Mirosław Szala

Pitting Corrosion of the Resistance Welding Joints of Stainless Steel Ventilation Grille Operated in Swimming Pool Environment

This work focuses on the pitting corrosion of ventilation grilles operated in swimming pool environments. The ventilation grille was made by resistance welding of stainless steel rods. Based on the macroscopic and microscopic examinations, the mechanism of the pitting corrosion was confirmed. Chemical composition microanalysis of sediments as well as base metal using scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS) method was carried out. The weldments did not meet the operating conditions of the swimming pool environment. The wear due to the pitting corrosion was identified in heat affected zones of stainless steel weldment and was more severe than the corrosion of base metal. The low quality finish of the joints and influence of the welding process on the weld metal microstructure lead to accelerated deposition of corrosion effecting elements such as chlorine.

Microstructural Characterisation of Co-Cr-Mo Casting Dental Alloys

The study compares the microstructure of three commercial dental cobalt matrix alloys with related chemical composition declared by the manufacturer. Casts were produced with lost wax method, then melted and casted with centrifugal induction casting machine. The Co-Cr-Mo alloys were casted according to the manufacturers procedure. The samples’ chemical composition and phase composition, respectively, using WDXRF (Wavelength Dispersive X-Ray Fluorescence) and XRD (X-ray Diffarction) methods were analysed. Casts microstructure by mean of LOM (Light Optical Microscopy), SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X-ray Spectroscopy) were investigated. Vickers hardness HV10 was measured. Quantitative microstructure evaluation was performed by means of computer image processing. The results of the chemical composition indicate the high stability of the chemical composition for alloy A. In case of alloys B and C, there was a significant difference in carbon content. Quantitative differences in image of microstructure between of castings A and B, C were noticed. The greater amount of precipitates was recorded for castings with higher carbon content. In all investigated castings, the presence of β matrix solution and M23C6 carbide precipitations was found.

INFLUENCE OF REPAINTING ON THE MECHANICAL PROPERTIES, SURFACE TOPOGRAPHY AND MICROSTRUCTURE OF POLYESTER POWDER COATINGS

The literature does not provide a systematic analysis of the effect of electrostatic powder coating repainting of structural and constructional aluminum elements on their technological parameters. It is industrial practice that worn or damaged coatings be repainted. It is crucial to determine the effect of electrostatic sprayed coatings repainting on their microstructure, roughness and mechanical properties. The aim of the work is to determinate the influence of repainting of powder deposited polyester coatings on their mechanical properties, roughness and microstructure. This study examined three different electrostatic spray epoxy coatings with matt, silk gloss and fine structure-matt finish. Test panels were prepared as singleand double-layer paint coatings on the aluminum alloy 6060 substrate. Hence, six test sets of coatings were deposited. Each set contained six samples. The microstructure of the cross section of coating was investigated by scanning electron microscopy (SEM) and light optical microscopy (metallographic and stereoscopy microscope). The chemical composition of coating was analyzed by the SEM-EDS method. The 2D surface roughness of singleand double-layer coatings and 3D surface topography maps were examined using a profile measurement gauge. The mechanical properties of coatings were measured by cupping, bending, impact, adhesion to substrate tests run according to standard procedures. As a result, the influence of repainting of polyester powder coatings on their properties was determined. The results demonstrate that repainting has no effect on the microstructure and coating adhesion to substrate as well as the bending test results and roughness of matt and silk gloss coatings. It has been found that repainting affects the results of impact and cupping tests as well as the roughness of samples with fine structure surface finish.