Aluminum metal matrix composites: a capable low-cost mirror substrate

Abstract

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.

Aluminium-Silicon Lightweight Thermal Management Alloys with Controlled Thermal Expansion

“…Such lightweight mirror design is highly beneficial for airborne applications. More detailed demonstration of lightweight mirror manufacture in this material and associated application-specific testing has been covered elsewhere [42,43]. Example components representing typical applications for each of the alloys are presented by Figure 10.…”

“…Such lightweight mirror design is highly beneficial for airborne applications. More detailed demonstration of lightweight mirror manufacture in this material and associated application-specific testing has been covered elsewhere [42,43]. An emerging topic in lightweight optical mirror design is additive manufacturing to enable complex structures for material and load optimization [44][45][46].…”

“…Particularly, for AyontEX 13, the rate of change of CTE with respect to temperature was very consistent with that of commercially pure nickel. This is important for reflective optical and instrument systems, where precise CTE matches to nickel plating layers are critical for both dimensional and thermal stability over broad operating conditions [2][3][4][5]42,43]. It should be noted that in the case of electroless plating, the nickel material will contain some level of phosphorus.…”