Qian Li¹, Fen Kai Yan¹, Nairong Tao¹, Ke Lu¹; ¹Institute of Metal Research, Chinese Academy of Sciences

Cracks often initiate at phase boundaries in conventional second phase reinforced alloys during cyclic loading, which limits their fatigue properties. We prepared a nanotwin strengthened 316L stainless steel consisting of nanotwinned and recrystallized grains by using plastic deformation and subsequent partial recrystallization annealing. Fatigue tests revealed that interfaces separating hard nanotwinned grains from soft recrystallized ones exhibited an excellent resistance to crack initiation. This is ascribed to the elastic homogeneity and cyclic deformation compatibility between nanotwinned and recrystallized grains. At small cumulative cyclic strains, nanotwinned grains deform compatibly with the recrystallized grains without noticeable strain localization at their interfaces. Nanotwins can accommodate cyclic plastic strains by interaction of dislocations with twin boundaries, especially through the motion of the well-ordered threading dislocations inside the twin lamellae. Therefore, improved fatigue property with high fatigue limit and fatigue ratio is achieved in the nanotwin strengthened stainless steel.