Contribution of Metallography to Production Problem Solutions II

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Authors: Ján Bezecný, Igor Barényi
Abstract: The paper describes practical examples of identification of rupture defect on steel components and its connection with the violating of the production process. Every violation of optimal production technology causes irreversible changes in the material that are visible on the fracture after breaking. Characteristics of the fracture allow the backward identification of specific technological reasons for defect fracture origin and consequent degradation of utility properties of the component. Documented examples include wide spectrum of production technologies where defective fractures can occur as are casting, forming, heat treatment or surface treatment. Wider notice is dedicated to the brittle fractures caused by non-optimal heat treatment. Presented fractures are documented by macroscopical as well as microscopical study using SEM microscope and they represent handy atlas of defects fractures with usage in real industrial practice.
Authors: Martin Švec, Pavel Kejzlar
Abstract: The research deals with the cause of destruction of pressure bottles heads during ordinary operation. The scanning electron microscope (SEM) equipped with an energy dispersive detector (EDX) for local chemical analysis was used for material investigation. The analysis revealed selected oxidation penetrating deep into the material causing the loss of cohesion of phase boundaries leading to brittle fracture.
Authors: Petr Jonšta, Irena Vlčková, Zdenĕk Jonšta, Mariusz Król
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.
Authors: Břetislav Skrbek
Abstract: The specifics of low-alloyed cast irons after EN 16124 standard of type GJS SiMo for high temperature applications of exhaust tracts of internal combustion piston engines. Boundary exposition temperature. Structure failure of cast iron by temperature overloading. Metalography, SEM, XRD of overexposed exhaust pipelines. Failure reason hypothesis of useful properties by exceeding of critical temperature.
Authors: Stanislav Krum, Františka Pešlová, Jakub Horník, Maxim Puchnin
Abstract: The paper deals with the influence of thermal load on functionality of the Toolox 33 hot work tool steel equivalent to the materials of W.Nr. 1.2311, 1.2312, 1.2738 and P20 in order to assess its suitability as a material for glass manufacture preform. Using light and electron microscopy it was shown that the steel was highly unfitting for this application where the steel comes into contact with the hot glass. Regarding the evaluation of the microstructure, it was shown that intense decarburization reflecting on the fracture behaviour of the surface layer during the thermal load has occurred. This fact was confirmed by a static tensile test and hardness measurements. Moreover, the thick layer of flakes has formed on the surface.
Authors: Ladislav Čelko, David Jech, Pavel Komarov, Michaela Remešová, Karel Dvořák, Ivo Šulák, Bedřich Smetana, Karel Obrtlík
Abstract: The contribution focuses on the description of failure mechanism of atmospheric plasma sprayed multilayer thermal barrier coatings subjected to calcia-magnesia-alumino-silicate (CMAS) environmental attack. To identify exothermic and endothermic reactions which occurred during heating/cooling by means of calorimetry was also utilized initial yttria stabilized zirconia (YSZ) powder subsequently used for thermal spraying of multilayer thermal barrier coating system (TBCs), CMAS powder later on utilized for thin layer deposition and its mixture. Atmospheric plasma spray technique was used to produce the TBCs on a grit blasted nickel-based superalloy substrates, where CoNiCrAlY powder was used for deposition of a bond coat and YSZ powder was sprayed as a top coat. In accordance to the aerospace standard the thin layer of CMAS was deposited on as sprayed TBCs samples surface from its colloidal solution by paint brush method. Burner-rig test, utilizing direct propane-oxygen flame, was used for thermal cyclic exposition of the multilayer coated samples at the temperature of 1150 °C. Samples after thermal cyclic exposure test were investigated by means of materialographic analysis approaches. The significant reduction in life-time of CMAS coated YSZ top coat was observed due to lower melting point phase formation and molten silicate crystallization within the pores providing the spallation identified as a major mechanism of TBCs failure.
Authors: Vladimír Mára, Jakub Horník, Elena Čižmárová, Jan Krčil, Pavlína Hájková
Abstract: The problematic of welding in terms of weld quality in dependence on service life of mechanical structures is discussed. Some examples of inadequate quality weld joints causing failure under load are described. Materials of the evaluated welds were following: S355 steel and Inconel 635 super alloy. Service conditions of homogeneous welds were different for both materials and weld quality was covered by Welding Procedure Specification. Using metallographic evaluation, the main problems were detected in a form of geometrical imperfections or insufficient penetration. These existing imperfections combined with static and dynamic load initiate the partial malfunction or failure of parts or constructions.
Authors: Pavel Kejzlar, Martin Švec, Zuzana Andršová
Abstract: The research deals with determination of the breaking cause of the screws used to attach the truck cabins. Scanning electron and light optical microscopy were used for engineering investigation of the fracture cause. Fractographical and structural analysis revealed fatigue mechanism of the screw fracture with morphology corresponding to the combination of tensile and bending stresses. Based on the acquired results a structural adjustment was recommended to the customer.
Authors: Lucie Páleníková, Lenka Klakurková, Pavel Gejdoš, Michaela Remešová, Martin Juliš, Ladislav Čelko
Abstract: In this article, the causes of damage of a cover were investigated by metallographic and fractographic analysis. The component part was made from non-alloy quality steel for cold forming DC04. The failure occurred during high temperature pulsation (90 °C, 7b, 1 Hz) after 180,000 cycles. This component part was fabricated by deep drawing. After this process’s step, outlets were soldered at 1100 °C/5 min. to this part and then whole component part was coated using method without any specification. The coating layer was formed of Zn-Ni. The last step in this process was hemming where all component parts were assembled together. This case study was solved using light and scanning electron microscopy. The chemical composition was detected by energy dispersive X-ray analysis.

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