. For longer exposure time, these particles are expected to grow into a ZrO2-network, creating a fast diffusion path for O, and compromising the oxidation protection offered by the coating.
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| 15. |
- Qiu, Ren, 1993, et al.
(författare)
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Atom probe tomography investigation of 3D nanoscale compositional variations in CVD TiAlN nanolamella coatings
- 2021
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 426
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Tidskriftsartikel (refereegranskat)abstract
- The cubic (Ti1−xAlx)Ny (TiAlN) phase with a nanolamella structure, synthesized via low pressure chemical vapour deposition (LPCVD), has been widely used in wear-resistant coatings during the latest years. The nanolamella structured TiAlN coatings contain periodic and epitaxially grown Ti-rich [denoted as Ti(Al)N] and Al-rich [denoted as Al(Ti)N] lamellae. However, the chemical compositions of these nano-structures have not been fully revealed. In this study, the microstructure of the nanolamella TiAlN coating was studied using scanning and transmission electron microscopy (SEM and TEM), and the chemical content was investigated using atom probe tomography (APT) that provides three-dimensional composition data with good accuracy and a spatial resolution down to the nanometer scale. It was found that over- and under-stoichiometries of N exist for the Ti(Al)N and the Al(Ti)N lamellae, respectively. According to the previous simulation results, such over- and under-stoichiometries are due to metal (Al and Ti) and N vacancies, respectively. The Al(Ti)N lamellae have a chemical formula of (Ti0.12Al0.88)N0.90, and have 10% N vacancies. The Ti(Al)N lamellae have a chemical formula of (Ti0.70Al0.30)0.97N, and have 3% metal (Al and Ti) vacancies. In addition to the nanolamella structure, compositional variations on a scale of a few nm were found in both types of lamellae. In the Ti-richest volumes, the composition corresponds to (Ti0.72Al0.28)0.88N so a maximum of 12% of metal vacancies exists. In the Al-richest volumes, the composition corresponds to (Ti0.07Al0.93)N0.64 so a maximum of 36% N vacancies exists. In addition, a small amount of Cl (around 0.1 at.%) was found in the coating, which could originate from the incomplete dissociation of chloride precursors during the CVD surface reaction.
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| 16. |
- Qiu, Ren, 1993, et al.
(författare)
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CVD TiAlN coatings with tunable nanolamella architectures
- 2021
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Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 413
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Tidskriftsartikel (refereegranskat)abstract
- In this work, Ti1-xAlxN (TiAlN) coatings were synthesized by low pressure chemical vapour deposition (LPCVD), and the influence of a rotational precursor gas supply on the coating microstructure was studied. The microstructure of the TiAlN coatings were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and electron backscattered diffraction (EBSD). It is shown that a rotational precursor gas supply induces an oscillatory surface reaction, which causes a nanolamella architecture. When the gas beam directly hits the sample, the local gas flow velocity is high, which increases the deposition rate of Ti and a Ti(Al)N lamella is formed. When the gas beam rotates away, the local gas velocity is low, so the deposition rate of Ti decreases, and an Al(Ti)N lamella is formed. As this is repeated a periodic nanolamella architecture is formed. The nanolamellae grow epitaxially on three {001} facets of the 111 textured grains, which leads to a pyramidal surface morphology. Without gas supply rotation, a high Al content cubic phase was still obtained, but no nanolamella was formed. This indicates that Ti-rich lamellae are not necessary to stabilize an Al-rich cubic TiAlN phase. In addition, spinodal decomposition is not likely to be the driving force behind the nanolamella formation in LPCVD TiAlN, as this would also have happened in the sample without a rotational gas supply. Finally, the nanolamella periodicity is found to be tunable via controlling the rotation speed of the precursor supply relative to the coating growth rate.
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| 17. |
- Qiu, Ren, 1993, et al.
