Investigation into the direct laser forming process of steam turbine blade

In order to achieve high precision and unidirectional solidification microstructure of steam turbine blade fabricated by direct laser forming (DLF), this study is focused on the influence of the laser scanning speed, specific energy and powder feeding rate on the forming characteristics of single cladding pass, which is elementary units in DLF, and a new method of columnar crystal preparation is investigated. Results show that both the metal powder stream and the laser specific energy are the most important factors, that control the high temperature behavior of molten pool so as to determine the micro-morphology of laser scanning track. Based on the optimum processing conditions, high definition steam turbine blade of 316L is fabricated (surface roughness Ra of 10.08 to 26.51 μm or so). The microstructure is of fish scale type by natural cooling after DLF, but it is first found that columnar crystals can be formed on the non-columnar crystal substrate of 316L by intermittent cooling with liquid argon. Therefore, the above investigations will benefit the rapid development of steam turbine blade.

► Powder stream and laser specific energy are the main factors.
► Steam turbine blades from 316 L powders can be fabricated by direct laser forming.
► Columnar crystal can be formed on the non-columnar crystal substrate of 316 L.