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On the Unified Interaction Parameter Formalism and Its Application in Critical Reassessment of Pearlitic Transformation in Fe-C-Mn System
No full textThe significance of local equilibria (LE) models in understanding phase transformations in multicomponent steels has been revisited and the necessity for a firsthand computational tool capable of estimating metastable ferrite–austenite and cementite-austenite phase boundaries along with possible LE modes has been realized. For this purpose, thermodynamically consistent Unified Interaction Parameter Formalism (UIPF) has been adopted owing to its computational simplicity. All the necessary parameters required for UIPF-based simulations in Fe–C–Mn system, have been evaluated in the present work. The UIPF-based framework has been shown to be a computationally simple yet an efficient tool for prediction of metastable phase boundaries at low temperatures and wide composition range in the Fe–C–Mn system, where most of the available commercial thermodynamic simulation packages have prediction limitation. The phase boundaries predicted using UIPF have been validated with those predicted by ThermoCalc®, wherever possible/available. Additionally, existing experimental data on growth rates, interlamellar spacing, and partitioning coefficients prevalent during pearlitic transformation in Fe–C–Mn systems have been used to validate the predictions by different LE models adopting UIPF, which in turn affirms the potential of UIPF in predicting thermodynamics and kinetics of phase transformation in Fe–C–Mn systems
Impact of stress-induced anisotropic modifications on magneto-impedance behavior of rapidly quenched CoFe-based microwires
No full textThe investigation addresses the role of Al in the devitrification stage of a series of (Co94Fe6)72.5Si12.5-xAlxB13Cr2 (X = 0, 2, 4, 6 at%) rapidly quenched microwires. The incorporation of Al displayed a reduction in primary onset and activation energy (A.E) while it facilitated the widening of the span between primary and secondary crystallization onsets. The Giant Magneto-Impedance (GMI) behavior was influenced by Al concentration as well as applied uniaxial stress. Optimal Al-containing alloy (x & SIM; 2 at%) displayed the signature of the asymmetric dual peak at the operating frequency of 1 MHz and its prospective application as a very low magnetic field sensor in pre-stressed conditions. However, with increasing stress, the asymmetric character transformed to the symmetric dual peak which is attributed to the transition of transverse anisotropy to circular anisotropy via helical anisotropy. High-stress sensitivity has been attributed to either dominant transverse or circular anisotropy. The transition of stress-induced anisotropies in microwires has been portrayed schematically to elucidate the transitions. & COPY; 2023 Elsevier B.V. All rights reserved
Effect of austempering time on bainite plate thickness and variant selection in a high carbon low alloy steel
No full textThe study investigates the microstructure and crystallographic orientation relationship in a high carbon nanostructured bainitic steel that is austempered at 250 degrees C for different durations. The resulting microstructures are examined using optical, scanning, and transmission electron microscopy (TEM). Quantitative and qualitative analyses of dislocation density are performed using X-ray diffraction (XRD) and electron-backscattered diffraction (EBSD) respectively. The study finds that longer austempering time reduces the dislocation density because of slowing down transformation kinetics due to the enrichment of carbon concentration to a level corresponding to T0 ' temperature in the retained austenite phase. The bainite plate thickness in the longer-duration sample shows abnormal growth rate at the edges of the sheaf. The abnormal thickening rate is attributed to the annihilation of dislocations after prolonged austempering because of slow kinetics. The thickness of the bainitic plate is predicted using an available empirical relation and critically compared with experimentally measured values. It is found that the empirical equation used to compute thickness overestimates the plate thickness due to the omission of factors such as dislocation density and austenite block size. The crystallographic orientation relationship between bainite and austenite is analyzed locally by TEM and over a broader area by EBSD. The results reveal that both the Kurdjumov-Sachs and Nishiyama-Wasserman relationships are present in the material in equal fractions and some specific variants are formed in the sample subjected to longer austempering
On the role of grain size variation on pitting corrosion and passive film behavior of Alloy 600H
