Mechanical stability of boron-based coatings grown on Incoloy 909 superalloy by thermochemical diffusion

Incoloy 909 superalloy was treated at 950 degrees C to form coatings of different chemical composition by thermochemical diffusion. Packing of the samples in reactive powders lead to the formation of iron borides (Fe2B and FeB) together with nickel boride, NiB, and nickel silicide, Ni2Si, on the surface of the alloy depending on the exposure time. X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy analyses suggest that growth of the coatings is controlled by diffusion of reactive species into the metal structure. Microabrasion wear resistance of the coated specimens was studied at 1 N load for a fixed sliding speed of 0.11 m s(-1) and it was compared against uncoated samples of the alloy. It was found that coating the alloy for 12 and 20 h increased the hardness of the alloy and therefore its wear resistance.