| 1. |
- 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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| 2. |
- Hedström, Peter, et al.
(författare)
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The 475 degrees C embrittlement in Fe-20Cr and Fe-20Cr-X (X=Ni, Cu, Mn) alloys studied by mechanical testing and atom probe tomography
- 2013
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 574, s. 123-129
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the 475 degrees C embrittlement in binary Fe-Cr and ternary Fe-Cr-X (X=Ni, Cu and Mn) alloys have been investigated. The mechanical properties were evaluated using microhardness and impact testing, and the structural evolution was evaluated using atom probe tomography (APT). The APT results after aging at 500 degrees C for 10 h clearly showed that both Ni and Mn accelerate the ferrite decomposition. No evident phase separation of either the Fe-20Cr or Fe-20Cr-1.5Cu samples was detected after 10 h of aging and thus no conclusions on the effect of Cu can be drawn. Cu clustering was however found in the Fe-20Cr-1.5Cu sample after 10 h aging at 500 degrees C. The mechanical property evolution was consistent with the structural evolution found from APT. Samples aged at 450 and 500 degrees C all showed increasing hardness and decreasing impact energy. The embrittlement was observed to take place mainly during the first 10 h of aging and it could primarily be attributed to phase separation, but also substitutional solute clustering and possibly carbon and nitrogen segregation may contribute in a negative way.
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| 3. |
- Hutchinson, B., et al.
(författare)
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Microstructures and hardness of as-quenched martensites (0.1-0.5%C)
- 2011
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Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 59:14, s. 5845-5858
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Tidskriftsartikel (refereegranskat)abstract
- Four commercial steels with carbon contents in the range 0.1-0.5 wt.% have been examined in the as-quenched condition using electron microscopy, X-ray diffraction and atom probe tomography. The austenite had been deformed 0%, 10% and 30% prior to brine quenching. No influence of this deformation was evident on the martensite hardness or in any of the microstructure measurements. Increasing carbon content showed a well-known marked effect on the hardness but resulted in little refinement in the grain structure of the martensite. All crystal structures were cubic; no evidence of tetragonality was seen even at the highest carbon level but some systematic changes in grain boundary misorientations existed. The content of carbon in true interstitial solid solution deduced from X-ray line shifts was small (similar to 0.02 wt.%), and was independent of the total carbon content in the steel. Atom probe tomography showed that carbon was almost completely segregated to lath boundaries and dislocations but with an increasing density of segregates in the higher carbon steels. Calculations of diffusion distances confirmed that the segregation patterns were compatible with autotempering of the martensite during quenching. Analysis of different possible contributions to strength leads to the conclusion that segregated carbon atoms at defects behave similarly to carbon in true solid solution and that this is the largest single factor controlling the strength of as-quenched martensite. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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| 4. |
- Johnson, Lars, et al.
(författare)
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Blind deconvolution of time-of-flight mass spectra from atom probe tomography
- 2013
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 1879-2723 .- 0304-3991. ; 132, s. 60-64
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Tidskriftsartikel (refereegranskat)abstract
- A major source of uncertainty in compositional measurements in atom probe tomography stems from the uncertainties of assigning peaks or parts of peaks in the mass spectrum to their correct identities. In particular, peak overlap is a limiting factor, whereas an ideal mass spectrum would have peaks at their correct positions with zero broadening. Here, we report a method to deconvolute the experimental mass spectrum into such an ideal spectrum and a system function describing the peak broadening introduced by the held evaporation and detection of each ion. By making the assumption of a linear and time-invariant behavior, a system of equations is derived that describes the peak shape and peak intensities. The model is fitted to the observed spectrum by minimizing the squared residuals, regularized by the maximum entropy method. For synthetic data perfectly obeying the assumptions, the method recovered peak intensities to within +/- 0.33 at%. The application of this model to experimental APT data is exemplified with Fe-Cr data. Knowledge of the peak shape opens up several new possibilities, not just for better overall compositional determination, but, e.g., for the estimation of errors of ranging due to peak overlap or peak separation constrained by isotope abundances. (C) 2013 Elsevier By. All rights reserved.
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| 5. |
- Johnson, Lars, et al.
(författare)
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Spinodal decomposition of Ti0.33Al0.67N thin films studied by atom probe tomography
- 2012
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 520:13, s. 4362-4368
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Tidskriftsartikel (refereegranskat)abstract
- Details of the phase decomposition in NaCl-structure Ti0.33Al0.67N thin films deposited by cathodic arc evaporation are studied by atom probe tomography. We demonstrate that as-deposited films are in the earliest stage of decomposition for which electron microscopy and x-ray diffraction indicate a single-phase solid solution. Annealing at 900 degrees C further activates spinodal decomposition of the films, although pockets of unde-composed material remain after 2 h. N preferentially segregates to the AlN and TiN domains, causing the TiAlN matrix to be understoichiometric, by the energetics of N vacancies in TiAlN. The corresponding modulation in stoichiometry implies a Kirkendall effect, caused by different Al and Ti diffusivities.
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| 6. |
- Kadkhodazadeh, S., et al.
