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- MakaleAçık Erişim2026Scopus SJRQ1Change in phase stability and transformation kinetics of NiTiCuW alloy after heat treatment at 650–850 °C
Tatar, Cengiz; Kök, Mediha; Kanca, M. Sait
In this study, the effects of different heat treatment temperatures (650 °C, 750 °C, and 850 °C) on the phase transformation behavior, microstructure, thermodynamic parameters, and microhardness of the NiTiCuW alloy, produced by adding tungsten (W) to the NiTiCu shape memory alloy, were investigated. The crystal structure change was determined by X-ray diffraction (XRD), the transformation temperatures were determined by differential scanning calorimetry (DSC), the microstructure was examined by scanning electron microscopy (SEM), and the mechanical properties were evaluated by Vickers microhardness measurements. XRD results showed that the reference and 850 °C samples were predominantly in the B2 (austenite) phase at room temperature, while martensitic phases (B19/B19′) became prominent at 650 °C and 750 °C. DSC analyses revealed that the transformation peaks became sharper at 650 °C and the R-phase transformation could be observed; at 750 °C, the peaks broadened, indicating a decrease in transformation stability. The austenite finish temperature (Af) increased from 2.1 °C (reference) to 52.9 °C at 650 °C and 60.3 °C at 750 °C, while it remained low (4.5 °C) at 850 °C. Thermodynamic evaluations showed that ΔS increased at 650 °C (0.053 J/g K) and decreased at 750–850 °C (≈0.032 J/g K). Microhardness reached its maximum value at 650 °C (398 Hv), decreased at 750 °C (271 Hv), and showed an upward trend again at 850 °C (351 Hv), compared to the reference value (243 Hv). These results indicate that the heat treatment temperature critically determines the functional and mechanical performance of the NiTiCuW alloy.
- MakaleYalnız künye2025Scopus SJRQ1Effect of Ohmic Heating on the Quality and Nutrient Preservation of Plum Marmalade: A Comparison With Conventional Heating
Ekici, Seymanur; Omac, Basri; Sabanci, Serdal
In this study, plum marmalade was prepared using the ohmic heating method at three distinct voltage gradients (30, 35, and 40 V/cm). The quality properties of the marmalade prepared this way were contrasted with those prepared using the conventional heating method. Total phenolic content (TPC), antioxidant activity (AA), vitamin C content, total color change (ΔE), hydroxymethylfurfural (HMF), and the amount of time needed for the process, including heating and evaporation, were all measured as part of the study. According to the findings, ohmic heating—specifically, a voltage gradient of 40 V/cm—significantly reduced the heating time when compared to the traditional method, which raised the stability of vitamin C, AA, and phenolic compounds. When ohmic heating was used instead of conventional heating, the amounts of TPC, AA, and vitamin C increased by 19.50%, 33.90%, and 149.12%, respectively. In comparison to traditional heating under atmospheric conditions, the results also showed that ohmic heating increased the amounts of gallic acid (40.61%), catechin (40.98%), chlorogenic acid (25.05%), and rutin (24.67%). Furthermore, the results showed that ohmic heating reduced the amount of HMF (34.34%) and ΔE (2.27%) in comparison to conventional heating. TPC, AA, vitamin C, gallic acid, catechin, chlorogenic acid, and rutin were higher than conventional heating; nevertheless, HMF and ΔE were lower than conventional heating at the applied ohmic heating process. The results obtained indicate a strong potential for an ohmic heating system as a rapid heating method for preserving nutritional value.
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İncele - MakaleAçık Erişim2018Scopus SJRQ3EFFECT OF POST-HEAT TREATMENT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Cu-Fe-Co POWDER ALLOY FABRICATED BY HOT PRESSING
Çelik, E.; Aslan, A. K.
In this study, the powder mixture which consists of Cu-Fe-Co was produced by using the method of hot pressing technique. In addition, effect of heat treatment process on microstructure and mechanical properties of this alloy was investigated. Following the hot pressing process applied on the samples, heat treatment was carried out at 950 degrees C for two different dwelling times (90 and 180 minutes). Measured density values were considered as physical characteristics, while hardness and fracture strength values were considered as mechanical characteristics. It was observed that porosity rates of hot pressed samples were decreased by increasing of temperature and pressing parameters. In this study it was observed that Cu was spread in matrix and filled the micro porosities. Hardness values were determined to be decreased as a result of grain growth after heat treatment process. That 4 fold increased elongation % values which were achieved by TRS experiments were observed as well.
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