In recent years, promising technique of deep cryogenic treatment (DCT) is taking a new step in improving properties of various materials, especially steels. This study is focusing on influence of ...selected heat treatment process involving deep cryogenic treatment on the microstructure and microstructural evolution of four different steel grades (bearing steel 100Cr6, cold work tool steel X210Cr12, hot work tool steel X38CrMoV5-3 and stainless steel X17CrNi16-2). The study was performed for different heat treatment conditions, focused on effectiveness of DCT when using different austenitizing and tempering temperatures. The evolution of the microstructure was investigated in a sequential manner with various analytical techniques. The study indicates that the microstructure and microstructural evolution and changes are strongly related to the chemical composition of steel and the predefined matrix microstructure. DCT increases precipitation of carbides and induce their more homogenous distribution. The magnitude of increased carbide precipitation after DCT is correlated with the higher carbon content, whereas the content of other alloying elements does not scale with the precipitation behavior. The obtained results indicate that incorporation of DCT with heat treatment with higher austenitizing and lower tempering temperature is the most suitable for improving steels’ properties with DCT, due to the stronger impact of DCT on the carbide precipitation and matrix modification.
Lateral flow immunoassays (LFIAs) are a simple diagnostic device used to detect targeted analytes. Wasted and unused rapid antigen lateral flow immunoassays represent mass waste that needs to be ...broken down and recycled into new material components. The aim of this study was to recover gold nanoparticles that are used as markers in lateral flow immunoassays. For this purpose, a dissolution process with aqua regia was utilised, where gold nanoparticles were released from the lateral flow immunoassay conjugate pads. The obtained solution was then concentrated further with gold chloride salt (HAuCl4) so that it could be used for the synthesis of new gold nanoparticles in the process of ultrasonic spray pyrolysis (USP). Various characterisation methods including scanning electron microscopy, transmission electron microscopy, ultraviolet-visible spectroscopy and optical emission spectrometry with inductively coupled plasma were used during this study. The results of this study showed that the recovery of gold nanoparticles from lateral flow immunoassays is possible, and the newly synthesised gold nanoparticles represent the possibility for incorporation into new products.
In the present study, wear behavior as a function of aging time was evaluated for the AlCoCrFeNi2.1 eutectic complex, concentrated alloy (CCA) consisting of B2 (BCC), and L12 (FCC) lamellae in the ...as-cast state. By aging the material at 800 °C up to 500 h, precipitation of a fine, evenly dispersed micro-phase inside the L12 takes place. From 500 h to 1000 h of aging, precipitates coarsen by the Ostwald ripening mechanism. Reciprocating wear tests were characterized by a prevailing abrasive wear mechanism, while adhesive and delamination wear components change with aging conditions. The L12 phase with lower hardness in the as-cast material preferentially deformed during the wear test, which was not the case after aging the material, i.e., with the presence of precipitates. Aging-induced changes show a similar trend for the coefficient of friction and L12 + precipitates phase fraction, whereas changes in specific wear rate are in a good agreement with changes in B2 phase fraction. In general, aging the AlCoCrFeNi2.1 CCA at 800 °C up to 500 h decreases its coefficient of friction due to reduced adhesive wear component and enhances its wear performance through precipitation strengthening.
The impact and fracture toughness of a nanostructured, kinetically activated bainitic steel was determined using Standard methods. Prior to testing, the steel was quenched in oil and aged naturally ...for a period of 10 days in order to obtain a fully bainitic microstructure with a retained austenite content below 1%, resulting in a high hardness of 62HRC. The high hardness originated from the very fine microstructure of bainitic ferrite plates formed at low temperatures. It was determined that the impact toughness of the steel in the fully aged condition improved remarkably, whereas the fracture toughness was in line with expectations based on the extrapolated data available in the literature. This suggests that a very fine microstructure is most beneficial to rapid loading conditions, whereas material flaws such as coarse nitrides and non-metallic inclusions are the major limitation for obtaining a high fracture toughness.
For the improvement of surface roughness, titanium joint arthroplasty (TJA) components are grit-blasted with Al2O3 (corundum) particles during manufacturing. There is an acute concern, particularly ...with uncemented implants, about polymeric, metallic, and corundum debris generation and accumulation in TJA, and its association with osteolysis and implant loosening. The surface morphology, chemistry, phase analysis, and surface chemistry of retrieved and new Al2O3 grit-blasted titanium alloy were determined with scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and confocal laser fluorescence microscopy, respectively. Peri-prosthetic soft tissue was studied with histopathology. Blasted retrieved and new stems were exposed to human mesenchymal stromal stem cells (BMSCs) for 7 days to test biocompatibility and cytotoxicity. We found metallic particles in the peri-prosthetic soft tissue. Ti6Al7Nb with the residual Al2O3 particles exhibited a low cytotoxic effect while polished titanium and ceramic disks exhibited no cytotoxic effect. None of the tested materials caused cell death or even a zone of inhibition. Our results indicate a possible biological effect of the blasting debris; however, we found no significant toxicity with these materials. Further studies on the optimal size and properties of the blasting particles are indicated for minimizing their adverse biological effects.
