Tomáš Kubina

Study of Thermal Stability of Ultra Fine-Grained Commercially Pure Titanium Wire Prepared in Conform Equipment

Titanium and its alloys are frequently used in many sectors, including the health care sector, where they outperform other materials. From the biocompatibility viewpoint, the preferred condition of these materials is ultrafine or nanostructured state. Processes based on severe plastic deformation (SPD) that are capable of producing microstructures with sizes of the order of nanometers are gaining importance these days. Their typical limitation is the small volume of material processed. One of available ways to enhancing the productivity is to combine the CONFORM continuous extrusion process with the ECAP method. This paper describes initial experience with this combined process in the CONFORM 315i machine, which is equipped with a specially-designed forming die chamber. Influence the number of passes through CONFORM machine on thermal stability was study by horizontal dilatometer and heat-flux calorimeter. The impact of deformation on the shift in recrystallization temperature of pure titanium was confirmed. The microstructure evolution and the grain growth behavior were investigated by electron back scattered diffraction (EBSD) technique. The deformed UFG titanium was annealed at a range of temperature (400-600 °C) for up to 6 h. The grain growth kinetics was characterized by calculating the grain growth activation energy Q and the time exponent n based on the experimental results for deformed material. Data for annealing temperatures of 550 and 600 °C allowed the values of the time exponent n = 0.19 and activation energy Q = 248 kJ/mol were calculated.

Non-Traditional Use of Torsion Plastometer in Physical Simulation of Steel Production

The present paper provides a picture of metallographic and plastometric research in the border areas of steel production and forming. The focus of the paper is simulation conducted in SETARAM plastometer. The SETARAM plastometer used in the experiments has been modified recently. The changes concerned predominantly its temperature measurement and control devices. The lower limit of its operating temperatures was reduced to approximately 400 °C. The purpose of the most recent upgrade was to allow investigation in the region of steel brittleness related to loading in their freezing range. It will be possible to explore the behaviour of steels under the conditions of continuous casting processes, solidification in crystallizers and deformation during solidification. Microstructures of various types of steels are presented upon small continuous deformation applied at high temperature, which lead to partial melting and resolidification of test bars. Various types of sheet rolling simulations with reduced finish temperatures conducted in the plastometer are described. Approaches to evaluating continuous torsion tests to fracture in the field of basic research into materials plasticity are presented as well. In terms of interrupted tests, the importance of the anisotropic interrupted test as a source of information for research is touched upon. In particular, demonstration is given of the potential for finding transformation temperatures governed by deformation in the 1.0583 steel grade. A physical simulation procedure involving strain-induced ferritic transformation has been developed on the basis of results of tests. Mechanical properties were measured on specimens processed in the simulation. Microstructures resulting from the thermomechanical simulation are discussed.

Electro-chemical monitoring of static recrystallization

The electro-chemical potentio-kinetic method has proved to be a sensitive technique for monitoring of static recrystallization in austenitic steel AISI 304 after its cold forming and annealing. Results obtained in this manner are in very good conformity with the results of metallographic and X-ray analysis, as well as with the measured values of hardness. Corrosion current density appeared to be a suitable criterion for evaluation of development of relaxation processes.