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Quench Temperature-Dependent Phase Transformations During Nonisothermal Partitioning
No full textAn attempt has been made to estimate the amount and composition of different phases formed during the simulated quenching and nonisothermal partitioning (Q&P) process in a dilatometer by matching the experimental dilation data with empirically determined dilation curve. The result highlights the carbon enrichment of austenite, as well as its partial transformation to secondary martensite and/or bainite, during the partitioning step. Also, an increase in quench temperature (QT) led to enhanced bainite or secondary martensite formation, as a result of reduced carbon enrichment of remaining austenite. Further Q&P experiments on bulk samples were carried out to understand the dependence of carbon diffusion and subsequent microstructure evolution with QT. Although the change in experimentally obtained retained austenite (RA) content with QT corroborates with the existing model predictions, the maximum amount of RA was observed at QT lower than predicted. The half-thickness of RA films increased with increasing QT, which substantiates the theoretical prediction of the diffusion distance of carbon atoms in austenite
One pot method to synthesize three-dimensional porous hydroxyapatite nanocomposite for bone tissue engineering
No full textA three-dimensional porous hydroxyapatite nanocomposite has been synthesized by a simple, less energy consuming and cost effective one-pot method. In this study, gelatin foam has been used as pore forming agent and incorporated in carboxymethyl cellulose-hydroxyapatite system in composite formation stage. A three-dimensional porous polymers-hydroxyapatite nanocomposite has been formed as a final product. The synthesized porous nanocomposite has been thoroughly characterized by different techniques. It was found that the nanocomposite is highly porous with almost 80% porosity, and has multi-scale pores from 2.5 to 900 mu m in size. Furthermore, the synthesized porous composite has compressive strength ~ 11.8 +/- 1.5 MPa and modulus ~ 0.243 +/- 0.031 GPa, in the range of cancellous bone. Moreover, the nanocomposite provides favorable environment to cells for proliferation, high alkaline phosphatase (ALP) activity and extracellular mineralization. In vitro degradation of synthesized nanocomposites was tested in simulated body fluid. Results ascertained that the synthesized porous hydroxyapatite nanocomposite would be a promising scaffold for bone tissue engineering
Reaction Kinetics of Fly Ash Geopolymerization by Analyzing Calorimetry Data
No full textGeopolymer synthesis, called as geopolymerization, is a complex process that consists of multiple steps such as the dissolution of alumina and silica, oligomer formation, gelation, structural rearrangement/crystallization and hardening with overlapping boundaries
The role of Se vacancies and Fe doping of nickel selenide in the water oxidation reaction
No full textThe catalytic activity and reactivity of catalysts can be varied by adopting methods such as composite formation, doping with foreign atoms, and creating vacancies. Researchers are studying different catalysts to obtain clean energy from renewable energy sources. Highly competent and potential catalysts toward the oxygen evolution reaction (OER) are required for commercialisation. Transition-metal diselenides are promising electrocatalysts for OER. Combining both experimental and theoretical results, we demonstrate that both Fe incorporation and Se vacancy engineering in the catalyst NiSe2 improve the electrocatalytic activity toward OER. Fe-doped NiSe2 with Se vacancies (V-Se-Ni0.70Fe0.30Se2) shows enhanced OER activity and requires an overpotential of 210 mV to achieve the current density of 10 mA cm(-2). This value is much lower than that of the benchmark catalyst IrO2/C. The results of density functional theory calculations show that both Fe doping and Se vacancies increase the density of states near the Fermi level, increasing the conductivity of the V-Se-Ni0.70Fe0.30Se2 catalyst. The calculations also reveal a decrease in the free energy of the reaction intermediates, resulting in enhanced electrocatalytic OER activity
Correction to: Evolution of PVA gels prepared without crosslinking agents as a cell adhesive surface. Gupta S, Webster TJ, Sinha A. J Mater Sci Mater Med. 2020 Jul 21;31(8):63. doi: 10.1007/s10856-020-06399-1. PMID: 32696134
No full textPhysical parameters (such as crosslinking density, crystallinity and mechanical properties) have been found to largely affect cellular behavior on polymer scaffolds. This study demonstrated that transparent pure Poly (vinyl alcohol) hydrogels prepared via a freeze-thaw method can be made to support cell adhesion by controlling physical parameters such as concentration and the number of freeze-thaw cycles. For a given number of freeze-thaw cycles, (specifically 45), polymer concentration dependent structural and mechanical properties (such as tensile strength and stiffness) were correlated with cell adhesion. The maximum cell attachment occurred on the hydrogels with the greatest mechanical properties, crystallinity and crosslinking density. The hydrogel surfaces were more favorable to human dermal fibroblasts than human lens epithelial cells and retained their transparency as well as dimensional stability with only a small degree of swelling. Fibroblast laden hydrogels showed extensive alkaline phosphatase activity which confirmed their healthy proliferation and function. In this manner, this study suggests that transparent Poly (vinyl alcohol) hydrogels prepared by the freeze thaw method described here should be further studied for numerous tissue engineering applications
