Papers by Author: Krzysztof Radwański

Abstract: The temperature-dependent mechanical stability of retained austenite in medium-Mn transformation induced plasticity 0.17C-3.3Mn-1.6Al-1.7Al-0.22Si-0.23Mo thermomechanically processed steel was investigated using scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods. Specimens were deformed up to rupture in static tensile tests in a temperature range 20–200°C. It was found that deformation temperature affects significantly the intensity of TRIP effect. In case of specimens deformed at temperatures higher than 60°C, a gradual temperature-related decrease in the stability of γ phase was noted. It indicates a progressive decrease of the significance of the TRIP effect and at the same time the growing importance of the thermally activated processes affecting a thermal stability of retained austenite.

Abstract: The work focuses on the analysis of microstructural features of retained austenite in a thermomechanically processed Si-Al TRIP-type steel microalloyed with Nb and Ti. Austenite amount was determined using XRD and EBSD. Combined methods of LM, SEM and EBSD were applied to reveal the morphology, grain size and distribution of structural constituents. It is possible to retain 14% of  phase enriched in C to about 1.14 wt.%. Retained austenite is uniformly located as blocky grains with a diameter up to 4.5 m in a fine-grained ferritic matrix or between bainitic ferrite laths as thin layers. Special crystallographic relationships between bainitic ferrite and retained austenite were identified on the basis of the analysis of misorientation angles and image quality values.

Abstract: . In this study, commercial Al was subjected to plastic deformation by multi-axial compression. The microstructure and mechanical properties in dependence on effective strain were studied. Aluminum was processed to effective strain f = 9.6. The misorientation distribution and subgrain/grain size were analyzed by using a scanning electron microscopy (SEM) equipment with electron back scattered diffraction (EBSD) facility. The dislocation microstructure was investigated by a scanning transmission electron microscope (STEM). The mechanical properties as: yield strength (YS), ultimate tensile strength (UTS), uniform and total elongation were performed on MTS QTest/10 machine equipped with digital image correlation method (DIC). Deformation of Al by the multi-axial compression leads to grain refinement to ultra-fine grains (UFGs) and improvement in strength properties. Material exhibits the following strength parameters: UTS: 129 MPa, YS: 124 MPa after deformation at f = 9.6. These values are about two times higher compared with initial state.

Abstract: In this study, commercial Cu was subjected to plastic deformation by compression with oscillatory torsion. Different deformation parameters were adopted to study their effects on the microstructure and mechanical properties of Cu. The deformed microstructure was characterized by using scanning electron microscopy (SEM) equipment with electron backscattered diffraction (EBSD) facility and scanning transmission electron microscopy (STEM). The mechanical properties were determined on an MTS QTest/10 machine equipped with digital image correlation. Can be found, that process performed at high compression rate and high torsion frequency is recommended for the refining grain size. The size of structure elements: average grain size (D) and subgrain size (d) reached 0.42 m and 0.30 m respectively, and the fraction of high angle boundaries was 35%, when the sample was deformed at a torsion frequency f= 1.6 Hz and compression rate v=0.04 mm/s. Deformation at these parameters leads to an improvement in strength properties. The strength properties are about two times greater than the initial state.

Abstract: The annealing behaviour of monocrystaline Cu processed by Cyclic Extrusion Compression (CEC) was investigated. The effect of the CEC strain on the annealing behaviour of submicrometer grained structure was studied by examination of the microstructural changes of the samples processed by two different CEC strains, 4.8 and 13.9 during annealing at 300oC for the time in the range from 1sec to 120 min. The results show that microstructure is stable up to an annealing time of 15 min. At a higher time of annealing (above 15 min), a gradual grain growth occurs.

Abstract: Different techniques have been used to introduce large strains into metals, for example torsion under pressure (HPT), cyclic extrusion compression (CEC), equal channel angular extrusion (ECAE), or accumulative roll bonding (ARB). Recent investigations are focused on analyzing new and alternative techniques for introducing severe plastic deformation (SPD) and to compare SPD techniques in terms of grain refinement and enhancement of properties. Compression with oscillatory torsion was applied to 0H18N9 austenitic steel to achieve a large strains. The microstructure was characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Formation of deformation twins and shear bands are responsible for the structure refinement in materials with low stacking fault energies (SFEs) such as austenitic steel. The investigations revealed, that nano-sized grains of 0H18N9 steel after processing by compression with oscillatory torsion are found in three different types of regions.