There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Metallurgy of cast iron.

The excellent property combination of ADI has opened new horizons for cast iron to replace steel castings and forgings in many engineering applications with considerable cost benefits. Thanks to the extensive research efforts made over the past few years, new processing techniques have opened even more opportunities for this very prospective material to acquire better combinations of strength, ductility, toughness, wear resistance as well as machinability. This review analyses the key features of those novel processing techniques and the resulted new applications of ADI. The survey firstly discusses the possible strengthening mechanism of ADI with special emphasis on the TRIP phenomena, associated with the deformation of ADI. Strength and toughness properties could be improved through the development of: Ausformed ADI; where mechanical processing component was added to the conventional heat treatment as a driving force to accelerate the rate of stage I austempering. Squeeze cast ADI; where superior quality ADI castings were produced through squeeze casting of molten iron in a permanent mold, followed by in‐situ heat treatment of the hot knocked‐out castings in the austenite range followed by normal austempering in a salt bath. Two step austempering to achieve finer ausferrite at higher undercooling during austempering treatment followed by austempering at higher temperature where higher austenitic carbon is promoted. The machinability and ductility of ADI may be considerably enhanced through the development of dual phase microstructures (ferrite+ausferrite or ferrite‐martensite by partial austenitization in the (α+γ+graphite) region followed by normal austempering. The abrasion resistance could be remarkably increased through the development of: Carbidic ADI‐ductile iron containing carbides subsequently austempered to form ausferritic matrix with an engineered amounts of carbides Bainitic/martensitic (B/M) ADI containing less expensive alloying elements such as Si and Mn in the range of 2.5‐3.0% This report discusses as well the recent trials to produce thin‐wall ADI castings.

Advances in the Metallurgy and Applications of ADI

Development of high entropy alloys: A review

Energy storage devices play an important role in our daily lives. As a kind of new materials, high-entropy alloys (HEAs) avoid the traditional “base element” concept and display a variety of interesting and unusual properties. HEAs have been considered promising electrode materials for energy storage and conversion technologies due to their excellent mechanical, chemical, and physical properties. Herein, we report a review on basic supercapacitor, such as differences in charge storing mechanism of electric double layer capacitive (EDLC)-, pseudocapacitive-, and battery-type electrode materials; differences in symmetric, hybrid, and asymmetric supercapacitor devices; and recent advances in HEAs as an electrode material for supercapacitors. The aim of this review is to combine newly emerge HEAs electrode materials with the basic concepts of supercapacitor and avoid the inflating misinterpretation in between the different energy storage systems. We also suggest critical points to be considered for high performance nanostructured HEAs as newborn electrode materials.

High entropy alloys as electrode material for supercapacitors: A review

The effect of niobium additions on the as-cast microstructure of a hypoeutectic high-Cr cast iron containing 2.2 wt.% C and 16.5 wt.% Cr was investigated. With increasing niobium content, t...

Enhancement of wear resistance and impact toughness of as cast hypoeutectic high chromium cast iron using niobium

This study reports the ex-situ and in-situ (one-pot) synthesis of a triazine covalent organic framework (COF)/graphene oxide (GO) nanocomposite. The materials are used to synthesize N-doped carbon (N-doped C)/reduced GO (rGO) via a simple carbonization step. The nanocomposites are used as electrode materials for supercapacitors. N-doped C/rGO synthesized via the in-situ method exhibits good electrochemical performance compared to the materials synthesized via the ex-situ procedure. N-doped C/rGO_In-situ offers a specific capacitance of 234 F·g−1 at the current density of 0.8 A·g−1. Two symmetric supercapacitor devices illuminate a white light-emitting diode (LED) lamp. A device using an N-doped C/rGO_In situ electrode shows high specific energy of 14.6 W·h·kg−1 and high specific power of 400 W·kg−1, with only a 14 % decrease in the capacitance performance after 3500 cycles. The simple synthesis procedure using the in-situ method and the high electrochemical performance of the synthesized materials may advance the exploration of an effective electrode material for supercapacitors. 

