NbC–Fe-graded composite coating was fabricated by in situ synthesis using a pure niobium plate and grey cast iron as the raw materials. SEM analysis demonstrates that the thickness of coating is about 400 μm. From the surface to the matrix, the volume fraction of NbC particulates continuously decreases from 95 to 0%, while the average particulate diameter gradually increases from 200 nm to 1 μm. Along the depth towards the matrix, the nano-hardness and elastic modulus of the graded coating decrease from 23.5 to 3 GPa and from 435 to 150 GPa, respectively. In addition, the fracture toughness (KC) of 8.62 MPa m1/2 is obtained on the surface of the coating by the Vickers indentation technique. And the fracture mechanism is intergranular cracking.
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