Extreme high-speed-rate laser directed energy deposition of high strength low carbon stainless steel coating with layered heterogeneous structure

Abstract

In this work, a ferritic stainless steel coating was manufactured via extreme high-speed-rate directed energy deposition (EHLDED). Microstructural features and tensile behavior were investigated and analyzed. The microstructural analysis confirmed that EHLDED coating was characterized by alternating patterns of columnar dendrites and fine equiaxed dendrites. The average size of the dendrites was less than 1 μm. High-resolution transmission electron microscopy showed that there were a large number of dislocation lines (DLs) and dislocation tangles (DTs) enriched at inter-dendritic solidification structures attributed to the ultrahigh cooling and solidification as well as molten pool movement. In addition, a small percentage of predominantly nanosize carbides with the size ranging from 50 to 90 nm were also observed in dendrites and inter-dendritic solidification structures. The EHLDED coating sample manufactured at the deposition speed of 40 m/min showed a higher strength of 1084 MPa with the ductility 1.27%. Results reveal that the ultra-fine dendrites accompanied with nanosize carbides prepared by EHLDED contributed to achieving high strength of low carbon stainless steel coatings.