Karabi Das

A review on the various synthesis routes of TiC reinforced ferrous based composites

The major thrust underlying the processing of Fe-based composites has been directed towards improving the wear resistance of steel or castiron by incorporating some reinforcing phase, e.g., carbides, oxides, etc. The present article provides a review on the various synthesis routes of TiC reinforced Fe-based composites, i.e., powder metallurgy, conventional melting and casting, carbothermic reduction, combustion synthesis, aluminothermic reduction, electron beam radiation, laser surface melting, and plasma spray synthesis, highlighting the advantages and disadvantages associated with the different routes of synthesis.

Charge storage and photoluminescence characteristics of silicon oxide embedded Ge nanocrystal trilayer structures

Metal-oxide-semiconductor capacitors with a trilayer structure consisting of the cap gate oxide, sputtered SiGe layers and thermally grown tunnel oxide were fabricated on p-Si substrates. The trilayer structures were rapid thermal annealed at 1000 °C in nitrogen atmosphere for different durations. Cross-sectional transmission electron micrographs revealed the complete isolation of Ge nanocrystals in the sandwiched structure annealed for a longer duration. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. Under optimized annealing conditions, an enhancement of the charge storage capability of nanocrystals was observed in agreement with the optical emission characteristics.

Characteristics of CdS nanowires grown in a porous alumina template using a two-cell method

CdS nanowires have been grown by a two-cell chemical method using a porous alumina template. Field-emission scanning and transmission electron microscopy show the growth of nanowires of diameters ranging from 100 to 110 nm and 50 to 60 nm for two different templates. The surface topography of the template filled with CdS has been studied using atomic force microscopy. The microstructural properties of the nanowires have been studied by high resolution x-ray diffraction. UV–visible spectroscopy of nanowires exhibits a clear blue shift due to quantum confinement. The photoluminescence spectra show green emission due to the defect states of the nanowires and the resonance Raman spectra revealed the stoichiometric phase of CdS with good crystallinity.

A Study on the Effect of Pulse Electrodeposition Parameters on the Morphology of Pure Tin Coatings

Pure Sn coatings are prepared by pulse current (PC) electrodeposition using aqueous acidic sulfate plating bath. The effects of various electroplating parameters such as current density, additive concentration, duty cycle, frequency, pH, bath temperature, and stirring rate (bath rotation) on the evolution of surface morphology of the coatings have been studied. The as-deposited coatings are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and surface profilometry. It is found that the current density, additive concentration, duty cycle, frequency, and pH have a major influence while temperature and stirring rate of the bath have a minor effect on the grain-size distribution. The mechanism involved in the morphology evolution and grain-size distribution due to the varying electroplating parameters has also been discussed.

Improved charge injection characteristics of Ge nanocrystals embedded in hafnium oxide for floating gate devices

Metal-oxide-semiconductor capacitors with a trilayer structure consisting of Ge+HfO2 layers sandwiched between HfO2 tunnel and cap oxides were fabricated on p-Si substrates. Ge nanocrystals embedded in SiO2 were also studied for comparison. Cross-sectional transmission electron micrographs revealed the formation of spherical shaped Ge nanocrystals. The optical and charge storage characteristics of trilayer structures were studied through photoluminescence spectroscopy and capacitance-voltage measurements, respectively. An enhancement of the charge injection capability into nanocrystals was observed for the device with HfO2 as tunnel and cap oxide. The optical emission characteristics support the carrier confinement in Ge nanocrystals embedded in oxide matrices.

Sintering mechanisms of attrition milled titanium nano powder

Detailed sintering studies have been carried out on attrition milled nanocrystalline titanium powder through isothermal dilatometry over a temperature range of 300–1250 °C along with microstructural and x-ray diffraction studies. The sintering behavior of attrition milled nanocrystalline titanium appears to be characterized by: (i) very low activation energies, (ii) high shrinkage anisotropy, (iii) very rapid grain growth in the beta range, and (iv) two kinds of densification processes, namely, intra-agglomerate and inter-agglomerate. Analysis of the kinetic data through sintering diagram approach indicates the operation of particle sliding and grain boundary rotation, type of mechanism in addition to the grain-boundary diffusion, and lattice diffusion as the dominant mass transport mechanisms.

Evolution of strain and composition of Ge islands on Si (001) grown by molecular beam epitaxy during postgrowth annealing

Self-assembled Ge islands have been grown using a Stranski–Krastanov growth mechanism on Si (001) substrates by solid source molecular beam epitaxy. We performed time varying annealing experiments at a representative temperature of 650 ° C to study the shape and size evolution of islands for a relatively high Ge coverage. Islands are found to coarsen due to heat treatment via structural and compositional changes through continuous strain relaxation. Different island morphologies, namely, “pyramids,” “transitional domes,” and “domes” are found during the annealing sequence. The dominant coarsening mechanisms for the temporal evolution of islands of as-grown and annealed samples are explained by the comprehensive analysis of Rutherford back scattering, Raman spectroscopy, high-resolution x-ray diffraction, and atomic force microscopy. A correlation of the morphological evolution with the composition and strain relaxation of grown islands is presented.

Order-disorder transformation of the body centered cubic phase in the Ti-Al-X (X = Ta, Nb, or Mo) system

The ordering of the bcc phase present in the Ti-Al-X (X = Ta, Nb, or Mo) system is investigated in this paper. There is a ternary phase of ordered bcc (B2) structure near the composition Ti-25Al-25X. All compositions mentioned in this paper are in atomic percent, unless mentioned otherwise. The phase reactions in Ti-33Al-17Ta alloy are examined in detail following solidification and solid-state processing treatments. It can be found from the differential thermal analysis (DTA) that the B2 phase in this alloy is stable up to 1205°C, where it experiences a solid-state order to disorder transformation. The rate of this ordering reaction is so high that it cannot be arrested by rapid solidification processing (RSP). The presence of thermal antiphase boundaries (APBs) in the microstructure confirms the solid-state ordering of the B2 phase from the disordered bcc phase. Ordering reactions involving the bcc phase in the Ti-Al-Nb and Ti-Al-Mo systems are also studied because of their similarity with the Ti-Al-Ta system. It can be found that they are also solid-state ordering reactions. In the Ti-25Al-25Nb alloy the B2 phase is ordered up to 1141°C; whereas in the Ti-25Al-25Mo alloy the B2 phase is ordered up to 1418°C.

Multi-objective optimization in wire-electro-discharge machining of TiC reinforced composite through Neuro-Genetic technique

This paper proposed a Neuro-Genetic technique to optimize the multi-response of wire electro-discharge machining (WEDM) process. The technique was developed through hybridization of a radial basis function network (RBFN) and non-dominated sorting genetic algorithm (NSGA-II). The machining was done on 5vol% titanium carbide (TiC) reinforced austenitic manganese steel metal matrix composite (MMC). The proposed Neuro-Genetic technique was found to be potential in finding several optimal input machining conditions which can satisfy wide requirements of a process engineer and help in efficient utilization of WEDM in industry.

Temperature dependent shape transformation of Ge nanostructures by the vapor-liquid-solid method

A vapor-liquid-solid method has been used to study the temperature dependent growth mechanism of Ge nanostructures on Au-coated Si (100) substrates. The formation of Ge nanodots, nanorods, and nanowires has been observed at different growth temperatures. The diameter of grown nanowires is found to be varying from 40 to 80 nm and that of nanorods from 70 to 90 nm, respectively. A comparative study has been done on three types of samples using x-ray diffraction and Raman spectroscopy. Photoluminescence spectra of grown nanostructures exhibit a broad emission band around 2.6 eV due to oxide related defect states.