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    Determination of fracture toughness of boride layers grown on Co1.21Cr1.82Fe1.44Mn1.32Ni1.12Al0.08B0.01 high entropy alloy by nanoindentation
    (Elsevier Sci Ltd, 2022) Gunen, Ali; Makuch, Natalia; Altinay, Yasemin; Carboga, Cemal; Dal, Serkan; Karaca, Yusuf
    Multiphase boride layers consisting of (CoFe)2B, (Fe0.4Mn0.6)B, Cr2Ni3B6 and (Cr0.4Mn0.6)B were formed on the surface of Co1.21Cr1.82Fe1.44Mn1.32Ni1.12Al0.08B0.01 high entropy alloy by powder-pack boronizing at 900 degrees C, 950 degrees C and 1000 degrees C for 4 h. The nanohardness (H), modulus of elasticity (E) and fracture toughness (KC) of the multiphase boride layers were determined based on the load-displacement (P-h) curves obtained in the nanoindentation tests. Three distinct regions were identified on the cross-sections of the produced layers: an outer layer consisting of MeB-type borides, an inner layer consisting of Me2B-type borides and the transition zone. The microstructural aspects of the layers were investigated using scanning electron microscopy, energy-dispersive Xray spectroscopy, and X-ray diffraction. Detailed analysis of the influence of the chemical composition on hardness, elastic modulus and fracture toughness in the three regions indicated that the most critical factor influencing the mechanical properties was the presence of chromium, iron and cobalt borides in the microstructure. Especially the formation of chromium borides reduced the fracture toughness of the transition zone.
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    Microstructure, hardness and high temperature wear characteristics of boronized Monel 400
    (Elsevier Science Sa, 2022) Kucuk, Yilmaz; Doleker, K. Mert; Gok, M. Sabri; Dal, Serkan; Altinay, Yasemin; Erdogan, Azmi
    Boronizing processes were carried out at 900 degrees C, 950 degrees C and 1000 degrees C for 2, 4 and 6 h to improve the wear performance of Monel 400 alloy. According to microstructure analyses and nanoindentation tests, Ni2B, FeNiB and FeB phases were detected as dominant phases in the boronized layer. Apart from this, it was observed that the amount of Cu deposits in the boronized layers increased depending on the increasing boronizing temperature. After the boronizing process, the boride layer thickness and hardness values were found to be in the range of 32-272 mu m and 12.76-17.83 GPa, respectively. From the results of dry sliding wear test, the wear volume loss values of the boronized Monel 400 alloy decreased by approximately 25 times compared to the untreated samples. The lowest volume loss value among all test samples was observed in the boronized sample at 950 degrees C for 4 h. In addition to the hardness value, it was determined that the morphology and mechanical properties of the boronized layer were also effective on the wear results. Plastic deformation, delamination and oxidation type wear mechanisms were observed as the dominant wear mechanisms in the room and high temperature tests of boronized samples.