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Evolution of geometrically necessary dislocation at the gamma-gamma ' interface and its effect on tensile deformation behaviour of disk super alloy
No full textThe evolution of geometrically necessary dislocation density (GND) at the gamma and primary gamma' interface during tensile deformation of turbine disk alloy was studied. Extensive electron microscopy analysis (i.e. EBSD and TEM) was carried out to explore the structure and GND evolution at the gamma-gamma' interfaces. It is found that GND value is highest for tensile test specimens at 800 degrees C, whereas the lowest for tensile specimen tested at 350 degrees C, and this is attributed to gamma/gamma' misfit (delta) value. At high-temperature tensile deformation (i.e. at 720 and 800 degrees C) specimen starts necking just after the yield point, compared to RT, 350 and 650 degrees C tensile tested specimens. It is evidenced from GND values and grain interior distortion that localized plastic deformation in gamma-matrix near to gamma-gamma' interfaces is the primary reason for necking just after yielding of material. Higher GND values and grain interior distortion are caused by the greater value of delta at high test temperature due to difference in thermal expansion between gamma and gamma'
Influence of extremely cold environmental conditions on interfacial fracture phenomenon of aerospace grade unidirectional composites
No full textAn investigation of interfacial fracture modelling of carbon fibre reinforced plastic (CFRP) laminates at the atmosphere similar to the cruise condition of an aircraft has been carried out in this article. The Mode I & Mode II fracture tests are carried out using specimen of aerospace grade composite (AS4/914) at - 550C. Compliance based methods for estimation of crack growth have been adopted for monitoring during the fracture tests. A new set of thermally influenced interfacial fracture properties are evaluated for AS4/914 laminates. A modified traction ? separation law has been derived for Mode-I loadings considering the influence of fibre bridging under influence of extremely cold environmental conditions. This law has been evaluated from the superposition of traditional bilinear law and derived bridging law. A significant reduction in interlaminar fracture toughness has been observed due to the fragile nature of the matrix under cold environment. Experimentally obtained interfacial fracture properties are implemented into the numerical formulation. Extended Isogeometric Analysis augmented with Cohesive Zone Modelling (XIGA-CZM) for unidirectional CFRP laminate has been enhanced and enriched with thermally influenced fracture toughness properties for further investigation. Results obtained from the present XIGA-CZM formulation shows a good agreement with experimentally obtained results. Scanning Electron Microscope (SEM) observation of fractured surfaces are carried out to investigate the nature of crack propagation in CFRP laminate at - 550C
Chloridizing Roasting of Spent NdFeB Magnet Using Ammonium Chloride
Get PDFThe thermogravimetry is a useful tool to understand the roasting behavior of ores and minerals. Roasting of spent rare earth magnet (NdFeB) has evolved as attractive method for recycling of rare earth elements (REE) to conserve their scarce resources. We studied the chloridizing roasting of spent magnets of wind turbines with an objective to selectively convert the REE into water soluble chlorides. TG-DTA of NdFeB powder shows the commence of oxidation above 300°C. Further TG-DTA studies of NdFeB-NH4Cl mixture corroborated with thermodynamic calculations indicates 300°C as suitable temperature for chloridizing roasting process to obtain the NdCl3 and Fe2O3
Thermochemical Simulation, Thermogravimetry and Roasting Studies for Selective Sulfation of Copper in Flash Smelter Dust.
Get PDFThe thermal studies are a useful tool to understand the conversion of chalcopyrite to copper sulfate. We carried out thermochemical simulation in combination with thermogravimetric studies to understand the sulfation behavior of copper and iron in a copper smelter dust sample and to predict suitable roasting condition. Different oxide and sulfate phases of Cu and Fe forms as function of temperature. A temperature range of 150-1000°C was applied; however, a 550-650°C was found suitable for selective sulfation of copper. Further tests in a tube furnace at 600°C for three hours ensured 96% Cu sulfation and only 2.1% Fe sulfation
Reactivity Alteration of Granulated Blast Furnace Slag by Mechanical Activation for High Volume Usage in Portland Slag Cement
No full textAugmenting granulated blast furnace slag (GBFS) content in Portland Slag Cement (PSC) beyond the conventional limit of 70% is the stimulus for this study. Such enhancement other than bringing down the carbon footprint of cement conserves natural resources. However, beyond 70% slag incorporation, early strength gain of PSC is meagre because of its low reactivity. This study explores mechanical activation (MA) of GBFS to alter its reactivity, and thereby raising the possibility of increased slag incorporation in PSC. MA of slag is carried in an eccentric vibration mill. Formulations with different MA slag contents and clinker are studied in terms of heat of hydration (using isothermal conduction calorimetry) and compressive strength (CS). CS of clinker-slag formulations augmented with the extent of MA. Hydration behaviour of these blends i.e. increased heat evolution, accelerated reactions etc. is in agreement with CS values. X-ray diffraction and TG-DTG employed as complimentary tools to comprehend the hydration process corroborate with CS results, and hydration characteristics. Thus, MA can be used to enhance the hydration characteristics (reactivity) of GBFS, and henceforth its content in PSC. Sufficiently activated slag incorporation even up to 90% yields comparable strength than commercial PSC at all ages of curing
On the extent of transformation of austenite to bainitic ferrite and carbide during austempering of high Si steel for prolonged duration and its effect on mechanical properties
