Ivana Marković

In the present study, the Sn78Bi22 alloy was investigated as a potential solder material. The study focused on the evaluation of thermal diffusivity and thermal conductivity over a defined temperature range, differential scanning calorimetry (DSC) analysis, and an assessment of soldering behavior through measurements of contact angle, spreading area, spreading ratio, and intermetallic compound (IMC) layer thickness. The investigated alloy exhibited reduced thermal diffusivity and thermal conductivity compared with literature data for pure Sn. DSC analysis indicated a decrease in melting temperature compared with pure Sn reported in the literature, resulting from the addition of Bi. Soldering behavior was evaluated as favorable, characterized by a thin IMC layer, a low contact angle on a Cu substrate, and high spreading ratio and spreading area. Based on these results, the Sn78Bi22 alloy shows potential for lead-free soldering applications.

The present work investigates the effect of Ni and Si additions on functional properties of Cu-30Zn brass. One base alloy without Ni and Si additions and one alloy with Ni and Si additions were prepared by conventional casting from high-purity Cu, Zn, Ni and Si, followed by solution annealing at 900 °C for 2 h and water quenching, cold pressing, and subsequent ageing at 300 °C for 8 h. Building on earlier studies of Ni₂Si-strengthened Cu-Zn and Cu-Ni-Si alloys, this processing route was selected to promote the formation of fine Ni-Si-rich precipitates within an α-brass matrix and to combine solid-solution and precipitation strengthening with acceptable electrical and thermal conductivities. The heat-treated alloys were characterized by measurements of electrical conductivity, Vickers microhardness (HV0.15), Leeb hardness (HLD) and thermal conductivity. Increasing Ni and Si contents is expected to raise hardness through solid-solution and Ni₂Si-type precipitation strengthening, while moderately reducing conductivity due to enhanced electron scattering by solute atoms and nanoscale particles. The results of this study provide composition-property guidelines for designing lead-free, precipitation-strengthened brasses based on the Cu-30Zn system.

The development of reliable lead-free solder alloys remains essential for applications in the electronics industry. This paper investigates the mechanical, electrical, and microstructural properties of a Sn78Bi22 solder alloy. The alloy was prepared by melting and casting, followed by a homogenization heat treatment. Tensile testing, Vickers microhardness measurements, electrical conductivity testing, and SEM/EDS microstructural analysis were performed at room temperature. The investigated alloy exhibited enhanced ultimate tensile strength (~93 MPa) and microhardness (45.5 HV0.05) compared with pure Sn, while electrical conductivity decreased to 5.4 MS/m. These changes were attributed to solid-solution strengthening, grain refinement, and the formation of a Bi-rich secondary phase, which also promoted brittle fracture during tensile testing. Microstructural observations revealed a Sn matrix with finely distributed Bi-rich phases, particularly along grain boundaries. The results contribute additional experimental data on the mechanical, electrical, and microstructural characteristics of non-eutectic Sn-Bi solder alloys.

The increasing demand for environmentally friendly electronic materials has encouraged the development of lead-free solder alloys and sustainable production technologies. Despite numerous alternatives, the eutectic Sn-0.7Cu alloy has been recognized as a promising candidate for lead-free solder applications due to its low cost, acceptable mechanical properties, and compliance with RoHS and WEEE regulations. This study investigates the effect of graphene nanoparticles, in the form of graphene nanosheets (GNS), on the microstructural and mechanical properties of Sn-0.7Cu matrix composites produced via powder metallurgy. GNS was incorporated into the matrix in small weight fractions (0, 0.02, 0.04, 0.06, 0.08, and 0.10 wt.%) to promote microstructural refinement and enhance the mechanical properties of the composites. Optical microscopy was used to characterize the microstructure of the sintered samples, while microhardness was measured using the Vickers method. The results indicate that increasing the graphene content significantly refines the grains, reducing the average grain size by approximately 54 % and increasing the microhardness by about 16 % compared to the base alloy.