(författare)
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Effects of gas flow on detailed microstructure inhomogeneities in LPCVD TiAlN nanolamella coatings
- 2020
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Ingår i: Materialia. - : Elsevier BV. - 2589-1529. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Depositing homogeneous TiAlN coatings with a high Al content on cutting tool inserts is a challenging task. In this work, high-Al cubic Ti1-xAlxN coatings (average x = 0.8) with periodic Ti(Al)N (x = 0.5) and Al(Ti)N (x = 0.9) nanolamellae structure were synthesized by low pressure chemical vapour deposition (LPCVD) with different gas flow velocities, and the detailed microstructure was investigated by electron microscopy and simulations. Using a high gas flow rate, the columnar TiAlN grains with regular periodic nanolamella structures disappeared, the coating became enriched in Ti and hexagonal AlN (h-AlN) formed in the coating. The high Ti content is suggested to be caused by the high gas flow rate that increases the mass transport of the reactants. However, this does not influence the Al-deposition much as it is mainly limited by the surface kinetics due to the relatively low deposition temperature. Density functional theory (DFT) modelling and electron microscopy showed that h-AlN tends to form on the Ti(Al)N phase with a specific crystallographic orientation relationship. The Ti enrichment due to high gas flow rate promotes the formation of h-AlN, which therefore deteriorates the nanolamella structure and causes the disappearance of the columnar TiAlN grains. Thus, by designing the CVD process conditions to avoid too high gas flow rates, homogenous TiAlN coatings with high Al content and nanolamella structures can be deposited, which should yield superior cutting performance.
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| 18. |
- Qiu, Ren, 1993, et al.
(författare)
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Facet identification in textured polycrystalline coatings by EBSD-aided SEM trace analysis
- 2024
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Ingår i: Materials Characterization. - 1044-5803. ; 209
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Tidskriftsartikel (refereegranskat)abstract
- Competitive growth usually occurs during deposition of polycrystalline coatings and is associated by the formation of crystal facets. Knowing the facet planes in the crystal coordinates is thus essential for understanding the coating growth process and optimizing corresponding experimental parameters. However, the crystal facets of polycrystalline coatings have not been explored enough due to a lack of easy-to-use experimental methods. In this work, we apply an electron backscattered diffraction (EBSD)-aided scanning electron microscopy (SEM) trace analysis for determining the crystal facets of the chemical vapour deposition (CVD) polycrystalline (Ti,Al)N and Ti(C,N) coatings. Using this method, the crystal orientation of an interesting grain relative to the specimen coordinates is first determined by the EBSD point analysis, and the crystal orientations of edges shared by neighbouring facets are then determined using trace analysis. Finally, the facet normals are calculated by the cross-product of the crystal orientations of edges on the corresponding facet. The (Ti,Al)N coating is found to have {100} crystal facets, which is consistent with the results obtained using transmission electron microscopy in previous work. The Ti(C,N) coating is found to have {211} crystal facets. In principle, the method proposed in this work can be applied to any crystals with planar facets and sharp edges. A possible improvement of the method is also discussed.
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| 19. |
- Qiu, Ren, 1993, et al.
(författare)
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Schmid factor analysis for chip flow induced plastic deformation of textured cubic carbonitride coatings
- 2022
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Ingår i: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 108
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Tidskriftsartikel (refereegranskat)abstract
- In high-speed metal machining, cutting tools in the form of cemented carbide inserts coated with thin wear-resistant coatings are commonly used. These coatings are often made of metal carbonitrides with cubic rock salt crystal structure and different growth textures. However, the influence of the crystallographic texture of the coatings on their wear by plastic deformation due to the chip flow during machining needs to be revealed further. In this work, in order to analyse the ability of polycrystalline fibre-textured coatings with a rock salt structure to undergo plastic deformation, a method was developed for calculating Schmid factors of such textured coatings as a function of the loading angle of an external force. The Schmid factors were calculated for coatings with 100 and 211 growth textures, and {100} <110>, {110}<110> and {111}<110> as possible slip systems. For the {111}<110> slip systems, the Schmid factors are not much influenced by the force angle and coating texture, which is contrary to the {100}<110> and {110}<110> slip systems. The simulations were compared to wear on the rake face of two textured Ti(C,N) coatings after short longitudinal turning tests. The variation of the degree of plastic deformation of Ti(C,N) coatings with growth texture and external force angle indicates that the dominant activated slip systems are {110}<110> using the machining conditions applied in this work.
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| 20. |
- Shoja, Siamak, 1980, et al.
