Abstract: Mixed Cu-Zn ferrites (for x = 0.66 to 0.99) are prepared by the double sintering ceramic method. Locally available low cost Fe2O3 with 0.5wt% of Si additive is used for this purpose which reduced the process price markedly and improves the properties of the ferrite produced. The chemical phase analysis carried out by X-ray powder diffraction method confirms the major phase of Cu-Zn ferrite structure. Lattice parameters, X-ray density and mass density along with porosity have been investigated to study the effect of composition. Lattice parameters shows a decreasing trend with increasing Cu content, x. whereas, both X-ray density and mass density increases with increasing x, which in turn decreases the porosity due to successive presence of Si in Fe2O3. This decrease in porosity along with chemical homogeneities, distribution of phases and grain formation were also observed from Scanning electron micrographs at different magnifications.
Abstract: The phenomenon of ultrafine-grain refinement of ferrite during transformational grain refinement (TGR) followed by static re-crystallization of vanadium micro-alloyed steels was studied. A substantial grain refinement (2.8m) was attained during TGR process by rolling at 900°C. Cold rolling with 70% of reduction introduced strain, utilized for re-crystallization during annealing at different temperatures. Electron Backscattered Diffraction (EBSD) technique was employed to quantify the low angle grain boundaries (LAGB) and high angle grain boundaries (HAGB) spacings and results were correlated with hardness drops during annealing process. At higher annealing times and temperatures the vanadium precipitates restricted the process of grain growth probably due to effective dispersion strengthenening. The abnormal grain growth during annealing, predicted previously for niobium steels, found absent in the present vanadium microalloyed steels.
Abstract: The present work describes the development of Fe-Co-Ni-Al-Ti-Cu permanent magnets. Magnetic and microstructural studies were carried out using microscopy, magnetometery and X-ray diffraction techniques. The results indicate that both microstructural and magnetic properties are sensitive to the heat treatment conditions. Magnetic properties in the studied alloys could be improved by controlling the annealed state microstructure and by efficiently aligning and elongating the nano-structured ferromagnetic α1 particles in <001> crystallographic directions. The best magnetic properties in the alloy Fe-34.7Co-15.3Ni-8.3Al-5.4Ti-3.9Cu is obtained as coercive force (Hc) of 1528Oe, residual magnetic induction (Br) of 7105G, saturation magnetization (Bs) of 19060G and maximum energy product ((BH)max) of 3.3MGOe.
Abstract: We report on the synthesis and investigation of magnetic properties of several new Gd based alloys suitable for their potential use in self-controlled hyperthermia treatment of cancer. Self-controlled hyperthermia is a non-invasive technique that employs heating of magnetic materials (ferromagnetic bulk sized thermo-seeds or magnetic nanoparticles) in a. c. fields to cure cancer cells. Magnetic materials with Curie temperature (Tc) in the range of 40-46oC are desired, as decreased magnetic coupling in paramagnetic regime (above Tc) provides a safeguard against overheating of normal cells. The need for developing such materials was dictated by the lack of existing magnetic materials with magnetic ordering temperature in the suitable range of hyperthermia applications. This study shows that these materials have high magnetization values and their Tc values can be varied linearly over a broad range by adjusting the composition of the constituent elements.
Abstract: Permanent magnet materials composed of transition and rare earth metals exhibit high energy products. Samarium cobalt magnets are developed and research is done to have high coercivity. Chemistry is varied from 34 to 36 weight percent of samarium in Sm1Co5 compound. Effect of chemistry and sintering treatment temperatures on final properties has been studied. Magnets are manufactured by powder metallurgical technique involving isostatic pressing and sintering in inert atmosphere at temperatures range of 1140-1170°C. Then the magnets are subject to post sintering aging treatment in temperature range of 800-900°C. It is observed that coercivity of Sm1Co5 magnet varies with aging temperature and can be improved by post sintering aging treatment.
Abstract: Sintered NdFeB magnets have complex microstructure that makes them susceptible to corrosion in humid or moist environments. The paper presents the anticorrosion characteristics of a novel Ni/Ti2N composite coating applied through electrodeposition and cathodic arc physical vapour deposition (CAPVD) to sintered NdFeB permanent magnets. The performance of composite coating was evaluated in simulated marine environment with the help of dc polarization techniques. The rate of coating degradation was also determined by employing ac electrochemical impedance spectroscopy (EIS). The coating morphology and surface chemistry were studied with scanning electron microscope (SEM). X-ray diffraction (XRD) was used for identification of component phases in the coating-substrate system. The results showed that the composite coating provided an adequately improved corrosion protection to the sintered NdFeB magnets in the simulated marine environment compared to the earlier reported ceramic and metallic coatings. The composite coating did not damage the magnetic properties of coating-substrate system that remained at par with the ceramic and nickel coating having copper interlayer.
