Study on the micro-structure and the nano-indentation responses of laser solid formed epitaxial Ni-based superalloy

Laser solid forming (LSF) is one of the most promising technologies which has been extensively applied for the reshape and fabrication of the thermal parts in gas turbine and aero-engine. In this paper, the Ni-based single crystal superalloy thin-walled parts were prepared by using the LSF technology. Then, the electron back-scatter diffraction (EBSD) and the scanning electron microscope (SEM) technologies were employed to characterize the micro-structure morphology and crystallographic orientation of grains. The dislocation density of Ni-based superalloy thin-walled parts was analyzed. The results showed that a remarkable micro-structure gradient with respect to different heights of repaired Ni-based superalloy thin-walled parts was observed after the LSF process while the micro-structure distribution in width direction is comparatively more uniform. In addition, the misorientation of crystallographic orientation can be attributed to the dislocation density. A higher dislocation density contributes to aggregation of massive low angle grain boundaries (LAGBs) and formation of high angle grain boundaries (HAGBs), which in return conversely reduces dislocation density within the material. Finally, the mechanical properties of the LSF epitaxial Ni-based superalloy were investigated by the cyclic creep and Nano-indentation tests. The results showed that with the increasing of repair height, the residual indentation depth increased, while the elastic modulus increased first and then decreased. Meanwhile, a lower hardness of the stray grain region was obtained comparing with that of the substrate. Within the stray grain region, the hardness decreases along the building direction.