Mohamed Azzaz

Influence of Temperature and Chloride Concentration on Passivation Mechanism and Corrosion of a DSS2209 Welded Joint

The passivity behavior of a 2209 duplex stainless steel welded joint was investigated using potentiodynamic polarization, Mott-Schottky analysis and EIS measurements. In order to evaluate the contribution of temperature, chloride concentration and microstructure, a sequence of polarization tests were carried out in aerated NaCl solutions selected according to robust design of a three level-three factors Taguchi L9 orthogonal array. Analysis of signal-to-noise ratio and ANOVA were achieved on all measured data, and the contribution of every control factor was estimated. The results showed that the corrosion resistance of 2209 duplex stainless steel welded joint is related to the evolution of the passive film formed on the surface. It was found that the passive film on the welded zone possessed n- and p-type semiconductor characteristics. With the increase of solution temperature and chlorides concentration, the corrosion resistance of the passive film is more affected in the weldment than in the base metal.

Grain Size Influence on Microwave Absorption Properties in Nanocrystalline Fe40Co60

The work we have undertaken consists of preparing nanocrystalline Fe40Co60 powders by the Mechanical Alloying (MA) route. Characterization of obtained powders was applied on two steps. First, structural properties were investigated. X-ray Diffraction (XRD) was used to identify the formation of a disordered α (Fe40Co60) solid solution with a bcc lattice after 60h milling. By the Halder-Wagner approach lattice size, average grain size and residual strain were fixed. The morphology of milled powders was investigated by Scanning Electron Microscopy (SEM). Then bulk specimens were prepared by cold compaction for microwave measurements. Microwave dielectric permittivity and conductivity were determined using cavity perturbation technique. Microwave absorbing characteristic was measured according to line transmission method. Results obtained confirm that the developed structure after milling is the main factor that influences the microwave properties of nanocrystalline Fe40Co60 powders compared to elemental Fe.

Structural, Mechanical and Magnetic Properties of Mechanically Alloyed Fe40Co60 Powders

In this work we report on the structural, mechanical and magnetic properties of mechanically alloyed Fe40Co60 powders. Alloying formation, grain size, lattice parameter and internal strain were investigated using X-Ray Diffraction (XRD) measurements. The morphological aspect of the nanostructured powders was analysed by means of the Scanning Electron Microscopy (SEM). Compacted pastilles with circular shape have been under Vickers test of micro Hardness and magnetic measurements of Hysterisis loops. Discussed results according to milling time show that after 60 h milling the grain refinement is about 15.59 nm with internal strain of around 0.5809 %. The micro hardness increases with the decrease of the grain size and the hysterisis loop at 60 h milling is enhanced in term of decreased coercivity.

How Fe60Co40 and Fe72Al28 Nano-Alloys Produced by Mechanical Alloying Behave when Exposed to Microwaves

Fe60Co40 and Fe72Al28 nano-alloys were synthesized from elemental powders via highenergy mechanical alloying. The prepared samples were characterized using X-ray diffraction, scanning electron microscopy and X-band waveguide to measure the reflection loss in a frequency range of 9-10 GHz. The XRD patterns show that disordered Fe60Co40 solid solution with a bodycentred cubic structure is formed for milling times longer than 12 h, and after 4h milling, the solid solution Fe72Al28 has been largely formed. Morphological studies indicate an average grain size of 10 to 15 nm. The microwave- absorbing characteristic reveal good performance for Fe60Co40 compared to Fe72Al28, the maximum reflection loss is about -12 dB for the absorber.

Structural and Mechanical Properties of Nanostructured Fe-Mn-C Alloys Prepared by Mechanical Alloying

The object of our research is to combine the properties of Mangalloys and nanoscale advantages in order to enhance the performance and extend the range of applications in the field of work-hardening parts such as railroad components, armor, and modern auto components. We have produced a high-manganese austenitic steel nanomaterial containing more than 12 wt% Mn, which is the level of Mn in Hadfield steel. This study experimentally determined the process of phase transitions involved in Fe–13 wt% Mn–1.2 wt% C alloy during mechano-synthesis and after subsequent annealing. The milling time ranged from 0.5 to 24 h. The unique features of the nanocrystalline structure and the changes in microstructure as a function of milling time were investigated by X-ray diffraction analysis, differential scanning calorimetry, and scanning electron microscopy coupled with EDX. The grain sizes and microstrain of the milled powder were determined. A thorough study has been done on the sample where a new phase fcc (at 24h of MA) was formed.The object of our research is to combine the properties of Mangalloys and nanoscale advantages in order to enhance the performance and extend the range of applications in the field of work-hardening parts such as railroad components, armor, and modern auto components. We have produced a high-manganese austenitic steel nanomaterial containing more than 12 wt% Mn, which is the level of Mn in Hadfield steel. This study experimentally determined the process of phase transitions involved in Fe–13 wt% Mn–1.2 wt% C alloy during mechano-synthesis and after subsequent annealing. The milling time ranged from 0.5 to 24 h. The unique features of the nanocrystalline structure and the changes in microstructure as a function of milling time were investigated by X-ray diffraction analysis, differential scanning calorimetry, and scanning electron microscopy coupled with EDX. The grain sizes and microstrain of the milled powder were determined. A thorough study has been done on the sample where a new phase fcc (at 24h of MA) was formed.

Syntheses and Characterization of Intermetallic Nanostructures Based on Mn

The nanocrystalline powders of Mn50Ni41Sn9 were prepared by ball milling using a PM 200-type RETSCH planetary ball mill. The morphological, microstructural, and structural characterizations of the nanostructured powders were carried out by scanning electron microscope, x-ray diffraction, first using the Williamson–Hall relation for the refinement of the diffraction peak profiles. The high-temperature thermal and magnetic properties of nanocrystalline alloy Mn50Ni41Sn9 were characterized at different temperatures using a vibrating sample magnetometer; differential scanning calorimetry was used to determine the transformation temperature and thermodynamic values in the Mn50Ni41Sn9 alloy.

Characteristics of Nanostructured Cr75Ni25 Alloy Powders Produced by High-Energy Ball Milling

Nanomaterial Cr75Ni25 alloy with a mean crystallite size of 8.3 nm and microstrain of 1.23% after 48h of milling was synthesized by mechanical alloying using a high energy planetary ball milling. The morphological changes and particles size were investigated by scanning electron microscopy and laser diffraction. Magnetic results were measured by Foucault currants, coercive field and residual magnetisation. Structural change during ball milling was evaluated by X-ray diffraction. It was found that the paramagnetic Cr0.8Ni0.2 phase with bcc structure appears for 12 h of milling.