Crystalline controlled cladding of Ni-base single crystal superalloy by diode laser

Abstract

Microstructure and crystallographic orientation in the surface-melted region and clad region by diode laser have been investigated using Ni-base single crystal superalloy CMSX-4. The laser power and scanning speed in laser surface melting and cladding were varied. The microstructure and crystal orientation were analyzed by optical microscopy, scanning electron microscopy and electron backscattered diffraction pattern. The surface-melted region under the low heat input condition was found to be solidified as the single-crystalline state with uni-directional dendrites which grew along the [001] directions. The surface-melted region under intermediate heat input condition was also single-crystalline with dendrites which grew along the [001], [010] and [100] directions. In contrast, the surface-melted region under high heat input condition was consisted of polycrystal with stray crystals. The theoretical analysis of growth direction of dendrite and the constitutional supercooling at the solidification front indicated that the stray crystal tended to be formed with low scanning speed and high laser power. Microstructural observation revealed that the cladding layer grew epitaxially on the base metal, and that crystalline controlled cladding could be achieved by laser cladding.Microstructure and crystallographic orientation in the surface-melted region and clad region by diode laser have been investigated using Ni-base single crystal superalloy CMSX-4. The laser power and scanning speed in laser surface melting and cladding were varied. The microstructure and crystal orientation were analyzed by optical microscopy, scanning electron microscopy and electron backscattered diffraction pattern. The surface-melted region under the low heat input condition was found to be solidified as the single-crystalline state with uni-directional dendrites which grew along the [001] directions. The surface-melted region under intermediate heat input condition was also single-crystalline with dendrites which grew along the [001], [010] and [100] directions. In contrast, the surface-melted region under high heat input condition was consisted of polycrystal with stray crystals. The theoretical analysis of growth direction of dendrite and the constitutional supercooling at the solidification front i...