M. Stefanon

Numerical solution of the inverse problem in the analysis of neutron small angle scattering experiments

Abstract A simple numerical procedure is presented to face particular problems encountered in the data analysis of small angle scattering studies of precipitation in complicated alloys. A suitable method for solving a least-squares problem with inequality constraints is suggested.

Investigation of Mg2Si precipitation in an Al-Mg-Si alloy by small angle neutron scattering

Abstract Small angle neutron scattering (SANS) was used to investigate the precipitation process in a high purity Al-Mg (0.72%)-Si(0.34%) alloy. In particular, the Mg 2 Si precipitation was studied as a function of ageing temperature on polycrystalline samples. The measurements were carried out at the D17 facility of the ILL in Grenoble. Coherent scattering cross-section curves were obtained for the different aged samples from which the size distribution functions of coherent and incoherent particles were determined. The SANS results are compared and discussed with reference to TEM observation and resistivity measurements.

Small angle neutron scattering investigation of the ageing process in Al-Mg-Si alloy

SANS measurements are presented to investigate the ageing process of a polycrystalline Al-Mg-Si alloy a 210°C. The growth of needle-shaped precipitates as a function of ageing time is observed, in accordance with TEM observations. The precipitated fraction estimated from the size distribution function agrees with resistivity measurements previously performed on the same alloy. Bidimensional scattering profiles are also given in the case of a single crystal; the data analysis is in progress.

Small-angle neutron scattering microstructural investigation of MANET steel

Abstract Previous results obtained by different microstructural techniques, including small-angle neutron scattering (SANS), suggested the presence of very small microstructural inhomogeneities in modified martensitic steel DIN 1.4914 (MANET), possibly CCr elementary aggregates. The present paper reports SANS measurements carried out on MANET samples submitted to various thermal treatments, aiming to check and to extend the previous results and to further characterize the microstructural features of this steel. Significant information is obtained by the analysis of the magnetic and nuclear components of SANS. The size distribution function of the inhomogeneities is also presented and discussed.

The generalised vibrational density of states of the metallic glass Fe40Ni40B20 determined by neutron inelastic scattering

The generalised vibrational density of states G( omega ) has been derived from inelastic neutron scattering measurements for the ternary transition metal-metalloid metallic glass Fe40Ni40B20. Two main energy bands are observed centred around 24 and 63 meV and separated by a shallow pseudo-gap near 50 MeV. The former band is mainly due to transition metal-transition metal interaction, the latter is associated to localised optical modes involving transition metal-boron bonds. Rather small differences, if any at all, have been observed for samples prepared by the metal spinning technique at different velocities of the rotating wheel. The neutron weighted G( omega ) have been used to calculate thermodynamic quantities like the temperature dependence of the specific heat and of the Debye temperature.

Structural study of Fe40Ni40B20 amorphous alloy

Abstract We present the results of a neutron diffraction study of the Fe 40 Ni 40 B 20 amorphous alloy. From the split first peak of the pair correlation function, the parameters of the TMTM and TMB (TM  Transition Metal) distributions are derived. Small changes of the chemical short-range order parameter are induced by the variation of the rate of quenching.