Abstract
A trial has been conducted to bond 1μm α-silicon carbide particles firmly with the Watts nickel matrix of the coating, by annealing the coating at temperatures as low as possible and at a reasonable rate. Formation of a strong bonding was found on annealing the coating at 600°C. The bonding reaction, as detected and characterized by tensile testing, X-ray diffraction, scanning and transmission electron microscopy, was found to have an incubation period of two minutes and then proceeded to form a bonding layer, which was a composite; SiC/Ni5Si2/Ni3Si/graphite/Ni. On further annealing at 600°C, the dispersed particles transformed into Ni3Si particles coated with graphite film. The bonding erased the easy crack at the particle/matrix interface, generated a ductility of the coatings, and doubled the tensile strength of a coating at 400°C. The strengthening was described in terms of the Orowan mechanism, wherein a reaction-induced particle growth was considered. Some properties of the coatings were described on the basis of the dense random packing of the dispersed particles. A reaction was found at the SiC/Ni interface even on 500°C annealing, but with the incubation period of about five hours.
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