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The aim of this study is to determine the cyclic oxidation behavior of boron carbide (B 4 C) in the air atmosphere at elevated temperatures. For this purpose, as-received B 4 C powders were characterized by XRD and SEM and then shaped by the cold pressing method for oxidation studies. Tests were performed in the air atmosphere at 800˚C and 1000˚C for 5, 10, 15 and 20 hours. Oxidation behavior of the samples was evaluated by weight changes. XRD, SEM and EDS analyses were also conducted on the oxidized samples. It was observed that cyclic oxidation behaviors of the samples depended on temperature and time. Based on the analyses results and the microstructure observations, volatilization of B 2 O 3 had a significant effect on the oxidation of the samples as the temperature increased.

Inconel superalloys are used substantially in high-temperature environments. However, these alloys suffer from corrosion and wear. Attempts to overcome these drawbacks involve coating the metal with different techniques and materials. In this study, a new method with increasing potential was utilized. Using the mechanical alloying process in a planetary ball mill vial, alloying and the Al-Si coatings were concurrently achieved on Inconel 625 substrates. Different process control agent (PCA) ratios, milling ball diameters, and milling times were used to improve coating properties. Macro and microstructure, morphology, microhardness, and roughness values of samples were evaluated and compared. Additionally, crystallographic and cross-sectional properties were investigated in order to optimize the processing conditions. The results indicated that increasing the diameter of the grinding ball enhanced the hardness and thickness of these coatings and increased the roughness values. Longer processing time also enhanced the thickness with mechanical values. However, under these conditions, coating homogeneity decreased, and incompatible regions were formed on the coatings. PCA content brought a refined grain structure, hence showed better mechanical properties. On the other hand, processing time should be increased to get a denser and thicker protective layer against the operational conditions.

The aim of this study is to determine the cyclic oxidation behavior of cubic boron nitride (c-BN) and hexagonal boron nitride (h-BN) in air atmosphere at elevated temperatures. For this purpose, as-received powders of both compounds were first characterized by XRD and SEM. c-BN and h-BN powders were shaped by cold pressing for oxidation studies. Tests were performed in air atmosphere at 800 • C and 1000 • C for 5, 10, 15 and 20 hours. After each oxidation test, the mass changes were measured. XRD, SEM and EDS analyses were conducted on the oxidized samples and the results were discussed.

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