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The strength-ductility trade-off is an eminent factor in deciding the mechanical performance of a material with regard to specific applications. The strength-ductility synergy is generally inadequate in as-synthesized high entropy alloys (HEAs); however, it can be tailored owing to its tunable microstructure and phase stability. Thermo-mechanical processing (TMP) allows the microstructure to be tailored to achieve desired strength-ductility combination. The additional attribute is evolution of texture, which also significantly influences the mechanical properties. This review presents a critical insight into the role of TMP to achieve superior strength-ductility symbiosis at room temperature in single-phase (FCC, BCC) and multiphase HEA. The role of overall processing strategy of HEAs encompassing rolling and subsequent annealing in relation to the evolution of microstructure and texture in have been discussed. Recently practiced severe plastic deformation processes have also shown promise in improving the strength-ductility combination. The relevance of these processes in the processing of HEAs has also been analysed. At the end, futuristic approaches have been elaborated to enable efficient as well as hassle-free process towards achieving the proficiency of strength-ductility in HEAs.

Filling the voids of cage forming compounds with loosely bound electropositive elements and by incorporating nano-sized secondary phases are promising approaches to enhance the thermoelectric figure of merit of these materials. Hence, in this work, by combining these two approaches-inserting In into the voids of skutterudite Co4Sb12 as well as dispersing nanoparticles (GaSb)-we have synthesized various samples via ball-milling and spark plasma sintering. InSb as the secondary phase of the matrix, mixed with GaSb, forms the solid solution Ga1-xInxSb. Nanocrystalline grains together with a few larger grains (10-30 μm) are found to be spread in In0.2Co4Sb12. The former is comprised of either InSb, GaSb or Ga1-xInxSb. Because of their identical space group and similar lattice parameters, InSb, GaSb and Ga1-xInxSb could not be detected separately in EBSD. High resolution transmission electron microscopy (HRTEM) was used to resolve different phases, which showed GaSb grains of size ∼10-30 nm and InSb grains of size ∼30-100 nm. Scattering of charge carriers at the interfaces of InSb, GaSb and Ga1-xInxSb as well as the matrix phases increased both the electrical resistivity and Seebeck coefficient. The multi-scale size distribution of grains, of both the matrix phase and the secondary phases, scattered phonons within a broad wavelength range, resulting in very low lattice thermal conductivities. As a result, an enhanced figure of merit of 1.4 was achieved for the (GaSb)0.1 + In0.2Co4Sb12 nanocomposite at 773 K.

The thermoelectric efficiency of skutterudite materials can be improved by lowering the lattice thermal conductivity via the uniform dispersion of a nanosized second phase in the matrix of filled Co

Barium lead titanate ferroelectric ceramic is a promising material for electronic devices at high frequency and high temperatures. These fine-grained ceramics were obtained at a low sintering temperature of 900°C within a short sintering time by means of a new sintering method – spark plasma sintering (SPS). The ceramics are highly densified to >99% of the theoretical X-ray density with homogeneous microstructures, signifying that the SPS process is effective for the densifying of compacts and the inhibition of exaggerated grain growth. Temperature dependence of dielectric constant of SPS pellets shows three times higher than the conventional sintering (CS) Ba0.8Pb0.2TiO3 (BPT) pellet. The variations in properties between SPS and CS materials are mainly because of the differences of the resultant microstructures, especially grain size, of the ceramics.

The figure of merit (zT) of a thermoelectric material can be enhanced by incorporation of nanoinclusions into bulk material. The presence of bismuth telluride (Bi

This study aims at determining the degradation aspect of pollutants from coke oven effluents such as phenols, aromatic hydrocarbons, and cyanide by aerobic mixed culture. Enriched mixed culture was developed from the sludge collected from aeration tank of a sewage treatment plant by serial enrichment technique. The acclimatized culture was able to degrade phenol, cresol, xylenol, quinoline, indole, and cyanide individually, for their concentrations usually found in coke oven wastewater. Xylenol and indole with concentrations above 250 mg/L were highly recalcitrant for biodegradation. A co-substrate such as glucose (1000 mg/L) had an adverse effect on the biodegradation of all the above pollutants; the degradation time was extended with the increase in the concentration of pollutant, although glucose was completely oxidized independent of the pollutant concentration. Biodegradation during mixed pollutant (100 mg/L of each organic compound) conditions were tested in presence of glucose (1000 mg/L) and glucose (1000 mg/L) with cyanide (2.5 mg/L). Aerobic microbes showed increased substrate affinity in the following order phenol > cresol > quinoline > indole > xylenol. The COD at the end of the experiment was found to be less than 0.5 mg/L showing no accumulation of intermediates. In the presence of glucose (1000 mg/L) and cyanide (2.5 mg/L), the lag phase for microbial growth was increased by several days and cyanide was found to be oxidized before the organic pollutants. Xylenol was highly recalcitrant during this experiment and was not degraded even after 20 days. The experimental results highlight the effect of high concentration of co-substrate (1000 mg/L) and the combined toxic influence of cyanide and organics on the microbes treating coke oven wastewater. These results and the ongoing work are aimed at developing high-rate bioreactors for efficient treatment of phenolics, aromatic hydrocarbons, and cyanide-containing wastes emanating from industrial activities.

