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Covering layers might have very important role in improving performance of many mechanical parts. These layers are usually designed to protect a substrate from the environment and enhance mechanical properties such as hardness. Blackening is a classical approach that is very demanding on resources. This process is based on the alkalisation of surface atoms and the transformation of formed hydroxides to oxides. Such an approach inspired us to carry out experiments resulting in preparation of protective layers with similar properties, by using stoichiometric spinel ferrite nanoparticles (MeFe2O4). Thus mechanical parts were covered with ferrite nanoparticles and heated in a furnace. Ferrite samples, which were used as precursor for the preparation of layers, were analysed with X-ray powder diffraction, energy dispersive X-ray spectroscopy and 57 Fe Mössbauer spectroscopy. The samples were analysed with ultrasonic hardness test, electron microscopy, and Mössbauer spectroscopy. The protection layers showed a higher hardness compared to untreated parts.

Selective laser melting (SLM) as an additive manufacturing method makes it possible to quickly produce complexly shaped three-dimensional (3D) metal specimens from a powder. This work describes how SLM affects the surface phase composition of a 3D printed specimen, as analyzed with conversion electron Mössbauer spectroscopy (CEMS), conversion X-ray Mössbauer spectroscopy (CXMS) and X-ray diffraction (XRD). Both stainless 1.4404 (CL20ES) steel and maraging 1.2709 (CL50WS) steel have been investigated. A transformation of the phase composition from the ferritic phase into an austenitic one was proven by comparing the initial CL50WS powder and the final specimen using CXMS. This transformation takes place during the SLM process. No transformation was identified in stainless steel. The differences identified via CEMS between the surface phase composition of the final non-annealed specimens and the surface of the final annealed specimens demonstrated the oxidation of the surface layer. The oxidation occurs during the annealing of the sample in surface layers less than 1 μm thick. The quality of the surface was examined using scanning electron microscopy (SEM), which presented imperfections on the face of the final specimen. Granules of the initial powder bonded to the surface of the specimen and both irregular and spherical pores were observed.

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