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Designing novel bulk metallic glass composites with a high aluminum content.

Chen ZP, Gao JE, Wu Y, Wang H, Liu XJ, Lu ZP - Sci Rep (2013)

Bottom Line: The long-standing challenge for forming Al-based BMGs and their matrix composites with a critical size larger than 1 mm have not been answered over the past three decades.These composites can be cast at extraordinarily low cooling rates, compatible with maximum rod diameters of over a centimetre in copper mold casting.However, the optimum content of Fe addition is strongly dependant on the total amount of the Al content in the Al-(CoCu)-(La,Ce) alloys.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.

ABSTRACT
The long-standing challenge for forming Al-based BMGs and their matrix composites with a critical size larger than 1 mm have not been answered over the past three decades. In this paper, we reported formation of a series of BMG matrix composites which contain a high Al content up to 55 at.%. These composites can be cast at extraordinarily low cooling rates, compatible with maximum rod diameters of over a centimetre in copper mold casting. Our results indicate that proper additions of transition element Fe which have a positive heat of mixing with the main constituents La and Ce can appreciably improve the formability of the BMG matrix composites by suppressing the precipitation of Al(La,Ce) phase resulted from occurrence of the phase separation. However, the optimum content of Fe addition is strongly dependant on the total amount of the Al content in the Al-(CoCu)-(La,Ce) alloys.

No MeSH data available.


Related in: MedlinePlus

Schematic illustration of the solidification process for the Al50(CoCu)5(LaCe)45−xFex(x = 0, 5, 10) alloys.
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f11: Schematic illustration of the solidification process for the Al50(CoCu)5(LaCe)45−xFex(x = 0, 5, 10) alloys.

Mentions: Based on the above observations, it can be speculated that effects of the Fe addition in the current alloy system on formation of the BMG matrix composites can originate from the composition partitioning during the solidification process. Based on the binary phase diagram of the Al-La, Al-Ce and Al-Fe systems38, it is known that the stability of all the involved phase is in the sequence of Al2(La,Ce), AlFe, Al2Fe and Al(La,Ce). Figure 11 schematically illustrates the possible solidification process of the alloys containing different Fe contents. As mentioned earlier, the dark Al2(La,Ce) phase would precipitate first in the alloy Al50(Co,Cu)5(La,Ce)45 with no Fe addition, followed by the peritectic reaction of L′ + Al2(La,Ce) → Al(La,Ce). Due to the peritectic reaction, the Al content in the remaining liquid was actually increased, resulting in a reduction in the GFA. Upon further cooling, the nanosized Al2(La,Ce) crystals embedded in the amorphous matrix were obtained. For the alloy added with 5% Fe, liquid phase separation seemingly occurred, and Fe-rich and Fe-depleted liquids were formed due to the positive heat of mixing between La, Ce and Fe. During solidification, the Al2(La,Ce) phase precipitated first out of the Fe-depleted liquid, followed by formation of the needle-like AlFe and the black Al2Fe phases from the Fe-rich liquid. Compared with that of the Al50(Co,Cu)5(La,Ce)45 alloy, the Al content in the residual liquid of the alloy containing 5 at.% Fe is effectively reduced (i.e., adjusting the composition closer to the eutectic point) due to formation of the AlFe and Al2Fe resulted from the phase separation, leading to the enhanced GFA. For the alloy doped with 10% Fe, the liquid phase separation will also take place. Nevertheless, the volume fraction of the Fe-rich liquid is increased due to the larger amount of Fe. During cooling, the dark Al2(La, Ce) phase still formed first from the Fe-depleted liquid. Subsequently, the AlFe phase precipitates out but without any formation of Al2Fe because of the high Fe content. At this stage, the surplus Al in the Fe-rich liquid will be dissolved in the remain liquid, thus leading to the increase in the Al content and promoting formation of more Al2(La, Ce) phase. Consequently, the volume fraction of the glass matrix is dramatically reduced.


