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Role of Microstructural Features in Toughness Improvement of zirconia toughened alumina

Journal of Minerals and Materials Characterization and Engineering 2016年第1期4卷 87-102页

作者： Olaniyi Fakolujo Ali Merati Mariusz Bielawski Manon Bolduc Michel Nganbe University of Ottawa Ottawa Canada National Research Council Canada NRC Aerospace Ottawa Canada Defence R&D Canada (DRDC Valcartier) Quebec Canada

Ceramics constitute an integral part of highly efficient armours due to their low density, high hardness, strength and stiffness. However, they lack toughness and multi-hit capability. Therefore, zirconia toughened alumina is investigated. The hardness is evaluated using Vickers, Knoop and instrumented indentations, while the fracture toughness is evaluated using the indentation technique and Charpy tests. The strength is evaluated using ring-on-ring, four point bend and drop weight tests. The Young’s modulus is evaluated using the unloading instrumented indentation curves. Microstructure, porosity and density are characterised using ultrasonic scanning, Archimedes principle, optical and scanning electron microscopy. Results show an indentation size effect on all mechanical properties. A substantial improvement in toughness is achieved through retardation of crack initiation by tetragonal-to-monoclinic phase transformation in zirconia particles, crack deviation thanks to appropriate grain structure, as well as energy absorption by densification due to remaining porosity. This improved toughness is expected to promote multi-hit capability.

关键词： zirconia toughened alumina Toughening Mechanisms Fracture Toughness Ballistic Performance and Multi-Hit Capability

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Instrumented and Vickers Indentation for the Characterization of Stiffness,Hardness and Toughness of zirconia toughened Al_2O_3 and SiC Armor

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Journal of Materials Science & Technology 2015年第8期31卷 773-783页

作者： Aleksandra Nastic Ali Merati Mariusz Bielawski Manon Bolduc Olaniyi Fakolujo Michel Nganbe Department of Mechanical Engineering University of Ottawa National Research Council Canada Defence R&D Canada(DRDC Valcartier)

Instrumented and Vickers indentation testing and microstructure analysis were used to investigate zirconia toughened alumina （ZTA） and silicon carbide （SIC）. Several equations were studied to relate the Vickers indentation hardness, Young＇s modulus and crack behavior to the fracture toughness. The frac- ture in SiC is unstable and occurs primarily by cleavage leading to a relatively low toughness of 3 MPa m1/2, which may be inappropriate for multi-hit capability. ZTA absorbs energy by plastic deformation, pore collapse, crack deviation and crack bridging and exhibits time dependent creep. With a relatively high toughness around 6.6 MPa m1/2, ZTA is promising for multi-hit capability. The higher accuracy of median equations in calculating the indentation fracture toughness and the relatively high c/a ratios above 2.5 suggest median type cracking for both SiC and ZTA. The Young＇s modulus of both ceramics was most accurately measured at lower indentation loads of about 0.5 kgf, while more accurate hardness and fracture toughness values were obtained at intermediate and at higher indentation loads beyond 5 kgf, respectively. A strong indentation size effect （ISE） was observed in both materials. The load independent hardness of SiC is 2563 HV, putting it far above the standard armor hardness requirement of 1500 HV that is barely met by ZTA.

关键词： zirconia toughened alumina Silicon carbide Armor Vickers indentation fracture toughness Elastic modulus Vickers hardness

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