Vol 125, No 7 (2024)

The remagnetization mechanisms of finite-length ferromagnetic cobalt atomic chains at the Pt(664) surface have been investigated. It has been found that the remagnetization of short chains occurs due to the simultaneous flipping of all magnetic moments. At longer chain lengths, remagnetization occurs through the formation of a Neel-type anti-clockwise domain wall. The remagnetization of long chains can be achieved through both the formation of anti-clockwise and clockwise domain walls. The energy barriers for remagnetization of atomic chains with lengths ranging from 5 to 100 atoms have been calculated using the geodesic nudged elastic band method. In the framework of the harmonic approximation of the transition state theory, frequency prefactors have been calculated. A non-monotonic and sufficiently strong dependence of the frequency prefactors on both the chain length and an external magnetic field has been identified. The magnetization curves of Co atomic chains have been constructed, and the residual magnetization values and coercive force of the chains have been determined. The dependences of the coercive force on the chain length, temperature, and remagnetization rate of the magnetic field have been analyzed.

The microtexture and microstructure of the industrial Ti–6Al–4V alloy almost in the single-phase α state, obtained using the thermomechanical treatment including the hot rolling, are studied by the X-ray diffraction analysis method and optical and transmission and scanning electron microscopy. It is established that the layered fine-grained microstructure in the cross section of the plate perpendicular to the rolling direction is characterized by selection of equiaxed globular α grains that obey Burgers orientation relationships and twinning orientations. The revealed distributions of α grains over dimensions and crystallographic orientations in the plate’s cross section are related to the peculiarities of distributions established for the plane of plate rolling. The structural mechanisms of generating the microtexture regions in the alloy are discussed.

Methods of transmission and scanning electron microscopy are used to study premartenstic states and their relation to martensitic transformations in the alloys Cu–38 wt% Zn and Cu–39.5 wt% Zn with shape memory effect. Analysis of the observed diffusion scattering of electrons is carried out, including in situ experiments at heating and cooling and the defect condition of the internal substructure of austenite and martensite. The crystallographic models of martensitic transitions β2 →β2′, β2 →β2′′, and β2 →γ2′ are proposed based on the crystallographic data obtained in the premartensitic state.

Short-range order in soft magnetic FeGa alloys containing from 3 to 25 at% Ga was studied using nuclear gamma resonance (Mossbauer) spectroscopy. The Mossbauer spectra were analyzed via fitting with subspectra corresponding to different configurations of the neighborhoods of the Fe atoms with Ga in the first and second coordination shells. It has been shown that in samples of alloys containing from 3 to 17 at% gallium, the short-range order is almost independent of the heat treatment conditions (quenching from a paramagnetic state or exposure in a ferromagnetic state) and is characterized by the presence of pairs of Ga atoms in the position of the second neighbors (B2-type clusters). At a Ga content of 17 to 21 at%, the portion of B2 clusters turns out to be significantly higher after quenching than after annealing, which correlates with the observed effect of heat treatment on the magnitude of magnetostriction. As the Ga concentration (21–25 at%) further increases, the observed features in the distribution of Ga atoms indicate the appearance and growth of D03 phase regions.

This paper presents a review of studies on pearlite, the most important structural constituent of carbon and low-alloy steels. It mainly focuses on the fine structure of pearlite revealed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Additionally, the paper highlights the key areas for future exploration to better understand the pearlite transformation in steels and the response of ferrite-cementite mixtures to different external loading conditions.

Al and its alloys have a wide range of applications thanks to their low density, cost, and superior specific strength. Especially Al–Cu matrix composites are promising alloys with superior microstructural and mechanical performance. Thanks to the formation of the intermetallic due to the contained Cu, they significantly improve the properties of their Al-based alloys. In this study, Pure aluminum reinforced mainly with Cu and SiC and ZrO₂ oxide and carbide-based ceramic particles were prepared by powder metallurgy. Three different values were determined for the Al–Cu content of the compositions, and these were produced in tube furnaces at 380°C and 580°C for 4 hours under an inert atmosphere using liquid phase sintering. According to the data of SEM and EDS analyses, microstructures formed in all samples were homogeneous. It was found that increasing sintering temperature increased microstructural densification. Adding mainly Cu and ceramic reinforcements to the microstructure significantly improved the hardness up to 2.05 times. Due to their intermetallic formation, the highest hardness values were determined in the samples containing high amounts of Cu, such as 173.73 HV. In the wear tests, it was observed that the samples sintered at high temperatures showed superior tribological performance. Also, the high Cu content improved the samples' friction behavior (COF). Since the increasing Cu content enhances intermetallic formation, superior wear resistance was observed in the samples containing a high amount of Cu sintered at higher temperatures up to 1.59 and 5.94 times. Optimum production parameters and chemical compositions were determined per the tests performed.