ALBERT

Description: 〈p〉Publication date: Available online 23 December 2019〈/p〉 〈p〉〈b〉Source:〈/b〉 Acta Materialia〈/p〉 〈p〉Author(s): Qizhong Wang, Cristina Ramírez, Connor S. Watts, Oscar Borrero-López, Angel L. Ortiz, Brian W. Sheldon, Nitin P. Padture〈/p〉 〈h5〉Abstract〈/h5〉 〈div〉〈p〉There is growing interest in using 2D graphene-related reinforcements to toughen brittle ceramics in nanocomposites. However, there is a lack of fundamental understanding of the toughening mechanisms and microstructural effects in such nanocomposites. To address this paucity, fully-dense nanocomposites of aluminum oxide (Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉) matrix and reduced graphene-oxide (rGO) reinforcements (∼5 vol%) of different average-thicknesses and orientations are fabricated and characterized. The interactions between stably propagating cracks and rGO in the Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/rGO nanocomposites are observed 〈em〉in situ〈/em〉 inside a scanning electron microscope (SEM). Toughening by pullout of thick rGO in the crack-tip wake in the cross-section orientation is found to be the most effective, which is consistent with the highest fracture toughness (〈em〉K〈/em〉〈sub〉IC〈/sub〉∼6.7 MPa.m〈sup〉0.5〈/sup〉) measured in those Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/rGO nanocomposites. Interestingly, upon unloading and reloading, the intact rGO crack-bridges appear to crinkle and uncrinkle without a remnant crease, respectively, which is a unique deformation property of multi-layer graphene-like materials. This points to a possible new cyclic-fatigue resistance mechanism in those nanocomposites. Sliding-wear properties of the Al〈sub〉2〈/sub〉O〈sub〉3〈/sub〉/rGO nanocomposites are also studied, where the hardness and microstructural heterogeneities are found to play dominant roles. The results from this study have implications for the creation of high-toughness, fatigue-resistant, and wear-resistant graphene-reinforced ceramic nanocomposites of the future.〈/p〉〈/div〉 〈h5〉Graphical abstract〈/h5〉 〈div〉〈p〉〈figure〉〈img src="https://ars.els-cdn.com/content/image/1-s2.0-S1359645419308742-fx1.jpg" width="301" alt="Image, graphical abstract" title="Image, graphical abstract"〉〈/figure〉〈/p〉〈/div〉