Defence Metallurgical Research Laboratory

About: Defence Metallurgical Research Laboratory is a facility organization based out in Hyderabad, India. It is known for research contribution in the topics: Microstructure & Alloy. The organization has 1208 authors who have published 2662 publications receiving 51663 citations.

Isothermal and thermomechanical fatigue behaviour of Ti–6Al–4V titanium alloy

Abstract: In this study, the overall view of in-house development of thermomechanical fatigue (TMF) test capability has been presented. Using this test facility, mechanical strain controlled in-phase (IP) and out-of-phase (OP) TMF behaviour of Ti–6Al–4V alloy has been investigated in the temperature range 100–400 °C with ramp heating and cooling rate of 2 °C/s. Isothermal low cycle fatigue (IF) tests have also been conducted at 100 °C and 400 °C for comparison with TMF data. The combined effect of development of tensile mean stresses and metallurgical degradation due to oxidation led to detrimental OP-TMF fatigue life as compared to IP-TMF and IF loading.

Studies on structural transformation and magnetic properties in Sm2Co17 type alloys

Abstract: Structural transformations and microstructural characterisation of Sm2Co17 alloys containing Fe, Cu and Zr at different stages of thermal processing have been investigated by X-ray diffraction, optical, scanning electron and transmission electron microscopes. Solution treated samples consist of a mixture of hexagonal TbCu7 (1:7 H) and rhombohedral Th2Zn17 (2:17 R) structure types of 2:17 phase. After isothermal aging, TbCu7 + Th2Zn17 structures transform into Th2Zn17 type structure with precipitation of Cu-rich hexagonal SmCo5 (1:5 H) and Zr-rich platelet phases. In addition to the main phases, a soft magnetic phase of composition Zr6(FeCo)23 is formed in alloys containing higher Zr composition. Isothermal aging studies reveal that magnetic properties show a peak value when aged at 1108–1123 K for 10 h. TEM studies show cellular precipitate structure with cell interiors having 2:17 R structure, while the fully coherent cell boundaries have the 1:5 H structure. Zr-rich platelets which run across many cells and cell boundaries were found to have 1:7 H structure.

Surface area and pore size studies of alumina gels

Abstract: Alumina gels were prepared using acid and base catalysts. Surface area and porosity of the gel-derived powders were studied with variations in catalyst type, catalyst-to-alkoxide molar ratio and heat-treatment temperature. The surface area decreased with increasing ratio of catalyst to alkoxide. Base-catalysed samples showed a higher surface area than acid-catalysed samples which were free from micropores and possessed only mesopores. Pore sizes and pore volumes were estimated using the Kelvin equation. Microporosity was determined using a standard isotherm concept. The specific surface area was found to decrease with increasing heat-treatment temperature.

Tailored Anisotropic Magnetic Chain Structures Hierarchically Assembled from Magnetoresponsive and Fluorescent Components

Abstract: The development of methods for controlling the organization of functional objects at a nanometer scale to build larger objects is of fundamental and technological interest. The unique electronic, magnetic, and optical properties of nanomaterials will be best utilized when they are well integrated into larger devices. A great deal of research is focused on such materials, particularly those with magnetic properties that can be exploited for the fabrication of ordered onedimensional (1D) chainlike assemblies. Pertinent targets include the synthesis of materials that have desirable anisotropic properties for electronic and optical devices. As this is a difficult task, different techniques have been employed including magnetic-field-induced (MFI) assembly, electric or magnetic dipole–dipole interactions, crystallographically specific orientation, non-uniform stabilizer distribution, templated synthesis to produce 1D nanostructured materials. However, an elegant approach would be to construct 1D chains consisting of structurally intricate units and functions. Suitable methods are still required to prepare aligned structures from nanoparticles suspended in an aqueous medium and to allow multifunctional properties to be imparted into such directional structures in a way that allows these additional properties to evaluated and exploited. Herein, we describe a method that provides opportunities for synthesizing materials that not only have a preferred 1D structure but that are also multifunctional. The strategy involves both designing and utilizing nanobuilding blocks to be linked together to generate aligned materials with anisotropic morphology and multifunctional properties. In the first step we assemble preformed nanoparticles (NPs) into a confined structure by using positively charged polypeptides as interparticle mediators while preserving the constituent nanoparticles functional properties. We have shown that the cationic polypeptides can undergo counterion condensation to form spherical aggregates by ionic cross-linking with either certain multivalent counteranions or nanoparticles which are capped with anionic species. The unique aggregation characteristics of these polycation–anion systems means that multiple nanoparticles can spontaneously assemble into microstructures. We have further shown that functionalities can also be integrated to give catalytic and optical properties. Herein, our approach is to use poly(l-lysine) (PLL) to cross-link with hydroxy pyrene trisulfonate (HPTS) and citrate-functionalized magnetic nanoparticles (MNPs) to afford magneto responsive fluorescent spheres (MFS). In a second step these spheres are magnetically aligned by virtue of magnetic dipole interactions to construct 1D anisotropic shapes. HPTS is a pyrene-based molecule and has been proved to be a versatile probe molecule in both chemistry and biology. The ability of HPTS, as an anionic multiple-point cross-linking center, to electrostatically bind cations on different polyelectrolyte chains can impart fluorescent properties to the resulting hybrid structures. To incorporate magnetic properties, we use citrate-functionalized Fe3O4 magnetic nanoparticles (MNPs) so that the ionic interaction of citrate with PLL can enable the formation of spherical MNP aggregates. The MNPs, synthesized by a co-precipitation method, are fully characterized to ensure their structure and the presence of the citrate functional group (Supporting Information, Figure S1). Scheme 1 illustrates our method to include both magnetic and fluorescent functions into the microspheres. Simultaneous columbic interactions between positively charged amine groups of PLL and the negatively charged carboxy groups on