Plastic flow behaviors of high-strength dual-phase Ni-SiOC nanocomposites

Abstract

High-strength materials with good plastic flow stability are highly desirable for structural applications. Refining grain size can effectively enhance flow strength but often cause plastic flow instability. Here, we demonstrated that nanosized amorphous ceramics SiOC impart a simultaneous enhancement of strength and plastic flow stability to Ni-based nanocomposites. The co-sputtered Ni-SiOC nanocomposites exhibit core (crystalline Ni)-shell (amorphous SiOC) nanostructures and develop nanograined Ni composite containing amorphous ceramic SiOC nanoparticles during annealing up to 800 °C. Corresponding to the developed microstructures, in-situ scanning electron microscope (SEM) micropillar compression tests at deformation temperatures range from room temperature (RT) to 400°C reveal that the core-shell nanostructure shows high strength of 2.5 GPa at RT and 1.6 GPa at 400 °C with compressive strain up to 40%, while the nanograined Ni composite containing amorphous ceramic nanoparticles exhibits high strength of 3.0 GPa at RT and 2.0 GPa at 400 °C with compressive strain up to 50%. Most intriguingly, both nanocomposites do not exhibit obvious strain hardening/softening behavior during compression up to 50%. The high strain rate sensitivity (0.02 at RT to 0.05 at 400 °C) and the small activation volume (8b3 at RT to 10b3 at 400 °C) that were measured based on strain rate jump tests suggest dislocation slips as dominant deformation mechanisms in Ni grains, which is further evidenced by microscopy. Superb plastic flow stability is attributed to microstructure-promoted plastic co-deformation between amorphous ceramics and Ni grains as confirmed by microstructure characterizations. Moreover, amorphous ceramic SiOC inhibit grain coarsening of Ni, preventing deformation induced softening.