Josef Zapletal

Evolution of microstructure and electrochemical corrosion characteristics of cold compacted magnesium

Abstract The main advantage of magnesium and its alloys is high specific strength and biocompatibility. A modern approach to magnesium-based materials preparation is powder metallurgy. This technique allows preparation of new materials with a unique structure, chemical composition, and controlled porosity. In this study, cold compaction of magnesium powder was studied. Magnesium powder of average particle size of 30 μm was compacted applying pressures of 100 MPa, 200 MPa, 300 MPa, 400 MPa and 500 MPa at laboratory temperature. Influence of compacting pressure was studied with microstructural and electrochemical corrosion characteristics analysis. The resulting microstructure was studied in terms of light and electron microscopy. Obtained electrochemical characteristics were compared with those of wrought magnesium. Compacting pressure had a significant influence on microstructure and electrochemical characteristics of prepared bulk magnesium. With the increase in compaction pressure, the porosity decreased. Compacting pressures of 300 MPa, 400 MPa and 500 MPa led to the similar microstructure of the prepared material. Polarization resistance of compacted magnesium was much lower and samples degraded faster when compared to wrought magnesium. Also, the corrosion degradation mechanism changed due to the microstructural differences between the material states.

Thermal Spray Technology and Casting in Renovation of Friction Bearings Surface

The contribution deals with an analysis of thick wear-resistant coatings produced on the surface of cast iron friction bearings by means of twin wire arc spraying or by pouring, with the aim of comparing the two manufacturing technologies. In addition to a detailed analysis of the microstructure and phase composition of the two types of coating, their mechanical and adhesion properties were established (using tensile and shear stress testing methods as well as cyclic thermal shocks).

The Optimization of the Isothermal Transformation Dwell of the ADI Obtained at Transformation Temperature of 380 °C

The structure of austempered ductile iron (ADI) matrix and consequently its mechanical properties are influenced by the heat treatment conditions, above all by the temperature and dwell length of isothermal transformation. The paper is focused on deeper understanding the interrelation between matrix mixture composition and static mechanical properties of ADI in dependence on the isothermal transformation dwell. Practical aim of the paper is to find the optimal isothermal transformation dwell range for ADI isothermally transformed at the temperature of 380 °C with emphasis on the level of static mechanical properties in tension. Microstructure and mechanical properties changes that proceed during isothermal transformation are observed and evaluated for the transformation dwells of 2, 5, 10, 25, 60, 120, 270, and 540 minutes.