Covalent organic frameworks (COFs)-derived nitrogen-doped carbon/reduced graphene oxide nanocomposite as electrodes materials for supercapacitors

The influence of heat treatment on microstructure and mechanical properties of high chromium white cast iron alloyed with titanium was investigated. The austenitizing temperatures of 980°C and 1150°C for 1 hour each followed by tempering at 260°C for 2 hours have been performed and the effect of these treatments on wear resistance/impact toughness combination is reported. The microstructure of irons austenitized at 1150°C showed a fine precipitate of secondary carbides (M6C23) in a matrix of eutectic austenite and eutectic carbides (M7C3). At 980°C, the structure consisted of spheroidal martensite matrix, small amounts of fine secondary carbides, and eutectic carbides. Titanium carbides (TiC) particles with cuboidal morphology were uniformly distributed in both matrices. Irons austenitized at 980°C showed relatively higher tensile strength compared to those austenitized at 1150°C, while the latter showed higher impact toughness. For both cases, optimum tensile strength was reported for the irons alloyed with 1.31% Ti, whereas maximum impact toughness was obtained for the irons without Ti-addition. Higher wear resistance was obtained for the samples austenitized at 980°C compared to the irons treated at 1150°C. For both treatments, optimum wear resistance was obtained with 1.3% Ti.

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Heat Treatment in High Chromium White Cast Iron Ti Alloy

SiMo ductile cast irons are used as high-temperature materials in automotive components, because they are microstructurally stable at high operating temperatures. The effect of different amounts of Si and Mo as well as the addition of 3 wt pct Al on the microstructure, high-temperature oxidation, and mechanical properties of SiMo ductile cast iron was studied. Dilatometric measurements of SiMo ductile iron exhibited obvious differences in the transformation temperature A
 1 due to presence of Al and the increase of Si. The microstructure of the SiMo alloys without Al addition showed outstanding nodularity and uniform nodule distribution. However, by adding 3 wt pct Al to low Si-SiMo ductile iron, some compacted graphite was observed. The results of oxidation experiments indicated that high Si-SiMo ductile iron containing 4 and 4.9 wt pct Si had superior resistance to lower Si-SiMo and SiMo ductile iron containing 3 wt pct Al. The results showed also that with increasing Si up to 4.9 wt pct or by replacing a part of Si with 3 wt pct Al, tensile strength increased while elongation and impact toughness decreased.

Microstructure and Hot Oxidation Resistance of SiMo Ductile Cast Irons Containing Si-Mo-Al

Ductile cast iron was developed by adding Aluminium (up to16 wt%Al). Effects of aluminium on microstructure, hardness, oxidation resistance at high temperature and damping capacity of cast iron were studied. Adding Al up to 4.0 wt% raised degree of graphitisation. More than 4.0 wt% up to 13.8 wt%Al showed precipitation of hard carbides. Hardness was increased signiﬁcantly by increasing Al due to formation of intermetallic compounds. More than 5.8 wt%Al showed a higher oxidation resistance due to formation of complex Fe-Al oxide, acted as a protective and adherent scale. Damping capacity of 2.6 and 4.0 wt%Al was increased as the volume fraction of graphite increased as well as the change of graphite from spheroidal to compacted ones. Damping capacity of 16 wt%Al was enhanced due to high ferrite (86%) containing graphite. However, decreasing of ferrite and disappearing of graphite as well as presence of carbides highly deteriorated damping capacity of 5.8, 9, 12.8 and 13.8 wt%Al cast iron.

Mervat M. Ibrahim

Papers

Enhancement of wear resistance and impact toughness of as cast hypoeutectic high chromium cast iron using niobium

Covalent organic frameworks (COFs)-derived nitrogen-doped carbon/reduced graphene oxide nanocomposite as electrodes materials for supercapacitors

Heat Treatment in High Chromium White Cast Iron Ti Alloy

Microstructure and Hot Oxidation Resistance of SiMo Ductile Cast Irons Containing Si-Mo-Al

Microstructure, hot oxidation resistance and damping capacity of Al- alloyed cast iron