Danny Segers

Influence of carbon on the microstructure of a Fe-Mn-Si-Cr-Ni alloy

The influence of the addition of C to the Fe-Mn-Si-Cr-Ni base material is investigated at room temperature. Steel samples were deformed during a tensile experiment up to a strain of 17%. Light optical microscopy (OM) and x-ray diffraction (XRD) gave information about the different micro-structural phases that exist in the deformed and the undeformed alloys. The evolution of the defect structure is followed by positron annihilation techniques such as Doppler broadening of annihilation radiation spectroscopy (DBAR) and the positron annihilation lifetime spectroscopy (PALS). During deformation a martensitic ε-phase is induced. The size of the martensite plates increases with increasing deformation.

Defect evolution during annealing of deformed FeSi alloys studied by positron annihilation spectroscopy

High silicon steel is widely used in electrical appliances. Alloying iron with silicon improves its magnetic performance. A silicon content up to 6.5 wt. % gives excellent magnetic properties such as high saturation magnetization, near zero magnetostriction and low iron loss in high frequencies. Their workability is greatly reduced by the appearance of ordered structures, namely B2 and D03, as soon as the Si content becomes higher than 3.5 wt. %. This limits the mass production by conventional rolling to this maximum percentage of Si. In this work a series of FeSi (7.5 wt. % Si) samples with different degrees of deformation are investigated with positron annihilation spectroscopy and optical microscopy (OM). The influence of annealing on the concentration of defects of different deformed FeSi alloys has been investigated by positron annihilation lifetime spectroscopy and Doppler broadening of the annihilation radiation. OM is used to investigate the microstructure of deformed samples before and after annealing. The values of the S parameter present a decrease for all studied FeSi alloys with the increase of the annealing temperature, being attributed to a decrease of the concentration of defects. A sudden increase of the S-parameter value at 600?°C was observed for all samples, which could be related to the change of the ordering of the FeSi alloys at that temperature. At 700 °C, the values of the S parameter decreased drastically and starting from 900?°C, they became constant. The microstructures of the alloys, investigated by OM, show that recrystallization is completed at 900?°C and the samples are mainly free of defects, which is in agreement with the positron annihilation lifetime data.

Construction and testing of a replica of Einstein’s “little machine”

Einstein developed his “little machine” to measure small electrical charges, but there are no publications that describe measurements done with this apparatus. We report on our construction of a replica of the little machine and on our tests of its performance.

Isochronal annealing of a deformed Fe-7.5 mass.% Si-steel

Abstract FeSi samples with 7.5 mass.% Si were cold deformed with a thickness reduction of 16% and isochronally annealed for one hour at different temperatures. Their microstructure was characterised using positron annihilation lifetime spectroscopy and electron backscatter diffraction. Positron annihilation mean lifetime values (τmean) decreased slightly with the increase in annealing temperature (20 to 600°C), a process related to recovery. In addition, τmean decreased significantly in the 700–900°C temperature range. The measured value of τmean is 106 ps, which is similar to the pure undeformed Fe after annealing at 900°C. Thus, the material is virtually free of defects at 900°C. Microscopy and diffraction studies showed a high amount of shear bands for the deformed sample. In the temperature range of 20–600°C, no recrystallisation was observed. According to the electron backscatter diffraction data, the recrystallisation starts after 700°C, and it is completed at 900°C.

Positron Implantation and Transmission Experiments on Free-Standing Nanometric Polymer Films

Positron transmission experiments were performed on free-standing poly(methyl-methacrylate) (PMMA) and polystyrene (PS) films of nanometric thicknesses made by spin coating. The power_law equation z1/2(E) )=(α/ρ)En was determined from the measurements of the S-parameter as a function of the positron implantation energy. These transmission experiments indicate that n = 1.90(±0.08) and α = 1.33(±0.10) μg cm-2 which deviates from the values found by Algers et al. (n = 1.71(±0.05) and α = 2.8(±0.2) μg cm-2) and the commonly used parameters (n = 1.6 and α = 4.0 μg cm-2).