In respect to the cost of constituents, Cu-Al-Ni alloys can be regarded as low-cost shape memory alloys. However, the processing is quite costly due to the brittleness of the ingots. Therefore it would be advantageous to produce semi-finished products directly from the melt via highly productive technique. A laboratory device for vertical continuous casting directly from the vacuum induction melting furnace was experimentally employed for continuous casting of the Cu-13 wt.% Al-4 wt.% Ni shape memory alloy. A water-cooled copper crystalliser with a graphite insert was used to cast Ø 16 mm strands. Diverse sets of casting parameters were tested, the average casting speeds being within the range from 250 mm min-1 to 625 mm min-1. The castability of the alloy using this technique was good. Strands were examined in the as-cast condition, and no cracks or other defects were discovered. Medium casting speeds resulted in good surface quality, and a fully martensitic microstructure was obtained even at the lowest average casting speed. The paper presents and discusses the surface quality, microstructures and mechanical properties.
COBISS.SI-ID: 17450518
The present work deals with the laminar natural convection in a square cavity with differentially heated side walls subjected to constant temperatures and filled with homogenous 0,4 wt. % aqueous solution of carboxymethyl cellulose (CMC) based Au, Al2O3, Cu and TiO2 nanofluids obeying the Power law rheological model. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields are coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles f volume fraction (0 % =( fi =( 10 %) on the heat transfer characteristics of CMC based nanofluids over a wide range of nanofluid Rayleigh number (10[sub]3 =( Ranf =( 10[sub]6). Accurate numerical results are presented in the form of dimensionless temperature and velocity variations, isotherms, mean Nusselt number and heat transfer enhancement. The results indicate clearly that the heat and momentum transfer characteristics are affected only by the nanofluid Rayleigh number, while the type of nanoparticles (i.e. thermo-phyisical properties) and their volume fraction have effect only on the heat transfer enhancement.
COBISS.SI-ID: 16722966
Golden nanoparticles of different sizes and shapes (spherical, cylindrical, triangular and round) where prepared during a synthesis of gold with ultrasonic spray pyrolysis (USP) and hydrogen reduction. The experimental investigations of the (USP) method were performed with an ultrasonic source of 0.8 MHz and 2.5 MHz, acting on the water solution of HAuCl4 forming aerosols with micron-sized and nanosized droplets. The results of the investigation show that the final shape and size of the Au particles depend on the characteristics of the solution and the frequency of the ultrasound. The second step of synthesizing the Au nanoparticles includes the subsequent thermal decomposition of the aerosol droplets in a hydrogen atmosphere between 260°C and 500°C. The investigations showed that the Au nanoparticles prepared in this way are smaller and more homogeneous.
COBISS.SI-ID: 17274390
This paper discusses the application of rapid solidification by the melt-spinning method for the preparation of thin NiTi-based ribbons. Generally, the application of rapid solidification via melt-spinning can change the microstructure, improving the ductility and shape memory characteristics and lead to small-dimensioned samples. Several thousand thermal cycles were performed on the trained ribbons using bending deformation procedure, continuously observing the changes in the shape memory and transformation behaviors. These changes are due to the appearance of an intermediate phase which was stabilized probably by the accumulation of defects introduced by thermomechanical training. The influence of training and thermal cycling on characteristics of ribbons was studied by x-ray diffraction and transmission electron microscopy and differential scanning calorimetry. The results displayed that bending training methods were useful in developing a two-way shape memory effect (TWSME). All samples show a shape memory effect immediately after processing without further heat treatment. The addition of copper in NiTi alloys was effective to narrow the transformation hysteresis. The W addition has improved the stability of the TWSME and mechanical properties. The TWSME of ribbons and its stability are well suited for important applications such as microsensors and microactuators.
COBISS.SI-ID: 16580118
The SiO2 thin films were deposited on the surfaces of stainless steel tapes and their activity was particularly investigated from the aspect of the number density of hydroxyl groups on their surfaces. The calculation procedure of density of active OH groups includes determination of average length of silica chains that constitute silica sol particles with almost uniform size, on the base of TGA analysis. The size of SiO2 particles is analyzed by TEM microscopy and dynamic light scattering method. Fibroblast (L929) cell densities on the surfaces of these films were investigated using phase contrast microcopy. It was shown that there is a relationship between OH group densities and density of attached cells. Besides, the cytotoxicity effect was studied and compared for various thermally treated SiO2 thin films.
COBISS.SI-ID: 16965910