International Scientific Journals
of Scientific Technical Union of Mechanical Engineering "Industry 4.0"

This study investigates the mechanisms of liquid-phase assisted sintering in high-entropy ceramics (HECs) using a nickel binder. The research focuses on the densification process of (Ti, Zr, Hf, Nb, Ta)C-based cermets with 10 vol% Ni, and how pressure influence liquid-phase extraction. Results show that eutectic reactions between Ni and carbide phases was observed during liquid formation below 1400°C. Microstructural analysis reveals a nickel-rich matrix, solid solutions, and NbC-based carbide inclusions in the extracted drop. These findings provide insights into optimizing processing parameters for advanced HEC-based composites.

The work aimed to evaluate the effect of microalloying titanium in proportions of 1 to 5 wt.% on the microstructure and microhardness of a precipitation-hardenable martensitic stainless steel. The standard chemical composition of martensitic steel 17-4PH was used, to which 1; 2; 3; 4 and 5 wt.% Ti was added, respectively. Microstructural analyses revealed changes in the crystal grains and precipitation effects from the solid solution of the alloy. Microhardness measurements were also performed, which demonstrated that withincreasing Ti content in the alloy the metallic matrix becomes harder. The study confirms that microalloying with Ti is beneficial for the development of martensitic stainless steels to increase mechanical properties, even without the application of subsequent heat treatments.
The results obtained in this work represent a starting point for the development of new customized alloy recipes, adapted to specific applications, where a high value of hardness, as well as microstructural stability or wear resistance are required.

The contact interaction between the metal matrix composite based on Ti64 and the B4C-based composite was investigated. It is shown that the interaction process is influenced by the annealing temperature and holding time. The phase that formed independently of the contact pair is TiB. However, the thickness of the products formed at the boundary depends on the contact pair. In case of the Ti64-B4C pair the thickness is 70 μm, while for (Ti64-40 wt% TiC)-B4C it becomes 10 μm. This significant difference in the thickness is due to the presence of refractory particles (TiC) in (Ti64-40 wt% TiC)-B4C couple, because the TiC phse reduce the diffusion of Ti into the contact zone.

Titanium–titanium boride (Ti/TiC) metal matrix composites have been widely identified as promising materials for various applications. The traditional ingot metallurgy processing strategies used to fabricate these materials are energy intensive and have fallen short of their perceived mass production potentials. Powder metallurgy processing of Ti/TiC composites from titanium and TiC powder blends, is currently widely used for the cost-efficient production of such composites. Additional processing by the method of hot pressing improves the structure and mechanical properties of this class of materials. The composites have the heterogenous microstructure with areas high hardness area over 1173 HV. While matrix and inclusions had the value of 700 HV.

The article presents the results of research aimed at assessing the quality of forgings depending on the forging parameters used. The forging and subsequent heat treatment processes revealed the occurrence of cracks in the forgings. The article examines the possible causes of cracks, which can be caused by carburizing annealing and loss of plasticity during stress relaxation. Tool wear and damage during forging also affect the formation of cracks. These factors were identified as key factors contributing to the formation of non-metallic oxide inclusions, the transfer of surface defects and the formation of lamellar propagation during subsequent heat treatment. The findings highlight the influence of tool conditions and process parameters on the quality and reliability of steel forgings..

This work is devoted to the study of a new technology for processing bar scrap – a precision shaft made of Cf53 structural steel (DIN 17212) that has proven its service life and produces high-quality finished metal products in the form of a screw reinforcement profile. The precision shaft used for recycling of its proven service life included two stages: preliminary deformation of the shaft on a radial shear rolling mill to obtain rods of the required diameter and create initial conditions for the formation of a gradient ultrafine-grained structure in the resulting screw profile; direct production of a screw profile with a gradient ultrafine-grained structure on a combined installation. The conducted research has shown that the new combined technological process of rolling bar scrap is feasible in practice and makes it possible to obtain a high-quality finished product from this scrap in the form of a screw reinforcement profile with a gradient ultrafine-grained structure.

Lithium disilicate glass-ceramic is one of the most commonly used aesthetic materials in fixed prosthetics that requires surface pre-treatment. Recent studies have begun to propose a femtosecond laser for processing to improve surface morphology and microstructure, but without defined parameters. Therefore, the aim of this study is to determine the optimal parameters for the surface morphology of lithium disilicate glass-ceramics. The untreated sample of lithium disilicate glass-ceramic was observed with an optical profilometer. It was then treated with a femtosecond laser, forming squares on the surface of the sample, which were observed with an optical profilometer, and the surface morphology was analysed with a scanning electron microscope. The results show that laser treatment with higher energy densities leads to an increased roughness of the surface.

