Ripple formations determine the heterogeneous microstructure of directed energy deposition (DED)-printed 316L components. (March 2023)

• Record Type: Journal Article
• Authors: Balhara, Himanshu; Botcha, Bhaskar; Wolff, Sarah J.; Bukkapatnam, Satish T.S.
• Is Part Of: Materials & design. Volume 227(2023)
• Publication Date: 2023-03
• Subjects: Directed Energy Deposition (DED) -- Ripples -- Microstructure -- 316L; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2023.111756
• Languages: English
• ISSNs: 0264-1275

Abstract

Graphical abstract: Highlights: Reports the effect of laser directed energy deposition (DED) parameters on the multi-scale microstructure, as well as the nature and the characteristics of the morphological formations on surface, namely, ripple waveforms and scan tracks. Establishes that the heterogeneities in the type, size and orientations of the microstructure and dendritic patterns on scan surface of DED-printed 316L components are informed by the ripple patterns. The complex waveform patterns of the ripples and their variations with laser power indicate that additional phenomena beyond the Marangoni effect determine the mass transport in the melt pool regions in a DED process. Abstract: This paper presents an experimental study to characterize the ripples and other morphological formations as well as their influence on the heterogeneous microstructure on the surfaces of the directed energy deposition (DED)-printed stainless steel (316L) components. While ripple formations in the welding literature have been studied extensively, they have not received much attention in the DED process. They are often wrongly conflated with the melt pool geometry. The experiments consisted of printing 10 mm cubic components on a hybrid machine tool (MTS 500 from Optomec) under nine different combinations of laser power, scan speed and dwell time. The ripple formations and the microstructure on the scan surface were subsequently observed and statistically characterized at four different magnifications on an optical microscope. The study establishes that the ripple traces are a main determinant of the dendritic structures, as well as the heterogeneous spatial distribution of the microstructure formations in DED-printed 316 components. The statistical characterization also highlights the limitations of the ripple waveform descriptors employed commonly in the welding literature and introduces spectral quantifiers to adequately capture the complex waveform patterns of ripples in DED.