DEFORMATION-BEHAVIOR OF TI-25AL-10NB-3V-1MO (SUPER ALPHA(2)) DURING ISOTHERMAL FORGING

Samples of plasma-melted Ti-25Al-10Nb-3V-1Mo (Super alpha(2)) have bee n isothermally upset forged in the beta-phase field. It has been found that Super alpha(2) has good hot workability and no cracks have been found on billet surfaces even when reduced in height by up to 70%. The maximum flow stress during forging varied from 33 MPa to 80 MPa over the range of conditions used. The forging pressure required for isothe rmal forging is strongly dependent on forging temperature and strain r ate; The experimental results have shown that isothermal forging can b e applied satisfactorily to deform Super alpha(2) billets within tempe rature and strain rate ranges of 1120-1180 degrees C and 0.005 s-0.5 s (-1) to more than 70% height reduction. A strain rate sensitivity expo nent (nl) of 0.2 and a deformation activation energy of 286 kJ mol(-1) are obtained for the forging conditions used and it is considered tha t the deformation mechanism of Super alpha(2), isothermally forged in the beta phase field is dynamic recovery and recrystallization togethe r with a diffusion-dependent process. An empirical forging flow equati on has been developed which is valid over the range of temperatures an d strain rates investigated. The equation acurately describes the temp erature and strain rate dependence of the forging peak flow stress.