Polycrystalline, high purity (99,995%) zinc ingot was subjected to KoBo type extrusion in room temperature. Material was extruded to form of a 2 mm diameter wire, extrusion die oscillated during process by an angle ±8_ at a frequency of 5 Hz and the extrusion speed was 0.5 mm/s. Final product was tested for tensile strength and yielded R0;2 ≈ 150MPa and Rm ≈ 250MPa. Microstructure of both extruded and initial materials was investigated by means of high resolution Electron Backscatter Diffraction (EBSD) in Quanta 3D FEG scanning electron microscope (SEM). Observations revealed that microstructure of extruded zinc sample is highly heterogeneous and consists of grains elongated slightly in the direction of extrusion. Grains dimensions ranges from over one hundred microns down to submicron scale while grains in the non-deformed material are equiaxed with mean diameter of approximately 200 microns. Other microstructure features such as intergranular bands and partly fragmented primary grains with subgrain structure are observed. Furthermore detailed study of local microstrains by Imaqe Quality Factor analysis are performed. Presence of Geometrically Necessary and Statistically Stored Dislocations is assessed. Thick areas of highly distorted lattice adjacent to High Angle Grain Boundaries are revealed. Microstrain mapping suggest composite-like microstructure of deformed material, that might explain its superior mechanical properties.
K. Sztwiertnia, J. Kawałko, M. Bieda and K. Berent
A. Korneva, G. Korznikova, A. Korznikov and K. Sztwiertnia
The paper presents the results of microstructure evolution studies of hard magnetic FeCr22Co15 alloy deformed until destruction by tension and torsion in the temperature range 725-850ºC. The temperatures and deformation rates resulted from the condition of superplasticity occurrence in the Fe-Cr-Co alloys. Observations of the longitudinal sections of the deformed samples in the scanning electron microscope showed the formation of a weak gradient microstructure with the highest grain refinement in the surface layer of the material. Increasing the deformation temperature from 725 to 850_C increased the homogeneity of the deformation along the tensile axis of the sample. It also brought about the increase of grain size and slight increase of the thickness of fine grains in the surface layer. The precipitation of the intermetallic σ-phase was also observed with its maximum amount in the zones of the highest deformation.
J. Kawałko, M. Bieda and K. Sztwiertnia
Observations of refined microstructure of Commercial Purity titanium for applications in biomedical devices has been carried out. Refinement of titanium microstructure has been performed in process with complex strain scheme. Materials investigated in this work were: Commercial Purity titanium grade 2 and grade 4. Samples of as received materials were subjected to plastic deformation in complex loading process of extrusion combined with oscillation twisting (KoBo extrusion). Both types of samples were deformed in single step of extrusion, in temperature of 450 °C, with extrusion ratio 19.14 and 12.25 for grade 2 titanium and grade 4 titanium, respectively. Initial mean grain diameter for both types of materials was approximately 30 μm. Samples were investigated by means of crystal orientation microscopy. In both cases considerable microstructure refinement has been observed. Microstructures of deformed samples are heterogenous and consist of both elongated and fine equiaxed grains. Elongated grains (lamellae) are separated by High Angle Grain Boundaries and feature internal structure with subgrains and dislocation walls. Grain refinement is stronger in material with higher extrusion ratio and mean grain diameter in this case is equal to 1.48 μm compared to 8.07 μm. in material with lower extrusion ratio. Mean misorientation angle (24° and 27° for grade 4 and grade 2 titanium) indicates high fraction of HAGBs in microstructures of KoBo deformed samples. Misorientation fluctuations inside grains have been analyzed and distinct curvature of crystal lattice have been observed. Hardness of samples after plastic deformation increased from 174.6±3.4 and 234.9±3.5 to 205.0±3.2 and 251.2±2.2 for titanium grade 2 and grade 4 respectively.
M. Bieda, S. Boczkal, P. Koprowski, K. Sztwiertnia and K. Pieła
Pure aluminium (6N) and commercially pure aluminium (99.7) was deformed by KOBO method. Microstructure and texture of both materials after deformation was analyzed by means of scanning and transmission electron microscopy. Advanced methods of crystallographic orientations measurements like Electron Backscatter Diffraction - EBSD (SEM) and microdiffraction (TEM) was used. Grain size distribution and misorientation between grains in cross and longitudinal sections of the samples were analyzed. Differences in size and homogeneity of the grains were observed in both materials. Pure aluminium was characterized by larger grain size in both sections of extruded material. Whereas commercially pure aluminium reveals smaller grain size and more homogeneous and stable microstructure.
K. Nalepka, K. Sztwiertnia, P. Nalepka and R.B. Pęcherski
Electron back-scattered diffraction (EBSD) studies carried out for the Cu/α−Al2O3 composites manufactured by pulsed laser deposition method and by the powder metallurgy enable to uncover a set of orientation relationships characteristic for materials of this type. The identified interfaces are categorized according to the bonding strength. Additionally, their microstructure is reproduced by molecular dynamic (MD) simulations. The obtained classification of the phase boundaries constitutes key information for effective composite design.
R. Bogucki, K. Sulikowska, M. Bieda, P. Ostachowski and K. Sztwiertnia
Analysis of the results of the microstructure and the mechanical properties change in AA1050 aluminum alloy of technical purity processed using ECAP (Equal Channel Angular Pressing) and KoBo deformation methods are presented in the paper.. ECAP process was performed according to Bc scheme in the range from 1 up to 10 passes. Changes of microstructure were analyzed using scanning electrone microscope equipped with electron backscattered diffraction (EBSD) system. Microstructure and fraction of high-angle grain boundaries in KoBo processed samples were similar to those observed in ECAP processed samples after four passes. The most significant microstructure refinement was observed in ECAP processed sample submitted to 10 passes. In ECAP method the systematic increase of mechanical properties was observed along with increase of deformation degree.
P. Koprowski, R. Bogucki, M. Bieda, J. Kawałko and K. Sztwiertnia
The annealing behavior of AA1050 aluminum alloy deformed by equal-channel angular pressing (ECAP) was studied experimentally. The material was subjected to extrusion through die with channels intersecting at an 90° angle. Samples were pressed for up to 8 passes using route BC, then cut into slices and subsequently annealed for 1 hour at temperatures from 100°C to 350°C. Hardness measurements were performed on each slice. Microstructure of material was analyzed in the longitudinal section by means of Electron Backscatter Diffraction system in a scanning electron microscope (EBSD/SEM). From the obtained sets of Kikuchi diffraction patterns orientation maps and Image Quality maps were determined. Grain size, disorientation distributions and crystallographic texture were also estimated. ECAP caused significant improvement of hardness, with stabilization after 4 passes. Refinement of microstructure was obtained with the increasing amount of passes. Material properties were stable during annealing at temperatures lower than 150°C. Annealing at higher temperatures caused a decrease in hardness corresponding to an increase of the grain size.