• Kishore

Articles written in Bulletin of Materials Science

• Electron microscopic studies on the effect of Sn addition on the ageing characteristics of Al-0.7% Mg2Si alloy

The effect of trace addition of Sn on the ageing characteristics of Al-0.7% Mg2Si has been studied by hardness measurements and transmission electron microscopy. The changes observed in the microstructural features have been explained on the basis of the strong interaction existing between Sn atoms and quenched-in vacancies. At ageing temperatures below 200°C Sn addition brings about a ratardation in the kinetics of G.P. zone growth whereas at higher ageing temperatures, it aided the precipitate nucleation and growth. The hardness data agree well with the deductions based on observations made on the thin foils.

• Some aspects of dislocation-precipitate interaction in under-aged aluminium-germanium alloy

The glide dislocation-precipitate interaction in under-aged alloy is investigated by microscopy and low-temperature deformation techniques. Slip-line features of room temperature deformed samples were observed by optical microscopy. From tensile tests at various temperatures the variation of flow stress withT2/3 was established. Comparing the present results with those obtained on the peak-hardened condition of the same alloy it is concluded that moving dislocation shear through the small rod-shaped germanium precipitates.

• Crystallization behaviour of Metglas 2826 MB (Fe40Ni38Mo4B18)

Differential scanning calorimetry, x-ray diffraction and transmission electron microscopy have been employed to determine the thermal stability and identify the crystalline phases on devitrification of Metglas 2826 MB. The glass crystallizes intoγ-FeNiMo and fcc (FeNi)23B6 with activation energies of 270 and 375 kJ mol−1 respectively. The reactions are primary and polymorphic in nature. The influence of Mo towards crystallization of Fe40Ni40B20 has been to enhance the formation of the fcc (FeNi)23B6 phase in preference to orthorhombic (FeNi)3B phase and to raise the thermal stability of the amorphous state.

• Role of alumina in flexure of glass/epoxy composites

The influence of particulate additions of alumina on the flexural properties of glass-fabric/epoxy composites was studied. The additions improved translaminar flexural strength, while decreasing interlaminar strength. The translaminar bending modulus showed an increasing trend whereas its interlaminar value showed a decrease, up to additions of 3 vol%. The mechanisms of deformation and the fracture features have been discussed with the aid of scanning electron microscopy.

• Repeated drop weight impacts and post-impact ILSS tests on glass-epoxy composite

E glass epoxy laminates of thicknesses in the range 2–5 mm were subjected to repeated impacts. For each thickness the number of hits to cause tup penetration was determined and the value of this number was higher the larger the thickness of the laminate tested. The C-scan, before and after impact, was done to obtain information regarding flaw distribution. Short beam shear test samples were made from locations at fixed distances from impact point and tested. The samples closer to the zone of impact showed lower strength values. Scanning fractography revealed shear deformation features for these samples and brittle fracture features for the region near the zone of impact.

• Study of fracture features in foam bearing glass epoxy composites subjected to repeated impacts

The paper reports the failure features observed in low mass repeatedly (pendulum) impacted glass epoxy composites with and without the mid section having either 2-layers or 3-layers of flexible foam. Features such as through width and inclined cracks as well as adhering of foam observed in the experiments are explained. The significance of the foam material in modifying the impact response of the composite is stressed.

• Sliding wear studies in glass-epoxy system through scanning microscopic observations

The work reports the wear occurring in a glass-epoxy composite system as a function of sliding distance for a constant sliding velocity and applied load. It is seen that the weight loss increases with increasing distance, but the gradient maintained all through is not the same. An attempt has therefore been made to correlate the weight loss with the scanning microscopic observations on the worn surfaces. It is found that in the early part, the wear of the resin/mat layer contributes to the phenomenon. The process of breakage of fibre into fragments and the resin debris formation accounts for the wear at a much later stage. The phenomenon occurring in between these two stages, is attributed to some of the broken fibres getting lodged in the matrix and agglomeration of the debris formed from the matrix material. Other features of interest are highlighted and discussed in this report.

