Papers by Author: P. Merino

Abstract: This paper describes how deep cryogenic treatment at 98K produces changes in the microstructure of a heat-treated aluminum alloy. It was observed how the sub-micrometric particles increased near and at the grain boundaries. This slight precipitation did not produce any modification in static mechanical properties. However, the compressive residual stresses of the material were higher after compared to before the treatment. Both these effects can enhance the life of this alloy through cryogenic treatment.

Abstract: In the present work the age hardening parameters of a 14Ni (200) maraging steel are studied in order to optimize mechanical properties of the steel. The initial characterization of the as received solution annealed steel has been carried out by optical and scanning electron microscopy (LOM and SEM), and hardness measurements. To identify the structural changes during ageing, differential scanning calorimetry (DSC) tests were performed. Different time-temperature combinations were considered for the precipitation hardening treatment of as-quenched material samples. After hardness measurements, three of these treatments were selected for an in depth study. The obtained microstructure at the maximum hardness peaks then analysed (LOM, SEM and TEM) and mechanical behaviour (strength, toughness and wear resistance) was studied for the final selection of the age hardening conditions.

Abstract: Research on the effect of ion implantation on the corrosion behaviour of metals has been carried out for years, but some difficulties arise in the comparison of the obtained results due to variations in experimental conditions (alloys, surface preparation, doses, experimental techniques...). This work tries to overcome those differences, presenting the effect of several elements (Ce+, N+, Cr+ and Cr+ N+) implanted in similar conditions on the pitting corrosion resistance of AISI 430 stainless steel. Potentiodynamic measurements in 1M NaCl demonstrate the beneficial effect of all the implanted elements, showing that Ce+ is the less efficient ion, while Cr+ N+ co-implantation gives the best results in terms of localized attack resistance. Pitting morphology is explained in terms of the XPS and GIXRD data that allow chemical and structural characterization of the implanted layer. Those results help to enlighten the protection mechanisms involved in the considered implantations.

Abstract: Surface analysis techniques (XPS and grazing incidence X-ray diffraction GIXRD) and electrochemical techniques have been combined to elucidate the effect resulting from Cr+ and N+ co-implantation in the formation and evolution of passive layers generated on two different stainless steels (AISI 430 and AISI 304L) in alkaline medium. The results show that the nitrides formed on AISI 430, identified as (Cr,Fe)2N1-x, are less resistant to dissolution while the nitride phase formed in AISI 304L, NCr with nanocrystalline structure, allows the compact growth of the oxide film.