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Highly porous nickel-based superalloys appear as attractive candidates to be applied e.g. as seals in gas turbine engines instead of honeycomb structures. Among various methods of producing open-porous materials, a space holder approach provides number of benefits regarding economic and ecological aspects of production. In this work, the pioneering results of microstructure and mechanical properties analyses of highly porous Hastelloy-X nickel superalloy produced by the space holder approach, are presented. The materials were fabricated by using spherical fine Hastelloy-X powders and carbamide particles as batch materials. A multi-step powder metallurgy and thermomechanical processing was applied to produce open porous samples having a total volumetric porosity of 50, 60 and 70%. The produced materials were subjected to non-destructive (X-ray computed tomography) and metallographic inspections. Mechanical properties of the porous Hastelloy-X samples were examined in static room temperature compression tests, to discuss the effect of obtained porosity on compressive response.

In this paper, the effect of applied multi-variant heat treatment on microstructure, phase composition and mechanical response of Haynes 282 nickel-based superalloy was investigated. For this reason, temperatures of both stages of standard two-stage aging treatment (i.e., 1010 °C/2 h + 780 °C/8 h) were extended to 900-1100 °C/2 h and 680-880 °C/8 h ranges, respectively. Consequently, 30 different variants of heat treatment were applied. The microstructural features of heat-treated samples were investigated by means of light microscopy and SEM/EDS methods, while mechanical properties were examined via microhardness measurements. It was found that by using various combinations of temperatures of the first and second stage of aging, the room temperature hardness of Haynes 282 alloy can be decreased by ~ 100 HV units or increased by up to 25 HV units as compared to that of the alloy subjected to the standard heat treatment schedule. The mechanical response of the alloy is determined by a complex structural evolution involving the secondary precipitation of γ′, M 23 C 6 and M 6 C phases, as well as their interaction with the fcc γ matrix.

Three variants of high-entropy alloys (HEAs) from the AlCoCuFeNi group, containing different amounts of Al and Cu, were developed and produced via induction melting and casting into ceramic moulds. The ingots were homogenized at 1000 °C for 10 h. Analyses revealed that variations in Al and Cu concentrations led to significant changes in the material’s microstructure, hardness, strength, and impact strength. In the equiatomic variant, differential scanning calorimetry revealed a peak associated with the phase transformation, indicating that this alloy’s microstructure consists of two distinct phases. In contrast, when the concentrations of Al and Cu are reduced, a single-phase microstructure is observed. The equiatomic variant (used as a reference) is characterized by its hardness and brittleness, exhibiting slight ductility, with a tensile strength of 80 MPa, a hardness of 400 HV5, and an impact strength of 1.9 J/cm2. However, with adjusted Al contents of 1/2 and Cu contents of 1/4, the alloy displays exceptional strength combined with good plasticity, achieving a tensile strength of up to 450 MPa with 60% elongation, and an impact strength of 215 J/cm2. The non-equiatomic variants exhibit a comparatively more straightforward microstructure and enhanced ductility, which may facilitate easier processing of these alloys. Fractography investigation revealed a ductile mode of fracture in the samples.

This work was focused on two particular phenomena contributing to a damage process of nodular cast iron under tensile stress: Internal destruction of graphite nodule and debonding at graphite/matrix (G-M) interface. The G-M debonding was analyzed depending on the phase characteristics of the metal matrix and with the increase in the distance of the observation field from the main crack surface. Typical morphological effects of decohesion in the graphite-matrix microregions related to an internal structure of graphite nodule were revealed and classified. The obtained results of the microscopic observations suggest that the path of both types of internal cracks in the graphite nodule passed through areas of weakened cohesion. Detailed microscopic observations allowed revealing some additional phenomena associated with G-M debonding along the G/M interface. In the most ductile of the tested alloys, with ferritic and ausferritic matrix, the G-M debonding was preceded by the formation of a layer of shifted graphene plates in the external envelope of the spheroid. In the alloys of polyphase pearlitic and ausferritic matrix, the revealed morphology of the G-M interface suggests that G-M debonding might be delayed by the interaction with some phase components as cementite lamellae and austenite plates.

High-entropy materials, characterized by complex chemical compositions, are difficult to identify and describe structurally. These problems are encountered at the composition design stage when choosing an effective method for predicting the final phase structure of the alloy, which affects its functional properties. In this work, the effects of introducing oxide precipitates into the matrix of a high-entropy TiCoCrFeMn alloy to strengthen ceramic particles were studied. The particles were introduced by the ex situ method, such as TiO2 in the form of anatase, and by the in situ method, consisting of the reconstruction of CuO into TiO2. In both cases, it was assumed that after the homogenization process, carried out at 1000 °C, ceramic precipitates in the rutile phase, commonly considered a stable allotropic form of TiO2, would be obtained. However, the microscopic observations and XRD analyses, supported by EDS chemical composition microanalysis and EBSD backscattered electron diffraction, clearly revealed that, regardless of the method of introducing oxides, the final strengthening phase obtained was a mixture of TiO2 in the form of anatase with the Magnelli phase of Ti2O3. In this work, phase reconstruction in the Ti-O system was analyzed using changes in the Gibbs free energy of the identified oxide phases.

