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DOE OSTI2025

Large‐Scale Statistically Meaningful Patterns (LSMPs) Associated With Precipitation Extremes Over Northern California

Abstract We analyze large‐scale statistically meaningful patterns (LSMPs) that precede extreme precipitation (PEx) events over Northern California (NorCal). We find LSMPs by applying k‐means clustering to the two leading principal components of daily 500 hPa geopotential height anomalies two days before the onset, from October to March during 1948–2015. Statistical significance testing based on Monte Carlo simulations suggests a minimum of four statistically distinguished LSMP clusters. The four LSMP clusters are characterized as Northwest continental negative height anomaly, Eastward positive “Pacific‐North American Pattern (PNA),” Westward negative “PNA,” and Prominent Alaskan ridge. These four clusters, shown in multiple variables, evolve very differently and have differing links to the Arctic and tropical Pacific regions. Using binary forecast skill measures and a new copula‐based framework for predicting PEx events, we find LSMP indices that are useful predictors of NorCal PEx events, with moisture‐based variables being the best predictors of PEx events at least 6 days before the onset, and the lower atmospheric variables being better than their upper atmospheric counterparts any day in advance tested. To ensure statistical rigor, the LSMPs analyzed here (with the modified acronym) include local tests of both significance and consistency, which are not always featured in the literature on large‐scale meteorological patterns.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2019

Effect of Tropical Nonconvective Condensation on Uncertainty in Modeled Projections of Rainfall

Abstract We find that part of the uncertainty in the amplitude and pattern of the modeled precipitation response to CO2 forcing traces to tropical condensation not directly involved with parameterized convection. The fraction of tropical rainfall associated with large-scale condensation can vary from a few percent to well over half depending on model details and parameter settings. In turn, because of the coupling between condensation and tropical circulation, the different ways model assumptions affect the large-scale rainfall fraction also affect the patterns of the response within individual models. In two single-model ensembles based on the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM), versions 3.1 and 5.3, we find strong correlations between the fraction of tropical large-scale rain and both climatological rainfall and circulation and the response to CO2 forcing. While the effects of an increasing tropical large-scale rain fraction are opposite in some ways in the two ensembles—for example, the Hadley circulation weakens with the large-scale rainfall fraction in the CAM3.1 ensemble while strengthening in the CAM5.3 ensemble—we can nonetheless understand these different effects in terms of the relationship between latent heating and circulation, and we propose explanations for each ensemble. We compare these results with data from phase 5 of the Coupled Model Intercomparison Project (CMIP5), for which some of the same patterns hold. Given the importance of this partitioning, there is a need for constraining this source of uncertainty using observations. However, since a “large-scale rainfall fraction” is a modeling construct, it is not clear how observations may be used to test various modeling assumptions determining this fraction.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2019

Surface Characteristics and Hardness Variations in Electrical Discharge Machining of Enhanced Nitrogen in Vanadium Steels

Enhanced nitrogen in steels containing vanadium causes fine precipitates of vanadium nitride, which improve the hardenability properties. However, understanding the response of such steels to electrical discharge machining (EDM) is incomplete and needs further investigation. Therefore, EDM of enhanced nitrogen in steels containing vanadium was compared with a similar compositional steel that was free of nitrogen. The surface morphology, microstructural alterations, microhardness variation, and compositional depth profiling of the samples machined by EDM in oil and deionized water dielectric liquids were examined. Microscopic studies were carried out using optical and scanning electron microscopy. Phases were identified by X-ray diffractometry, and elemental depth profiling was performed using glow discharge optical emission spectroscopy. The hardness of the resolidified and heat-affected layers was measured using a Vickers type microhardness tester. The results of this study revealed that the dissolved nitrogen in steel decreased the probability of surface cracks and resulted in a softer resolidified layer structure when machining in the oil dielectric liquid. Thus, the presence of nitrogen reduced the formation of tension-induced martensite in the resolidified layer. Moreover, the heat-affected zone below the resolidified layer exhibited a uniform and harder structure, compared with the steel without nitrogen content, indicating the fast nature of the thermal cycles in EDM. The free nitrogen in steel did not dissociate during sparking; therefore, precipitation strengthening occurred in the heat-affected zone.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Understanding the interaction of extension twinning and basal-plate precipitates in Mg-9Al using precession electron diffraction

