A method of manufacturing hydrogel coatings designed to increase the hydrophilicity of polyurethanes (PU) is presented. Coatings were obtained from polyvinylpyrrolidone (PVP) by free radical polymerisation. The authors proposed a mechanism of a two-step grafting - crosslinking process and investigated the influence of reagent concentration on the coating’s physical properties - hydrogel ratio (HG) and equilibrium swelling ratio (ESR). A surface analysis of freeze-dried coatings using scanning electron microscopy (SEM) showed a highly porous structure. The presented technology can be used to produce biocompatible surfaces with limited protein and cell adhesive properties and can be applied in fabrication of number of biomedical devices, e.g. catheters, vascular grafts and heart prosthesis.
The influence of ion implantation on the structure and properties of polymers is a very complex issue. Many physical and chemical processes taking place during ion bombardment must be taken into consideration. The complexity of the process may exert both positive and negative influence on the structure of the material. The goal of this paper is to investigate the influence of H+, He+ and Ar+ ion implantation on the properties of polypropylene membranes used in filtration processes and in consequence on fouling phenomena. It has appeared that the ion bombardment caused the chemical modification of membranes which has led to decrease of hydrophobicity. The increase of protein adsorption on membrane surface has also been observed.
The modified surface layers of Mg enriched with Al and Si were fabricated by thermochemical treatment. The substrate material in contact with an Al + 20 wt.% Si powder mixture was heated to 445ºC for 40 or 60 min. The microstructure of the layers was examined by OM and SEM. The chemical composition of the layer and the distribution of elements were determined by energy dispersive X-ray spectroscopy (EDS). The experimental results show that the thickness of the layer is dependent on the heating time. A much thicker layer (1 mm) was obtained when the heating time was 60 min than when it was 40 min (600 μm). Both layers had a non-homogeneous structure. In the area closest to the Mg substrate, a thin zone of a solid solution of Al in Mg was detected. It was followed by a eutectic with Mg17Al12and a solid solution of Al in Mg. The next zone was a eutectic with agglomerates of Mg2Si phase particles; this three-phase structure was the thickest. Finally, the area closest to the surface was characterized by dendrites of the Mg17Al12phase. The microhardness of the modified layer increased to 121-236 HV as compared with 33-35 HV reported for the Mg substrate.
In current casting technology of cored, thin walled castings, the modifying coating is applied on the surface of wax pattern and, after the
removal of the wax, is transferred to inner mould surface. This way the modification leading to grain refinement occur on the surface of
the casting. In thin walled castings the modification effect can also be seen on the other (external) side of the casting. Proper reproduction
of details in thin walled castings require high pouring temperature which intensify the chemical reactions on the mould – molten metal
interface. This may lead to degradation of the surface of the castings. The core modification process is thought to circumvent this problem.
The modifying coating is applied to the surface of the core. The degradation of internal surface of the casting is less relevant. The most
important factor in this technology is “trough” modification – obtaining fine grained structure on the surface opposite to the surface
reproduced by the core.
Paper presents the results of research on modified surface grain refinement method used in investment casting of hollow, thin-walled parts
made of nickel based superalloys. In the current technology, the refining inoculant is applied to the surface of the wax pattern and then, it
is transferred to the ceramic mould surface during dewaxing. Because of its chemical activity the inoculant may react with the liquid metal
which can cause defects on the external surface of the cast part. The method proposed in the paper aims to reduce the risk of external
surface defects by applying the grain refiner only to the ceramic core which shapes the internal surface of the hollow casting. In case of
thin-walled parts the grain refinement effect is visible throughout the thickness of the walls. The method is meant to be used when internal
surface finish is less important, like for example, aircraft engine turbine blades, where the hollowing of the cast is mainly used to lower the
weight and aid in cooling during operation.
The effect of laser processing on the structure, microstructure and hardness of high-speed steel produced by powder metallurgy was investigated. The samples were surfaces remelted with impulse CO2 laser radiation under different operation conditions. In the remelted layer, the presence of full remelting, partial remelting and heat affected zones was detected. As a result of concentrated laser beam treatment, microstructures characteristic of the rapid crystallization process were observed. The microstructure in the full remelting zone was characterized by a fine microdendritic structure with the average distance between the secondary axes of dendrites below 1 µm and the dissolution of primary carbides. Retained austenite was found in the remelted samples, the amounts of which depended on the treatment parameters and grew with an increase in the speed of the laser beam movement. There was no unequivocal effect of the distance of the irradiated surface from the focus of the beam focusing system on the content of retained austenite. Due to the presence of retained austenite in the remelted part, the hardness decreased by about 23% compared to the hardness of the material before the treatment. On the other hand, laser processing leads to strong refinement of the microstructure and eliminates the residual porosity of powder steels, which can increase the toughness and cutting performance of steel. The research also showed the possibility of shaping the geometry of the remelting zone by the appropriate selection of machining parameters
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