Ni/TiC composite electrodeposition on the surface of Ni-based superalloy

Abstract

Composite electrodeposition technology was used to form Ni/TiC composite coatings on a Ni-based filler metal to introduce dispersive and uniform particles during the welding process. Scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were used to study the effects of composite electrodeposition parameters (current density, electrodeposition temperature and TiC particle concentration) on coating microstructure (the porosity, deposition percentage of particle, surface morphology and preferred orientation of the coating). Finally, an arc welding was performed to study the effect of TiC particle introduction on the weld microstructure. By observation, the increase in current density from 6 A/dm2 to 8 A/dm2 reduced the deposition percentage of TiC particle from 12.7% to 6.0%. The maximum deposition percentage of TiC particle was 14.2% at the optimum deposition temperature of 45 °C. According to the result, the ratio of nickel sulfate concentration to TiC particle concentration was proved to have main effect on surface flatness and porosity of coating, the coating with the best flatness and lowest porosity was prepared with TiC particle concentration of 30 g/L in electrolyte. In addition, the composite coating deposited on the smooth surface showed good bonding with the substrate. Welding tests indicated that the introduction of TiC particles increased the tortuosity of the grain boundaries and refined the grains. The average grain size of the weld decreased from 224.24 to145.88 μm at a particle content of 1.0%. The average grain diameter decreased by 34%. The strain fracture (STF) test shows that at the most sensitive temperature of DDC (1050 °C), the critical strain of DDC is increased to 3.5% after the introduction of TiC particles (which is close to the performance of FM-82), while the DDC critical strain of the original welding material FM-52M is 2.4%. The result shows that the DDC resistance of the weld has been improved.