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This paper investigates the phase formation in Ti-13Mo-2Fe (wt pct) during aging. Ti-13Mo-2Fe prevented athermal ω formation after solution treatment. However, the high diffusivity of Fe favored isothermal ω formation and growth during aging. Furthermore, a secondary BCC phase was detected in the aged sample. The isothermal ω generates Mo- and Fe-enriched regions that may drive the spinodal decomposition of the parent β at 400 °C. The simulation showed a good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

This study analyzes the effects of replacing Ta by Nb (at.% basis) in the phase transformation temperatures, Scheil solidification behavior, and microstructural mechanical features of a Nb-modified as well as conventional Mar-M247 superalloys. Both alloys were directionally solidified at a withdrawal rate of 18 cm/h under a thermal gradient of about 80 °C/cm. DSC results were compared to thermodynamic simulations of phase transformation temperatures and showed a good correlation. The replacement of Ta by Nb has not altered the solidification path of Mar-M247, keeping the sequence L → L + γ → L + γ + MC → L + γ + MC + γ/γ′ eutectic. Due to the segregation of Hf and Zr to the very last liquid to solidify, a low melting point γ/Ni5(Hf,Zr) constituent was observed. The as-solidified microstructures of both Mar-M247(Nb) and Mar-M247 were constituted of columnar dendrites of gamma matrix (γ) phase with cuboidal gamma-prime (γ′) precipitates. In addition, γ/γ′-eutectic was observed in the interdendritic region along with MC carbides in blocky, script (blocky dendritic), needle-like and fine nodular morphologies. Both alloys contained about 1.5 vol.% of MC carbides. The MC carbides in Mar-M247(Nb) and Mar-M247 are, respectively, Nb-rich and Ta-rich, with only a limited amount of Hf being detected in the MC phase. The yield stress of Nb-modified Mar-M247 showed higher values up to 750 °C. For higher temperatures, above 800 °C, a conventional Mar-M247 presented a higher value of yield stress. [ABSTRACT FROM AUTHOR]

Among titanium alloys, the β-type is the most indicated for orthopedic implants due to the reduced elastic modulus compared with α + β alloys. To improve osseointegration, the growth of a self-ordered titania nanotube layer onto the surface of titanium alloy implant pieces is a strategy used to accelerate bone growth. In this paper, the effects of heat treatment for titania nanotube crystallization on Ti-Nb and Ti-Nb-Sn alloys on the phase transformation, the Vickers hardness, and the elastic modulus of the substrate were investigated. TiO layers were grown onto cold-rolled Ti alloy substrates by anodization, and crystallization to anatase was followed by glazing-angle high-temperature X-ray diffraction with a heating ramp of 288 K/min to 623 K, where the samples were held for up to 4 h. The dynamic of the α- and ω-phase formation/dissolution was followed by X-ray diffraction. Transmission electron microscopy was used to confirm the presence of the α- and ω-phases and their volumes and dimensions. As a result of the TiO crystallization heat treatment, a continuous increase in the hardness was observed for the Ti-35Nb and Ti-35Nb-2Sn alloys, which is attributed to dissolution of α″ and the formation of ω precipitates. The same feature was observed for the elastic modulus. In the Ti-35Nb-4Sn alloy, the reverse decomposition of martensite resulted in the β phase and later in α phase precipitation. The aging of this alloy resulted in a homogeneous distribution of a high volumetric fraction of fine and dispersed α phase, which resulted in a hardness increase from 220 to 270 HV. This coupled heat treatment resulted in high hardness, low elastic modulus, and a nanotube with an anatase crystal phase. [ABSTRACT FROM AUTHOR]

