Michael Sweeney, Sean Colling, Jarrett Schmidt, Alex Few, Jason Echols, Patrick Reardon, Don Douthit, Nick Farrah, Peter Lewis, Andrew Tarrant, Martyn Acreman
SupremEX® 640XA Al-SiC MMC and AyontEX™ 13 Al-Si alloy are advanced aluminum-based materials developed by Materion Corporation that are under consideration for mirrors and related precision structures for high performing land, sea, air, and space applications. SupremE X® 640XA is a Metal Matrix Composite (MMC) with a 6061B aluminum alloy matrix reinforced with 40vol.% ultrafine Silicon Carbide particles and is harder, lighter, and stiffer than Titanium 6Al4V with excellent fracture toughness and fatigue resistance. AyontEX™ 13 is a hypereutectic Aluminium-Silicon alloy and is both lighter and stiffer than aluminum alloy 6061-T6. Both materials also have CTEs that are well matched to that of electroless nickel plating (13ppm/°C) commonly used for mirror applications. Our investigations demonstrate that these materials can sustain requisite properties of finished mirrors operating at visible wavelengths and over broad ranges of operational temperature. A 150mm aperture finished light-weighted concave spherical test mirror was designed and manufactured according to developed manufacturing guidelines for both materials and is representative of design forms for airborne and space applications. Optical finishing operations inclded diamond point turning (DPT) and loose abrasive polishing. By use of laser interferometry, mirror figure stability was verified after multiple thermal cycles. Similar interferometric measurements were then repeated when subjecting the test mirrors to hot and cold temperature excursions under vacuum. These experiments were also performed both before and after the application of electroless nickel plating. Also considered were concepts for precision structures that are best fitted to the unique manufacturing-related characteristics of these materials.
Low cost, high performance lightweight Aluminum mirror provides an alternative to glass ceramic, ceramic, and exotic metal mirrors. NASA funded several lightweight Aluminum mirror technology development efforts for future space and balloon-borne infrared telescope programs. As part of these efforts, subscale Al-SiC metal matrix composite, Aluminum-6061 and Aluminum-5083 mirrors, and additive manufactured AlSi10Mg mirrors were evaluated at room temperature to 20 degrees Kelvin for its optical performance. This paper will discuss objectives, material properties, fabrication, cryogenic testing infrastructure and instrumentation, thermal test results, modelling effort compared to empirical data, and lessons learned.
Outpost Technologies designed, manufactured, and tested a 0.305-meter aluminum-silicon carbide metal matrix composite (Al-SiC MMC) mirror for infrared balloon gondola observatory application. Al-SiC MMCs, such as Materion’s SupremEX®, have high specific stiffness, excellent thermal conductivity, and lower CTE than most conventional metals. Furthermore, recent research and development efforts support a brand-new material for investigation: AyontEX™ 13 aluminum-silicon (Al-Si) alloy. Outpost identified significant cost and capability gaps in mirror substrate design trades between ultra-premium beryllium and SiC and conventional aerospace materials and proposes new materials for consideration. The Al-SiC MMC and Al-Si alloy programmatic and technical value proposition combines considerable improvements in specific stiffness and thermal performance at minimal costs increases over aluminum substrates. Assuming congruent geometry, SupremEX® 640XA Al-SiC MMCs reduce gravity sag errors by 47% and increases mirror and structural modes by 35% versus aluminum 5000 and 6000 series without affecting system mass. AyontEX™ 13 also exhibits higher specific strength and stiffness compared to aluminum and shows promise as an uncoated mirror substrate with optical surface finish properties achieved during diamond turning. Outpost presents study results, manufacturability assessments, and ground test concepts for TRL-advancing activities to bring the SupremEX® and AyontEXTM materials before future optics programs as highly capable and low-cost mirror substrates. Lastly, a discussion of ongoing and future work for ultraviolet (UV) and large (> 1.25-meter) Al-SiC MMC and Al-Si alloy applications.
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