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    Effect of cryogenic treatment on wear behavior of Sleipner cold work tool steel
    (Elsevier Ltd, 2023) Kara, Fuat; Küçük, Yılmaz; Özbek, Onur; Özbek, Nursel Altan; Gök, Mustafa Sabri; Altaş, Emre; Uygur, İlyas
    Cryogenic treatment, also known as subzero heat treatment, is a cooling process that complements conventional heat treatment to improve the properties of metals. Unlike coatings, it is a one-time, inexpensive, permanent operation that affects the entire part. This method is mainly applied to tool steels used in mold making. In this study, the changes caused by the effects of shallow and deep cryogenic treatment on Sleipner cold work tool steel were investigated in terms of microhardness, microstructure, coefficient of friction (COF), and wear rate (WR). For this purpose, the test specimens were subjected to the cryogenic treatments performed at two different temperatures (?80 ºC for the shallow cryogenic treatment (SCT) and ? 180 ºC for the deep cryogenic treatment (DCT)) and various retention times (12 h, 24 h for SCT and 12 h, 24 h, 36 h for DCT). Dry sliding wear tests were carried out under different loads (10 N and 20 N) and varying test durations (60, 120, and 240 min) at a constant sliding speed of 0.075 m/s. According to the microhardness results, it was determined that the cryogenic treatment increased the hardness by 6.53 %. According to the microstructure investigations, a more homogeneous structure was observed with the cryogenic treatment, and secondary carbide precipitations were detected. It was observed that the conventional heat-treated (CHT) sample gave the highest COF value with an average coefficient of friction of 0.63. The lowest COF value of 0.58 was observed in the DCT-12 sample. After the wear tests, the lowest wear rate value for both load values was obtained from the DCT-36 specimen. © 2023 Elsevier Ltd
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    Optimization of Cutting Conditions, Parameters, and Cryogenic Heat Treatment for Surface Roughness in Milling of NiTi Shape Memory Alloy
    (Springer, 2022) Altaş, Emre; Erkan, Ömer; Özkan, Derviş; Gökkaya, Hasan
    This study discusses the milling of Nickel-Titanium (NiTi) alloy, one of the innovative and widely used shape memory alloy (SMA). During the face milling operations, the average surface roughness (R-a) was investigated depending on the change in machining parameters, cutting conditions, and cryogenic heat treatment. Experiments were carried out with uncoated and two different coated (PVD, CVD) cutting tools with untreated, shallow (- 80 degrees C) and deep (- 196 degrees C) cryogenic heat treatment. In addition, experiments were carried out using Ethylene Glycol (EG), and boron added Ethylene Glycol (EG+5%BX) cutting fluids as well as dry cutting condition. In the cutting experiments, three different cutting speeds (20-35-50 m/min), three different feeds (0.03-0.07-0.14 mm/tooth), and 0.7 mm fixed cutting depth was used as machining parameters. In the milling mechanism of NiTi shape memory alloys, how the cutting parameters affect the surface quality is discussed in detail. In this context, the cutting parameters were successfully optimized using Taguchi and ANOVA methods. The study is innovative in terms of evaluating the effect of different cutting fluids and cryogenic heat treatment. The results showed that CVD-coated cutting tool, - 196 degrees C cryogenic heat treatment, EG+5%BX cutting fluid, 50 m/min cutting speed, and 0.03 mm/tooth feed are the optimal parameters for the minor surface roughness. In addition, it has been determined that progress is the most influential parameter. On the other hand, ANOVA results showed that the most significant variable on the R-a was feed rate with 42.99%, and then cutting tool type 20.27%, cutting fluid 20.25%, cutting speed 11.68%, and cryogenic heat treatment 1.95%, respectively.