Decoupling Stable Cyclic Deformation From Defect Accumulation in Metals.

Fatigue resistance in metals is fundamentally constrained by a long-standing dilemma: the strain hardening required to suppress deformation localization is typically achieved through the accumulation of dislocations and other defects that ultimately promote fatigue damage. Whether cyclic plasticity can be sustained without progressive defect storage remains an unresolved question. Here we demonstrate that this limitation can be overcome through the introduction of amorphous nanoparticles into a crystalline metal matrix. We uncover a cyclic deformation regime characterized by sustained resistance to strain localization yet minimal net defect accumulation over prolonged loading. During cyclic deformation, the amorphous nanoparticles function as efficient dislocation sinks, continuously mitigating defect accumulation in the metallic matrix, while their elastic deformation via reversible shear transformations provides apparent strain hardening of the overall material. These synergistic mechanisms effectively preserve the microstructural integrity of both the metallic matrix and the amorphous nanoparticles over millions of loading cycles, leading to a fatigue life of more than 105 cycles at a fatigue ratio of 0.95, and a ratcheting rate one to three orders of magnitude lower than all known metals and alloys.