Vol 120, No 7 (2019)

The influence of the cross-section geometry of metal nanowires on the dielectric tensor has been examined. Diagonal and off-diagonal components of the dielectric tensor were calculated taking the size dependence of the Fermi energy into account within the free-electron model using the boundary-shape perturbation method. The effect of variation of the eccentricity of the cross section, the effective radius, and the composition of nanowires on frequency dependences of the real and imaginary parts of components of the dielectric tensor was studied. Calculations were performed for Ag, Cu, and Al.

FeGa thin films have been deposited onto (100)-oriented GaAs and (001)-oriented Si substrates at different temperatures by pulsed laser deposition. It has been shown that at different substrate temperatures, magnetic properties of FeGa films greatly change, which is mainly dependent on different crystal textures. The presence of the structure consisting of D0₃-ordered grain phase and bcc α-Fe crystal structure (A2) has been revealed using X-ray diffraction analysis. The diffraction peak of FeGa (001) direction, which ‎corresponds to the D0₃-ordered granular phase, was observed when the temperatures of the GaAs substrate were 400 and 600°C. The diffraction peak that corresponds to (110) direction of the bcc A2 structure has appeared at 800°C. However, the FeGa film on the Si substrate did not demonstrate any obvious structural change. The changes in the magnetic properties can be mainly attributed to changes in the roughness and the lattice mismatch between FeGa and Si.‎

Nano-sized precipitates in centrifugally cast Cu–0.43Cr–0.22Zr alloy and their evolution during subsequent solid-solution treatment and aging were investigated by TEM and HRTEM. They are particles of Cr and Cu–Zr phase, such as Cu₅₁Zr_14. Many nano-sized precipitates are found in the cast alloy; they will get smaller or disappear during solid-solution treatment and the dissolved atoms are inhomogeneously distributed in the copper matrix and form aggregations up to generation of very tiny clusters after solution quenching. Furthermore, aging treatment will create many new nano-sized precipitates, and causes the inherited precipitates being recovered and the clusters being grown, resulting in the formation of more and finer precipitates in the aged alloy in comparison with the case of the as-cast alloy. Therefore, it can be inferred that the more the tiny precipitates formed in the as-cast alloy, the more the precipitates in the aged alloy. The treatment combining solid-solution one and aging is beneficial to the formation of more and finer precipitates in a Cu–Cr–Zr alloy.

Formation of heat affected zone (HAZ) when welding is considered as weakest link across transition joint. Characterization of this zone is a key issue to reduce the effect of embrittlement; hence appropriate welding parameters were adopted. In the present study, HAZ simulation was done for boron modified P91 steel using Gleeble. It has been observed that matrix was martensitic in nature for coarse-grain HAZ (CGHAZ)/fine-grain HAZ (FGHAZ) whereas for inter-critical HAZ (ICHAZ), matrix was ferrite + martensite containing primary carbides. The size and fraction of carbides varied with peak temperature. Presence of boron influenced the microstructural characteristics of different zones by influencing precipitation nature and fractional characteristic of phases. Substantial variation in hardness was obtained before and after post-weld heat treatment (PWHT). In this respect, simulated samples exhibited maximum hardness at CGHAZ and after PWHT the same region showed minimum hardness. Short-term impression creep testing of simulated sub-HAZs was done, which revealed embrittling effect in ICHAZ, whereas embrittlement shifted to CGHAZ after PWHT. Based on conventional nomenclature for weldment failures, it is confirmed that PWHT shifted type-IV failure (ICHAZ) to type-III failure (CGHAZ) in boron modified P91 steel.

The microstructure of the Al–0.3Sn–0.3Cu alloy and Al–0.3Sn–0.3Cu–0.15Zr alloy has been examined by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), the mechanical properties have been evaluated by the tensile strength and microhardness tests. After addition of Zr, fine Al₃Zr precipitates provide a core for Sn during the solidification process; at the same time, Sn plays an important role in the distribution of θ(Al₂Cu) phase. These reasons lead to demixing of the β(Sn) phase and Al₂Cu phase obviously during the extrusion. Under the joint action of Al₃Zr and Sn, the Sn–θ(Al₂Cu) quasi-binary phase is distributed in the matrix uniformly. The Al₃Zr particles hinder the dislocation slip, make the intermediate subboundaries keep a stable state, and enhance the recrystallization resistance. Based on these reasons, the mechanical properties of the Al–0.3Sn–0.3Cu–0.15Zr alloy have been significantly improved.

The excess volume of edge dislocations and their pileups has been calculated within the framework of the nonlinear theory of irreversible deformations. It has been shown that the existence of a free volume at dislocations is the consequence of the asymmetry of a change in the energy of crystal lattice with respect to the tension or compression. It has been established that the influence of pressure on the plasticity of metals is determined by the value of the excess volume of the major carriers of plastic deformation entering into the defective subsystem of materials. The influence of the excess volume of dislocations on the processes of self-diffusion along the dislocation lines has been examined.