Production and characterization of Cuzr-Re based bulk amorphous/nanocrystal composite

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2017
Sıkan, Fatih
Bulk metallic glasses have recently attracted much attention due to their high mechanical strength both in amorphous and in the amorphous/nanocrystal composite form along with their high glass forming ability. However, factors such as having a low plastic strain limit their potential application as structural materials. In this present work, ternary (Zr50Cu40Al10)100–xSmx (x:0-4 at. %) amorphous alloys were produced by melt-spinning in ribbon form and suction casting in bulk form within the diameter range of 1 to 3 millimeters. The amorphous and the devitrified states of these alloys were investigated with scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and scanning differential calorimetry (DSC), Atom Probe Tomography (APT) techniques. Mechanical behavior of these alloys were investigated using compression and hardness testing. Failure modes and structures were analyzed using SEM as well. Furthermore, micro-mechanical testing experiments were conducted in order to get insights on the mechanical behavior of amorphous and partially crystalline specimens in nano and micro scale. Sm addition up to 4 at. % lead to nanocrystallization of approximately 5-10 nm spherical Cu2Sm phase for (Zr50Cu40Al10)96Sm4 alloy. Further growth of Cu2Sm phase was thought to be hindered due to solute pile-up of Zr atoms at phase boundary and insufficiency of Sm atoms in amorphous phase. Since the amount of Sm atoms in amorphous matrix can be controlled by adjusting Sm content during alloying, nanocrystal size can be adjustable for such systems. Precipitation of Cu2Sm nanocrystals were found to increase strength and hardness of (Zr50Cu40Al10)96Sm4 alloy; however, caused a significant embrittlement problem. Adjusting size and distributions of these nanocrystals may prove useful in eliminating this embrittlement problem. This study demonstrates how complex microstructures can be formed in a metallic glass to make a composite structure during devitrification and how these structures can be tuned for better properties.  

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Citation Formats
F. Sıkan, “Production and characterization of Cuzr-Re based bulk amorphous/nanocrystal composite,” M.S. - Master of Science, Middle East Technical University, 2017.