High strength and high ductility in nickel matrix nanocomposites reinforced by carbon nanotubes and onion-like-carbon hybrid reinforcements

Carbon nanotubes (CNTs) and onion-like-carbon (OLC) hybrid reinforced nickel (Ni) matrix nanocomposites were prepared by spark plasma sintering technique under 1100 degrees C and 70 MPa using Ni powders with various amounts of CNTs (0.25-1.0 wt%). The microstructures and mechanical properties of the nanocomposites were investigated systematically. Experimental results showed that most of the CNTs maintained their integrity at the interface of the Ni matrix, but part of CNTs were transformed into OLC. The pulsed direct current field in the SPS and the catalytic effect of the Ni matrix played the key role for this phase transformation. With addition of 0.75 wt% CNTs, the hardness, sigma(t-0.2) and sigma(ts) of the nanocomposites were increased by 57.1%, 30.3% and 95.1% respectively, compared to pure Ni, while the tensile ductility was also improved by 19.5%. The strengthening and toughening mechanisms are mainly the efficient load transfer and Orowan mechanism with the hybrid reinforcements of CNTs and OLCs. (C) 2019 Elsevier B.V. All rights reserved.