Papers by Keyword: DRX

Abstract: Fe-10wt% La (OH)₃ composite powders have been fabricated by ball milling, under argon atmosphere for milling periods of 0, 5 and 10 h, respectively. Changes in structural, morphological, thermal and magnetic properties of the powders during mechanical alloying and during subsequent annealing have been examined by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM). XRD results: showed the formation of new phases (Fe and LaFeO3 perovskite) created through the ball milling. The results showed that the crystalline size of ball milled powders decreased with increasing the milling time. In fact, after 10 h of ball milling, La (OH)₃ changes from nanostructure in amorphous structure. The magnetic measurements display a distinct saturation magnetization and coercivity.

Abstract: From the hard and anti-corrosions coatings, we found the chromium carbides, these components were discovered by large studies; like thin films since years ago. They were pointed a good quality for the protection of steel, because of their thermal and mechanical properties for this reason, it was used in many fields for protection. Plus: their hardness and their important function in mechanical coatings. The aim of this work joins a study of the effect of the thermal treatment on mechanical and structural properties of the Cr/steel system. Thin films were deposited by cathodic magnetron sputtering on the steel substrates of 100C6, contain 1% wt of carbon. Samples were annealing in vacuum temperature interval between 700 to 1000 °C since 45 min, it forms the chromium carbides. Then pieces are characterising by X-ray diffraction, X-ray microanalysis and scanning electron microscopy. Mechanical properties are analysing by Vickers test. The X-ray diffraction analyse point the formation of the Cr₇C₃, Cr₂₃C₆ carbides at 900°C; they transformed to ternary carbides in a highest temperature, but the Cr₃C₂ doesn’t appear. The X-ray microanalysis shows the diffusion mechanism between the chromium film and the steel sample; from the variation of: Cr, Fe, C, O elements concentration with the change of annealing temperature. The variation of annealing temperature shows a clean improvement in mechanical and structural properties, like the adhesion and the micro-hardness.

Abstract: Ternary Fe₇₂Al₂₆Sn₂ and Cu₇₀Fe₁₈Co₁₂ alloys were obtained by mechanical alloying of pure Fe, Al, Sn, Cu and Co powders using a high energy ball mill. X-ray diffraction and electron microscopy supported by magnetic measurements have been applied to follow changes in the microstructure, phase composition and magnetic properties in dependence on milling time. With the increase of milling time all Al and Sn atoms dissolved in the bcc Fe and the final product of the MA process was the nanocrystalline Fe (Al, Sn) solid solution in a metastable state with a large amount of defects and mean crystallite size of 5 nm. However, the obtained crystallite size value is about 10 nm for the ball milled Cu₇₀Fe₁₈Co₁₂ powders. The electron microscope observations show the morphology of powder particles. Magnetic properties of the nanocrystalline mechanically alloyed FeAlSn and CuFeCo were also investigated and were related to the microstructural changes.

Abstract: Commercial copper and iron powders were used as starting materials. These powders were mechanically alloyed to obtain Cu_(100-x) Fe_x supersaturated mixture. The milling duration was chosen in such a way as to obtain a nanostructured mixture and to form a supersaturated solid solution of CuFe; the powder mixture was used to deposit CuFe on a glass substrate. The elaboration of our films has been carried out using thermal evaporation process (physical vapor deposition) under 1 × 10^-6 mbar vacuum from an electrically heated tungsten boat, using the supersaturated solid solution Cu_(100-x) Fe_x powder obtained by mechanical alloying. The films deposition has been done on glass substrates. In this study, we present the composition effect on the structural and magnetic proprieties of Cu_(100-x) Fe_x powder and thin films. The chemical composition, structural and magnetic proprieties of milled powders and thin films were examined by SEM, TEM, XRD, XRF and VSM.

