The formation mechanism of the nano-equiaxed (α+β) duplex phases structure during aging process after high pressure torsion deformation

Abstract

The aim of this study was to investigate the effects of the nano equiaxed (α+β) duplex phases (NEDP) structure on the mechanical properties of metastable β type titanium alloy. To achieve this, the Ti-3.5Al-5Mo-4V (Ti-B20) alloy was subjected to high pressure torsion (HPT) deformation and aging treatment. The results demonstrated that the NEDP (α+β) structure exhibited high thermal stability even after prolonged aging. Through systematic transmission electron microscopy (TEM) characterization, it was confirmed that the formation of the NEDP structure was attributed to the generation of crystal defects such as dislocation cells and dislocation pile-ups during HPT deformation. In addition, it was found that the orientation relationship between the α and β phases was [21̅1̅0]α//[111]β after prolonged aging, and the interlocked of coherent interface between the α and β phases allowed the NEDP (α+β) structure to maintain its thermal stability during long-term aging. Therefore, this paper provides valuable guidance for the fabrication of nano-equiaxed dual-phase structures.