(författare)
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On the influence of varying the crystallographic texture of alumina CVD coatings on cutting performance in steel turning
- 2022
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Ingår i: International Journal of Machine Tools and Manufacture. - : Elsevier BV. - 0890-6955. ; 176
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the mechanisms at the tool/chip interface during metal cutting is crucial in the production of almost every metallic component used in engineering applications. It is critical to have rapid, durable, and reliable machining processes. This work contributes to the understanding of mechanisms occurring on the tool in the secondary shear zone, and it is focusing on the tool side of the contact. Crystallographic textured Chemical Vapor Deposited (CVD) α-Al2O3 coated cutting tools are dominating the steel turning area, as they show an increased performance compared to coatings with randomly oriented grains. In this study, we investigate the effect of three different CVD α-Al2O3 textures on the initial rake crater behavior. This was done using a turning test designed to generate crater wear only in the alumina layer, which was deposited onto an inner Ti(C,N) layer, which in turn was deposited on a cemented carbide insert. With this approach, the influence of the underlying coating layer and substrate was reduced. Pre- and post-machining characterization of the different contact areas on the surfaces of the three textured CVD α-Al2O3 coatings, (0001)(0001), (011‾2) and (112‾0), was performed using scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and energy dispersive X-ray spectroscopy (XEDS). Plastic deformation, micro-rupture, abrasion and chemical reactions with the workpiece material are all identified as mechanisms involved in crater formation during turning. For the (0001)-textured coating, the observed low wear-rate is attributed to homogeneous basal-slip dominating plastic deformation, while for the (011‾2) and (112‾0) textures the main deformation mechanisms are attributed to heterogeneous plastic deformation, causing micro-rupture and abrasion, leading to higher wear-rates. The effect of a larger coating grain size is mainly seen as the formation of wider ridges and valleys, while the effect on wear rate was limited.
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| 21. |
- Slabanja, Mattias, 1976, et al.
(författare)
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Early stages of phase separation using three-dimensional atom probe and atomistic modelling
- 2007
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Ingår i: Surface and Interface Analysis. ; 39, s. 178-
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Tidskriftsartikel (refereegranskat)abstract
- The early stages of clustering in Al-14.8 Mg alloy have been studied using atomistic modelling and 3DAP analysis. Atomistic modelling was based on first-principles quantum mechanical calculations and Monte Carlo (MC) based techniques. A good agreement between the experimental results and simulated data was obtained showing the appropriateness of the theoretical approach used. It has been shown that after 720 h at 35 °C (308 K) clustering of Mg was clearly detectable in the experimental alloy. The simulated data after 200 MC steps corresponded well to the experimental results obtained after ageing for 720 h.
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| 22. |
- Stiller, Krystyna Marta, 1947, et al.
(författare)
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Atom probe tomography of interfaces in ceramic films and oxide scales
- 2016
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Ingår i: MRS Bulletin. - : Springer Science and Business Media LLC. - 0883-7694 .- 1938-1425. ; 41:1, s. 35-39
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Tidskriftsartikel (refereegranskat)abstract
- Atomic-scale characterization of interfaces in ceramic materials is needed in order to fully understand their electronic, ionic, mechanical, magnetic, and optical properties. The latest development of laser-assisted atom probe tomography ( APT), as well as new specimen preparation methods, have opened the realm of ceramics for structural and chemical characterization with high sensitivity and nearly atomic spatial resolution. This article reviews recent APT investigations of interfaces in thin nitride films and thermally grown oxides: TiAlN layers and oxide scales on alumina- and chromia-formers and Zr alloys. The selected examples highlight the role of interfaces in the decomposition of films and in transport processes.
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| 23. |
- Stiller, Krystyna Marta, 1947, et al.
(författare)
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Atom probe tomography of oxide scales
- 2013
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 79:3-4, s. 227-238
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Tidskriftsartikel (refereegranskat)abstract
- Atom probe tomography, APT, is the only microstructural method that can routinely analyse and position individual atoms in a material with a spatial resolution of 0.1-0.5 nm. Recent implementation of pulsed-laser to APT made investigation of less conducting materials, such as oxides, feasible. In this paper a short description of the principle of the techniques is presented, followed by examples of recent APT studies of thermally grown oxide scales produced on alumina formers (Pt-modified NiAl diffusion coating and FeCrAl alloy), at the crack tips in a Ni-based alloy and on a Zr-alloy. Additionally, results from preliminary studies of ZnO and MgO bulk materials are shown. The obtained information on the atomic scale about the chemistry variations in the scales and at the metal oxide interfaces provides valuable insights into oxidation processes. © 2012 Springer Science+Business Media New York.
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| 24. |
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| 25. |
- Thuvander, Mattias, 1968, et al.
