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In this study, Ferrite A (undoped barium hexaferrite), Ferrite B (MnCuNi-doped barium hexaferrite), Ferrite C (MnCuSr-doped barium hexaferrite), Ferrite D (MnCoNi-doped barium hexaferrite) and Ferrite E (MnCoSr-doped barium hexaferrite) powders were prepared by sol-gel processing. The produced powders were calcined at 550 degrees C for 6 h and sintered at 1000 degrees C for 5 h to obtain the required phases. The powders were characterized by differential thermal analysis/thermogravimetric analysis (DTA/TG), X-ray diffractometry (XRD) and scanning electron microscopy (SEM), and vibrating-sample magnetometry (VSM). The XRD patterns indicated that the pure barium ferrite phase was not obtained. The presence of M-type BaFe11.6Mn0.4O19 was confirmed in the Ferrite B and Ferrite D patterns. In the Ferrite C pattern, there were the phases of BaFe12O19, Ba2Cu2Fe12O22(X or Z-type) and Sr3Fe2O6.16. The Ba0.5Sr0.5Fe12 phase was easily observed in the Ferrite E pattern. The results showed that the dopant materials significantly change the particle shape of Ferrite A powders, but also lower the value of the coercivity. A higher saturation magnetization was observed for the Ferrite D powder.

The current study focuses on the microabrasion wear and microstructural properties of CoNiCrAlY coatings fabricated on nickel-based superalloy substrates using atmospheric plasma spraying (APS), high-velocity oxygen fuel (HVOF), and cold gas dynamic spraying (CGDS) methods. The microabrasion tests were performed on the samples for different durations in order to understand the wear mechanism of thermally sprayed coatings and influence of the coating microstructure on the wear mechanism. The microstructures of as-sprayed coatings and wear mechanisms on the worn coatings were investigated. Initial surface topography was examined using a surface profilometer. Coating hardness measurements were performed with a microhardness tester. The lateral fracture was observed as the wear mechanism on the samples. The wear resistance of the coatings has changed with the surface features of the samples depending on the coating production process.

A significant improvement in efficiency has been achieved by using thermal barrier coatings (TBCs) in gas turbines and diesel engines. A typical TBC is a multilayered coating system that comprises an oxidation-resistant metallic bond coating (BC) and a thermally insulating ceramic top coating (TC). Under service conditions an Al2O3 inter-layer, the thermally grown oxide (TGO), forms in the interface between the bond and the top coating, by a chemical reaction between the metallic aluminum from the BC material and the oxygen that comes from the environment through the pore channels of the TC. The aim of the present study is to describe the TGO formation on metallic bond coats deposited using the high-velocity oxygen fuel (HVOF) spraying technique. Therefore. TBCs that consist of a YSZ top (ZrO2 + 8 % Y2O3) and YSZ-Al2O3 double-layer systems with CoNiCrAlY bond coats were deposited on Inconel 718 super-alloy substrates. The bond coats were applied via HVOF, with the ceramic top coats being applied by atmospheric plasma spraying (APS) as well. The oxidation behaviors of the TBC systems were investigated. The oxidation tests were performed at 1000 degrees C in an air atmosphere for (8, 24, 50) h. The formation and growth of the TGO layers and the microstructural changes during the oxidation tests were scrutinized systematically. The results indicate that the TBC coating with the YSZ-Al2O3 double layer had a higher oxidation resistance and a lower TGO layer growth than that of the traditional TBC system. Likewise, the initial state of the porosity plays a critical role in enhancing or limiting the growth of the TGO scale in the TBC.