Influence of heat input on microstructure and fracture toughness property in different zones of X80 pipeline steel weldments
No full textIn this paper, microstructure observations and mechanical behaviour of fusion line and offsetting positions from fusion line by 1, 2 and 3 mm were analysed. For the welding of X80 pipeline steel plates, different magnitudes of heat inputs such as high heat input (HHI) 25 kJ/cm, medium heat input (MHI) 20 kJ/cm and low heat input (LHI) 15 kJ/cm were employed. Critical values of J-integral (J(0.2)) and crack tip opening displacement (CTOD0.2) for predetermined regions in the X80 weldment were determined as per ASTM-E1820a. M-A constituents of different sizes such as small (1-2 mu m), large >2 mu m and slender (>4 mu m) were observed in the microstructure of subzones of weldments for different heat inputs. Formation of granular bainite, M-A constituents and inclusions of Ti, Si, Mo in the microstructure impaired fracture toughness property. In the X80 weldment, the fusion line (FL) for HHI was found weakest in terms of fracture resistance, which subsequently increases the risk of fracture
Metallurgical Perspective on Quench and Partitioned Advanced High Strength Steels
No full textThe present article provides an insight into different types of advanced high strength steel, with a special emphasis on the quench and partitioned (Q&P) steels. The quench and partitioned steel contain the retained austenite and martensite in the microstructure. The softer retained austenite phase improves the ductility and toughness, whereas the desired strength is provided by martensite. Due to this unique microstructural combination, these steel grades are being investigated extensively in recent times and are a potential candidate for automotive and other applications. Therefore, different aspects of these steels, such as design, processing, and applications, are reviewed in the present article. In addition, the suitability of these grades for hot-dip galvanizing is also discussed briefly
Early stage phase separation of AlCoCr0.75Cu0.5FeNi high-entropy powder at the nanoscale
No full textHigh entropy alloys are generally considered to be single phase material. This state is, however, typically a non-equilibrium state after fabrication at high cooling rates. Phase constitution after fabrication or heat treatment is mostly known for isothermal annealing only and for casts as well as rapidly quenched alloys. Knowledge on early phase separation stages of high entropy alloys and their mechanisms are missing so far. Here, we present results on phase separation at intermediate cooling rates, by characterization of gas atomized powder of the AlCoCr0.75Cu0.5FeNi alloy. Although investigation by X-ray diffraction and Electron Backscatter Diffraction indicates a single-phase nature of the powder particles, aberration-corrected scanning transmission electron microscopy and atom probe tomography reveal a nanoscale phase separation into Ni–Al-rich B2 and Fe–Cr-rich A2 regions as well as a high number density of 3.1 × 1024 Cu-rich clusters per m3 in the B2 matrix. The observed phase separation and cluster formation are linked to spinodal decomposition and nucleation processes, respectively. The study highlights that adequate characterization techniques need to be chosen when making statements about phase stability and structural evolution in compositionally complex alloys
Effect of lead alloying on corrosion characteristics of galvanized coatings exposed in atmosphere, simulated laboratory and a service environment
No full textRole of alloying of lead in hot dip galvanized coating deposited on mild steel wire on their corrosion characteristics are studied exposing them in industrial, coastal urban environments and laboratory simulated electrolytes. Various corrosion evaluation techniques namely mass loss, electrochemical impedance spectroscopy and direct current polarization methods are used to assess corrosion characteristics of the wires. Corrosion products formed on the exposed samples and cross section of the coatings are analyzed by X-Ray Diffraction, Raman Spectroscope and Scanning Electron Microscope. Lead is observed to change the corrosion characteristics of the coatings with change in constituents of the environments. In saline electrolytes, alloying of lead is found to accelerate the corrosion rate. This metal deposits as cluster on top layer of the galvanized coatings and acts as strong cathodes with respect to the zinc and accelerates the corrosion rate. In sulfurous environments, a stifling effect on rate of corrosion is noted which is attributed to the formation of stable and moisture insoluble sulfate compounds of lead on the surface of the coating
Vacuum furnaces for metallurgical processing
Get PDFLarge scale vacuum furnaces are becoming crucial in metallurgical processes like melting, casting,
heat treatment, degassing, annealing and brazing. The vacuum conditions help in reducing contamination (like
oxidation) and improve the micro-structure to get favourable metallurgical properties for industrial applications. The vacuum also reduces the melting and boiling points of metals and alloys, thereby reducing the electrical power requirement in high temperature furnaces for clean metallurgical processing. The present paper describes the design criteria of vacuum metallurgical furnaces involving vacuum equipment, heating elements and process instrumentation