The use of carbon nanotubes as microstructural stabilizing phase in metal matrix composites processed by severe plastic deformationThursday (29.09.2016) 15:45 - 16:00 Part of:
One major concern with single-phase materials processed by severe plastic deformation is their microstructural instability given by a predominance of low angle grain boundaries, specifically when the accumulated deformation is low. A potential way to circumvent this issue is the use of second phases dispersed throughout the material, which can act as stabilizing phases that may hinder the grain boundaries and dislocations mobility.
In this work, we analyse the microstructural thermal stability and mechanical properties of carbon nanotube (CNT)-reinforced Ni matrix composites processed by high pressure torsion (HPT), containing different CNT concentrations (1, 2 and 3 wt.%). A thorough structural characterisation of the CNTs at the different processing steps was carried out by means of Raman spectroscopy, not observing any significant modification of the CNT structure.
After HPT, the composites showed a significant increase in hardness, which is directly related to the microstructural refinement and resembling a Hall–Petch behaviour. Regarding the thermal stability, an annealing was performed on all samples at a homologous temperature of 0.33, which exceeds the grain growth onset temperature for these composites. The addition of CNTs aided in the stabilization of the microstructure by pinning the grain boundaries, which remained, to a certain degree, after the thermal treatment.
Our results highlight the feasibility of HPT post-processing CNT-reinforced composites, with the aim of reducing the mean grain size and thus, improving the properties without compromising the structural features of the reinforcement and improving their distribution within the matrix.