F. Audebert

Aluminum-base Al-Fe-Nb amorphous and nanostructured alloys

The aim of this work is to contribute to the development of new, high specific strength Al alloys. Particularly, this research was focused on alloys with improved thermal properties so that they could withstand the subsequent compacting processes required for obtaining dense products without losing their properties. With this criterion the Al-Fe-Nb system was chosen. This paper presents the preliminary results concerning Al-rich Al-Fe-Nb amorphous and nanostructured alloys as well as their evolution with temperature.

Mechanical and corrosion behaviour of Al-Fe-Nb amorphous alloys

The development of new nanostructured and amorphous Al-alloys gives much hope to develop new improved light materials with high specific strengths and good corrosion resistance. In a previous work [1], the amorphicity range in Al-rich Al-Fe-Nb alloys produced by the melt-spinning technique was determined. In this work, the mechanical and corrosion behaviour of these alloys in the amorphous and partially amorphous states, is reported. The mechanical characterisation was carried out by microhardness and nanoindentation tests, the latter in order to determine Youngs modulus. The corrosion behaviour has been evaluated by means of potentiodynamic polarisation techniques in a chloride containing solution. Results have been compared with those obtained for crystalline alloys with the same chemical composition. X-ray photoelectron spectroscopy (XPS) has been used to analyse the oxide film formed in melt-spun samples during the rapid quenching under air atmosphere. The Al-Fe-Nb fully amorphous alloys exhibit low Youngs moduli, high microhardness values and a good corrosion behaviour.

Corrosion behaviour of Ni-B-Sn amorphous alloys

In a previous work it was found that the addition of a small quantity of tin increases the glass forming ability (GFA) of the Ni-B binary system. Glass formation was observed in the nickel rich corner of the Ni-B-Sn ternary system for a tin content less than 15 at.%. The present work is concerned with the evaluation of the corrosion behavior of alloys belonging to the nickel-rich corner of the Ni-B and Ni-B-Sn systems in the amorphous and crystalline state, using electrochemical techniques.

Approach to the atomic structure of amorphous Al-Fe-Nb

Abstract The atomic structure and the glass-forming ability of amorphous Al-Fe-Nb have been explored in this study. The study has been carried out by means of scattering vector analysis of the structure factor obtained from X-ray spectra. The X-ray spectra show a pre-peak in the structure factor, which is attributed to chemical short-range order, together with the main amorphous peak. The average interatomic distances A1-Tm (Tm = transition metal) and Al-Al are shortened, and the strong interaction between Al and Fe must be responsible for the short-range order. The atomic size ratio criterion is discussed below, and it is proposed that the short-range order could be similar to the order of the quasicrystalline icosahedral phase in the Al-Fe-X alloys.

Effect of Nb on nanoquasicrystalline Al-based alloys

Nanoquasicrystalline Al-based alloys, containing icosahedral particles in an α-Al matrix, exhibit high strength at elevated temperature. The metastability of the quasicrystals can limit the use of these alloys. In the present work, the microstructural evolution of Al93(Fe3Cr2)7 and Al93Fe3Cr2Nb2 (at%) alloys was studied using heat treatments and structural characterization by XRD, TEM and STEM-EDX analysis. It was observed that the Nb is dissolved in the Al–Fe–Cr icosahedral phase. This provides higher thermal stability, retaining the fine nanoquasicrystalline microstructure for longer times at high temperature.

Yttria and ceria doped zirconia thin films grown by pulsed laser deposition

The Yttria stabilized Zirconia (YSZ) is a standard electrolyte for solid oxide fuel cells (SOFCs), which are potential candidates for next generation portable and mobile power sources. YSZ electrolyte thin films having a cubic single phase allow reducing the SOFC operating temperature without diminishing the electrochemical power density. Films of 8 mol% Yttria stabilized Zirconia (8YSZ) and films with addition of 4 weight% Ceria (8YSZ + 4CeO2) were grown by pulsed laser deposition (PLD) technique using 8YSZ and 8YSZ + 4CeO2 targets and a Nd-YAG laser (355 nm). Films have been deposited on Soda-Calcia-Silica glass and Si(100) substrates at room temperature. The morphology and structural characteristics of the samples have been studied by means of X-ray diffraction and scanning electron microscopy. Films of a cubic-YSZ single phase with thickness in the range of 1-3 µm were grown on different substrates.

