Influence of microwave heating on metallurgical and mechanical properties of Ni-40Cr 3 C 2 composite clads in the context of cavitation erosion resistance characteristics

Abstract

Surface modification is one of the most reliable solutions for protecting the material damage in hydraulic turbines due to cavitation phenomena. However, the conventional coating/cladding process has many drawbacks like high porosity, weak adhesion strength, and poor fracture toughness. In contrast, the cladding process with microwave hybrid heating can overcome these limitations. Hence, this study aims to develop the microwave processed composite clad of Ni-based alloy with 40% Cr₃C₂ (by wt.) on SS-316 substrate in the domestic microwave oven of 2.45 GHz frequency and 900 W power. The selection of the material system for this study was based on mitigating the effect of cavitation erosion. The thorough metallurgical and mechanical characterization of the developed composite clad was done. Microstructural characterization using scanning electron microscopy revealed that the developed composite clads had a uniform thickness of 600 µm and free from interfacial cracks and visible pores (measured porosity ∼1.67% – as per ASTM B276). Uniformly dispersed hexagonal and stripe type carbides precipitate in the Ni-based alloy matrix of the composite clad was observed through scanning electron microscopy images. X-ray diffraction analysis shows that various hard carbides (SiC, Ni₃C, Cr₃Ni₂SiC, Cr₇C₃, and NiC) and intermetallic (Ni₃Fe, Ni₂Si, and Cr₃Si) phases were formed during microwave heating. The microhardness, flexural strength, fracture toughness of the Ni-40Cr₃C₂ clads were evaluated. The results reveal that the composite clad possesses microhardness = 605 ± 80 HV_0.3 (∼3 times SS-316), flexural strength = 813.23 ± 16.2 MPa, and fracture toughness = 7.44 ± 0.2 MPa√m. The appropriate value of these properties makes this composite clad suitable for cavitation erosion resistance application.