Increasing the elevated-temperature strength of a beta titanium alloy through thermomechanically-induced phase tranformation

The effects of temperature and thermomechanical loading on the elevated-temperature tensile strength, deformation behavior, and phase transformation were studied for a low-cost metastable beta titanium alloy: Ti-13Cr-1Fe-3Al (wt.%). In-situ and ex-situ tensile tests were performed at temperatures between 25 °C to 500 °C. TEM was performed to investigate the phase transformation behavior, and the strength and Vickers hardness were compared at different loading conditions. The beta phase transformed to the omega phase under a combination of load and time at temperature. The temperature range of the phase transformation was investigated by dynamic mechanical analysis and compared with data from differential scanning calorimetry and electrical resistivity techniques. Slip trace analysis indicated that dislocation slip is the primary deformation mechanism. Both temperature and thermomechanical loading have a significant influence on deformation mode, phase transformation, and tensile strength, which can be increased by over fifty percent at elevated temperatures

Benefits of greenhouse gas mitigation on the supply, management, and use of water resources in the United States

Climate change impacts on water resources in the United States are likely to be far-reaching and substantial because the water is integral to climate, and the water sector spans many parts of the economy. This paper estimates impacts and damages from five water resource-related models addressing runoff, drought risk, economics of water supply/demand, water stress, and flooding damages. The models differ in the water system assessed, spatial scale, and unit of assessment, but together provide a quantitative and descriptive richness in characterizing water sector effects that no single model can capture. The results, driven by a consistent set of greenhouse gas (GHG) emission and climate scenarios, examine uncertainty from emissions, climate sensitivity, and climate model selection. While calculating the net impact of climate change on the water sector as a whole may be impractical, broad conclusions can be drawn regarding patterns of change and benefits of GHG mitigation. Four key findings emerge: 1) GHG mitigation substantially reduces hydro-climatic impacts on the water sector; 2) GHG mitigation provides substantial national economic benefits in water resources related sectors; 3) the models show a strong signal of wetting for the Eastern US and a strong signal of drying in the Southwest; and 4) unmanaged hydrologic systems impacts show strong correlation with the change in magnitude and direction of precipitation and temperature from climate models, but managed water resource systems and regional economic systems show lower correlation with changes in climate variables due to non-linearities created by water infrastructure and the socio-economic changes in non-climate driven water demand

Feeding ecology of pelagic larvae of English sole Parophrys vetulus and butter sole Isopsetta isolepis off the Oregon coast

The food habits of the 2 dominant larval pleuronectids off the Oregon coast - English sole Parophrys vetulus and butter sole Isopsetta isolepis - were analysed. Most specimens were collected during January-April 1971 and March-April 1973. As is typical of larval fishes, I. isolepis larvae ingested a variety of prey which changed with increasing fish size. Small larvae fed predominantly on tintinnids, invertebrate eggs, and nauplii, whereas large larvae consumed more copepodite and adult copepods. In contrast, the diet of P. vetuluslarvae is very specific; appendicularians (Oikopleura spp.) comprised 97% of the total number of food items consumed in 1973. Both P. vetulus larvae and appendicularians are most abundant during fall and winter when total zooplankton concentrations off Oregon are low. I. isolepis larvae are most abundant during spring when upwelling stimulates productivity. In 1971, seasonal abundance peaks of P. vetulus larvae and appendicularians did not coincide. During this year, larvae fed less on appendicularians than in 1973 (66% of the total number of food items), and more on other food sources such as tintinnids, invertebrate eggs, and nauplii. In 1971 more P. vetulus larvae had empty guts than in 1973; this observation suggests increased starvation. In addition, fewer large larvae were present in 1971, perhaps due to higher mortality rates. Hence, in contrast to I. isolepis larvae, P. vetulus larvae are dependent upon a specific prey; a mismatch of P. vetulus and appendicularian abundance peaks may result in significant food-related mortality

In Situ Observations of the Deformation Behavior and Fracture Mechanisms of Ti-45Al-2Nb-2Mn+0.8 vol pct TiB₂

