Michaela Remešová

Comparative Analysis of Hard Anodized Layer on Aluminium Alloy

Hard anodized layers were produced by two different manufacturers on the same type of aluminium alloy on a vacuum pump part of complex shape. The sulphuric acid/water solution was used to produce alumina layers, which were subsequently sealed in demineralized water. A comparative analysis based on metallographic methodology, with the aim to control the stability of alumina formation process and to identify its defects, was performed by means of light and scanning electron microscopy, surface profilometry and microhardness measurements. To determine the thickness of alumina layers, the image analysis was also used.

Analysis of Causes of Fractures of Terminal Board Bolts

The paper sums up the results of a complex analysis, using metallographic, microfractograpic and other methods, with the aim of establishing the cause of fractures appearing in bolts of a terminal board. The analysis has shown unambiguously that the bolt failure was a synergic effect of inadequately performed heat treatment and hydrogenation that occurred in course of surface treatment via pickling and subsequent zinc plating.

Application of Metallographic Analysis Techniques for Detection and Identification of Spray Paint Defects

The paper is focused on the metallographic analysis of spray paint films with defects. The painting has two important roles. Firstly, it protects the substrate material (ferrous, nonferrous and plastic) and secondly, it improves the appearance of the surface. Appearance and quality of painting film play an important role in the industry (automotive, aerospace, consumer electronics, etc.). Defects of spray painting film, which have a negative effect on the appearance of the product, can be detected and further analysed by common methods used in metallography. Such methods are very effective tool for revealing the cause of defects and their elimination within the technological process (degreasing, cleaning, pickling, drying, technological discipline, etc.). In this paper, defects were characterized by high-resolution digital microscope (LM) and scanning electron microscope (SEM) equipped with energy dispersive X-ray analyser (EDX).

Failure Mechanism of Yttria Stabilized Zirconia Atmospheric Plasma Sprayed Thermal Barrier Coatings Subjected to Calcia-Magnesia-Alumino-Silicate Environmental Attack

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.

Influence of Microstructure on Machinability of Material and its Final Surface Quality

Mechanical properties, such as hardness, yield strength and tensile strength, are very often considered as the only key factor for selecting technological parameters of materials machining. Analysis of the microstructure and specific microstructural parameters is not performed until serious problems occur during otherwise common machining processes. This study reports a few case studies, dealing with such problematics, which resulted from underestimation of the knowledge of macrostructure and microstructure of material. It deals with problems such as uncommon surface defects after machining or impossibility to use current technological machining processes when machining new batch of material.

Causal Analysis of Damage of a Cover

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.

Evaluation of Surface Degradation of Deoxidized AW-AlMg0.7Si Alloy

Corrosion of aluminium alloys due to chlorides is not rare in industrial practice. When detected, it is necessary to decide whether and how to remove the corroded areas and also to find the appropriate method for protection against further degradation. Appearance and quality of final surface is key factor in such cases. This study deals with final surface quality of aluminium alloy components and the extent of degradation after corrosion attack and subsequent chemical surface cleaning. Two AW-AlMg0.7Si alloy pipes, fabricated by two individual producers, were analyzed in order to reveal extent of atmospheric corrosion after the storage in the industrial area. Further analysis evaluated the influence of such degradation on final surface quality after surface cleaning by chemical way, using two different methods, namely deoxidizing and subsequent passivation. Special attention was paid to the influence of initial surface roughness on quality of final surface.

Preparation of Metallographic Samples with Anodic Layers

Anodization is an electrochemical process that converts the metal surface into a decorative, durable, corrosion-resistant, anodic oxide coatings. The thickness of the resulting layer depends on the process parameters (voltage, current, type of electrolyte, concentration and temperature of the electrolyte). In this work, the preparation of zinc metallographic samples with anodic layer is described. Samples prepared by anodic oxidation on the zinc substrate are rather brittle and porous. During the mounting, cutting, grinding and polishing the layer can be deformed which can affect the layer thickness measurements. The problem is to determine the boundary between anodic layer and resin. The cross-sectional micrographs were observed by scanning electron microscopy with the aim to improve anodic layers thickness measurements by means of digital image analysis.

Analysis of Surface Layer Defects on Carburized Steel Component after Alkaline Blackening

Alkaline blackening is one of the most popular surface treatment technology of components with the requirement for higher surface corrosion resistance, increased hardness, and the decorative appearance.This contribution deals with the appearance of surface defects on carburized steel components after the process of alkaline blackening, which appeared to be red shiny stains on an otherwise black matte surface of the component. The occurrence of defects on surface was observed several days after the alkaline blackening process. By means of metallographic methods, direct connection between surface defects and the microstructure of the material was found.Contribution further deals with the influence of microstructure and technological parameters on the quality of the final surface layer of the components.

Anodizing of Zinc-Titanium Alloy in NaOH and KOH Baths

Electrochemical process of conversion coatings formation on Zn-Ti alloy surface during one-step anodizing process was studied in NaOH and KOH electrolytes over the range of voltages (4-50 V) and constant time in order to investigate parameters for the origin of anodic zinc coating. Stainless steel was used as a counter electrode and electrolyte during the anodizing process was agitated by compressed air. Coatings microstructures and morphology were characterized by means of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Surface topography was investigated prior and after the anodizing using non-contact optical 3D profilometer. It was found that high voltage (50 V) and low concentrations of electrolyte (0.04 and 0.1 mol/L NaOH) led to origin of white coloured oxide coatings, while lower voltage (4 and 6 V) and higher concentrations of electrolyte promote the origin of black coloured oxide coatings. Concentration of electrolyte and voltage influenced the thickness of conversion coatings and its surface morphology. Moreover, the surface morphology of the coatings was also influenced by the heterogeneity of substrate alloy.