Ternary alloys of the Sn-Ag-Cu (SAC) system represent one of the most widely used lead-free solder materials due to their favorable mechanical properties and compliance with environmental regulations aimed at eliminating toxic lead from electronic components. Among these alloys, SAC338 (Sn-3.3Ag-0.8Cu) is recognized as one of the most promising alternatives to conventional Sn-Pb solders. Despite their ecological advantages, SAC alloys still exhibit challenges associated with the growth of intermetallic compounds and microstructural instability. The aim of this study was to investigate the influence of graphene nanosheet (GNS) additions on the microstructural properties of SAC composite. SAC composite containing up to 0.09 wt.% GNS were produced using powder metallurgy procedures. The results showed that the addition of GNS contributed to a more homogeneous microstructure and refinement of intermetallic phases such as Cu6Sn5 and Ag3Sn. The addition of GNS improves the wettability of the composite solder by reducing the wetting angle, which enables better spreading of the molten solder and improves the quality of solder joints. From an environmental perspective, these improvements contribute to enhanced durability and longer service life of electronic components, leading to reduced material consumption, lower maintenance frequency, and decreased generation of electronic waste.

In this study, various contents of graphene nanosheets (GNS) were successfully incorporated into Sn-0.7Cu base alloy by powder metallurgy (PM) technique to form Sn-0.7Cu-xGNS composite materials. The synthesis process included mixing and mechanical alloying, compacting and sintering. The effects of GNS on the microstructure, wettability, microhardness and melting properties were investigated. Optical and scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS) revealed that the distribution of GNS in the solder matrix became more evident as the content of GNS increased. The reinforcement particles were homogeneously distributed at the grain boundaries, resulting in a finer β-Sn structure. The melting temperatures of the synthesized composites, determined by differential scanning calorimetry (DSC), are slightly higher than those of the Sn-0.7Cu base alloy. Incorporating GNS into the Sn-0.7Cu matrix enhanced microhardness up to 15.65% and reduced the contact angle between the composite solder and copper substrate up to 48.6%, significantly improving wettability.

This paper focuses on the investigation of thermal and electrical properties of copper alloys produced at Copper Mill Sevojno. The investigated copper alloys include high-purity copper (Cu-DHP) and a series of brass alloys with different zinc content (CuZn15, CuZn28, CuZn30, CuZn37). The samples were subjected to different thermomechanical treatments, including annealing at different temperatures and plastic deformation to different degrees, resulting in soft, semi-hard, or hard material states. Measurements of thermal diffusivity, specific heat capacity, and thermal conductivity were carried out in the temperature range from 25 to 400 °C using the light flash method (Discovery Xenon Flash, DXF-500). Differential scanning calorimetry (DSC) was applied to determine thermal characteristics, while electrical conductivity was measured using the “Institut Dr. Förster Sigmatest 2.063” device. The results showed significant differences between the samples, depending on their chemical composition and thermomechanical treatment. For instance, Cu-DHP demonstrated the highest thermal and electrical conductivity, while conductivity for a series of brass alloys decreased with increasing zinc content. The collected data provide a clearer picture of the behavior of these alloys, especially in terms of heat and electrical transport.

The influence of solution and aging treatment on the microstructure and mechanical properties of a low nickel/iron CuAl9Ni3Fe3 alloy were studied using the scanning electron microscope (SEM) and measuring hardness, tensile strength, elongation, and microhardness of the main phases. The alloy exhibits a complex microstructure, consisting of a mixture of the different κ precipitates distributed in α or β/β’ phases, which was significantly dependent on conducted heat treatments. After optimal heat treatment (quenching from 900°C/1 h; aging at 400°C/1 h), the hardness and tensile strength significantly increased compared to an as-cast alloy of approximately 60% and 110%, respectively. The excellent mechanical properties are attributed to the precipitation of the nano κ phase from β’ martensite matrix during aging.

In this study, the emphasis was placed on investigating the influence of various thermomechanical treatment parameters on the mechanical properties and microstructure of S275JR steel. This steel is commonly classified as a non-alloy structural steel. According to the EN 10025-2 standard, it must exhibit a minimum Charpy impact toughness of 27 J at 20 °C. In the experimental part of the study, the steel was subjected to different thermomechanical treatments, and the effects of these parameters on hardness, impact toughness, and microstructure were evaluated. The applied regimes included normalization, quenching, 8% plastic deformation after quenching by cold rolling, and tempering at temperatures ranging from 100 °C to 250 °C for 30 minutes. The primary goal was to determine whether, and under which thermomechanical conditions, the impact toughness decreases below the prescribed limit of 27 J. Normalization eliminated the as-received microstructure and resulted in grain refinement, leading to an increase in both hardness and toughness. Subsequent quenching caused a significant rise in hardness, the formation of martensite, and a pronounced drop in toughness. The introduction of deformation after quenching further reduced toughness, accompanied by a slight increase in hardness. Finally, tempering produced a modest improvement in toughness, raising it above the minimum values required by the standard.