The deformation and fracture mechanisms of a nearly lamellar Ti-45Al-2Nb-2Mn (at. pct) + 0.8 vol pct TiB₂ intermetallic, processed into an actual low-pressure turbine blade, were examined by means of in situ tensile and tensile-creep experiments performed inside a scanning electron microscope (SEM). Low elongation-to-failure and brittle fracture were observed at room temperature, while the larger elongations-to-failure at high temperature facilitated the observation of the onset and propagation of damage. It was found that the dominant damage mechanisms at high temperature depended on the applied stress level. Interlamellar cracking was observed only above 390 MPa, which suggests that there is a threshold below which this mechanism is inhibited. Failure during creep tests at 250 MPa was controlled by intercolony cracking. The in situ observations demonstrated that the colony boundaries are damage nucleation and propagation sites during tensile creep, and they seem to be the weakest link in the microstructure for the tertiary creep stage. Therefore, it is proposed that interlamellar areas are critical zones for fracture at higher stresses, whereas lower stress, high-temperature creep conditions lead to intercolony cracking and fracture.The authors are grateful to Industria de Turbo Propulsores, S.A. for supplying the intermetallic blades. Funding from the Spanish Ministry of Science and Innovation through projects MAT2009-14547-C02-01 and MAT2009-14547-C02-02 is acknowledged. The Madrid Regional Government supported this project partially through the ESTRUMAT grant P2009/MAT-1585. C.J.B. acknowledges the support from Grant SAB2009-0045 from the Spanish Ministry of Education for his sabbatical stage in Madrid.Publicad

Water Body Temperature Model for Assessing Climate Change Impacts on Thermal Cooling

We develop and test a physically based semi-Lagrangian water body temperature model to apply climatological data and thermal pollution from river-based power plants to historical river flow data in order to better understand climate change impacts on surface water temperature and thermal power plant withdrawal allowances. The model is built for rapid assessment and use in Integrated Assessment Models. We first test the standalone model on a 190km river reach, the Delaware River, where we have detailed flow and temperature data. An R2 of 0.88 is obtained on hourly data for this initial test. Next, we integrate the standalone temperature model into a series of models—rainfall-runoff model, water demand model, water resource management model, and power plant uptake and release model—for the contiguous USA (CONUS), with about 19,000 segments total. With this system in place, we then validate the standalone water temperature model within the system for 16 river stations throughout the CONUS, where we have measured daily temperature data. The model performs reasonably well with a median R2 of 0.88. A variety of climate and emissions scenarios are then applied to the model to test regions of higher vulnerability to river temperature environmental violations, making use of output from two GCMs and six emissions scenarios focusing on projections out to 2050. We find that the two GCMs project significantly different impacts to water temperature, driven largely by the resulting changes in streamflow from the two models. We also find significantly different impacts on the withdrawal allowed by thermal power plants due to environmental regulations. Potential impacts on generation are between +3% and -4% by 2050 for the unconstrained emissions case and +3.5% to -2% for the stringent GHG mitigation policy (where 1% is equivalent to 32 TWh, or about 3 billion USD/year using 2005 electricity prices). We also find that once-through cooling plants are most vulnerable to climate change impacts, with summer impacts ranging from -0.8% to -6% for the unconstrained emissions case and +2.1% to -3.7% for the stringent GHG emissions case

Larval dispersal in a changing ocean with an emphasis on upwelling regions

Dispersal of benthic species in the sea is mediated primarily through small, vulnerable larvae that must survive minutes to months as members of the plankton community while being transported by strong, dynamic currents. As climate change alters ocean conditions, the dispersal of these larvae will be affected, with pervasive ecological and evolutionary consequences. We review the impacts of oceanic changes on larval transport, physiology, and behavior. We then discuss the implications for population connectivity and recruitment and evaluate life history strategies that will affect susceptibility to the effects of climate change on their dispersal patterns, with implications for understanding selective regimes in a future ocean. We find that physical oceanographic changes will impact dispersal by transporting larvae in different directions or inhibiting their movements while changing environmental factors, such as temperature, pH, salinity, oxygen, ultraviolet radiation, and turbidity, will affect the survival of larvae and alter their behavior. Reduced dispersal distance may make local adaptation more likely in well-connected populations with high genetic variation while reduced dispersal success will lower recruitment with implications for fishery stocks. Increased dispersal may spur adaptation by increasing genetic diversity among previously disconnected populations as well as increasing the likelihood of range expansions. We hypothesize that species with planktotrophic (feeding), calcifying, or weakly swimming larvae with specialized adult habitats will be most affected by climate change. We also propose that the adaptive value of retentive larval behaviors may decrease where transport trajectories follow changing climate envelopes and increase where transport trajectories drive larvae toward increasingly unsuitable conditions. Our holistic framework, combined with knowledge of regional ocean conditions and larval traits, can be used to produce powerful predictions of expected impacts on larval dispersal as well as the consequences for connectivity, range expansion, or recruitment. Based on our findings, we recommend that future studies take a holistic view of dispersal incorporating biological and oceanographic impacts of climate change rather than solely focusing on oceanography or physiology. Genetic and paleontological techniques can be used to examine evolutionary impacts of altered dispersal in a future ocean, while museum collections and expedition records can inform modern-day range shifts

