On the basis of dielectric measurements performed in a wide temperature range (173–373 K), a comprehensive analysis of the dielectric and electrical properties of magnetite nanoparticles electrical conduction mechanism of compressed spherical shaped Fe₃O₄ nanoparticles was proposed. The electrical conductivity of Fe₃O₄ nanoparticles was related to two different mechanisms (correlated barrier hopping and non-overlapping small polaron tunneling mechanisms); the transition between them was smooth. Additionally, role of grains and grain boundaries with charge carrier mobility and with observed hopping mechanism was described in detail. It has been confirmed that conductivity dispersion (as a function of frequencies) is closely related to both the long-range mobility (conduction mechanism associated with grain boundaries) and to the short-range mobility (conduction mechanism associated with grains). Calculated electron mobility increases with temperature, which is related to the decreasing value of hopping energy for the tunneling of small polarons. The opposite scenario was observed for the value of electron hopping energy.

This paper presents the evaluation of durability for the material of repair welded joints made from (13HMF) 14MoV6-3 steel after long-term service, and from material in the as-received condition and after long-term service. Microstructure examinations using a scanning electron microscope, hardness measurements and creep tests of the basic material and welded joints of these steels were carried out. These tests enabled the time of further safe service of the examined repair welded joints to be determined in relation to the residual life of the materials. The evaluation of residual life and disposable life, and thus the estimation and determination of the time of safe service, is of great importance for the operation of components beyond the design service life. The obtained test results are part of the materials’ characteristics developed by the Institute for Ferrous Metallurgy for steels and welded joints made from these steels to work under creep conditions.

Alloys based on magnesium are of considerable scientific interest as they have very attractive mechanical and biological properties that could be used to manufacture biodegradable materials for medical applications. Mechanical alloying is a very suitable process to obtain alloys that are normally hard to produce as it allows for solid-state diffusion via highly energetic milling, producing fine powders. Powders obtained by this method can be sintered into nearly net-shape products, moreover, their phase and chemical composition can be specifically tailored. This work aims to investigate the effect of milling time on the density, microstructure, phase composition, and mechanical properties of Mg-Zn-Ca-Pr powders processed by high energy mechanical alloying (HEMA) and consolidated by spark plasma sintering (SPS). Thus, the results of XRD phase analysis, particle size distribution (granulometry), density, mechanical properties, SEM investigation of mechanically alloyed and sintered Mg-Zn-Ca-Pr alloy are presented in this manuscript. The obtained results illustrate how mechanical alloying can be used to produce amorphous and crystalline materials, which can be sintered and demonstrates how the milling time impacts their microstructure, phase composition, and resulting mechanical properties.

This article employed the fused deposition modelling (FDM) method and gas-pressure infiltration to manufacture alumina/AlSi12 composites. Porous ceramic skeletons were prepared by FDM 3D printing of two different alumina powder-filed filaments. The organic component was removed using a combination of solvent and heat debinding, and the materials were then sintered at 1500 °C to complete the process. Thermogravimetric tests and DTA analysis were performed to develop an appropriate degradation and sintering program. Manufactured skeletons were subjected to microstructure analysis, porosity analysis, and bending test. The sintering process produced porous alumina ceramic samples with no residual carbon content. Open porosity could occur due to the binder’s degradation. Liquid metal was infiltrated into the ceramic, efficiently filling any open pores and forming a three-dimensional network of the aluminium phase. The microstructure and characteristics of the fabricated materials were investigated using high-resolution scanning electron microscopy, computer tomography, hardness testing, and bending strength testing. The developed composite materials are characterized by the required structure—low porosity and homogenous distribution of the reinforcing phase, better mechanical properties than their matrix and more than twice as high hardness. Hence, the developed innovative technology of their manufacturing can be used in practice.

Magnesium-based alloys are widely used in the construction of automotive, aviation, and medical applications. The solutions presently used for the production of biodegradable materials are characterized by considerable energy consumption and limitations resulting from the use of different devices and technologies. The proposed material is easier to manufacture due to mechanical alloying (MA). Thanks to the MA process, it is possible to carefully tailor the desired chemical composition and microstructure. There are many parameters that can be modified during synthesis in order to obtain an alloy with the desired microstructure and specific expected alloy properties. The duration of grinding of the alloy, the size and number of balls, and the protective atmosphere have a great influence on the process of mechanical alloying and the properties of the obtained products. So, the aim of this work was to determine the influence of milling time on the phase composition and structure of Mg-based alloy synthesis products. The tested samples were milled for 5, 8, 13, 20, 30, 50, and 70 h. X-ray diffraction analysis (XRD) and scanning electron microscopy studies (SEM) with energy-dispersive spectroscopy (EDS) were performed to obtain the powder morphology and chemical composition of Mg_66−xZn₃₀Ca₄Ag_x (where x = 1, 2) powders. Structure characterization based on the Rietveld refinement and crystallite size determination based on the Williamson–Hall theory of milling products were also carried out.

Sanicro 25 (22Cr25NiWCoCu) is a newly developed austenitic stainless steel used in the boiler pressure superheaters and reheaters with ultra-supercritical high-efficient parameters. The paper presents the results of microstructure testing and secondary phase separation processes after 20,000 h ageing at 700 and 750 °C. In the initial stage of ageing, the precipitation of numerous very small M₂₃C₆ chromium carbides and Laves phase were observed. The long-term ageing related to temperature revealed the existence of secondary phases: M₂₃C₆, MX, NbCrN, Laves phase and σ phase. The test results presented in the paper are part of the developed material characteristics to be used for predicting the service life of the material of components operated under creep conditions.