Volume 101, Issue 3

Charles Crussard actively participated in the foundation of the IRSID laboratory in 1948. He integrated this institute in 1952 as chief of the Physical Metallurgy Department and among the scientific fields that he initiated were the plasticity and the recrystallisation of steels. Nowadays, these are still active research fields at the ArcelorMittal Research laboratory (formerly called IRSID) and the purpose of this paper is to illustrate the heritage of the research subjects that Crussard initiated and how his vision has influenced our work at IRSID.

Electrolytic copper powder, inert gas atomized prealloyed copper powder containing 3.5 wt.% Al, and a mixture of copper and commercial Al 2 O 3 powder particles (4 wt.% Al 2 O 3 ) were milled separately in a high-energy planetary ball mill for up to 20 h in air. The milling was performed in order to strengthen the copper matrix by grain size refinement and Al 2 O 3 particles. Milling in air of prealloyed copper powder promoted formation of fine dispersed Al 2 O 3 particles by internal oxidation. Hot-pressing (800 °C for 3 h in argon at a pressure of 35 MPa) was used for compaction of milled powders. Compacts from 5 and 20 h milled powders were additionally subjected to high temperature exposure (800 °C for 1 and 5 h in argon) in order to examine their thermal stability and electrical conductivity. The effect of different size and the amount of Al 2 O 3 particles on strengthening, thermal stability and electrical conductivity of the copper-based composites was studied. The results were discussed in terms of the effects of the grain size refinement along with micro- and nano-sized Al 2 O 3 particles on the strengthening of the copper matrix.

The stability of the microstructure at high temperatures was studied in an experimental Co–Re-based alloy. The experimental alloy is mainly strengthened by Cr-carbides, particularly by those in the form of thin lamellar plates. Electron microscopic investigation on samples exposed for up to 1 000 h to temperatures of 1 000 and 1 200 °C showed that Cr 23 C 6 type carbides present in the alloy in different morphologies are unstable at these temperatures. It was also observed that the alloy hardness dropped after exposing the samples to elevated temperatures and much of this loss occurred within the first 100 h. In-situ diffraction measurements with synchrotron radiation showed that carbide dissolution started as early as 3 h of holding at 1 000 °C. Moreover, in-situ small angle neutron scattering results indicated that the carbides at the grain boundaries and the blocky carbides dissolve first and then the thin lamellar carbides. Further, the enrichment of Cr in the Co-matrix phase, which took place due to the dissolution of Cr-carbides, stabilized a Cr–Re-rich σ phase. Although the dissolution of lamellar carbides results in a significant loss of strength, the formation of σ phase with extremely high hardness partly compensated the for loss. The σ phase is stable even at 1 200 °C.

We have successfully prepared NdGaO 3 films with the (h00) preferred orientation on YSZ(100) single crystalline substrate by metal – organic deposition. The structure and morphology of the NdGaO 3 films were investigated by X-ray diffraction and atomic force microscopy. It was found that the crystal orientation of the NdGaO 3 films depends on the heat treatment temperature and time. An optimal growth condition for highly textured NdGaO 3 films was obtained. The analysis by atomic force microscopy showed that the NdGaO 3 films are smooth and pinhole-free. Our results showed that the NdGaO 3 films prepared by the low-cost production method of metal – organic deposition could serve as a crystalline substrate with perovskite structure for many kinds of oxide electronic devices.

It is shown that a minimum derivation of the recently published unified equation for the temperature dependence of the self-diffusion coefficient in liquid metals can be also obtained from the similarity of interatomic potentials, using dimensional analysis. This relation is extended for the determination of the pressure and composition dependence of the self-diffusion coefficients by the use of pressure and composition dependent scaling parameters (melting point, atomic volume and mass).

The relationship between the microstructures and the properties of nano-scale Fe–Co magnetic particles formed in a copper alloy was investigated. Several structural aspects and physical properties of Fe–Co precipitates were investigated simultaneously using transmission electron microscopy, high resolution transmission electron microscopy, and superconducting quantum interference device magnetometry. The microstructure and magnetic properties of precipitates comprising both Fe and Co atoms evolved with isothermal annealing at 873 K. We found that the evolution of small coherent precipitates obeys the Ostwald ripening law; however, the coarsening rate of the particles increased after coherent particles transformed into incoherent precipitates. The coercive force varied, correlating with the evolution of precipitates.

