Laser-directed energy deposition of CuCrZr alloy: from statistical process parameter optimization to microstructural analysis

Laser-directed energy deposition (LDED) is a suitable manufacturing technology for processing CuCrZr alloy that has recently gained interest to be used in high heat flux applications due to its unique thermal properties. Despite its promising properties, the successful deposition of CuCrZr alloy through LDED processing is impeded by its low laser-material absorptivity and high thermal conductivity. To address this challenge, a systematic investigation was conducted using a 2-kW disk laser with a wavelength of 1064 nm and a coaxial nozzle head, as detailed in this study. In that regard, process parameter optimization is exercised first to achieve proper deposition, then the microstructure, and microhardness of single tracks are investigated. In this study, a two-step statistical optimization approach utilizing response surface methodology (RSM) is employed to optimize the geometrical characteristics of the tracks, while laser power, scanning speed, and powder feed rate are considered input variables. The laser power of 1550 W, scanning speed of 4.5 mm/s, and feed rate of 12 g/min are found as the optimum set of process parameters that yield acceptable single-track geometries with proper bead shape and sufficient amount of dilution as well as the maximum deposition rate. Furthermore, the results from the microstructural characterization by optical microscopy, SEM, and EBSD reveal the correlation between the microstructure and the process parameters. Increasing the laser power (P) from 1250 to 1550 W and decreasing the combined parameter of powder feed rate over scanning speed (F/V) from 0.05 to 0.036 g/mm resulted in a noticeable increase in columnarity of the grain structure from 41 to 51.5%. Finally, the microhardness results revealed a moderate transition of hardness from the top of the bead to the bottom of the melt pool for all samples.