A. Calka - Academia.edu (original) (raw)
Papers by A. Calka
Scripta Metallurgica, 1987
MRS Proceedings, 1998
ABSTRACTTwo unconventional methods of cold-work: (a) controlled mechanical (ball) milling (under ... more ABSTRACTTwo unconventional methods of cold-work: (a) controlled mechanical (ball) milling (under shear conditions), and (b) shock-wave (explosive) loading at ˜5 GPa shock pressure were applied to two cubic intermetallics: (a) Mn-stabilized cubic (L12) titanium trialuminide (AI3Ti(Mn)) and (b) B2 iron aluminide (FeAl). The long-range order (LRO) parameter S of both intermetallics decreases and their lattice constants increase with increasing milling time providing strong evidence that the mechanical milling disorder is due to antisite-atom pairs. A nanocrystalline structure is being formed in both intermetallics upon milling. A shock-wave loading gives rise to only a partial disorder of both A13Ti(Mn) and FeAl but their lattice constants are not affected (no point defects formation). Annealing at 600°C results in the restoration of LRO and lattice constants as well as microstructural evolution in Fe-45A1.
Key Engineering Materials, 1987
Metals Technology, 1978
AbstractThe formation and stability of splat-cooled metallic glasses of compositions Cu6oMe40 and... more AbstractThe formation and stability of splat-cooled metallic glasses of compositions Cu6oMe40 and Cu6oMe40 were investigated by the X-ray diffraction method and calorimetry. The TTT curves (time-temperature-transformation) and activation energies of crystallization, obtainedfrom differential scanning calorimetry curves arepresented. The thermal stability of these glasses and the ability of copper-base alloys toform glasses are explained in terms of alloying components.
Hyperfine Interactions, 1986
... Magn. Mat. 22 (1980) 79. /11/ DM Roy and DG Pettifor, J. Phys. F:Metal Phys. 7 (1977) L183. /... more ... Magn. Mat. 22 (1980) 79. /11/ DM Roy and DG Pettifor, J. Phys. F:Metal Phys. 7 (1977) L183. /12/ DL Hilliamson, S. Nasu and U. Gonser, Acta Metall. 24 (1976) 1003. /13/ GL Whittle and SJ Campbell, to be published. /14/ DL Williamson, W. Keune and U. Gonser, Proc. lnt. Conf. ...
Journal of Materials Research, 1988
Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scan... more Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and...
Journal of Alloys and Compounds, 2006
When magnesium powder containing small additions of certain multiple valence transition metal oxi... more When magnesium powder containing small additions of certain multiple valence transition metal oxides (TMOs) is ball milled in hydrogen, the hydrogenated Mg-based product can show remarkable improvements in hydrogen absorption/desorption properties. Using a magnetically controlled Uni-Ball-Mill, small amounts of the iron oxides, Fe 2 O 3 and Fe 3 O 4 , were ball milled with Mg powder in a hydrogen atmosphere (Mg to Fe atomic ratio; 20:1). Milling products as well as samples used in hydrogen absorption/desorption experiments were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. TG analysis combined with DSC revealed a higher hydrogen storage capacity for the Mg + Fe 2 O 3 + H 2-milled product (6 wt% H) compared with 5 wt% H for Mg + Fe 3 O 4 + H 2. XRD revealed that during heating, both iron oxides were reduced to pure Fe, a result not previously reported for similar materials milled using different milling devices. For both samples, there was little difference found in the decomposition temperature of the as-prepared MgH 2 and rehydrogenated composites. However, storage capacity degradations were observed for the rehydrogenated composites (4 wt% H storage capacity for MgH 2 + Fe 2 O 3 and 4.4 wt% H for MgH 2 + Fe 3 O 4). The higher capacity degradation of rehydrogenated MgH 2 + Fe 2 O 3 composite is also believed to be a result of the reduction reaction, during which more magnesium was consumed than was consumed by the same amount of Fe 3 O 4. The results also were related to the particular ball-milling equipment and low-energy shearing milling mode employed, which promoted the development of a nanostructural hydride product which subsequently changed structure significantly during the first desorption cycle.
