Ferromagnetic mixed tribridged dinuclear copper(II) complex [Cu2(OAc)2(OH)(dpa)2]PF6 · H2O (dpa = 2,2′-dipyridylamine): 3D superstructure based on hydrogen bond and π…π interaction

A new dinuclear complex [Cu₂(OAc)₂(OH)(dpa)₂] PF₆ · H₂O (1) is prepared and structurally and magneto-structurally characterized. The monocationic core contains one acetate in familiar bidentate η¹:η¹:μ₂-bridge and another in the rare monoatomic bridge along with one hydroxo intermediary. 1 packs through N–H…O and O–H…O hydrogen bonds and π…π interaction resulting a 3D supramolecular continuum and displays high-energy intraligand ¹(π − π^*) fluorescence and intraligand ³(π − π^*) phosphorescence in glassy solution.     

Integrated Computational Materials Engineering (ICME) Approach to Design of Novel Microstructures for Ti-Alloys

In this overview, we present integrated CAPHAD and phase-field modeling with critical experiments to explore a newly discovered, nonconventional, solid–solid phase transformation pathway based on the so-called pseudo-spinodal mechanism. We show that this new transformation pathway offers a new design strategy for Ti alloys with extremely fine and uniform α + β microstructures that could potentially have highly attractive balances of mechanical properties. To broaden the processing window for such a mechanism to operate, we also explore a different nonconventional transformation pathway that involves precursory phase separation. In addition, the variant selection process during the β → α transformation leading to macrozones is investigated and the results could shed light on how to control processing conditions to avoid or reduce microtexture at both the individual β grain level and the overall polycrystalline sample level.     

On the Role of C Addition on α Precipitation in a β Titanium Alloy

The onset of α nucleation in a carbon containing β-titanium alloy has been investigated by coupling atom probe tomography (APT) with transmission electron microscopy. The analysis of the APT results indicates that in addition to ω precipitates that can act as potential α nucleation sites, carbon atoms tend to form clusters within the β-matrix, which in turn give rise to additional nucleation sites for α, resulting in finer scale α precipitates due to increased nucleation density.     

Laser-Deposited In Situ TiC-Reinforced Nickel Matrix Composites: 3D Microstructure and Tribological Properties

A new class of Ni-Ti-C-based metal-matrix composites has been developed using the laser-engineered net shaping? process. These composites consist of an in situ formed and homogeneously distributed titanium carbide (TiC) phase reinforcing the nickel matrix. Additionally, by tailoring the Ti/C ratio in these composites, an additional graphitic phase can also be engineered into the microstructure. Serial-sectioning, followed by three-dimensional reconstruction of the microstructure in these composites, reveals homogeneously distributed primary and eutectic titanium carbide precipitates as well as a graphitic phase encompassing the primary carbides within the nickel matrix. The morphology and spatial distribution of these phases in three dimensions reveals that the eutectic carbides form a network linked by primary carbides or graphitic nodules at the nodes, which suggests interesting insights into the sequence of phase evolution. These three-phase Ni-TiC-C composites exhibit excellent tribological properties, in terms of an extremely low coefficient of friction while maintaining a relatively high hardness.     

Complementary techniques for the characterization of thin film Ti/Nb multilayers

An aberration corrector on the probe-forming lens of a scanning TEM (STEM) equipped with an electron energy-loss spectrometer (EELS) and X-ray energy-dispersive spectrometer (XEDS) has been employed to investigate the compositional variations as a function of length scale in nanoscale Ti/Nb metallic multilayers. The composition profiles of EELS and XEDS were compared with the profiles obtained from the complementary technique of 3D atom probe tomography. At large layer widths (h≥7 nm, where h is the layer width) of Ti and Nb, XEDS composition profiles of Ti/Nb metallic multilayers are in good agreement with the EELS results. However, at reduced layer widths (h≈2 nm), profiles of EELS and atom probe exhibited similar compositional variations, whereas XEDS results have shown a marked difference. This difference in the composition profiling of the layers has been addressed with reference to the effects of beam broadening and the origin of the signals collected in these techniques. The advantage of using EELS over XEDS for these nanoscaled multilayered materials is demonstrated.     

