Papers by Author: Concepción Tojal

Abstract: Titanium is a material used in biomedicine for osseous implants due to their low density and biocompatibility. Its use in this field is limited by the lack of similarity of their stiffness with the stiffness of bones. In order to reduce this difference, powder metallurgy offers ways to develop porous materials with a reduced stiffness. The main objective of this work is to develop titanium scaffolds by space-holder technique, concretely with using two different spacers: Ammonium bicarbonate and sodium chloride. It has been studied the best way for remove spacer of green compacts, which have been sintered in high vacuum. Materials obtained by using of two spacers, have been analyzed in order to value different results in porosity, microstructural and mechanical properties. The stiffness of new materials was obtained by testing of three points in bending. This research shows that the manufacturing method of porous materials for bone replacement using space holder technique with ammonium bicarbonate or sodium chloride, allows obtained samples with slightly difference in physical, microstructural and mechanical properties.

Abstract: Being an effective sintering enhancer boron is gaining relevance for obtaining high density PM steels. Thermodynamic calculations are an important tool for studying the roll of alloying elements in the formation of a liquid during sintering. In the present work, the system Fe-Cr-B was obtained by combining up to date thermodynamic descriptions for the subsystems Fe-Cr, Cr-B and B-Cr. The calculations were carried out with Thermo-Calc software to predict isothermal sections for the ternary diagram for 1210 and 1250°C. The analysis of the isothermal sections indicates that the solid phases in equilibrium with the liquid are M₂B and a-BCC solid solution. The generation of the liquid is based on a eutectic reaction (Lða+(FeCr)₂B) involving the mixed borides previously formed. On the other hand, simulations for PM steels with constant boron but higher chromium content allowed realising that the formation of the liquid may be completely inhibited, within the temperature range under consideration, as materials with too high Cr/Fe ratios are used. This study was also supported by selected experiments which were in excellent agreement with the thermodynamic calculations.