Search Results (12)

To increase the mechanical and improve the operational properties of the AlSi25Cu4Cr and AlSi25Cu5Cr alloys, combinations of the alloying elements Ni, Co and Mo were used. The AlSi25Cu4Cr alloy was additionally alloyed with both Ni and Mo and Ni, Co and Mo, and the AlSi25Cu5Cr alloy was alloyed with Co and Mo in different concentrations. The dental alloys “wiron light” and “wironit” were used to introduce the elements Ni, Co, Mo, as well as additional amounts of Cr into the composition of the base compositions. The thermal analysis recorded a decrease in the liquidus and solidus temperatures of the base alloys, as well as a narrowing of their crystallization temperature range as a result of the added alloying elements. The influence of the used chemical elements on the phase composition of the alloys was established by X-ray diffraction. The elements Cr and Mo do not form secondary strengthening phases but dissolve in the α-solid solution. The results of the corrosion tests conducted in 1 M HCl solution and 1 M H₂SO₄ solution for 336 h and 504 h show that the elements Ni, Co and Mo improve the corrosion resistance of the alloys. Full article

Investigation of high-entropy alloys in form of bulk samples as well as thin films is currently one of the fastest growing areas in the study of metal alloys. In this paper, a bulk sample of FeNiCoCuCr high-entropy alloy ingot with equimolar composition is prepared by the laboratory arc melting method under an argon atmosphere and used as a source target for deposition of thin films on Si (111) single-crystalline substrates using a novel ionized jet deposition method. The morphology, chemical composition, and real crystalline structure of the target and the prepared layers were characterized by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy, and X-ray and neutron diffraction methods. Transfer coefficients characterizing the mass transport between the target and the grown film were calculated for each of the constituting metallic elements as the ratio of the atomic concentration found in the prepared film divided by its concentration in the deposition target. The dependence of the obtained transfer coefficients on the IJD acceleration voltage is discussed with respect to the main physical and geometric parameters of the deposition process, and their correlations with the cohesive energy of the elements forming the HEA are proposed. Full article

Railway wheels are usually attached to axles by press-fitting; therefore, the mechanical processes taking place during operation can result in failure, with fatal consequences for the axle seats. This manuscript describes the effect of laser hardening on the residual stress state, microstructural parameters (lattice defects—dislocations, crystallites, microstrains, etc.), and mechanical properties of laser-hardened EA1N steel railway axles under fatigue life conditions. Differences were found between ground, single-track, and multi-track hardened surfaces. Tensile residual stresses, low dislocation densities and hardnesses, and different microstructures (tempered cubic martensite) were found at the overlapped tracks and at the boundary of the heat-affected zone and bulk surface compared with the hardened zone. As a result, the surface treatment of axle seats by laser hardening improved the fatigue failure resistance compared with untreated seats. Optimal properties of the integrity of the axle seat surface were achieved, including fatigue resistance, which seems to be positively influenced mainly by sufficient hardness and the appropriate microstructure. The influence of the other investigated parameters was not evident, and was reduced by the presence of fretting corrosion and press-fitting. Full article

This study deals with two different aspects of the high-strength low-alloyed 1100 MC steel. The first is associated with the remarkable heterogeneity (linked with surface decarburization) in the surface state produced during sheet rolling with respect to the sheet width. The variable thickness surface layer exhibits a microstructure different from that of the deeper bulk. Variation in the thickness of the thermally softened near-surface region strongly affects Barkhausen noise as well. This technique can be considered a reliable tool for monitoring the aforementioned heterogeneity. It can also be reported that the opposite sides of the sheet are different with respect to the surface state, the heterogeneity distribution, and the corresponding Barkhausen noise. These aspects indicate different conditions during hot rolling followed by rapid quenching on the upper and lower rollers. Furthermore, it was found that the degree of decarburizing and the corresponding surface heterogeneity is also a function of C content, and steels with lower C content exhibit less pronounced surface heterogeneity. The second aspect is related to the remarkable asymmetry in Barkhausen noise emission with respect to two consecutive bursts. This asymmetry is due to the presence of remnant magnetization in the sheet produced during manufacturing. The remnant magnetization is coupled to the magnetic field produced by the excitation coil of the Barkhausen noise sensor and strongly contributes to the aforementioned asymmetry. The remnant magnetization attenuates the domain wall mobility, which results in weaker Barkhausen noise. Moreover, the Barkhausen noise envelopes and the extracted features such as the position of the envelope maximum and its width are strongly affected by the remnant magnetization. Insufficient demagnetization makes the body magnetically softer and makes a wider range of magnetic fields in which Barkhausen noise emission can be detected. As soon as sufficient removal of this remnant magnetization is carried out in the vanishing magnetic field (demagnetization), the aforementioned remarkable asymmetry is fully lost. Full article

