Characteristics of Bi-metallic Interfaces Formed During Direct Energy Deposition Additive Manufacturing Processing
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INTRODUCTION
ADDITIVE manufacturing (AM) processes are being evaluated for reducing the fabrication time and costs in various applications. The ability to directly print complex shapes with internal features in difficult to machine alloys is making this an attractive alternative to traditional subtractive manufacturing which requires subsequent assembly of multiple parts. AM processes for metal use either powder bed fusion (PBF) or direct energy deposition (DED).[1–3] Each process has their associated tradeoffs in terms of feature resolution and deposition rate. PBF printing has the highest resolution of feature size but is limited to slow deposition of monolithic components that fit within the powder box. In contrast, DED processes have lower feature resolution but are applicable to rapid deposition of larger scale components using multiple materials. DED processes
RYAN ANDERSON, JORDAN TERRELL, and JUDY SCHNEIDER are with the Department of Mechanical and Aerospace Engineering, University of Alabama in Huntsville, Huntsville, AL 35899. Contact e-mail: [email protected] SEAN THOMPSON is with the US Army CCDC Aviation and Missile Center, Redstone Arsenal, AL 35898. PAUL GRADL is with the NASA Marshall Space Flight Center, Huntsville, AL 35812. Manuscript submitted December 14, 2018. Article published online May 31, 2019. METALLURGICAL AND MATERIALS TRANSACTIONS B
use an energy source, such as a laser or plasma arc to directly build a component from feedstock, which can be either powder or wire. Several industries utilize bi-metallic material combinations in high heat flux applications.[4–6] Often these designs include an outer nickel (Ni)-based superalloy, selected for strength at elevated temperatures, joined to a copper (Cu) alloy, selected for thermal conductivity. Using this material combination in regeneratively cooled combustion chambers and nozzles for liquid rocket engine applications requires fabrication of large structures.[6] DED can print at these length scales and would greatly reduce the time and hence fabrication cost by eliminating multiple processing steps for one-step fabrication of bi-metallic components. However, little is known about the resulting interface formed as the metals are directly deposited on one another.[7–9] This study characterizes the resulting bi-metallic interface formed between Inconel 625 and C18150 in specimens fabricated by two different DED processes. Characterization techniques include microscopy and indention testing across the interface.
II.
BACKGROUND
In all DED processes, the heat source can be co-mounted onto either a robotic arm or a computer numerical control (CNC) platform. This configuration increases the degrees of freedom available for the
VOLUME 50B, AUGUST 2019—1921
deposition of material in the build. Typically, the heat source and feed system are fixed horizontally with the part rotating beneath the heat source. Wire-fed DED processes can use either a pulsed plasma arc, as shown in Figure 1, or a pulsed laser as shown in Figure 2. A wire feedstock is fed into t
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