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Introduction/Objective. The objective was to determine the degree of conversion (DC), cross-link density, percentage of leachable monomers, flexural strength (FS), and hardness (HV) of nanohybrid, nanofilled bulk-fill, giomer, fiber-reinforced, and low-shrinkage composites. Methods. Standardized specimens (n = 5/group) of Tetric EvoCeram Bulk Fill, Filtek Bulk Fill, Beautifil, EverX posterior, Kalore, Filtek Z250 (microhybrid control), and Tetric EvoCeram (nanohybrid control) were subjected to micro-Raman spectroscopy, three-point bending, and HV. Cross-linking density and leachable monomers were ascertained based on the ratio of HV and DC before and after immersion in absolute ethanol. Results. DC was in the range 50.4?70.5%, the highest for Filtek Bulk and the lowest for Kalore. The highest %DC change was in Beautifil (10.3%) and the lowest in Filtek Bulk (1.4%) and Z250 (1.28%). FS ranged between 78.9 MPa (TEC) and 126.7 MPa (Filtek Bulk). HV ranged between 58.6 (Kalore) and 113.9 (Z250) and significantly decreased post-immersion (19?55%). HV48h inversely correlated to HV% loss (r = -0.761), whilst DC positively correlated with FS (r = 0.893). Conclusion. Filtek Bulk, EverX, and Z250 showed the highest DC. The lowest DC and mechanical properties were observed for Kalore. The greatest cross-link density was shown by Filtek Bulk. There were up to 10% of leachable monomers. DC and FS positively correlated.

Metal matrix composites (MMCs) belong to a group of modern materials owing to their excellent technological, mechanical, and physical properties such as excellent wear and corrosion resistance, high electrical and thermal conductivity, improved strength and hardness. Final properties of MMCs are affected equally by all steps of its manufacturing process. It is shown that by using adequate process parameters to obtain starting materials (reaching the specific size, shape, and reactivity) the control of volume fraction and distribution of reinforcements within the matrix can be achieved. For this purpose, mechanical alloying has been appointed as a good approach. MMCs can be produced using powder metallurgy, ingot metallurgy, and additive manufacturing techniques. Combining high-energy ball milling with these techniques enables the design of an innovative processing route for MMCs manufacturing. Mechanochemical process (achieved using high-energy ball milling) was employed in three manufacturing procedures: hot pressing, compocasting, and laser melting/sintering for obtaining of the suitable powder. These production routes for MMCs manufacturing were the subject of this work. The aim of MMCs design is to establish an optimal combination of production techniques merged into the cost-effective fabrication route for obtaining MMCs with required properties. © 2021, Association of Metallurgical Engineers of Serbia. All rights reserved.

A titanium alloy with 12 mass% molybdenum was produced using the cold crucible levitation melting technique. By varying the process parameters, microstructures with and without Mo segregation could be obtained. The effects of Mo segregation and ω-phase precipitation on the mechanical properties of the β-type Ti-12 mass% Mo alloy were investigated through nanoindentation measurements. The homogeneous precipitation of an isothermal ω-phase occurred in the samples without Mo segregation, while denser ω-precipitates were detected in the Mo-lean regions of the heterogeneous microstructure. Microstructural examination of ingots was done by X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD). The obtained results revealed the presence of bright and dark stripes in the heterogeneous microstructure; these corresponded to the Mo-rich and Mo-lean regions, respectively. A comprehensive analysis of Mo heterogeneity in the Ti-12Mo alloy suggested that Mo segregation had a significant effect on the mechanical properties as well as the distribution of the ω-phase within the grains. The regions with higher Mo contents (and lower amounts of the ω-precipitates) exhibited the lowest hardness and elastic modulus values. Similarly, the indentation marks made within the β-grains oriented almost along the direction were characterised by lower elastic modulus values and in most cases, were followed by the formation of higher pile-ups (as compared to those corresponding to the indents made within grains with an orientation close to the direction).

Copper-based alloys and composites, owing to their convenient properties, are being considered essential materials in various industries. Since copper possesses an ability to develop high corrosion resistance, putting it in the domain of a desirable material in the manufacturing of valves, pipes, and also systems that carry industrial gases and aqueous fluids. Its usage is also invaluable for cables and electrical wires. This review paper describes diversity in copper alloy processing techniques (powder and ingot metallurgy) which are alongside the phase transformation kinetics interpreted and explained in detail. Furthermore, the focus is put on the copper alloys, as well as the kinetics present in these systems, with the application being highlighted. Correlation between physical properties and phase transformation kinetics in copper alloys is made. It is shown that if certain alloying elements are to be added, different properties could be improved. The effect of phase precipitation on phase transformation kinetics of copper alloys is shown by studying the Cu–15Ni–8Sn alloy.

