Erica L Corral
Publications
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.
Spark plasma joining is used to join ZrB2-SiC composites with seamless microstructures at the joint that results in retention of high-temperature mechanical and oxidation properties after joining. Our approach uses a spark plasma sintering furnace and Zr-B powder filler layers to join the parts together. The joining processing parameters used to optimize the joint microstructure were filler composition, target temperature, hold time, and volume of filler. A filler of 1 mm(3) and spark plasma joining conditions at 1800 degrees C for 300 s resulted in the formation of a joint region that was indistinguishable from the bulk substrates. Room and high-temperature (1350 degrees C) shear strengths of joined substrates measured equal to baseline substrates and oxidation behavior for joined and baseline substrates were equivalent after static air oxidation at 1700 degrees C. X-Ray diffraction measurements show the joint is composed of ZrB2 and ZrC. We found the joining mechanism to be solid-state bonding of ZrB2 that formed from the Zr-B filler and reaction bonding by the formation of ZrC. Spark plasma joining rapidly joins ZrB2-SiC and probably other conductive ultra high-temperature ceramic composites, and has the potential to impact the rapid assembly and joining of complex thermal protection material systems.