1990

In many cases the production of advanced ceramics is still limited in reliability and reproducibility of material performances by inadequate technologies. Above all this is due to the fact that a real control of all the microstructure parameters (chemical composition, phases distribution and composition, surface compositional gradients, grain size, etc.), on which the properties of the ceramic mainly depend, has not been yet achieved.

The structure and physicomechanical properties of mortars with added polymer emulsions were compared with those of a pure mortar after curing for 3, 7 and 28 days. No changes were observed in the crystal growth of the hydrated phases. The emulsions did, however, provoke a shift of the pore distribution curve towards higher mean radius values, although this shift became more and more negligible as curing proceeded. Total porosity was more contained when the additive was present, since its fluidifying effect enabled a lower initial water/cement value to be used.

A study has been made in order to determine the transition α (h.c.p.) ⇒ β (b.c.c.) temperatures in some two-phase α-β titanium alloys for industrial use: for this aim D.T.A. tests and for comparison, specific metallographic analyses on samples specially heat treated have been carried out.

The chemical and physical characteristics of ion-nitrided surface layers, obtained on α-β titanium alloys, are examined and correlated both with the working conditions adopted in the ion-nitriding process and with the alloy chemical composition. Besides the influence of the working parameters on the morphology and on the microstructures of the ion-nitrided surface layers, mainly the alloy element distributions both in surface coatings and in the substrate are analysed for five α-β titanium alloys of industrial use, and for titanium c,p.

Results of a Differential Scanning Calorimetry (DSC) investigation on precipitation hardening in solubilized 6061 aluminum alloy and its composites reinforced with SiC whiskers are reported. The exothermic and endothermic effects in DSC traces of these materials (in the solubilized state) have been attributed to phase formation and reversion on the base of the 6061 AA ageing sequence described in previous TEM studies. Apparent activation energies have been calculated according to the Ozawa method in non-isothermal conditions. The ageing sequence in composites is analogous to that of 6061 AA.