No abstract

Real-time synchrotron ultrasmall-angle X-ray scattering measurements were performed during the tensile deformation of crystalline phase I poly(1-butene) (P1B). For comparison, high-density polyethylene (HDPE) was also studied. During tensile deformation, the main contribution to the scattering intensity is due to platelike cavities in the case of P1B, whereas very rarely such cavity scattering is observed in the case of HDPE. At small deformations, the platelike cavities were found to occur only in those lamellae whose normals are perpendicular to the stretching direction. This effect is due to the blocky substructure of the crystalline lamellae. At large orientations these cavities reorient turning their normal gradually perpendicular to the stretching direction; this effect is due to the preferential orientation of the polymer chains. Nevertheless, a fraction of the cavities with their normal parallel to the stretching direction are preserved at large deformation. It was found that there exists a critical thickness of cavities below which no stable cavity could be observed. The strain of the cavities with their normal parallel to the stretching direction is proportional to the macroscopic strain but with smaller values.

An experimental study of the effect of MgO content in the MgB 2 powder used for ex situ made composite wires was carried out. Two single-core MgB 2 /Fe/Cu wires were made using commercial MgB 2 powders from Alfa Aesar containing different fraction of MgO. Critical temperature and critical currents of as-deformed and heat-treated wires were measured. The differences between the wires are discussed and correlated with the MgO content. It was found that by increasing the amount of MgO, the inter-grain connectivity worsens, but well distributed and low size MgO particles improve flux pinning.

The phase evolution inside Fe-sheathed wires containing precursor powders consisting of a mixture of Mg and B has been studied in situ by means of x-ray diffraction with hard synchrotron radiation (90 keV). Mg was found to disappear progressively during the heating stage. At 500• C, the intensity of the Mg diffraction lines is reduced by about 20%. This effect is partly attributable to MgO formation. The MgB 2 phase was detected from 575• C. Fe 2 B was forming at the interface between the sheath and the ceramic core at sintering temperatures of 780 and 700• C, but not at 650• C. The formation rate of this phase is strongly dependent on the heat treatment temperature. Its presence can be readily detected as soon as the average interface reaction thickness exceeds 150-200 nm.

Residual stresses in CO2 laser beam welded AA6056 Al-sheets of 3.2 and 6.0 mm thicknesses were studied using neutron and high-energy X-ray diffraction. The influence of the temper T4 and T6 before welding, the effect of sheet thickness in T6 temper, and the effectiveness of post-weld heat treatments T6 and T78 for the reduction of residual stresses in the sheets welded initially in the T4 temper were examined. It was found that tensile longitudinal stresses were significantly higher when welded in T6 than in T4. With the increase in the sheet thickness from 3.2 to 6.0 mm, the residual stress profile was affected more than the stress level when welded in T6. For 3.2 mm sheet, the post-weld heat treatments T6 and T78 did not lead to a significant reduction in residual stresses when welded in T4.