Abstract: This paper presents preliminary results of modified Montmorillonite samples and the surface treatment with hydrochloric acid were investigated. The modification of this Montmorillonite surface, negatively charged and exchanged by organic cations such as alkylammoniums (Trimethylexadecyl C16 and Trimethyloctadecyl C18), yields a modified Montmorillonite (MMt). The resulting organo-mineral material acquires an organophilic character which could be used in several applications. The organically modified MMts were prepared by an ion exchange process in which sodium ions were replaced by alkylammonium ions. This material, used in the present work, is an Algerain montmorillonite obtained from MAGHNIA (West Algeria). Octadecyltrimethylammonium and hexadecyltrimethylammonium chlorides, utilized here as surfactants activators to organophilize the Montmorillonite. The microstructure of this modified Montmorillonite was characterized by XRD-diffraction with which the effects of the intercalation associated to the conformation of the long hydrocarbon chain were investigated. The results obtained showed that the amounts of hydrochloric acid added to these modified materials affect considerably the conformation of the intercalated surfactants. Their physical characteristics were determined by infrared spectrophotometer (FT-IR) and their chemical modification revealed that their thermal properties have been advantageously improved.

Abstract: The effect of strain rate and strain on the hot compression behaviour of Ti6Al4V has been analysed to understand the microstructural evolution and restoration behaviour. Cylindrical samples with partially equiaxed grains were deformed in the α+β region at different thermo-mechanical conditions. EBSD has been used to study the microstructural behaviour and the restoration mechanisms. The microstructural evolution showed a complex restoration behaviour, where both fragmentation and nucleation of new grains have been observed. The volume fraction of the equiaxed grains increased with an increase in the strain, but oppositely decreased with the strain rate. At the same time the average grain size of the equiaxed grains decreased with an increase in both the strain and strain rate. The measured activation energy for deformation revealed a good agreement with reported values in the literature.

Abstract: The dynamic recrystallization (DRX) behavior of the new lead-free machinable brass was investigated by compression tests on a Gleeble-1500 thermal mechanics simulator in the temperatures range of 823-973 K and strain rates ranging from 0.01 to 1 s^-1. On the basis of the hot compression data, critical stress (strain) or peak stress (strain) were determined with the assistance of the strain hardening rate versus stress curves. The dynamic recrystallization kinetics model of the lead-free machinable brass was established to evaluate the DRX behavior. The results will be beneficial to optimizing hot working processes of this new lead-free machinable brass.

Abstract: Dynamic recrystallization (DRX) characteristics of an 5182 Al alloy was investigated at temperatures ranging from 673 K-773 K and constant strain rates of 0.01 s^-1, 0.1 s^-1, 1 s^-1, 10 s^-1, and 50 s^-1. The average grain size of the as-casted alloy was 160 μm and was refined to 20 μm via deformation at 773 K, 50 s^-1 to a strain level of 0.5 (40%). The true stress-strain curves were determined and divided into two main groups based on the temperatures and strain rates. The activation energy of the DRX in the examined aluminum alloys was calculated, being 175,87 kJ/mol. During the crystallization process compound phases were crystallized along the border of initial grains due to the great content of Mg, Mn and Fe. It was deduced from the metallography examination that most of the new grains formed via necklacing mechanism from the mentioned borders during the DRX.

Abstract: The influence of the strain sequence during slab hot rolling (also known as “roughing”) on the evolution of austenite in plain carbon, C-Mn-V and C-Mn-Nb-Ti-V steels was investigated. Reheating and roughing simulations were conducted in a Bähr deformation dilatometer using a constant austenitising temperature, constant soaking time and various heating rates and roughing strain sequences. Stress analysis was used to quantify the austenite softening behaviour and the prior austenite grain size was measured from quenched specimens. The austenite grains of the plain carbon steel were coarser than those of both microalloyed steels, with the C-Mn-Nb-Ti-V grade being the finest due to effective pinning of the grain boundaries. Pass strains greater than 0.2 were sufficient for initiation of dynamic recrystallisation (DRX) for the C-Mn and C-Mn-V steels and led to uniform austenite microstructure with austenite grain sizes less than 40µm after the roughing stage.