Epitaxial laser deposition of single crystal Ni-based superalloys: Repair of complex geometry

A multi-track single crystal structure produced by laser cladding can be succeeded on a flat but failed on complex geometry for single crystal superalloys repair. It was always accompanied with stray grains and cracks when the complex shape defects were repaired by laser cladding. According to analysis, the geometrical profile of the defect may change the heat dissipation condition during laser cladding so that it promotes to form stray grains locally. In this paper, the off-axis heat flow angle (beta) which was defined by the heat flow direction and the dendritic growth direction, was used to evaluate the formation of stray grains. Results showed that dendrites grew epitaxially along the preferred crystal orientation which was closer to heat flow. In addition, stray grains could not be formed in the epitaxial columnar dendrite region until the beta was more than the critical value of 30 degrees. Two preferred orientations competed for growth perpendicular to each other when the beta was close to 45 degrees. Therefore, the repair principle was proposed that the beta was not more than 30 degrees ensured by geometrical profile design, and a v-groove defect was successfully guided and repaired.