Effect of stress level on the high temperature deformation and fracture mechanisms of Ti-45Al-2Nb-2Mn-0.8 vol. pct TiB²: an 'In Situ' experimental study

The effect of the applied stress on the deformation and crack nucleation and propagation mechanisms of a gamma-TiAl intermetallic alloy (Ti-45Al-2Nb-2Mn (at. pct)-0.8 vol. pct TiB2) was examined by means of in situ tensile (constant strain rate) and tensile-creep (constant load) experiments performed at 973 K (700 °C) using a scanning electron microscope. Colony boundary cracking developed during the secondary stage in creep tests at 300 and 400 MPa and during the tertiary stage of the creep tests performed at higher stresses. Colony boundary cracking was also observed in the constant strain rate tensile test. Interlamellar ledges were only found during the tensile-creep tests at high stresses (sigma > 400 MPa) and during the constant strain rate tensile test. Quantitative measurements of the nature of the crack propagation path along secondary cracks and along the primary crack indicated that colony boundaries were preferential sites for crack propagation under all the conditions investigated. The frequency of interlamellar cracking increased with stress, but this fracture mechanism was always of secondary importance. Translamellar cracking was only observed along the primary crack.Funding from the Spanish Ministry of Science and Innovation through projects (MAT2009-14547-C02-01 and MAT2009-14547-C02-02) is acknowledged. The Madrid Regional Government partially supported this project through the ESTRUMAT grant (P2009/MAT-1585). CJB acknowledges the support from the Spanish Ministry of Education for his sabbatical stay in Madrid (SAB2009-0045).Publicad

The effects of thermomechanical history on the microstructure of a nickel-base superalloy during forging

The effect of thermo-mechanical history on hot compression behaviour and resulting microstructures of a nickel base superalloy is presented. Hot compression tests were carried out on HAYNES® 282® specimens to varying strains from 0.1 to 0.8. Both single pass and multi-pass tests were completed. 60 minute inter-pass times were utilized to accurately replicate industrial forging practices. The effect of dynamic, metadynamic and static recrystallization during inter-pass times on flow stress was investigated. The study showed the presence of yield peaks in the flow stress data which have been identified in previous studies and thought to be due to solute atoms pinning dislocations, but in this work are shown to be due to friction. The resulting microstructures were analysed using scanning electron, optical microscopy and EBSD to relate grain size and homogeneity with flow stress data. The study showed a negligible difference between multi-pass and single pass tests for strain increments above 0.2. Therefore, when modelling similar low strain and strain rate forging processes inHAYNES® 282®, previous forging steps can be ignored

Competition for water for the food system

Although the global agricultural system will need to provide more food for a growing and wealthier population in decades to come, increasing demands for water and potential impacts of climate change pose threats to food systems. We review the primary threats to agricultural water availability, and model the potential effects of increases in municipal and industrial (M&I) water demands, environmental flow requirements (EFRs) and changing water supplies given climate change. Our models show that, together, these factors cause an 18 per cent reduction in the availability of worldwide water for agriculture by 2050. Meeting EFRs, which can necessitate more than 50 per cent of the mean annual run-off in a basin depending on its hydrograph, presents the single biggest threat to agricultural water availability. Next are increases in M&I demands, which are projected to increase upwards of 200 per cent by 2050 in developing countries with rapidly increasing populations and incomes. Climate change will affect the spatial and temporal distribution of run-off, and thus affect availability from the supply side. The combined effect of these factors can be dramatic in particular hotspots, which include northern Africa, India, China, parts of Europe, the western US and eastern Australia, among others

Precipitate Redistribution During Creep of Alloy 617

Nickel-based superalloys are being considered for applications within advanced nuclear power generation systems due to their high temperature strength and corrosion resistance. Alloy 617, a candidate for use in heat exchangers, derives its strength from both solid solution strengthening and the precipitation of carbide particles. However, during creep, carbides that are supposed to retard grain boundary motion are found to dissolve and re-precipitate on boundaries in tension. To quantify the redistribution, we have used electron backscatter diffraction and energy dispersive spectroscopy to analyze the microstructure of 617 after creep testing at 900 and 1000°C. The data were analyzed with respect to location of the carbides (e.g., intergranular vs. intragranular), grain boundary character, and precipitate type (i.e., Cr-rich or Mo-rich). We find that grain boundary character is the most important factor in carbide distribution; some evidence of preferential distribution to boundaries in tension is also observed at higher applied stresses. Finally, the results suggest that the observed redistribution is due to the migration of carbides to the boundaries and not the migration of boundaries to the precipitates