M. Valli

Non-Destructive Investigation of Microporosity in Marbles by means of Small Angle Neutron Scattering

Abstract Small-angle neutron scattering (SANS) measurements have been carried out on different marble and limestone samples, of relevance to cultural heritage safeguard, to investigate the micropore distribution in the size range between 10 and 1000 A. Different varieties of marbles have been studied using a CaCO 3 single crystal, pore-free, as a reference. A series of red scaglia limestone samples has also been tested obtaining for this material, very reproducible results. Namely identical SANS cross-sections are found for specimens issued from a modern quarry and for samples issued from a historical building. Furthermore, the micropore volume distribution functions obtained by Fourier transformation of the SANS data are in accordance with porosimetry results for pore sizes larger than approximately 500 A. The results of SANS measurements carried out to try and distinguish close and open microporosity are also reported.

Study of He-bubble growth in α-particle implanted F82H-mod martensitic steel

This paper presents the results of a small-angle neutron scattering (SANS) study of He-bubble growth in martensitic steel F82H-mod. The investigated samples had been homogeneously implanted with 400 appm He at 250°C, then submitted to 2 h annealings up to 975°C, together with a non-implanted sample of the same material (one for each temperature) serving as a reference to isolate the SANS signal arising from the He-bubbles. An as-implanted sample was also investigated together with its thermal reference. The He-bubble volume distributions, obtained from the SANS data and discussed with reference to uncertainties arising from background subtraction, show that the uniform distribution of the as-implanted sample, with bubbles approximately 15 A in size, evolves during high temperature annealing into a bimodal one with a secondary population of bubbles as large as 100 A approximately.

Microstructural characterisation of F82H-mod. steel using small-angle neutron scattering

Small-angle neutron scattering (SANS) measurements have been carried out on samples of F82H-mod. martensitic steel submitted to different treatments: (a) hardening, (b) tempering and (c) ageing. Size distribution functions referable to the precipitates, formed during the different treatments are obtained both for nuclear and magnetic SANS components. The results, discussed making reference to transmission electron microscopy (TEM) observations and microhardness measurements, show that while samples of groups (a) and (c) exhibit a stable microstructure, marked differences are detected varying the tempering temperature, especially at 550°C (where a fine precipitation is observed) and for temperatures higher than 850°C (formation of delta ferrite).

SANS study of microstructural evolution in oxide strengthened EUROFER steel after heat treatments

Oxide dispersion strengthened (ODS) reduced activation ferritic/martensitic steels are being developed for structural applications in future fusion reactors since they would allow consistently increasing the operation temperature The 9%CrWVTa Eurofer-97 steel has been selected as a base material strengthened by Y2O3 contents of 0.3 and 0.5 wt% and produced in a powdermetallurgical route by mechanical alloying and hot isostatic pressing (HIP). The mechanical properties are strongly correlated with Y2O3 particle average size and spatial distribution, therefore small-angle neutron scattering (SANS) is quite useful to investigate how these evolve in the course of the production steps. Solid polycrystalline samples as well as mechanically alloyed powders have been investigated after thermal treatments thus simulating the HIP conditions. The obtained SANS results show that annealing at high temperature results in a redistribution of scattering centres sizes, which might be attributed to the growth of small Yttria particles and possibly of larger carbides.