Browsing by Author "Mandev, Yesim Zeynep"

Now showing 1 - 2 of 2

Effects of Laser Powder Bed Fusion Process Parameters on Porosity, Liquid Retention, and Thermal and Surface Properties for 316L, CoCrW and Ti6Al4V Alloys
(Springer, 2025) Mandev, Yesim Zeynep; Mandev, Emre; Yetim, Ali Fatih
Laser powder bed fusion (LPBF) offers several key advantages, including design flexibility, the ability to produce complex geometries and the fabrication of porous materials. These advantages have greatly expanded the range of applications for products manufactured using LPBF. Recently, there has been a significant increase in the use of LPBF products in thermal applications. In these applications, which involve intricate solid-fluid interface interactions, and thermal and surface properties of solids play a crucial role in heat flow interactions. This study focused on producing samples using the LPBF method with three different alloys: 316L, CoCrW and Ti6Al4V. The samples were subsequently analyzed for relative porosity, liquid retention, and thermal and surface properties. The influence of various laser process parameters, specifically energy density, on these properties was examined. The production processes conducted at various energy densities yielded porosity levels of approximately 7-32%, 2-20% and 3-16% for 316L, CoCrW and Ti6Al4V materials, respectively, in comparison with the theoretical density. Thermal conductivity values for 316L, CoCrW and Ti6Al4V samples ranged from 15.1 to 12.9, 7.9 to 7.1 and 6.1 to 5.8 W/m.K, respectively. Similarly, the average surface roughness was observed to vary in the range of 7.5-9.6, 8.3-10.5 and 8.9-10.3 mu m for 316L, CoCrW and Ti6Al4V samples. Based on the obtained results, the samples were evaluated in terms of their suitability for thermal applications. Among the investigated alloys, 316L alloy is determined to have potential for thermal applications (extended surface applications, transpiration cooling, etc.) due to its efficient liquid retention feature, relatively high thermal conductivity and moderate surface roughness. Moreover, the 316L stainless steel proved to be more cost-effective, as it allowed for production at low energy density and had a relatively affordable material cost. Additionally, relatively easy porosity controlling in 316L alloy LPBF productions and leveraging its ability to fabricate porous structures hold great promise for further advancements in thermal application products.
Tribological Performance of Ceramic-Based Films Under Different Tribo-Test Media and Vacuum Conditions
(Redakcia Kovove Materialy, 2023) Mandev, Yesim Zeynep; Yetim, Ali Fatih
The influence of different ceramic-based coatings on the adhesion and wear resistance of M2 high-speed steels has been investigated under different tribo-test conditions. For this purpose, TiN, CrN, and DLC films were deposited on the substrates and silicon wafers by a magnetronsputtering PVD system. Structural, mechanical, and tribological properties of coated samples were examined with SEM, XRD, tribotester, microhardness and scratch tester. The sliding wear tests were performed under air, dry nitrogen, oil, and vacuum environments. It was seen that the highest hardness and residual stress values were obtained from the TiN-coated samples, while the lowest hardness and residual stress values were seen in the CrN-coated specimen. It was determined that the hardness and residual stress values of the coating were the most effective parameters between film and substrate adhesion. Therefore, it was observed that high hardness and residual stress had negative effects on critical load values. Tribological tests showed that the wear and friction behaviors differed from each other according to the coating type and tribo-test conditions. Both the lowest friction coefficient values and wear rates were obtained from the oil tribo-test environment. The lowest friction coefficient and wear rate values were achieved in DLC-coated samples.