The effect of cooling rate on eutectoid decomposition in a near eutectoid (Ti-5.5 at.% Cu) alloy has been investigated in a systematic manner by coupling scanning electron microscopy, transmission electron microscopy and atom probe tomography studies. Thus, the competition between nucleation and growth of proeutectoidαplates from pre-existingβgrain boundaries, and eutectoid decomposition (α + Ti2Cu) via a pearlitic mechanism has been studied as a function of cooling rate, using a Jominy-end quenched sample that was cooled from the high-temperature singleβphase. When the alloy was subjected to very fast cooling (160 K/s), proeutectoidαplates, supersaturated in Cu, are formed along with a highly refined lamellar eutectoid product between theseαplates. In contrast, intermediate (9 K/s) and slow (2 K/s) cooling results in considerably coarser proeutectoidαplates as well as lamellar eutectoid products. With the decrease in the cooling rate, there was a substantial increase in the volume fraction of the lamellar eutectoid product and the composition of all decomposition products approached their equilibrium values. Also, the slowest cooled sample (2 K/s) exhibited substantially rougher and irregular interfaces between the proeutectoidαand the lamellar eutectoid product, which seems to promote the cooperative growth of lamellarα + Ti2Cu. Irrespective of the cooling rate, nucleation of the lamellar eutectoid (α + Ti2Cu) product appears to only occur at the interface between the proeutectoidαplates and theβmatrix. [ABSTRACT FROM AUTHOR]

Zone refining has been extensively used as a process of final purification of materials. Extensive theoretical and experimental efforts have been made to improve the purification efficiency of zone refining by optimizing parameters such as the length and the number of passes of the liquid zone. In the present study, a genetic algorithm (GA) integrated to a mass transfer numerical model has been used in the search of optimized operational parameters of the zone refining process. Experiments were carried out with naphthalene as the reference material having rhodamine as the impurity. Transparent organic substances, such as naphthalene, have been widely used as metals analogues materials because they allow in situ observations of microstructure evolution. Numerical predictions of the impurity profile along the refined naphthalene ingot is also ascertained by the present experimental data. Zone refining experiments were carried out by varying the zone length in each zone pass in order to permit the optimized data to be compared. It was found that the use of a GA integrated to the numerical mass transfer model has permitted the planning of operational conditions which are able to increase the purification efficiency up to 40% if compared with that attained when using conventional simulation approaches. [ABSTRACT FROM AUTHOR]

As the Sn-Se eutectic solidification produces a lamellar structure, formed by SnSe and SnSe2 compound, which are p and n semiconducting type, respectively, the SnSe-SnSe2 in situ composite is a promising material to be used in photovoltaic device manufacturing. In this work, the Sn-Se alloys corresponding to the eutectic composition as well as to SnSe and SnSe2 composition were processed by direction solidification at several solidification rates in a vertical Bridgman-Stockbarger crystal growth unit. The aim of the experiments was to evaluate the eutectic microstructure behavior as a function of directional solidification parameters. The obtained microstructures were analyzed by using X-ray diffraction and scanning electron and optical microscopies. The results obtained show that a very regular and aligned structure formed by the SnSe and SnSe2 solid phase can be achieved. It was found that the presence of imperfections in the eutectic microstructure depends on the growth rate, and mainly, on the alloy homogenization process. [ABSTRACT FROM AUTHOR]

We critically examined the performance of probabilistic streamflow forecasting in the prediction of flood events in 19 subbasins of the Doce River in Brazil using the Eta (4 members, 5 km spatial resolution) and European Centre for Medium‐Range Weather Forecasts (ECMWF; 51 members, 32 km resolution) weather forecast models as inputs for the MHD‐INPE hydrological model. We observed that the shapes and orientations of subbasins influenced the predictability of floods due to the orientation of rainfall events. Streamflow forecasts that use the ECMWF data as input showed higher skill scores than those that used the Eta model for subbasins with drainage areas larger than 20,000 km2. Since the skill scores were similar for both models in smaller subbasins, we concluded that the grid size of the weather model could be important for smaller catchments, while the number of members was crucial for larger scales. We also evaluated the performance of probabilistic streamflow forecasting for the severe flood event of late 2013 through a comparison of observations and streamflow estimations derived from interpolated rainfall fields. In many cases, the mean of the ensemble outperformed the streamflow estimations from the interpolated rainfall because the spatial structure of a rainfall event is better captured by weather forecast models. [ABSTRACT FROM AUTHOR]

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012. [ABSTRACT FROM PUBLISHER]