High deposition rate powder- and wire-based laser directed energy deposition of metallic materials: A review

High deposition rate laser directed energy deposition (HDR-DED) technology, including powder- and wire-based laser directed energy deposition, has emerged recently to fulfil the requirements for the rapid and near-net manufacturing of large-scale and high-performance components. Compared with conventional laser directed energy deposition, HDR-DED requires higher laser energy input for melting substantial metal powders to achieve high deposition rates, which inevitably results in unique thermal histories and thus brings new opportunities and challenges in the fabrication and repair of metallic materials. However, the HDR-DED of metallic materials for industrial applications remains limited owing to inadequate systematic understanding regarding the forming process and controllability problems according to existing fragmented reports. Therefore, a comprehensive and holistic review is essential to elucidate the effect of significantly increasing the deposition rate (from ∼60 cm3/h to higher than 150 cm3/h, or more than 1000 cm3/h) on process optimization, system development, microstructure, and performances. Herein, typical nickel-based superalloys and titanium alloys are presented to demonstrate the technical features, process control, unique microstructure evolution, and mechanical properties associated with HDR-DED technology. The current mechanical property benchmarks for metallic materials prepared via HDR-DED are summarized and evaluated. In addition, the heat transfer behavior of melt pools, the formation mechanism of microstructures and the underlying strengthening mechanism for HDR-DED process are discussed. Finally, perspectives regarding materials developments, mechanisms explorations, process optimizations and system improvements for HDR-DED technology are presented.