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

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

ion. The oxidative addition mechanism was originally proposed22i because of the lack of a strong rate dependence on polar factors and on the acidity of the medium. Later, however, the electrophilic substitution mechanism also was proposed. Recently, the oxidative addition mechanism was confirmed by investigations into the decomposition and protonolysis of alkylplatinum complexes, which are the reverse of alkane activation. There are two routes which operate in the decomposition of the dimethylplatinum(IV) complex Cs2Pt(CH3)2Cl4. The first route leads to chloride-induced reductive elimination and produces methyl chloride and methane. The second route leads to the formation of ethane. There is strong kinetic evidence that the ethane is produced by the decomposition of an ethylhydridoplatinum(IV) complex formed from the initial dimethylplatinum(IV) complex. In D2O-DCl, the ethane which is formed contains several D atoms and has practically the same multiple exchange parameter and distribution as does an ethane which has undergone platinum(II)-catalyzed H-D exchange with D2O. Moreover, ethyl chloride is formed competitively with H-D exchange in the presence of platinum(IV). From the principle of microscopic reversibility it follows that the same ethylhydridoplatinum(IV) complex is the intermediate in the reaction of ethane with platinum(II). Important results were obtained by Labinger and Bercaw62c in the investigation of the protonolysis mechanism of several alkylplatinum(II) complexes at low temperatures. These reactions are important because they could model the microscopic reverse of C-H activation by platinum(II) complexes. Alkylhydridoplatinum(IV) complexes were observed as intermediates in certain cases, such as when the complex (tmeda)Pt(CH2Ph)Cl or (tmeda)PtMe2 (tmeda ) N,N,N′,N′-tetramethylenediamine) was treated with HCl in CD2Cl2 or CD3OD, respectively. In some cases H-D exchange took place between the methyl groups on platinum and the, CD3OD prior to methane loss. On the basis of the kinetic results, a common mechanism was proposed to operate in all the reactions: (1) protonation of Pt(II) to generate an alkylhydridoplatinum(IV) intermediate, (2) dissociation of solvent or chloride to generate a cationic, fivecoordinate platinum(IV) species, (3) reductive C-H bond formation, producing a platinum(II) alkane σ-complex, and (4) loss of the alkane either through an associative or dissociative substitution pathway. These results implicate the presence of both alkane σ-complexes and alkylhydridoplatinum(IV) complexes as intermediates in the Pt(II)-induced C-H activation reactions. Thus, the first step in the alkane activation reaction is formation of a σ-complex with the alkane, which then undergoes oxidative addition to produce an alkylhydrido complex. Reversible interconversion of these intermediates, together with reversible deprotonation of the alkylhydridoplatinum(IV) complexes, leads to multiple H-D exchange

Activation of c-h bonds by metal complexes

Hydrogen Production by Molecular Photocatalysis

Transition metal catalyzed oxidative functionalization of carbon-hydrogen bonds

https://www.tandfonline.com/doi/pdf/10.1088/1468-6996/9/1/013002

Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

Creep is a time-dependent mechanism of plastic deformation, which takes place in a range of materials under low stress-that is, under stresses lower than the yield stress. Metals and alloys can be designed to withstand creep at high temperatures, usually by a process called dispersion strengthening, in which fine particles are evenly distributed throughout the matrix. For example, high-temperature creep-resistant ferritic steels achieve optimal creep strength (at 923 K) through the dispersion of yttrium oxide nanoparticles. However, the oxide particles are introduced by complicated mechanical alloying techniques and, as a result, the production of large-scale industrial components is economically unfeasible. Here we report the production of a 9 per cent Cr martensitic steel dispersed with nanometre-scale carbonitride particles using conventional processing techniques. At 923 K, our dispersion-strengthened material exhibits a time-to-rupture that is increased by two orders of magnitude relative to the current strongest creep-resistant steels. This improvement in creep resistance is attributed to a mechanism of boundary pinning by the thermally stable carbonitride precipitates. The material also demonstrates enough fracture toughness. Our results should lead to improved grades of creep-resistant steels and to the economical manufacture of large-scale steel components for high-temperature applications.

