Improving strength-ductility synergy of twinning-induced plasticity steel by introducing a sandwich structure via submerged double-face friction stir processing

Twinning-induced plasticity steels typically exhibit remarkable plasticity and ultimate tensile strength, but the inferior yield strength has become a bottleneck limiting their application. In this work, a unique gradient sandwich structure that aims to break the bottleneck was successfully fabricated using a submerged double-face friction stir processing technique. The sandwich structure is composed of a coarse-grained zone in the core and two ultrafine-grained zones on the surfaces. An ultrahigh yield strength (1215 MPa) which is 2.2 times that of the as-received base material (543 MPa) is achieved for the sandwich structure. Additionally, significant elongation (19%) and corrosion resistance are retained simultaneously. The coordinated deformation and effective strain transfer between the ultrafine-grained zones and coarse-grained zone facilitate the dispersion of stress and uneven deformation, which contributes to the excellent strength-ductility of the sandwich structure. This work provides a feasible method for fabricating high-performance steels.