Microstructure Evolution of CET-Free Epitaxial Growth NiCoCrAlYTa Coating by Electron Beam Cladding

Abstract

Some unavoidable factors in the operating environment could damage single-crystal components of nickel-based single-crystal superalloys. This work prepared an epitaxial growth NiCoCrAlYTa repaired coating without the columnar-to-equiaxed transition (CET) phenomenon on a nickel-based single-crystal superalloy by electron beam cladding. The microstructure of two cross-sections and two surfaces at different depths were characterized. Moreover, the formation mechanism of coating dendrite was revealed by studying the relationship between coating dendrite size, growth direction, and solidification rate. The microstructure evolution and crystal growth orientation of the coating were investigated. The microstructural investigation of the sample revealed that the dendrites’ orientations on the coating’s horizontal section were different, and its characteristics were highly visible on the surface of the coating. The crystal growth orientations of the coating on the vertical cross-section parallel/perpendicular to the scanning direction of the electron beam were also different. Moreover, the average primary dendrite arm spacing (PDAS) of the columnar dendrite in the different areas of the coating was different and increased from 2 μm to 4 μm. The oxidation resistance of the coating at 1000 °C was about three times higher than that of the substrate.