Kara, Levent; Yılmaz, Oğuzhan; Korkmaz, Habip Gökay; Kaş, Mustafa; Bol, Nevzat; Toros, Serkan

Additive manufacturing (AM) technologies are prone to microstructural and mechanical anisotropy, driven primarily by directional solidification and the non-uniform thermal history associated with their layer-by-layer fabrication. This problem is more pronounced in Wire Arc Additive Manufacturing (WAAM), where elevated heat input and large molten pools increase thermal gradients and favor columnar grain development accompanied by δ-ferrite segregation in stainless steels. To address these issues, post-processing strategies such as inter-pass rolling, hammer peening, and heat treatment are frequently implemented. Nevertheless, regardless of being partially effective, these methods will add more processing steps that will result in an increase of time and costs. In this context, the present study seeks solutions to commonly reported limitations in the WAAM fabrication of AISI 316LSi stainless steel, which is widely used in industrial applications, by varying the wire feed speed (WFS) to regulate heat input with the aim of improving microstructural characteristics and mechanical performance. Accordingly 3 different heat input was attained by changing WFS in the system of CMT based WAAM method. Based on this approach, subsequent microstructural analysis revealed changes in δ-ferrite morphology from skeletal δ-ferrite to more refined lathy and globular forms across the investigated conditions. Within the examined processing parameters, samples corresponding to higher heat input levels, associated with increased wire feed speed (WFS), showed reduced anisotropy in grain orientation. Furthermore, samples produced under these conditions exhibited yield strength values of approximately 390 MPa, ultimate tensile strength values of approximately 620 MPa, and enhanced impact toughness, accompanied by a reduction in anisotropy. Overall, the findings indicate that adjustment of heat input during WAAM provides a viable process-engineering route for microstructural refinement and anisotropy reduction in AISI 316LSi stainless steel.

Keleş-Dayauç, Ayşenur; Baran-Acımert, Özlem

Because of its superior mechanical properties, excellent thermal stability, high wear and heat resistance and remarkable resistance to chemical agents, B4C films are extensively utilized in a variety of industries, including armor materials and wear-resistant components. B4C films can be coated in a variety of ways. This study was aimed to obtain optimum structural, mechanical and tribological properties of B4C films grown by electrophoretic deposition (EPD) and RF magnetron sputtering techniques. The structural properties of the B4C films were investigated by SEM and XPS analysis. The tribological properties and the electrochemical properties were carried out using a wear tester and a corrosion tester, respectively. Examining the observed polarization resistance reveals that AISI 4140 steel has the lowest resistance (15.33 × 106 Ω cm2) and the B4C film with EPD has the highest resistance (347.5 × 106 Ω cm2). It was also observed that B4C films significantly reduced the coefficient of friction of the AISI 4140 steels. The AISI 4140 substrate and B4C films coated by RF magnetron sputtering and EPD have wear rates of 1.45*10−4 mm2/Nm, 1.22*10−4 mm2/Nm, and 9*10−4 mm2/Nm, respectively.

Aslan Çakır, Mevra; Yetim, Tuba; Yetim, Ali Fatih; Çelik, Ayhan

The oxide coatings obtained with both superhydrophobic and superoleophobic properties on CP-Ti samples, which are frequently used as biomaterials, were produced using the solgel dip-coating method. The obtained oxide-coated titanium samples have been performed using XRD, SEM, EDS, 3D optical profilometer, optical tensiometer. After the coating process, electrochemical corrosion experiments were performed to determine the electrochemical properties. As in vitro cytotoxicity test of untreated and coated samples, MTT and LDH release tests were performed and their biocompatibility properties were evaluated. As a result of the experiments, it was observed that the resistance of the surface to corrosion current increased considerably due to the low free surface energy values of the film obtained with the superamphiphobic coating after the solgel dip coating. As a result of the in vitro cytotoxicity test of oxide-coated superamphihobic titanium material surfaces, it was determined that the biocompatibility increased after 24 h. It has been observed that the superhydrophobic and superoleophobic films obtained after coating have self-cleaning, antibacterial, and anticorrosion properties.

Aslan Çakır, Mevra

This study investigated niobium pentoxide (Nb2O5) thin films deposited by the sol-gel spin coating method on a Ti45Nb alloy, which are used in biomedical applications. To obtain a monoclinic Nb2O5 coating film and improve the properties of the films, the samples were annealed in an air atmosphere at 1300 °C for 2 hours. XRD, EDS, SEM, tensiometer, and potentiostat/galvanostat/ZRA studies were used to characterize the thin film coatings. In studies of the electrochemical performance in biological systems, the phosphate buffered saline (PBS) and the simulated body fluid (SBF) solutions were used to simulate bodily fluids for wettability and corrosion tests. In PBS solutions, the coated sample had a higher positive corrosion potential (E corr) of − 92 mV and a lower corrosion current density (I corr) of 2.86 × 10−6 mA/cm2 compared to the uncoated Ti45Nb. In the SBF solution, I corr values of 1.36 × 10−4 mA/cm2 and 7.37 × 10−5 mA/cm2 were obtained for the untreated and coated samples, respectively. The results obtained from the electrochemical corrosion tests of the hydrophilic Nb2O5-coated Ti45Nb samples indicated considerable improvement in the corrosion resistance relative to that of the untreated Ti45Nb alloy, as shown by a decrease in corrosion current density and an increase in the corrosion resistance.

Baran Acımert, Özlem; Çavlan, Sedat; Keleş Dayauç, Ayşenur; Hopkins, Lynne

TiCN coatings are applied to tool steels surfaces to increase tool life because of attractive properties such as high hardness and toughness. The addition of different alloy elements to the structure of TiCN leads to significant improvements in their mechanical and tribological properties. In this study, to increase the life of AISI H13 tool steel, TiCN and Ta-doped TiCN coatings were deposited by Closed Field Unbalanced Magnetron Sputtering system and the effects of Ta on the structural, mechanical and tribological properties of TiCN coatings were investigated. The effect of the Ta target current has been studied by varying its value from 0 to 3 and to 6A. Structural properties were determined by SEM, XRD and XPS. Mechanical properties were obtained by nanoindentation and adhesion tests. A pin-on-disk tribotest device was used to determine the tribological properties (friction coefficient and wear rate). With the addition of Ta to TiCN, an increase in the thickness of the coatings and a decrease in grain size were observed. The amount of C-C (sp3) increased in TiCN coatings with increasing Ta target current. Increased sp3 amount increased the hardness of the coatings. The results show that the increasing amount of Ta improves the mechanical and tribological properties of TiCN coatings. In addition, TiCN and Ta-TiCN coatings significantly improved the mechanical and tribological properties of substrate.