Abstract:
The composites of 6061 and 2014 aluminum alloys reinforced with alumina particles have been subjected to solutionizing treatment at 540 °C for various lengths of time up to 20 hours. The two composites show different behavior when the hardness is measured as a function of solutionizing time. The 6061 aluminum alloy containing 0.1, 0.15 and 0.2 volume fractions of alumina (VFAP) show a continuous increase in hardness values as a function of solutionizing time while 2014 alloy shows softening under almost identical experimental conditions. The grain growth law has been found to be observed in both composites and their monoliths. The aging behavior as influenced by the solutionizing seems to be affected by the solutionizing time in an identical fashion. Even though the monoliths indicate a decrease in time required to get the peak hardness (TPH) values the composites show an initial decrease and then increase in TPH values at 200 °C as a function of solutionizing time. The bonding between the particles and the matrix in the two composites has been found to improve as a result of longer solutionizing time as can be seen by the SEM fractographs for the samples deformed to fracture during room temperature tensile testing.
Abstract:
The grain growth law has been verified for a range of grain sizes produced in three composites containing 6061 aluminum alloy matrix and 0.10, 0.15 and 0.20 volume fractions of alumina particles (VFAP), with particle sizes of 10, 15 and 20 μm respectively, by solutionizing at 540°C for different times. The solutionizing time affects the (a) microstructures developed at the interface between the particles and the matrices and (b) age hardening characteristics, microstructures and microhardness values, at 200°C.
Abstract:
Carbon-carbon (C-C) composites are attractive materials for hypersonic flight vehicles but they oxidize in air at temperatures >500°C and need thermal protection systems to survive aerothermal heating. We investigated using multilayers of high-temperature ceramics such as ZrB2 and SiC to protect C-C against oxidation. Our approach combines pretreatment and processing steps to create continuous and adherent high-temperature ceramic coatings from infiltrated preceramic polymers. We tested our protective coatings at temperatures above 2600°C at the National Solar Thermal Testing Facility using controlled cold-wall heat flux profiles reaching a maximum of 680 W/cm2. © 2008 The American Ceramic Society.
Abstract:
The chemical compatibility between sealing glasses and interconnect materials for solid oxide fuel cells (SOFCs) has been studied in SOFC environments. Two borate-based glass compositions were sealed to interconnect materials, 441 stainless-steel (441SS) and Mn 1.5Co 1.5O 4-coated 441SS. The Mn 1.5Co 1.5O 4-coated 441SS coupons were analyzed as-received using X-ray diffraction (XRD) and electron probe microanalysis (EPMA) to obtain structural information and concentration profiles, respectively. The concentration profiles and the lack of Fe-containing phases present in the XRD spectrum show Fe is present throughout the coating, suggesting that Fe is partially substituted in the Mn 1.5Co 1.5O 4 spinel. The glass-metal coupons were heat treated in air at 750°C for 500 h. The specimens were analyzed by EPMA and scanning electron microscope (SEM) to obtain images of the glass microstructure at the interface, to verify seal adherence, and to record concentration profiles across the glass-metal interface, with an emphasis on Cr. In total, four seal configurations were tested and analyzed, and in all cases the glasses remained well adhered to the metal and coating, and there was no microstructural evidence of new reaction phases present at the interface. There was slight diffusion of Cr from the 441SS into the sealing glasses, and Cr diffusion was hindered by the coating on the coated 441SS samples. © 2009 The American Ceramic Society.
