Effect of defocus amount of nanosecond laser line spot on the laser ablation characteristics of nickel-based superalloys.

Nickel-based superalloy (DZ411), which has excellent physical and mechanical properties at high temperature, is widely used in the manufacture of high-temperature components in the aerospace field. Laser processing is an advanced special processing technology that can be used to improve the surface properties of nickel-base superalloys. In this paper, a new laser processing technology was investigated by using the line spot formed by the adjustment of diffractive optical elements. The influence of defocus amount on the line spot ablation of nickel-based superalloy was analyzed. The characteristic sizes, surface morphologies, and elements distribution of line spot ablation were observed. The results show that the groove ablated by the line spot is the longest at the focused position, while the narrowest and deepest groove is produced at the − 0.5 mm defocus position instead of the focused position, which is caused by the plasma shielding effect. And the machining trace of the groove processed at the − 0.5 mm defocus position is the most uniform one and rich in Ni at the center of the groove, making the − 0.5 mm defocus position the most suitable machining position. Under the observation of the electron scanning microscope, the grooves ablated by the line spot in the focus and the nearby areas are relatively flat. As the defocus amount increases, the irregular spherical melts begin to appear in the center of the groove formed by the line spot ablation. Thermal cracks occur on the workpiece surface at the position where the defocus amount is too large. EDS analysis shows that the vicinity of Al, Ti, and Ta elements in the focus increased significantly, and it is easy to form intermetallic compounds with Ni in the matrix. The edge of the line spot is in full contact with the air, resulting in obvious oxidation of the material, and the Al element is significantly increased. According to this data, it is speculated that Al₂O₃ oxide protective film is formed in this specific area. This work can provide guidance for the process optimization of line spot high efficiency processing of nickel-based superalloys. [ABSTRACT FROM AUTHOR]