The evolution of nano-scale Fe particles precipitated in a Cu – Fe alloy has been examined from the viewpoint of the relationship between the microstructure and magnetic properties, using conventional, high-resolution and Lorentz electron microscopy, and magnetic measurements. It has been revealed that spherical Fe particles have a tendency to align along the <001> direction in a Cu matrix at the early stage of precipitation. A twin-like structure developed when spherical Fe particles grew to approximately 40 to 60 nm in size. Lorentz microscopy was successfully applied to determine the direction and magnitude of the magnetic momentum of Fe particles.

The effect of grain size reduction on the corrosion inhibitor adsorption of nanocrystalline Fe produced by pulse electrodeposition was characterized using tafel polarization curves and electrochemical impedance spectroscopy. The grain size of a nanocrystalline surface was determined by means of scanning electron microscopy. The tests were carried out in 0.1 M sodium perchlorate (NaClO 4 ) and 0.1 M sodium sulphate (Na 2 SO 4 ) aqueous solutions separately. Results obtained revealed that the inhibition effect and corrosion protection of sodium nitrite inhibitor in near-neutral aqueous solutions increased as the grain size decreased from microcrystalline to nanocrystalline. This was attributed to the increased number of the active sites caused by nanocrystalline surface.

Creep damage by pore nucleation and growth limits the lifetime of components subjected to loading at high temperature. In this work, the creep damage evolution in the aluminium matrix composite AA6061 + 22 % (Al 2 O 3 ) P is observed in-situ by the fast-tomography technique using a miniature creep device. Reconstructions of the gauge volumes of the creep samples show particle delamination, pore formation and growth at 300 °C and additional particle fracture at 200 °C during the creep process. The results reveal that both the number of pores and the total pore volume show exponential growth with creep time, whereas the average volume of individual pores remains almost constant. The total pore volume increases linearly with the creep strain with a stress-dependent factor of proportionality.

The effect of increasing the amount of added grain refiner (Al-5Ti-B) and combined electromagnetic field on grain size and morphology has been investigated in horizontal direct chill casting of 7075 aluminum alloy. The results show the grain size and the grain morphology are both changed with increasing the amount of Al-5Ti-B added. The grain size continuously decreased with increasing the addition of grain refiner. The slope of the grain size versus grain refiner content curve changes at the point of 0.1 wt.% Al-5Ti-B, and the slope coefficient before the point is larger than that of after the point. The results related to the conglobulation of the nuclei. Without grain refiner additions, an obvious transition in grain size and morphology is observed with the application of combined electromagnetic field. The grain refining efficiency of combined electromagnetic field decreases with increasing the amount of grain refiner. However, even when the addition of grain refiner is 2 wt.% Al-5Ti-B, 24 % grain size reduction is still observed due to the effect of the combined electromagnetic field. This result shows that the combined electromagnetic field can enhance the grain refining efficiency of grain refiner.

NiWO 4 powders have been synthesized by reaction between NiCl 2 and Na 2 WO 4 aqueous solutions and following calcinations at different temperatures. X-ray diffraction and scanning electron microscopy analysis were used to characterize the powders. Single phase NiWO 4 powders were formed above a calcining temperature of 600 °C. X-ray diffraction analysis indicated that the NiWO 4 powders had a monoclinic structure and particle size of 26.8 nm and 30.3 nm for calcining temperatures of 600 °C and 700 °C, respectively. A little increase in intensity of the X-ray diffraction peaks was observed when increasing the calcining temperature from 600 °C to 700 °C. Scanning electron microscopy indicated that powders had uniform and very small particle size. The powders showed a broad blue-green emission band. The broad band of NiWO 4 powders calcined at 600 °C consisted of 423.2 nm (2.93 eV), 487.3 nm (2.54 eV) and two weak bands at 447.0 nm (2.77 eV), and 532.0 nm (2.33 eV). Small shifts in the peaks of excitation and luminescence and small increases in intensities were observed when increasing calcining temperature to 700 °C. The films were deposited using the sol-gel method and using the precipitate as starting materials. The deposited films showed a similar blue-green emission to that of the powders.