(författare)
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Quantitative atom probe analysis of carbides
- 2011
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 111:6, s. 604-608
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Tidskriftsartikel (refereegranskat)abstract
- Compared to atom probe analysis of metallic materials, the analysis of carbide phases results in an enhanced formation of molecular ions and multiple events. In addition, many multiple events appear to consist of two or more ions originating from adjacent sites in the material. Due to limitations of the ion detectors measurements generally underestimate the carbon concentration. Analyses using laser-pulsed atom probe tomography have been performed on SiC, WC, Ti(C,N) and Ti 2 AlC grains in different materials as well as on large M 2 3C 6 precipitates in steel. Using standard evaluation methods, the obtained carbon concentration was 6-24% lower than expected from the known stoichiometry. The results improved remarkably by using only the 13 C isotope, and calculating the concentration of 12 C from the natural isotope abundance. This confirms that the main reason for obtaining a too low carbon concentration is the dead time of the detector, mainly affecting carbon since it is more frequently evaporated as multiple ions. In the case of Ti(C,N) andTi 2 AlC an additional difficulty arises from the overlap between C 2 + ,C 2+ 4 and Ti 2+ at the mass-to-charge 24 Da. © 2010 Elsevier B.V.
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| 26. |
- Andersson, Jörgen, 1973, et al.
(författare)
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Microstructure development during tempering of the hot-work tool steel Uddeholm QRO 90 Supreme
- 2009
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Ingår i: Proc. 8th Int Tooling Conf., Eds. P Beiss, C Broeckmann, S Franke and B Keysselitz, RWTH Aachen Univ, Aachen, Germany. - 3861307006 ; II, s. 611-623
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Konferensbidrag (refereegranskat)
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| 27. |
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| 28. |
- Andrén, Hans-Olof, 1947, et al.
(författare)
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Microstructure evolution of a Z-phase strengthened 9-12% Cr steel
- 2011
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Ingår i: The 8th International Charles Parsons Turbine Conference, Portsmouth, UK, September 5th - 8th, 2011.
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Konferensbidrag (refereegranskat)abstract
- A new alloy design concept for martensitic / ferritic steels aiming for 650°C – the Zphasestrengthened steels – has been developed in Europe. These new steels areexpected to have good corrosion and creep resistance, which is attributed to a high Crcontent (up to 12 %) and a dense distribution of stable Z-phase precipitates.This paper reports a study of the microstructure evolution of a trial Ta-containing Zphasestrengthened steel. Samples with different aging times, from 24 hours to 10,000hours, were investigated by using scanning electron microscopy and transmissionelectron microscopy. Mainly two types of precipitates, Z-phase and Laves phase, werefound. The size distribution of the precipitates was analysed. It was found that Zphaseprecipitates, with very small initial size, have a very low coarsening rate.
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| 29. |
- Andrén, Hans-Olof, 1947
(författare)
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Microstructure of a high boron 9-12% chromium steel
- 2008
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Ingår i: 34th MPA-Seminar “Materials and Components Behaviour in Energy & Plant Technology”, Materialprüfungsanstalt Universität Stuttgart 2008 (CD-ROM only). ; , s. 8.1-8.11
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Additions of small amounts of boron (10-100 ppm) to 9-12% chromium steels are often made since they have been found to be beneficial for the creep strength up to and above 600°C. The effect of boron is to restrict the coarsening of M23C6 precipitates during service. It was found that increasing the boron content from 9 to 40 ppm gave a decrease in coarsening constant at 600°C by a factor of 2. The present understanding of boron solution, non-equilibrium grain boundary segregation, incorporation into M23C6, and diffusion is reviewed in the paper. A very high boron addition (300 ppm) was made in the trial TAF steel already in the 1950’ies. The microstructure of a similar trial steel, FT3B, has been studied detail. In this steel large Mo, Cr, Fe and V containing metal borides are formed rather than the expected BN, with the crystal structure M3B2. Nitrogen is therefore still available for the formation of VN. Due to tempering at a low temperature (690°C) to a high strength (830 MPa), this steel contained a dense distribution of very small VN precipitates, 5-15 nm in size. A similar VN distribution is probably the cause of the still unsurpassed creep strength of the TAF steel.
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| 30. |
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| 31. |
- Angseryd, Jenny, 1979, et al.
