Development of Optimized Printing And Postprocessing Parameters And Associated Component Performance Data For Additively Manufactured Stainless Steel Components For Sustainment Applications

N. Michaud, R. Shealy
REM Surface Engineering,
United States

Keywords: additive manufacturing, stainless steel, postprocessing, surface finishing

Summary:

Additive Manufacturing (AM) is revolutionizing many industries, including the aerospace and space industries. AM allows for rapid printing, reduced lead times, and complex designs/features not possible via traditional manufacturing. AM has facilitated a range of new alloys with extremely high mechanical and performance characteristics, representing great potential for components such as firing chambers and fuel nozzles. Unfortunately, as-printed AM components also carry many inherent challenges that can hinder performance or even lead to critical component failure, hindering access to the benefits described above. These defects include partially sintered/unsintered powders, surface waviness/roughness, and surface and near-surface porosity as artifacts of the printing process. REM Surface Engineering has been a leading provider of isotropic superfinishing services for decades. We have recently adapted our existing technologies and developed new technologies to create a superfinishing process capable of remediating all surface and near surface defects on AM components. In combining unique chemical polishing and chemical/mechanical polishing, we are able to remediate all surface defects, as well as near surface defects, and polish internal channels/non-line-of-sight surfaces (which traditional processes cannot accomplish). Furthermore, the process has been proven to significantly increase fatigue life and performance over as-printed parts. Since being awarded our first Phase I NASA SBIR contract in 2018, REM has received over $7 million in federal funding to further develop processes for NASA Marshall and NASA JPL as well as Air Force Armament and Sustainment division’s unique needs. These efforts include developed/developing finishing techniques for Nickel-based superalloys (Inconel 625, Inconel 718, NASA HR-1, JBK-75), Copper (GrCOP-42, GrCOP-84), Aluminum alloys (Al-6061-RAM2, Scalmalloy, A7050, Ti-6Al-4V, F357), and Stainless Steel alloys (17-4, 15-5, 316L) and we have also successfully developed guidelines for the production of high-use IN-718 AM components. Implementation projects are underway for ongoing research and processing of full-scale propulsion components for NASA as well as Commercial Space customers. This presentation highlights ongoing REM efforts to develop chemistries and processes for alloys of interest to federal and commercial manufacturing – specifically Stainless Steel-based alloys (SSA). Surface and near-surface defects, such as roughness/waviness, porosity, or partially sintered metallic powder, are remediated by controlled material removal to yield smooth planarized surfaces. This extends to modification of internal cavity surfaces as well, provided the cavity is accessible. For example complex coolant passages can be incorporated into the walls of firing chambers or rocket nozzles without the lingering burden of imperfections which can create an environment for crevice corrosion or FOD. During this SBIR Phase II effort, REM is targeting chemistries and processes for multiple SSA’s and will be testing said processes on increasingly complex component geometries. The end-goal of this effort will be the development and optimization of formulas and processes that will be able to achieve Surface Material Removal targets on components made from SSA’s of interest in order to enable the further utilization of Additive Manufacturing for our end-users in the Air Force Armament Program Office.