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Ali Günen,Ömer Saltuk Bölükbaşı,Yasin Özgürlük,Derviş Özkan,Okan Odabaş,İlyas Somunkıran 대한금속ᆞ재료학회 2023 METALS AND MATERIALS International Vol.29 No.2
This study focused on chromium addition (0 wt%, 3 wt%, 6 wt%, 9 wt% and 12 wt%) on the boride layer formation, microhardness,fracture toughness and elevated temperature friction and wear behaviour of alloys formed by powder metallurgy(P/M). The boride layers obtained on P/M alloys were characterized by examining density, porosity, surface roughness,scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, surface profilometry, microhardness,and fracture toughness. The addition of Cr has a significant effect on both boride layer formation and friction-wearbehaviour of P/M alloys. Increasing the Cr addition up to 6 wt% has an improving effect on the microhardness, fracturetoughness and wear resistance of the P/M alloys, whereas in the case of 9–12 wt% Cr addition causes exfoliation in the boridelayer and low fracture toughness, thus reducing wear resistance. Coefficients of friction and wear volume losses at elevatedtemperatures are higher than room temperature. The best wear resistance at room temperature was obtained in the samplecontaining 3 wt% Cr with the highest fracture toughness, while the best wear resistance at 250 °C and 500 °C was obtainedin the sample containing 6 wt% Cr, where the highest hardness value was obtained.
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Ali Günen,Ömer Saltuk Bölükbaşı,Yasin Özgürlük,Derviş Özkan,Okan Odabaş,İlyas Somunkıran 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.3
This study focused on chromium addition (0 wt%, 3 wt%, 6 wt%, 9 wt% and 12 wt%) on the boride layer formation, microhardness,fracture toughness and elevated temperature friction and wear behaviour of alloys formed by powder metallurgy(P/M). The boride layers obtained on P/M alloys were characterized by examining density, porosity, surface roughness,scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, surface profilometry, microhardness,and fracture toughness. The addition of Cr has a significant effect on both boride layer formation and friction-wearbehaviour of P/M alloys. Increasing the Cr addition up to 6 wt% has an improving effect on the microhardness, fracturetoughness and wear resistance of the P/M alloys, whereas in the case of 9–12 wt% Cr addition causes exfoliation in the boridelayer and low fracture toughness, thus reducing wear resistance. Coefficients of friction and wear volume losses at elevatedtemperatures are higher than room temperature. The best wear resistance at room temperature was obtained in the samplecontaining 3 wt% Cr with the highest fracture toughness, while the best wear resistance at 250 °C and 500 °C was obtainedin the sample containing 6 wt% Cr, where the highest hardness value was obtained.
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Kasparek Max,Ivgin Tunca Rahşan,Özgül Okan 한국응용곤충학회 2024 Journal of Asia-Pacific Entomology Vol.27 No.1
To analyse geographic variation patterns and assess the applicability of biogeographical rules in insects, the West Palaearctic anthidiine bee Eoanthidium insulare serves as an excellent model. This species showcases a highly variable black-and-yellow colour pattern, with a distribution spanning over 4400 km from the Adriatic Sea to the Pamir Mountains and extending over 1660 km in a south-north direction. We examined 214 specimens from all geographic regions of its distribution and identified a significant increase in both body size and the proportion of black in the integument from south to north. This phenomenon may be attributed to a more efficient exploitation of solar energy through a larger integument surface area (Bergmann’s Rule) and enhanced heat retention due to lower skin reflectance (Thermal Melanism Hypothesis). These two processes, therefore, complement each other. However, despite the cooler climates at higher altitudes, we found no correlations between body size and alti tude. Furthermore, while we observed an increase in the proportion of black in the integument from east to west, there was no significant increase in body size. Notably, no correlation between body size and body colouration was identified, suggesting that size and colour adaptation are independent processes. Given that the various colour and size patterns were identified as clinal rather than discontinuous, and the intraspecific genetic distance across the distribution area was remarkably low (0.00138), featuring only four distinct haplotypes of the mitochondrial COI region DNA sequence, we suggest that the subspecies E. i. persicolum and E. i. lemesium be regarded as synonymous with the nominate subspecies (syn. nov.). These findings suggest that, although Berg mann’s Rule and the Thermal Melanism Hypothesis can account for certain aspects of geographic variation in the body size and colouration of E. insulare, their effects may be influenced or superimposed by factors such as genetic constitution.
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