No full textIn this work, the effect of grain size variation on the pitting corrosion as well as the passivation behavior of the Alloy 600H has been critically assessed by various electrochemical techniques. The grain size modifications have been achieved by a series of thermal and thermo-mechanical processing. The potentiodynamic polarization study has revealed that the coarse-grained specimens exhibit higher corrosion and pitting resistance than the fine-grained ones. This has been attributed to the greater extent of random high-angle grain boundary (RHAGB) surface area in the fine-grained specimens, which acted as favorable locations for pit initiation. The electrochemical impedance spectroscopy (EIS) result has indicated the formation of more imperfect (nonstoichiometric) passive layers in fine-grained specimens due to the predominant presence of high energy and defective RHAGBs surface. Moreover, the Mott-Schottky analysis has revealed that the fine-grained specimens generate higher defect densities at the interfaces, which leads to passive film instability due to increased mobility of cation interstitial and cation vacancies at the interfaces
Effect of Si on the evolution of plasticity mechanisms, grain refinement and hardness during high-pressure torsion of a non-equiatomic CoCrMnNi multi-principal element alloy
No full textThe present study unraveled the defining role of small silicon (Si) addition (5 atomic %) in dramatically altering the plasticity mechanisms, grain refinement, and hardening response of a non-equiatomic CoCrMnNi multi-principal element alloy (MPEA) during high-pressure torsion (HPT) processing. Both the Si-free and the Si-added MPEAs had a face-centered cubic (FCC) structure and were subjected to a quasi-constrained HPT processing at 6 GPa pressure to different numbers of turns (0.5 and 5). Microstructure evolution was studied at the center and edge of the HPT-processed discs using X-ray diffraction line profile analysis (XLPA) and transmission electron microscopy (TEM). Si addition altered the predominant plasticity mechanism from micro-band formation to extensive occurrence of nano-twinning at the early stage of HPT processing. At later stages of HPT processing, both alloys exhibited deformation twinning but its propensity was considerably higher for the Si-added MPEA, as revealed by-50% higher twin fault probability. Additionally, the Si-added MPEA showed-30% higher dislocation density at any given stage of HPT processing compared to the Si-free MPEA. A significantly accelerated nano-structuring coupled with a finer saturation grain size was observed in the Si-added MPEA (34 nm for Si-free versus 23 nm for Si-added). These effects can be explained by the influence of Si addition on lowering the stacking fault energy (SFE) (from 40 mJ/m2 in Si-free to 20 mJ/m2 in Si-added MPEA) and increasing the solute pinning effect of Si on lattice defects. The plasticity mechanisms at the nano-scale were also influenced by the presence of Si as confirmed by the formation of nano-twins and stacking faults inside the nano-grains for the Si-added and Si-free MPEAs, respectively. The differences in plasticity mechanisms and microstructure evolution resulted in enhanced hardness in the early stages of HPT processing for the Si-added MPEA, but the difference in hardness between the two alloys tended to be reduced at higher strains
On Fabrication of Inconel 718 Slab by Wire Arc Additive Manufacturing: Study of Built Microstructure and Mechanical Properties
No full textA slab of dimension (152 x 25 x 18) mm(3) is successfully fabricated through Cold Metal Transfer + Metal Inert Gas-based Wire Arc Additive Manufacturing (WAAM). 4.3 kg/h deposition rate is achieved. WAAMed Inconel 718 exhibits dendritic microstructure which grows along the build direction. In the solid solution matrix of Ni-Cr-Fe, the Laves phase, Nb-rich MC-type carbides, and delta (d) phases are detected. The average tensile strength along the horizontal direction is obtained as similar to 824 MPa. Location-specific microstructure evolution causes a significant extent of property anisotropy predominantly along the build direction. The horizontal tensile specimen extracted from the bottom region of the slab exhibits the highest tensile strength (UTS), while the lowest tensile strength is obtained for the specimen extracted from the middle zone of the fabricated slab. Temperature data as recorded by the thermocouples are utilized to understand the complex heat interaction phenomena during the WAAM process. Laves phase is completely dissolved during homogenization treatment thus microstructure of the aged specimen only consists of the strengthening phase, i.e., gamma'' (Ni3Nb) and Nb-rich MC carbides
Environmental Impact Assessment in the Entire Life Cycle of Lithium-Ion Batteries
No full textThe growing demand for lithium-ion batteries (LIBs) in smartphones, electric vehicles (EVs), and other energy storage devices should be correlated with their environmental impacts from production to usage and recycling. As the use of LIBs grows, so does the number of waste LIBs, demanding a recycling procedure as a sustainable resource and safer for the environment. This review paper analyses and categorizes the environmental impacts of LIBs from mining their constituents, their usage and applications, illegal disposal, and recycling. Compared to recycling, reusing recovered materials for battery manufacturing would lessen the environmental footprints and reduce greenhouse gas emissions (GHG) and energy consumption. Thus, to prevent pollution and safeguard the environment, it is necessary to consider recycling spent LIBs and improving production and disposal methods. The present study offers a comprehensive overview of the environmental impacts of batteries from their production to use and recycling and the way forward to its importance in metal replenishment. The life cycle assessment (LCA) analysis is discussed to assess the bottlenecks in the entire cycle from cradle to grave and back to recycling (cradle)