Precession electron diffraction is used to characterize the interaction between ${10\bar{1}2}$ tensile twins and basal plate-like precipitates in a post-deformed, precipitate-dispersed Mg-9Al micropillar. We observed a heterogeneous distribution of precipitates in the micropillar sample, which enabled the study of the different stages involved in twin precipitate interactions. We show that twin nucleation was promoted, taking place on the surface, as well as from the interior of the micropillar. Twin tip propagation and twin growth were hindered by the precipitates. Twin tips either were arrested by precipitates and new twins formed on the other side of the precipitate, or continued to grow around the precipitate without the re-nucleation events. During twin thickening, the precipitates did not significantly alter the shear-dominant twin boundary migration mechanism, as evidenced by the relatively flat twin boundaries around the partially embedded precipitates. However, the twin boundary migration was retarded by the precipitates, especially in regions confined by closely-spaced precipitates.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Structural and Phase Transformations in Alloys during Spark Plasma Sintering of Ti + 23.5 at % Al + 21 at % Nb Powder Mixtures

We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α{sub 2} and Nb{sub 2}Al phases and small precipitates of the O-phase (intermetallic compound Ti{sub 2}AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.

36 MATERIALS SCIENCE↗

NASA NTRSDate not supplied

Guided Design of Alloys, Strengthened via Precipitation

Using theoretical and computational guidance, we are designing stronger middle and high-entropy alloys and superalloys for the airspace applications. We focus on improving mechanical properties of materials at cryogenic and elevated temperatures. Here we discuss basic science and fundamental theory that are being used for guided design of next-generation alloys. As examples, we consider the medium-entropy NiCoCr alloy and precipitated superalloys with a local phase transformation strengthening. This research is funded by NASA’s Aeronautics Research Mission Directorate (ARMD) via Transformational Tools and Technologies (TTT) Project.

Alloys↗

DOE OSTI2019

Tracking Aerosol Convection Interactions ExpeRiment (TRACER) Science Plan

Convective clouds play an important role in the Earth’s climate system as a driver of large-scale circulations and a primary mechanism for the transport of heat, moisture, aerosols, and momentum throughout the troposphere. Despite their climatic importance, multi-scale models continue to have persistent biases produced by insufficient representation of convective clouds. This is the result of an incomplete understanding of key processes such as convective initiation, updraft and downdraft dynamics, cloud and precipitation microphysics, and aerosol-convection interactions.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Precipitation behavior of α phase during aging treatment in a β-quenched Ti-7333

Highlights: • The precipitation behaviors of α precipitate are investigated in the hot-rolled Ti-7333. • The formation of the V-shaped α configuration is closely related to the variant selection of α phase. • The angle between the closely packed direction of α{sub GB} and GB plane plays a key role on the precipitation of α{sub GB}. - Abstract: In this work, the precipitation behavior of α phase during the isothermal aging treatment was investigated in the β-quenched Ti-7333. The results indicate that dislocations contribute to the precipitation of α phase with a dot-like morphology at the beginning of aging treatment, and these dot-like α precipitates holding the same Burgers orientation relationship (BOR) with respect to the β matrix coalesce into the platelet morphology. The platelet-like α precipitates that orientate to different growth directions combine with each other to form the V-shaped configuration. And the formation of this configuration is closely related with the variant selection (VS) of α phase, which is resulted from the perfect accommodation of transformation strain within the β matrix. Meanwhile, it is found that low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) can be decorated by α phase during the aging treatment, and its precipitation degree significantly depends on the angle between the closely packed direction of αGB and the GB plane. The volume fraction of α phase increases with increasing aging time, and this increasing volume fraction eventually results in the increase in micro-hardness of the alloy.

36 MATERIALS SCIENCE↗

DOE OSTI2024

The Physics behind Precipitation Onset Bias in CMIP6 Models: The Pseudo-Entrainment Diagnostic and Trade-Offs between Lapse Rate and Humidity

