High operating temperatures can have very deleterious effects on the long-term performance of high-Cr, creep-resistant steels used, for example, in the structural components of power plants. For the popular creep-resistant steel X20CrMoV12.1 we analysed the processes of carbide growth using a variety of analytical techniques: transmission electron microscopy (TEM) and diffraction (TED), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The evolution of the microstructure after different aging times was the basis for a much better understanding of the boundary-migration processes and the growth of the carbides. We present an explanation as to why some locations are preferential for this growth and using EBSD we were able to define the proper orientational relationship between the carbides and the matrix.

We describe a two-step synthesis of pure multiwall MoS₂ nanotubes with a high degree of homogeneity in size. The Mo₆S₄I₆ nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H₂S/H₂ mixture leads to the MoS₂ nanotubes still grouped in hedgehog-like morphology. The described method enables a large-scale production of MoS₂ nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo₆S₄I₆ nanowires and the MoS₂ nanotubes. The unit cell parameters of the Mo₆S₄I₆ phase are proposed. Blue shift in optical absorbance and metallic behavior of MoS₂ nanotubes in two-probe measurement are explained by a high defect concentration.

We have investigated the impact of the process parameters for the selective laser melting (SLM) of the stainless steel AISI 316L on its microstructure and mechanical properties. Properly selected SLM process parameters produce tailored material properties, by varying the laser’s power, scanning speed and beam diameter. We produced and systematically studied a matrix of samples with different porosities, microstructures, textures and mechanical properties. We identified a combination of process parameters that resulted in materials with tensile strengths up to 711 MPa, yield strengths up to 604 MPa and an elongation up to 31%, while the highest achieved hardness was 227 HV10. The correlation between the average single-cell diameter in the hierarchical structure and the laser’s input energy is systematically studied, discussed and explained. The same energy density with different SLM process parameters result in different material properties. The higher energy density of the SLM produces larger cellular structures and crystal grains. A different energy density produces different textures with only one predominant texture component, which was revealed by electron-backscatter diffraction. Furthermore, three possible explanations for the origin of the dislocations are proposed.

18Ni-300 maraging steel manufactured by selective laser melting was plasma nitrided to improve its wear and corrosion resistance. The effects of a prior solution treatment, aging and the combination of both on the microstructure and the properties after nitriding were investigated. The results were compared with conventionally produced 18Ni-300 counterparts subjected to the same heat- and thermo-chemical treatments. The plasma nitriding was performed under the same conditions (temperature of 520 °C and time of 6 h) as the aging in order to investigate whether the nitriding and the aging could be carried out simultaneously in a single step. The aim of this work was to provide a better understanding of the morphology and chemical composition of the nitrided layer in the additive-manufactured maraging steel as a function of the prior heat treatments and to compare the wear and corrosion resistance with those of conventional maraging steel. The results show that nitriding without any prior aging leads to cracks in the compound layer, while nitriding of the prior-heat-treated additive-manufactured maraging steel leads to benefits from the thermochemical treatment in terms of wear and corrosion resistance. Some explanations for the origins of the cracks and pores in the nitride layers are provided.

We present the modification of Ti-6Al-4V surfaces with a diode end-pumped Nd:YVO4 laser by varying the distance between laser-produced micro(μ)-channels. We analyzed the influence of laser texturing on the morphology, microstructure, surface and corrosion properties of Ti-6Al-4V. SEM imaging reveals a characteristic μ-channel pattern with different scan line separations, while electron backscatter diffraction (EBSD) indicates that laser texturing with the current parameters influences the microstructure up to 2 µm deep with the most significant influence at the tips, where melting and rapid solidification occur. The Vickers hardness test indicates a surface hardening effect of the laser-textured compared to the as-received Ti-6Al-4V surfaces. The XPS analysis showed that the oxide layer on the laser-textured samples was considerably thicker compared to the as-received sample, at 20 and 7 nm, respectively. We observed that the wettability was strongly correlated with the scan line separation. The results show increased hydrophobicity with increased scan line separation. The corrosion resistance was improved for laser-textured surfaces compared to the as-received surface and increased with the scan line separation.

The morphology of the eutectic chromium carbides in the microstructure of as-cast AISI D2 tool steel was modified by adding small amounts of rare-earth elements (REEs) to the melt. As a result of these REE additions the eutectic carbide morphological type was changed from lamellar to globular. Similar phenomena have already been reported for various tool steels, but no complete theoretical explanation has been provided. Here, we propose a new model that is derived from first-principles thermodynamic calculations based on the phase-field modeling of the eutectic reaction. Using this new approach, where the decomposition of the phase-boundary surface-energy term is divided into the isotropic and anisotropic parts, we were able to account for the transition from a lamellar to a globular eutectic morphology in REE-modified AISI D2 tool steel.