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M. C. Bouleklab et al.
temperature ranges from 35 to 75 and 135 to 200 °C for the Fe–Cu specimens, a
range of 50–150 °C for the Fe–Cu-MWCNT(0.5), and a range of 500–625 °C for the
Fe–Cu-MWCNT(1.0) are highlighted by us as such, where there may be a significant
manifestation of shrinkage.
Both structural and phase transformations determine the dilatometric behavior of
the Fe–Cu-MWCNT composites in the temperature range above 500 °C. The main
ones among them at higher concentrations of CNT are increase of the copper solid
solution content in α-Fe and increase in the content of γ-Fe due to the α-Fe → γFe phase transformation with temperature increasing; the formation of iron oxides
following formation the bonds such as M–O-CNT and the formation of carbides in
the surface layer of iron grains.
The output of the L/L 0 (T) dependences at the maximum when the temperature
reaches ≥800 °C and the decrease of the CTE value at T ≥ 650 °C must be associated
with sintering, which is known to begin for iron–copper–carbon powder compacts
at temperatures of ~500–530 °C.
Increasing of the MWCNT content up to 2% suppresses the effects of thermal
expansion and radically (two orders of magnitude) reduces the amount of CTE. This
fact should be considered as a consequence of the cumulative effect of the formation of the carbide in the surface layer of iron grains, the blocking of copper to
iron particles incorporation by carbon atoms and the leveling of its influence, the
placement of copper in the intergranular space, changes in the α-Fe → γ-Fe transformation processes, separation of iron, carbides, and carbon nanotubes fractions,
and the formation of MWCNTs layer of and the products of their decomposition
between metallic grains and changes in the sintering conditions.
Milling and further processing of samples lead to the destruction of the MWCNTs,
and the loss of carbon atoms in the formation of oxides and carbides is a source of
the MWCNT defects that was confirmed by the data of the macro- and micro-Raman
scattering.
Significant heterogeneity of the of carbon material distribution over the samples
and the dispersion of the particle size in the range of 25–80 nm are the sources of the
variety of MWCNT’s influence on the above-mentioned processes of interactions
and transformations.
The results obtained in this paper, in our opinion, are very interesting on the
scientific side and are an important contribution to nanotechnology. They determine
the important role of MWCNTs in the formation of Fe–Cu metallic nanocomposites and confirmed that mechano-chemical synthesis is an effective method for the
development of new types of nanoscaled composite materials.
Acknowledgments The work was financially supported by the State budgets of Ukraine and
Algeria via Ministry of Education and Science of Ukraine and Ministry of Higher Education and
Scientific Research of Algeria, respectively.
M. C. Bouleklab et al.
temperature ranges from 35 to 75 and 135 to 200 °C for the Fe–Cu specimens, a
range of 50–150 °C for the Fe–Cu-MWCNT(0.5), and a range of 500–625 °C for the
Fe–Cu-MWCNT(1.0) are highlighted by us as such, where there may be a significant
manifestation of shrinkage.
Both structural and phase transformations determine the dilatometric behavior of
the Fe–Cu-MWCNT composites in the temperature range above 500 °C. The main
ones among them at higher concentrations of CNT are increase of the copper solid
solution content in α-Fe and increase in the content of γ-Fe due to the α-Fe → γFe phase transformation with temperature increasing; the formation of iron oxides
following formation the bonds such as M–O-CNT and the formation of carbides in
the surface layer of iron grains.
The output of the L/L 0 (T) dependences at the maximum when the temperature
reaches ≥800 °C and the decrease of the CTE value at T ≥ 650 °C must be associated
with sintering, which is known to begin for iron–copper–carbon powder compacts
at temperatures of ~500–530 °C.
Increasing of the MWCNT content up to 2% suppresses the effects of thermal
expansion and radically (two orders of magnitude) reduces the amount of CTE. This
fact should be considered as a consequence of the cumulative effect of the formation of the carbide in the surface layer of iron grains, the blocking of copper to
iron particles incorporation by carbon atoms and the leveling of its influence, the
placement of copper in the intergranular space, changes in the α-Fe → γ-Fe transformation processes, separation of iron, carbides, and carbon nanotubes fractions,
and the formation of MWCNTs layer of and the products of their decomposition
between metallic grains and changes in the sintering conditions.
Milling and further processing of samples lead to the destruction of the MWCNTs,
and the loss of carbon atoms in the formation of oxides and carbides is a source of
the MWCNT defects that was confirmed by the data of the macro- and micro-Raman
scattering.
Significant heterogeneity of the of carbon material distribution over the samples
and the dispersion of the particle size in the range of 25–80 nm are the sources of the
variety of MWCNT’s influence on the above-mentioned processes of interactions
and transformations.
The results obtained in this paper, in our opinion, are very interesting on the
scientific side and are an important contribution to nanotechnology. They determine
the important role of MWCNTs in the formation of Fe–Cu metallic nanocomposites and confirmed that mechano-chemical synthesis is an effective method for the
development of new types of nanoscaled composite materials.
Acknowledgments The work was financially supported by the State budgets of Ukraine and
Algeria via Ministry of Education and Science of Ukraine and Ministry of Higher Education and
Scientific Research of Algeria, respectively.