Conditional instability and the buoyancy of plumes drive moist convection but have a variety of representations in model convective schemes. Vertical thermodynamic structure information from Atmospheric Radiation Measurement (ARM) sites and reanalysis (ERA5), satellite-derived precipitation (TRMM3b42), and diagnostics relevant for plume buoyancy are used to assess climate models. Previous work has shown that CMIP6 models represent moist convective processes more accurately than their CMIP5 counterparts. However, certain biases in convective onset remain pervasive among generations of CMIP modeling efforts. Here we diagnose these biases in a cohort of nine CMIP6 models with sub-daily output, assessing conditional instability in profiles of equivalent potential temperature θ e and saturation equivalent potential temperature θ es in comparison to a plume model with different mixing assumptions. Most models capture qualitative aspects of the θ es vertical structure, including a substantial decrease with height in the lower free troposphere associated with the entrainment of subsaturated air. We define a “pseudo-entrainment” diagnostic that combines subsaturation and a θ es measure of conditional instability similar to what entrainment would produce under the small-buoyancy approximation. This captures the trade-off between larger θ es lapse rates (entrainment of dry air) and small subsaturation (permits positive buoyancy despite high entrainment). This pseudo-entrainment diagnostic is also a reasonable indicator of the critical value of integrated buoyancy for precipitation onset. Models with poor θ e /θ es structure (those using variants of the Tiedtke Scheme) or low entrainment runs of CAM5, and models with low subsaturation, such as NASA-GISS, lie outside the observational range in this diagnostic.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2012

Effects of proton irradiation on nanocluster precipitation in ferritic steel containing fcc alloying additions

Newly-developed precipitate-strengthened ferritic steels with and without pre-existing nanoscale precipitates were irradiated with 4 MeV protons to a dose of ~5 mdpa at 50 C and subsequently examined by nanoindentation and atom probe tomography (APT). Irradiation-enhanced precipitation and coarsening of pre-existing nanoscale precipitates were observed. Copper partitions to the precipitate core along with a segregation of Ni, Al and Mn to the precipitate/matrix interface after both thermal aging and proton irradiation. Proton irradiation induces the precipitation reaction and coarsening of pre-existing nanoscale precipitates, and these results are similar to a thermal aging process. The precipitation and coarsening of nanoscale precipitates are responsible for the changes in hardness. The observation of the radiation-induced softening is essentially due to the coarsening of the pre-existing Cu-rich nanoscale precipitates. The implication of the precipitation on the embrittlement of reactor-pressure-vessel steels after irradiation is discussed.

Zhang, Zhongwu↗

DOE OSTI2017

Aerosols and their Impact on Radiation, Clouds, Precipitation & Severe Weather Events

Aerosols, the tiny particles suspended in the atmosphere, have been in the forefront of environmental and climate change sciences as the primary atmospheric pollutant and external force affecting Earth’s weather and climate. There are two dominant mechanisms by which aerosols affect weather and climate: aerosol-radiation interactions (ARI) and aerosol-cloud interactions (ACI). ARI arises from aerosol scattering and absorption, which alters the radiation budgets of the atmosphere and surface, while ACI is rooted to the fact that aerosols serve as cloud condensation nuclei and ice nuclei. Both ARI and ACI are coupled with atmospheric dynamics to produce a chain of complex interactions with a large range of meteorological variables that influence both weather and climate. Elaborated here are the impacts of aerosols on the radiation budget, clouds (microphysics, structure, and lifetime), precipitation, and severe weather events (lightning, thunderstorms, hail, and tornados). Depending on environmental variables and aerosol properties, the effects can be both positive and negative, posing the largest uncertainties in the external forcing of the climate system. This has considerably hindered our ability in projecting future climate changes and in doing accurate numerical weather predictions.

aerosol↗

DOE OSTI2018

Influence of duplex ageing on secondary α precipitates and mechanical properties of the near β-Ti alloy Ti-55531

Highlights: • High strength β-Ti alloys are widely used for their excellent properties. • To reach an excellent combination of strength and ductility, it is attractive to explore the right heat treatment system. • While compared to the conventional single-step ageing process, duplex ageing could change the development and refinement of secondary α precipitations in near/metastable β-Ti alloys resulting varying in performance. • Therefore it is of scientific significance and engineering value to understand the influence of duplex ageing on the formation of secondary α precipitates and mechanical properties for this type of alloy. - Abstract: This paper presents the results of studies on the microstructure and mechanical properties of a near β-Ti alloy processed with different ageing approaches. Influences of intragranular ultrafine α precipitates and grain boundary α layer on mechanical properties in Ti-55531 alloy were analyzed. The results indicate that the precipitation microstructure of the duplex aged alloy exhibits a uniform size and acicular α precipitated orientation shows an angle of approximately 60°. While the morphology of secondary α precipitates in single-step aged samples appear the irregular distribution and heterogeneous size. With the final ageing time increasing, the morphology of intragranular α precipitates and grain boundary α phase brings out a distinct coarsening. The single-step aged alloy can yield a better combination of the ultimate tensile strength (1265 MPa) and ductility (9%). However, the ultimate tensile strength of the duplex aged alloy even reaches 1368 MPa but it breaks at the stage of elastic deformation. The fracture mode of Ti-55531 alloy changes from predominantly dimple fracture in single-step aged samples to predominantly faceted and cleavage type fracture in duplex aged samples causing by the differences of intragranular α precipitates and the interface between grain boundary α layer and intragranular microstructure.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Advanced processing of EBSD data to distinguish the complex microstructure evolution of a Cu-Ni-Si alloy induced by fatigue

