Papers by Author: Eric Fleury

Abstract: Positron annihilation lifetime spectroscopy (PALS) has been applied to study if the microstructure changes in Co80Zr10V10 and Co65Zr10V25 metallic glasses after heat treatment. Samples in as-quenched state were isothermally annealed at chosen temperatures in the temperature range 100°C - 580°C for 1 hour. In spite of differences of chemical composition and magnetic properties the obtained dependencies of positron lifetime on annealing temperature do not differ significantly for lower temperatures. The higher increase of positron lifetime for Co65Zr10V25 than that for Co80Zr10V10 indicates differences in crystallization in the two metallic glasses studied.

Abstract: With the aim of replacing Pd coating layer currently used for the dissociation and recombination of hydrogen molecules, the performance of Nb and Ta thin layers as catalystforhydrogen permeationwas evaluated at 673 K.Although not as efficient as Pd, Nb and Ta coating layers can nevertheless provide a reasonable H2 dissociation and recombination rates. Thereduced values of hydrogen permeabilityin comparison to that of Pd were explained by the reduced catalytic properties of Nb and Ta and the formation of hydrides on the surface.

Abstract: The hydrogen permeation properties of the Pd-coated Ni37.5Nb27.5Zr25Co5Ta5 amorphous membranes have been investigated at 673 and 723K for 720 hours (1 month). Values of the hydrogen permeability during these long term tests were found to be reduced of about 50 and 30 % at 673 and 723K, respectively. The reduction in the hydrogen permeability could be correlated to the change in the composition of the coating as well as at the interface between Pd coating and Ni-based amorphous membrane.

Abstract: Grain boundary serrations were produced in heat-resistant austenitic stainless steel containing Cu by applying after solution heat-treatment a holding time in the range 700-800oC between 30 minutes to 3 hours. These special treatments provide an enhancement of the tensile ductility of about 40 and 113%at room temperature and 750oC, respectively, while no significant change in the yield stress and tensile strength could be observed.

Abstract: The compositional dependency of the glass forming ability (GFA), magnetic and mechanical properties of the Fe52Co20B20Si4Nb4 bulk metallic glass was investigated by means of the partial substitution of Co either by Al, V or Mo elements. A minor concentration of these elements enabled an increase of the GFA and fully amorphous rods of 4 mm diameter were successfully fabricated for the Fe52Co19B20Si4Nb4Al1, Fe52Co17B20Si4Nb4V3 and Fe52Co17B20Si4Nb4Mo3 alloys. While the addition of Al resulted in an increase of the magnetization saturation, V appeared as the most effective element to enhance the plastic deformation under compression.

Abstract: In this paper, we present results of an investigation on the physical, mechanical, chemical properties and processing ability of the Cr2AlC ternary carbide bulk material synthesized by hot pressing technique. The combination of excellent properties indicated that Cr2AlC ternary carbide alloy could be potential candidate materials as bipolar plates in polymer membrane fuel cell (PEMFC).

Abstract: The hydrogenation characteristics and embrittlement behavior of Ti50Zr(50-x)Cux alloys (x=25,33,40) are reported. The hydrogenation kinetics decreased with increasing Zr-content. Though the Ti50Zr25Cu25 alloy showed the slowest kinetics, it absorbed large amount of hydrogen (~2.4 wt.%) and exhibited the best resistance against hydrogen embrittlement. The excellent characteristics of Ti- Zr-Cu alloys in hydrogen environment indicated that they are promising materials in future for energy applications.

Abstract: Ti50Zr25Cu25 in-situ composite ribbons consisting of metastable β-Ti crystalline phase in an amorphous matrix was studied for its structural stability and mechanical properties after hydrogenation. On annealing, dissolution of the metastable β-Ti phase occurred. On hydrogenation, upto ~60 at.% hydrogen was obtained and hydrogen-induced amorphization occurred. The fracture strength of the hydrogenated composite indicated that it was mechanically stable even for high hydrogen contents.

Abstract: This works deals with the deposition of Ti-Zr-Ni icosahedral quasicrystalline powders by low vacuum plasma spray technique and the performances of the resulting coating layers. The microstructure of the coatings, as analyzed by X-ray diffraction and TEM techniques, consisted of nanometer-sized W-Ti50Zr35Ni15 1/1 cubic approximant and TiZrNi Laves phases as well as a low volume fraction of submicrometer-sized ZrO2 phase. The absence of the icosahedral phase in the coating layers was explained by the loss of Ti during plasma spraying. The shift in the composition and the presence of the ZrO2 phase within the coating layers are believed to be responsible for the reduced microhardness and corrosion performances evaluated by electrochemical tests in a Hanks’ Balance Salt Solution at 37oC.

Abstract: An important characteristic of a steam power plant is its ability to maintain reliability and safety of the plant against frequent start-ups and load changes. Transient regimes arising during start-ups, shut-downs and load changes give rise to unsteady temperature distribution with time in steam turbine rotor(HP/IP), which results in non-uniform strain and stress distribution. The rapid increase of temperature and rotational speed during starts-ups, especially, makes conditions more severe and causes main components’ damage and reduction of life span for steam turbine. Thus accurate knowledge of thermal and centrifugal stresses are required for the integrity and lifetime assessment for the turbine rotor. So far, only elastic calculations are currently performed for simplicity. However, it is well known that the materials of steam turbine rotor deform inelastically at high temperature. Existing models proposed to describe the viscoplastic(rate-dependent) behavior are rather elaborate and difficult to incorporate with computer simulations in the case of complex structures. In this paper, the life assessment for steam turbine rotor was established by combining the inelastic behavior and the finite element method. The inelastic analysis was particularly focused on viscoplastic behavior that is simple enough to be used effectively in computer simulation and matches the essential features of the time-dependent inelastic behavior of materials reasonably well for cyclic loading under non-isothermal conditions. Using this study, life consumption of steam turbine rotor can be obtained.