Materials Science Forum Vols. 537-538

Abstract: Temperature dependence of different parameters (the position of the inflexion point and the saturation value on the root main square, RMS, values versus exciting field curves) of the Barkhausen noise is measured in structural steel (S 235 JRG1). It is shown that while the position of the inflexion point remained constant, the RMS value at the inflexion point and saturation value increased with the increasing temperature, T. Most interestingly the field required for saturation decreased with decreasing temperature and had a breakpoint at about 200K. Breakpoints at the same temperature on the critical exponents versus temperature functions (i.e. on the β(T) and α(T) curves, where β and α are the exponents of the probability distributions of peak heights and durations, respectively) were also observed. This temperature can be identified as the ductile-brittle transition temperature.

Abstract: The technical textiles are very sensitive materials. To measure the elongation of such a material needs special care. A photographic procedure has been investigated to measure the plain elongation of textile specimens. It is especially suitable for long-term measuring programs. Some experimental results measured by the described method are published.

Abstract: Color etching is a widely used technique for visualizing different phases in metallic materials. Its advantage to the traditional etching techniques is that it gives additional information within one phase, namely, the color shade of a given phase can change in a certain range. This paper demonstrates that, due to the physics of the color etching, the shade of a phase also depends on the crystallographic orientation of the investigated grain. As a test material, spheroidal graphite cast iron was used, and individual grain orientation was identified by automated electron back scattering diffraction (EBSD). Results showed that there is a strong correlation between grain orientation and the shades obtained by color etching.

Abstract: When investigating the wear phenomena often there is a need for studying the wear process on the basis of variable parameters (microstructure, surface roughness, and load). A new experimental method was developed thorough several set of tests, by which the effects of the mentioned parameters in the wear process can be examined. The method is based on the ball/plane contact which is suitable for examination of the local wear phenomena. There is a point like contact at the beginning of the experiments. The equipment gives the opportunity to analyse the “behaviour” of the specimens depending on the given load (normal load), on the rotations per minute, and on the surface roughness (Ra). The roughness of the counter ball does not change during the tests because of the random walk motion of the ball. A good understanding of the microstructure and its influence on wear resistance is of great importance to designers and engineers in selecting wear-resistant materials [1]. Under conditions of severe wear, the original structure with higher hardness does not exhibit a better wear resistance [2]. The experimental results demonstrate the influence of the local microstructure on the mechanism of the wear process and the dependancy of wear resistance as a function of the microstructure.

Abstract: In this work we present the investigations on the determination of the mechanism of sodium loss in High Pressure Sodium (HPS) lamps. The transport through the ceramic arc tube consists of several steps (solution in the ceramics, diffusion through the ceramics, leaving the bulk phase, evaporation from the surface). Among the listed processes the mechanism of the diffusion was investigated by model-experiments. A ceramic arc tube was applied as a reactor chamber, in which polycrystalline ceramic plates were heated at 600-1100°C in controlled Na and Xe atmosphere. The sodium diffusion profiles developed by the heat-treatment were measured by XPS and SIMS and from the measurements we tried to draw a conclusion about the mechanism of sodium diffusion through the ceramic discharge tube. The ceramic discharge tube were measured by X- ray diffraction, too. We found traces of some Na-O-Al compound.

Abstract: A new type of vibrating sample magnetometer (VSM) was designed for measuring the magnetic properties of soft and hard magnetic materials is described. The developed instrument differs from the traditional Foner type because in our system the motion of the specimen is parallel with the lines of the external magnetic field. Therefore, this instrument can be called parallel motion vibrating sample magnetometer (PMVSM). The special vibrating system contains a vibrating rod which holds the specimen. This arrangement can make the sample replacement and positioning fast and convenient. Because of the versatility of the PMVSM instrument it could be a useful measuring device for materials science laboratory and educational purposes as well.

Abstract: In this work the magnetic anisotropy of the 15Mo3 type steel was investigated which was induced by deterioration process caused by thermal shock fatigue. The applied thermal shock fatigue investigation can model the material degradation due to long term service in high temperature environment. The 15Mo3 steel is widely used as reheating pipeline base material of power plant boilers. Magnetisation curves were measured to characterise the induced magnetic anisotropy due to thermal shock fatigue process. A parallel motion vibrating sample magnetometer (PMVSM) which was designed at the Department of Materials Science and Engineering of BUTE was used for the magnetic measurements.

Abstract: This paper presents an overview about results of mechanical testing of human tendon. We are dealing with the main function of tendon and touching on typical insurance of tendon and reconstruction of them. Since the material characteristic of tendon and dynamic models of them are not known there was made a lot of uniaxial tension test and based on measuring results built up a linear lumped model for dynamic simulation using the synthesis method. As results we can already provide quantitative data about mechanical bearing capacity of tendon beside known qualitative categories. Paper shows a well working fixing technology for tendons during tension test.

Abstract: Year by year the user and process site of steelmarket keep growing and lay claim to the steelmakers. The researchers, developers and technologists use every effort to try to produce steels with compound properties. From claim of users –especially the Automotive Industry – developed the DP- (Dual Phase) and TRIP - steels (TRansformation Induced Placticity). In the Automotive Industry draft mostly the claim of loose of weight and increase the safety reserve.Welding of these Advanced High Strenght Steels (AHSS does have but very few publications and studies approach the subject). This study is about problems of weldability of Dual Phase and TRIP – steels. Welding difficulties were associated with hard and brittle spot weld nuggets and fusion weld heat affected zones being caused by nitrid. Our aim is to develop a welding procedure giving good quality of spot weld, thus the problem of hardened and brittle spot welds would cease to exist.

Abstract: In recent years, several attempts have been made to characterize the geometric structure of fullerenes by means of topological shape factors in order to predict their physical properties and stability. In this paper, we present a simple method to estimate the stability of fullerenes on the basis of quantitative topological criteria. This approach is based on the concept of the generalized combinatorial curvatures defined on the set of simple graphs embedded on a closed surface without boundary (sphere, torus, projective plane, Klein bottle). It is shown that starting with the computed generalized combinatorial curvatures several novel topological indices can be generated. From computations performed on a set of C40 and C60 fullerenes, we concluded that the four topological shape factors tested (Λ(-1), (-1), Λ(1) and (1)) could be successfully used to preselect the most stable fullerene isomers.