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New γ' strengthened nickel-base superalloy compositions are described that, when forged and properly heat treated, demonstrate superior resistance to fatigue crack growth accompanied by very good high temperature properties. Parts can be fabricated (e.g., using conventional cast and wrought processing) from these alloys without encountering difficulty in forging.
Phenylethynyl-terminated poly(arylene ethers) synthesized in wide range of molecular weights by adjusting monomer ratios and adding appropriate amounts of 4-phenylethynyl-4'-fluorobenzophenone to monomers to end-cap oligomers during polymerization. Have low molecular weights and low melt viscosities, and are easily processed as adhesives, composites, and moldings. Thermally cured to provide materials that are crosslinked and insoluble in common organic solvents. Exhibit increased resistance to solvents, greater tensile moduli, and better high-temperature properties. Useful as adhesives, composite matrices, and moldings, especially in applications in which combination of toughness and resistance to solvents needed.
Phenylethynyl-terminated poly(arylene ethers) are prepared in a wide range of molecular weights by adjusting monomer ratio and adding an appropriate amount of 4-fluoro- 4'-phenylethynyl benzophenone during polymer synthesis. The resulting phenylethynyl-terminated poly(arylene ethers) react and crosslink upon curing for one hour at 350 C to provide materials with improved solvent resistance, higher modulus, and better high temperature properties than the linear, uncrosslinked polymers.
Four phenylethynyl amine compounds - 3 and 4-aminophenoxy-4'-phenylethynylbenzophenone, and 3 and 4-amino-4'-phenylethynylbenzophenone - were readily prepared and were used to endcap imide oligomers. Phenylethynyl-terminated amide acid oligomers and phenylethynyl-terminated imide oligomers with various molecular weights and compositions were prepared and characterized. These oligomers were cured at 300 to 400 C to provide crosslinked polyimides with excellent solvent resistance, high strength and modulus, and good high temperature properties. Adhesive panels, composites, films, and moldings from these phenylethynyl terminated imide oligomers gave excellent mechanical performance.
Four phenylethynyl amine compounds - 3 and 4-aminophenoxy-4'-phenylethynylbenzophenone, and 3 and 4-amino-4'-phenylethynylbenzophenone - were readily prepared and were used to endcap imide oligomers. Phenylethynyl-terminated amide acid oligomers and phenylethynyl-terminated imide oligomers with various molecular weights and compositions were prepared and characterized. These oligomers were cured at 300 to 400 C to provide crosslinked polyimides with excellent solvent resistance, high strength and modulus, and good high temperature properties. Adhesive panels, composites, films, and moldings from these phenylethynyl terminated imide oligomers gave excellent mechanical performance.
As NASA seeks to fulfill its goals of exploration and understanding through missions planned to visit the moons of Saturn and beyond, a number of challenges arise from the idea of deep space flight. One of the first problems associated with deep space travel is electrical power production for systems on the spacecraft. Conventional methods such as solar power are not practical because efficiency decreases substantially as the craft moves away from the Sun. The criterion for power generation during deep space missions are very specific, the main points requiring high reliability, low mass, minimal vibration and a long lifespan. A Stirling generator, although fairly old in concept, is considered to be a potential solution for electrical power generation for deep space flight. A Stirling generator works on the same electromagnetic principles of a standard generator, using the linear motion of the alternator through the stationary stator which produces electric induction. The motion of the alternator, however, is produced by the heating and cooling dynamics of pressurized gases. Essentially heating one end and cooling another of a contained gas will cause a periodic expansion and compression of the gas from one side to the other, which a displacer translates into linear mechanical motion. NASA needs to confirm that the materials used in the generator will be able to withstand the rigors of space and the life expectancy of the mission. I am working on the verification of the epoxy adhesives used to bond magnets to the steel lamination stack to complete the stator; in terms of in-service performance and durability under various space environments. Understanding the proper curing conditions, high temperature properties, and degassing problems as well as production difficulties are crucial to the long term success of the generator. system and steel substrate used in the stator. To optimize the curing conditions of the epoxies, modulated differential scanning calorimetry analysis was done as a function of cure time and temperatures. Adhesion bond strength was tested at various temperatures with lap shear samples using Hiperco 50 substrate to ensure that the proper adhesive is being used. To try and solve the problem of bondline thickness, micro glass beads of 0.0017" in diameter were investigated to see if any other physical properties of the epoxy were affected. Efforts will be made to develop a standard, optimized, fabrication process/procedure of sub-scale magnet-stator assemblies for various adhesive performance evaluation studies under simulated generator conditions. Also, accelerated aging testing will be done in a pressurized canister with stator assembly samples for three years to verify if any degassing or thermal degradation of the epoxy occurs. The necessity of verifying the correct epoxy adhesive system for the stator magnet in the SRG is crucial because failure of the stator assembly would jeopardize the electrical system, and thereby the entire mission itself. My work involves specimen fabrications, testing, and data analyses of the epoxy adhesive system for the stator magnet in the SRG is crucial because failure of the stator assembly would jeopardize the electrical system, and thereby the entire mission itself.
