Search results for "engineering.material"
showing 10 items of 2352 documents
Scale composition and oxidation mechanism of the Ti–46Al–8Nb alloy in air at 700 and 800 °C
2011
It is known that the oxide scale formed on TiAl alloys is generally composed of a mixture of alumina (Al2O3) and titania (TiO2). The presence of niobium changes the activities of Ti and Al and influences the kinetics of oxidation and oxide layer composition. In this work, the Tie46Ale8Nb alloy was subjected to cyclic oxidation in air at 700 � C (for 2 and 24 h) and 800 � C (for 300 h). Scale composition was analyzed by means of different techniques including X-ray photoelectron spectroscopy, X-ray diffraction and secondary ion mass spectroscopy. The scale consisted of several layers. The outer layer was built of alumina (amorphous or with very fine grains), whereas the inner layer e mainly …
Crosslinked Spherical Nanoparticles with Core-Shell Topology
2000
Core–shell microgels are crosslinked nanosized spherical particles with a chemical composition that is different on the surface compared to the core region. By employing a core with special optical properties, e.g., a core labeled either with organic dye molecules or noble metal clusters (see Figure), these particles are perfectly suited as optical tracers in diffusion measurements. Here, the shell may be important for several reasons: (i) as a protective coating to suppress any influence of the labels on particle mobility, (ii) to optically separate individual particles even at high concentrations, and (iii) to compatibilize the particles with e.g., polymeric chains. Recent developments in…
FINITE DIFFERENCE METHOD-BASED SIMULATION OF TEMPERATURE FIELDS FOR APPLICATION TO ORTHOGONAL CUTTING WITH COATED TOOLS
2005
ABSTRACT A finite difference method was proposed to model the effect of a variety of tool coatings on the magnitude and distribution of temperatures through the tool-chip contact region and the coating/substrate boundaries. For each workpiece-tool pair tested the intensity of uniformly distributed heat flux and relevant analytically obtained values of the heat partition coefficient were assumed to change with variations of cutting speed and the corresponding friction. In this case the simulation of an orthogonal machining of AISI 1045 steel was performed using special computing algorithm with elementary balances of induced energies (MBE). It is concluded that the temperature contours obtain…
Influence of the mode of introduction of a reactive element on the high temperature oxidation behavior of an alumina-forming alloy. Part I: Isotherma…
2004
Several routes of yttrium introduction were applied to test the high temperature oxidation performance of a FeCrAl alloy. Isothermal oxidation tests were described in a previous paper (Part I of this paper in this journal, 2004, 55, 352). Cyclic oxidation tests were performed in air under atmospheric pressure on blank specimens, Y 2 O 3 sol-gel coated-, Y 2 O 3 metal-organic chemical vapor deposited (MOCVD)-, yttrium ion implanted-alloys, as well as on a steel containing 0.1 wt.% of yttrium as an alloying element. For the 20 hours cycles, all the samples, except FeCrAl-0.1Y, exhibit weight losses after a few cycles, indicating drastic spallation of the oxide scales. The MOCVD coated specime…
Reactive Element (Y,Ce) Effect on Stresses Determined In-Situ during Iron Oxidation at 800°C
2001
In-situ stress determinations by X-ray diffraction have been performed during pure iron oxidation (p(O 2 ) = 2 x 10 -3 Pa, T = 800°C). On yttrium implanted specimens the stress level is close to zero before oxidation. On CeO 2 coated specimens, the initial compressive stress due to surface polishing is not modified by the coating. During oxidation, the in-situ compressive stress value determined in the Fe (1-x) O scale, is not strongly dependent upon the reactive element nature. Nevertheless, the stress evolution during cooling and residual stresses determined after cooling to room temperature are very different. Blank and CeO 2 coated specimens show relatively high compressive stresses whe…
Laser shock processing with two different laser sources on 2050‐T8 aluminum alloy
2011
PurposeThe purpose of this paper is to conduct a comparative study of the surface modifications induced by two different lasers on a 2050‐T8 aluminum alloy, with a specific consideration of residual stress and work‐hardening levels.Design/methodology/approachTwo lasers have been used for Laser shock peening (LSP) treatment in water‐confined regime: a Continuum Powerlite Plus laser, operating at 0.532 mm with 9 ns laser pulses, and near 1.5mm spot diameters; a new generation Gaia‐R Thales laser delivering 10 J‐10 ns impacts, with 4‐6mm homogeneous laser spots at 1.06 mm. Surface deformation, work‐hardening levels and residual stresses were analyzed for both LSP conditions. Residual stresses …
Oxidation mechanism of the Inconel 601 alloy at high temperatures
2010
The Inconel 601 alloy oxidation was performed in air, in the temperature range 1000-1150 °C, during 90 h. Kinetic results show that the parabolic behavior is always followed in this temperature range. The Arrhenius plot of the kp values shows two different activation energies. Between 1000 and 1050 °C the activation energy is E a1 = 160 ± 10 kJ/mol. In the 1050-1150 °C temperature range a higher value is calculated E a2 = 252 ± 20 kJ/mol. The E a2 value and the X-ray diffraction (XRD) results and scanning electron microscope (SEM) energy dispersive X-ray spectroscopy (EDS) examinations are in accordance with a scale growth mechanism limited by a growing Cr 2 O 3 scale acting as a diffusion …
Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure
2011
One of challenges in improving the performance and cost-effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR – area specific resistance – value). Such degradation are unacceptable regarding the long-term operation (>40 000 h). A previous study 1 demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) l…
High temperature alloy chloridation at 850°C
2007
The resistance of eight alloys against chloridation was tested at 850 °C in Ar/Cl 2 (2.5% Cl 2 ) for 15 min. Pre-oxidation treatments were performed for 1 h and 8 h at 850°C in order to produce a thin, adherent and protective oxide scale able to improve the chloridation behaviour of the tested materials. The chloridised sample morphologies were compared to the morphologies observed on the non pre-oxidised samples. The alloys containing a large amount of iron did not exhibit any chloridation resistance, even after pre-oxidation, and were severely damaged. The nickel based alloys gave interesting results but were also attacked by chloride, probably by the "active oxidation" mechanism. The dur…
High temperature alloy chloridation at 850°C. Part I: Comparison of Ni-based and Fe-based alloy behaviour
2007
Eight alloys were tested under Ar/Cl 2 atmosphere at 850 °C for 15 min and 1 h. Their gross and net weights were evaluated together with the base metal consumption. Macroscopic and microscopic micrographs, associated with chemical analyses and X-ray diffraction gave the composition and microstructure of the corrosion products. Huge differences were observed if one compared the nickel based alloy behaviour to that of the iron based alloy. Molybdenum and tungsten could also play a role, but it was not clearly defined until now. A tentative evaluation of the best candidates will be given, according the experimental conditions of this work and the chosen criteria. A corrosion index was establis…