Highlights: • Microstructure investigation of the fatigue behaviour of a Cu-Ni-Si alloy • Use of ECCI and EBSD to investigate the microstructure evolution related to fatigue dislocations structures • Characterisation of local plastic accommodation through EBSD misorientation criteria - Abstract: The present work aims at identifying the evolution of the microstructure of a Cu-Ni-Si (Corson alloy) alloy after low cycle fatigue by means of advanced electron microscopy analysis techniques (SEM-ECCI, Orientation Imaging Microscopy by means of SEM-EBSD and TEM). Deep attention is paid on the material subjected to high cyclic strains where a transient cellular dislocation structure transformed into precipitate free bands. It is shown that the formation of dislocation cells leads to a high GROD and high GOSaera value and its standard deviation. However, the presence of precipitate free bands results in the low GOSarea level and its low standard deviation.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Effect of Nb and Cu on the high temperature creep properties of a high Mn–N austenitic stainless steel

The effect of Nb and Cu addition on the creep properties of a high Mn–N austenitic stainless steel was investigated at 600 and 650 °C. In the original high Mn–N steel, which was initially precipitate-free, the precipitation of M{sub 23}C{sub 6} (M = Cr, Fe) and Cr{sub 2}N took place mostly on grain boudaries during creep deformation. On the other hand, the minor addition of Nb resulted in high number density of Z-phases (CrNbN) and MX (M = Nb; X = C, N) carbonitrides inside grains by combining with a high content of N, while suppressing the formation of Cr{sub 2}N. The addition of Cu gave rise to the independent precipitation of nanometer-sized metallic Cu particles. The combination of the different precipitate-forming mechanisms associated with Z-phase, MX and Cu-rich precipitates turned out to improve the creep-resistance significantly. The thermodynamics and kinetics of the precipitation were discussed using thermo-kinetic simulations. - Highlights: • The creep rupture life was improved by Nb and Cu addition. • The creep resistance of the steel A2 in this study was comparable to that of TP347HFG. • The size of Z-phase and MX carbonitride did not change significantly after creep test. • The nanometer sized Cu-rich precipitate was observed after creep. • The predicted size of precipitates by MatCalc agreed well with measured size.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Precipitation process in a Mg–Gd–Y alloy grain-refined by Al addition

The precipitation process in Mg–10Gd–3Y (wt.%) alloy grain-refined by 0.8 wt.% Al addition has been investigated by transmission electron microscopy. The alloy was given a solution treatment at 520 °C for 6 h plus 550 °C for 7 h before ageing at 250 °C. Plate-shaped intermetallic particles with the 18R-type long-period stacking ordered structure were observed in the solution-treated state. Upon isothermal ageing at 250 °C, the following precipitation sequence was identified for the α-Mg supersaturated solution: β″ (D0{sub 19}) → β′ (bco) → β{sub 1} (fcc) → β (fcc). The observed precipitation process and age hardening response in the Al grain-refined Mg–10Gd–3Y alloy are compared with those reported in the Zr grain-refined counterpart. - Highlights: • The precipitation process in Mg–10Gd–3Y–0.8Al (wt.%) alloy has been investigated. • Particles with the 18R-type LPSO structure were observed in the solution state. • Upon ageing at 250 °C, the precipitation sequence is: β″ → β′ → β1 (fcc) → β. • The Al grain-refined alloy has a lower hardness than the Zr refined counterpart.