(författare)
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An in-depth investigation of the cutting speed impact on the degraded microstructure of worn PCBN cutting tools
- 2011
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 271:9-10, s. 2610-2618
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Tidskriftsartikel (refereegranskat)abstract
- The impact of an increased cutting speed on the degradation of a low content polycrystalline cubic boron nitride (PCBN) tool material is investigated by advanced microscopy techniques. The locally affected microstructure of worn PCBN cutting tools, after dry hard turning, is studied by high precision in situ lift-out cross sections taken from across the crater, formed on the rake face. The cross sections are studied with scanning electron microscopy, transmission electron microscopy (TEM) with electron energy loss spectroscopy and, primarily, energy filtered TEM.Advanced analysis techniques are crucial to illustrate the degradation mechanisms taking place locally at micro- and nano-metre levels during the machining operation. Results show that a higher cutting speed drastically affects the wear surface of the cutting edge. While an adherent layer, consisting of elements from the workpiece material, covers practically the whole wear surface at a lower cutting speed, it is only partially distributed at a higher cutting speed. Results also show significant differences in the local microstructure of the affected worn zone with an increase in cutting speed. The chemical degradation will go from tool-workpiece interface wear with smooth wear surfaces and almost no interaction with material below the wear surface at lower cutting speed to a severe penetration into the tool material by partially oxidised Fe-rich features at higher cutting speed. The more aggressive degradation behaviour at the higher cutting speed is also more localised. Single chemically worn cBN grains are for example shown. The dominating wear mechanism is shown to be chemical degradation, which accelerates with a higher cutting speed. The cBN phase is more affected than the major matrix phase, Ti(C,N).
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| 32. |
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| 33. |
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| 34. |
- Angseryd, Jenny, 1979, et al.
(författare)
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Nanostructure of a cubic BN cutting tool material
- 2015
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Ingår i: International Journal of Refractory Metals and Hard Materials. - : Elsevier BV. - 0263-4368 .- 2213-3917. ; 49:1, s. 283-287
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Tidskriftsartikel (refereegranskat)abstract
- Advanced microscopy techniques, laser assisted atom probe tomography and electron energy loss spectroscopy in transmission electron microscopy are used to investigate in detail the microstructure of a polycrystalline cubic boron nitride tool material. During sintering at high pressure superhard cubic boron nitride combines with hard ceramic Ti(C,N) to form a dense material. Diffusion in Ti(C,N) and reactions between Ti(C,N), cBN and additives result in the formation of several nitride, oxide and boride phases in a complex mixed microcrystalline and nano- crystalline microstructure.
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| 35. |
- Angseryd, Jenny, 1979, et al.
(författare)
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Quantitative APT analysis of Ti(C,N)
- 2011
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 111:6, s. 609-614
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Tidskriftsartikel (refereegranskat)abstract
- A specially produced Ti(C,N) standard material, with a known nominal composition, was investigated with laser assisted atom probe tomography. The occurrence of molecular ions and single/multiple events was found to be influenced by the laser pulse energy, and especially C related events were affected. Primarily two issues were considered when the composition of Ti(C,N) was determined. The first one is connected to detector efficiency, due to the detector dead-time. The second one is connected to peak overlap in the mass spectrum. A method is proposed for quantification of the C content in order to establish the C/N ratio. A correction was made to the major C peaks, C at 6 and 12 Da, with the 13C isotopes, at 6.5 and 13 Da, according to the known natural abundance. In addition, a correction of the peak at 24 Da, where C and Ti overlap, is proposed based on the occurrence of single/multiple events for respective element. The results were compared to the results from other techniques such as electron energy loss spectroscopy, chemical analysis and X-ray diffraction. After applying the corrections, atom probe tomography results were satisfactory. Furthermore, the content of dissolved O in Ti(C,N) was successfully quantified. © 2011 Elsevier B.V.
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| 36. |
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| 37. |
- Barberis, P., et al.
(författare)
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Discussion
- 2011
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Ingår i: ASTM Special Technical Publication.16th International Symposium on Zirconium in the Nuclear Industry, Chengdu, Sinchuan Province, 9-13 May 2010. - 0066-0558. - 9780803175150 ; 1529 STP, s. 647-648
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 38. |
- Bhadeshia, H K D H, et al.
(författare)
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Coalesced bainite
- 2006
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Ingår i: Transactions of the Indian Institute of Metals. ; 59, s. 689-694
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Tidskriftsartikel (refereegranskat)
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| 39. |
- Eriksson, Johan, 1987, et al.