Copper matrix composite materials have exhibited a high potential in applications where excellent conductivity and mechanical properties are required. In this study, the machine learning models have been applied to predict the hardness of the copper matrix composite materials (CuMCs) produced via the powder metallurgy technique. Six different machine learning regression models were employed. The observed CuMCs were reinforced with two different volume fractions (2 vol.% and 7vol.%) of ZrB2 particles. Based on experimental work, we extracted the independent variables (features) like the milling time (MT, Hours), dislocation density (DD, m-2), average particle size (PS, μm), density (ρ, g/cm3), and yield stress (σ, MPa) while the Vickers hardness (MPa) was used as the dependent variable. Feature selection was performed by calculation the Pearson correlation coefficient (PCC) between the independent and dependent variables. The predictive accuracy higher than 80% was achieved for Cu-7vol.% ZrB2 and lower for the Cu-2vol.% ZrB2.

High-temperature nanoindentation measurements were employed to reveal the fundamental deformation behavior of γ and γ′ single-phase in nickel-based superalloy at various temperatures. The single-crystal samples of each phase with the equilibrium chemical compositions as in the conventionally utilized alloy were used to elucidate the temperature-dependent behavior of the individual phase leading to a further interpretation of each phase effect in the intensively used dual-phase alloy. Nanoindentation tests were conducted at room and elevated temperatures on the γ and γ′ single-phase using the Berkovich diamond indenter probe, and the Hysitron's xSol800 high-temperature stage. The noiseless load-displacement curves were obtained owing to thermal stability up to 1073 K and 873 K on the γ and γ′ sample, respectively. Furthermore, load-displacement curve shows a clear plasticity initiation in a strain burst as “pop-in” on a loading segment. The number of pop-in events in load-displacement curves of both, the γ and γ′ samples, increases with temperature. The elastic modulus and hardness of the γ phase decrease as the temperature increases, while the γ′ phase demonstrates thermal stability up to 573 K, indicating the γ′ phase domination for the high-temperature property in the dual-phase alloy. At small-scale mechanical property measurements no inverse temperature dependence of hardness was detected for the γ′ phase as a consequence of the multi-axial stress state with high hydrostatic pressure. Further, real-time topographical observations of the surface with increasing temperature reflect the behaviors of slip deformation and oxidation evolution.

The possibility to use natural zeolite - clinoptilolite as a host material for radioactive Cs immobilization has been investigated. Cs-exchanged form of clinoptilolite which was prepared by treatment of clinoptilolite powder with 0.25 M CsCl solution was compacted. Both, powder and powder compact of exchanged clinoptilolite were thermally treated at 1200°C. The XRPD analysis showed that Cs was successfully immobilized after heat treatment by formation of stable cesium dodecaoxo-alumopentasilicate in both, powder sample and compact. The newly formed compound showed satisfactory Cs ions retention during leaching test. The sintered compact showed somewhat better resistance to Cs leaching than the thermally treated powder. The compressive strength of sintered compact was close to 200 MPa which is more than enough for easy handling and safe storage. [Projekat Ministarstva nauke Republike Srbije, br. 45012]

The present work demonstrates a procedure for synthesis of stainless steel powder by gravity sintering method. As an additive to the basic powder, NiB powder was added in the amount of 0.2 - 1.0 wt.%. Gravity sintering was done in vacuum, at the temperatures of 1100°C-1250°C, in the course of 3 - 60 min, using ceramic mould. Structural characterization was conducted by XRD, and microstructural analysis by optical and scanning electron microscope (SEM). Mechanical properties were investigated by tensile tests with steel rings. Density and permeability were determined by standard techniques for porous samples. Gravity sintered stainless steel with NiB addition had more superior mechanical and physico-chemical properties compared to stainless steel obtained by standard powder metallurgy procedures - pressing and sintering. [Projekat Ministarstva nauke Republike Srbije, br. 172005]

The copper alloy with 7vol.% ZrB2 examined in this study was consolidated via powder metallurgy processing (PM) by combining mechanical alloying and hot pressing process. Structural changes, morphological properties and elemental analysis of the hotpressed samples were studied as a function of milling time with the use of X-ray diffraction, scanning electron microscopy (SEM) equipped with an energy dispersive X-ray spectrometry (EDS). Also, mechanical properties of the Cu-7vol.%ZrB2 alloy was investigated. Distribution of ZrB2 particles and presence of agglomerates in the Cu matrix directly depend on the milling time and show strong influence on hardness, compressive and electrical properties of Cu-ZrB2 alloys. [Projekat Ministarstva nauke Republike Srbije, br. 172005]

Biomorphous beta-SiC ceramics were produced from several species of wood such as ash, wild cherry, black alder, Persian walnut, sessile oak and European hornbeam. The wood was pyrolysed, impregnated with tetraethyl orthosilicate (TEOS) sol in repeated cycles and thermally treated at 1800 degrees C in vacuum. Four specimen groups included charcoal and three groups with 1, 3 and 5 cycles of impregnation were analyzed. Flexural and compressional strength of charcoal and woodlike SiC ceramics were measured using three-point and compression testing in different directions. Experimental results showed that mechanical properties of woodceramics were improved by repeating of impregnation cycles. Porosity measurement, dilatometric analysis, XRD and SEM analysis were used to study the macroscopical and microscopical properties of the resulting biomorphic SiC ceramics. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.