Designing novel bulk metallic glass composites with a high aluminum content.

Chen ZP, Gao JE, Wu Y, Wang H, Liu XJ, Lu ZP - Sci Rep (2013)

Schematic illustration of the solidification process for the Al50(CoCu)5(LaCe)45−xFex(x = 0, 5, 10) alloys.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842084&req=5

f11: Schematic illustration of the solidification process for the Al50(CoCu)5(LaCe)45−xFex(x = 0, 5, 10) alloys.
Mentions: Based on the above observations, it can be speculated that effects of the Fe addition in the current alloy system on formation of the BMG matrix composites can originate from the composition partitioning during the solidification process. Based on the binary phase diagram of the Al-La, Al-Ce and Al-Fe systems38, it is known that the stability of all the involved phase is in the sequence of Al2(La,Ce), AlFe, Al2Fe and Al(La,Ce). Figure 11 schematically illustrates the possible solidification process of the alloys containing different Fe contents. As mentioned earlier, the dark Al2(La,Ce) phase would precipitate first in the alloy Al50(Co,Cu)5(La,Ce)45 with no Fe addition, followed by the peritectic reaction of L′ + Al2(La,Ce) → Al(La,Ce). Due to the peritectic reaction, the Al content in the remaining liquid was actually increased, resulting in a reduction in the GFA. Upon further cooling, the nanosized Al2(La,Ce) crystals embedded in the amorphous matrix were obtained. For the alloy added with 5% Fe, liquid phase separation seemingly occurred, and Fe-rich and Fe-depleted liquids were formed due to the positive heat of mixing between La, Ce and Fe. During solidification, the Al2(La,Ce) phase precipitated first out of the Fe-depleted liquid, followed by formation of the needle-like AlFe and the black Al2Fe phases from the Fe-rich liquid. Compared with that of the Al50(Co,Cu)5(La,Ce)45 alloy, the Al content in the residual liquid of the alloy containing 5 at.% Fe is effectively reduced (i.e., adjusting the composition closer to the eutectic point) due to formation of the AlFe and Al2Fe resulted from the phase separation, leading to the enhanced GFA. For the alloy doped with 10% Fe, the liquid phase separation will also take place. Nevertheless, the volume fraction of the Fe-rich liquid is increased due to the larger amount of Fe. During cooling, the dark Al2(La, Ce) phase still formed first from the Fe-depleted liquid. Subsequently, the AlFe phase precipitates out but without any formation of Al2Fe because of the high Fe content. At this stage, the surplus Al in the Fe-rich liquid will be dissolved in the remain liquid, thus leading to the increase in the Al content and promoting formation of more Al2(La, Ce) phase. Consequently, the volume fraction of the glass matrix is dramatically reduced.

Bottom Line: The long-standing challenge for forming Al-based BMGs and their matrix composites with a critical size larger than 1 mm have not been answered over the past three decades.These composites can be cast at extraordinarily low cooling rates, compatible with maximum rod diameters of over a centimetre in copper mold casting.However, the optimum content of Fe addition is strongly dependant on the total amount of the Al content in the Al-(CoCu)-(La,Ce) alloys.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China.

ABSTRACT
The long-standing challenge for forming Al-based BMGs and their matrix composites with a critical size larger than 1 mm have not been answered over the past three decades. In this paper, we reported formation of a series of BMG matrix composites which contain a high Al content up to 55 at.%. These composites can be cast at extraordinarily low cooling rates, compatible with maximum rod diameters of over a centimetre in copper mold casting. Our results indicate that proper additions of transition element Fe which have a positive heat of mixing with the main constituents La and Ce can appreciably improve the formability of the BMG matrix composites by suppressing the precipitation of Al(La,Ce) phase resulted from occurrence of the phase separation. However, the optimum content of Fe addition is strongly dependant on the total amount of the Al content in the Al-(CoCu)-(La,Ce) alloys.

No MeSH data available.


Related in: MedlinePlus