The effect of crystallite size and applied DC bias voltage on dielectric permittivity of CuO was studied using impedance spectroscopy. The measurements were performed at room temperature in a wide frequency range of 1 Hz to 1 MHz under applied DC bias voltages from 0 to 3 V in the periodic increment of 0. 2 V. The observed applied DC bias voltage effect on giant dielectric constant (e{open}? = 104) were analyzed with 'grain boundary double Schottky potential barrier height model'. The percentage of tunability (T %) at the frequency 100 Hz is found to be 45. 5% for the case of nanocrystalline CuO in contrast to 0% tunability in bulk CuO. � 2013 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.

Vehicle weight in the aerospace and automotive industries directly impacts carbon emissions and fuel efficiency. An increase in the use of magnesium alloys in structural applications to replace aluminum alloys will result in lighter vehicles. However, the strength of magnesium alloys is lower than that of aluminum alloys. Grain refinement can significantly improve the mechanical properties of alloys. This study investigates the refining potential and fading of Al-5Ti-1B and Al-1Ti-3B grain refiners in AZ91E magnesium alloy. The grain refiners were added at 0.1, 0.2, 0.5 and 1.0 wt.% levels. These alloys were added to the molten AZ91E magnesium alloy at 740C (1364F) and stirred for 30 seconds. To examine fading of the grain refiners, they were allowed to settle for 5, 10 and 20 minutes in the molten magnesium alloy prior to pouring. The prototype castings were characterized using optical microscopy, SEM and TEM. The average grain size of the base alloy, AZ91E decreased significantly with the addition of the grain refiners. Minimum average grain sizes were obtained using 0.1 wt.% Al-5Ti-1B and 1.0 wt.% Al-1Ti-3B. For both refiners, grain refinement was attributed to TiB 2 particles providing nucleating sites and grain growth restriction. In addition, AIB 2 particles provided nucleating sites in the case of Al1Ti-3B refiner. Proper choice of the type and quantity of grain refiner additions for grain refinement with an understanding of the fading effects will enable improvement of mechanical properties at minimal cost. The improved mechanical properties of these refined magnesium alloys will promote their use for more structurally demanding applications. Copyright � 2011 American Foundry Society.

Nanocrystalline p-type semiconductor copper aluminum oxide (CuAlO2) has been synthesized by mechanical alloying using freshly prepared Cu2O and α-Al2O3 nanocrystals in toluene medium. A study on structural property performed with different alloying and post annealing durations, by X-ray diffraction (XRD) reveals the formation of single phase with average crystallite size ∼45 nm. Optical absorbance onset at 364.5 nm confirms its wide band gap nature (Eg = 3.4 eV) and the fluorescence emission behaviour (390 nm) confirms its direct band type transition. The activation energy for electrical conduction has been calculated by Arrhenius plots using impedance measurement. Both grain and grain boundary conductivity takes place with almost equal activation energies of ∼0.45 eV. The paper discusses synthesis, structural, optical and electrical properties of delafossite CuAlO2 in detail.

Mechanism and Kinetics of Alloying and Nanostructure Formation by Mechanical Methods

Studies of the stress corrosion cracking behaviour of an Al–Li alloy (8090) in the underaged, peak aged and overaged conditions were conducted using a constant load technique in a chloride containi...

Nanocrystalline Pb 1 − x Zn x (Zr 0.53 Ti 0.47 )O 3 (where x = 0, 0.04, 0.08 and 0.12) abbreviated as PZZT has been synthesized by high-energy ball milling of mixture of oxides (mechanical alloying, MA). Detailed analysis of XRD patterns of this composition suggests the formation of single phase. The substitution of Zn 2 + cation at the Pb site shows the decrease in the electrical properties, the broadening of permittivity peak and decrease in phase transition temperature (T c ).

