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Pb-2.2 wt% Sb alloy was directionally solidified in 1, 2, 3 and 7 mm diameter crucibles. Pb-Sb alloy presents a solutally
unstable case. Under plane-front conditions, the resulting macrosegregation along the solidified length indicates that
convection persists even in the 1 mm diameter crucible. Al-2 wt% Cu alloy was directionally solidified because this alloy was
expected to be stable with respect to convection. Nevertheless, the resulting macrosegregation pattern and the microstructure
in solidified examples indicated the presence of convection. Simulations performed for both alloys show that convection
persists for crucibles as small as 0.6 mm of diameter. For the solutally stable alloy, Al-2 wt% Cu, the simulations indicate that
the convection arises from a lateral temperature gradient.
Author
Convection; Crucibles; Directional Solidification (Crystals); Lead Alloys; Tin Alloys; Alloying
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NONMETALLIC MATERIALS
Includes physical, chemical, and mechanical properties of plastics, elastomers, lubricants, polymers, textiles, adhesives, and ceramic
materials. For composite materials see 24 Composite Materials.
20030022688 NASA Glenn Research Center, Cleveland, OH, USA
Development of Advanced Thermal and Environmental Barrier Coatings Using a High-heat-flux Testing Approach
Zhu, Dongming; Miller, Robert A.; January 2003; 22 pp.; In English; 27th Annual International Conference on Advanced
Ceramics and Composites, 26-31 Jan. 2003, Cocoa Beach, FL, USA; Original contains black and white illustrations; No
Copyright; Avail: CASI; A03, Hardcopy
The development of low conductivity, robust thermal and environmental barrier coatings requires advanced testing
techniques that can accurately and effectively evaluate coating thermal conductivity and cyclic resistance at very high surface
temperatures (up to 1700 C) under large thermal gradients. In this study, a laser high-heat-flux test approach is established for
evaluating advanced low conductivity, high temperature capability thermal and environmental barrier coatings under the
NASA Ultra Efficient Engine Technology (UEET) program. The test approach emphasizes the real-time monitoring and
assessment of the coating thermal conductivity, which initially rises under the steady-state high temperature thermal gradient
test due to coating sintering, and later drops under the cyclic thermal gradient test due to coating cracking/delamination. The
coating system is then evaluated based on damage accumulation and failure after the combined steady-state and cyclic thermal
gradient tests. The lattice and radiation thermal conductivity of advanced ceramic coatings can also be evaluated using laser
heat-flux techniques. The external radiation resistance of the coating is assessed based on the measured specimen temperature
response under a laser- heated intense radiation-flux source. The coating internal radiation contribution is investigated based
on the measured apparent coating conductivity increases with the coating surface test temperature under large thermal gradient
test conditions. Since an increased radiation contribution is observed at these very high surface test temperatures, by varying
the laser heat-flux and coating average test temperature, the complex relation between the lattice and radiation conductivity
as a function of surface and interface test temperature may be derived.
Author
Thermal Control Coatings; High Temperature Tests; Ceramic Coatings; Laser Heating
20030032188 NASA Langley Research Center, Hampton, VA, USA
Thermal/Mechanical Response of a Polymer Matrix Composite at Cryogenic Temperatures
Whitley, Karen S.; Gates, Thomas S.; March 2003; 32 pp.; In English; 43rd AIAA/ASME/ASCE/AHS/ASC Structures,
Structural Dynamics and Materials Conference, Apr. 2002, Denver, CO, USA; Original contains black and white illustrations
Contract(s)/Grant(s): 721-21-10-01
Report No.(s): NASA/TM-2003-212171; L-18269; NAS 1.15:212171; No Copyright; Avail: CASI; A03, Hardcopy
In order for polymeric-matrix composites to be considered for use as structural materials in the next generation of space
transportation systems, the mechanical behavior of these materials at cryogenic temperatures must be investigated. This paper
presents experimental data on the residual mechanical properties of a carbon-fiber polymeric composite, IM7/PETI-5, both
before and after aging. Both tension and compression modulus and strength were measured at room temperature, -196C, and
-269 C on five different laminate configurations. One set of specimens was aged isothermally for 576 hours at -184 C in an
unconstrained state. Another set of corresponding specimens was aged under constant uniaxial strain for 576 hours at -184 C.
Based on the experimental data presented, it is shown that trends in stiffness and strength that result from changes in
temperature are not always smooth and consistent. Moreover, it is shown that loading mode and direction are significant for
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