The ionized jet deposition (IJD) method is applied to the preparation of thin films composed of refractory HfNbTiTaZr high-entropy alloy (HEA). Due to its stoichiometric reliability, the IJD method provides a flexible tool for deposition of complex multi-element materials, such as HEAs. Scanning electron microscopy, energy-dispersion spectroscopy, confocal microscopy, and X-ray diffraction methods are used to characterize the influence of the applied accelerating voltage of the IJD deposition head ranging from 16 to 22 kV on the resulting morphology, chemical composition, thickness, crystalline structure, and phase composition of the layers prepared as 10 mm-wide strips on a single stainless-steel substrate. With a low accelerating voltage applied, the best surface homogeneity is obtained. Transfer coefficient values characterizing the elemental transport between the bulk target and the grown layer are evaluated for each constituting element and applied voltage. With the IJD accelerating voltage approaching 22 kV, the coefficients converge upon the values proportional to the atomic number of the element. Such voltage dependence of the IJD elemental transport might be used as a suitable tool for fine-tuning the elemental composition of layers grown from a single deposition target. Full article

Most power plants use the Rankine cycle, where the heat supplied to water and steam is converted into mechanical work; therefore, most components have to be made of heat-resistant steel. Sufficient mechanical properties must be ensured for welded pipes to meet stringent requirements. Therefore, laser-welded 5 mm thick heat-resistant pressure vessel steel plates were subjected to various mechanical tests, including high-cycle fatigue tests. The microstructural notches were determined using X-ray diffraction too to determine critical areas that are susceptible to crack initialization and affect the service life. Finally, a functional model of the pressure vessel subsequently verified the results and assumptions. The presented results ensure the transferability of the results to real-life applications and outline the promising application potential of laser welding for producing vessels and pipes from heat-resistant steel in the industry. Full article

Hot working tool steel (AISI H13) is one of the most common die materials used in casting industries. A die suffers from damage due to friction and wear during its lifetime. Therefore, various methods have been developed for its repair to save costs to manufacture a new one. A great benefit of laser additive manufacturing (cladding) is the 3D high production rate with minimal influence of thermal stresses in comparison with conventional arc methods. Residual stresses are important factors that influence the performance of the product, especially fatigue life. Therefore, the aim of this contribution is to correlate the wide range of results for multilayer cladding of H13 tool steel. X-ray and neutron diffraction experiments were performed to fully describe the residual stresses generated during cladding. Additionally, in-situ tensile testing experiments inside a scanning electron microscope were performed to observe microstructural changes during deformation. The results were compared with local hardness and wear measurements. Because laser cladding does not achieve adequate accuracy, the effect of necessary post-grinding was investigated. According to the findings, the overlapping of beads and their mutual tempering significantly affect the mechanical properties. Further, the outer surface layer, which showed tensile surface residual stresses and cracks, was removed by grinding and surface compressive residual stresses were described on the ground surface. Full article

