EBSD Analysis of Metal Matrix Nanocomposite Microstructure Produced by Powder Metallurgy

Abstract

The development of metal nanocomposites reinforced by carbon nanotubes (CNTs) remains a focus of the scientific community due to the growing need to produce lightweight advanced materials with unique mechanical properties. However, for the successful production of these nanocomposites, there is a need to consolidate knowledge about how reinforcement influences the matrix microstructure and which are the strengthening mechanisms promoting the best properties. In this context, this investigation focuses on the study of the reinforcement effect on the microstructure of an Ni-CNT nanocomposites produced by powder metallurgy. The microstructural evolution was analysed by electron backscattered diffraction (EBSD). The EBSD results revealed that the dispersion/mixing and pressing processes induce plastic deformation in the as-received powders. The dislocation structures produced in those initial steps are partially eliminated in the sintering process due to the activation of recovery and recrystallization mechanisms. However, the presence of CNTs in the matrix has a significant effect on the dislocation annihilation, thus reducing the recovery of the dislocation structures.

Effect of Morphology and Structure of MWCNTs on Metal Matrix Nanocomposites

“…The fraction of these grain boundaries is lower for NTX5 and Nanocyl CNTs and almost inexistent for NTX1 CNTs. In previous works [39], a higher fraction of low-angle grain boundaries was observed for nanocomposites when compared with those in the sample of Ni without reinforcement. The deformation mainly originated during the production of the samples, especially in the dispersion and mixing steps, which were eliminated during the sintering of the Ni matrix.…”

“…While for the Ni sample, grains without dislocations were observed, the nanocomposites are characterized by the presence of plastic deformation related to the presence of dislocation cells. As already mentioned in previous works [39,41,42], this plastic deformation occurs during the powder metallurgy route that for the nanocomposites is not eliminated in the last step of the process-sintering. During sintering, the dislocation rearrangement did not occur in the same way for the nanocomposites and for the Ni sample without reinforcement.…”

“…The nickel powders (Goodfellow Cambridge Ltd., Huntingdon, UK) used in the present study were carefully characterized by optical microscopy (OM), scanning electron microscopy (SEM) and even electron backscattered diffraction (EBSD) in previous works [39,40].…”

“…The mixture and dispersion were ultrasonicated in isopropanol for 15 min, filtered and dried. The powder mixtures were pressed with 900 MPa and subsequently sintered at 950 • C under vacuum for 120 min, based on the conditions reported for the better ones described in previous studies [39][40][41].…”

Characterization of Ni–CNTs Nanocomposites Produced by Ball-Milling

“…This cleanup procedure checks for an incorrect indexing indication in each point of the map, including isolated or low-confidence factor points. The plotted EBSD maps, inverse pole figures (IPFs), kernel average misorientation (KAM), and grain orientation spread (GOS) were obtained, and the data were treated similarly to the maps used in a previous study [53].…”