The presented work considers the influence of the hafnium and molybdenum to zirconium ratio of Ti20Ta20Nb20(HfMo)20-xZrx (where x = 0, 5, 10, 15, 20 at.%) high-entropy alloys in an as-cast state for potential biomedical applications. The current research continues with our previous results of hafnium's and molybdenum's influence on a similar chemical composition. In the presented study, the microstructure, selected mechanical properties, and corrosion resistance were investigated. The phase formation thermodynamical calculations were also applied to predict solid solution formation after solidification. The calculations predicted the presence of multi-phase, body-centred cubic phases, confirmed using X-ray diffraction and scanning electron microscopy. The chemical composition analysis showed the segregation of alloying elements. Microhardness measurements revealed a decrease in microhardness with increased zirconium content in the studied alloys. The corrosion resistance was determined in Ringer's solution to be higher than that of commercially applied biomaterials. The comparison of the obtained results with previously reported data is also presented and discussed in the presented study.

• Klíčová slova
• corrosion resistance, high-entropy alloys, mechanical properties, microstructure, multi-component alloys,
• Publikační typ
• časopisecké články MeSH

Copper generally exhibits high electrical conductivity but has poor mechanical properties. Although alloying can improve the latter characteristic, it usually leads to a decrease in electrical conductivity. To address this issue, a promising approach is to enhance the performance of copper while maintaining high electrical conductivity through optimized deformation processing, which refines the structure and increases mechanical properties. This paper focuses on assessing the effects of rotary swaging, a form of deformation processing, on microstructures and substructures of electroconductive copper bars. This analysis is complemented by experimental measurements of electrical conductivity. The results demonstrate that gradual swaging, i.e., applying different swaging ratios, influences the structure-forming processes and consequently affects the electrical conductivity. The increased electrical conductivity was found to be associated with the elongation of the grains in the direction of the electron movement.

• Klíčová slova
• EBSD, copper, electrical conductivity, microstructure, rotary swaging, texture,
• Publikační typ
• časopisecké články MeSH

This paper deals with a study of additively manufactured (by the Selective Laser Melting, SLM, method) and conventionally produced AISI 316L stainless steel and their comparison. With the intention to enhance the performance of the workpieces, each material was post-processed via hot rotary swaging under a temperature of 900 °C. The samples of each particular material were analysed regarding porosity, microhardness, high cycle fatigue, and microstructure. The obtained data has shown a significant reduction in the residual porosity and the microhardness increase to 310 HV in the sample after the hot rotary swaging. Based on the acquired data, the sample produced via SLM and post-processed by hot rotary swaging featured higher fatigue resistance compared to conventionally produced samples where the stress was set to 540 MPa. The structure of the printed samples changed from the characteristic melting pools to a structure with a lower average grain size accompanied by a decrease of a high fraction of high-angle grain boundaries and higher geometrically necessary dislocation density. Specifically, the grain size decreased from the average diameters of more than 20 µm to 3.9 µm and 4.1 µm for the SLM and conventionally prepared samples, respectively. In addition, the presented research has brought in the material constants of the Hensel-Spittel formula adapted to predict the hot flow stress evolution of the studied steel with respect to its 3D printed state.

• Klíčová slova
• 316L steel, high cycle fatigue, hot compression testing, hot rotary swaging, microstructure, selective laser melting,
• Publikační typ
• časopisecké články MeSH

The constant effort of all metal alloy manufacturing technologies and processes is to improve the resulting quality of the processed part. Not only the metallographic structure of the material is monitored, but also the final quality of the cast surface. In foundry technologies, in addition to the quality of the liquid metal, external influences, such as the behaviour of the mould or core material, significantly affect the cast surface quality. As the core is heated during casting, the resulting dilatations often lead to significant volume changes causing stress foundry defects such as veining, penetration and surface roughness. In the experiment, various amounts of silica sand were replaced with artificial sand and a significant reduction in dilation and pitting of up to 52.9% was observed. An important finding was the effect of the granulometric composition and grain size of the sand on the formation of surface defects from brake thermal stresses. The specific mixture composition can be considered as an effective prevention against the formation of defects instead of using a protective coating.

• Klíčová slova
• CERABEADS, artificial ceramic sands, foundry moulding mixture, silica sands, surface defects, surface roughness, surface structure, thermal expansion, veining,
• Publikační typ
• časopisecké články MeSH

The presented work aimed to investigate the influence of the hafnium/(zirconium and molybdenum) ratio on the microstructure, microhardness and corrosion resistance of Ti20Ta20Nb20(ZrMo)20-xHfx (where x = 0, 5, 10, 15 and 20 at.%) high entropy alloys in an as-cast state produced from elemental powder and obtained via the vacuum arc melting technique. All studied alloys contained only biocompatible elements and were chosen based on the thermodynamical calculations of phase formation predictions after solidification. Thermodynamical calculations predicted the presence of multi-phase, body-centered cubic phases, which were confirmed using X-ray diffraction and scanning electron microscopy. Segregation of alloying elements was recorded using elemental distribution maps. A decrease in microhardness with an increase in hafnium content in the studied alloys was revealed (512-482 HV1). The electrochemical measurements showed that the studied alloys exhibited a high corrosion resistance in a simulated body fluid environment (breakdown potential 4.60-5.50 V vs. SCE).

• Klíčová slova
• corrosion resistance, high entropy alloys, mechanical properties, microstructure, multi-component alloys,
• Publikační typ
• časopisecké články MeSH