Effect of maximum applied cyclic stress on fretting fatigue stress distribution of flat-on-flat modified 9Cr-1Mo steel contact: Finite element analysis
No full textFretting fatigue experiments were conducted on a modified 9Cr-1Mo (P91) steel under flat-on-flat contact with maximum applied cyclic stress (sigma max) levels of 450 MPa, 500 MPa, and 550 MPa at a stress ratio of 0.3 and a contact pressure of 100 MPa. A decrease in the cyclic life was observed with an increase in sigma max. Chaboche model with isotropic and kinematic hardening was employed in finite element analysis to evaluate the stress distribution near the contact pad and along the contact surface under fretting fatigue conditions. In addition, the contact-related parameters such as contact pressure, contact shear stress, and relative tangential motion were also assessed. The relative tangential motion was found to increase with increasing sigma max. Besides, the peak values of normal stress (parallel to the applied loading direction) and maximum principal stress were observed around the leading and trailing edges of the contact pad at the sigma max. The amplitude of relative tangential motion and slip zone increases with sigma max. The orientations of the principal plane and shear plane to the applied cyclic loading direction are - 89.5 degrees and - 134.5 degrees, irrespective of the sigma max. The fracture surface of the failed specimen revealed that the direction of the crack was nearly perpendicular to the applied stress. Smith-Watson-Topper parameter was used for estimating the crack initiation life with sigma max. It has been noticed that the fraction and dominance of crack initiation or propagation phase depend on the imposed cyclic condition for the steel
Development of a novel biocollector for flotation of low grade graphite ore
Get PDFMineral processing plants operate at a capacity of hundreds/thousands of tons per day. Accordingly, chemical reagents’ usage also increases proportionally. Stringent norms toward environmental sustainability question the usage of chemical reagents, especially in large quantities and tailings disposal in open areas. Hence, bioreagents have gained great interest. Froth flotation is by far
the most practiced processing route for fines beneficiation and low-grade ore upgradation, especially for naturally hydrophobic minerals. Flotation being a physicochemical separation technique, flotation reagents selection
plays a pivotal role in the process performance. A novel environmental-friendly biocollector, an extract from the leaves of Vitex negundo, was used as a flotation collector in the present investigation for beneficiating a low grade
graphite ore with 8.67% fixed carbon. A three-factor and three-level Box-Behnken Design (BBD) under Response Surface Methodology (RSM) was employed to study the effects of important process variables such as grinding time, depressant dosage, and collector dosage on the responses, namely, ash percent of final concentrate and its recovery. A final graphite concentrate with 4.24% ash and 14.42% yield was obtained using the developed biocollector
by flotation of low-grade graphite ore with 89.47% ash content. The degree of significance of input variables was determined using ANOVA. Regression models for ash content, % of final concentrate, and its %recovery were obtained from BBD analysis. It showed that the grinding time has
a significant influence on the process followed by depressant dosage on the grade of final concentrate and collector dosage on its recovery
Managing Mining and Minerals Processing Wastes_chapter9
No full textManaging Mining and Minerals Processing Wastes: Concepts, Design and Applications presents fundamental knowledge in waste management in mining and minerals processing and summarizes recent advances. The book offers readers insights into innovative ways to manage waste in the mining and minerals industry. Sections cover a brief introduction to this topic and an explanation of waste generation, and how to manage the six types of waste, including waste rock, mill tailings, coal refuse and coal fly ash, quarry waste, metallurgical slugs and washery rejects. The title then emphasizes the management of hazardous waste, the acid mine drainage and the lifecycle assessment of waste management.
Finally, the book considers current and emerging challenges. This publication offers a comprehensive background to waste management in mining and minerals processing and a summary of recent advances and innovative strategies for managing each kind of waste