• Characterization of reinforced syntactic foams using ultrasonic imaging technique

Non-destructive evaluation of defects like voids in syntactic foam reinforced with epoxy compatible chopped strand glass fibres, employing ultrasonic C-scan immersion through transmission method, was under-taken. The results showed that in four of the five similarly processed foam samples, the voids were uniformly spread while in the fifth, which was processed by a different route, a large spread of low dense area was noticed emphasizing the influence that processing technique has on the amount of voids present in the composites.

• Analysis of filler--fibre interaction in fly ash filled short fibre-epoxy composites using ultrasonic NDE

Size and aspect ratio are believed to influence the rheology or the flow in the mixture and in turn the mechanical performance of the composites. Fillers and fibres when used in combination are expected to complement each other's performance resulting in better properties for the composite. They also reduce the extent of matrix polymer required in the system. Composites involving fillers and fibres individually and in combination are studied for the level defect population using NDE and the mechanical performance under compression correlated with such an analysis. It was found that inclusion filler-fibre combination besides yielding better physical properties like density also yielded improved mechanical properties like strength and modulus. These properties showed an improvement of about 30-40% as compared to the ones where a single reinforcement either ash or fibre was used. Further, they exhibited uniform distribution of defects whose population was least compared to the situation where only one component (either filler or fibre) as reinforcement was tried.

• Structural and electrical measurements of CdZnSe composite

The 𝐼–𝑉 characterization and the electrical resistivity of selenium rich Se85Cd15–𝑥Zn𝑥 (𝑥 = 0, 3, 7, 11 and 15) system at room temperature have been studied. Samples were obtained using melt cooling technique. So prepared samples were then characterized in terms of their crystal structure and lattice parameter using X-ray diffraction method. The materials were found to be polycrystalline in nature, having zinc blend structure over the whole range of zinc concentration. The measurements of 𝐼–𝑉 characteristics have been carried out at different temperatures from room to 140°C. The electrical resistivity of the samples with composition at room temperature has been found to vary between maximum 2.7 × 108𝛺 m and minimum 7.3 × 105𝛺 m and shows a maximum at 3 at. wt.% of Zn. The carrier activation energy of the samples with composition has also been determined and found to vary from 0.026 eV to 0.111 eV.

• Effect of increased manganese addition and mould type on the slurry erosion characteristics of Cr–Mn iron systems

The wear resistance of high chromium iron is well recorded. However, the same is not the case as regards the use of manganese at higher percentages in high chromium irons and its influence on wear behaviour. Hence, this work highlights the slurry wear characteristics of chromium ($\Box$ 16–19%) iron following the introduction of manganese at two levels i.e. 5 and 10%. It is known that the wear properties are dictated by the microstructural features. To alter the structure, the cooling rate of casting has been varied by adopting two different types of moulds (i.e. sand and metal) and subsequently subjecting to thermal treatment. The as-cast and heat treated samples are examined for microstructure and then evaluated for hardness and slurry erosion properties. As the manganese content is increased from 5 to 10%, the hardness showed a decrease in value both in the as-cast and heat treated conditions. The slurry erosion loss, expectedly, showed an increase irrespective of the sample condition (i.e. mould type/heat treatment adopted). The findings are corroborated with the microstructural features obtained through optical and scanning electron microscopy.

• Combustion synthesis of graphene and ultracapacitor performance

Graphene sheets are synthesized by a simple method starting from graphitic oxide as a precursor. Reaction of graphitic oxide at 250 °C with a combustion mixture of urea and ammonium nitrate results in the formation of thin graphene sheets. Graphene formation is characterized by XRD, TGA, XPS and TEM. Graphene materials synthesized by thismethod are investigated as an ultracapacitor material. Specific capacitance values of about 70 F/g are obtained at a current density of 100 mA/g by usingKOH as an electrolyte.

• Bulletin of Materials Science

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Volume 42 | Issue 6
December 2019

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Posted on July 25, 2019