Proposed concepts for an ambitious mission to explore Jupiter's three icy moons place significant demands on the various spacecraft systems. There are many challenges related to the high output power conversion systems being considered, and one example is the need to ensure system compatibility at all levels. The utilization of appropriate materials for component structures is important to ensuring long mission life. Refractory metal alloys have attractive high-temperature properties in inert environments, but these alloys are sometimes susceptible to contamination. Potential material compatibility issues exist between refractory metal candidates and more conventional alloys. Nb-1Zr has long been considered one of the most well characterized refractory alloys that is well suited for elevated-temperature use and liquid-metal compatibility. However, previous studies have suggested that niobium alloys can not co-exist in a closed system with traditional stainless steels or superalloys due to transport of contaminants. The relevance of this information to a proposed power conversion system is discussed. Also, experiments and fundamental calculations are being performed to determine contamination transport from candidate superalloys to Nb-1Zr in a closed system with an inert carrier gas. Potential protective schemes are explored to ensure system level compatibility between the refractory alloy Nb-1Zr and a nickel-based superalloy.
One key factor that limits the performance of current gas turbine engines is the temperature capability of hot section structural components. Silicon-based ceramics, such as SiC/SiC composites and monolithic Si3N4, are leading candidates to replace superalloy hot section components in the next generation gas turbine engines due to their excellent high temperature properties. A major stumbling block to realizing Si-based ceramic hot section components is the recession of Si-based ceramics in combustion environments due to the volatilization of silica scale by water vapor. An external environmental barrier coating (EBC) is the most promising approach to preventing the recession. Current EBCs are based on silicon, mullite (3A12O3-2SiO2) and BSAS (barium strontium aluminum silicate with celsian structure). Volatility of BSAS, BSAS-silica chemical reaction, and low melting point of silicon limit the durability and temperature capability of current EBCs. Research is underway to develop EBCs with longer life and enhanced temperature capability. Understanding key issues affecting the performance of current EBCs is necessary for successful development of advanced EBCs. These issues include stress, chemical compatibility, adherence, and water vapor stability. Factors that affect stress are thermal expansion mismatch, phase stability, chemical stability, elastic modulus, etc. The current understanding on these issues will be discussed.
Four phenylethynyl amine compounds--3 and 4-aminophenoxy-4'-phenylethynylbenzophenone, and 3 and 4-amino-4'-phenylethynylbenzophenone--were readily prepared and were used to endcap imide oligomers. Phenylethynyl-terminated amide acid oligomers and phenylethynyl-terminated imide oligomers with various molecular weights and compositions were prepared and characterized. These oligomers were cured at 300.degree. C. to 400.degree. C. to provide crosslinked polyimides with excellent solvent resistance, high strength and modulus and good high temperature properties. Adhesive panels, composites, films and moldings from these phenylethynyl terminated imide oligomers gave excellent mechanical performance.
Ceramic environmental barrier coatings (EBC) and SiCSiC ceramic matrix composites (CMCs) will play a crucial role in future aircraft propulsion systems because of their ability to significantly increase engine operating temperatures, improve component durability, reduce engine weight and cooling requirements. Advanced EBC systems for SiCSiC CMC turbine and combustor hot section components are currently being developed to meet future turbine engine emission and performance goals. One of the significant material development challenges for the high temperature CMC components is to develop prime-reliant, high strength and high temperature capable environmental barrier coating bond coat systems, since the current silicon bond coat cannot meet the advanced EBC-CMC temperature and stability requirements. In this paper, advanced NASA HfO2-Si based EBC bond coat systems for SiCSiC CMC combustor and turbine airfoil applications are investigated. The coating design approach and stability requirements are specifically emphasized, with the development and implementation focusing on Plasma Sprayed (PS) and Electron Beam-Physic Vapor Deposited (EB-PVD) coating systems and the composition optimizations. High temperature properties of the HfO2-Si based bond coat systems, including the strength, fracture toughness, creep resistance, and oxidation resistance were evaluated in the temperature range of 1200 to 1500 C. Thermal gradient heat flux low cycle fatigue and furnace cyclic oxidation durability tests were also performed at temperatures up to 1500 C. The coating strength improvements, degradation and failure modes of the environmental barrier coating bond coat systems on SiCSiC CMCs tested in simulated stress-environment interactions are briefly discussed and supported by modeling. The performance enhancements of the HfO2-Si bond coat systems with rare earth element dopants and rare earth-silicon based bond coats are also highlighted. The advanced bond coat systems, when integrated with advanced EBC top coats, showed promise to achieve 1500 C temperature capability, helping enable next generation turbine engines with significantly improved engine component temperature capability and long-term durability.