The study concerns cooling curves of AlSi9Cu3(Fe) alloy, into which iron (in the form of Al-Fe master alloy – as a substitute for scrap) was introduced with a content of 0.5 to 1.5wt.%. Crystallization analysis by ATD and microstructure studies of Al-Si-Mg(Fe) alloys revealed that up to approximately 0.4wt.% Fe, the formation of iron phases does not significantly affect the microstructure. They are part of multicomponent eutectics such as α(Al)+(Al2Cu,Fe)+β(Si) or α(Al)+(AlXFe;CuYSiZ)+β(Si), which crystallize after the formation of the α(Al)+β(Si) eutectic. In the range of about 0.5wt.%Fe to 0.9wt.%Fe, there is a pre-eutectic crystallization of iron phases, mainly the lamellar-neutectic phase β-Al5FeSi. At more than 1.0wt.%Fe, the morphology of this phase becomes even more unfavorable (due to primary crystallization) and is accompanied by numerous clusters of shrinkage porosity. Such a microstructure has an adverse effect on mechanical properties, primarily affecting plastic properties (yield strength and elongation). To prevent this, the positive impact of manganese additive (in the form of AlMn20 master alloy) was found to transform the morphologically unfavorable β-Al5FeSi phase into α-Al15(Fe,Mn)3Si2 phase with dendritic structure.

Abstract. The structure and some properties of magnetostrictive powder materials of the Fe .Ga and .Fe-(Ga+Al) systems, obtained by sintering at a temperature of 1150 oC in a neutral Ar environment for 1 h, were studied. The structure and phase composition of the obtained materials were studied. Mechanical tests of the samples were carried out, corrosion resistance was determined and magnetostrictive properties of samples of the composition Fe-Ga and Fe-1.7Al-19.3Ga were evaluated as the most promising for use as magnetostrictive materials. An increase in hardness and level of compressive strength of the material of the composition Fe-1.7Al-19.3Ga compared to materials of the composition Fe-21.4Ga was revealed. In terms of corrosion resistance, these materials are corrosion-resistant materials (3-4 points on a 10-point scale of corrosion resistance). The highest level of magnetostriction is possessed by materials of the dual composition Fe 21.5 wt.%Ga (>210 ppm). The material with the composition Fe 19.3 wt. % Ga-1.75 wt. % Al, which had a lower level of compressive elasticity, also differed in a lower value of magnetostriction (130 ppm). The level of magnetostriction of the studied materials is within the requirements for commercial deformed Fe-Ga alloys (galfenols).

New types of materials have been developed for years, including titanium-based alloys, which have the potential for various applications. Due to the combination of their very good mechanical properties with outstanding corrosion resistance and excellent biocompatibility, titanium alloys are developing into materials that can be used in aerospace, automotive, energy systems and especially in medicine. A fundamental understanding of the phase transformations that occur at high temperatures in all these cases, especially during cooling from elevated temperatures, is necessary to achieve optimal mechanical properties of titanium alloys. It is known that the mechanical properties of titanium alloys depend on a significant extent upon the microstructure. Therefore, it is very important to understand the nature of the phase transformations that occur under different heat treatment conditions the leads to microstructure development of titanium alloys microstructure. The aim of this article is to review the current state of knowledge and previous research and to point out some of the most interesting phase transformations of titanium alloys.

In this study, the tribological behavior of new generation cast irons (SiNb and SiW) developed as an alternative to cast irons containing high silicon and molybdenum (SiMo) is investigated under dry friction conditions. All cast irons are produced by sand mold casting as Y blocks according to ASTM A536-84 standard and metallurgical characterization studies have revealed that they all have spheroidal graphite and dispersed carbides like Mo-rich M6C, Nb-rich MC and W-rich M6C type depending on the alloying element, within a ferritic matrix. Although no significant change is observed in the spherical morphology of graphite in cast iron matrices, a significant change is observed in the amount of graphite and image analysis studies reveal that the graphite content (area-%) in SiNb and SiW cast irons is 4,02 and 4,30, respectively, compared to SiMo cast iron (5,80). A significant change in the hardness of cast irons is also determined depending on the microstructural features; SiNb (228 ± 7 HV10) and SiW (218 ± 5 HV10) cast irons have higher hardness values compared to SiMo cast iron (192 ± 5 HV10). Cast irons and alumina ball as counterpart material are subjected to a tribological interaction for 150 m under dry friction conditions at a nominal load of 10 N and a ball sliding speed of 0.08 m/s and the findings indicate that (i) the coefficient of friction (CoF) decreases as the graphite content increases, with SiMo having the lowest CoF (0.023), followed by SiW (0.025), and SiNb showing the highest CoF (0.040), (ii) the specific wear rate increases as the hardness decreases, therefore, SiMo has the highest specific wear rate, whereas SiNb demonstrates the lowest specific wear rate and (iii) adhesive wear is the dominant wear mechanism for all ductile cast irons due to the presence of their ferritic matrix.

The main reason to perform this research investigation was to find a reason for appearing failures in exploratory condition of a part holder of breaking shoe beam. This part is incorporated in an assembly in railway wagon. This part together with few others was damaged in exploratory condition. It means that cracks were noticed on these parts. Some parts were completely broken. Because of that purchaser of parts complained of received parts to the producer. One of these parts was delivered to Prof Cvetkovski to find a reason and to give opinion about the reason for failure. The damaged parts are made of cast steel SG60/SE300. Many types of investigation was performed in order to solve this problem. As first visual control was done. After that, radiographic control was made. Investigations continued with determination of chemical composition and macro and micro metallography and determination of non-metallic inclusions. Finally mechanical testing like tensile testing, hardness measurement and impact toughness were performed too. Performed research confirmed that typical casting defects in the investigated part like the hot tears, slag inclusions, shrinkage porosity and segregation are the main reasons for failure of the delivered parts, holder of breaking shoes i.e. appearing of cracks or their completely fracture.