Feasibility analysis of obtaining tri-modal microstructure by multi-pass conventional forging combined with dual heat treatment for near-α titanium alloy with different initial microstructures

Conventional forging followed by dual heat treatment (near-β and two-phase field heat treatments) is a feasible technique aimed at obtaining tri-modal microstructure in near-α titanium alloys. In view of the enlargement and integration of aerospace structural parts as well as the microstructure diversification of original billet, the Ti–6242S alloy specimens with three different initial microstructures were subjected to multi-pass conventional forging and dual heat treatment. The flow behavior and microstructure evolution of material were analyzed. The results indicated that lamellar α has a stronger ability to coordinate deformation than equiaxed α. The more lamellar α in the microstructure, the slower the microstructure reconstruction during deformation interruption. It is feasible to obtain tri-modal microstructure by any pass conventional forging and dual heat treatment for the initial equiaxed or duplex microstructure, and two passes are more appropriate. The difference between initial equiaxed and duplex microstructures is gradually eliminated through a series of microstructure evolutions during the subsequent heat treatment. For initial lamellar microstructure, a kind of microstructure with multi-scale equiaxed α can be formed after multi-pass conventional forging. The spheroidization fraction of lamellar α is significantly increased with the increase of deformation pass. Tri-modal microstructure can be obtained through three-pass forging and dual heat treatment.