High power selective laser melting of crack sensitive nickel-base alloy CM247LC, including dimensional analysis and modelling

Abstract

High power parameters with increased scan velocities and beam diameters are investigated, to decrease the production time for crack sensitive alloy CM247LC. Results are compared to crack-free reference LPBF-samples in the low power range. The re-scaling approach for the high power range is based on the constant maximum laser intensity from the reference parameters in the low power range. While keeping the laser power to scan velocity ratio constant, the re-scaling approach, also called “intensity approach”, provides an initial estimation for the laser spot size in the high power range. The investigated cracks from the high power range are identified as “re-melting cracks”. Solidification or hot cracks are not observed, since the crack healing effect for those kinds of cracks still occurs. Furthermore, a melt pool depth range is discovered, where not only solidification cracks can be avoided, but also re-melting cracks, which are resulting from higher laser power inputs. This theory can be proven by further laser spot size optimization, where the melt pool depth comes closer to the mentioned range. The Archimedean density and crack density results, in case of the 600 W power parameter with 2400 mm/s scan velocity and a beam diameter of 164 µm, are close to the one obtained from the reference samples, based on 200 W. With the intensity approach and laser beam diameter optimization, the production time can be reduced by 300%. Based on dimensional analysis, a model, which combines the samples density with the crack density through the melt pool depth, is presented. Six main and two additional process and laser parameters are taken into relation. The result from the model and the measured values from experiments are in agreement. Additionally, the influence of the doubled layer thickness and an increased hatch distance by 50% with varying scan velocities on the Archimedean density and crack density is analysed.