Process maps and optimal processing windows based on three-dimensional morphological characteristics in laser directed energy deposition of Ni-based alloy

Abstract

Constructing processing window to fabricate defect-free components with high forming quality and desired performance has been crucial in directed energy deposition. Due to its complexity as a mass and energy time-dependent system, it is still a key problem to be solved for laser powder-fed additive manufacturing to choose opportune processing parameters. In this paper, single scan track experiments were conducted under various combinations of processing parameters including laser power, scanning speed and powder feeding rate. Scan tracks had been thoroughly investigated through three-dimensional information including surface, longitudinal section and transverse section, which were correlated to each other in showing track morphological characteristics in directed energy deposition. Surface ripples, resembling fish scale in welding and chevron in selective laser melting, were found in directed energy deposition under low powder feeding rate and high linear energy density. Furthermore, several quantitative indexes, which were dimensionless mean roughness and ripples’ interval in surface, dimensional roughness in longitudinal section and dilution rate in transverse section, were used to evaluate the forming quality. These quantitative indexes were found to be closely related to the defects in additive manufacturing, and forming quality and accuracy of additive-manufactured components. Relationship between proposed indexes and processing parameters was studied and the mechanism behind it was also discussed. Five states which were no fusion, lack of fusion, optimum, rough surface and undesired dilution rate were distinguished based on the proposed quantitative indexes. Finally, a processing window based on these indexes was proposed for the laser powder-fed additive manufacturing for Inconel alloys. It is found that powder feeding rate affects the distribution of the five states and laser power, scanning speed affect the range of the five states.