Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al ₃ Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al ₃ Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium. Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al ₃ Zr particles and found to be rod shaped and identified to be cubic ordered L 1 ₂ phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al ₃ Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al ₃ Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy.     

Development of calcium phosphate based apatite from hen’s eggshell

Stoichiometric hydroxyapatite with Ca/P molar ratio, 1.67, was synthesized using hen’s eggshell as calcium source and phosphoric acid by precipitation method. Conventional EDTA titration and gravimetric methods were adopted to estimate the amount of calcium and phosphorous, respectively. Fourier-transform infrared (FT-IR) and X-ray diffraction (XRD) techniques were employed to investigate the formation of the HAP phase. Thermal analysis (TG-DTA) was carried out to investigate the thermal stability of HAP powder. FT-IR spectra show the characteristic peaks for phosphate and hydroxyl groups. XRD results reveal that the major characteristic peaks of HAP appear in the region of approximately 26°, 28°, 29°, 30–35°, 39°, 46°, 49° and 50° (2θ) and also indicate that there are no occurrences of secondary phases during HAP formation. TG-DTA result depicts that the synthesized HAP was stable up to 1300°C.     

Many electron effects in semiconductor quantum dots

Semiconductor quantum dots (QDs) exhibit shell structures, very similar to atoms. Termed as ’artificial atoms’ by some, they are much larger (1 100 nm) than real atoms. One can study a variety of manyelectron effects in them, which are otherwise difficult to observe in a real atom. We have treated these effects within the local density approximation (LDA) and the Harbola-Sahni (HS) scheme. HS is free of the self-interaction error of the LDA. Our calculations have been performed in a three-dimensional quantum dot. We have carried out a study of the size and shape dependence of the level spacing. Scaling laws for the Hubbard ‘U’ are established.     

An X-ray diffraction study of defect parameters in a Ti-base alloy

Detailed studies based on the well established method of Fourier line shape analysis have been made on the X-ray diffraction profile of hexagonal titanium alloy of nominal composition Ti-6.58% Al-3.16% Mo-1.81% Zr-008% Fe-0.012% N-0.0078% C. While deformation fault probability, α, has been found to be quite high compared to that of pure titanium, the deformation growth fault parameter, β, shows a negative value ruling out the presence of growth fault in this alloy in the deformed state.     

A study of phase separation in ternary alloys

We have studied the evolution of microstructure when a disordered ternary alloy is quenched into a ternary miscibility gap. We have used computer simulations based on multicomponent Cahn-Hilliard (CH) equations for c _A and c_B, the compositions (in mole fraction) of A and B, respectively. In this work, we present our results on the effect of relative interfacial energies on the temporal evolution of morphologies during spinodal phase separation of an alloy with average composition, c_A = 1/4, c_B = 1/4 and c_c = 1/2. Interfacial energies between the ‘A’ rich, ‘B’ rich and ‘C’ rich phases are varied by changing the gradient energy coefficients. The phases associated with a higher interfacial energy are found to be more rounded than those with lower energy. Further, the kinetic paths (i.e. the history of A-rich, B-rich and C-rich regions in the microstructure) are also affected significantly by the relative interfacial energies of the three phases.     

Low cycle fatigue behaviour of Ti-6Al-5Zr-0-5Mo-0-25Si alloy at room temperature

Low cycle fatigue (LCF) behaviour of the near α titanium alloy, Ti-6Al-5Zr-0.5Mo-0.25Si (LT26A), was investigated in the (a + β) as well as β treated conditions at room temperature. LCF tests were carried out under total strain controlled mode in the range of Δε_t/2: from ±0.60% to ±1.40%. The alloy shows cyclic softening in both the conditions. Also it exhibits dual slope Coffin-Manson (C-M) relationship in both the treated conditions.     

Dispersion and rheological studies of Y-PSZ tape casting slurry

Different solvent systems in combination with three different dispersants were tried to find out the suitable solvent-dispersant combination, which give optimum dispersion of PSZ. Based on sedimentation, viscosity and rheology characteristics, zeotropic ethanol : xylene with a ratio of 50 : 50 along with 0.5 wt% phosphate ester was found to be the best solvent and dispersant combination. Optimized tape casting slurry was prepared using PEG 600 and BBP as plasticizers and PVB as the binder. Cyclohexanone was used as the homogenizer. The optimized slurry composition with 58% solid loading exhibited shear-thinning pseudoplastic rheological behaviour. Y-PSZ tapes of ∼ 50 Μm thickness free from visible defects were cast with a green tape density of 55%.     

