Abstract
Nano-scale precipitation strengthened steels have drawn increasing attention from the materials community recently due to their excellent mechanical behaviors at room temperature, high specific strength to weight ratio, superior radiation resistivity, good weldability, and many more to mention. With the advent of technology, such as synchrotron X-ray, atom probe tomography (APT), and high resolution transmission electron microscopy (HR-TEM), probing precipitates down to the atomic level has been made possible. In this paper, various nano-scale precipitate strengthened steels are compiled with the aim to identify the effects of size and number density of precipitates on the mechanical properties. Besides, the strengthening mechanisms, slip systems, and dislocation-precipitate interactions are reviewed. Moreover, the nucleation and stability of precipitates are also discussed. Finally, the challenges and future directions of the nano-scale precipitate strengthened steels are explored.
Highlights
Precipitation hardening is one of the oldest yet effective methods in improving the mechanical properties of steels
These results suggest a high number of density of ultra-fine precipitates will bring a dramatic strength improvement without a significant (
Zhang et al [1] argued that strengthening due to dislocation shearing mechanism merely comes from the precipitate size effect; for example, the maximum yield strength is obtainable by optimizing the size and number density of precipitates
Summary
Precipitation hardening is one of the oldest yet effective methods in improving the mechanical properties of steels. No reduction of the uniform elongation was observed, suggesting a small increment (0.6 nm in diameter) in the size of precipitates while maintaining a high number density (in the order of 1024 m−3 ) through nano-scale-co-precipitation can produce a large strength improvement (43% increase from 434 MPa to 622 MPa) at no expense of ductility. A pronounced YS increment of 700 MPa was obtained, but it came with a great sacrifice of uniform elongation (about 9%), most probably due to the relatively large (>3 nm) and low number density of precipitates (3.6 × 1023 m−3 ) These results suggest a high number of density (in the order of 1024 ) of ultra-fine precipitates (diameter of 2 to 6 nm) will bring a dramatic strength improvement without a significant (
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