Numerical experimental investigation on the epitaxial growth of columnar crystal in laser metal direct forming of DZ125L super-alloy

The effect of scanning methods and overlap rate on the temperature field and microstructure evolution of DZ125L super-alloy elementary unit in laser metal direct forming is investigated numerically and experimentally. The results show that temperature field in the molten pool leads to the epitaxial growth of columnar crystal from the substrate; the columnar crystal grows highest at the center position; it is multi-directional crystal at the high part. For double-track forming, the temperature field and the change of microstructure in the overlap zone are strongly influenced by the scanning method and the overlap rate; the back-and-forth scanning method easily leads to the change of the solidified direction; the epitaxial growth of columnar crystal between cladding tracks is obtained when the overlap rate is big enough. The results of calculation agree well with that of experiment.