Background
Instrumentation for space and high vacuum applications is typically composed of an assembly of metallic and ceramic parts. Attachment of these dissimilar materials to one another may be accomplished in a variety of ways. To minimize parts count and mass without sacrificing performance, hermetic bonds between metals and ceramics can be made by brazing the joints together.
One of the challenges in brazing metals to ceramics is the management of joint interface stresses arising from the mismatch in thermal expansion between metals and ceramics. The entire assembly is heated and maintained at a high temperature to allow the braze material to flow into the joint by capillary action. This research program is exploring additive manufacturing (AM) technology as an alternative to brazing. AM may provide a novel way to forge hermetic bonds between metals and ceramics for space and high vacuum use.
This effort is part of the focused internal research program Metals Additive Kickoff Emphasizing Research Synergies (MAKERS).
Approach
A series of AM test specimens and assemblies of increasing complexity will be fabricated and tested. Individual AM parts, AM parts welded to one another and to conventionally manufactured parts, and finally AM parts bonded to ceramics will all be assessed. Performance characteristics evaluated will include: vacuum outgassing and quantification of virtual leaks, leak tightness of joints, and structural integrity of joints. Additionally, issues discovered with adapting AM parts for space applications will also be investigated as they are uncovered.
Accomplishments
Titanium AM tubes were manufactured and tested. Testing of these parts revealed good machinability and leak tightness up to ultra-high vacuum levels. After this baseline performance was verified, the program has focused on creation of more complex assemblies with AM components. A test fixture was designed to enhance the capabilities of the metal powder bed fusion machine. This fixture modifies the build volume to allow construction of AM parts directly onto a variety of different substrates. The first set of ceramics for bonding trials are currently in fabrication.
SwRI, using internal research and NASA funds, has developed a series of advanced mass spectrometers for use in space science missions, culminating in a flight unit currently in production for the NASA Europa Clipper Mission. The current mass spectrometer uses a bolted construction to attach and align numerous ceramic to metal joints. The instrument requires hard vacuum for operation, thus a separate vacuum cover assembly, with electrical feedthroughs, is required for instrument function. The novel ceramic to metal bonding method being researched is directly applicable to the next generation of mass spectrometers. It would allow the instrument to serve as its own vacuum chamber, resulting is significant mass savings. No specific externally funded efforts have yet resulted from this internal research project.