Microstructure evolution of Cr coatings on Cu substrates prepared by mechanical alloying method

Production and Characterization of Al-Si Coatings Fabricated by Mechanical Alloying Method on Inconel 625 Superalloy Substrates

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.

Two steps CrAlFeSi coating on low carbon steel prepared by mechanical alloying and its oxidation properties

Two steps CrAlFeSi coating has been fabricated on low carbon steel via mechanical alloying methods and its oxidation properties have been elucidated thoroughly. First, Al coating was deposited on the low carbon steel substrate via mechanical alloying for 1 h. Afterward, CrAlFeSi coating was deposited on Al coating using the same technique for 2 h. The effect of annealing at 650 °C on the oxidation behavior of two steps CrAlFeSi coatings was examined thoroughly. The microstructure of the coating layer before and after annealing was relatively similar. Microholes and microcracks were found in the coating layer of the substrate before and after annealing. Intermetallic phases were observed in the samples along with the major elements. The mass gain after cyclic oxidation at 800 °C in the air atmosphere for a substrate with two coating layers reduced by a factor of 10 compared to the substrate without coating layer, which is likely due to the formation of Al2O3 on the outer layer during the oxidation process. The thin layer of Al2O3 protects the inner layer from severe oxidation. Therefore, the two steps coating of CrAlFeSi on the low carbon steel can be used as an alternative method for reducing the oxidation at high temperature.