Deformation behavior of BCC tantalum nanolayered composites with modulated layer thicknesses

H Sun and A Kumar and CV Singh, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 761, 138037 (2019).

DOI: 10.1016/j.msea.2019.138037

The metallic nanolayered composite composed of alternating nanocrystalline and coarse-grain layers of the same element features stronger bonding interlaminar interfaces than that consisting of different elements; therefore, it is less vulnerable to brittle interfacial fracture. Despite numerous studies on face-centered-cubic (FCC) metallic nanolayered composites, the structure-mechanical property relationships of body-centered-cubic (BCC) metallic nanolayered composites have yet to be elucidated. Using molecular dynamics simulations, we investigated the deformation and fracture mechanism of BCC tantalum (Ta) nanolayered composites, composed of alternating nanocrystalline and single-crystalline layers. Our findings reveal that unlike FCC nanolayered composites, whose main deformation mechanism is twin nucleation, BCC nanolayered composites favor twin thickening, which rotates the whole single-crystalline layer to the twin orientation and finally eliminates all twin boundaries in the single-crystalline layer. Such preference for twin thickening is attributed to its much smaller energy barrier than that for twin and dislocation nucleation. The fracture of Ta nanolayered composites is caused by intergranular cleavage cracks, originated from the intersection of twin boundaries and grain boundaries. In the range of strain rates used by MD simulations (10(7)/s similar to 10(9)/s), rising strain rates leaves less time for crack coalescence and propagation at each load increment, thus enhancing the fracture strength and strain of BCC nanolayered composites.

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