Niobium is the best and excellent metal for many different industrial applications. Europe has not a Niobium reserve
whereas Brazil has a major Niobium mining and produce %90 of the Niobium in the world as a raw material [5, 7,
8]. However, the processing of this metal beginning from mining up to the advance processing for the real manufacturing
engineering applications is very expensive and require a sophisticated equipment and investment. However, very huge
amount of scraps of the niobium coming from manufacturing of the pieces is not reprocessed efficiently as valuable and
economic way because quasi all of the scarps goes to the waste. The niobium scraps as an important secondary source of the
raw materials should be evaluated for the manufacturing of the new composite design. As not possible to extract in an
economical way, the recycling of niobium could be a sustainable occasion for the industrial applications [6, 9–16].
The present work review of the efficient and sustainable recycling of the fresh scraps of niobium metal in the frame of the
common research project carried out between UNICAMP-Brazil and SUPMECA-France. Fresh scrap aluminium (AA 7075)
matrix composites were designed as an alternative economic composite by using the combined method, sinter + forging
through the powder metallurgy route. Fresh scrap Niobium powder was used as main reinforcement element. As secondary
reinforcements, fine Ni-Al intermetallic powder were added in the matrix. At the first stage of the common research project,
mechanical and physical and chemical properties have been evaluated depending on the composition.
6.2 Experimental Conditions
In this study, an alternative low cost aluminium matrix composite (AMCs) was designed from the fresh scrap recycled chips of
aluminium alloy (AA7075) provided by aeronautic company in Brazil. Fresh scrap niobium chips coming from the machining
and other scraps in different sizes were gas atomized. After atomization, aluminium and niobium scraps were homogenized by
high energy milling with planetary ball mill for 1 h and doped to prepare the matrix. At the second stage, other reinforcements
were added to prepare five different compositions. Each composition was homogenized by ball milling for 4 h again with a
ratio of ball/powder 20:1. To obtain a homogenous mixture with good wettability of the reinforcements with the matrix, pure
nano aluminium (3 wt %) powder was added in the each mixture. Again, 2 wt % Zn-Stearate was also added in the each
mixture for the lubrication and hindering the oxidation of the mixture during the milling. Final compositions were given in the
Table 6.1. The chemical composition of AA7075 as provided by the aeronautic company was given in the Table 6.2.
Microstructural analyses performed by of scanning electron microscope (SEM). The dispersion of reinforcement particles
in the matrix and interface at matrix/reinforcements was also evaluated.
Micro hardness tests (HV 0.1 ) tests were conducted on the polished and etched specimens. The micro hardness values were
measured and the values are variables between 400–700 HVN with Æ15% accuracy for the composites designed here under
the laboratory conditions.
All the density measurements of the specimens were carried out by using Archimedes method. These values changed
between 2.85 and 3.15 g/cm
3 with Æ05% accuracy respectively.
Quasi-static compression tests were carried out with a Zwick mechanical test system at the strain rate of 1 mm/min. For
each manufacturing process 3–4 cylindrical specimens (H/D ! 1.5) were used.
After sintering of all of the composite, only first three composites (Nb-I, Nb-II and Nb-III) were processed the combined
method called sinter + forging [5, 6, 8, 9, 12–16], Last two composites (Nb-IV and Nb-V) was only sintered.
Table 6.1 Compositions of the composites prepared in two groups (wt. %)
Composition Name
Matrix: AA7075
Nb
Ni-Al
TiB 2
B 4 C
TiC
Mo
Nb-I
Balance
40
10
–
–
–
–
Nb-II
Balance
40
–
10
–
–
–
Nb-III
Balance
40
–
–
10
–
–
Nb-IV
Balance
40
–
–
–
10
–
Nb-V
Balance
40
–
–
–
–
10
Table 6.2 Chemical composition of scrap AA 7075 (wt. %)
