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    A comparative study on the microstructure, mechanical properties, wear and corrosion behaviors of SS 316 austenitic stainless steels manufactured by casting and WAAM technologies
    (Elsevier, 2023) Gurol, Ugur; Kocaman, Engin; Dilibal, Savas; Kocak, Mustafa
    Replacing the traditional casting method with wire arc additive manufacturing (WAAM) to produce complex shaped parts will lead to using cost-effective technology even for challenging engineering applications depending on their geometry and number of the parts to be produced. This work performed a comparative study on the stainless steel 316 parts manufactured by WAAM and sand casting to reveal the microstructural, mechanical, wear, and corrosion behaviors. The WAAM components were manufactured using three different cooling dwell times and compared in terms of microstructures with the as-cast and heat-treated cast parts to reveal the properties of the WAAM parts. It was concluded that WAAM is a viable engineering alternative to the casting technology. Results showed that the WAAM and cast parts revealed similar microstructures, including delta ferrite and austenite phases, but the cast parts had a coarser grain and lower amount of delta ferrite due to slower cooling during the solidification. The yield and tensile strength of WAAM parts showed an increasing trend with the increase in dwell time, and on average, their yield strength was similar to 1.5 times higher than in cast parts due to the smaller grains and more elevated delta-ferrite content resulting from rapid cooling. Furthermore, the greatest wear resistance was obtained in the cast parts after solution annealing heat treatment followed by water quenching. In contrast the highest corrosion resistance was obtained from WAAM parts produced using a dwell time of 120 sec. In conclusion, WAAM technology can be an excellent alternative to casting technology for producing stainless-steel parts with optimized process parameters.
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    Comparison of the mechanical properties and drilling performance of the AISI 316 parts produced with casting, LPBF and WAAM
    (Springer Science and Business Media Deutschland GmbH, 2024) Kocaman, Engin; Köklü, Uğur; Morkavuk, Sezer; Coşkun, Mert; Koçar, Oğuz; Dilibal, Savaş; Gürol, Uğur
    AISI 316 stainless steel parts are widely utilized in many industrial fields with a vast scope of applications. These steel parts, which are used in many fields, can be produced using different production methods, but the mechanical properties of the parts produced with different processes may be different, and the machinability characteristics will also be different. In this study, the drilling machinability characteristics of AISI 316 stainless steel parts manufactured via cast, LPBF and WAAM methods were experimentally investigated and compared considering thrust force generation, burr analysis and chip morphology. In order to clarify the differences in machinability behavior among the tested samples, the corresponding microstructure, microhardness and mechanical strength (yield strength, UTS and elongation) were also examined in detail. The experimental results showed the manufacturing method, and particularly cooling rate, significantly affecting the microstructure, mechanical response and further machinability characteristics; besides, due to higher cutting forces generation, the machinability of the parts produced by additive manufacturing methods (LPBF and WAAM) is more difficult compared to the parts produced by conventional manufacturing methods (cast and cast-HT).
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    Effect of post-deposition heat treatments on high-temperature wear and corrosion behavior of Inconel 625
    (Elsevier Ltd, 2025) Kocaman, Engin; Gürol, Uğur; Günen, Ali; Çam, Gürel
    This study uses the arc-directed energy deposition method to fabricate and heat treatment of a Ni-based Inconel 625 wall structure. Heat treatment involved solution treatment at 980°C with and without aging at 720°C, comparing results to the as-built condition. The effects of these heat treatments were analyzed through microstructural investigations, nanoindentation tests, and high-temperature wear and corrosion tests in 0.5 M NaCl and 0.5 M HCl solutions. In the as-built state, the Inconel 625 alloy exhibited a columnar dendritic structure predominantly composed of a gamma matrix along with Laves phase and MC carbides. Solution treatment dissolved the Nb-rich Laves phases and encouraged the formation of needle-like particles in regions with high Nb segregation, while also reducing voids and minimizing corrosion susceptibility along grain boundaries. This resulted in the formation of a uniform oxide layer on the surface, significantly enhancing wear and corrosion resistance. Both heat-treated samples showed improvements in mechanical ratios such as H/E, H³/E², and H²/2E in the WAAM-produced Inconel 625 alloy, resulting in a 67 % enhancement in wear resistance compared to the as-built sample. Corrosion tests also revealed that solution treated samples showed the highest corrosion resistance, followed by aged treatment and as-built samples, respectively. In conclusion, this study provides a thorough understanding of the substantial impact of heat treatments on the microstructure, mechanical properties, and corrosion resistance of Inconel 625, offering valuable insights for advancements in the field.