Dissolvable Supports in Powder Bed Fusion-Printed Stainless Steel

Abstract

This work demonstrates, for the first time, two approaches for dissolvable supports in powder bed fusion-printed metal parts. Expanding on our recent innovations with dissolvable supports in multimaterial direct energy deposition printing, this work brings dissolvable support capabilities to additive manufacturing systems that are limited to single-material builds. First, a direct dissolution approach is demonstrated with the supports electrochemically dissolved. While this process works, it is not self-terminating and maintaining dimensional accuracy for complex geometries is thus difficult. The second approach incorporates a sensitizing agent during the normal stress, relieving thermal annealing step to decrease the chemical stability of the top 100-200 lm of the component surface. The component is then etched under etching conditions with a high selectivity toward the ''sensitized'' surface over the base component material. This creates an etching process that self-terminates once the sensitized layer is removed. These two processes are first demonstrated using 17-4 PH stainless steel. Direct dissolution was conducted under anodic bias in a solution of HNO 3 / KCl/HCl; 120 lm of material were removed from the component's surface. For the self-terminating dissolution process, surface sensitization was done by exposing the sample to sodium hexacyanoferrate at 800°C for 6 h to carburize the top 100-200 lm of the sample. This carburization process captures the protective chromium in chromium carbide precipitates and renders the surface sensitive to chemical and electrochemical dissolution. The self-terminating etching reaction was demonstrated under anodic bias in a solution of HNO 3 /KCl. Open circuit potentials were measured at 10 s and 1 h, and polarization curves were used to identify the corrosion potential. Self-termination was verified by monitoring component diameter over time, and 120 lm of material were removed from the sensitized surface of the component. To further test the self-terminating sensitized approach, a set of 316 stainless steel interlocking rings were fabricated to demonstrate that this approach scales to large components with complex geometry. For these parts, this approach replaced 4-5 days of machining operations with a 32.5 h electrochemical bath.Opposite page: Dissolvable metal supports for Powder Bed Fusion (PBF) printed metals demonstrated with interlocking stainless steel rings. Photo credit: Owen Hildreth.

Support Thickness, Pitch, and Applied Bias Effects on the Carbide Formation, Surface Roughness, and Material Removal of Additively Manufactured 316 L Stainless Steel

“…(a) Potentiodynamic polarization plot of the as-printed sample (blue) and the sensitized sample (red). 13 Sensitization drops E corr by 600 mV, opening up a wide processing window where the sensitized region can be dissolved while the underlying component is cathodically protected. (b) Sensitized support showing the intragranular carbides and intergranular carbides for the support and the part.…”

Support Structures for Additive Manufacturing: A Review

“…The shortcoming is that this method is limited to producing eutectic alloys. Recently, Lefky et al [59], for the first time, brought dissolvable supports into powder bed based metal printers that are limited to single-material builds.…”

Complementary use of pulsed and continuous wave emission modes to stabilize melt pool geometry in laser powder bed fusion

“…Such strategies can be limited to the part geometry. The use of support structures can become invasive as the post-22 processing effort significantly increases [43]. Another approach is to use different scan strategies, tiling the larger sections to smaller ones as in the form of stripes, squares, or more complex fractal shapes [44].…”