Grain structure and texture control of additive manufactured nickel-based superalloy using quasi-continuous-wave laser directed energy deposition

The quasi-continuous-wave laser directed energy deposition (QCW-DED) process was proposed to control the grain structure and texture of additive manufactured nickel-based superalloy. The microstructure characteristics and solidification mechanisms of QCW-DED under different pulse frequencies were investigated by means of experiment and numerical simulation. The QCW-DED greatly modifies the solidification conditions and introduces the periodical re-melting of molten pool. The high pulse frequency promotes the epitaxial growth of columnar dendrites due to the slant-line-like molten-pool boundary, the inhibited columnar to equiaxed transition (CET) and the high-frequency remelting of molten pool. As a result, a high-intensity texture composed of regular zigzag grains was obtained. Owing to the semicircular molten-pool boundary, the promoted CET and the limited molten-pool remelting effect, the low pulse frequency inhibits the epitaxial growth of dendrites and develops a random texture composed of equiaxed or misoriented grains. This work provides a controllable processing window for tailoring the grain structure and texture using QCW-DED.