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  • Küçük Resim
    Öğe
    Hardness Behavior of Alumina-Zirconia Nanocomposites Synthesized by Gel Process
    (Polish Acad Sciences Inst Physics, 2013) Sahin, O.; Hasde, A.; Gocmez, H.; Tuncer, M.; Cetinkara, H. Ali; Guder, H. Salih; Sahin, E.
    The alumina-zirconia composites are one of the relatively good and promising candidates for biomaterials application, due to biocompatibility and their mechanical properties that combines high flexural strength with a high toughness. The aim of the present work is to analyze the mechanical properties of these composites, where zirconia content was varied from 5 to 50 wt%. The citrate gel method, similar to the polymerized complex method, was used to synthesize these ceramics. Scanning electron microscopy, X-ray diffraction and microhardness tests are used to characterize synthesized materials. The examined material exhibits the behaviour of indentation size effect. Modified proportional resistance model are used to analyze the load dependence of the microhardness. X-ray diffraction analysis was used to calculation of the grain size and dislocation density. It is found that hardness is decreased when the zirconia content increases with enlargement of grain size. DOI: 10.12693/APhysPolA.123.299
  • Küçük Resim
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    Mechanical Properties of Nanocrystalline Tetragonal Zirconia Stabilized with CaO, MgO and Y2O3
    (Polish Acad Sciences Inst Physics, 2013) Sahin, O.; Demirkol, I.; Gocmez, H.; Tuncer, M.; Cetinkara, H. Ali; Guder, H. Salih; Sahin, E.
    The citrate gel method, similar to the polymerized complex method, was used to synthesize homogeneous tetragonal zirconia at 1000 degrees C. Nanocrystalline tetragonal phase has been fully stabilized at wide temperature range with 10 mol.% CaO, MgO, and Y2O3 addition. Scanning electron microscopy, X-ray diffraction, and microhardness tests are used to characterize synthesized materials. The grain size and dislocation density were calculated from X-ray diffraction data. The examined material exhibits indentation size effect behavior. Results revealed that the Vickers and Knoop microhardness are dependent on indentation test load. Geometrically necessary dislocation model and modified proportional resistance model are used to analyze the load dependence of the microhardness. The highest hardness values were obtained for the samples with CaO addition; however the lowest values were acquired for sample stabilized with Y2O3 by using both Knoop and Vickers techniques. This situation might be explained using the Hall-Fetch relation. DOI: 10.12693/APhysPolA.123.296
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    Öğe
    Preparation of Fine-Grained Silicon-Nitride Ceramics and their Characterization by Depth-Sensing Indentation Tests
    (Polish Acad Sciences Inst Physics, 2015) Sahin, O.; Guder, H. S.; Uzun, O.; Sahin, E.; Sopicka-Lizer, M.; Gocmez, H.; Artunc, E.
    Both pressureless-sintered and dense, fine-grained silicon nitride ceramics were produced from mechanochemically activated nitride-based precursors. Scanning Electron Microscopy (SEM), Transmition Electron Microscopy (TEM), X-Ray Diffraction (XRD) and an ultra-low load microhardness tester were used to characterize these ceramics. Depth-sensing indentation (DSI) tests in the range of 200-1800 mN were performed on the silicon nitride ceramic to determine dynamic hardness (H-d) and reduced elastic modulus (E-r) values. These values were deduced by analyzing the unloading segments of the DSI curves. It was found that both H-d and E-r exhibits a significant indentation load dependence. Nix-Gao (NG) model was used to analyze the dynamic hardness data in the calculation of the load independent hardness value.
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    Öğe
    Vickers and Knoop Indentation Microhardness Study of ?-SiAION Ceramic
    (Polish Acad Sciences Inst Physics, 2011) Guder, H. S.; Sahin, E.; Sahin, O.; Gocmez, H.; Duran, C.; Cetinkara, H. Ali
    In this paper, analysis and interpretation of mechanical property measurements of beta-SiAION ceramic were reported. Indentation microhardness of beta-SiAION ceramic was measured using the Knoop and Vickers indenters. The analysis of the Vickers indentation microhardness data reveals the reverse indentation size effect that is the apparent microhardness increases with increasing applied indentation test load. However, the Knoop indentation microhardness data exhibit indentation size effect that is the apparent microhardness increases with decreasing applied test load. The experimental Knoop microhardness data was analyzed using Meyer's law, elastic-plastic deformation model, proportional specimen resistance model, and Hays-Kendall's model. As a result, modified proportional specimen resistance model is found to be the most effective one for the load-independent (Hu) microhardness determination of the SiAION ceramic. It was seen that different models used to analyze the data obtained from the Vickers indentation do not give the same intrinsic hardness value. We also present the calculation of the Young modulus, E, of the beta-SiAION ceramic.