Element
Al
Cu
Fe
Mg
Mn
Si
Ni
Zn
Cr
Zr
wt. %
Balance
1.48
0.23
2.11
0.07
0.10
0.01
5.29
0.22
0.02
36
E. Bayraktar et al.
whereas Brazil has a major Niobium mining and produce %90 of the Niobium in the world as a raw material [5, 7,
8]. However, the processing of this metal beginning from mining up to the advance processing for the real manufacturing
engineering applications is very expensive and require a sophisticated equipment and investment. However, very huge
amount of scraps of the niobium coming from manufacturing of the pieces is not reprocessed efficiently as valuable and
economic way because quasi all of the scarps goes to the waste. The niobium scraps as an important secondary source of the
raw materials should be evaluated for the manufacturing of the new composite design. As not possible to extract in an
economical way, the recycling of niobium could be a sustainable occasion for the industrial applications [6, 9–16].
The present work review of the efficient and sustainable recycling of the fresh scraps of niobium metal in the frame of the
common research project carried out between UNICAMP-Brazil and SUPMECA-France. Fresh scrap aluminium (AA 7075)
matrix composites were designed as an alternative economic composite by using the combined method, sinter + forging
through the powder metallurgy route. Fresh scrap Niobium powder was used as main reinforcement element. As secondary
reinforcements, fine Ni-Al intermetallic powder were added in the matrix. At the first stage of the common research project,
mechanical and physical and chemical properties have been evaluated depending on the composition.
6.2 Experimental Conditions
In this study, an alternative low cost aluminium matrix composite (AMCs) was designed from the fresh scrap recycled chips of
aluminium alloy (AA7075) provided by aeronautic company in Brazil. Fresh scrap niobium chips coming from the machining
and other scraps in different sizes were gas atomized. After atomization, aluminium and niobium scraps were homogenized by
high energy milling with planetary ball mill for 1 h and doped to prepare the matrix. At the second stage, other reinforcements
were added to prepare five different compositions. Each composition was homogenized by ball milling for 4 h again with a
ratio of ball/powder 20:1. To obtain a homogenous mixture with good wettability of the reinforcements with the matrix, pure
nano aluminium (3 wt %) powder was added in the each mixture. Again, 2 wt % Zn-Stearate was also added in the each
mixture for the lubrication and hindering the oxidation of the mixture during the milling. Final compositions were given in the
Table 6.1. The chemical composition of AA7075 as provided by the aeronautic company was given in the Table 6.2.
Microstructural analyses performed by of scanning electron microscope (SEM). The dispersion of reinforcement particles
in the matrix and interface at matrix/reinforcements was also evaluated.
Micro hardness tests (HV 0.1 ) tests were conducted on the polished and etched specimens. The micro hardness values were
measured and the values are variables between 400–700 HVN with Æ15% accuracy for the composites designed here under
the laboratory conditions.
All the density measurements of the specimens were carried out by using Archimedes method. These values changed
between 2.85 and 3.15 g/cm
3 with Æ05% accuracy respectively.
Quasi-static compression tests were carried out with a Zwick mechanical test system at the strain rate of 1 mm/min. For
each manufacturing process 3–4 cylindrical specimens (H/D ! 1.5) were used.
After sintering of all of the composite, only first three composites (Nb-I, Nb-II and Nb-III) were processed the combined
method called sinter + forging [5, 6, 8, 9, 12–16], Last two composites (Nb-IV and Nb-V) was only sintered.
Table 6.1 Compositions of the composites prepared in two groups (wt. %)
Composition Name
Matrix: AA7075
Nb
Ni-Al
TiB 2
B 4 C
TiC
Mo
Nb-I
Balance
40
10
–
–
–
–
Nb-II
Balance
40
–
10
–
–
–
Nb-III
Balance
40
–
–
10
–
–
Nb-IV
Balance
40
–
–
–
10
–
Nb-V
Balance
40
–
–
–
–
10
Table 6.2 Chemical composition of scrap AA 7075 (wt. %)
Element
Al
Cu
Fe
Mg
Mn
Si
Ni
Zn
Cr
Zr
wt. %
Balance
1.48
0.23
2.11
0.07
0.10
0.01
5.29
0.22
0.02
36
E. Bayraktar et al.