(författare)
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An atom probe tomography study of the chemistry of radiation-induced dislocation loops in Zircaloy-2 exposed to boiling water reactor operation
- 2021
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 550
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Tidskriftsartikel (refereegranskat)abstract
- This study is complementary to previous atom probe tomography (APT) studies of irradiation effects in the zirconium alloy Zircaloy-2. Using APT in voltage pulse mode, a difference in morphology was observed between clusters of Fe and Ni and clusters of Fe and Cr in Zircaloy-2 exposed to a high fast neutron fluence in a commercial boiling water reactor. The Fe–Ni clusters were disc-shaped with a diameter of 5–15 nm, whereas the Fe–Cr clusters were spheroidal with a diameter of approximately 5 nm. Both types of clusters appeared to be located at irradiation-induced -type dislocation loops aligned in layers normal to the -direction. The concentration of Fe was higher in the Fe–Cr clusters than in the Fe–Ni clusters. The dilute Fe–Ni clusters, which seem to be segregation of Fe and Ni inside the loops, had formed on all three families of first-order prismatic planes with some deviation from perfect -axis alignment. The Fe–Cr clusters might be very small precipitates with a nucleation associated with the loops.
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| 40. |
- Eriksson, Johan, 1987, et al.
(författare)
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Nanoscale chemistry of Zircaloy-2 exposed to three and nine annual cycles of boiling water reactor operation — an atom probe tomography study
- 2022
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115. ; 561
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Tidskriftsartikel (refereegranskat)abstract
- Atom probe tomography was used in this work to study the metal close to the metal/oxide interface in the zirconium alloy Zircaloy-2 exposed to three and nine annual cycles of operation in a commercial boiling water reactor. The two exposure times correspond to before and after the onset of acceleration in corrosion, hydrogen pickup, and growth. The alloying elements Sn, Fe, Cr, and Ni were observed to be redistributed after exposure. After both three and nine cycles, clusters containing Fe and Cr and typically of a spheroidal shape with an approximate diameter of 5 nm were observed to be located in layers presumed to be layers of -loops. On average, the cluster number density was slightly higher after nine cycles, with larger and more Cr-rich clusters. However, there were large grain-to-grain variations, which were larger than the differences between the two exposure times. Ni was only occasionally observed in the clusters. Sn was observed to be slightly enriched in the Fe–Cr clusters, but the Sn concentration was higher between than inside the layers of clusters. After nine cycles, clusters of Sn were detected in regions that were depleted of Fe and Cr. Enrichment of Sn, Fe, and Ni at features that appeared to be -component loops was observed after nine cycles, whereas no such features were observed after three cycles. Enrichment of Sn and Fe, and small amounts of Cr and Ni, was observed at grain boundaries after both exposure times. After three cycles, a partially dissolved second phase particle of Zr(Fe,Cr)2 type that contained about ten times more Cr than Fe was observed.
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| 41. |
- Eriksson, Johan, 1987, et al.
(författare)
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Solute Concentrations in the Matrix of Zirconium Alloys Studied by Atom Probe Tomography
- 2023
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Ingår i: ASTM Special Technical Publication. - 0066-0558. ; STP1645, s. 149-172
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Konferensbidrag (refereegranskat)abstract
- This work indicates that the matrix content of the alloying elements iron, chromium, and nickel in as-produced commercial Zircaloy-2-type materials is lower than what has been indicated by many previous studies. Atom probe tomography in voltage pulse mode was used to study the matrix content of solutes in Zircaloy-2 of type LK3/L and a similar model alloy, called Alloy 2, of the same heat treatment. Both alloys were analyzed in the as-produced state and after reactor exposure. In the as-produced materials, the concentrations of iron, chromium, and nickel were all below the detection limits of around 10 wt. ppm. After reactor exposure, these alloying elements were observed to reside in clusters at loops, and the matrix content (including clusters) of iron had increased to about 1,200 wt. ppm in the fueled region of the rod and to about half that value in the plenum region. The chromium content in the fueled region was approximately 100 wt. ppm, and the nickel content was approximately 200 wt. ppm. In the plenum region, the content of these elements was lower. However, due to an uneven distribution of clusters, there was a wide scatter in the measured concentrations in the irradiated materials. Additionally, the matrix concentrations of solute elements in (nonirradiated) Zircaloy-2 were investigated for a series of samples subjected to a annealing at 770◦C followed by cooling at different rates. From these measurements, the solubilities at 770◦C were estimated to be around 65 wt. ppm for chromium, at least 37 wt. ppm for iron, and below 9 wt. ppm for nickel. Slow cooling resulted in virtually no iron, chromium, or nickel in the matrix. The concentration of aluminum in the matrix was observed to be between 10 and 20 wt. ppm for all a-annealed samples and for the as-produced materials of commercial heat treatment.
