Study on effects of powder and flake chemistry and morphology on the properties of Al-Cu-Mg-X-X-X powder metallurgy advanced aluminum alloys

The effects of alloy chemistry and particulate morphology on consolidation behavior and consolidated product properties in rapid solidification processed, powder-metallurgical Al-3Li-1.5Cu-1Mg-0.5Co-0.2Zr and Al-4.4Cu-1.5Mg-Fe-Ni-0.2Zr extrusions and forgings were studied. Microstructures and mechanical properties of both alloys are largely unaffected by particulate production method (vacuum atomization, ultrasonic atomization, or twin-roller quenching) and by particulate solidification rates between 1000 and 100,000 K/s. Consolidation processing by canning, cold compaction, degassing, and hot extrusion is sufficient to yield mechanical properties in the non-Li-containing alloy extrusions which are similar to those of 7075-Al, but ductilities and fracture toughnesses are inferior owing to poor interparticle bonding caused by lack of a vacuum-hot-pressing step during consolidation. Mechanical properties of extrusions are superior to those of forgings owing to the stronger textures produced by the more severe hot working during extrusion. The effects on mechanical properties of dispersoid size and volume fraction, substructural refinement, solid solution strengthening by Mg, and precipitate size and distribution are elucidated for both alloy types

Effects of Phragmites australis (Common Reed) Invasion on Nitrogen Cycling, Porewater Chemistry and Vegetation Structure in a Brackish Tidal Marsh of the Rhode River, Maryland

Phragmites australis is one of the most widespread invasive species in wetland habitats of North America. Conversion of existing wetland ecosystems to Phragmites-dominated communities decreases overall plant diversity and alters biogeochemical cycles, which can negatively affect ecosystem processes. Previous studies demonstrated that Phragmites has a significantly greater above-ground nitrogen demand than native plants, likely due to its greater biomass. To evaluate how invasion by Phragmites alters standing stock nitrogen, I measured above- and below-ground biomass and nitrogen stocks in both the invasive and native plant communities to examine how Phragmites is meeting its documented increased nitrogen demand in the Rhode River, a sub-estuary of the Chesapeake Bay in Edgewater, Maryland. I also quantified deep N uptake using a 15N tracer study. I found that Phragmites roots significantly deeper than native marsh grass communities and has the ability to utilize deeper nitrogen pools and take up nitrogen from deeper depths. This enhanced rooting structure gives the invasive Phragmites the ability to potentially access lower salinity water, as well as tap nutrients unavailable to native marsh plant communities

Silicon based substrate with yttrium silicate environmental/thermal barrier layer

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a yttrium silicate

Silicon based substrate with environmental/ thermal barrier layer

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a barium-strontium alumino silicate

Silicon based substrate with calcium aluminosilicate environmental/thermal barrier layer

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a calcium alumino silicate

Silicon based substrate with calcium aluminosilicate/thermal barrier layer

A barrier layer for a silicon containing substrate which inhibits the formation of gaseous species of silicon when exposed to a high temperature aqueous environment comprises a calcium alumino silicate

Modelling the impact of refinishing processes on COTS components for use in aerospace applications

Commercial off the shelf components (COTS) are being adopted by electronic equipment manufacturers for use in aerospace applications. To ensure that these components meet the quality and reliability standards, refinishing processes, such as hot solder dip and laser deballing/reballing, are used to replace component lead-free solder terminations with tin–lead solder. These processes provide a risk mitigation strategy against tin whiskers induced short circuit failures. Being an additional step to the subsequent PCB assembly process it is important that this additional process does not impose significant thermo-mechanical stress which can impact subsequent reliability. As part of a major study in collaboration with industry partners, process models have been developed to predict the thermo-mechanical behaviour of components when subjected to the refinishing process. This paper details the techniques used to provide model input data (e.g., process parameters and package geometric/materials data) as well as the development and application of these modelling techniques to the refinishing process

Oxidation behavior of molybdenum silicides and their composites

A key materials issue associated with the future of high-temperature structural silicides is the resistance of these materials to oxidation at low temperatures. Oxidation tests were conducted on Mo-based silicides over a wide temperature range to evaluate the effects of alloy composition and temperature on the protective scaling characteristics and testing regime for the materials. The study included Mo{sub 5}Si{sub 3} alloys that contained several concentrations of B. In addition, oxidation characteristics of MoSi{sub 2}-Si{sub 3}N{sub 4} composites that contained 20--80 vol.% Si{sub 3}N{sub 4} were evaluated at 500--1,400 C