Analysis of microstress in neutron irradiated polyester fibre by X-ray diffraction technique

Microstresses developed in the crystallites of polymeric material due to irradiation of high-energy particle causes peak broadening and shifting of X-ray diffraction lines to lower angle. Neutron irradiation significantly changes the material properties by displacement of lattice atoms and the generation of helium and hydrogen by nuclear transmutation. Another important aspect of neutron irradiation is that the fast neutron can produce dense ionization at deep levels in the materials. The polyethylene terephthalate (PET) fibre of raw denier value, 78.2, were irradiated by fast neutron of energy, 4.44 MeV, at different fluences ranging from 1×10⁹ n/cm² to 1 × 10¹² n/cm². In the present work, the radiation heating microstresses developed in PET micro-crystallites was investigated applying X’Pert-MPD Philips Analytical X-ray diffractometer and the effects of microstresses in tensile strength of fibre measured by Instron have also been reported. The shift of 0.45 cm⁻¹ in the Raman peak position of 1614.65 cm{−1} to a higher value confirmed the development of microstresses due to neutron irradiation using micro-Raman technique. The defects due to irradiation were observed by SEM micrographs of single fibre for virgin and all irradiated samples.     

Optical properties of lead-bismuth cuprous glasses

The optical transmission and absorption spectra in UV- VIS were recorded in the wavelength range 350–800 nm for different glass compositions in the system (CuO) _x (PbO) ₅₀−x(Bi₂O₃)₅₀ (x = 2.5, 5.0, 7.5, 10.0, 12.5, 15.0, 20.0). Absorption coefficient (α), optical energy gap (E_opt), refractive index (n_D), optical dielectric constant (ε′_∞), measure of extent of band tailing (ΔE), constant (β) and ratio of carrier concentration to the effective mass (N/m*) have been reported. The effects of compositions of glasses on these parameters have been discussed. It has been indicated that a small compositional modification of the glasses lead to an important change in all the optical properties including non-linear behaviour. The optical parameters were found to be almost the same for different glasses in the same family.     

Microstructural studies on variation of defect parameters in Zr-Sn alloys and their transition with interchange of solvent and solute in Zr-Ti and Ti-Zr alloy systems by modified Rietveld method and Warren-Averbach method

The effects of deformation and the transition of microstructural defect states with the interchange of solvent and solute in Ti-Zr and Zr-Ti alloys of six different compositions and Zr-Sn alloys in three different compositions have been investigated by X-ray diffraction line profile analysis. The detailed analysis of the X-ray powder diffraction line profiles was interpreted by Fourier line shape analysis using modified Rietveld method and Warren-Averbach method taking silicon as standard. Finally the microstructural parameters such as coherent domain size, microstrains within domains, faulting probability and dislocation density were evaluated from the analysis of X-ray powder diffraction data of Zr base Sn, Ti and Ti base Zr alloys by modified Rietveld powder structure refinement. This analysis confirms that the growth fault, β, is totally absent or negligibly present in Zr-Ti, Ti-Zr and Zr-Sn alloy systems, because the growth fault, β, has been observed to be either negative or very small for these alloy systems. This analysis also revealed that the deformation fault, α, has significant presence in titanium-base zirconium alloy systems but when zirconium content in the matrix goes on increasing beyond 50%, this faulting behaviour suffers a drastic transition and faulting tendency abruptly drops to a level of negligible presence or zero. This tendency has also been observed in Zr-Sn alloys signifying high stacking fault energy. Therefore, Zr and Zr-base alloys having high stacking fault energy can be used as hard alloys in nuclear technology at high temperature.     