(författare)
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Towards quantitative three-dimensional characterisation of buried InAs quantum dots
- 2011
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Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 326:1
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Konferensbidrag (refereegranskat)abstract
- InAs quantum dots grown on InP or InGaAsP are used for optical communication applications operating in the 1.3 - 1.55 μm wavelength range. It is generally understood that the optical properties of such dots are highly dependent on their structural and chemical profiles. However, morphological and compositional measurements of quantum dots using transmission electron microscopy can be ambiguous because the recorded signal is usually a projection through the thickness of the specimen. Here, we discuss the application of scanning transmission electron microscopy tomography to the morphological and chemical characterisation of surface and buried quantum dots. We highlight some of the challenges involved and introduce a new specimen preparation method for creating needle-shaped specimens that each contain multiple dots and are suitable for both scanning transmission electron microscopy tomography and atom probe tomography.
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| 7. |
- Karlsson, Johan, 1984, et al.
(författare)
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Atomically resolved tissue integration
- 2014
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 14:8, s. 4220-4223
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Tidskriftsartikel (refereegranskat)abstract
- In the field of biomedical technology, a critical aspect is the ability to control and understand the integration of an implantable device in living tissue. Despite the technical advances in the development of biomaterials, the elaborate interplay encompassing materials science and biology on the atomic level is not very well understood. Within implantology, anchoring a biomaterial device into bone tissue is termed osseointegration. In the most accepted theory, osseointegration is defined as an interfacial bonding between implant and bone; however, there is lack of experimental evidence to confirm this. Here we show that atom probe tomography can be used to study the implant-tissue interaction, allowing for three-dimensional atomic mapping of the interface region. Interestingly, our analyses demonstrated that direct contact between Ca atoms and the implanted titanium oxide surface is formed without the presence of a protein interlayer, which means that a pure inorganic interface is created, hence giving experimental support to the current theory of osseointegration. We foresee that this result will be of importance in the development of future biomaterials as well as in the design of in vitro evaluation techniques.
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| 8. |
- Karlsson, Johan, 1984, et al.
(författare)
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Localized controlled drug delivery from mesoporous implants
- 2014
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Ingår i: Technical Proceedings of the 2014 NSTI Nanotechnology Conference and Expo, NSTI-Nanotech 2014. Washington, DC, United States, 15-18 June 2014. - 9781482258271
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Konferensbidrag (refereegranskat)abstract
- Mesoporous materials possess both a well-defined topography on the nanometer scale, and they may serve as hosts for drugs. In this work, titanium implants coated with mesoporous TiO2 thin films have been evaluated both in vitro and in vivo. Material characterization showed that, long-range ordered mesoporous TiO2, with a pore-size of 6 nm, and a narrow pore-size distribution were obtained. An in vivo study demonstrated that the films were robust enough to withstand the implantation procedure. The in vitro apatite formation experiments showed that formation of apatite was higher on the mesoporous surface compared to its nonporous counterpart. In a separate in vivo study, two osteoporosis drugs, alendronate (ALN) and raloxifene (RLX), were immobilised into the nanoporous oxide films. The in vitro drug release tests carried out showed a sustained release of both drugs. The osteogenic response after 28 days of implantation of the drug-loaded implants showed a significantly improved bone fixation.
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| 9. |
- Ohlund, Ceic, et al.
(författare)
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Effect of Ti on Evolution of Microstructure and Hardness of Martensitic Fe-C-Mn Steel during Tempering
- 2014
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Ingår i: ISIJ International. - : Iron and Steel Institute of Japan. - 0915-1559 .- 1347-5460. ; 54:12, s. 2890-2899
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Tidskriftsartikel (refereegranskat)abstract
- The effect of the addition of 0.042 wt.% of titanium on the relation between the evolution of the microstructure and the softening kinetics of quenched martensite in high-purity Fe-C-Mn steel has been studied during tempering at 300 and 550 degrees C. The evolution of the microstructure is characterized by measuring the cementite particle size, the martensite block size, the area fraction of martensite regions which contain a high dislocation density, the macroscopic hardness, the nano-hardness of martensite blocks boundaries, the nano-hardness of the matrix and the TiC-precipitate size during tempering. Nucleation of TiC-precipitates take place during annealing at 550 degrees C and starts earlier in regions close to the block boundaries, after 5-10 minutes, and thereafter in the matrix, after 10-30 minutes, due to the higher dislocation density in the regions close to the block boundaries. The TiC-precipitates slow down the recovery in regions of high dislocation density compared to the alloy without TiC-precipitates. The TiC-precipitates increase the macroscopic hardness of the steel after 30 minutes annealing at 550 degrees C. The growth of TiC-precipitates in martensite is simulated in good agreement with experimental observations by a model that takes into account: 1) capillarity effects, 2) the overlap of the titanium diffusion fields between TiC-precipitates, and 3) the effect of pipe diffusion of titanium atoms via multiple dislocations. The average, experimentally-observed, TiC-precipitate size is 69 +/- 48 Ti atoms.
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| 10. |
- 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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