Synthesis of Nickel Aluminide- Nano Diamond Composite Coating on Hastelloy X Ni-Base Superalloy

The wear and hardness properties of the protective aluminide coatings can be enhanced by reinforcing the surface, using hard materials such as diamonds. In this research, prior to the aluminizing process by pack cementation, an intermediate NickelNano diamond (Ni-ND) layer was fabricated on the surface of the Ni-based superalloy Hastelloy X with electroplating process. The electroplating of Ni-ND layer was accomplished by continuous direct current in nickel Watts electroplating bath containing 1 and 4 g/l ND particles. The coated and uncoated samples were aluminized by pack cementation method using aluminum, ammonium chloride and alumina powders. The aluminizing process was designed as a two-step procedure at 760 °C following the annealing process at 1080 °C. The cross-sections of the coated specimens were studied by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) analysis. The results showed that during aluminizing process, the nano-diamond particles prolonged the nickel and aluminum diffusion path and as a consequence, the aluminum content of the coating layer was increased. This gave rise to the conversion of the Ni-based intermediate composite layer into an aluminum-rich NiAl layer. The hardness of the treated coating with ND particles was significantly higher than the untreated coating in a way that microhardness of the coating with no ND particles was 663 Vickers while the coating containing ND particles showed a value of about 968 Vickers.