Papers by Author: Kinga Rodak

Abstract: This paper focuses on the effect of rolling with cyclic movement of rolls (RCMR) on microstructure refinement, mechanical properties and electrical conductivity of CuCr0.6 alloy after applying different heat treatments (quenching and aging). It was found that the presence of second phase particles obtained during aging treatment has a significant effect on the formation of ultrafine grain (UFG) structure during the RCMR processing. The presence of high dislocation density inside subgrains and presence microshear bands are the marked features of the microstructure after aging at 500^°C/2h and RCMR deformation. Whereas after aging at 700^°C/24h and RCMR processing, fine precipitates were effective in inhibiting the grain/subgrain boundary motion. The RCMR processed alloy after aging at 500^°C/2h shows high mechanical strength attributed to the high density of coherent precipitates and ultrafine grained structure. The RCMR processing induces a significant reduction of the electrical conductivity for samples at quenching state but for samples at aging state electrical conductivity was restored thanks to precipitation process.

Abstract: The results of the microstructure and hardness investigations of the Cu-0.8Cr alloy after application of severe plastic deformation (SPD) implemented by rolling with the cyclic movement of rolls (RCMR) are presented in this paper. Performed substructure investigations showed that using the RCMR method can refine the microstructure of Cu-0.8Cr alloy to the ultrafine scale. The structure of the Cu-0.8Cr alloy was analyzed using light microscope (LM) and scanning transmission electron microscope (STEM). The quantitative studies of the substructure was performed with "MET-ILO" software, on the basis of images acquired on STEM microscope.

Abstract: The article presents the dynamic mechanical properties of two types of high manganese austenitic steels. The investigation were carried out for the wide range of strain rates from 1×10^-4s^-1 up to 4×10³s^-1 using servo-hydraulic testing machine and Hopkinson bar for the quasi-static and dynamic loading regime, respectively. The mechanical properties at different strain rates as well as the SEA indicator calculated were carried out on the base of the results of impact tests. In the next step, the microstructure of the steel after different deformation rate was observed and analyzed by light microscope in order to disclose a TWIP effect.

Abstract: The influence of initial soaking and parameters of plastic deformation on the deformability of A-286 superalloy have been presented. The hot-torsion tests were executed at constant strain rates of 0.1 and 1.0 s^-1, at testing temperatures in the range 900-1150°C and were conducted until total fracture of the samples. Plastic properties of the alloy were characterized by worked out flow curves and the temperature relationships of flow stresses and strain limits. Activation energy for hot working Q was assessed for the alloy after two variants of previous heating, i.e. 1100°C/2 h and 1150°C/2 h.

Abstract: The influence of prolonged aging on the precipitation process of intermetallic phases, as well as carbide and boride in an Fe-Ni superalloy has been studied. The samples were subjected to a solution heat treatment at 980°C for 2 h and water quenched, and then aged at 715, 750 and 780°C for 0.5-500 h. The samples were analysed using transmission electron microscopy (TEM) and X-ray diffraction. Direct measurements on the electron micrographs allowed to calculate the mean diameter () of the γ’ phase. The growth step of the γ’ phase particles has been analysed on the basis of the LSW theory, as well as the activation energy of the γ’ phase coagulation has been estimated.

Abstract: In the paper, results of impact bending tests of a high-manganese steel of X30MnAlSi26-4-3 grade are presented. The tests were carried out using a flywheel machine, suitable for dynamic tensile tests and impact bending tests in the range of linear velocity of the forcing element from 5 ÷ 40 m/s. The obtained test results were compared with the results of impact resistance of the studied steel determined using Charpy machine. Structural investigations were carried out using light microscope and scanning transmission electron microscopy. Creating a mechanical twins at different strain rates was analyzed. The surfaces of fractures formed in the break point during bending tests were analyzed, and they indicate a presence of mixed transcrystalline fractures with a predominance of plastic fractures. Substructure studies revealed the presence of mechanical twinning induced in a high strain rate for the X30MnAlSi26-4-3 steel.

Abstract: The complex microstructure of as-cast AlSi7Mg alloy has been investigated. Microstructure observations were done using light microscopy, scanning electron microscopy and transmission electron microscopy. Chemical composition of the microstructure constituents was investigated by means of energy dispersive spectrometry, conducted both during SEM and STEM investigations. Selected area diffraction was used to identify the phases in the alloy. Microstructure of the alloy in the as-cast condition consists of Al-Si eutectic and intermetallic phases in the interdendritic regions. These are: Mg₂Si, α-AlFeMnS, β-AlFeSi and π-AlFeSiMg phases. What is more, number of fine precipitates were found within the α-Al dendrites. Only the occurrence of U1 (MgAl₂Si₂) phase has been confirmed.

Abstract: This paper presents the results of dynamic deformation tests performed on aluminum alloy PA4. The studiem was carried out by using rotary hammer, in the range of high rate of deformation: 400 – 2000 s^-1. The test were carried using a rotary hammer of RSO type owned by Silesian Technical University in Institute of Technology Metals. Before the dynamic deformation, the heating treatment was carried out allowed for eliminating structural effects resulting from the previous technological treatments and for obtaining the homogenous grain structure. The tests were carried out with linear velocity in the range of 5 – 30 m/s. After deformation the following mechanical characteristics were determined: deformation limit ε_g, strain rate , tensile strength UTS, impact strength U. Independently of the dynamic deformation tests were carried out tensile test under static conditions. Moreover bending test were performed on Charpy type hammer with initial impact energy equal 300 J. The analysis of the microstructure was carried out using scanning electron microscopy Hitachi S–3400 N.

Abstract: The results presented in this paper are concerned with the microstructure and the mechanical properties of the AlMg5 alloy subjected to severe plastic deformation by multiple compression in two orthogonal directions. Four experiments with an increasing number of passes were conducted on the Gleeble MAXStrain system in order to obtain various effective strain levels. The deformed microstructure was investigated by means of the light microscopy (LM) and the scanning transmission electron microscopy (STEM). The mechanical properties were determined for the most deformed, central parts of samples. Investigations revealed that severe cold deformation of the AlMg5 alloy leads to strong grain refinement. Moreover, fragmentation of large intermetallic inclusions and their regular distribution were obtained in the analysed, central parts of the samples. Microstructural changes led to significant improvement in the strength properties. After reaching the effective strain of 9, the AlMg5 alloy exhibited UTS, YS and HV values almost two times higher than corresponding values determined for the starting, annealed material.

Abstract: The microstructure of Al processed by compression with oscillatory torsion (COT) method have been studied. This method was applied to refine the grain structure to ultrafine dimension. The aim of the study was to examine how severe plastic deformation technique (COT) - alter the microstructure. The second aim is to understand the mechanism of grain refinement. The microstructure was characterized using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) equipped with electron back scattered diffraction (EBSD) facility.