Microstructure evolution along build direction for thin-wall components fabricated with wire-direct energy deposition

• Published in: Rapid prototyping journal Vol. 27; no. 7; pp. 1289 - 1301
• Main Authors: Kulkarni, Janmejay Dattatraya, Goka, Suresh Babu, Parchuri, Pradeep Kumar, Yamamoto, Hajime, Ito, Kazuhiro, Simhambhatla, Suryakumar
• Format: Journal Article
• Language: English
• Published: Bradford Emerald Publishing Limited 03.08.2021; Emerald Group Publishing Limited
• Subjects: Additive manufacturing; Anisotropy; Arc deposition; Boundary conditions; Convection cooling; Cooling; Cooling curves; Electron backscatter diffraction; Evolution; Gas metal arc welding; Heat; Heat treating; Laminates; Lasers; Mechanical properties; Microhardness; Microstructure; Modelling; Near net shaping; Phase transitions; Production methods; Rapid prototyping; Rapid solidification; Substrates; Thermal analysis; Wire; Multi-layer microstructure evolution; Wire-direct energy deposition (W-DED); Metal additive manufacturing; Mechanical properties; Microstructure; Thin-wall components; Wire-arc additive manufacturing (WAAM)
• DOI: 10.1108/RPJ-04-2020-0085
• ISSN: 1355-2546

Purpose The use of a gas metal arc welding-based weld-deposition, referred to as wire-direct energy deposition or wire-arc additive manufacturing, is one of the notable additive manufacturing methods for producing metallic components at high deposition rates. In this method, the near-net shape is manufactured through layer-by-layer weld-deposition on a substrate. However, as a result of this sequential weld-deposition, different layers are subjected to different types of thermal cycles and partial re-melting. The resulting microstructural evolution of the material may not be uniform. Hence, the purpose of this study is to assess microstructure variation along with the lamination direction (or build direction). Design/methodology/approach The study was carried out for two different boundary conditions, namely, isolated condition and cooled condition. The microstructural evolution across the layers is hypothesized based on experimental assessment; this included microhardness, scanning electron microscopy imaging and electron backscatter diffraction analysis. These conditions subsequently collaborated with the help of thermal modeling of the process. Findings During a new layer deposition, the previous layer also is subject to re-melt. While the newly added layer undergoes rapid cooling through a combination of convection, conduction and radiation losses, the penultimate layer, sees a slower cooling curve due to its smaller exposure area. This behavior of rapid-solidification and subsequent re-melting and re-solidification is a progressing phenomenon across the layers and the bulk of the layers have uniform grains due to this remelt-re-solidification phenomenon. Research limitations/implications This paper studies the microstructure variation along with the build direction for thin-walled components fabricated through weld-deposition. This study would be helpful in addressing the issue of anisotropy resulting from the distinctive thermal history of each layer in the overall theme of metal additive manufacturing. Originality/value The unique aspect of this paper is the postulation of a generic hypothesis, based on experimental findings and supported by thermal modeling of the process, for remelt-re-solidification phenomenon followed by temperature raising/lowering repetitively in every layer deposition across the layers. This is implemented for different types of base plate conditions, revealing the role of boundary conditions on the microstructure evolution.