Microstructural and Mechanical Properties of a NiCoCrAlY Coating Prepared by laser Cladding on a Compacted graphite Cast iron surface
H. Liu, G. Yu, X.L. He, H.F. Yang and Z.T. Han
Laser cladding with synchronous powder feeding on the surface of compacted graphite cast iron (CGCI) was conducted using NiCoCrAlY powder in this research, with the aim of obtaining coatings mainly consisting of directional columnar crystals in the microstructure. A metallographic microscope, scanning electron microscope (SEM), X-ray diffractometer (XRD), and Vickers hardness tester were used to analyse the dilution rate, bonding properties, microstructure, and microhardness of the coating. The research results showed that: the alloy coating mainly consisted of the dendrites of γ (Fe, Ni) and the carbide phases of Cr7C3 and Cr23C6 between grain boundaries. Meanwhile, it was discovered that the powder feed rate can significantly influence the crystalline state within the coating: with increasing powder feed rate, the microstructure of the coating was gradually converted from dendrites with poor directivity to columnar crystals with strong directivity, and the average microhardness was reduced owning to the decrease of the amount of Cr7C3 and Cr23C6 phases.
Keywords: Nd:YAG laser, compacted graphite cast iron (CGCI), NiCoCrAlY powder, laser cladding, columnar crystal growth, bonding interface, microhardness, powder feed rate