Materials Science Forum Vol. 729

Abstract: This paper wants to find one of the solutions to control the coated surface properties. The surface layers control is not easy. We have a very simple test like hardness test to get some important information of the surface, but in case of the coatings we need to do this test very circumspectly. The hardness test results always depend on the surface roughness, the coating microstructure, the layer thickness and the type and load of the hardness test. The chose method was the nanohardness test which gave the penetration depth us function of the very small load.

Abstract: There is an active research work in the field of amorphous alloys since the discovery of metallic glasses, half a century ago [. In contrast with crystalline alloys, amorphous one have unique material properties, e.g. high yield strength, superior elastic limit, high corrosion resistance, unique acoustical properties [2,. Producing amorphous alloys, it is first necessary to quantify the forming of structure and define the amorphous amount. All of the methods to determine the structure have advantages and disadvantages. An accurate determination of amorphous volume fraction can be accomplished by transmission electron microscopy (TEM), this observation is much localized [ and the evaluation is difficult. The most common techniques to determine the amorphous fraction are XRD and DSC methods, which reflect the entire sample [. However, XRD has a detection limit depending on the type of equipment. Apart from this fact, it is an admitted method in researches, if the XRD reflexion shows an amorphous halo. Amorphous fraction transformed to crystalline can be measured by DSC. This method is much sensitive to impurities, especially oxygen, which can influence on the results.

Abstract: Hydraulic system is commonly used in the modern strip rolling mills to adjust the gap between the work rolls. Automatic gauge control based on the hydraulic systems is commonly used in modern strip rolling mills to adjust the gap between work rolls. The dynamic control of rolling gap and force is achieved by using electro-hydraulic servo actuators so-called hydraulic capsules which can adjust the rolling gap dynamically for high rolling force. The basic aim of the paper is to define an observer which could forecast the required maintenance of hydraulic cylinder using parameter estimation of the mill model.

Abstract: There are several methods to evaluate the antimicrobial efficiency of the plastics. In recent work we intended to collect these methods together and compare. There are some methods, which are basically used in the microbial practice for testing antibiotics, and give a good ground for testing other materials. Some other simple methods exist, which can also be used, so the contact between the sample and the inoculums can be solved in many ways.

Abstract: As a result of the collective efforts of engineers and physicians modern medicine is one of the most developed discipline nowadays. The invention of stents is one of the most important result of these works. With development of stents artery narrowing, which can often lead to death, can be efficiently treated. The stent is a biocompatible mesh, which is inserted into the narrowed section of the artery to dilate and prop up its wall hereby it ensures continuous blood flow. The bio-and haemocompatibility of stents have to be sufficient to avoid significant recurrent stenosis (restenosis). Better biocompatibility can be achieved using surface treatments such as chemical etching, electropolishing and coatings. In our research we developed self-expandable stents made of shape memory Ni-Ti alloy called nitinol. In this article the present stage of our work, the electropolishing experiments are summarized. A new electropolishing cell was worked out by using special stent holder to lead the current to the stent, which made possible the even electropolishing of the stent surface. The electrolyte, which was applied, contains less than 5% of perchloric acid. A current interval was determined which will be sufficient to determine the optimal polishing parameters, such as polishing time and current density with further researches.

Abstract: During brazing of austenitic stainless steel with copper based brazing material a common failure occurs, namely that the brazing material solutes along grain boundaries, which look like cracks. This unfortunate effect occurred when AISI 304 steel is brazed. To avoid this unwanted effect since the cracks propagate mainly on high angle grain boundaries our goal was to enhance the number of special coincident site lattice type grain boundaries with thermomechanical treatment. Experiments were performed for 1, 48 and 72 hour heat treatments at different level of cold rolled materials. After the thermomechanical treatment significant decrease in the crack size was found in depth and width, respectively. The grain boundaries were investigated on electro polished samples in an electron microscope with electron backscattered diffraction technique. The brazing was made with Boehler SG-CuSi3 brazing material.

Abstract: Certain phase transitions take place at a given temperature in the equilibrium phase diagrams, the values of their temperatures can exactly be measured so it is an essential task to calculate these values by a high accuracy. New parameters were introduced into the ESTPHAD equation for calculating the so-called non-variant points. By using the ESTPHAD method, the accuracy of calculations are compared to the data used for the calculations so the exact calculation of the temperatures of non-variant points are defined as compared to the data used for the calculations.

Abstract: This paper deals with the recrystallization of high purity copper. Cold rolled specimens heat treated in the DSC apparatus by constant heating rate to chosen temperatures, after that water quenched producing partially recrystallized microstructure. Microstructure of samples investigated by EDSB.

Abstract: In this article the complex research and development project of the laser cutting micromachining of nitinol alloys are shown. The laser cutting parameters of the 1.04 mm inner diameter and 0.1 mm wall thickness nitinol tubes are also shown. The laser cutting parameters of micromachining and the cut surface of nitinol tubes are summarized when 3 mJ pulse energy, 0.02 ms pulse duration, 6 bar Ar gas pressure, 3000 Hz frequency, 10 mm/s rotation speed and 5 mm/s² speed-up were used. The effect of the laser cutting to the raw material is characterized by microstructural and micromechanical examinations. A detailed description is given of the energy input by laser beam machining. The pulse and the impact of the applied pressure parameters of the gas to the raw material are also shown.

Abstract: This work studies the effect of multiple forging (MF), followed by cold rolling, on the tensile and bending behavior of Al 7075 alloy. The raw material was received as a rod shape. The specimens were subsequently cut and annealed at 450 °C for 30 minutes. The cylindrical specimens were subjected to MF at 250°C for three passes, then the bulk of multiple forging specimens were faced rolling at room temperature. Three different base materials were tested, raw material (as received then annealed), MF material, and rolled sheet. Hardness test, tensile test, and bending test were carried out in order to measure the mechanical properties, which are affected by the MF and cold rolling. It has been proved that the MF base specimens have higher tensile strength and better maximum elongation comparing with the raw material specimens. Rolled sheets specimens have got the highest tensile strength and lowest ductility. The result of bending test was similar to the tensile test results, beside these mechanical tests some metallographic samples were performed to help finding an explanation of this properties change.