The nanocrystalline Pb 1− x Gd x (Zr 0.53 Ti 0.47 ) 1− x /4 O 3 (where x =0.04, 0.08 and 0.12) (PGZT) has been synthesized by a high-energy ball milling (mechanical activation synthesis) followed by sintering. The nanocrystalline PGZT obtained by this route has exceptionally high dielectric constant. X-ray diffraction studies showed that PGZT has tetragonal structure at all the compositions studied. Detailed studies of dielectric properties of PGZT as a function of temperature show a non-relaxor type ferroelectric diffused phase transition.

The nanocrystalline Gd-doped lead titanium zirconate (PGZT) with the composition Pb0.92Gd0.08(Zr0.53Ti0.47)0.98O3 has been synthesized by a combination of high-energy ball milling [mechanical alloying (MA)] and sintering. PGZT prepared by MA followed by high-temperature sintering has a higher dielectric constant compared to that of the conventional technique. PGZT shows a nonrelaxor ferroelectric behavior but has diffuse ferroelectric–paraelectric phase transition. The activation energy of the material was found sensitive to its crystallite size.

The influence of heating rate on the microstructure and magnetic properties of the Fe3B/Nd2Fe14B nanocomposite permanent magnet materials produced by the crystallization of the Nd4.5Fe73B18.5Co2Cr2 amorphous alloy has been studied.

This paper reports the crystallization sequence of ternary Mg 65 Cu 25 Y 10 , Mg 80 Cu 10 Y 10 and Mg 80 Cu 15 Y 5 amorphous alloys. Nanodispersions of Mg 2 Cu, hcp-Mg and fcc-Mg ranging from 5 to 20nm have been observed in the melt-spun Mg 65 Cu 25 Y 10 , Mg 80 Cu 10 Y 10 and Mg 80 Cu 15 Y 5 alloys, respectively. The brittleness of melt-spun Mg-Cu-Y based alloys appears to be due to the nanodispersions of Mg 2 Cu intermetallic phase. On the other hand, nanodispersions of terminal solid solution such as hcp-Mg or fcc-Mg in the amorphous matrix lead to good ductility in the melt-spun Mg-rich alloys. The results also indicate that the glass forming ability and the thermal stability of amorphous phase are not improved by additions of quaternary elements such as Ni, Al, Zn and Mm to Mg-Cu-Y based alloys.

This article reports a novel, eco-friendly herbal method to synthesize Cu nanoparticles in large scales. Cu nanoparticles are an alternative to Ag and Au nanoparticles and have potential applications in many industrial areas. Many synthetic routes have been documented for the preparation of copper nanoparticles, but very few routes are eco-friendly and large-scale. We report here the preparation of Cu nanoparticles from aqueous CuSO4 using non-toxic and inexpensive materials like curd, milk, and herbal extracts such as tamarind and lemon juice as capping agents. X-ray diffraction and transmission electron microscopy show that produced particles are nanocrystalline copper 20-50 nm in size with a face-centered cubic structure. Fourier-transformed infrared spectroscopy evidences the role of organic acids in the capping process. The novelty of this work is the synthesis of Cu nanoparticles from CuSO4 without electricity and using non-toxic, cheap capping agents. � 2013 Springer-Verlag Berlin Heidelberg.

Grain boundary effect on the room temperature dielectric behavior in mechanically alloyed nanocrystalline CuAlO2 has been investigated using impedance spectroscopy under the applied DC bias voltages 0 V to 4. 8 V in a periodic interval of 0. 2 V. Analysis of impedance data confirms the existence of double Schottky potential barrier heights (?b) between two adjacent grains (left and right side) with grain boundary and its influences in dielectric relaxation time (?), dielectric constant (e{open}?) and dielectric loss (tan ?) factor. Also, clear evidence on the suppression of ?b was demonstrated in the higher applied bias voltages with the parameter ?. At equilibrium state, ? is 0. 63 ms and it was reduced to 0. 13 ms after the 3. 2 V applied DC bias. These observed DC bias voltage effects are obeying 'brick layer model' and also elucidates ?b is playing a crucial role in controlling dielectric properties of nanomaterials. � 2013 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.

A new synthesis route with high energy ball milling and microwave sintering is used to obtain nanocrystalline BiFeO3 with improved dielectric and magnetic properties. Electrical and magnetic properties are compared with a conventionally sintered microcrystalline BiFeO3. It is found that the dielectric constant is increased more than one order of magnitude, electrical resistivity by six orders of magnitude and remnant polarization value is increased by 4-5 times for nanocrystalline BiFeO3 in comparison to conventionally sintered microcrystalline BiFeO3. Nanocrystalline BiFeO3 is seen to have ferromagnetic behavior whereas microcrystalline BiFeO3 is known to be antiferromagnetic.