Iron core–gold shell (Fe@Au) nanoparticles are prominent for their magnetic and optical properties, which are especially beneficial for biomedical uses. Some experiments were carried out to produce ...Fe@Au particles with a one-step synthesis method, Ultrasonic Spray Pyrolysis (USP), which is able to produce the particles in a continuous process. The Fe@Au particles were produced with USP from a precursor solution with dissolved Iron (III) chloride and Gold (III) chloride, with Fe/Au concentration ratios ranging from 0.1 to 4. The resulting products are larger Fe oxide particles (mostly maghemite Fe2O3), with mean sizes of about 260–390 nm, decorated with Au nanoparticles (AuNPs) with mean sizes of around 24–67 nm. The Fe oxide core particles are mostly spherical in all of the experiments, while the AuNPs become increasingly irregular and more heavily agglomerated with lower Fe/Au concentration ratios in the precursor solution. The resulting particle morphology from these experiments is caused by surface chemistry and particle to solvent interactions during particle formation inside the USP system.
Annealing of a Nanostructured Bainitic Steel Kirbiš, Peter; Feizpour, Darja; Kaker, Henrik ...
Metallography, microstructure, and analysis,
02/2020, Letnik:
9, Številka:
1
Journal Article
Machinability as a material property is dependent upon the scale of the microstructure as well as distribution, cohesion, and physical properties of the hard particles. Traditionally, this is ...accomplished by additions of inclusion forming elements such as sulfur, lead, or arsenic. However, this embrittlement is not reversible with heat treatment, and therefore, it is of interest to exploit the natural brittleness of nano-materials with a low density of mobile dislocations. With this in mind, a newly developed nanostructured bainitic steel was annealed at 953 °K (680 °C). The microstructural changes during annealing were studied using hardness measurements and high-resolution transmission electron microscopy.
The elucidation of spontaneous growth of metal whiskers from metal surfaces is still ongoing, with the mainstream research conducted on Sn whiskers. This work reports on the discovery of Pb whisker ...growth from Bi-Mg-Pb solid pools found in common machinable aluminum alloy. The whiskers and hillocks display unique morphologies and complex growth that have not been documented beforehand. In contrast to typical understanding of whisker growth, the presented Pb whiskers show a clear nanocrystalline induced growth mechanism, which is a novel concept. Furthermore, the investigated whiskers are also found to be completely composed of nanocrystals throughout their entire length. The performed research gives new insight into nucleation and growth of metal whiskers, which raises new theoretical questions and challenges current theories of spontaneous metal whisker growth. Additionally, this work provides the first microscopic confirmation of recrystallization growth theory of whiskers that relates to oriented attachment of nanocrystals formed within an amorphous metallic matrix. The impact of mechanical stress, generated through Bi oxidation within the pools, is theoretically discussed with relation to the observed whisker and hillock growth. The newly discovered nanocrystalline growth provides a new step towards understanding spontaneous metal whisker growth and possibility of developing nanostructures for potential usage in sensing and electronics applications.
For the improvement of surface roughness, titanium joint arthroplasty (TJA) components are grit-blasted with Alsub.2Osub.3 (corundum) particles during manufacturing. There is an acute concern, ...particularly with uncemented implants, about polymeric, metallic, and corundum debris generation and accumulation in TJA, and its association with osteolysis and implant loosening. The surface morphology, chemistry, phase analysis, and surface chemistry of retrieved and new Alsub.2Osub.3 grit-blasted titanium alloy were determined with scanning electron microscopy (SEM), X-ray energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and confocal laser fluorescence microscopy, respectively. Peri-prosthetic soft tissue was studied with histopathology. Blasted retrieved and new stems were exposed to human mesenchymal stromal stem cells (BMSCs) for 7 days to test biocompatibility and cytotoxicity. We found metallic particles in the peri-prosthetic soft tissue. Ti6Al7Nb with the residual Alsub.2Osub.3 particles exhibited a low cytotoxic effect while polished titanium and ceramic disks exhibited no cytotoxic effect. None of the tested materials caused cell death or even a zone of inhibition. Our results indicate a possible biological effect of the blasting debris; however, we found no significant toxicity with these materials. Further studies on the optimal size and properties of the blasting particles are indicated for minimizing their adverse biological effects.
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