International Journal of Hydrogen Energy, 2009
In this work, MgH2–SiC–Ni was prepared by magneto-mechanical milling in hydrogen atmosphere. Scan... more In this work, MgH2–SiC–Ni was prepared by magneto-mechanical milling in hydrogen atmosphere. Scanning electron microscope mapping images showed a homogeneous dispersion of both Ni and SiC among MgH2 particles. Based on the differential scanning calorimetry traces, the temperature of desorption is reduced by doping MgH2 with SiC and Ni. Hydrogen absorption/desorption behaviour of the samples was investigated by Sievert's method
Journal of Alloys and Compounds, 2009
Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using Rapid reduction of copper... more Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using electrical discharge assisted meachanical milling (EDAMM) electrical discharge assisted meachanical milling (EDAMM)
1992. Digests of Intermag. International Magnetics Conference
physica status solidi (a), 1990
Further data, completing an earlier report, are presented on the temperature and angular dependen... more Further data, completing an earlier report, are presented on the temperature and angular dependence of microwave magnetic resonances in a series of amorphous Ni73TM5Si12B10 (TM = Ni, Co, Fe) metallic glasses with TM concentrations less than that required for ferromagnetism. It is found that the Ni paramagnetism is gradually supplemented by the appearance of ferromagnetic competition due to Ni-substitution by Co and in particular by Fe atoms. For Fe containing samples well defined reentrant behaviour is observed. The magnetic resonance reveals marked anomalies at lower temperatures: i) a second resonance signal at g = 4.3, which can be attributed to a highly anisotropic EPR signal from Ni3+, ii) a strong positive g-shift and changes of relative resonance line intensity in Fe containing samples which can be attributed to the existence of mixed phases, with both, spin glass and ferromagnetic characters. To describe the experimental data a unidirectional effective anisotropy energy is introduced in the resonance equations. The results obtained show compositional and temperature dependence. Weitere Daten, die eine fruhere Arbeit vervollstandigen, werden zur Temperatur- und Winkelabhangigkeit von magnetischen Mikrowellenresonanzen in einer Reihe von amorphen metallischen Ni73TM5Si12B10 (TM = Ni, Co, Fe)-Glasern mit TM-Konzentrationen, die kleiner als die fur Ferromagnetismus geforderten sind, angegeben. Es wird gefunden, das der Ni-Paramagnetismus graduell erganzt wird durch das Auftreten von ferromagnetischer Konkurrenz infolge von Ni-Substituierung durch Co- und insbesondere durch Fe-Atome. Fur Fe-haltige Proben wird ein gut definiertes Wiedereintrittsverhalten beobachtet. Die magnetische Resonanz zeigt deutliche Anomalien bei niedrigen Temperaturen: 1) ein zweites Resonanzsignal bei g = 4,3, das einem stark anisotropen EPR-Signal von Ni3+ zugeordnet werden kann, 2) eine starke positive g-Verschiebung und Anderungen der relativen Resonanzlinienintensitat in Fe-haltigen Proben, die der Existenz von gemischten Phasen zugeschrieben werden kann sowohl mit Spinglas- als auch ferromagnetischem Charakter. Um die experimentellen Werte zu beschreiben, wird eine uniaxiale effektive Anisotropieenergie in die Resonanzgleichung eingefuhrt. Die erhaltenen Ergebnisse zeigen Zusammensetzungs- und Temperaturabhangigkeit.
IEEE Transactions on Magnetics, 1990
ABSTRACT
Scripta Metallurgica et Materialia, 1992
Physica B-condensed Matter - PHYSICA B, 2000
Titanium nitride of FCC B1 structure forms readily on milling Ti in nitrogen and ammonia environm... more Titanium nitride of FCC B1 structure forms readily on milling Ti in nitrogen and ammonia environments. Rietveld refinements of time-of-flight neutron diffraction patterns show that stoichiometric TiN is produced on milling Ti in nitrogen, whereas the off-stoichiometric nitride TiN0.7, associated with the presence of hydrogen, is formed on milling in ammonia. The transformation of Ti to the nitride proceeds more rapidly in ammonia due to the catalytic effect of hydrogen.