The aim of this work was to analyze the effect of steam oxidation when TP347HFG grade steel was exposed to industrial conditions for 125 000 hrs at 568 °C under 16.5 MPa pressure. The testing material was acquired from one of the coal power plants operating in Poland. Comprehensive investigations were carried out on the outer surface and cross section of the exposed sample using XRD, SEM/EDS and TEM. The analysis revealed the development of a fine grain oxide scale thickness spanning from 20 to 200 µm, consisting Fe 2 NiO 4 (78 %), Cr 1.3 Fe 0.7 O 3 , Fe 2 O 3 (0.8 %) and Fe 3 Co (0.8 %). Cross-sectional observations showed the formation of grains rich in Nb precipitates type MX carbonitrides surrounded by M 23 C 6 carbides developed as a continuous net at the grain boundaries. The extent of material degradation under the influence of temperature, pressure and exposure time has been meticulously discussed. Graphical Abstract

Boron-doped molybdenum silicides have been already recognized as attractive candidates for space and ground ultra-high-temperature applications far beyond limits of state-of-the-art nickel-based superalloys. In this work, we are exploring a new method for fabricating Mo–Si–B alloys (as coatings or small bulk components) by utilizing a pressure-less reactive melt infiltration approach. The basic assumption of this approach is a synthesis of binary and/or ternary and complex intermetallic phases (silicides, borides, borosilicides), through a direct interaction of Si–B melt with molybdenum. The main purpose of this work was to examine the effect of temperature and time of Si–B melt interaction on the structure and morphology of the formed reaction products. For this purpose, sessile drop experiments were carried out on the eutectic Si–3.2B (wt%) alloy/Mo couples at temperature varying between 1385 and 1550 °C and holding time between 10 and 30 min. The solidified sessile drop couples were subjected to microstructural characterization by means of light microscopy and scanning electron microscopy analyses performed both at “top-view” and cross-sectioned interfaces. The phases formed within the interaction zone were identified by using TEM/SAED and XRD techniques. It was documented that a thickness of both main product layer (MoSi2 + Mo5Si3) and boron-rich interlayer increases with raising temperature and time of the Si–B melt interaction with Mo substrates.

Silicon has recently been recognized as a potentially attractive phase change material for ultra-high-temperature latent heat thermal energy storage (LHTES) and conversion systems. It has been proposed that the utilization of silicon’s latent heat should drastically increase the performance of LHTES devices in terms of operational temperatures and available energy density. Nevertheless, in order to ensure a high reliability and long lifetime of the system, proper ceramic materials that are able to withstand contact heating and cooling cycles during consecutive melting/solidification steps need to be examined and selected. Previously, we have documented that hexagonal boron nitride (h-BN) is the only ceramic that shows non-wettability and limited reactivity in contact with molten silicon at temperatures up to 1650°C. In this work, we present for the first time the results of experimental research on the performance of a Si/h-BN system upon cycling melting/solidification processes. For this reason, the Si/h-BN couple was subjected to a sessile drop experiment containing 15 cycles of heating/cooling between 1300°C and 1450°C. During the test, temperatures of specific events as well as contact angle values were recorded. After the test, the structure and surface morphology of the solidified Si/h-BN couple were characterized by means of scanning electron microscopy.

The last decades have seen a huge growth in the investigation of intermetallic compounds at the interfaces of laminated composites due to their useful features. In this research, effects of the formation of intermetallic compounds on tensile properties and wear resistance of Ni/Ti composites produced by cross-accumulative roll bonding (CARB) process have been examined at different annealing times and temperatures. Scanning electron microscopy (SEM) images demonstrated that the layers were well bonded together, but Ni layers experienced instabilities in light of plastic deformation. The EBSD results showed lamellar structure and crystallographic texture on Ti and Ni layers during plastic deformation. According to X-ray diffractometer (XRD) and energy-dispersive spectrometer (EDS) analyses, NiTi 2 and NiTi were present in all annealed samples. The thickness of intermetallic compounds grew with an increase in annealing temperature and time. However, this growth led to a decrease in tensile strength while the values of elongation fluctuated. Based on the results of the wear test, the composite became more resistant to wear when the thickness of intermetallic layers increased. The surfaces of these layers with less roughness and lower coefficients of friction facilitated the movement of steel pin on samples during the wear test. Furthermore, wear mechanisms of adhesion, abrasion, and delamination were observed, and they were more noticeable at higher loads and lower annealing temperatures and times.

The contact heating (CH) sessile drop and capillary purification (CP) methods were applied for a fundamental study concerning the wettability and reactivity of liquid Si-16.2 at. pct Ti alloy (eutectic composition) in contact with glassy carbon (GC) and SiC at T = 1450 °C under an Ar atmosphere. Different spreading stages with different slopes, depending on the starting conditions of the materials used, where observed. On the contrary, the final contact angle value seemed not affected and the values of θ ≈ 44 deg ± 2 and θ ≈ 42 deg ± 2 where displayed on GC and SiC, respectively. The solidified Si-Ti eutectics/GC and Si-Ti eutectics/SiC samples were examined both at the top of the drop and at the cross section by scanning electron microscopy (SEM)/energy-dispersive spectroscopy (EDS). The presence of a SiC layer as unique reaction product at the Si-Ti eutectics/GC interface, confirmed that wettability is mainly driven by reactivity. Contrarily, as nonreactive system, at the Si-Ti eutectics/SiC interface a weak dissolution of SiC substrate was detected.