Spectroscopic investigations of Cu2+ in Li2O-Na2O-B2O3-Bi2O3 glasses

Pure and copper doped glasses with composition,x Li ₂ O-(40-x)Na ₂ O-50B ₂ O ₃-10Bi ₂ O ₃,have been prepared over the range 0 ≤ x ≤ 40. The electron paramagnetic resonance (EPR) spectra of Cu²⁺ ions of these glasses have been recorded in the X-band at room temperature. Spin Hamiltonian parameters have been calculated. The molecular bonding coefficients, α² and β², have been calculated by recording the optical absorption spectra in the wavelength range 200–1200 nm. It has been observed that the site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The density and glass transition temperature variation with alkali content shows non-linear behaviour. The IR studies show that the glassy system contains BO₃ and BO₄ units in the disordered manner.     

Fine structure at the diffusion welded interface of Fe3Al/Q235 dissimilar materials

The interface of Fe ₃ Al/Q235 dissimilar materials joint, which was made by vacuum diffusion welding, combines excellently. There are Fe ₃ Al, FeAl phases and α-Fe (Al) solid solution at the interface of Fe ₃ Al/Q235. Aluminum content decreases from 28% to 1.5% and corresponding phase changes from Fe ₃ Al with DO ₃ type body centred cubic bcc structure to α-Fe (Al) solid solution with B2 type bcc structure. All phases are present in sub-grain structure level and there is no obvious brittle phases or micro-defects such as pores and cracks at the interface of Fe ₃ Al/Q235 diffusion joint.     

Microstructure and electrical conductivity of Al-SiCp composites produced by spray forming process

Al- SiC_p composites have been synthesized by spray forming process with variation in particle flow rate, size of reinforcement particles and their volume fraction. The microstructure of composites and their electrical conductivity have been investigated. The results showed a uniform dispersion of large size particulate phase in the matrix of the primary α- phase with its equiaxed grain morphology. However, clustering of small size particles was observed at the grain boundary and grain junctions. The grain size of the composite materials was observed to be lower than that of the base Al- alloy. The composite materials invariably indicated their lower electrical conductivity compared to that of the monolithic Al- alloy. The electrical conductivity of composites decreased with increase in the volume fraction and decrease in size of the reinforcement particles. A high flow rate of particles during spray deposition resulted in a decrease in its conductivity. These results are explained in the light of thermal mismatch between the matrix and the reinforcement phases resulting in generation of high dislocation density. The droplet- particle interaction and resulting microstructure evolution during the spray deposition of the composites are discussed.     

Synthesis, characterization and conductivity studies of polypyrrole-fly ash composites

In situ polymerization of pyrrole was carried out in the presence of fly ash (FA) to synthesize polypyrrole-fly ash composites (PPy/FA) by chemical oxidation method. The PPy/FA composites have been synthesized with various compositions (10, 20, 30, 40 and 50 wt%) of fly ash in pyrrole. The surface morphology of these composites was studied with scanning electron micrograph (SEM). The polypyrrole-fly ash composites were also characterized by employing X-ray diffractometry (XRD) and infrared spectroscopy (IR). The a.c. conductivity behaviour has been investigated in the frequency range 10²–10⁶ Hz. The d.c. conductivity was studied in the temperature range from 40–200°C. The dimensions of fly ash in the matrix have a greater influence on the observed conductivity values. The results obtained for these composites are of greater scientific and technological interest.     

External stimuli response on a novel chitosan hydrogel crosslinked with formaldehyde

Keeping in mind the significance of hydrogels as an external stimuli sensitive super absorbing material, some transparent covalent hydrogels of chitosan were prepared by crosslinking with varying amounts of formaldehyde solution used as crosslinking agent. The characteristics of hydrogels were investigated by Fourier transform infrared (FT-IR) spectroscopy and swelling experiments. The effect of crosslinking agent on water absorbency has been investigated. The hydrogels exhibited a relatively higher swelling ratio in the range of 2066–3306% and equilibrium water content (EWC) in the range of 95-38–97 06% at pH 7 and 35°C temperature. The influence of external stimuli such as pH, temperature, and ionic strength of the swelling media on equilibrium swelling properties has been observed. Hydrogels showed a typical pH and temperature responsive behaviour such as low pH and high temperature has maximum swelling while high pH and low temperature show minimum swelling. An increase in the ionic strength of swelling media caused a continuous decrease in the swelling of hydrogels at both acidic and basic pH.     

