Coaxial laser directed energy deposition with wire of thin-walled duplex stainless steel parts: Process discontinuities and their impact on the mechanical properties

Abstract

The topic of this paper is the process stability and its influence on the tensile material properties of duplex stainless steel manufactured via coaxial laser directed energy deposition with wire. The influence of slight changes in the prescribed offset per layer and laser power on the process stability, occurrence of discontinuities, and mechanical properties of duplex stainless steel 2209 parts was investigated. If the prescribed offset or laser power was too high, overheating of the melt-pool was observed. Otherwise, plunging of the wire through the melt-pool occurred. Stable processing was achieved by the adaptation of prescribed offset and laser power according to limited exponential growth laws. The overheating of the melt-pool leads to unsalvageable instabilities, whereas plunging of the wire through the melt-pool leads to self-stabilization by lowering the effective deposition rate and layer height. The discontinuities at sites, where wire plunged through the melt-pool are limited to the surface of the parts. The microstructure and tensile mechanical properties are unaffected by the presence of the surface discontinuities when they are removed by a machining step. The yield strength, ultimate tensile strength, and fracture strain exhibit a strong directionality, which can be explained by the anisotropy and inhomogeneity of the microstructure consisting of austenite-rich layers and ferrite-rich layer bands.