Jan_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J A N U A R Y 2 0 1 6 2 0 Fig. 4 — Typical microstructure of a HIP’d specimen. Courtesy of NASA. Microhardness testing was per- formed on one fully processed speci- men. The specimen ranged from 432 to 466 HV 200 (44-47 HRC). Weld devel- opment showed no defects at 20 × magnification. DEVELOPMENT CHALLENGES A few challenges occurred during

crack-like defect. The dark feature is a defect at the surface level only. It is pos- sible that the feature is a relative offset between different layers of the parts. Additionally, all production parts were accidentally stress relieved in air, which was evident when the parts came out with a brown color. The concernwas that the integral mesh would embrit- tle due to oxidation. The z orientation tensile specimen cross-sectioned for the build pause feature was also exam- ined for oxidation. Less than 0.001-in. oxidation was observed. Following manufacturing, all parts were subjected to an acceptance vibration test to mim- ic flight conditions. All parts passed and no integral meshes were damaged. POST-MISSION EVALUATION Orion’s Exploration Flight Test 1 was successful and the passive vents performed their function without inci- dent. After landing and recovery, vents were removed from the vehicle and ex- amined. Visual inspection revealed no defects. CONCLUSIONS Additive manufacturing was an ideal process for making these vent assemblies because it reduced individ- ual part count and eliminated mesh welding. It also improved the material “buy-to-fly” ratio because the previ- ous design included machining the thin housing from a large piece of bar. Further, developing the manufacturing process on lightly loaded parts such as these vents allows innovation with low technical risk. Several improvements and addi- tional steps should be considered in the future. First, the tensile specimens did not reflect the exact part geometry. It is possible that specimen size (and sub- sequent microstructure, heating, and cooling rates) affects material proper- ties. No work was done to correlate the effect of specimen size or geometry. Vents were nonstructural parts made from a high-strength alloy, so the ef- fects of specimen sizes and geometry were not a major concern. However,

Fig. 5 — Defects in the integral mesh of a development part.

development. Initial parts had dimen- sional errors while the AM process was being refined. For example, defects in the integral mesh are shown in Fig. 5. One part was scrapped due to unconsolidated material in one of the mounting flanges. This was evident af- ter minor machining of the area near the bolt hole revealed a crosshatch pat- tern with visible voids. Also, there was a pause in the build cycle of one of the production parts, which was caused by a power bump. The machine was off for a few

hours before the process was restarted. Visual inspection of the as-printed part reveals a dark horizontal line (Fig. 6). The build pause feature was also present near the end of the z orienta- tion (vertical) tensile specimen (Fig. 7). Ideally, this feature would have been in the test region of the tensile specimen, but was not. So the tensile specimen was cross-sectioned and metallurgically evaluated. There was no evidence of a microstructural anomaly or a crack or

Fig. 6 — As-manufactured part with build pause visible.