Characterization of face-centered cubic structure and deformation mechanisms in high energy shot peening process of TC17

The face-centered cubic structure (fcc) and its deformation behaviors, as well as the distinctive role of fcc-Ti in nanocrystallization in TC17 subjected to high energy shot peening (HESP), were investigated by using comprehensive high-resolution transmission electron microscopy (HRTEM). The results showed that there was a stress-induced fcc-Ti in TC17 with a lattice constant of 0.420–0.433 nm and the B-type orientation relationship between the hcp-Ti and the fcc-Ti as [2-1-10]_hcp//[-110]_fcc and (0001)_hcp//(111)_fcc, which was accomplished by the gliding of Shockley partial dislocations with Burgers vector of 1/3[01-10] on the basal plane. The deformation twinning dominated the subsequent deformation of fcc-Ti, producing two types of {111}<11-2> twins with different characteristics. Among them, the I-type twin with complete structure was generated by successive gliding of Shockley partial dislocations with the same Burgers vector of 1/6[11-2]. In contrast, the cooperative slip of three Shockley partials, whose sum of Burgers vectors was equal to zero, produced the II-type twin with zero net macroscopic strain. And then, the emission of Shockley partial with the Burgers vector of 1/6[11-2] on every three (111)_fcc planes resulted in the formation of a 9R structure. Due to the dissociation effect of lamellar fcc-Ti and the superior deformation ability of fcc structure, the occurrence of fcc-Ti effectively promoted surface nanocrystallization of TC17.