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

The coarsening behavior of martensite lath has been investigated by means of transmission electron microscopy for tempered martensitic 9 wt.% Cr–(0, 1, 2, 4 wt.%) W steels during creep at 823–923 K. During creep, the recovery of excess dislocations, the agglomeration of carbides and the coarsening of laths take place. The coarsening of laths with absorbing excess dislocations is the major process in the creep acceleration. The coarsening rate of lath decreases with increasing W concentration, which is correlated with the rate of Ostwald ripening of M23C6 carbides. The progressive local-coalescence of two adjacent laths boundaries near the Y-junction causes the movement of Y-junction, resulting in the coarsening of lath.

Coarsening behavior of lath and its effect on creep rates in tempered martensitic 9Cr–W steels

Alloy design of creep resistant 9Cr steel using a dispersion of nano-sized carbonitrides

Research and Development of Heat-Resistant Materials for Advanced USC Power Plants with Steam Temperatures of 700 °C and Above

The growth behavior of MX carbonitrides during aging and creep was investigated for 9Cr–0.5Mo–1.8W–VNb steel (ASME-P92). The stress exponent of minimum creep rate decreases with increasing testing temperature. The value of stress exponent is 5.7 at 1023 K over a wide range of stress examined, while the value is 12.7 at 923 K. The low stress exponent at 1023 K may be due to the growth of MX carbonitrides during creep. The MX carbonitrides grow to a size of 60 nm during aging at 1023 K for 400 h. The size is much larger than the critical value over which the coherent strain between the MX and matrix decreases. The growth rate of the MX carbonitrides is larger in gauge portion than in head portion of crept specimens, implying a stress or strain effect.

Creep behavior and stability of mx precipitates at high temperature in 9cr–0.5mo–1.8w–vnb steel

Great advancement has been achieved in the analysis of specific microstructure instability causing a loss of creep strength at 550 °C and above, the prediction of onset time of the creep strength loss and theoretical modeling of precipitation sequences in power plant steels A number of new alloy-design concepts based on microstructure stabilization have been proposed for the development of highly creep-resistant bainitic 3Cr and martensitic 9–12Cr steels with higher creep rupture strength than existing high strength steels such as T23 and P92

Fujio Abe

Papers

Coarsening behavior of lath and its effect on creep rates in tempered martensitic 9Cr–W steels

Alloy design of creep resistant 9Cr steel using a dispersion of nano-sized carbonitrides

Research and Development of Heat-Resistant Materials for Advanced USC Power Plants with Steam Temperatures of 700 °C and Above

Creep behavior and stability of mx precipitates at high temperature in 9cr–0.5mo–1.8w–vnb steel

Bainitic and martensitic creep-resistant steels