Creep-strengthening of steel at high temperatures using nano-sized carbonitride dispersions

Part 1 General: Introduction The development of creep-resistant steels Specifications for creep-resistant steels: Europe Specifications for creep-resistant steels Production of creep-resistant steels for turbines. Part 2 Behaviour of creep-resistant steels: Physical and elastic behaviour of creep-resistant steels Diffusion behaviour of creep-resistant steels Fundamental aspects of creep deformation and deformation mechanism map Strengthening mechanisms in steel for creep and creep rupture Precipitation during heat treatment and service - Characterisation, simulation and strength contribution Grain boundaries in creep resistant steels Fracture mechanism map and fundamental aspects of creep fracture Mechanisms of creep deformation in steel Constitutive equations for creep curves and predicting service life Creep strain analysis in steel Creep crack growth behaviour and creep-fatigue behaviour of steels Creep strength of welded joints of ferritic steels Fracture mechanics: understanding in microdimensions Mechanisms of oxidation and corrosion and the influence of steam oxidation on service life of steam power plant components. Part 3 Applications: Alloy design philosophy of creep-resistant steels Using creep-resistant steels in turbines Using creep-resistant steels in nuclear reactors Creep damage - Industry needs and future R&D.

Creep-resistant Steels

In order to improve the long-term creep strength of 9%Cr steel, the stabilization of martensitic microstructure in the vicinity of prior austenite grain boundaries during creep has been investigated by the addition of boron and by a dispersion of nano-size MX nitrides. Creep tests were carried out at 923 K for up to about 3×10 4  h. Boron is enriched in the M 23 C 6 carbides during aging and creep, especially in the vicinity of prior austenite grain boundaries. This reduces the coarsening rate of M 23 C 6 carbides, which effectively stabilizes the martensitic microstructure in the vicinity of prior austenite grain boundaries. A dispersion of nano-sized MX nitrides but no M 23 C 6 along boundaries also gives rise to excellent pinning force for migrating boundaries during creep, as shown by approximately two orders of magnitude longer time to rupture than ASME-P92. The stabilization of martensitic microstructure retards the onset of tertiary or acceleration creep, which results in lower minimum creep rate and longer time to rupture.

Stabilization of martensitic microstructure in advanced 9Cr steel during creep at high temperature

The distributions and precipitated amounts of M23C6 carbides and MX-type carbonitrides with decreasing carbon content from 0.16 to 0.002 mass pct in 9Cr-3W steel, which is used as a heat-resistant steel, has been investigated. The microstructures of the steels are observed to be martensite. Distributions of precipitates differ greatly among the steels depending on carbon concentration. In the steels containing carbon at levels above 0.05 pct, M23C6 carbides precipitate along boundaries and fine MX carbonitrides precipitate mainly in the matrix after tempering. In 0.002 pct C steel, there are no M23C6 carbide precipitates, and instead, fine MX with sizes of 2 to 20 nm precipitate densely along boundaries. In 0.02 pct C steel, a small amount of M23C6 carbides precipitate, but the sizes are quite large and the main precipitates along boundaries are MX, as with 0.002 pct C steel. A combination of the removal of any carbide whose size is much larger than that of MX-type nitrides, and the fine distributions of MX-type nitrides along boundaries, is significantly effective for the stabilization of a variety of boundaries in the martensitic 9Cr steel.

Fujio Abe

Papers

Precipitate design for creep strengthening of 9% Cr tempered martensitic steel for ultra-supercritical power plants

Creep-strengthening of steel at high temperatures using nano-sized carbonitride dispersions

Creep-resistant Steels

Stabilization of martensitic microstructure in advanced 9Cr steel during creep at high temperature

Effect of carbon concentration on precipitation behavior of M23C6 carbides and MX carbonitrides in martensitic 9Cr steel during heat treatment