Hall-Petch relations and strengthening of Al-ZnO composites in view of grain size relative to interparticle spacing

We investigated the Hall-Petch relations in Al-ZnO composites with different matrix grain size (D) relative to interparticle spacing (L). For samples with D>L, it was found that grain refinement as described by Hall-Petch relation and particle strengthening by Orowan mechanism both significantly contribute to the strengthening of the composites. For samples with D <= L, variation of microhardness with grain size was found to follow a good Hall-Petch relation with an enhanced Hall-Petch slope. Our study indicates the different coupling of strengthening mechanisms in metal matrix composites with different microstructure length scales. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.