Papers by Author: Zdenĕk Jonšta

Abstract: Cobalt-based superalloys are among the most important materials for application in the demanding conditions of the glass industry. These superalloys with extended life are due to their excellent heat-resistant properties an important part of glass tools, especially of spinning discs. In the submitted paper, a material analysis of the commercially produced cast cobalt superalloy for spinning discs, including metallographic analysis supplemented by an electron X-ray analysis of minority phases, is carried out. An assessment of harmful gases, in particular oxygen and nitrogen, has also been carried out. They appear to be the cause of defects that often lead to the subsequent degradation of the material.

Abstract: This paper presents the results of structural phase analysis of MAR-M247 superalloy. Analysis was performed at initial and in as casted state after various type of solution annealing in the range 900 °C to 1240 °C with cooling in water. Presented polycrystalline alloy is heat resisting nickel superalloy, especially usable for highly strained components in the industry producing stationary gas turbines and aircraft engines. Analysis was performed using of a Quanta FEG 450 scanning electron microscope with micro-analytic system Trident APEX-4 which have identified presented minor phase. Attention was also paid to its eventual changes after different type of solution annealing.

Abstract: The paper presents the results of material analysis of material of the main bearing of the underground mine hoisting engine, which degraded after a time shorter than the guaranteed service life. The material analysis was performed using metallographic and electron microscope analyses. Cutting of the samples was made by water jet in order to avoid affecting of the structure.

Abstract: Thepaper deals with an experimental measurement of the transformation temperatures of Co-base alloy. Temperatures were determined by means of DTA-method during controlled heating and cooling. The samples in an as-received state were analysed at heating/cooling rates of 2, 5, 10 and 20 °C/min with the use of the equipment Setaram SETSYS 18TM (DTA-method). The samples after various heat treatments were analysed at heating/cooling rate of 5 °C/min by Setaram SETSYS 18TM (DTA-method). On the basis of evaluation of the results the influence of heating/cooling rate on shift of the transformation temperatures was determined. The influence of heat treatment on shift of the transformation temperatures was also studied. The samples in an as-received state and the samples after heat treatment were alsosubjected to the phase analysis by scanning electron microscopy using the microscope JEOL JSM-6490LV equipped with an energy dispersive analyser EDAX (EDS INCA x-act). The individual phases were identified by semi-quantitative X-ray microanalysis.

Abstract: Contamination of steel by excessive amount of non metallic inclusions leads tosignificant deterioration of its quality and consequent degradation. Cause of degradation of forgedrotors for steam turbines made of NiCrMoV steel grade is examined in this paper. Metallographicand electron-microscopic analyses were performed, including X-ray microanalysis for detecting thepurity of the forging being examinated. Concurrently, the consequence of failed technologicalproduction process, namely the influence of broken brick for argon blowing at the casting ladle, wasalso examined.

Abstract: The presented paper deals with comparison of spur gears classical and modern hardening process of the bending fatigue properties. It concerned particularly the hardened surface of the tooth flank using optical source of electromagnetic radiation. The results of fatigue tests were obtained on a servo-hydraulic testing machine LFV 100 kN made by walter+bai ag. These tests were defined by the standard ISO 6336 as method B, when testing is carried out under reference conditions close to the real operation. Comparison of test samples is also carried out on the basic of the achieved local hardness and hardened layer thickness in the tooth root, which is an initiation of fatigue crack.

Abstract: This article deals with testing of fatigue properties of hardened gears at bending. These tests are defined by the standard ISO 6336 - method B, when testing is carried out under reference conditions close to the real operation. This type of testing may be helpful to evaluate the influence of new materials, design parameters, production technology, or the effects of surface finishing. The first part of this article deals with the theory of fatigue testing methodology using modified stair-case method and characteristics of the testing machine. The second part of the paper is devoted to the characteristics of the experimental material and the results achieved. The case hardened steel gears alloyed by Cr-Ni-Mo were selected for the experiment. Hardened gears were subjected to local hardness measurement and subsequently the bending fatigue tests were performed. Ruptured samples were analyzed using a scanning electron microscope. The local bending stress was determined using the modified computational model based on the ISO 6336 standard methodology. The focus of this work consisted in evaluation of the influence of the filler root surface treatment on fatigue limit at bending on the basis of the realized experiments and their confrontation with the equivalents specified in the standards ISO 6336 and ČSN 01 4686.

Abstract: In the paper we present measurements of transport physical parameters such as thermal conductivity, diffusivity and specific heat capacity and dc electrical conductivity as well as the mechanical values E*, tg δ for rubber compounds filled by different ratio of silica - carbon black fillers. From presented results it is possible to see that proper filler concentration (rubber blend - silica - carbon black) rising all thermal parameters as well as mechanical properties represented by complex Young’s modulus and so, maintains the good mechanical parameters of the blend and finally it also lowers the electrical resistance. All trends are favourable for the improvement of useful rubber blends properties.

Abstract: In this paper, we present the results of complex thermo-mechanical analysis (CTMA). In the technical point of view CTMA contains both thermovision camera and tensile machine which are in a perpendicular position. We have measured the cooling curve of the sample after its tensile deformation. On the basis of an exponential model of cooling body with respect to Biot number Bi value it is possible to calculate the specific heat capacity , thermal diffusivity and thermal conductivity . The method has been tested on a variety of materials and the results have been compared to those in charts or obtained by reference independent experiments. We obtained a very good agreement of all gathered experimental results with those of comparative ones. We also measured mechanical properties of materials such as yield stress, tensile strength, Young´s modulus of elasticity and ductility.

Abstract: The present work is focused on complex evaluation of crack profiles, created around Vickers indents in two types of cutting tool ceramics, namely in the Al2O3 + ZrO2 ceramics and -Si3N4. The geometry of Vickers indents is investigated using two different evaluation methods. The first one is based on the application of serial sectioning from the indented specimen surface. The second method consists in the layer removing from plane perpendicular to the indented surface. These evaluation methods are convenient for determine the shape of created cracks and profiles of deformed area developed around the investigated indents. The mentioned methods contribute to the understanding of physical engineering principles resulting from the radial/median and lateral crack formation as the important characteristics influencing the reliable technical application of investigated ceramic materials.