β transus influence on α-β titanium alloys behaviour in ion-nitriding process

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 correlation between β transition temperatures, treatment temperatures and the behaviour of the tested alloys in the ion-nitriding process has been examined: thus, it has been possible to define in which measure the selection of the treatment temperature, with reference to the B transition temperatures, determines the phases present in the nitrided surface layers and their mutual distribution. Finally, the morphological characterization of the hardened surface layers, obtained through the thermochemical nitriding treatment, has been defined: in particular, the nitrogen distribution in the phases present in the surface layers has been studied by means of back scattered electron analysis techniques.