The global increase in air travel will require commercial vehicles to be more efficient than ever before. Advanced turbine hot section materials are a key technology required to keep fuel consumption and emission to a minimum. Ceramic matrix composites (CMCs) are the most promising material to revolutionize turbine hot section materials because of their excellent high‐temperature properties. Rapid surface recession due to volatilization by water vapor is the Achilles heel of CMCs. Environmental barrier coatings (EBCs), which protect CMCs from water vapor, is an enabling technology for CMCs. The first CMC component entered into service in 2016 in a commercial engine, and more CMC components are scheduled to follow within the next few years. One of the most difficult challenges to CMC components is EBC durability because failure of EBC leads to a rapid reduction in CMC component life. Novel EBC chemistries, creative EBC designs, and robust processes are required to meet EBC durability challenges. Engine-relevant testing, characterization, and lifing methods need to be developed to improve EBC reliability. The aim of this Special Issue is to present recent advances in EBC technology to address current EBC challenges.
It is found that the mechanical properties of fibrous refractory composite insulation (FRCI) can be improved if a higher calcination temperature is used before final processing. The results also reveal that a higher density FRCI containing 60 wt pct aluminoborosilicate fibers will exhibit minimal surface recession at 1480 C in a convective-heating environment. Another finding is that the material performance in the convective-heating environment is limited by the coating and the temperature capability of its emittance agent. A table is included giving the coating compositions used with the composite insulation and tested in the convectively heated environment at a surface temperature of 1480 C.
Collision integrals for the transport properties of dissociating air at high temperatures
Cold pressing and sintering techniques were used to produce ceramic bodies in which the major phase was beta prime Si3-Al-O-N4 solid solution. A variety of foreign oxides were used to promote liquid phase sintering, and this resulted in the incorporation of additional solid phases in the ceramic bodies which controlled elevated temperature properties. None of the bodies studied to date exhibited both adequate high temperature mechanical properties and oxidation resistance. Criteria are suggested to guide the formulation of bodies with improved high temperature properties.
An Al–10Ce-8Mn (wt%) alloy was designed and fabricated by laser powder bed fusion additive manufacturing (AM). The rapid cooling rates of the AM process produced a refined microstructure with a large fraction of reinforcing intermetallic phases. The tensile properties of the alloy were characterized in the as-fabricated state and following thermal exposure. The properties of the as-fabricated microstructure showed exceptional high-temperature performance and strength retention at elevated temperatures up to 400 °C relative to benchmark wrought Al and AM Al alloy properties. Characterization of the microstructure and thermodynamic modeling of the ternary Al–Ce–Mn system rationalized the solidification and solid-state phase transformations. Finally, analysis of the relevant strengthening mechanisms for both the as-fabricated and thermally exposed conditions was performed.
Lime refractory fabrication and properties for high temperature applications, describing production of calcium oxide grain by sintering process from commercial calcium hydroxide
Fiber-reinforced thermoset composites are a class of materials that address the arising needs from the aerospace and hypersonic industries for high specific strength, temperature-resistant structural materials. Among the high-temperature resistant thermoset categories, phenolic triazine (PT) cyanate esters stand out thanks to their inherent high degradation temperature, glass transition temperature, and mechanical strength. Despite the outstanding properties of these thermosets, the performance of carbon fiber composites using PT cyanate esters as matrices has not been thoroughly characterized. This work evaluated PT and carbon fiber composites’ compressive properties and failure mechanisms with different fiber arrangements. A PT resin with both plain weave (PW) and non-crimped unidirectional (UD) carbon fiber mats was analyzed in this research. Highly loaded thermoset composites were obtained using process temperatures not exceeding 260 °C, and the composites proved to retain compressive strength at temperatures beyond 300 °C. Compressive testing revealed that PT composites retained compressive strength values of 50.4% of room temperature for UD composites and 61.4% for PW composites. Post-compressive failure observations of the gage section revealed that the mechanisms for failure evolved with temperature from brittle, delamination-dominant failure to shear-like failure promoted by the plastic failure of the matrix. This study demonstrated that PT composites are a good candidate for structural applications in harsh environments.
Abstract High-temperature alloy design requires a concurrent consideration of multiple mechanisms at different length scales. We propose a workflow that couples highly relevant physics into machine learning (ML) to predict properties of complex high-temperature alloys with an example of the 9–12 wt% Cr steels yield strength. We have incorporated synthetic alloy features that capture microstructure and phase transformations into the dataset. Identified high impact features that affect yield strength of 9Cr from correlation analysis agree well with the generally accepted strengthening mechanism. As a part of the verification process, the consistency of sub-datasets has been extensively evaluated with respect to temperature and then refined for the boundary conditions of trained ML models. The predicted yield strength of 9Cr steels using the ML models is in excellent agreement with experiments. The current approach introduces physically meaningful constraints in interrogating the trained ML models to predict properties of hypothetical alloys when applied to data-driven materials.