Papers by Author: Ludwik Błaż

Abstract: There are several known severe plastic deformation (SPD) methods, which allow receiving nano-grained structure of materials. One of the methods is called the KOBO method (the name is composed of the first two letters of the surnames of the inventors: KOrbel and BOchniak). The method was used for extrusion of copper alloys at room temperature to manufacture thin-wall tubes. During the KOBO extrusion, reversible cyclic torsion of the material results in multiple changing the deformation path. Hence, a heavy localized plastic flow leads to shear bands development that reduces the total strain hardening effect and results in effective structure refinement. In particular, thin-wall tubes produced from single-phase copper alloys, intensively cooled close to the die outlet, had homogeneous structure consisting of fine grains/subgrains of a few hundreds nanometers in size. The final structure of the material is practically independent on the initial structure of processed billets. If the accelerated cooling of extruded material was omitted, grain coarsening to the size of dozens of micrometers was observed. In multi-phase copper alloys, the grain refinement was limited to about 1 μm, both for intensively cooled and air-cooled products.

Abstract: The effect of hot deformation process on the structure within the temperature range corresponding to the g→a+P transformation was tested for commercial carbon steel containing of 0.158% C. Hot compression tests were performed at computer controlled constant cooling rate. Before testing CCT diagrams were carefully determined in order to fit hot deformation conditions to the g→a+P phase transformation range. The material microstructure was examined by means of optical and electron transmission microscopy. It was found that ferrite, pearlite or bainite were typical microstructural components observed at hot deformed samples. Localized distribution of pearlite or bainite that resulted from flow localization was observed rarely. Precipitation of carbides on ferrite grain boundaries is the most typical microstructural effect of the hot deformation/precipitation interaction that was noted for the most of hot deformed samples.