Mechanism of high temperature mechanical properties enhancement of Ni-based superalloys repaired by laser directed energy deposition: Microstructure analysis and crystal plasticity simulation

The high-temperature tensile and fatigue performance play a crucial role in the applications of repaired Ni-based superalloys by Laser directed energy deposition (LDED). This work investigates the effect of microstructure on the high temperature (650 °C) mechanical behaviors of GH4169 superalloys repaired by LDED with the microstructure characterizations and crystal plasticity modelling. Results indicate that the solution and aging heat treatment (STA) is necessary to homogenize the distributions of precipitations. Microstructure characterizations and crystal plasticity modelling imply that the plasticity deformations occur mainly in columnar dendrites of fusion area and twin grains of substrate, which enhance the tensile strength and elongation rate of repaired area and demonstrates comparable characteristics with the casting alloy. At the same time, the existence of the Laves phase and carbide cannot eliminate the dynamic strain aging phenomenon of repaired material. Similarly, under high stress levels (850– 950 MPa), the fatigue performance of repaired material is primarily influenced by the plastic deformation and exhibits similarity to that of the substrate; however, under low stress levels (650– 750 MPa), it is primarily influenced by the presence of defects, resulting in an obviously longer fatigue life for the substrate.