Abstract: Neodymium based magnets are the powerful permanent magnet of today. This paper will discuss iron based rare earth magnets. NdFeB sintered magnet material has been developed. The magnets are produced by powder metallurgy route involving hydrogen decrepitation technique for making fine powder. After melting and casting, the NdFeB alloy is subject to hydrogen atmosphere. Hydrogen slowly absorbs into the solid alloy and makes it brittle, which upon milling becomes fine powder. Hydrogen is then removed by placing the powder at temperature around 800°C under vacuum. Then the powders are pressed under isostatic conditions and sintered at temperature range of 1020–1050°C. Post sintering is done at 800°C and 580°C followed by quenching. Energy product in the range of 8 MGOe is achieved.
Abstract: Elgiloy is Co based alloy (40wt%Co, 20wt%Cr, 15wt%Ni, 14wt%Fe and 7wt%Mo). It was strengthened by cold work and is capable of additional hardening by aging. The effects of solution treatment, cold working and age-hardening on the microstructure of elgiloy were investigated using optical microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM). As rolled strips were solution treated at 1065°C/1hr. These solution treated strips were then reduced 50% by cold rolling. After cold-deformation both є-hcp phase and fcc deformation twins are also considered to coexist at room temperature. The cold worked strips were then age hardened at (450-600)°C. The age hardened strips showed formation of additional є-phase (via α f c c є h c p transformation).
Abstract: A report on the crystal growth, luminescence and scintillation characteristics of two developed scintillators, CsCe2Cl7 and Cs2NaCeCl6 are presented. CsCe2Cl7 is a new scintillation material. These crystals were grown by the Czochralski pulling technique. The X-ray diffraction technique was used to verify the structure of crystals. Under the X-ray excitation emission, the CsCe2Cl7 showed a broad emission band in the wavelength range from 370 to 470 nm while the Cs2NaCeCl6 crystal showed a spectrum in the wavelength range from 370 to 440 nm. The energy resolutions (FWHM of peak position) for the 662 keV full energy peak of 5.5% and 8.3% were observed at room temperature for the CsCe2Cl7 and Cs2NaCeCl6 crystals, respectively. The scintillation decay time measurement curves showed that, CsCe2Cl7 crystal has a single exponential decay function with a decay time of 50 ns. The Cs2NaCeCl6 crystal exhibited three main decay time components, a short component with a decay time constant of 91 ns and 36% intensity, an intermediate component with a decay time constant of 601 ns and intensity 33%, followed by a long component with a 3.2 µs decay time constant and an intensity of 31% of the total light yield. On the basis of the scintillation results of these materials grown, it is believe that these scintillation crystals can find a place in medical imaging and radiation detection system.
Abstract: Aluminum alloys generally contain constituent particles. The population density and size these particles are important while considering fatigue performance. In present study, the crack growth process in stage II in the rolled plate of a high strength aluminum alloy AA 2219 was studied on samples prepared along the rolling direction. A three fold approach was adopted to understand the fatigue crack growth process: i) microstructural analysis ii) fatigue testing iii) post-fracture analysis. Microstructural analysis revealed a high density of constituent particles in the material. EDS analysis showed that the particles were mainly of CuAl2 type. However, particles with high concentration of Fe and Mn were also present in the material. Fatigue crack propagation tests were performed by using middle tension (MT) specimens prepared in rolling direction under constant amplitude loads. The da/dN vs ΔK plot on log-log scale showed a sigmoidal shape with a sharp increase of crack growth rate in the steady state regime.
Topographical features were studied to understand the interaction of fatigue crack with the microstructural features. Post fracture analysis revealed that the macro fracture appearance changed with the change of stress level. However, the general mechanism of crack growth, in all the stress levels studied, was by formation of striations. At lower stress levels almost flat region with striations is present upto the final fracture. The crack growth surface showed crystallographic features with crack propagation almost perpendicular to the loading direction. However, a comparatively tortuous fatigue region was evident in the sample tested at high level of stress. The observation of crack path surface at high magnification did not reveal any influence of particles on the crack growth process. However, in sections taken from the fractured samples cracking and debonding of the constituent particles was observed near the fatigue crack path.