36 MATERIALS SCIENCE↗

DOE OSTI2018

The Mechanical and Microstructural Changes of Sn-Ag-Bi Solders with Cooling Rate and Bi Content Variations

The purpose of this study is to investigate the influence of cooling rate and Bi addition on the microstructure evolution and mechanical properties of Sn-3.5Ag alloy. A series of Sn-3.5Ag-xBi solders has been fabricated with Bi content in the range of 0.5-3.5 wt.%. After solution heat treatment at 170 °C for 24 h and subsequent aging heat treatment at 100 °C for 2 h, samples were divided into two groups. One group was rapidly quenched into iced water (water quenching) for the fast cooling rate (20 °C/s), while the second group was slowly cooled (furnace cooling) in the furnace for the slow cooling rate (0.2 °C/s) after the furnace reflow. The microstructural evolutions of the present solders have been investigated using x-ray diffraction and scanning electron microscopy. The microhardness was measured to correlate the mechanical properties to alloy compositions and cooling rate. It was found that the microhardness of Sn-3.5Ag-xBi solders increased with increasing cooling rate. The indentation creep curves have been evaluated from the obtained microhardness values. Results revealed the steady-state creep rate decreased with increasing Bi content exhibiting an anomalous behavior at 2.5Bi. The reason for improved creep resistance of Sn-3.5Ag-xBi solders is the result of the combination of the solid solution strengthening and precipitation strengthening of Bi. The mean values of stress exponent indicated that the operative creep mechanism is dislocation climb.

36 MATERIALS SCIENCE↗

NASA NTRS2012

Tropical Rainfall Measuring Mission (TRMM) Precipitation Data and Services for Research and Applications

Precipitation is a critical component of the Earth's hydrological cycle. Launched on 27 November 1997, TRMM is a joint U.S.-Japan satellite mission to provide the first detailed and comprehensive data set of the four-dimensional distribution of rainfall and latent heating over vastly under-sampled tropical and subtropical oceans and continents (40 S - 40 N). Over the past 14 years, TRMM has been a major data source for meteorological, hydrological and other research and application activities around the world. The purpose of this short article is to inform that the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) provides TRMM archive and near-real-time precipitation data sets and services for research and applications. TRMM data consist of orbital data from TRMM instruments at the sensor s resolution, gridded data at a range of spatial and temporal resolutions, subsets, ground-based instrument data, and ancillary data. Data analysis, display, and delivery are facilitated by the following services: (1) Mirador (data search and access); (2) TOVAS (TRMM Online Visualization and Analysis System); (3) OPeNDAP (Open-source Project for a Network Data Access Protocol); (4) GrADS Data Server (GDS); and (5) Open Geospatial Consortium (OGC) Web Map Service (WMS) for the GIS community. Precipitation data application services are available to support a wide variety of applications around the world. Future plans include enhanced and new services to address data related issues from the user community. Meanwhile, the GES DISC is preparing for the Global Precipitation Measurement (GPM) mission which is scheduled for launch in 2014.

Liu, Zhong↗

DOE OSTI2014

Effect of long-term aging on microstructure and local behavior in the heat-affected zone of a Ni–Cr–Mo–V steel welded joint

Evolution of microstructure, micro-hardness and micro-tensile strength behavior was investigated in the heat-affected zone of a Ni–Cr–Mo–V steel welded joint after the artificial aging at 350 °C for 3000 h. After detailed characterization of microstructures in optical microscopy, scanning electron microscopy and transmission electron microscopy, it is revealed that the change of martensite–bainite constituent promotes more homogeneous microstructure distribution. The aging treatment facilitates redistribution of carbon and chromium elements along the welded joint, and the micro-hardness is increased slightly through the welds due to enrichment of carbon. The types of precipitates in the weldment mainly include M{sub 3}C, MC, M{sub 2}C and M{sub 23}C{sub 6}. The carbides in base metal, weld metal and coarse-grained heat-affected zone are prone to change from ellipsoidal to platelet form whereas more uniform spherical carbides are observed in the fine-grained zone. Precipitation and coarsening of M{sub 23}C{sub 6} near the fusion line, and formation of MC and M{sub 2}C, are responsible for the tensile strength decrease and its smooth distribution in the aged heat-affected zone. This implies that the thermal aging can relieve strength mismatch in the weldments. - Highlights: • Microstructure homogeneity improved in HAZ after long-term aging. • Tensile strength decreased in HAZ due to precipitation and coarsening of M{sub 23}C{sub 6}. • Strength mismatch in NiCrMoV steel welds was relieved after aging at 350 °C × 3000 h.

36 MATERIALS SCIENCE↗