The grain boundary space charge depletion layer in nanocrystalline alpha phase CuSCN is investigated by studying electrical properties using impedance spectroscopic analysis in frequency domain. The measurements were performed at room temperature in wide frequency range 1 Hz to 1 MHz under various DC bias applied voltages ranges from 0 V to -2.1 V. The effect of bias on grain and grain boundary contribution electrical conductivity has been investigated by equivalent circuit model using non-linear least squares (NLLS) fitting of the impedance data. Three order of magnitude variation of grain boundary conductivity was observed for varying 0 V to -2.1 V. Variations in the ?ac clearly elucidate the DC bias is playing crucial role on grain boundary double Schottky barriers of nanocrystalline ?-CuSCN. Copyright � 2011 Author(s).

The structures of melt-spun, and subsequently annealed, Zr70Pd30 alloys, which form a nanosized icosahedral quasicrystalline phase during the primary crystallization of the amorphous phase, have been investigated by means of electron-diffraction pair-distribution-function (PDF) analysis. The PDF analysis for this alloy was performed by precise measurements of elastic halo-electron-diffraction intensities. Possible structure models for as-quenched and annealed amorphous structures were constructed with the help of reverse Monte Carlo simulations. In order to obtain the local atomic structures, the Voronoi-polyhedra analysis was performed. A considerable number of icosahedral clusters with Zr atoms in the center are present in the simulated structure of the as-quenched state, and the number of the clusters increases by annealing.

A few studies have focused on the preparation of metal matrix composites (MMC) reinforced with CNTs. In these composites there is evidence of poor interfacial bonding between the CNTs and the metal matrix, and this may be detrimental to the mechanical properties Furthermore, agglomeration of the CNTs may produce an uneven dispersion within the matrix which reduces their effectiveness. These are the challenges that need to be addressed in optimizing the synthesis of CNT metal matrix composites. In the present investigation, nanocrystalline AA4032 alloy reinforced with CNTs in different fractions was produced by high energy ball milling. The Raman spectra and TEM observations revealed multi‐walled CNTs that are used as reinforcement in the composite. TEM observations revealed nanocrystalline matrix of AA4032 alloy composite along with uniform distribution of CNTs.

The present letter reports the formation of the icosahedral phase during crystallization of amorphous Zr65−xCu27.5Al7.5Ox (x=0.43% and 0.82%) alloys. Three-dimensional atom probe studies have revealed that the quasicrystalline phase is enriched in oxygen. This, together with the fact that no icosahedral phase forms at low oxygen level (0.14%), clearly establishes that the quasicrystalline phase in Zr-based metallic glasses is stabilized by oxygen.

Nanocrystalline ferroelectric Pb 0.92Sm 0.08(Zr 0.53Ti 0.47) 0.98O 3 with high dielectric constant has been synthesized by mechanical alloying (high energy ball milling). The ferroelectric material exhibits novel behavior when its crystallite size falls below a critical length scale of 40 nm. We observed phenomena such as significant decrease in dielectric constant and phase transition from Tetragonal to Cubic structure on reduction in crystallite size below 40 nm. Copyright � 2009 American Scientific Publishers All rights reserved.

A theoretical approach for predicting glass forming ability of transition metal alloys is proposed. This is an attempt for synergistic understanding of the effects of thermodynamics and local geometry on glass forming ability. The enthalpy of formation has been estimated by a modified Miedema's model and used as a criterion for stability. The lattice strain energy has been estimated by a modified Miracle's model. The coordination numbers of the solute centered clusters have been used for establishing a set of inequalities that demarcate geometrically favored composition regimes. Glass formation within the geometrically favored areas is dictated by thermodynamics. � 2008 American Institute of Physics.

In the present paper the authors studied isolated metallic films made from the same material used for making metallic foams, and then characterised their properties. Metal films were made from a liquid aluminium alloy reinforced with ceramic particles of known concentration. Melts without such particles were also investigated. It is shown that stable films could not be made from Al-Si alloy having no particles, and just extremely thin and fragile films could be made from commercially-pure Al. In contrast, aluminium alloys containing particles such as SiC and TiB2 allowed pulling thin, stable films, which did not rupture. Significant thinning of films was observed when the particle concentration in the melt decreased. By in situ X-ray monitoring of liquid films during pulling, film thickness and drainage effects within the liquid film could be studied. The morphology and microstructure of films was characterised after solidification. Our work shows that the question of how foams are stabilised can be studied using a simplified system such as a film, instead of having to deal with the multitude of different structural elements present in a foam. � the Owner Societies.

