SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Research on three classes of materials that show potential for allowing significant increases in operating temperatures in gas turbine engines is discussed. Monolithic ceramics, ceramic matrix composites, and carbon-carbon composites are discussed. Sintering, hot pressing, and densification are discussed.
The results of past dynamic crack arrest experiments involving structural ceramics and ceramic composites are reviewed and analyzed. The lack of dynamic crack arrest in very brittle materials is discussed and contrasted with dynamic crack arrest in somewhat brittle metallic and polymeric materials. Numerical analyses show that the lack of crack arrest is due to reduced dynamic fracture resistance of the material and is not due to the kinetic energy.
Thermostructural ceramics and ceramic-matrix composites are attractive in numerous aerospace applications; the noncatastrophic fracture behavior and flaw-insensitivity of continuous fiber-reinforced CMCs renders them especially desirable. The present development status evaluation notes that, for most highly-loaded high-temperature applications, the requisite fiber-technology base is at present insufficient. In addition to materials processing techniques, the life prediction and NDE methods are immature and require a projection of 15-20 years for the maturity of CMC turbine rotors. More lightly loaded, moderate temperature aircraft engine applications are approaching maturity.
An account is given of the advantages of ceramics-based materials systems in thermostructural applications in aircraft propulsion, spacecraft propulsion and power systems, aerospace (transatmospheric) vehicles, and space structures. Prototype component applications are evaluated with a view to further technical requirements entailed by the implementation of such ceramic components. Typical near-term applications are the Space Shuttle's thermal protection system and high temperature aircraft thermal insulators; a major long-term development goal is that of integrally bladed turbine rotors in aircraft gas turbines. The fiber technology required for highly loaded/high temperature operations is not yet mature; use temperatures are restricted to 1100-1300 C.
A fiber-reinforced composite composed of a BaO-Al2O3-2SiO2 (BAS) glass ceramic matrix is reinforced with CVD silicon carbide continuous fibers. A slurry of BAS glass powders is prepared and celsian seeds are added during ball melting. The slurry is cast into tapes which are cut to the proper size. Continuous CVD-SiC fibers are formed into mats of the desired size. The matrix tapes and the fiber mats are alternately stacked in the proper orientation. This tape-mat stack is warm pressed to produce a 'green' composite. The 'green' composite is then heated to an elevated temperature to burn out organic constituents. The remaining interim material is then hot pressed to form a silicon carbide fiber-reinforced celsian (BAS) glass-ceramic matrix composite which may be machined to size.
A hyridopolysilazane-derived ceramic fiber reinforced monoclinic celsian phase barium aluminum silicate glass-ceramic matrix composite material is prepared by ball-milling an aqueous slurry of BAS glass powder and fine monoclinic celsian seeds. The fibers improve the mechanical strength and fracture toughness and with the matrix provide superior dielectric properties.
Contents include the following: Motivation. Current light weight insulation. Advantages of preceramic-polymer-derived ceramic foams. Rigid insulation materials. Tailor foam microstructures. Experimental approach. Results: sacrificial materials, sacrificial fillers. Comparison of foam microstructures. Density of ceramic foams. Phase evolution and properties: oxidation behavior. mechanical properties, aerothermal performance. Impact damage of microcellular foams. Conclusions.
Environment-conscious, biomorphic ceramics (Ecoceramics) are a new class of materials that can be produced with renewable resources (wood) and wood wastes (wood sawdust). These materials have tailorable properties with numerous potential applications. Silicon carbide-based ecoceramics have been fabricated by the infiltration of wood-derived carbonaceous preforms with oxide and silicon based materials. The wood-derived carbonaceous preforms have been shown to be quite useful in producing porous or dense materials with different microstructures and compositions. The microstructure and mechanical properties (flexural strength, fracture toughness, elastic modulus, and compressive strength) of a wide variety of Sic-based ecoceramics have been measured. Ecoceramics have tailorable properties and behave like ceramic materials manufactured by conventional approaches. In this presentation the fabrication approach, microstructure, and thermomechanical properties of a wide variety of Sic-based Ecoceramics will be reported.
The papers examine new findings and present technologically significant environmental effects and limitations relating to ceramic materials, their properties, and their uses. The effects of thermal and thermochemical factors, thermal shock, concentrated stresses, and severe mechanical environments are considered, as well as stress corrosion, hydrostatic stress, and electromagnetic and nuclear radiation environments. Individual items are abstracted in this issue.
The surface treatment of powders is discussed. Stability of ceramic powders and surfaces and the improvement of moldability are addressed. Characteristics of surface treatment technology are given, including formation of inorganic surface-treated layers, liquid phase reactions, gas treatment, surface treatment by coupling agents, and the formation of results of surface treatment.
A slurry of BSAS glass powders is cast into tapes which are cut to predetermined sizes. Mats of continuous chemical vapor deposition (CVD)-SiC fibers are alternately stacked with these matrix tapes. This tape-mat stack is warm-pressed to produce a 'green' composite which is heated to burn out organic constituents. The remaining interim material is then hot-pressed to form a BSAS glass-ceramic fiber-reinforced composite.
Explore the source record for details and available documents.
We have used microwaves to induce self-propagating high temperature synthesis (SHS) in the reaction 3TiO(sub 2)+3C+(4+x)Al ---> 3TiC+2Al(sub 2)O(sub 3)+xAl. The SHS process was studied for x = 0 and 4, with and without the application of uniaxial pressure. A TE102 microwave cavity mode internally ignited the samples using less than 50 watts. The resultant microstructure of the microwave processed samples were compared to SHS products obtained using a conventional hot wire ignition technique. Uniaxial stresses along the vertical axis of approximately 1400 and 200 psi were applied simultaneously as the SHS reactions were initiated in some of the conventional and microwave processed samples, respectively. SEM photomicrographs will be presented that show the different microstructural features of the products using the microwave and hot wire techniques.
Not Available
Noble-metal braze applied to appropriately prepared zirconia parts produces a gas-tight, durable seal that can withstand temperature of 825 C for over 2000 hours without deterioration.
Explore the source record for details and available documents.
A fracture mechanics investigation of 2D woven Nicalon SiC/SiC and Nicalon SiC/LAS has been undertaken. An energy approach has been adopted to characterize and quantify the fracture properties of these materials. Chevron-notched bend specimens were tested in an edgewise configuration in which the crack propagated perpendicular to the ply direction. R-curves were obtained from repeated loading and unloading of specimens using several methods of data reduction. Values correconding to the plateau regions of the R-curves were taken as steady-state crack-growth resistance. These ranged from 37 to 63 kJ/sq m for 2D-SiC/LAS and 2.6 to 2.8 kJ/sq m for 2D-SiC/SiC composites.
Explore the source record for details and available documents.