Materials Science Forum
ABSTRACT
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993
ABSTRACT
Materials Science and Engineering: A, 1989
Scripta Metallurgica, 1987
MRS Proceedings, 1998
ABSTRACTTwo unconventional methods of cold-work: (a) controlled mechanical (ball) milling (under ... more ABSTRACTTwo unconventional methods of cold-work: (a) controlled mechanical (ball) milling (under shear conditions), and (b) shock-wave (explosive) loading at ˜5 GPa shock pressure were applied to two cubic intermetallics: (a) Mn-stabilized cubic (L12) titanium trialuminide (AI3Ti(Mn)) and (b) B2 iron aluminide (FeAl). The long-range order (LRO) parameter S of both intermetallics decreases and their lattice constants increase with increasing milling time providing strong evidence that the mechanical milling disorder is due to antisite-atom pairs. A nanocrystalline structure is being formed in both intermetallics upon milling. A shock-wave loading gives rise to only a partial disorder of both A13Ti(Mn) and FeAl but their lattice constants are not affected (no point defects formation). Annealing at 600°C results in the restoration of LRO and lattice constants as well as microstructural evolution in Fe-45A1.
Key Engineering Materials, 1987
Metals Technology, 1978
AbstractThe formation and stability of splat-cooled metallic glasses of compositions Cu6oMe40 and... more AbstractThe formation and stability of splat-cooled metallic glasses of compositions Cu6oMe40 and Cu6oMe40 were investigated by the X-ray diffraction method and calorimetry. The TTT curves (time-temperature-transformation) and activation energies of crystallization, obtainedfrom differential scanning calorimetry curves arepresented. The thermal stability of these glasses and the ability of copper-base alloys toform glasses are explained in terms of alloying components.
Hyperfine Interactions, 1986
... Magn. Mat. 22 (1980) 79. /11/ DM Roy and DG Pettifor, J. Phys. F:Metal Phys. 7 (1977) L183. /... more ... Magn. Mat. 22 (1980) 79. /11/ DM Roy and DG Pettifor, J. Phys. F:Metal Phys. 7 (1977) L183. /12/ DL Hilliamson, S. Nasu and U. Gonser, Acta Metall. 24 (1976) 1003. /13/ GL Whittle and SJ Campbell, to be published. /14/ DL Williamson, W. Keune and U. Gonser, Proc. lnt. Conf. ...
Journal of Materials Research, 1988
Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scan... more Isothermal devitrification of Pd85Si15 amorphous alloys has been analyzed using differential scanning calorimetry (DSC) and x-ray diffractometry. Both as-quenched and aged amorphous ribbons were investigated. Crystallization of aged samples starts from the surface and proceeds several micrometers into the bulk. The product of this process is a layer of strongly textured palladium (111) followed by a mixture of Pd2Si, Masumoto MSI phase, and untextured palladium. Next, the crystallization occurs via a different (bulk) mechanism, resulting in a mixture of Masumoto MSII phase and untextured palladium. The bulk mechanism is the only one observed in as-quenched samples. The surface and bulk crystallization mechanisms are spatially decoupled and, therefore, the corresponding DSC data can be analyzed separately. This has been done according to the Kolmogorov–Johnson–Mehl–Avrami model and also using the recently developed concept of local value of Avrami exponent n. For both the surface and...
Journal of Alloys and Compounds, 2006
When magnesium powder containing small additions of certain multiple valence transition metal oxi... more When magnesium powder containing small additions of certain multiple valence transition metal oxides (TMOs) is ball milled in hydrogen, the hydrogenated Mg-based product can show remarkable improvements in hydrogen absorption/desorption properties. Using a magnetically controlled Uni-Ball-Mill, small amounts of the iron oxides, Fe 2 O 3 and Fe 3 O 4 , were ball milled with Mg powder in a hydrogen atmosphere (Mg to Fe atomic ratio; 20:1). Milling products as well as samples used in hydrogen absorption/desorption experiments were characterized by scanning electron microscopy (SEM), X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. TG analysis combined with DSC revealed a higher hydrogen storage capacity for the Mg + Fe 2 O 3 + H 2-milled product (6 wt% H) compared with 5 wt% H for Mg + Fe 3 O 4 + H 2. XRD revealed that during heating, both iron oxides were reduced to pure Fe, a result not previously reported for similar materials milled using different milling devices. For both samples, there was little difference found in the decomposition temperature of the as-prepared MgH 2 and rehydrogenated composites. However, storage capacity degradations were observed for the rehydrogenated composites (4 wt% H storage capacity for MgH 2 + Fe 2 O 3 and 4.4 wt% H for MgH 2 + Fe 3 O 4). The higher capacity degradation of rehydrogenated MgH 2 + Fe 2 O 3 composite is also believed to be a result of the reduction reaction, during which more magnesium was consumed than was consumed by the same amount of Fe 3 O 4. The results also were related to the particular ball-milling equipment and low-energy shearing milling mode employed, which promoted the development of a nanostructural hydride product which subsequently changed structure significantly during the first desorption cycle.