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| 42. |
- Fedorova, Irina, et al.
(författare)
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Analyzing Boron in 9-12% Chromium Steels Using Atom Probe Tomography
- 2019
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Ingår i: Microscopy and Microanalysis. - 1435-8115 .- 1431-9276. ; 25:2, s. 462-469
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Tidskriftsartikel (refereegranskat)abstract
- Microscopy Society of America 2019. Small additions of boron can remarkably improve the long-term creep resistance of 9-12% Cr steels. The improvement has been attributed to boron segregation to grain boundaries during quenching, and subsequent boron incorporation into certain families of precipitates during tempering. However, the detailed mechanisms are not yet fully understood. Atom probe tomography (APT) is an excellent technique for gaining insights into boron distribution, however, in order to acquire accurate analysis of boron in 9-12% Cr steels using APT, there are several key challenges. In order to better understand and address these challenges, we developed a novel method for site-specific APT specimen preparation, which enables convenient preparation of specimens containing specifically selected grain boundaries positioned approximately perpendicular to the axis of the APT tip. Additionally, when analyzing boron at boundaries and in carbides (as diluted solute) and borides, a widening of the profile of boron distribution compared to other elements was repeatedly observed. This phenomenon is particularly analyzed and discussed in light of the evaporation field of different elements. Finally, the possible effects of detector dead-time on quantitative analysis of boron in metal borides are discussed. A simple method using 10B correction was used to obtain good quantification.
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| 43. |
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| 44. |
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| 45. |
- Golpayegani, Ardeshir, 1975, et al.
(författare)
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An EFTEM study on Z-phase nucleation in martensitic chromium steels
- 2006
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Ingår i: Materials for Advanced Power Engineering 2006, Eds. J Lecomte-Beckers, M Carton, F Schubert and PJ Ennis. Schriften der Forschungszentrum Jülich GmbH (2006), Reihe Energitechnik. - 1433-5522. ; 53:III, s. 1267-1274
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Konferensbidrag (refereegranskat)
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| 46. |
- Golpayegani, Ardeshir, 1975, et al.
(författare)
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Mechanism for beneficial effect of boron addition on creep resistance of 9-12% chromium steels
- 2006
-
Ingår i: International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2005; Phoenix, AZ; United States; 29 May 2005 through 3 June 2005. ; 1, s. 461-466
-
Konferensbidrag (refereegranskat)abstract
- Energy filtered transmission electron microscopy has been used to study two similar steels after long time aging, with different boron additions, to measure the effect of B on coarsening rate of M23Ce precipitates. The mechanism behind the effect of boron could either be a drastic decrease in the energy of the interface between M23C6 and matrix or a decrease in flux of atoms from a shrinking precipitate to a growing one. We suggest that the latter mechanism is operating, based on atom probe (APFIM) measurements of boron solubility in the matrix and the detection of Mo-B clustering.
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| 47. |
- Golpayegani, Ardeshir, 1975, et al.
(författare)
-
Microstructure of a Creep-Resistant 10 Pct Chromium Steel Containing 250 ppm Boron
- 2011
-
Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 42:4, s. 940-951
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of a trial martensitic chromium steel containing a high content of boron (250 ppm) was characterized in detail in the as-tempered and aged conditions. This steel has a similar composition and heat treatment as the TAF steel that still is unsurpassed in creep strength among all 9 to 12 pct chromium steels. Characterization was performed by using scanning electron microscopy, energy-filtered transmission electron microscopy, secondary ion mass spectroscopy, and atom probe tomography. Focus was placed on investigating different types of precipitates that play a key role in improving the creep resistance of these steels. The low tempering temperature of 963 K (690 A degrees C) is enough for the precipitation of the full volume fraction of both MX and M23C6. A high boron content, more than 1 at. pct, was found in M23C6 precipitates and they grow slowly during aging. The high boron level in the steel results in metal borides rather than BN with the approximate formula (Mo0.66Cr0.34)(2)(Fe0.75V0.25)B-2. Two families of MX precipitates were found, one at lath boundaries about 35 nm in size and one dense inside the laths, only 5 to 15 nm in size.
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| 48. |
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| 49. |
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| 50. |
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