Study of the Corrosion Resistance of Cr3C2-NiCr-Based Gradient Detonation Coatings

This study presents a comparative investigation of the structure, adhesion and corrosion properties of homogeneous and gradient Cr3C2-NiCr detonation coatings formed on the surface of 12Kh1MF steel. A Cr3C2-NiCr composite powder with a composition of 75/25 and a particle size of 10–45 µm was used to apply the coatings, using a CCDS2000 detonation spraying system. A homogeneous coating was formed at a constant gas mixture filling ratio of 57 per cent, whilst a gradient coating was obtained by sequentially varying the filling ratio from 57 to 64 to 73 per cent, which ensured the formation of layers with different structural and phase states. An investigation of the microstructure and elemental composition revealed a uniform distribution of components in the homogeneous coating and a regular variation in the Cr and Ni content across the thickness of the gradient coating. X-ray phase analysis identified the presence of the Cr3C2, Cr3Ni2 and CrNi3 phases. Corrosion resistance was assessed using the potentiodynamic polarization method in a 3.5 per cent Na2SO4 solution and through long-term tests in hydrochloric acid mist with the addition of CuCl2·2H2O, lasting up to 1000 h. The polarization curves of the gradient coating were shifted towards the region of lower current densities, indicating a slowing down of both anodic and cathodic electrochemical processes. In the tested specimens, visible corrosion was first observed on the homogeneous coating after 456 h, whereas no visible corrosion damage was observed on the gradient coating after 1000 h. Mass loss amounted to 1.14 per cent for the homogeneous coating and 0.17 per cent for the gradient coating. The enhanced corrosion resistance of the gradient coating is due to its denser layered structure and the barrier effect of the interlayer boundaries, which prevent the propagation of through-cracks and the penetration of the aggressive medium to the ‘coating-substrate’ interface. The results obtained demonstrate the potential of forming a Cr3C2-NiCr gradient structure to enhance the protective and operational characteristics of detonation coatings.