Additive manufacturing of stellite 6 superalloy by direct laser metal deposition – Part 1: Effects of laser power and focal plane position

Abstract

This paper surveys the additive manufacturing (AM) of stellite 6 Cobalt-based superalloy by direct laser metal deposition method (DLMD) experimentally. In the present research, a coaxial nozzle head coupled with a continuous fiber laser with a maximum power of 1 kW was used. The purpose of the current research is investigating two strategies for DLMD additive manufacturing; the first one was changing the focal plane position of the laser beam inside the powder stream, 4 mm above and 4 mm below the powder concentration plane, and the second one was investigating the variation of the laser power (100–300 W). Some characteristics such as the geometrical dimensions (height and width), microhardness profile, grain size, and microstructure of the 3D printed wall samples were studied. The stability of the additively manufactured wall in terms of height was investigated. The results indicated that locating the focal plane position above the substrate, led to the more interaction area between the laser beam and powder stream and caused the higher height of the AMed wall. Results showed that when the focal plane position is near to the powder stream focus, the more stability will be obtained. By locating the laser spot point 2 mm above the powder concentration plane, better stability achieved. Increasing the laser power has a reverse effect on the height and stability: the more laser power, the higher height of the AMed wall, and the less stability observed. Results indicate that the laser power of 100 and 150 W has the highest height stability. The trend of changes in the grain size of the samples shows that the beginning and the end of the AMed wall are more significant than the sample’s center and the trend of the microhardness variation is in a reverse regime of the grain size. Also, the average grain size will be increased when the laser power increased. The largest and the smallest average grain size are 3.13 μm and 2.11 μm for the highest and the lowest laser power, respectively.