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Experiments were performed to investigate laser-heating-induced changes in the surface properties of metals and composite structural materials commonly used in aerospace applications. The objective of this test series was to determine the effect of surface heating on the 1.3-µ m-wavelength laser re ectance of these materials. Re ectance measurements were made using a unique hemiellipsoidal re ectometer. Polished metals, plated metals, and composite materials were tested to determine their temperature-dependent re ectance characteristics in vacuum and air environments. This experiment series produced temperature-dependent, 1.3-µ m laser re ectance curves for use in surface degradation analyses. All of the nishes investigated on duplex stainless-steel substrates increase the low-temperature, 1.3-µ m re ectance compared to the unpolished steel. However, the re ectance decreases dramatically at elevated temperatures when the surfaces discolor. The large re ectance transition observed for the polished and plated steel coupons in air also occur in vacuum. The polished aluminum alloys had a higher 1.3-µ m re ectance than the plated aluminum samples throughout the temperature range. The elevated temperature reectance of S-glass epoxy is irradiance dependent. Low irradiance creates a black char. A higher irradiance can ignite the char and form a lighter, more re ective surface.

Compressive and tensile creep were measured on UOz doped with 0.4 wt % niobia at controlled oxygen potentials. Kinetic results were almost identical, irrespective of the nature of the applied stress, but differences in after-test microstructures were observed. Formation of "plastic" UOz with increases in strain rate of more than two orders of magnitude were recorded when oxygen potential changed from -560 to -410 kJ/mol; this was associated, primarily, with the formation of the Nh4+ ion. Over the same range of oxygen potential, creep activation energy decreased linearly from -425 to -225 kJ/ mol. In contrast, strain rate and activation energy for undoped U 0 2 remain almost constant under these conditions.

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