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1
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Effects of Pulse Duration on Structure and Surface Characteristics of Micro-Arc Oxidation Coatings Formed on Aluminum Alloy

100%
Yilmaz M., Şahin O.
Acta Physica Polonica A
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2016
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vol. 129
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issue 4
673-676
EN
Micro arc oxidation (MAO) of aluminum alloy samples was studied using bipolar pulses with various pulse durations under constant duty cycle. The processing times were chosen as 20, 30 and 40 minutes. The X-ray diffraction (XRD) technique, scanning electron microscope (SEM), surface roughness measurement (R_a) and indentation tests were employed to investigate the phase distribution, microstructure, surface properties and hardness of the coatings, respectively. By increasing the pulse duration and processing time, coatings with different surface roughness, thickness and hardness were fabricated.
2
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Improving the Surface Properties of Cp-Ti by Pulsed Electro-Spark Deposition

81%
Yılmaz M., Atar E., Şahin O., Kayalı E.
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vol. 125
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issue 2
593-596
EN
Al-Ti intermetallic compounds were coated by electro-spark deposition. Commercially pure titanium (Cp-Ti) (grade 2) and aluminum rods were used as substrate and electrode materials, respectively. During the electro-spark deposition experiments the following pulse parameters in a group were used: pulse current amplitude, pulse duration and pause between the pulses of a pulse group with 100-300-500 A, 50-100 μs, and 100 μs, respectively. Al-Ti coatings having a thickness range of 15-30 μm were formed on the surface of titanium substrate using electro-spark deposition process. The coating properties such as the roughness and the thickness increased with increasing pulse duration and pulse current amplitude. The mass transfer coefficient decreased with increasing pulse current amplitude and pulse duration. The quality of the adhesion characters of the coatings, determined by Rockwell-C adhesion test, becomes worse from HF-2 to HF-4, due to increase of pulse current amplitude. Depending on the electro-spark deposition process parameters, the coating formed as AlTi or as layered structure consisting of AlTi+AlTi_3 when pulse current amplitude increases. The Al-Ti coatings include some micro cracks lying throughout the coating from surface to interface which is nature of this process. The maximum cross-sectional hardness of the coatings were in the range of 800-1150 HV.
3
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Nanomechanical Behaviour and Surface Roughness of New Generation Dental Fissure Sealants

71%
Arslanoğlu Z., Altan H., Kale E., Bılgıç F., Şahin O.
Acta Physica Polonica A
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2016
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vol. 130
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issue 1
388-393
EN
The aim of this study is the comparative evaluation of surface roughness, elastic modulus and hardness values of some new generation fissure sealants using nanoindentation method and triboindenter. In this study, we have tested five different materials of dental fissure sealant in five groups with six specimens in each. Tested specimens were prepared from the following materials; Fuji Triage as a glass ionomer, Glass Seal as a glass carbomer, Ultra Seal XT Hydro, Teethmate F-1 and Defence Chroma as three resin composites. In the study, Hysitron Triboindenter TI 950 machine was used for nanohardness measurements. This machine has load resolution of less than 1 nN and displacement resolution of 0.04 nm. Data were statistically analysed using one-way analysis of variance (ANOVA) and Kolmogorov-Smirnov Z tests. Hardness values of Fuji Triage, Glass Seal, Ultra Seal XT Hydro were fairly close. Same situation was seen between Teethmate F-1 and Defence Chroma. However, hardness values of the Teethmate F-1 and Defence Chroma was lower than in other examined materials. We can also say that the Defence Chroma has the lowest elastic modulus and Fuji Triage has the highest one among the examined materials. Surface of Teethmate F-1 was the roughest. On the other hand, Ultra Seal XT Hydro has the smoothest surface.
4
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Preparation of Fine-Grained Silicon-Nitride Ceramics and their Characterization by Depth-Sensing Indentation Tests

61%
Şahin O., Güder H., Uzun O., Şahin E., Sopicka-Lizer M., Göçmez H., Artunc E.
Acta Physica Polonica A
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2015
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vol. 128
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issue 2B
B-355-B-359
EN
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.
5
Content available remote

Vickers and Knoop Indentation Microhardness Study of β-SiAlON Ceramic

61%
Güder H., Şahin E., Şahin O., Göçmez H., Duran C., Ali Çetinkara H.
Acta Physica Polonica A
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2011
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vol. 120
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issue 6
1026-1033
EN
In this paper, analysis and interpretation of mechanical property measurements of β-SiAlON ceramic were reported. Indentation microhardness of β-SiAlON 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 (H_{LI}) microhardness determination of the SiAlON 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 β-SiAlON ceramic.
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