International Journal of Hydrogen Energy, 2009
In this work, MgH2–SiC–Ni was prepared by magneto-mechanical milling in hydrogen atmosphere. Scan... more In this work, MgH2–SiC–Ni was prepared by magneto-mechanical milling in hydrogen atmosphere. Scanning electron microscope mapping images showed a homogeneous dispersion of both Ni and SiC among MgH2 particles. Based on the differential scanning calorimetry traces, the temperature of desorption is reduced by doping MgH2 with SiC and Ni. Hydrogen absorption/desorption behaviour of the samples was investigated by Sievert's method
Journal of Alloys and Compounds, 2009
Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using Rapid reduction of copper... more Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using Rapid reduction of copper sulfide (Cu2S) with elemental Fe and Mg using electrical discharge assisted meachanical milling (EDAMM) electrical discharge assisted meachanical milling (EDAMM)
1992. Digests of Intermag. International Magnetics Conference
physica status solidi (a), 1990
Further data, completing an earlier report, are presented on the temperature and angular dependen... more Further data, completing an earlier report, are presented on the temperature and angular dependence of microwave magnetic resonances in a series of amorphous Ni73TM5Si12B10 (TM = Ni, Co, Fe) metallic glasses with TM concentrations less than that required for ferromagnetism. It is found that the Ni paramagnetism is gradually supplemented by the appearance of ferromagnetic competition due to Ni-substitution by Co and in particular by Fe atoms. For Fe containing samples well defined reentrant behaviour is observed. The magnetic resonance reveals marked anomalies at lower temperatures: i) a second resonance signal at g = 4.3, which can be attributed to a highly anisotropic EPR signal from Ni3+, ii) a strong positive g-shift and changes of relative resonance line intensity in Fe containing samples which can be attributed to the existence of mixed phases, with both, spin glass and ferromagnetic characters. To describe the experimental data a unidirectional effective anisotropy energy is introduced in the resonance equations. The results obtained show compositional and temperature dependence. Weitere Daten, die eine fruhere Arbeit vervollstandigen, werden zur Temperatur- und Winkelabhangigkeit von magnetischen Mikrowellenresonanzen in einer Reihe von amorphen metallischen Ni73TM5Si12B10 (TM = Ni, Co, Fe)-Glasern mit TM-Konzentrationen, die kleiner als die fur Ferromagnetismus geforderten sind, angegeben. Es wird gefunden, das der Ni-Paramagnetismus graduell erganzt wird durch das Auftreten von ferromagnetischer Konkurrenz infolge von Ni-Substituierung durch Co- und insbesondere durch Fe-Atome. Fur Fe-haltige Proben wird ein gut definiertes Wiedereintrittsverhalten beobachtet. Die magnetische Resonanz zeigt deutliche Anomalien bei niedrigen Temperaturen: 1) ein zweites Resonanzsignal bei g = 4,3, das einem stark anisotropen EPR-Signal von Ni3+ zugeordnet werden kann, 2) eine starke positive g-Verschiebung und Anderungen der relativen Resonanzlinienintensitat in Fe-haltigen Proben, die der Existenz von gemischten Phasen zugeschrieben werden kann sowohl mit Spinglas- als auch ferromagnetischem Charakter. Um die experimentellen Werte zu beschreiben, wird eine uniaxiale effektive Anisotropieenergie in die Resonanzgleichung eingefuhrt. Die erhaltenen Ergebnisse zeigen Zusammensetzungs- und Temperaturabhangigkeit.
IEEE Transactions on Magnetics, 1990
ABSTRACT
Scripta Metallurgica et Materialia, 1992
Physica B-condensed Matter - PHYSICA B, 2000
Titanium nitride of FCC B1 structure forms readily on milling Ti in nitrogen and ammonia environm... more Titanium nitride of FCC B1 structure forms readily on milling Ti in nitrogen and ammonia environments. Rietveld refinements of time-of-flight neutron diffraction patterns show that stoichiometric TiN is produced on milling Ti in nitrogen, whereas the off-stoichiometric nitride TiN0.7, associated with the presence of hydrogen, is formed on milling in ammonia. The transformation of Ti to the nitride proceeds more rapidly in ammonia due to the catalytic effect of hydrogen.
Materials Science Forum
ABSTRACT
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1993
ABSTRACT
Materials Science and Engineering: A, 1989