Onur Saray

Conversion degree, microhardness, microleakage and fluoride release of different fissure sealants

The purpose of this study was to determine the degree of conversion (DC), microhardness, microleakage and fluoride release of a nano-filled resin based fissure sealant (Grandio Seal, GS) and compare it with an un-filled resin based fissure sealant (Clinpro, CL) and a glass-ionomer based fissure sealant (Fuji Triage, FT). Disk shaped specimens were prepared from tested fissure sealants to determine the DC, Vicker hardness (VHN) and fluoride release (FR). The DC and VHN of each material was evaluated after 24 h. The cumulative fluoride concentrations were evaluated at 1 h, 6 h, 12 h, 1, 7, 15 and 30 days. For microleakage evaluation, fissure sealants were applied to the etched and dried enamel surfaces of sound third molar teeth according to the manufacturers instructions (n=10). After the thermocycling and mechanical loading procedures, microleakage assessments were carried out. Data were analyzed using one-way ANOVA followed by a post hoc Tukey test, the Kruskal Wallis and Mann-Whitney U test (p<0.05). Results revealed differences regarding DC between all groups: FT (89%) > GS (55.02%) > CL (%51.10) (p<0.05). The VHN values were significantly different among all groups in the following order: GS > FT > CL (p<0.05). FT exhibited significantly higher microleakage scores compared to the CL and GS sealants (p<0.05). The FR of FT was significantly greater than CL and GS (p<0.05). Nano-filled resin based sealant can be used as an alternative to other fissure sealant materials because of its superior hardness results and feasible sealing ability.

Enhancement in mechanical behavior and wear resistance of severe plastically deformed two-phase Zn-Al alloys

Abstract The microstructural evolution, tensile response and wear properties of a two-phase Zn – Al alloy (Zn-8 wt.% Al, ZA-8) have been studied after severe plastic deformation by equal channel angular extrusion (ECAE). The experimental results reveal that the strength levels of the ECAE processed samples were considerably improved regardless of the processing route. More importantly, the elongation at fracture was dramatically increased after ECAE. The optimum tensile properties (high strength and high ductility) were reached after eight ECAE passes following route BA. It was also found that the wear rate of severe plastically deformed ZA-8 is considerably lower than that of the as-cast alloy, especially under high applied pressures, demonstrating improved wear resistance of ZA-8. Moderate strength and high ductility along with improved wear resistance in the ECAE processed ZA-8 samples in comparison with the brittle as-cast alloy makes these alloys attractive for wear-sensitive structural applications.

Enhancement of Tensile Ductility of Severe Plastically Deformed Two-Phase Zn-12Al Alloy by Equal Channel Angular Extrusion

Tensile properties (mainly the ductility and fracture mode) of two-phase Zn-12Al alloy subjected to severe plastic deformation (SPD) via multi-pass equal-channel angular extrusion (ECAE) following route-Bc were investigated. As a result of ECAE processing, elongation to failure (as a ductility) of the alloy increased substantially and continuously with increasing the number of ECAE passes. However, the majority of the tensile strains are obtained in the state of plastic instability and therefore the uniform strains achieved along the gage length are very limited for this alloy. On the other hand, the strength of the alloy increased with increasing the number of passes up to 2, above which it decreased. The alloy sample after four ECAE passes exhibited 168% total elongation to failure at room temperature, which was 26 times higher than that of the as-cast one. This result indicates that multi-pass ECAE is effective on improving the tensile ductility of binary Zn-Al alloys. The fracture mode of the as-cast alloy samples completely changed after multi-pass ECAE and the brittle fracture behavior of the as-cast alloy was transformed into the ductile mode after processing.

Room Temperature Superplasticity in Fine/Ultrafine-Grained Zn-Al Alloys with Different Phase Compositions

Three Zn-Al alloys, namely Zn-22Al, Zn-5Al and Zn-0.3Al, were subjected to equal-channel angular pressing (ECAP), and the effect of ECAP on their microstructure and room temperature (RT) superplastic behavior were investigated in detail referring to previous studies reported by the authors of the current study. ECAP remarkably refined the microstructures of three alloys as compared to their pre-processed conditions. While the lowest grain size was achieved in Zn-22Al alloy as 200 nm, the grain sizes of Zn-5Al and Zn-0.3Al alloys were ~540 nm and 2 µm, respectively, after ECAP. After the formation of fine/ultrafine-grained (F/UFG) microstructures, all Zn-Al alloys exhibited superplastic behavior at RT and high strain rates. The maximum superplastic elongations were 400%, 520% and 1000% for Zn-22Al, Zn-5Al and Zn-0.3Al alloys, respectively. It is interesting to point out that the highest RT superplastic elongation was obtained in Zn-0.3Al alloy with the largest grain size, while Zn-22Al alloy having the lowest grain size showed the minimum superplastic elongation. This paradox was attributed to the different phase compositions of these alloys. The formation of Al-rich α/α phase boundaries, where grain boundary sliding is minimum comparing to Zn-rich η/η and η/α phase boundaries of Zn-Al alloys, is the lowest level in Zn-0.3Al alloy among all the alloys. Therefore, it can be concluded that if it is desired to achieve high superplastic elongation in Zn-Al alloys at RT, keeping Al content at a possibly minimum level seems to be the most suitable way.

Texture Evolution of IF-Steel Sheets Processed by Equal-Channel Angular Sheet Extrusion (ECASE)

Interstitial-Free steel (IF-steel) sheets were severe plastically deformed using a continuous equal-channel angular extrusion/pressing technique called “Equal-Channel Angular Sheet Extrusion (ECASE). After processing, texture development as well as microstructural alteration and tensile properties were investigated. The microstructural investigations revealed that the processed sheets exhibited a dislocation cell and/or subgrain structures with mostly low angle grain boundaries. It was also observed that the strength of the processed sheets increased substantially after ECASE processing in the expense of ductility. It was shown that the ECASE has moderate influence on the texture of IF-steel sheets through route A. Intially there was θ partial fiber which changes to {110}θ with straining.