Energetic effects of dopants on the eutectoid decomposition of Nb–Si in situ composites

The influences of doping elements (Ti, Zr, Hf, V, Ta, Cr, Mo, W and Al) on the heats of formation of Nb, Nb₅Si₃ and Nb₃Si have been studied using first-principles pseudopotential plane-wave method based on density functional theory. Site preferences of dopants in Nb₅Si₃ and Nb₃Si intermetallics are first determined by comparing the heats of formation of the systems with different site occupations of the doping atoms. The partitionings of dopants between the equilibrium phases Nb and Nb₅Si₃ of Nb–Si in situ composites are then discussed and compared with experimental results. Phase partitioning behaviours of the alloying elements are found to depend strongly on the number of their valence electrons. By calculating the enthalpy of reaction regarding the eutectoid decomposition of Nb₃Si phase, we conclude that Ta is a Nb₃Si stabiliser while other dopants destabilise Nb₃Si at the investigated concentration.     

Production of recrystallized nano-grains in a fine-grained Cu–Zn alloy

A fine-grained Cu–30%Zn alloy sheet was rolled at 77 K to induce ultrafine mechanical twins. Subsequent annealing of the rolled alloy at temperatures up to 543 K led to the uniform appearance of recrystallized ultrafine grains (UFGs), which contained numerous annealing twins. Average grain sizes of 150 ～ 300 nm were produced in this way. The formation of such UFGs during annealing is attributed to the high nucleus density associated with the fine initial grain size as well as to the high densities of mechanical twins and dislocations produced by cryorolling. The high driving force for recrystallization enabled the use of relatively low annealing temperatures, which limited the subsequent grain growth.     

Effect of Mg content on Portevin–Le Chatelier band strain in Al–Mg sheet alloys

Experimental measurements of stress drops and band strains in type-B Portevin–Le Chatelier (PLC) bands were carried out for 5xxx series Al–Mg sheets with Mg content between 1.8 and 4.5?wt%. While the stress drops increase with global strain, the band strain values in all the samples follow a common linear relationship with global strain. The results indicate that the type-B PLC band strain is independent of solute content at given strain rate.     

Many-body potential for nitrogen in α-iron

N atom is one of the most frequent foreign interstitial atoms in α-iron along with C atoms. The Fe–C potential has been well-developed and can reproduce many significant interactions of C with point defects present in α-iron. However, there exists no satisfactory Fe–N potential to describe the interactions of N with point defects. Here, we develop a many-body potential for N in α-iron. The potential parameters are determined by fitting to ab initio data, which includes energetics, configurations, and relaxations of Fe atoms close to N atom. This potential successfully describes the interactions of Fe–N across a wide range of defect environments. The potential employs the embedded atom method form and hence is appropriate for large-scale molecular dynamics simulation.     

Valence band structure of the NiAl–Mo alloy from the photoelectron spectrum

The valence band structures of the NiAl–Mo alloy was investigated by photoelectron spectroscopy. The valence band spectra of the NiAl–Mo alloy was shifted away from the Fermi level so that the Ni-d-band centroid moved to a higher energy by 0.22 eV as Mo was added. A possible explanation lied in the overlap of Ni-d bands in the energy with Mo-d and Al-p bands. The participation of Mo-d bands was correlated with the site preference of Mo in NiAl alloys.     

Wentzel–Kramers–Brillouin solution of cut-off frequency for horizontal shear (SH) waves in various inhomogeneous thin films

The Wentzel–Kramers–Brillouin method is employed to study the cut-off frequencies of the horizontal shear waves in a freestanding functionally graded piezoelectric–piezomagnetic material film with the electrically and magnetically open boundary conditions. An analytical solution, which could be used in analyzing the problems of various functionally graded materials, is proven to have high precision by analytical analysis and a numerical example. The results reveal that the set of cut-off frequencies is a series of approximate arithmetic progressions. A theoretical foundation based on the relationship between the cut-off frequencies and the materials’ gradient property is established for nondestructive evaluation.     

Direct evidence that an apparent splitting pattern of gamma particles in Ni alloys is a stage of coalescence

High-resolution electron microscopy is used to determine the translation order domains of gamma particles in arrangements formed during Ostwald ripening in the alloy Ni-12at.%Al. Such arrangements have been often identified with the operation of a mechanism of particle splitting in the late stages of the coarsening process, that is when the elastic strain contribution becomes predominant. It is shown that the translation order domains are not identical in such a particle array. This leads to the conclusion that particle splitting is not necessarily the mechanism responsible for the formation of such characteristic particle arrangements. Instead, particle migration can also be considered to be the responsible mechanism for the formation of such a correlated gamma-particle spatial distribution observed in Ni-based alloys.     

Kant and German idealisms

This paper considers whether Hegel's master/slave dialectic in the Phenomenology of Spirit should be considered as a refutation of solipsism. It focuses on a recent and detailed attempt to argue for this sort of reading that has been proposed by Frederick Beiser – but it argues that this reading is unconvincing, both in the historical motivations given for it in the work of Jacobi and Fichte, and as an interpretation of the text itself. An alternative reading of the dialectic is proposed, where it is argued that the central problem Hegel is concerned with is not solipsism, but the sociality of freedom.     

Hume's Experimental Method

In this article I attempt to reconstruct David Hume's use of the label ‘experimental’ to characterise his method in the Treatise. Although its meaning may strike the present-day reader as unusual, such a reconstruction is possible from the background of eighteenth-century practices and concepts of natural inquiry. As I argue, Hume's inquiries into human nature are experimental not primarily because of the way the empirical data he uses are produced, but because of the way those data are theoretically processed. He seems to follow a method of analysis and synthesis quite similar to the one advertised in Newton's Opticks, which profoundly influenced eighteenth-century natural and moral philosophy. This method brings him much closer to the methods of qualitative, chemical investigations than to mechanical approaches to both nature and human nature.