NASA Langley Research Center
Hampton, Virginia

Materials

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Responsible Parties: Page Content: William H. Kinard Page Construction: Thomas H. See

The Long Duration Exposure Facility (LDEF) greatly extended the range of data available for metals exposed to the low-Earth orbit (LEO) environment. The effects of LEO exposure on metals includes meteoroid&debris impacts, cosmic rays, solar particles, solar radiation, thermal cycling, oxidation, and contamination. The LDEF environment primarily affected metals surface properties. Surface property changes afford a means to study the environment as well as in-space stability of metals. Effects studied included changes in surface texture, oxidation depth, erosion depth, material growth, contamination, concentration of surface elements, physical properties, thermal properties, and optical performance.

A wide variety of metallic materials were flown on LDEF. These included pure metals, alloys, metallic coating on selected substrates, and metal matrix composites. Aluminum, gold, titanium, copper, steel, and lead were used in specific engineering applications ranging from the structural members to meteoroid&debris impact collection plates, nuts and bolts, ballast, and thermal panels.

Metal alloys flown on LDEF include Monel, brass, bronze, Inconel, copper-beryllium, copper-nickel, tin-lead, and stainless steel. With the exception of the Monel wires on experiment AO038 and the stainless steel bolts, these materials were experiment hardware and generally not subject to direct exposure. Except for the stainless steel, investigations carried out on these materials have been limited in scope. No anomalies of any kind have been identified as due to these materials.

Metals are higly variable in their response to the LEO environment. Gold and platinum are nonreactive. Osmium forms a volatile oxide and is rapidly eroded under exposure to atomic oxygen. Silver, which forms a nonprotective oxide, is rapidly eroded. Other metals (Al, Cu, Ga, Ge, Ir, Mo, Ni, Ti, and Sn) show some level of reaction unless protected. Contamination is a major contributor to exposure effects on metal surfaces. Absorptance is significantly greater for bare aluminum than for chromic-anodized aluminum. Emittance is significantly less for aluminum than for chromic-snodized aluminum. The surface properties of both bare aluminum and chromic-anodized aluminum are little changed by exposure to LEO environmental conditions. Magnesium in aluminum alloys is preferentially oxidized relative to aluminum. An oxide coating forms on exposure of copper to atomic oxygen that impedes further oxidation. The oxide coating adversely affects the optical properties of copper. Copper without surface protection may be used for extended periods of time in aplications where thermal management and optical performance requirements are not critical.

In summary, effects of exposure on metals ranged from essentially no effect, to surface color changes due to contamination deposits, to some degradation due to oxidation, to extreme damage and loss of material under atomic oxygen exposure. The changes to the metals are essentially due to surface or near-surface effects. For materials which form non-passivating oxides, the damage can be extensive over time.

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