No full textIn this work, the effect of holding durations (10-60min) during austempering at 300, 350 and 400 degrees C on the structure and properties of a 0.61C-1.71Si-0.86Mn steel has been studied. At all the austempering temperatures, austenite fraction gradually decreases with the increase in holding duration. Austempering temperature has been found to influence the rate of depletion of austenite. The effect of Mn and Si content of steel on the extent of transformation of austenite to bainitic ferrite and carbides during prolonged austempering holding has also been looked at. Analysis drawn from existing literature along with the current data shows that along with Si, Mn also plays an important role in controlling the rate of transformation of austenite to bainitic ferrite and carbide
Reaction Mechanism of In-situ Carbon in Hematite Ore Pellet during Induration
No full textCarbon is used in the hematite ore pellet as a partial heat source for induration. Apart from this, it has several other roles in the pellet. To achieve the maximum benefit of carbon in pellet quality improvement and energy reduction, a detailed study on the mechanism of C reaction in hematite pellets is required. Although some investigators have reported improvement in pellet properties on using carbon, its detailed analysis is still lacking. For this, the study on the reaction mechanism during induration is essential, which has not been done so far. To alleviate the above knowledge gap, the reaction mechanism of in-situ carbon has been studied through thermodynamic analysis and experimentation in this work. The possibility of evolving carbon monoxide and carbon dioxide during the burning of carbon at the initial stage has been analyzed from the thermodynamic study. The produced carbon monoxide gas may partially reduce the iron oxides in the pellet. This in-situ reduced iron oxide may be beneficial in the sintering of pellets. The possibility of reduction of ferric oxide in pellets followed by its re-oxidation in the final stage has been studied thermodynamically and experimentally. This study helps to understand the mechanism of in-situ carbon reaction during induration and its role in improving the quality of pellets and reducing energy consumption. It is found that the use of carbon enhances diffusion bonding in acidic pellets and both diffusion and slag bonding in basic pellets. The use of 1.5% carbon reduces the induration temperature by 50 K
Strength-Ductility Trade-Off in Dual-Phase Steel Tailored via Controlled Phase Transformation
No full textThe controlled phase transformation approach is a new generation of microstructure engineering for enhancing ductility in ultrafine-grained materials. The present study aims to extend this concept to dual-phase steel for enhanced tensile ductility at high strength. In this study, cold-rolled steel was subjected to annealing at different processing conditions to develop the core–shell microstructure constituting martensite core and ferrite as shell in the matrix. Controlled austenite decomposition was adopted in designing a core–shell-type structure. The evolved microstructure was characterized using a scanning electron microscope and electron backscatter diffraction technique. The results showed that the uniaxial tensile deformation of dual-phase structured steels had a remarkable strength–ductility trade-off. The ductility was increased anomalously at high martensite fractions. Further, the mechanism of damage activity leading to void nucleation and microcrack formation was studied in post-tensile fractured specimens to establish a correlation with tensile deformation characteristics. The possibility and outcomes of this approach are also reported here
Effect of annealing on structure and properties of pulse electroplated Ni-W alloy coating
No full textThe structure and properties of Ni-W alloy coatings, deposited through pulse-plating route from an
aqueous sulphate-citrate bath, have been evaluated and compared with those of coatings annealed under vacuum
for durations of 2 h, 4 h or 6 h. The effect of annealing on microstructural evolution of the alloy coatings has
been examined with emphasis on identification of constituent phases by X-ray diffraction, along with studies of their morphology by scanning and transmission electron microscopy with selected area electron diffraction. Annealing of Ni-W alloy coatings has resulted in the replacement of globular cluster-type appearance by a faceted morphology with the increase in crystallite size and reduction of the micro-strain in the alloy matrix. Both Nanoindentation hardness and elastic modulus of the coatings appear to reach their peak values on annealing for 2 h owing to the formation of NiW and Ni4W intermetallic phases. However, on annealing for durations ≥4 h, the hardness is decreased owing to grain coarsening, whereas the Young’s modulus is lowered due to diffusion of Cu from the substrate. The corrosion resistance of the annealed Ni-W alloy coatings, evaluated through potentiodynamic polarization technique, is found to be inferior as compared to that of the as-deposited coatings
Coal Burn Ash: A Sustainable Future Resource for Critical Metals Production
No full textIn view of increasing global demand of rare earth metals (REMs), less availability and limited natural resources compelled the researchers to develop the feasible processes to recover REMs from alternative secondary resources. Present book chapter is focused to explore possibility of coal bottom ash utilization for REMs extraction as well as highlights the hydrometallurgical processes for the selective separation and recuperation of REMs from alternative sources carried out at CSIR-NML, India in collaboration with KIGAM, South Korea. REMs containing coal and its byproducts are need to be beneficiated, thus require grinding to release the encapsulated REMs which are interlocked with host particle. REMs recovery process consists of beneficiation-leaching and advance hydrometallurgical separation processes. Coal ash will have tremendous possibility for commercial exploitation of REMs after scale-up and pilot trials