A new combustion route to γ-Fe2O3 synthesis

A new combustion route for the synthesis of γ-Fe ₂ O ₃ is reported by employing purified a-Fe ₂ O ₃ as a precursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the reaction is completed in a single step yielding magnetic iron oxide i.e. γ-Fe ₂ O ₃ .The as synthesized γ-Fe ₂ O ₃ is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on magnetic properties is also presented.     

Synthesis, characterization and gas sensing property of hydroxyapatite ceramic

Hydroxyapatite (HAp) biomaterial ceramic was synthesized by three different processing routes viz. wet chemical process, microwave irradiation process, and hydrothermal technique. The synthesized ceramic powders were characterized by SEM, XRD, FTIR and XPS techniques. The dielectric measurements were carried out as a function of frequency at room temperature and the preliminary study on CO gas sensing property of hydroxyapatite was investigated. The XRD pattern of the hydroxyapatite biomaterial revealed that hydroxyapatite ceramic has hexagonal structure. The average crystallite size was found to be in the range 31–54 nm. Absorption bands corresponding to phosphate and hydroxyl functional groups, which are characteristic of hydroxyapatite, were confirmed by FTIR. The dielectric constant was found to vary in the range 9–13 at room temperature. Hydroxyapatite can be used as CO gas sensor at an optimum temperature near 125°C. X-ray photoelectron spectroscopic studies showed the Ca/P ratio of 1.63 for the HAp sample prepared by chemical process. The microwave irradiation technique yielded calcium rich HAp whereas calcium deficient HAp was obtained by hydrothermal method.     

Abrasive wear behaviour of bio-active glass ceramics containing apatite

In this study, abrasive wear behaviour of bio-active glass ceramic materials produced with two different processes is studied. Hot pressing process and conventional casting and controlled crystallization process were used to produce bio-active ceramics. Fracture toughness of studied material was calculated by fracture toughness equations using experimental hardness results of the bio-active glass ceramic material. Two fracture toughness equations in the literature were used to identify the wear behaviour of studied ceramics. Wear resistance results that identified with both of the equations were similar. The results showed that the abrasive wear resistance of the bio-active glass ceramics produced with hot pressing process was found to be higher than that of the ceramics produced by conventional casting and controlled crystallization process.     

Synthesis and magnetic study of Co-Al substituted calcium hexaferrite

A series of calcium substituted polycrystalline ferrite ceramics with magnetoplumbite structures were synthesized using perfect stoichiometric mixtures of oxides with chemical composition, CaAl_xCo_xFe_12−2xO₁₉ (x = 2−5), by standard ceramic technique. The variation in the values ofH _candM _s,which depends on the additive content and the temperature, was studied by means of a vibration magnetometer. The strong variation observed in coercivity, saturation magnetization and Curie temperature with chemical composition give rise to the possibility of controlling these properties and hence applying these compounds in the millimeter— microwave range.     

Enhancement of mechanical properties of Al–Mg–Si alloys by means of manganese dispersoids

Abstract

The effects of Mn dispersoids on the enhancement of mechanical properties in Al–Mg–Si(–Mn) alloys have been studied to develop a new high Mn alloy which does not need an aging heat treatment after a shaping process (i.e. extrusion process). By adding Mn to Al–Mg–Si alloys, sphere- or rod shaped Mn dispersoids of a size ranging from 0·05 to 0·5 μm are formed by the use of proper heat treatments. The as extruded alloys containing 1·0 wt-%Mn are measured to have higher tensile properties with good ductility, as compared with those of the commercial Al alloy 6N01 (Al–0·69Mg–0·79Si–0·48Cu–0·27Zn–0·37Mn–0·3Cr– 0·11Ti, wt-%). These phenomena are obtained from the dispersion hardening effect and homogeneous deformation by Mn dispersoid particles acting as obstacles to dislocation movement. Comparing the fatigue crack growth behaviour between the high Mn alloys and the commercial 6N01 alloy in the as forged condition, high Mn alloys are shown to have higher fatigue crack growth resistance and show a more tortuous crack path. This result can be explained by the increasing energy absorption through crack deflections and tortuous crack paths by the Mn dispersoids.