Nanostructured Al-Mm-Ni-(Fe,Co) Alloys Produced by Devitrification

Amorphous and nanocrystalline structures can easily be obtained in quate rnary systems, containing Al, lanthanide metal (Ln) and two late trans i io metals. Replacement of Ln by Mischmetal (Mm) reduces the cost of the materials st udied, as Mm is several times cheaper that pure lanthanide elements. Fully amorphous ribbons of Al-Mm -Ni-(Fe,Co) alloys, containing 4 and 5 at.% of Mm, were produced by the melt-spi nning technique. Structures, consisting of nanoparticles, embedded in amorphous matrix we re obtained by additional isothermal annealing of the initially fully amorphous al loys. X-ray diffractometry, transmission electron microscopy and differential scanning calorim etry were used for characterisation of the crystallization process and its products. It was found that the replacement of Al by Mm increases the thermal stability of the alloys. Isothermal annealing was found to be an effective method for producing a new group of nanocry stalline Al-based alloys. Introduction Amorphous and nanostructured Al-based alloys are interesting, mainly for their excellent mechanical properties. Amorphous Al-based alloys exhibit tensile st rength about twice that of the highest values for commercial crystalline Al-based alloy s [1]. Structures consisting of a mixture of fcc-Al nanoparticles and an amorphous matrix further improve tensile strength and microhardness, combined with good bending ductility [2]. To date such str uctures have been obtained in ternary and quaternary systems, containing lanthanide met al (Ln) and transition metals (TM), by isothermal annealing of initially fully amorphous ribbons [3,4]. Re placing Ln by Mm (Ce-50.3 at.%, La-43.5 at.%, Pr-5.9 at.% and Nd-0.3 at.%) reduces t he cost of the materials studied, as Mm is several times cheaper than pure la nthanide elements. Mixed structures of fcc-Al nanoparticles embedded in amorphous matrix wer e obtained by devitrification of amorphous Al-Mm-Ni-Cu alloys [5]. The objective of the current work was to investigate the effect of annealing temperature and chemical c omposition on the volume fraction of fcc-Al nanoparticles produced. Experimental Ingots of quaternary Al 88Mm5Ni5(Fe,Co)2, Al88Mm4Ni5(Fe,Co)3 and Al87Mm5Ni5(Fe,Co)3 alloys were prepared from pure elements by arc melting in an argon atmosphere. During melt spinning, the melt is ejected from the crucible onto a rotating coppe r wh el at peripheral speeds of 30 40 m s . By this technique, it is possible to quench the melt at a rate of 10-10 K s. The resulting ribbons were typically 2-3 mm wide and 30-40 m thick. Nanostructures were obtained by isothermal annealing of initially fully amorphous ribbons. The microstructures of the ribbons were studied by X-ray diffraction (XRD) using CuKα radiation and by transmission electron microscopy (TEM). Crystallization emperatures and heat of crystallization were determined by differential scanning calor imetry (DSC). The volume Solid State Phenomena Online: 2003-06-20 ISSN: 1662-9779, Vol. 94, pp 71-74 doi:10.4028/www.scientific.net/SSP.94.71

Contribution to the study of the MgNiSn system

A new phase was observed in the MgNiSn system by metallographic examination, X-ray diffraction and Mössbauer spectroscopy. Quantitative analysis with electron probe micro-analysis showed that its composition was Mg75Ni15Sn10. The solubility of Sn in Mg2Ni was also determined.

Al Effect on the Structure of the Spray Formed Fe88Si12 (at%) Alloy

Fe-Si alloys have excellent soft magnetic properties, specially around 12 at% Si. However, its industrial application is limited because of the lack of ductility, which causes cracking during rolling operations for the fabrication of thin sheets. The reason of the brittleness of the high silicon alloys is a disorder/order reaction at low temperatures. The aim of this work is to analyze the effect of the addition of Aluminum on the crystalline structure of Fe-Si alloys. Samples with a chemical composition of Fe88Si12 and Fe87Si12Al1 (at%) were prepared by Spray Forming. The structure was studied by means of X-ray diffraction and Mössbauer Spectroscopy. The presence of the DO3 and α- Fe phases were observed

Hot Extrusion of Nanostructured Al Alloy Powder: Extrusion Ratio and Temperature Effect on the Microstructure and Mechanical Properties

A nanostructured aluminium alloy powder, prepared by rapid solidification via gas atomization, was consolidated into bulk material under various processing conditions via hot extrusion. The microstructure modifications and mechanical properties of the consolidated alloys as a function of the extrusion conditions were investigated. The increase in the extrusion-load with the increase of extrusion-rate and decrease of temperature are shown and discussed in association with the modification in the microstructures. The differences in mechanical properties measured by compressive tests are also discussed in association with the extrusion parameters. Furthermore, suggestions are given for rationalising the extrusion ratio and temperature conditions for the consolidation of nanostructured aluminium alloy powders via hot extrusion.