Microstructural and electrochemical corrosion properties of electroless Ni-P-TaC composite coating

Ceramic particles are frequently used as reinforcements in electroless Ni-P coating to enhance the mechanical and electrochemical properties. Tantalum carbide (TaC) is a well-known refractory ceramic material, with excellent mechanical properties such as high hardness and fracture toughness. However, its performance as a composite additive has not yet been investigated in the electroless Ni-P coating system. A detailed surface and microstructural analysis have been carried out to explain the mechanical hardness, as well as corrosion-resistant behavior of as-plated and heat treated Ni-P and Ni-P-TaC coating systems. Nanocrystallites of Ni and Ni3P phases along with incorporated TaC particles are distributed in heat treated composite coating as revealed by XRD and TEM analysis. A unique amorphous interface between TaC particle and coating matrix is observed in the Ni-P-TaC composite coating that has provided a protective layer to the corrosion attack at the grain boundaries and defects presented in the coatings. The phase and thermal oxidation behavior of Ni-P and Ni-P-TaC system studied via temperature-dependent Raman measurement show that the coating systems are stable in ambient environment up to 500 °C. The electrochemical corrosion test suggests good corrosion resistance properties of the heat treated Ni-P-TaC composite coating over as-plated Ni-P coating.