The increasing incidence of trauma in medicine brings with it new demands on the materials used for the surgical treatment of bone fractures. Titanium, its alloys, and steel are used worldwide in the treatment of skeletal injuries. These metallic materials, although inert, are often removed after the injured bone has healed. The second-stage procedure—the removal of the plates and screws—can overwhelm patients and overload healthcare systems. The development of suitable absorbable metallic materials would help us to overcome these issues. In this experimental study, we analyzed an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. From this alloy we developed screws which were implanted into the rabbit tibia. After 120, 240, and 360 days, we tested the toxicity at the site of implantation and also within the vital organs: the liver, kidneys, and brain. The results were compared with a control group, implanted with a Ti-based screw and sacrificed after 360 days. The samples were analyzed using X-ray, micro-CT, and a scanning electron microscope. Chemical analysis revealed only small concentrations of zinc, strontium, and magnesium in the liver, kidneys, and brain. Histologically, the alloy was verified to possess very good biocompatibility after 360 days, without any signs of toxicity at the site of implantation. We did not observe raised levels of Sr, Zn, or Mg in any of the vital organs when compared with the Ti group at 360 days. The material was found to slowly degrade in vivo, forming solid corrosion products on its surface. Full article

In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn–0.8Mg–0.2Sr (wt.%) alloy on a rabbit model. An alloy screw was implanted into one of the tibiae of New Zealand White rabbits. After 120 days, the animals were euthanized. Evaluation included clinical assessment, microCT, histological examination of implants, analyses of the adjacent bone, and assessment of zinc, magnesium, and strontium in vital organs (liver, kidneys, brain). The bone sections with the implanted screw were examined via scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). This method showed that the implant was covered by a thin layer of phosphate-based solid corrosion products with a thickness ranging between 4 and 5 µm. Only negligible changes of the implant volume and area were observed. The degradation was not connected with gas evolution. The screws were fibrointegrated, partially osseointegrated histologically. We observed no inflammatory reaction or bone resorption. Periosteal apposition and formation of new bone with a regular structure were frequently observed near the implant surface. The histological evaluation of the liver, kidneys, and brain showed no toxic changes. The levels of Zn, Mg, and Sr after 120 days in the liver, kidneys, and brain did not exceed the reference values for these elements. The alloy was safe, biocompatible, and well-tolerated. Full article

Posthumanism and transhumanism are philosophies that envision possible relations between humans and posthumans. Critical versions of posthumanism and transhumanism examine the idea of potential threats involved in human–posthuman interactions (i.e., species extinction, species domination, AI takeover) and propose precautionary measures against these threats by elaborating protocols for the prosocial use of technology. Critics of these philosophies usually argue against the reality of the threats or dispute the feasibility of the proposed measures. We take this debate back to its modern roots. The play that gave the world the term “robot” (R.U.R.: Rossum’s Universal Robots) is nowadays remembered mostly as a particular instance of an absurd apocalyptic vision about the doom of the human species through technology. However, we demonstrate that Karel Čapek assumed that a negative interpretation of human–posthuman interactions emerges mainly from the human inability to think clearly about extinction, spirituality, and technology. We propose that the conflictual interpretation of human–posthuman interactions can be overcome by embracing Čapek’s religiously and philosophically-inspired theory of altruism remediated by technology. We argue that this reinterpretation of altruism may strengthen the case for a more positive outlook on human–posthuman interactions. Full article

Pipeline transport uses millions of kilometers of pipes worldwide to transport liquid or gas over long distances to the point of consumption. High demands are placed, especially on the transport of hazardous substances under high pressure (gas, oil, etc.). Mostly seamless steel pipes of various diameters are used, but their production is expensive. The use of laser-welded pipes could significantly reduce the cost of building new pipelines. However, sufficient mechanical properties need to be ensured for welded pipes to meet stringent requirements. Therefore, laser-welded 10 mm thick pressure vessel steel plates were subjected to various mechanical tests, including high-cycle fatigue tests. Furthermore, the microstructural parameters and the state of residual stresses were determined using X-ray and neutron diffraction, which could affect fatigue life, too. The critical areas for possible crack initialization, especially in and near the heat-affected zone, were found using different tests. The presented results outline the promising application potential of laser welding for the production of pipes for high-pressure pipelines. Full article