Defect and Diffusion Forum Vol. 448

Abstract: The objective of this study is to investigate the tribological properties of detonation-sprayed (Ti,Cr)C-Ni coatings under dry and lubricating conditions. The (Ti,Cr)C-based coatings with 25 wt.%, and 33 wt.% of Ni binder were applied onto steel substrates by detonation spraying. Microreciprocating wear tests were performed under dry and lubricating conditions with water, diesel, biofuel, aviation fuel and oil as a lubricating environment. Post-test examination of wear tracks was performed using interference profilometry and SEM analysis. The (Ti,Cr)C-Ni detonation-sprayed coatings exhibit a dense microstructure, featuring well-bonded splats composed of fine (Ti,Cr)C particles and Ni-based binder. The lowest wear rates of the (Ti,Cr)C-25wt.%Ni and (Ti,Cr)C-33wt.%Ni coatings are observed in an oil environment. Instead, the wear rates of both coatings are highest in a water environment. The (Ti,Cr)C-25%wt.Ni detonation-sprayed coating is characterized by an increased wear rate in the water environment as compared with (Ti,Cr)C-33%wt.Ni due to more intensive brittle failure in the water environment.

Abstract: This paper presents experimental results on the processing of complex concentrated alloy with a nominal composition of A_0.35CoCrFeNi. The alloy was produced by vacuum induction melting and tilt casting. The microstructure of the as-cast CCA consists of dendritic and interdendritic regions homogenized by heat treatment at 1360 °C. After rotary swaging at room temperature, the microstructure is characterized by an abundance of dislocations and continuously intersecting slip bands. Annealing experiments were carried out in the temperature range of 1150 °C – 1300 °C and different holding times to determine the parameters of grain growth kinetics. Phase and chemical analysis were investigated using XRD and EDS methods. The activation energy of recrystallization in the studied composition was 458 kJ mol^-1. The influence of grain size on room temperature mechanical properties and tensile properties was determined. The hardening coefficients k_h and k_σ, calculated using the Hall-Petch relation, were 277.5 HV µm^-1/2 and 655 MPa µm^-1/2, indicating the effectiveness of grain boundary hardening in the studied single-phase CCA.

Abstract: To prepare bulk single-crystal REBCO superconductors by the new single-direction growth method (SDMG: Single-Direction Melt-Growth), it is necessary to produce a large-area seed of high quality, for example, based on EuBCO. Since the samples prepared by the SDMG method copy the structure of the seed, for the production of large-area seeds it is necessary to optimize the time-temperature regime in order to grow seeds with a suitable structure and composition and minimize structural defects (limiting the amount of subgrains and others). A higher growth rate was used in comparison with the standard growth rates used to produce EuBCO seeds of larger dimensions. The increased growth rate in the crystal growth window reduces the outflow of the melt from the sample, and thus it is possible to achieve a single-crystal sample in the entire volume of the precursor. The samples were produced at different growth rates: 1; 2; 3 and 5 °C/h. The microstructure of the samples was studied by polarized light microscopy and scanning electron microscopy. The size and distribution of Eu211 particles in the sample volume and the subgrain structure were studied on the fabricated samples.

Abstract: The aim of the study was to prepare samples suitable for testing the shape memory phenomenon in ceramic systems. Testing would be carried out by preparing micro-objects with dimensions in the order of micrometers using SEM/FIB techniques, and subsequent testing using a nanoindenter. The article deals with the influence of the preparation method on the properties of samples prepared by conventional annealing and spark plasma sintering. Two commercial powders were used, namely PSZ-10C and PSZ-20C. The microstructure of the samples, fracture surfaces and HV hardness, as well as indentation hardness were evaluated on the prepared samples. It was shown, that both conventional annealing and SPS can be used for preparation of samples with a suitable grain size, but also that the preparation method has a significant impact on the properties of the sample. Depending on the preparation method, the grain size varied from approximately 1 μm to 50 μm. There is also difference in the character of the fracture surfaces and in the hardness of the samples, where a difference in indentation hardness from approximately 10 GPa to approximately 20 GPa was measured.

Abstract: Austenitic stainless steels (ASSs) are characteristic with a combination of good mechanical and corrosion properties. Therefore, they are used in the primary circuits of nuclear power plants. Under the influence of a corrosive environment containing chloride ions and mechanical loading, the phenomenon of stress corrosion cracking occurs in ASSs. SCC can also be initiated by the surface condition of ASSs. Machining is usually the last stage of production, during which a significant deformed zone with high residual tensile stresses can be created, which can accelerate the initiation of stress corrosion cracking. Research is focused on analyzing the influence of final turning on microstructural changes of the surface-machined layer caused by various turning parameters (e.g.: cutting speed, feed, depth of cut, cutting tool geometry). No significant microstructure changes were observed between the samples by light microscopy, so we focused on transmission electron microscopy (TEM) on thin lamellas prepared using the focus ion beam (FIB) technique. TEM observation confirmed the presence of a deformed zone and a passivation layer. In the case of the sample that was turned with a higher feed and cutting speed, the passivation layer was discontinuous. Such a microstructural change can significantly affect the corrosion resistance of ASS.

Abstract: This study investigated the impact of as-printed and heat-treated additively produced 2507 super duplex stainless steel (also known as SDSS) on microstructure and hardness distribution. Optical microscopy was used to examine the phase transformations of the steel during the as-printed (untreated) and solution-annealed treatment stages of samples. The relationship between microstructure and hardness distribution (center and edge) was studied. Because the LPBF process cools rapidly, the SDSS shows that the main phase in as-printed samples is ferrite, with 5% austenite. The fully balanced microstructure is forming when the solution annealing is performed, with austenite content about 52%. The hardness of SDSS is strictly related to the material microstructure, where the fully ferritic structure shows higher hardness 50.16–46.18 HRC, while the balanced duplex microstructure reveals lower values 34.58–32.26 HRC.