Nanoindentation studies on rapidly solidified Zr80Pt20 and Zr75Pd25 binary alloys with nanocrystalline, nanoquasicrystalline, and amorphous microstructures are reported. The results indicate that the hardness and elastic modulus are the highest for a mixture of amorphous and nanoquasicrystalline state among the various microstructures studied. Nanoquasicrystalline phase has high hardness and elastic modulus in comparison to amorphous and nanocrystalline phases. The hardness to modulus ratio is close to 0.1 in both the alloys, irrespective of the phase/phase mixture studied indicating that the bonding in these alloys is of covalent nature. In Zr80Pt20, all the phases/phase mixtures have higher hardness and modulus in comparison to similar microstructures in Zr75Pd25 due to higher bond energies caused by more negative heat of mixing in the former case.

Transparent semiconductor CuAlO2 in nanodimension was prepared by mechanical alloying of Cu2 O and ? -Al2 O3 powders in toluene medium. The formation of single phase CuAlO2 with an average crystallite size of 45 nm was confirmed by x-ray diffraction analysis. The nanocrystalline nature of CuAlO2 was confirmed by atomic force microscopy. Frequency-dependent dielectric property measurements and the relaxation behavior were studied using impedance spectroscopy. Dielectric relaxation time estimated from the modulus curves was found to be decreasing with increase in temperature. The existence of stretched exponent parameter ?

Amorphous structure generated by mechanical alloying (MA) is often used as a, precursor for generating nanocomposites through controlled devitrification. The amorphous forming composition range of ternary Al-Ni-Ti system was calculated using the extended Miedema's semi-empirical model. Eleven compositions of this system showing a wide range of negative enthalpy of mixing (-Delta;Hmix) and amorphization (-?Hamor) of the constituent elements were selected for synthesis by MA. The Al 88Ni6Ti6 alloy with relatively small negative ?Hmix (-0.4 kJ/mol) and ?Hamor (-14.8 kJ/mol) became completely amorphous after 120 h of milling, which is possibly the first report of complete amorphization of an Al-based rare earth element free Al-TM-TM system (TM = transition metal) by MA. The alloys of other compositions selected had much more negative ?Hmix and Hamor but they yielded either nanocomposites of partial amorphous and crystalline structure or no amorphous phase at all in the as-milled condition, evidencing a high degree of stability of the intermetallic phases under the MA environment. Hence, the negative ?Hmix and ?Hmix amor are not so reliable for predicting the amorphization in the present system by MA. ? Indian Academy of Sciences.

A modified VERL-process (Vacuum evaporation on running liquids) employing high pressure magnetron sputtering has been used for the preparation of suspensions with metal nanoparticles. The method has been tested for Ag- and Fe-suspensions by varying the pressure of the Argon sputtering atmosphere in the range of 1 to 30 Pa. A narrow particle size distribution with a mean particle size ranging from 5–18 nm has been found. The mean particle size increases with increasing Argon pressure in the pressure range under investigation. A descriptive model for the process of particle formation as a function of sputtering gas pressure is given.

Nanocrystalline ZnO particles were prepared using the high-energy ball milling technique and investigated with electron paramagnetic resonance (EPR), impedance, and Raman spectroscopy to reveal the origin of surface and core defects. We observed two distinct EPR signals with different g-factors, g ∼ 2.0 and ∼1.96, indicating EPR-active defects on the surface and core, respectively. Using the semi-empirical core-shell model, we identified that sufficiently small nanocrystals (below 30 nm) can show p-type character. The model can also explain the origin of the non-linearity of the U-I behaviour in nanocrystalline ZnO.

Dielectric relaxation in sol-gel-derived anatase titanium oxide nanocrystals (6, 9, and 20 nm) has been investigated using impedance spectroscopy in a wide frequency range from 1 Hz to 1 MHz as a function of applied DC bias voltage, ranging from 0 to 4.2 V in a periodic interval of 0.3 V. Under the equilibrium condition, around three order of magnitude variations in the dielectric relaxation time (?) was observed for the grain size if reduced to 6 nm from 20 nm. An unambiguous evidence for the absence of such a crystallite size effect was experimentally observed in higher biased conditions because of grain boundary Schottky potential barrier height suppression. These experimental results obey the grain boundary double Schottky barrier model. � 2011 American Institute of Physics.