A Feasibility Study on Directed Energy Deposition of SS 316L with Coaxial Wire-powder Feeding

Abstract

Compared to single wire/powder feeding, the directed energy deposition (DED) technique with coincident wire-powder feeding enables the fabrication of metallic parts with high deposition efficiency and performance. The existing investigations on DED process with wire-powder feeding utilized the combination of lateral wire feeding and coaxial/lateral powder feeding. In addition, they found that the deposition efficiency and final performance can be improved by increasing the wire injection angle in a vertical plane. However, the DED of metallic parts with coaxial wire-powder feeding remains unexplored due to the machine limitation. In this paper, we studied the effects of powder feed rates on the surface quality, defects, and microstructure of as-built SS 316L parts with coaxial wire-powder feeding. The results found that the surface finish of wire-deposited samples is much better than as-built samples fabricated with high powder feeding rates. In addition, the dual feedstock DED process has a higher susceptibility to porosity than pure wire deposition due to the entrapped gas in powder particles, and the porosity increases with the powder feed rate. Moreover, the wire-deposited samples present more distinct melt pool boundaries than those fabricated with wire-powder feeding. With an increase in powder feed rate, the grain size and grain boundary thickness in the fusion areas experience a decrease first and subsequent increase. This paper will provide guidelines for the efficient production of high-performance metallic alloy/composites with coaxial wire-powder feeding.