Incipient Plasticity and Shear Band Formation in Bulk Metallic Glass Studied Using Indentation

This study focuses on investigating certain aspects of deformation in bulk metallic glasses (BMGs) based on nanoindentaion and microindentation studies. Using a Berkovich indenter in nanoindentation, the incipient plasticity or early stages of deformation have been studied for a typical BMG, Vitreloy 1. From a critical analysis of the load-displacement curves, the initial displacement burst, often associated with the initiation of shear bands, was found to occur at a value close to the theoretical shear stress of the material. The deformation behavior below these indents, including the formation of shear bands, has been investigated by transmission electron microscopy. The evidence suggests structural changes associated with possible expansion of free volume within the shear bands, especially in the case of deformation under higher loads. Furthermore, while the possibility of nanocrystallization within the shear bands cannot be ruled out, the experimental results do not conclusively indicate the occurrence of such a phenomenon. This article is based on a presentation given in the symposium entitled “Materials Behavior: Far from Equilibrium” as part of the Golden Jubilee Celebration of Bhabha Atomic Research Centre, which occurred December 15–16, 2006 in Mumbai, India.

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In situ nitridation of titanium–molybdenum alloys during laser deposition

In situ nitridation during laser deposition of titanium–molybdenum alloys from elemental powder blends has been achieved by introducing the reactive nitrogen gas during the deposition process. Thus, Ti–Mo–N alloys have been deposited using the laser engineered net shaping (LENS^TM) process and resulted in the formation of a hard α(Ti,N) phase, exhibiting a dendritic morphology, distributed within a β(Ti–Mo) matrix with fine scale transformed α precipitates. Varying the composition of the Ar + N₂ gas employed during laser deposition permits a systematic increase in the nitrogen content of the as-deposited Ti–Mo–N alloy. Interestingly, the addition of nitrogen, which stabilizes the α phase in Ti, changes the solidification pathway and the consequent sequence of phase evolution in these alloys. The nitrogen-enriched hcp α(Ti,N) phase has higher c/a ratio, exhibits an equiaxed morphology, and tends to form in clusters separated by ribs of the Mo-rich β phase. The Ti–Mo–N alloys also exhibit a substantial enhancement in microhardness due to the formation of this α(Ti,N) phase, combining it with the desirable properties of the β-Ti matrix, such as excellent ductility, toughness, and formability.     

In vitro antioxidant activity of different cultivars of banana flower (Musa paradicicus L.) extracts available in India

Abstract: Six different cultivars of banana flowers (Musa paradicicus) (Kathali, Bichi, Shingapuri, Kacha, Champa, and Kalabou) were analyzed for the content of polyphenol expressed as gallic acid equivalent and flavonoid expressed as quercetein equivalent, and the in vitro total antioxidative activities of the flower extracts were compared with standard and expressed as trolox equivalent. The reducing power, 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) and 2,2‐azinobis(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical cation (ABTS?⁺) scavenging activities, inhibition of lipid peroxidation in a linoleic acid emulsion system, and liposome peroxidation system were measured and compared with respective standard antioxidants. Iron‐mediated Fenton reaction was carried out to evaluate the protective effect of the extract of banana flower (Kacha cultivar) against H₂O₂‐induced DNA damage. The Kacha variety contains the maximum amount of polyphenol (11.94 ± 0.03 mg of gallic acid equivalent/g of dry weight) and flavonoid (0.174 ± 0.001 g of quercetin equivalent/g of polyphenol). It also has the highest total antioxidant capacity, DPPH radical scavenging activity, and ABTS?⁺ radical scavenging activity with a least EC₅₀ value of 0.051 mg/mL. Hepatic cell damage in iron‐mediated Fenton reaction caused by free radicals is reduced by the banana flower extract. On the basis of the results obtained, the banana flowers are found to be a potential source of natural antioxidants. This is the first report on the antioxidant properties of the extracts from banana flowers. The study suggests that the flowers of M. paradicicus that are found in India and consumed as vegetable can provide valuable functional ingredients that help in the prevention of oxidative stress.