One of the prevailing problems for materials produced by powder metallurgy is contamination from various sources. This work deals with the influence of process parameters and presence of process control agents (PCA) on the contamination level of materials produced by means of mechanical alloying (MA) technology, densified with spark plasma sintering (SPS). The equiatomic CoCrFeNi high-entropy alloy (HEA) was manufactured by the said methodology. For clear comparison, the 316L austenitic steel powder was milled and densified with identical conditions as a reference material. Both materials were milled in argon and nitrogen atmospheres for various times from 5 to 30 h. Chemical analysis of contamination by carbon, oxygen, and nitrogen within the powder and bulk materials was carried out using combustion analyzers. The microstructural analysis of powders and bulk samples was carried out using scanning electron microscopy (SEM) with focus on contaminant phases. The results show that carbon contamination increases with milling time. It is caused by wear of milling vial and balls made from high-carbon steels. Increase of carbon content within consolidation using SPS was also observed. The oxygen contamination also increases with milling time. It is more pronounced in the CoCrFeNi alloy due to higher oxidation of powder surfaces prior to milling. Milling of powders using nitrogen atmosphere also causes an increase of nitrogen content in both HEA and AISI 316L. The use of PCA (ethanol) during milling even for a short time (30 min) causes significant increase of carbon and oxygen contamination. The ways to decrease contamination are discussed in the paper.

The work is focused on the preparation of bulk immiscible Cu-Fe-based alloys by powder metallurgy. Three samples with chemical composition Cu70Fe30, Cu70Fe15Co15, and Cu50Fe25Co25 were prepared by mechanical alloying and spark plasma sintering (SPS). Microstructure evolution during sintering and the effect of Co on the resulting microstructure and hardness of the bulk samples were evaluated. Despite the immiscibility of Cu with Fe and Co, the FCC supersaturated solid solution was formed upon mechanical alloying. This supersaturated solid solution was decomposed during SPS and fine microstructure, consisting of separated BCC and FCC phases, was formed. The results showed that cobalt influenced the particle size of milled powders as the particle size of Cu70Fe30 alloy was about an order of magnitude higher compared to other alloys. Cobalt also affected the resulting microstructure of bulk samples, however, its effect on the hardness was negligible. It has been shown that powder metallurgy can be used for the preparation of bulk immiscible alloys with the fine microstructure consists of separate phases, which can be individually alloyed by the selected elements, and therefore, powder metallurgy can be considered as a suitable alternative to the more used casting.

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Eutectic high-entropy alloys (EHEA), also known as multi-principle component alloys (MPCA), are a group of materials exhibiting promising mechanical properties. The principle of the alloy is to achieve sufficient ductility due to the presence of the soft phase and, at the same time, increased strength due to the hard phase. In order for the newly discovered types of materials to be used commercially, it is necessary to verify their behaviour in technological operations such as welding processes. Therefore, the objective of the experiment was to evaluate the heterogeneous welded joint of the AlCoCrFeNi2.1 alloy with commercially used austenitic steel EN 1.4301 by electron beam welding. The parameters used during the process were previously verified on homogeneous joints. Subsequent observations were made by light and electron microscopy supplemented by chemical analysis. The mechanical properties of the formed joint were verified by a Vickers hardness test.

One of the main limitations of laser powder bed fusion technology is the residual stress (RS) introduced into the material by the local heating of the laser beam. RS restricts the processability of some materials and causes shape distortions in the process. Powder bed preheating is a commonly used technique for RS mitigation. Therefore, the objective of this study was to investigate the effect of powder bed preheating in the range of room temperature to 400 °C on RS, macrostructure, microstructure, mechanical properties, and properties of the unfused powder of the nickel-based superalloy Inconel 939. The effect of base plate preheating on RS was determined by an indirect method using deformation of the bridge-shaped specimens. Inconel 939 behaved differently than titanium and aluminum alloys when preheated at high temperatures. Preheating at high temperatures resulted in higher RS, higher 0.2% proof stress and ultimate strength, lower elongation at brake, and higher material hardness. The increased RSs and the change in mechanical properties are attributed to changes in the microstructure. Preheating resulted in a larger melt pool, increased the width of columnar grains, and led to evolution of the carbide phase. The most significant microstructure change was in the increase of the size and occurrence of the carbide phase when higher preheating was applied. Furthermore, it was detected that the evolution of the carbide phase strongly corresponds to the build time when high-temperature preheating is applied. Rapid oxidation of the unfused powder was not detected by EDX or XRD analyses.