In this paper an integrated model has been utilized to predict thermo-mechanical behavior during friction stir welding of an aluminum alloy. A finite element code, ABAQUS, is employed to solve the governing equations of heat conduction and plastic deformation, while a rigid – viscoplastic material behavior is utilized and effects of different thermal and mechanical boundary conditions are considered in the simulation. To assess the accuracy of the model, predicted results have been compared with experimental data and good agreement has been observed.

The paper reports a study of temperatures of phase transitions of nine samples of real grades of low-alloyed steels, including one sample of pure iron, using differential thermal analysis. Temperatures of phase transitions were measured in the low-temperature interval (20 – 1 000 °C). Investigated systems were analysed at selected rates of heating/cooling and then temperatures of phase transitions for zero heating/cooling rate were determined. The results obtained are compared with temperatures of the equilibrium metastable diagram Fe – C, with results from the software IDS and with temperatures of phase transitions calculated according to relations published in available literature. It follows from the results that differences, sometimes considerable ones, still exist between experimental and theoretical data, which implies the necessity for further systematic research in this area.

Equal channel angular extrusion (ECAE) experiments of an extruded Mg–Zn–Y–Zr alloy with an intense basal texture were performed up to 8 passes at 250 and 350 °C through route Bc (billets with a rotation of 90° in the same direction between passes) and route A (without rotation between passes). It was found that under these ECAE conditions significant grain refinement was achieved. The initial texture of the alloy gradually altered as the number of ECAE passes increased. The ductility of the alloy was improved in all the cases after eight passes. The yield strength of the alloy ECAEed through route Bc considerably decreased with the passes increasing, as a result of the formation of the texture component with the basal planes inclined at about 45° to the ECAE direction. The yield strength of the material ECAEed at 250 °C with a finer grain structure was considerably lower than that at 350 °C with a coarser grain structure. This abnormal phenomenon was attributed to more crystals in the former being oriented to be more favorable for basal slip.

The 3-D heat conduction equation was numerically solved and the temperature distribution inside two special metallic frames, loaded with the proper number of reinforced bars, encased by normal strength concrete in the final columnar form, and subject to intense fire conditions, was computed by time. Typical temperature profiles were applied for the simulation of the cellulosic and hydrocarbon kinds of fire. Heat transfer by radiation and convection was included in the surrounding the column medium under fire, testing various convective heat-transfer coefficients. Computational results were analyzed until the critical time period in which the integrity and the mechanical strength of the column were reversible, considering fire abatement until that time.

High-speed cutting is one of the key issues in mould manufacturing. But to apply high-speed milling to mould manufacturing, unlike conventional milling, it is necessary to define specific cutting parameters. This article aims to define the influence of milling strategies and cutting parameters, such as cutting speed, feeding speed, cutting tool tilting angle, on the process stability. Long tool life and cutting strategy have a major influence on the results of machining hardened steel. Machining with drawing cut and down-cutting in copper and with drawing cut and up-cutting in hardened steel gave the best results with respect to tool wear and surface quality. Tool approach across the feeding direction results in heavy impact loads on the tool which lead to heavy tool wear and substantial dimensional deviations. Good surface quality is achieved in machining of a work piece of 2 363 steel (X100CrMoV51) hardened to 60 HRC, using the strategy of up-cutting with drawing cut and a tool approach with a tilting angle of 15 degrees. While up-cutting allows for achieving better surface quality, down-cutting provides longer tool life than up-cutting for all angles of approach.

The effect of solution heat treatment on the age hardening capacity of dendritic and globular AlSi7Mg0.6 alloys was investigated in the present work to find out if solution treatment times are in fact shorter for rheocast parts. The morphology of the α-Al matrix, whether dendritic or globular, has no effect on the response of the alloy to T6 treatment. A solution treatment at 540 °C for 2 h suffices to fully solutionize the Mg and Si and the age hardening capacity of the AlSi7Mg0.6 alloy is impaired when it is 1 h or shorter. This is true for both dendritic and globular alloys. The expected favourable impact of the globular structure on the solution treatment times is believed to be offset by the relatively coarser structure in the globular alloy with respect to its dendritic counterpart.