Effect of crystallization conditions of pulse die forging on structure formation in TiAl-and Ti3Al-base alloys

The structure and properties of alloys based on TiAl and Ti₃Al titanium aluminides obtained by the method of pulse die forging are studied. It is shown that the content of aluminum and the changes in the structural factors (the grain size and the width of Ti₃Al lamellas) that control the strength characteristics of TiAl-base alloys with lamellar structure are correlated.     

Chemical Processes During Energy‐Saving Preparation of Lightweight Ceramics

Lightweight glass‐ceramic material similar to foam glass was obtained at 700°C–800°C directly from alkali‐activated silica clay and zeolitized tuff without preliminary glass preparation. It was characterized by low bulk density of 100–250 kg/m³ and high pore size homogeneity. Chemical processes occurring in alkali‐activated silica clay and zeolitized tuff were studied using X‐ray diffraction, thermal gravimetry, IR‐spectroscopy, and scanning electron microscopy. Pore formation in both compositions is caused by dehydration of hydrated sodium polysilicates (Na₂O·mSiO₂·nH₂O), formed during alkali activation. Additional pore‐forming gas source in alkali‐activated zeolitized tuff is trona, Na₃(CO₃)(HCO₃)·2H₂O, formed during interaction between unbound NaOH and CO₂ and H₂O from air. Influence of mechanical activation of raw materials on chemical processes occurring in alkaline compositions was also studied.     

A layer radiowave absorber based on double-period lattices of resistive squares

A radiowave-absorbing composite material based on double-period lattices of resistive squares is considered. Methods of the electric circuit and long line theories are applied to obtain expressions for the estimate of the effective permittivity of such a composite. It is shown that the frequency dependence of the effective permittivity of the realized composite is close to the relaxation value. The reflection characteristics of a radiowave absorber based on a composite with double-period lattices of resistive squares are investigated. It is found that, for such a radiowave absorber, the ratio of the difference of the extreme wavelengths of its operating band (corresponding to the minus-10-dB reflection level) to the thickness of the radiowave absorber is within an interval of 4.2–4.5.     

The structure and magnetic properties of a heat-resistant nickel-base alloy after a high-temperature deformation

The structure of a turbine blade made of the ChS-70V alloy has been studied after operation in an experimental regime at 880°C. A considerable change in the structural state of the alloy indicates the presence of an extremely high level of stresses in the material. During the operation, the magnetic susceptibility of the alloy increases by two orders of magnitude. The possible structure objects responsible for a change in the magnetic susceptibility are the complexes of superstructure intrinsic stacking faults inside the intermetallic phase.     

Enhancement of magnetic losses in hybrid polymer composites with MnZn-ferrite and conductive fillers

Polymer composites (PCs) with a polyurethane (PU) matrix filled with magnetic filler (MnZn ferrite) and hybrid polymer composites (HPCs) consisting of this magnetic filler and various types of conductive fillers (carbon black, carbon fibers, aluminum powder, polypyrrole) are prepared. The matrix structure of a HPC is formed (i) by a polymer filled with conductive filler, which forms the skeleton of an infinite cluster, and (ii) by ferrite particles that are larger than conductive particles. Thus, an HPC represents an ensemble of ferrite particles each of which is surrounded by a conductive medium and can be considered as a “core–shell” structure. The development of a core–shell structure is evidenced by the lower electric percolation threshold in an HPC compared with that in PU filled with conductive filler. Magnetic and dielectric spectra of PCs and HPCs are studied in the frequency range from 1 MHz to 10 GHz. Hybrid systems exhibit a considerable enhancement of magnetic losses compared with PCs. The enhancement of magnetic losses in HPCs is due to the conduction currents that are induced in the conductive shell by a microwave magnetic field.     

A random telegraph signal in tunneling silicon p–n junctions with GeSi nanoislands

Technical Physics Letters - We have experimentally discovered random telegraph signal generation in tunneling silicon p +–n + junctions with embedded self-assembled GeSi nanoislands. The...     

Use of mechanoactivation for obtaining hydrides of titanium aluminides

The hydrogen storage capacity of titanium aluminides Ti(Al,Nb) (β₀) and Ti₃ (Al,Nb) (α₂) subjected to mechanoactivation has been investigated. It has been found that the mechanoactivation in a hydrogen atmosphere makes it possible to obtain hydrides of titanium aluminides with a hydrogen concentration of up to 1.8 wt % at room temperature without enhanced requirements for purity and pressure of the supplied hydrogen. The release of hydrogen from such samples in a vacuum begins at a temperature of about 175°C.