Z. Bojar - Academia.edu (original) (raw)
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Papers by Z. Bojar
Metallurgical and Materials Transactions A, 2015
Results of the electron backscatter diffraction (EBSD) study on structural changes in Armco iron ... more Results of the electron backscatter diffraction (EBSD) study on structural changes in Armco iron subjected to severe plastic deformation by differential speed rolling (DSR) with different values of roll speed mismatch (R = 1, 2, 3, and 4) are shown in the present article. Results of the EBSD microstructure evaluation reveal that a differentiation of roll speeds results in an effect of structure refinement-iron samples processed with high roll speed mismatch are characterized by a high fraction of grains with submicron size. A microtexture examination shows that the DSR process leads to an overall texture weakening effect and a displacement (a shifting to different ''stable'' positions) of the basic rolling texture components, due to an additional presence of a simple shear component in the deformation gradient imposed to the material. Despite the higher hardness of the DSR-processed samples, results of the EBSD strain analysis indicate that some part of the stored deformation energy is released during rolling with an additional presence of shear strain. This finding points toward the possibility of activating a dynamic transformation of the material structure into some more stable state. However, since the observed structural changes take place inside deformation bands and do not lead directly to the formation of a fully equiaxed grain structure, it seems to be more reasonable to call the observed structure transformation a subgrain structure evolution through accumulated shear deformation, which may be related to the dynamic recovery process.
Materials & Design, 2011
In this work, a novel processing routine for the fabrication of graded metal/intermetallic materi... more In this work, a novel processing routine for the fabrication of graded metal/intermetallic materials is shown. It is a combined process that begins with ''layer by layer'' manufacturing of the 3-D components from the elemental metal powders under computer-aided design and manufacturing (CAD/CAM), followed by low-temperature uniaxial pressing under cycle loading and subsequent sintering at high temperature. The ability to fabricate heterogeneous metal-intermetallic materials with a continuous and/or discrete intermetallic gradient was demonstrated by producing graded Fe/FeAl materials as an example. The microstructure of the graded Fe/FeAl materials was investigated with X-ray diffractometer (XRD) and scanning electron microscope (SEM) coupled with a backscattered electron detector (BSE) and an energy dispersive spectrometer (EDS). In both of the investigated materials, Fe and FeAl intermetallic compounds with different amounts of Al and aluminum oxides were found. The mechanical properties of the graded Fe/FeAl materials were examined with a static compression test. The Fe/FeAl material with a continuous gradient exhibited higher compression strength than the material with a discrete gradient.
Protetyka stomatologiczna
Intermetallic coatings were produced by ablation of the FeAl and Ni 3 Al alloys using a KrF laser... more Intermetallic coatings were produced by ablation of the FeAl and Ni 3 Al alloys using a KrF laser (l ¼ 0:248 mm, t $ 20 ns). The energy densities of laser radiation used for deposition were in the range 2-12 J/cm 2 . Fine-grained microstructure of thickness in the range from 50 to 1000 nm was formed in the deposited films. The thickness of deposited layers was dependent on substrate temperature and ion energy. Diffractometric measurements have shown that at high laser energy fluence in the case of the FeAl target, the matrix comprises the polycrystalline Fe 3 Al intermetallic phase, while at low fluence the matrix comprises a solid solution of aluminum in iron (amorphous phase). In the case of the Ni 3 Al target, the matrix comprises the polycrystalline Ni 5 Al 3 orthorombic and Ni 3 Al 4 cubic phases. The results of the stoichiometric analysis and morphology examinations of deposited layers are also discussed. #
Metallurgical and Materials Transactions A, 2015
Results of the electron backscatter diffraction (EBSD) study on structural changes in Armco iron ... more Results of the electron backscatter diffraction (EBSD) study on structural changes in Armco iron subjected to severe plastic deformation by differential speed rolling (DSR) with different values of roll speed mismatch (R = 1, 2, 3, and 4) are shown in the present article. Results of the EBSD microstructure evaluation reveal that a differentiation of roll speeds results in an effect of structure refinement-iron samples processed with high roll speed mismatch are characterized by a high fraction of grains with submicron size. A microtexture examination shows that the DSR process leads to an overall texture weakening effect and a displacement (a shifting to different ''stable'' positions) of the basic rolling texture components, due to an additional presence of a simple shear component in the deformation gradient imposed to the material. Despite the higher hardness of the DSR-processed samples, results of the EBSD strain analysis indicate that some part of the stored deformation energy is released during rolling with an additional presence of shear strain. This finding points toward the possibility of activating a dynamic transformation of the material structure into some more stable state. However, since the observed structural changes take place inside deformation bands and do not lead directly to the formation of a fully equiaxed grain structure, it seems to be more reasonable to call the observed structure transformation a subgrain structure evolution through accumulated shear deformation, which may be related to the dynamic recovery process.
Materials & Design, 2011
In this work, a novel processing routine for the fabrication of graded metal/intermetallic materi... more In this work, a novel processing routine for the fabrication of graded metal/intermetallic materials is shown. It is a combined process that begins with ''layer by layer'' manufacturing of the 3-D components from the elemental metal powders under computer-aided design and manufacturing (CAD/CAM), followed by low-temperature uniaxial pressing under cycle loading and subsequent sintering at high temperature. The ability to fabricate heterogeneous metal-intermetallic materials with a continuous and/or discrete intermetallic gradient was demonstrated by producing graded Fe/FeAl materials as an example. The microstructure of the graded Fe/FeAl materials was investigated with X-ray diffractometer (XRD) and scanning electron microscope (SEM) coupled with a backscattered electron detector (BSE) and an energy dispersive spectrometer (EDS). In both of the investigated materials, Fe and FeAl intermetallic compounds with different amounts of Al and aluminum oxides were found. The mechanical properties of the graded Fe/FeAl materials were examined with a static compression test. The Fe/FeAl material with a continuous gradient exhibited higher compression strength than the material with a discrete gradient.
Protetyka stomatologiczna
Intermetallic coatings were produced by ablation of the FeAl and Ni 3 Al alloys using a KrF laser... more Intermetallic coatings were produced by ablation of the FeAl and Ni 3 Al alloys using a KrF laser (l ¼ 0:248 mm, t $ 20 ns). The energy densities of laser radiation used for deposition were in the range 2-12 J/cm 2 . Fine-grained microstructure of thickness in the range from 50 to 1000 nm was formed in the deposited films. The thickness of deposited layers was dependent on substrate temperature and ion energy. Diffractometric measurements have shown that at high laser energy fluence in the case of the FeAl target, the matrix comprises the polycrystalline Fe 3 Al intermetallic phase, while at low fluence the matrix comprises a solid solution of aluminum in iron (amorphous phase). In the case of the Ni 3 Al target, the matrix comprises the polycrystalline Ni 5 Al 3 orthorombic and Ni 3 Al 4 cubic phases. The results of the stoichiometric analysis and morphology examinations of deposited layers are also discussed. #