Wyniki 1-2 spośród 2 dla zapytania: authorDesc:"Krzysztof J. Kurzydlowski"

Surface modification of titanium subjected to hydrostatic extrusion

Czytaj za darmo! »

The basic technology for producing large volumes of bulk nanocrystalline metals is based on the Severe Plastic Deformation (SPD) methods, which enable refining the structure from the micrometric to the nanometric level. The microstructural changes are accompanied by a significant improvement of the mechanical strength and hardness [1÷7]. One of the SPD methods is hydrostatic extrusion, employed in the present experiments, which has been proven to efficiently refine the grains in aluminum, copper, nickel and steel [8÷12]. Our earlier studies have shown that hydroextrusion can also be used for producing nanostructured titanium [13÷15] with an equivalent diameter of grains about 60 nm and substantially increased strength and hardness. The chief difficulty in producing nanocrystalline titanium by HE is that the reduction of the rod cross-section must be realized gradually in many passes. Other disadvantageous effects that occur during HE of Ti are: the high extrusion pressure, the recurrent elastic deformation, the stick slip effect (stepwise displacement of the material) and a considerable wear of the die resulting from the tribological conditions. The aim of the study was to reduce or eliminate these adverse effects, and thereby to optimize the hydroextrusion process of titanium. To this end the surface of titanium was subjected to various modifications. The beneficial effect of Ti-Al coatings was shown in our earlier publications [15, 16]. Even though the extrusion pressure was reduced, the Ti-Al layers underwent wear in a short time. In the present study, the Ti billets were covered with Al coatings of various thicknesses. The effect of these coatings on hydroextrusion process, the surface topography of the Ti products and their microstructure after the extrusion were investigated. The maximum strain was also determined that could be applied in a single and two extrusion passes. MATERIALs AND PROCESSING The material examine[...]

Frustules of Didymosphenia geminata as a modifier of resins DOI:10.15199/28.2018.5.2

  1. INTRODUCTION Didymosphenia geminata (Lyngbye), is a freshwater diatom, which produces siliceous shell and mucilage material in the form of stalks, which attach it to substrates in water, such as stones, plant or debris. This species received increasing interest in recent years, due to its geographical expansion [1÷3]. In the last decade, the massive occurrence of D. geminata has been reported in Europe, Asia [4] and other locations like New Zealand [4], the United States of America [5], Canada [6], Chile and Argentina [7]. Among the diatom species, with the length of 80÷140 μm [8] and width of 35÷45 μm [8], D. geminata is classified as large. The structure and chemical composition of the diatom D. geminata stalks have been recently a subject of extensive investigations, the results of which are given in Ehrlich et al. [9]. These investigations were driven by the idea of using the stalks as biomaterial. The aim of the present study was to set the stage for engineering applications of the D. geminata shells, called frustule, by exploring their properties as a filler of polymeric resins. Due to large variations in morphology, and hierarchical architecture (Fig. 1) the diatoms have been used in advanced materials applications, i.e.: in filtration [10, 11], absorption/insulation, fabrication of photonic crystals [12÷14], and drug delivery [15]. Also, it should be noted that the diatoms can be farmed on an industrial scale [16, 17], thus opening the space for the use in mass-production. In analysing potential advantages of using diatom frustule for modification of polymer composites [18, 19] and production “green" eco-polymers [19, 20], it should be noted that biological materials achieve mechanical properties, which are far beyond those man-made materials [21]. On the other hand, because of their unique micro- and nanostructural features, testing of the mechanical properties of the frustule is a challenging exerci[...]

 Strona 1